Step by Step® Ultrasound in Gynecology Jaideep Malhotra, Nidhi Gupta, Narendra Malhotra, Neharika Malhotra, Kuldeep Singh
INDEX
Page numbers followed by f refer to figure, fc refer to flowchart, and t refer to table.
A
Abdominal examination 240, 277
Abnormal uterine bleeding 241, 246, 247, 253
classification of 241, 253
clinical evaluation of 241, 254
differential diagnosis of 241, 255
investigations of 241, 255
management of 242, 272
Abortion 264
missed 136
previous 185
Abruptio placenta 47
Abscess 264
Absorption 5
Acute lower abdominal pain evaluation of 242
non-gynecological causes of 242, 263
Acute pelvic inflammatory disease 187, 192f, 250, 251
diagnosis of 243, 275
differential diagnosis of 243, 276
history of 234
Acute pelvic pain 254
ultrasonography in 241, 250
Adenomyoma 260
Adenomyosis 97, 113, 228, 229, 233, 234, 240, 247, 251, 253, 270
Adhesions 234, 235, 240
Adnexa 58, 246
Adnexal mass 154, 222, 250, 254, 259, 264
Adnexal pathology 269
Adnexal tenderness 240, 277
Adrenal hyperplasia, congenital 279
Allergens 235
Allergy 256
Amenorrhea 195, 197, 246, 254, 264
American Fertility Society Classification 139
Amniotic fluid, reduced 213
Anal sphincter 245
Androgen 241, 243
insensitivity syndrome 279
secreting tumors 279
Anemia 212
Anorexia nervosa 278
Anovulation 165
Anteflexion 75
Anterior wall
submucous fibroid 109f
subserous fibroids 105f
Anteversion 75
Antimüllerian hormone 241, 243
Anxiety 233, 269
Appendicitis, acute 263, 276
Arcuate artery calcification, multiple foci of 71f
Ascites 245
Ascitic fluid, aspiration of 252
Asherman's syndrome 143f, 151
Assisted reproductive technique 185
protocol 299fc
Atrophy 229
Audible sound waves 1
Audio volume 34
B
Bacterial vaginosis 256
Basal layer 76
Battery injury 43
Beam profile 6
Benign ovarian lesions, ultrasonographic features of 242, 274
neoplastic lesions, management of 243, 274, 275
Beta hCG 196
level, correlation of 197
Bimanual examination 254, 269
Biopsy, endometrial 276
Bladder tumor 261
Bleeding 246
types of 270
Blob sign 203
Blood
flow velocity 23f
pressure, elevated 212
Bowel 190
symptoms 239, 254
tumor 261
Breast
cancer 47
cyst 47
Brenner tumor 249, 26
Broad ligament myomas 272
C
Calcifications 97
Cancer, endometrial 224, 248, 251, 254
Candida 268
vaginitis 256
Carcinoma, endometrial 133
Cavity
abdominal 197
endometrial 98f, 108f, 244
Cervical
biopsy 259
canal 99f, 180f
cancer 118f, 254, 258
arcinoma 183
disorders 179
ectopic pregnancy 198
fibroid 179
lesions 291fc
myomas 272
polyp 182, 270
pregnancy 183, 204
stenosis 183, 251
Cervicitis 256
Cervix 59, 117f, 205f, 260
lesions of 256
normal 95f, 180f
Cesarean section scar 227
Chemotherapy 279
Chlamydia 240
trachomatis 256
Cholecystitis, acute 263
Chronic pelvic inflammatory disease 232, 233, 269
signs of 243, 277
symptoms of 243, 277
Chronic pelvic pain 230, 230t, 239t, 240t, 254, 277
causes of 233t, 236t
evaluation of 231fc, 242, 265
gynecological causes of 234t
management of 231fc
ultrasonography in 241, 250
urological causes of 235t
Clue cells 257
Cogwheel appearance 250
Color Doppler 162
Color flash 38
Color flow 97
baseline 32
display 30
imaging 30
mapping 178
pattern 204
Color inversion 32
Color misregistration artifact 38
Comparative power output test 42
Complete blood count 240
Complex adnexal mass 250
Compression elastography 18
Conception, retained products of 225
Continuous-wave Doppler 23
Copper-containing devices 216
Cornual pregnancy, ruptured 198
Corpus luteal cyst 203f
Corpus luteum 203
cyst 89f, 159f, 162, 248, 273
Crohn's disease 263
Cryptomenorrhea 184, 185
Cul-de-sac 81, 93f, 190, 246, 250, 252
Cystadenocarcinoma
mucinous 177
serous 174
Cystadenofibroma 204
Cystadenoma 204
mucinous 174, 249
serous 174, 249, 261
Cystic adnexal masses 204
Cystic degeneration 100f
Cystic lesions 155
Cystitis 263
interstitial 233, 235, 238
Cysts 250
anechoic 155
complex 161
endometrial 249
endometriotic 261
extraovarian 162f
functional 248, 261, 273
hemorrhagic 165f
peritoneal inclusion 193
simple 155
D
Deep dyspareunia 269
Deep pelvic endometriosis 237
Depression 233, 269
Depth gain compensation 19
Dermatitis 268
Dermoid 172f, 173f
cyst 167
Dilation and curettage 288fc
Discharge
causes of 242, 258
color of 267
nature of 267
odour of 267
Diverticular disease 237
Diverticulitis 276
Dominant follicle 87f
Doppler effect 21
Double uterus 145f, 146f
Down syndrome 47
Doxycycline 232
Dysmenorrhea 230, 234, 239, 246, 254, 264
evaluation of 242, 266
Dyspareunia 230, 234, 239, 254, 264, 269
causes of 242, 268
clinical evaluation of 242
superficial 268
Dysuria 235, 239
E
Ectopic gestations 207
Ectopic implantation
incidence of 195
sites of 195
Ectopic pregnancy 46, 136, 185, 195, 199, 203f, 207, 250, 251, 264, 276, 290fc
management of 197
ruptured 208f
sonographic features of 199
Elastography 18
Electronically steered systems 9
Embryo 185
Emergency studies 46
Empty sella syndrome 278
Endocavity ultrasound systems 13
Endocervical growth 259
Endometrial abnormalities 241, 247
Endometrial hyperplasia 121, 221, 228, 229, 254, 292fc
clinical evaluation of 242, 272
history of 242, 272
Endometrial thickness 76f, 117f, 245, 248, 300
Endometrioid tumor 177
Endometriomas 163f, 204, 264, 273
bilateral 164f
Endometriosis 230, 233235, 239, 240, 269, 277, 297fc
investigations in 243
Endometritis 120, 120f
Endometrium 57, 76, 77f, 78f, 97, 100f, 109f111f, 120, 130f, 221, 270
ablation of 228
atrophic 226, 254
echogenic irregular 120f
inflammation of 120
Episiotomy 268
Estrogen deficiency vaginitis 254, 258
Exercise 278
Extraovarian adnexal areas 58
F
Fallopian tube 60, 81, 82, 161, 188, 190, 260
abnormalities of 185
carcinoma 189
inflammation of 187
normal 187f
Female pelvis 59
anatomy of 61f
normal 69
Fetal
anomaly 47
death, misdiagnosis of 46
heart sounds 212
parts, absence of 212
Fever 258, 264
Fibroids 97, 119f, 151, 225
color flow in 97
complications of 112
interstitial 106f, 108f
multiple
seedling 107f
submucosal 98f
number of 97
pedunculated 204
polyps 109f
position of 97
size of 97
sonographic evaluation of 295fc
subserous 106f
ultrasound features of 104
Fine-needle aspiration cytology 252
Flow direction 24
Flow distortion 28
Flow pattern 25, 27
Flow velocity 25
waveform 124f
Flow volume 29
Fluid
collection 117f, 118f, 131f
debris 250
endometrial 134
loculi 58
Foley catheter 151
Follicles 245
multiple 166
Follicular cyst 160, 248, 273
Follicular monitoring 248
Folliculogenesis 91
Free fluid 58, 250
Frequency 235, 239
selection 20
Frozen pelvis 277
Full blood count 258
Fundal panmural fibroid 100f, 103f
G
Genetic abnormalities 283fc
Genital tract
congenital anomalies of 246
structural abnormalities of 242, 270
Genital ulcer 254
Germ cell tumors 261, 273
Gestational age 213
Gestational sac 203, 205f, 206f, 250
absence of 250
increased transverse diameter of 213
Gestational trophoblastic neoplasia, development of 214t
Gonococcal infection 256, 257
Gram stain 258
Gram-negative diplococci 258
Ground glass appearance 162, 163f, 249
Growth 245, 254
endometrial 259
retardation 213
Gynecological complications 53
Gynecological diseases, common 241, 282fc
Gynecological disorder, history of 239
Gynecological origin, acute abdominal pain of 242, 264
Gynecological pain 289fc
Gynecological ultrasound 53
Gynecology
common symptoms in 241, 253
Doppler in 54
Gynecomastia 221
H
Hanafy lens technology 11
Harmonic imaging 16
Heavy menstrual bleeding 234, 270
Hematometra 118f, 251
Hematosalpinx 118f
Hemoperitoneum 264
diagnosis of 252
Hemorrhage 162, 250
HIV serology 258
Hormone replacement therapy 222, 229
Hyaline degeneration 99f
Hydatidiform mole
diagnosis of 213t
signs of 212t
symptoms of 212t
Hydrocephalus 47, 278
Hydrometrocolpos 116f
Hydrosalpinges 233
Hydrosalpinx 189, 191f, 204, 251, 260, 277
Hydroureteronephrosis 277
Hyperandrogenism 165
Hyperechoic foci 249
Hyperemesis gravidarum 212
Hyperplasia 253, 270
benign endometrial 224
Hyperthyroidism 213
signs of 212
Hypoplastic left heart syndrome 47
Hypoplastic uterus 144f
Hypothalamopituitary-ovarian
axis 285f
Hysterectomy 239
history of 234
Hysteroscopy 143f, 146f
Hysterosonogram 223
I
Incomplete septae 250
Infection 219, 246, 278
Infertility 54, 234, 246, 248, 277
ultrasound evaluation of 299fc
Inflammatory bowel
disease 233, 236
syndrome 276
Infundibulum 82
Intermenstrual bleeding 270
Internal iliac vessels 154f
Intertrigo 267
Intracardiac transducers 14
Intraluminal transducers 14
Intramural fibroid 98f, 107f
Intraoperative transducers 14f
Intraovarian blood flow 167f
Intrauterine adhesions 141f
Intrauterine contraceptive device 120, 136, 137f, 138f, 185, 215, 217, 218
history of 234
localization of 246
Intrauterine growth restriction 48
Intrauterine pregnancy 199
sonographic features of 199
Irritable bowel syndrome 233, 235, 236, 276
Irritable colon 238
K
Knobology 19, 31
L
Laminar flow 27
Laparoscopy 164f, 198, 240
Left cornual fibroid 104f
Left paraovarian cyst 162f
Leiomyoma 233, 253, 270
submucous 248
Leiomyosarcoma 106
Levonorgestrel-containing devices 216
Lichen
planus 267, 268
sclerosis 268
Limb, absent 47
Loculi, multiple 194f
Lost intrauterine contraceptive device 218, 220
Low backache 277
Lower abdominal mass 242, 254, 260
evaluation of 242, 260262
Low-versus high-resistance flow 26
Lumbar spine, examination of 240
Lymph nodes 245, 252
Lymphadenitis, mesenteric 263
Lymphoma 261
M
Magnetic resonance imaging 277
Malignancy 253, 270
diagnosis of 252
Malpractice, causes of 43
Mass 234
abdominal 240, 252, 254
complex 250
descending per vaginum, evaluation of 242, 262
intracavitary 228
small 245
Medical ultrasound, basic principles of 52
Menometrorrhagia 130f
Menopausal problems 296fc
Menopause 226, 269
Menstrual abnormalities 277
Menstrual cycle 93f
proliferative phase of 85f
Menstrual outflow obstruction 278
Menstrual problems 287fc
Menstruation after apparent menopause, recurrence of 229
Mesonephric remnants 260
Molar cysts, presence of 211f
Molar pregnancy 136
pelvic ultrasound of 211f
Morgagni hydatid cyst 161
Müllerian anomalies, ASRM classification of 241, 244
Müllerian ducts 81
Multicystic ovaries 291fc
Multiple cystic spaces 134f
Multiple endocervical glands 181f
Multiple mature follicles 156f
Muscles, spasm of 269
Musculoskeletal disorders 233
Mycobacterium tuberculosis 120
Myofascial pelvic pain syndrome 233
Myoma 247, 251, 260, 272
anatomical classification of 242, 272
intracavitary 229
red degeneration of 264
submucous 251
Myometrial invasion 248
Myometritis 97, 116
Myometrium 58, 76, 77f, 97, 113f, 114f, 130f
anterior 114f
atrophic 118f
posterior 114f
N
Nabothian cysts 179, 181f
Necklace sign 166
Neoplasms, benign 273
Nerve entrapment 233
Neutrophils 258
Noncyclic pain 230
Non-neoplastic ovarian lesions 241, 248
Normal ovary 84f, 155f, 156f, 245
dimensions of 242, 273
Normal uterus 95f
ultrasonography of 241, 247
O
Obstruction 115
Obturator internus muscle 154f
Oligoovulation 165
Oophorectomy 239
Organs, intra-abdominal 245
Ovarian artery 160f
Ovarian cyst 212
rupture of 264, 276
torsion of 250, 251, 264, 276
Ovarian dermoid 170f, 171f, 173f
Ovarian disorder 154
differential diagnosis of 154
Ovarian dysgenesis 278
Ovarian endometrioma 162
Ovarian enlargement, benign conditions causing 242, 273
Ovarian follicle, thick-walled 204
Ovarian follicular cyst, simple 293fc
Ovarian fossa 154f
Ovarian hyperstimulation syndrome 273
Ovarian malignancy 251
Ovarian mass 241, 252, 277
evaluation of 178
Ovarian neoplasm 168, 294fc
Ovarian pregnancy 207
Ovarian remnant syndrome 233, 236
Ovarian size 300
Ovarian torsion 46
Ovarian tumor 296fc
Ovarian volume 91f
Ovary 53, 58, 60, 82, 90f, 91f, 154f, 191f, 201f, 261
chocolate cyst of 162
granulosa cell tumor of 254
neoplastic lesions of 241, 249
remnant 234
Ovulation 256
Ovulatory dysfunction 253
P
Paget's disease 267
Pain
abdominal 195
acute 264
chronic 232
cyclic exacerbation of 234
functional 276
location of 239
lower abdominal 277
neuropathic 233
postoperative 246
types of 239
Pallor 212
Pancreatitis, acute 263
Panmural fibroid 100f, 102f
Pap smear 258, 259
Paraovarian cyst 161
Partial hydatidiform mole 213
diagnosis of 213t
Pediculosis 267
Pelvic adhesions 233
Pelvic anatomy, normal 53
Pelvic congestion syndrome 233, 234, 237, 240
Pelvic examination 212, 240, 277
abnormal 246
Pelvic infection 246
acute 257
Doppler studies suggestive of 276
Pelvic inflammatory disease 116, 185, 230, 234, 239, 240, 292fc
Pelvic kidney 194f
Pelvic mass 240, 247, 252, 254, 277
Pelvic organs, examination of 241, 246
Pelvic pain
evaluation of 242
non-gynecological causes of 242, 263
Pelvic sonography 62, 65
Pelvic ultrasonography, techniques for 241, 245
Pelvic viscera 94
Doppler evaluation of 93
Peptic ulcer, perforated 263
Per rectal examination 240
Per speculum examination 240, 277
Pericystic vascularization 162
Perimetrium 81
Peripheral vessels 103f
Peristalsis, active 39
Peritoneal cavity 250
Peritrophoblastic blood flow 206f
Pinworm 256
Placenta
cystic spaces in 213
previa 47, 49
Polycystic ovary 164, 165, 167f, 291fc
syndrome 228, 229
Polyp 132f, 133f, 152f, 229, 245, 247, 251, 253, 254
abnormality 270
endometrial 109f, 121, 130f, 131f, 151, 225, 254
multiple 227
Postcoital bleeding 270
Post-endometrial ablation 229
Posterior wall
panmural fibroid 99f
submucous fibroid 110f, 111f
subserous fibroid 104f, 105f
Postmenopausal bleeding 245, 248, 270, 298fc
causes of 241, 254
Postmenopausal estrogen deficiency 268
Postmenopausal hormone replacement therapy 227
Postradiation scarring 269
Post-void fullness 235
Pouch of Douglas 58, 93, 190, 192f, 193, 193f, 194f, 197, 245, 269
Power Doppler 33
Pre-eclampsia 212, 213
signs of 212
Pregnancy 207, 219, 260
interstitial 205f
intra-abdominal 207
test
negative 221
positive 264
Previous infection, history of 277
Primary amenorrhea 144f
causes of 243, 278
evaluation of 243, 279, 280
Proteinuria 212
Pruritus 254
vulvae 242, 267
clinical evaluation of 242, 267
Pseudo sac 197
Psoriasis 267, 268
Psychiatric disorders, history of 239
Psychosomatic disorders 233
Puberty
delayed 246
precocious 221, 246
Pubic symphysis, separation of 233
Puborectalis muscle 245
Pulse
echo 52
instruments 52
inversion 16
Pulsed-Doppler transducer 22f
Pus
aspiration of 252
drainage of 252
in cul-de-sac 250
Pyometra 258, 259
Pyoperitoneum, diagnosis of 252
Pyosalpinx 250, 264
Q
Quality control tests 42
R
Radiotherapy 279
Range gate cursor 31
Rectovaginal modules 249
Rectovaginal septum 245
Remnant ovary 240
Renal calculus 263
Residual ovary 240
Resistive index 166f
Retroflexion 75
Retroversion 75
Ring of fire pattern 203f
Rokitansky protuberance 167
Rotterdam criteria 164
S
Sacroiliac joints, examination of 240
Sacroiliitis 233
Saline infusion
sonography 241, 251
study 222, 223
Salpingectomy 198
Salpingitis 264
acute 187
chronic 188
Salpingostomy 198
Scabies 267
Seborrhea 268
Secondary amenorrhea, evaluation of 243, 281
Sepsis, systemic signs of 264
Sexual dysfunction 233
Shear-wave elastography 19
Simple anechoic functional cyst 157f
Single uterine horn 140
Small intestine 204
Solid ovarian tumor 177
Solid right ovarian mass 177f
Solitary nabothian cyst 182f
Sonohysterography 121, 143, 143f, 150f, 151f
Sound wave propagation 1
Speculum examination 254
Spina bifida, missed 47
STD, history of 234
Stimulation multiple follicles 88f
Stratum
basale 76
functionale 76
Stress 278
Stromal tumors 273
Subendometrial flow, moderate 129f
Subendometrial stromal vacuolation 248
Submucosal fibroid 104f, 107f, 110f, 112f
Surgery 268
history of 239
Swelling 254
Syphilis, serology for 258
T
Tachycardia 212, 258
Tamoxifen 223, 227
therapy 248
Tardy reporting 48
Tenderness 231, 254, 264, 277
Teratoma 204
benign cystic 261
Theca lutein cysts 161, 213, 214, 248, 273
Theoretical training program 51
Thick endometrium 122f124f, 126f, 127f
Thin endometrium 128f
Thyroid 279
storm 212
Thyrotoxicosis 212
Tissue
harmonic imaging 16
vibration 39
Total hydatidiform mole 210
Transabdominal scan 69, 72f, 172f
Transabdominal sonography 62, 95f
Transabdominal ultrasound 146f, 202f, 208f
Transducer 7
care 40
focal zone 6
formats 15
frequency 5
selection 21
Transeophageal echocardiography transducer 13f
Transesophageal transducers 14
Transvaginal scan 69, 145f, 156f, 172f
Transvaginal sonography 62, 73f, 96f, 185, 198
Transvaginal transducer 13f
Transvaginal ultrasound 146f, 206f, 259
Trauma 278
Tremor 212
Trichomonas 268
vaginalis 256, 257
Trichomoniasis 267
Trilaminar appearance 222
Trophoblastic embolization 212
Tubal evaluation 189
Tubal ligation 235
Tubal surgery, previous 185
Tuberculosis 239, 257
diagnosis of 252
Tubo-ovarian abscess 167, 250
Tubo-ovarian complex 167, 188
Tubo-ovarian mass 240, 250, 260, 277
Tumors
endometroid 261
epithelial 261
malignant 249
mucinous 261
Turner syndrome 278
Twin ectopic pregnancies 202f
U
Ultrasonography 162, 213, 241, 248
basics in 1
indications for 241, 245
Ultrasound 196
examination 197
guided procedures 241, 252
transducers 12f
Ureteric calculus 263
Urethral syndrome 233, 235
Urinary bladder 62
Urinary incontinence 246
Urinary tract infection 276
chronic 233, 235
recurrent 235
Uterine 260
abnormalities 241, 247
anomalies 247, 248
congenital 139
calcifications 116
cavity 97, 109f, 110f, 143, 126f, 151f, 211f
contour 108f
distortion of 104
corpus 73f, 99f, 110f, 136f
disorders 95
enlargement 104, 254, 264
fundus 137f
musculature 97
myoma, subclassification of 242, 272
size 300
synechiae 140
tenderness 240
wall, posterior 107
Uterosacral ligaments 240
Uterovaginal agenesis 278
Uterus 53, 57, 59, 69, 72f, 79f, 80f, 96f, 117f, 201f, 213, 246, 250, 278
acutely retroverted 269
adenomyotic 113f
anteverted 72f-74f, 96f
body of 272
evaluation of 95
infantile 70f
irregularly enlarged 264
multiparous 300
myometrium 106f
nulliparous 300
postmenopausal 300
prepuberty 300
retroverted 74f, 75f, 269
septate 122f, 146f
size of 97
subseptate 147f
V
Vagina
abnormal 183
lesions of 256
Vaginal atresia 116f, 286f
Vaginal bleeding 195, 212, 213, 221, 288fc
causes of 225
irregular 195, 270
Vaginal discharge 240, 242, 253, 254, 259, 267, 269, 276
causes of 241, 242, 256
clinical evaluation of 242, 258
investigations of 242, 257
Vaginal infections, diagnosis of 242, 257
Vaginal swab 240
Vaginal vault 80f, 81f, 184f
Vaginismus 268
causes of 242, 268
Vaginitis 256, 268
signs of 269
Venereal disease research laboratory 240
Venous drainage 82, 90
Vesicles, passage of 212
Vesicular mole 260
Vessels, arrangement of 178
Vulva, Paget's disease of 267
Vulval cancer 267
Vulval lesions 268, 269
Vulvar vestibulitis 268
Vulvodynia 268
Vulvovaginitis 256, 267
W
Wobble sign, positive 169
X
XX/XY gonadal agenesis 278
XY gonadal agenesis 283fc
Y
Yolk sac 185, 205f
×
Chapter Notes

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Basics in UltrasonographyCHAPTER 1

 
BASIC PHYSICS
In order to obtain the best image possible, basic fundamentals of ultrasound wave physics must be understood and applied.
 
Audible Sound Waves
Audible sound waves lie between 20 and 20,000 Hz: Ultrasound uses sound waves between l and 30 MHz.
 
Sound Wave Propagation
Sound waves need a media to travel and do not exist in a vacuum, and propagation in gases is poor because the molecules are widely separated.
The closer the molecules are, the faster the sound wave moves through a medium, so bone and metals conduct sound exceedingly well.
 
Effect on Image
Air-filled lungs and gut containing air conduct sound so poorly that they cannot be imaged with ultrasound instruments. Structures behind them cannot be seen.2
A neighboring soft-tissue or fluid-filled organ must be used as a window through which to image a structure that is obscured by air.
An acoustic gel must fill the space between the transducer and the patient, otherwise sound will not be transmitted across the air-filled gap.
Bone conducts sound at a much faster speed than soft tissue.
Because ultrasound instruments cannot accommodate the difference in speed between soft tissue and bone, current systems do not image bone or structures covered by bone.
 
Pulse-Echo Principle (Figs. 1.1A and B)
Because the crystal in the transducer is electrically pulsed, it changes shape and vibrates, thus producing sound waves that propagates through the tissues.
The crystal emits sound for a brief moment and then waits for the returning echo reflected from the structures in the plane of the sound beam.
When the echo is received the crystal again vibrates, generating an electrical voltage comparable to the strength of the returning echo.
 
Effect on Image
Greyscale imaging shows echoes in varying levels of grayness, depending on the strength of the interface.
 
Beam Angle to Interface (Fig. 1.2)
The strength of the returning echo is related to the angle at which the beam strikes the acoustic interface. The more nearly perpendicular the beam is, the stronger the returning echo will be smooth. Interfaces at right angles to the beam are known as specular reflectors.3
zoom view
Figs. 1.1A and B: The pulse-echo principle. (A) The electrical pulse strikes the crystal and produces a sound beam, which propagates through the tissues; (B) Echoes arising from structures are reflected back to the crystal, which in tum vibrates, generating an electrical impulse comparable to the strength of the returning echo.
zoom view
Fig 1.2: Beam angle to interface.
4
Echoes reflected at other angles are known as scatter.
 
Effect on Image
To demonstrate the borders of a body structure, the transducer must be placed so that the beam strikes the borders more or less at a right angle.
It is worthwhile to attempt to image a structure from different angles to produce the best representation. (Fig. 1.3).
zoom view
Fig. 1.3: When visualizing a structure, it is important to scan at several different angles to find the best possible interface (thick arrows). Only a few echoes return from the interfaces at an oblique angle to the beam—specular reflections (thin arrows). Most of the echoes are scattered.
5
 
Tissue Acoustic Impedance
The returning echo's strength also depends on the differences in acoustic impedance between the various tissues in the body.
Acoustic impedance relates to tissue density; the greater the difference in density between two structures, the stronger the returning interface echoes defining the boundaries between those two structures on the ultrasound image will be.
 
Effect on Image
Structures of differing acoustic impedance (such as the gallbladder and the liver) are much easier to distinguish from one another than are structures of similar acoustic texture (e.g. kidney and liver).
 
Absorption and Scatter
Because much of the sound beam is absorbed or scattered as it travels through the body, it undergoes progressive weakening (attenuation).
 
Effect on Image
Increased absorption and scatter prevent one from seeing the distal portions of a structure. In obese patients, the diaphragm is often not visible beyond the partially fat filled liver.
Fibroids may absorb so much sound that their posterior borders may be difficult to define.
 
Transducer Frequency
Transducers come in many different frequencies-typically 2.5, 3.5, 5, 7, and 10 MHz.6
Increasing the frequency improves resolution but decreases penetration.
Decreasing the frequency increases penetration but diminishes resolution.
 
Effect on Image
Transducers are chosen according to the structure being examined and the size of the patient. The highest possible frequency should be used because it will result in superior resolution. Pediatric patients can be examined at 5–10 MHz.
Lower frequencies (e.g. 2.5 MHz) permit greater penetration and may be needed to scan larger patients.
 
Beam Profile (Fig. 1.4)
The sound beam varies in shape and resolution.
Close to the skin, it suffers from the effect of turbulence, and resolution here is poor. Beyond the focal zone, the beam widens.
 
Effect on Image
Information that appears to be present in the near field may actually be an artifact. Structures beyond the focal zone are distorted and difficult to see. A structure as small as a pinhead may appear to be half a centimeter wide.
 
Transducer Focal Zone
Sound beams can be focused in a similar fashion to light. Most systems use electronic focusing which permits the transducer to be focused at one or more variable depths. The sonographer can alter the focus level electronically.7
zoom view
Fig. 1.4: Diagram of the waveforms in a sound beam. Unequal waveforms in the near field (Fresnel zone). Widening of focal beam (Fraunhofer zone) beyond the focal zone.
 
Effect on Image
To achieve high resolution chose a transducer with a proper focal zone or use a electronically focusing set at the right depth.
 
INSTRUMENTATION
 
Transducers
The transducer assembly consists of five main components (Fig. 1.5).
  1. The transducer crystal is composed of a piezoelectric material, most commonly lead zirconate titanate. It converts the electrical voltage into acoustic energy upon transmission and acoustic energy to electrical energy upon reception.8
    zoom view
    Fig. 1.5: Diagram showing transducer construction. Matching layers of material decrease the size of the main bang acoustic interface that occurs between the crystal and the skin. Backing material acts as a damping tool to stop secondary reverberations of the crystal. The crystal is constructed of piezoelectric material, which can convert electrical impulses into sound waves and vice versa.
  2. The matching layers lie in front of the transducer element and provide an acoustic connection between the transducer element and the skin.
  3. Damping material is attached to the back of the transducer element to decrease secondary reverberations of the crystal with returning signals.
  4. The transducer case provides a housing for the crystal and damping layer and insulation from interference by electrical noise.
  5. The electronic cable contains the bundle of electrical wires used to excite the transducer elements and receive the returned electrical impulses.
There are several types of transducer elements:9
  1. Mechanical transducers
    • The transducer crystal is physically moved to provide steering for the beam
    • Less commonly used in modern equipment than phased-array transducers
    • Often used in volume transducers for 3D or 4D applications.
  2. Oscillating transducer (volume)
    • The drive motor and transducer array are housed in the transducer case
    • The motor drives the transducer array back and forth to generate an image (Fig. 1.6).
  3. Electronically steered systems
    • In this type of transducer, multiple piezoelectric elements are used and a separate electrical signal is provided for each element
      zoom view
      Fig. 1.6: Oscillating transducer (volume).
      10
    • Steering and focusing occur by sequentially exciting individual elements across the face of the transducer
    • Focusing is controlled electronically by the operator through placement of the focal zone or focus caret
    • The images are displayed in a sector, vector, linear, or curved linear format.
  1. Linear sequenced arrays (Fig. 1.7)
    • Multiple transducer elements are mounted on a straight or curved bar.
    • Groups of elements are electronically pulsed at once to act as a single larger element
    • Pulsing occurs sequentially down the length of the transducer face, moving the sound beam from end to end
    • Linear arrays produce a rectangular shaped image which is used in breast, small parts, vascular, and musculoskeletal imaging
    • Curved arrays provide a large fan-shaped image with a curved apex. These transducers are most commonly used in obstetric, gynecologic, abdominal, and endocavity imaging.
  2. Phased array
    • The phased array consists of multiple transducer elements mounted compactly in a line
      zoom view
      Fig. 1.7: Linear sequenced array.
      11
      zoom view
      Fig. 1.8: Wedge-shaped field.
    • All elements are pulsed as a group with small time delays to provide beam steering and focusing
    • The resulting image is in a sector or vector format and is particularly useful in cardiac and intercostal imaging (Fig. 1.8).
    Matrix Array (Multi-O Array, 1.5D Array, 2D Array) Transducers:
    • This type of transducer utilizes multiple rows of elements to form a matrix of crystals (Fig. 1.9)
    • Through the use of multiple pulses, these crystals may be pulsed in sequence to create a very thin elevation plane (slice thickness), which yields increased resolution.
 
Hanafy Lens Technology
  • This is another technique used to create a very thin slice thickness that is uniform throughout the field of view12
    zoom view
    Fig. 1.9: Various ultrasound transducers.
  • With this technology, the transducer crystals are cut in a planoconcave fashion (Figs. 1.10A and B), which creates crystals that are thin in the center and thicker at the edges
  • The thinner center will ring at a higher frequency (focusing in the near field), and the thicker edges will ring at a lower frequency (focusing in the far field), automatically creating a uniform elevation plane (slice thickness) throughout the field of view.
 
Special Transducers
Special transducers (Fig. 1.11) have been produced to help view specific areas:
  • Small parts (7.5–15MHz) transducer
  • Rectal transducers in longitudinal (linear) and transverse (radial) configurations (biplane)
  • Biopsy transducer
  • Doppler probes.13
zoom view
Figs. 1.10A and B: Transvaginal transducer. Transeophageal echocardiography transducer.
 
Endocavity Ultrasound Systems
The transducer array, which can be a linear, curved, or phased array (or mechanical sector) scanner, is placed at the end of the transducer shaft. This transducer shaft is inserted into the rectum or vagina to produce high-resolution images of the male or female pelvic organs.14
zoom view
Fig. 1.11: lntraoperative transducers are designed to allow easy access to anatomy.
 
Transesophageal Transducers
A transesophageal transducer may be introduced into the esophagus to visualize the heart and provides a higher resolution image than does transthoracic echocardiography.
 
Intraluminal and Intracardiac Transducers
  • Smaller transducers at the ends of catheters can be introduced into vessels, the biliary duct, or the ureter (transluminal transducers)
  • These transducers allow close visualization of the anatomy that is being examined, but are not commonly used
  • Intracardiac catheters have been developed more recently. A small catheter (IOF or BF), which may be introduced into the right heart, provides very high-resolution imaging and may be used for interventional and electrophysiology applications.15
 
Operative Systems
Standard ultrasound systems are modified so they can be used in a sterile fashion in the operating room. Special high-frequency ultrasound probes are used for this purpose. Intraoperative transducers are designed with a size and shape to allow easy handling and positioning during intraoperative procedures.
 
Transducer Formats
There are a variety of transducer formats available in modern equipment, each suited to particular scanning applications.
Linear array: The linear format provides a rectangular image. This transducer is most useful in “small parts” and vascular imaging.
Vector: A vector format provides a trapezoidal image. This small foot-print transducer is often used in abdominal, gynecologic, and obstetric applications.
Sector: The sector image is wedge-shaped and is commonly used in cardiac, abdominal, gynecologic, obstetric, and transcranial imaging.
Curved array: A curved array transducer will provide a large field of view with a convex near field. This transducer is most commonly used in obstetrics; however, other applications include abdominal and gynecologic imaging.
 
NEW TECHNIQUES FOR IMPROVING THE IMAGE
 
3D Imaging Systems
  • 3D imaging capabilities have been increasing in popularity’ over recent years
  • It is most commonly used in obstetric and cardiac imaging to evaluate the surface of structures or to evaluate orthogonal planes16
  • It utilizes specialized transducers which relate the transducers position to the ultrasound system allowing for a very accurate display of the acoustic echoes.
 
4D Imaging Systems
  • 4D imaging systems use specialized transducers to display the real-time motion of a 3D image
  • These are most commonly used for obstetric and cardiac applications
  • The transducers are commonly mechanical transducers, which are held in place while the ultrasound system controls the acquisition of the images by “rocking” the transducer crystals and displaying the 4D images.
 
Harmonic Imaging
  • Images are obtained from returning signals, which are a multiple of the transmitted (fundamental) frequency
  • The harmonic signal is created from the compression and relaxation of tissues during sound propagation
  • It is helpful to reduce noise and clutter in an image, especially in technically difficult patients; however, harmonic imaging may suffer from decreased penetration due to the higher receive frequency.
 
Tissue Harmonic Imaging and Pulse Inversion
  • With traditional ultrasound techniques, the ultrasound system transmits a pulse of a specific frequency and receives a pulse of the same frequency. This frequency is known as the fundamental frequency
  • As this fundamental frequency travels through tissues, the tissues compress and expand with the variations in acoustic pressure, resulting in the generation of additional ultrasound frequencies, known as harmonics17
  • The harmonic frequencies are multiples of the transmitted fundamental frequency
  • The challenge for the ultrasound system is to separate the clean harmonic signals from the fundamental signals. Tissue harmonic imaging removes noise from images, especially in patients who are difficult to image
  • The simplest separation method is to lengthen the transmitted pulse
  • Pulse inversion techniques utilize multiple pulses on transmit which vary in phase, which is maintained on transmit and receive
  • The harmonic signals generated by the tissue have a different shape and phase than that of the transmitted pulse
  • By summing the received pulses, the ultrasound system cancels the fundamental frequencies (destructive interference) and adds the harmonic signals (constructive interference)
  • This technique often results in reduction in frame rate.
 
Image Compounding
Multiple ultrasound frames are averaged together to produce an image with increased contrast resolution.
 
Compound Imaging/Sie Clear Multiview Spatial Compounding/Sona CT Cross Beam Imaging
Image compounding averages multiple ultrasound frames to produce an image with increased contrast resolution.18
Image compounding may use image frames of varying frequency (transmit or frequency compounding) or by utilizing image frames from varying angles (spatial compounding). They are of the following types:
Frequency Compounding
Frequency compounding uses multiple transmit pulses to obtain images of the same area with different frequencies
  • It provides an increase in contrast resolution and penetration.
Spatial Compounding
  • This technique interrogates the same area of interest from various locations
  • By averaging these ultrasound frames, the speckle pattern is reduced and will provide an image with increased contrast resolution
  • Spatial compounding may occur by varying the transmitted beam's location, varying the transducer position, or by varying the location of the receive beam.
Speckle Reduction Imaging
Speckle reduction imaging is processing algorithm that reduces image speckle. The resultant images appear smoother and have increased contrast resolution as compared to the image without speckle reduction.
Elastography
  • Elastography is an ultrasound technique used to evaluate the relative stiffness of tissue as compared to the surrounding area
  • Results may be qualitative or quantitative in nature.
Compression elastography: It is a qualitative imaging technique that utilizes manual compression to present the 19relative stiffness of tissue through a color or black/white overlay of the image. It is most commonly used in breast imaging.
Shear-wave elastography: It is a technique that utilizes an electronic push pulse to provide compression of tissues. The speed of the shear wave generated by the tissue compression may then be measured. It is most commonly used in the evaluation of the liver.
 
KNOBOLOGY
Learning to use the knobs effortlessly is an important part of the art of ultrasound imaging.
 
Gain
The system gain controls the degree of echo amplification or brightness of the image. Care must be taken with the use of gain. Too much overall gain can fill fluid-filled structures with artifactual echoes, whereas too little gain can negate real echo information.
 
Depth Gain Compensation
The depth gain compensation (DGC) attempts to compensate for acoustic loss of sound waves by absorption, scatter, and reflection and to show structures of the same acoustic strength with the same brightness, no matter what the depth is.
 
Dynamic Range (Dynamic Contrast/Log Compression)
The dynamic range (log compression) is the range of intensities from the largest to the smallest echo that a system 20can display. Changing the log compression does not affect the number of gray shades in the image; instead, it varies the display of the gray shades.
 
Edge Enhancement (Preprocessing)
The preprocessing control alters the edges of the image pixels to accentuate the transition between areas of different echogenicities, making the borders sharper.
 
Frequency Selection (MultiHertz)
Frequency selection allows the user to optimize the imaging for the best resolution or penetration. Increasing the frequency will improve resolution but sacrifice penetration.
 
Maps (Postprocessing)
Maps alter image esthetics by placing more or less emphasis on specific echo intensities. Changing the map may aid the user in evaluating pathology.
 
Persistence
It is a frame-averaging function that allows echo information to be accumulated over a longer period of time. By increasing the persistence subtle tissue texture differences will be enhanced and by decreasing it the moving structures are evaluated more easily.
 
Speckle Reduction Imaging
Speckle reduction imaging (SRI) is an image processing algorithm that reduces image speckle for enhanced contrast 21resolution. Higher SRI settings result in images with a smoother appearance and increased contrast resolution, as compared to the image without speckle reduction.
 
Zoom
The zoom function allows image magnification by increasing the pixel size, although this change results in image degradation.
 
Write Zoom (Res)
With write zoom, a box is placed on the screen, and the area seen within the box can be expanded to fill the screen.
 
Transducer Selection
The transducer selection feature allows the user to activate the transducer of choice.
 
Calipers
Caliper markers are available to measure distances. The ellipsoid measurement is an added feature in most units. A dotted line can be created around the outline of a structure to calculate either the circumference or the area.
 
DOPPLER AND COLOR FLOW PRINCIPLES
Doppler physics as it relates to diagnostic ultrasonography concerns the behavior of high-frequency sound waves as they are reflected off moving fluid (usually blood) (Fig. 1.12).
 
Doppler Effect
When a high-frequency sound beam meets a moving structure, such as blood flow in a vessel, the reflected sound returns at a different frequency. The speed (velocity) of the moving structure can be calculated from this frequency shift (Fig. 1.13). The returning frequency will be increased if flow is toward the sound source (transducer) and will be decreased if flow is away from the sound source.22
zoom view
Fig. 1.12: Diagram of a pulsed-Doppler transducer demonstrating the direction of the transmitted sound beam toward the flow of blood and the receiving sound beam back to the transducer.
 
Clinical Correlation
The Doppler effect is helpful in localizing blood vessels and determining optimal sites for velocity measurements. Veins typically have a low-pitched hum, whereas arteries have an alternating pattern with a high-pitched systolic component and a low-pitched diastolic component.23
zoom view
Fig. 1.13: Diagram showing the components of the Doppler equation. φ, angle of insonation of the vessel; c, speed of sound in tissue (–1,540 m/ sec). (Fr: return frequency; Ft: sending frequency; V: blood flow velocity).
 
Continuous-wave Doppler
The sound beam is continuously emitted from one transducer crystal and is received by the second. Both transducers are encased in one housing.
  • Dedicated continues-wave (CVV) Doppler pencil probes.
  • Imaging CW Doppler.
 
Clinical Correlation
Vascular surgeons use CW Doppler to check for the presence or absence of flow in superficial arteries. CW Doppler is also sometimes used to monitor umbilical artery flow. Because 24the cord lies in the amniotic fluid, no other confusing vessels are within the ultrasonic beam.
 
Pulsed Doppler
A Doppler sound beam is sent and received (pulsed) over a short period of time. Because the time that the Doppler signal takes to reach the target can be converted to distance, the depth of the site sampled is known.
The pulsed sound beam is “gated.” Only those signals from a vessel at a known depth are displayed and analyzed.
 
Clinical Correlation
Pulsed Doppler is used to detect the presence of blood flow in a select vessel at a given depth when there are several vessels within the ultrasonic beam. Clots can appear echo-free, so a real time image may erroneously appear to show a normal vessel even if it is occluded. Doppler will detect no flow. Flow from other vessels outside the region of the gate is not analyzed because only the gated area is examined.
 
Flow Direction
The direction of blood flow can be discovered by assessing whether the frequency of the returning signal is above or below the baseline in a suspect vessel. Flow toward the transducer is traditionally displayed above the baseline, and flow’ away from the transducer is shown below the baseline.
 
Clinical Correlation
Flow in the portal vein is sometimes reversed when pressure in the liver increases in portal hypertension; flow away from the liver is known as hepatofugal and indicates that the portal pressure is so high that flow has been reversed. A memory 25aid that some sonographers find useful to remember this often confusing terminology, is “fugitives flee.” Flow toward the liver is known as hepatopetal. Flow direction analysis allows the diagnosis of the abnormal hepatofugal flow.
 
Flow Pattern
The pattern of flow can be assessed with Doppler ultrasound. Typically, a vein shows a continuous rhythmic flow in diastole and systole and emits a lower pitched signal than does arterial flow. Arterial flow has an alternating high-pitched systolic peak and a much lower diastolic level.
 
Clinical Correlation
Veins may be confused with arteries in real time.
 
Flow Velocity
The velocity of blood flow can be deduced from the arterial waveform (Fig. 1.14). If the peak systolic flow frequency and the angle at which the beam intersects the vessel are known, a simple formula allows the calculation of velocity (Fig. 1.13). The velocity calculation formula is only accurate if the angle of the Doppler beam to the interrogated vessel is less than 60 degrees.
zoom view
Fig. 1.14: Diagram of an arterial spectral waveform in a low resistance bed.
26
 
Clinical Correlation
Velocity is an important factor in calculating the severity of carotid stenosis. Generally, the more severe the stenosis is, the greater the velocity through the narrowed vessel will be. As the vessel becomes critically occluded, however, flow velocity will diminish.
 
Low- versus High-resistance Flow
Doppler flow analysis allows the detection of two types of arterial flow: a high-resistance (Fig. 1.15) and a low-resistance pattern.
The high-resistance pattern has a high systolic peak and a low diastolic flow.
Low-resistance arterial systems demonstrate a biphasic systolic peak and a relatively high level of flow in diastole.
Resistance index (RI) is commonly calculated by the following formula:
zoom view
Fig. 1.15: Diagram of an arterial spectral waveform in a high resistance bed.
27
zoom view
An alternative technique, known as the pulsatility index (PI), evaluates the diastolic flow in a different fashion. A cursor is run along the superior aspect of the systolic and diastolic flow envelope, and the mean is calculated by the system.
PI = (Systolic velocity – Mean flow)/(Systolic velocity)
In obstetrics, the A/B or systolic-diastolic (SID) ratio is commonly used:
zoom view
All three of these parameters (RI, PI, and SID ratio) are just different mathematical constructs that attempt to estimate the relative difference in flow velocity between systole and diastole.
 
Clinical Correlation
If a high-resistance pattern is seen where there is normally a low-resistance appearance, such as in the common carotid or renal artery, vessel narrowing is present. Quantifying the severity of the resistance may help in clinical management.
A high-resistance pattern is usually seen in the vessel supplying the ovaries in the proliferative phase of the cycle.
If a low resistance pattern (RI < 0.4) is seen within an ovarian mass, carcinoma is more likely.
 
Flow Pattern within a Vessel (Laminar Flow)
In a normal vessel, the velocity of blood is highest in the center of a vessel and is lowest closer to the wall. This condition is termed laminar flow. When there is a wall irregularity or if the artery is angled, the flow is distorted and may be greatest 28when it is closest to the vessel wall. Stenosis markedly increases the flow velocity—through an area of narrowing, whereas vessel dilatation decreases the speed of flow.
 
Clinical Correlation
To accurately measure the flow velocity in a tortuous carotid artery, place the sample volume (the area that is gated) at the center of the highest flow. Listening to the audible signal is useful in determining the site for optimal measurement. A high-grade stenosis will have a shrill, chirping sound.
 
Flow Distortion
Normal laminar flow at and immediately beyond an area of wall irregularity or stenosis is disturbed, resulting in abnormal spectral waveforms. Flow distortion (nonlaminar) is characterized by high velocities in both systole and diastole. The presence of many echoes within the sonic window is termed spectral broadening and may indicate considerable flow disturbance.
 
Clinical Correlation
Flow disturbance in an artery such as the carotid may indicate pathologic atheromatous changes.
 
Flow Changes beyond a Narrowed Area (Poststenotic Changes)
Poststenotic changes in arterial flow may be seen in the next few centimeters beyond a narrowed area. When there is severe stenosis, the systolic peak in the poststenotic area will be lower (more rounded) with lower velocities throughout diastole. The acceleration slope of the systolic peaks (peak 29systole) will be diminished. This pattern is known as the tardus et parvus abnormality. In less severe obstruction, the spectral waveform may resume the normal high- or low-resistance flow appropriate for that artery.
 
Clinical Correlation
Detecting a poststenotic pattern is particularly valuable in evaluating the renal arteries because the usual site of stenosis, adjacent to the aorta, is rarely seen owing to the presence of bowel gas. Poststenotic changes may also be seen in the common carotid artery when the stenosis involves the origin of the common carotid. The waveform of the other common carotid should be evaluated for comparison. Large calcified plaques may obscure the area of stenosis, so one may be dependent on poststenotic changes to determine the severity of narrowing.
 
Flow Volume
The flow volume through a given vessel can be roughly estimated if the velocity of flow and the vessel diameter are known.
 
Clinical Correlation
The calculation of flow volume is important in situations in which a low level of flow is associated with inadequate function, e.g. penile arterial flow.
 
Aliasing
If there is a marked frequency shift with a high measured velocity, the signal may return after the next pulse has started. This condition is called aliasing.30
To compensate for aliasing, increase the velocity range (PRF). Lowering the baseline may also prevent aliasing.
 
Clinical Correlation
If aliasing is present, the peak signal will be inaccurately measured as lower than it really is, and the severity of the stenosis will be incorrectly measured.
 
Color Flow Imaging
Color flow assigns different hues to the red blood cells in a vessel depending on their velocities and the direction of the blood flow relative to the transducer. This allocation is based on the Doppler principle.
 
Clinical Correlation
The site of maximum flow can be visualized quickly so that the pulsed Doppler gate can be inserted where the flow is highest.
 
Color Flow Display and Direction within a Vessel
In most systems, flow toward the transducer is allocated red, and flow away from the transducer is allocated blue. The flow velocity is displayed with faster velocities in brighter colors and slower velocities in darker colors. The fastest velocity may be displayed in yellow or white. Turbulent flow will demonstrate a mixture of colors.
As with pulsed Doppler, optimal images are only obtained at an oblique angle. If a vessel runs a straight course, flow at 90 degrees to the color box will not be displayed. The angle of 31the color box region of interest (ROI) can be adjusted to the left or right when linear steering is available; otherwise, the probe can be manually angled to provide the angle needed to receive the returning signals.
 
Clinical Correlation
Soft plaque may be missed on gray scale but a flow void will be seen using color flow. Sometimes, soft plaques may show no changes on grayscale. Once correct color allocation has been made, normal vessels will fill with color.
 
Knobology: Doppler and Color Flow
 
Range Gate Cursor (Sample Volume)
The Doppler sample volume is displayed on the B-scan image. This cursor, which may be presented as a box or two parallel bars, indicates the depth and area from which the Doppler signal is obtained.
 
Region of Interest
This box is used to restrict the color display of a blood flow image and to eliminate an unnecessary display of color.
 
Inversion and Direction of Flow and Its Relation to Baseline (Doppler)
When blood flow is moving toward the transducer, sound waves of high frequency are reflected, and positive signals are seen above the baseline. Blood cells that are moving away from the transducer appear as negative signals below the baseline. Both veins and arteries can show flow in either direction because interpreting flow direction depends on the angle of the vessel to the transducer.32
 
Color Inversion
As in spectral Doppler, the display of color is dependent on the angle of the flow to the transducer.
 
Color Flow Baseline
Blood flow toward the transducer will be shown within the measurable range of colors above the color bar baseline. Blood flow away from the probe will be displayed in the range of colors below the baseline.
 
Velocity Scale/Velocity Range/PRF (Doppler)
The range of velocities that can be seen in the spectral display is determined by the PRF value. Higher velocity vessels (e.g. carotid) requires a high PRF; therefore, the velocity range should be increased.
 
PRF (Color Flow)
The range of velocities used in color flow is lower compared to the spectral waveform because the average Doppler shift frequency is displayed rather than the peak velocity. Depending on the color map used, lower PRF values may present a shift to a different color, representing a slightly higher velocity flow (i.e. white or yellow).
 
Sweep Speed (Doppler Only)
The rate at which the spectral information is displayed can be adjusted using the sweep speed controls. A slow speed (e.g. 25 mm/sec), a moderate speed (e.g. 50 mm/sec), or a fast speed (e.g. 100 mm/sec) can be selected.33
 
Wall Filter (Doppler)
Blood flow signals that are not wanted can be eliminated by using the wall filter.
 
Filter (Color Flow)
A phenomenon called color flash, caused by cardiac or peristaltic motion or by transducer movement, produces a flash of spurious color in an area where there is no real flow. The area of interest can be concealed by the flash artifact.
 
Gain (Doppler and Color Flow)
The gain controls alter the spectral waveform and the color flow image. Inadequate gain results in an image in which the vessel is incompletely filled with color or in which no spectral Doppler signal can be obtained in areas of slow flow.
 
Angle Correct Bar (Flow Vector)
An angle correct bar is situated within the range gate cursor. This bar should be aligned with the direction of blood flow. The angle created by the insonating ultrasound beam and this bar must be known if the flow velocity is to be deduced from the frequency of the returning Doppler signal. The angle should be less than 60 degrees.
 
Power Doppler
Power Doppler utilizes the amplitude of the Doppler signal to generate the ultrasound image. Areas with high concentrations of blood cells will appear in brighter colors while lower concentrations of blood cells will appear in darker colors. This technique is more sensitive for subtle 34flow than is conventional color flow Doppler. Power Doppler typically does not provide any directional information and is particularly useful for evaluating the presence of flow or low flow in small or subtle vessels (e.g., ovarian masses).
 
Audio Volume
The Doppler sound will be heard from the built-in speakers. Usually, there are independent speakers for both forward and reverse flow. The control varies the volume of the Doppler sound.
 
Cursor Movement Control
The cursor (range gate cursor and ROI) movement can be manipulated by means of a trackball or a joystick.
 
Measurements
The standard measurement unit used in displaying the spectral waveform is velocity (m/sec or cm/sec). When dealing with a high grade stenosis, obtain maximum velocities at and just beyond the area of lumen narrowing.
 
Pitfalls
 
Incorrect Angle
A waveform that appears to indicate a distal obstruction is displayed in a vessel; however, no plaque is seen in the vessel.
 
Correction Technique
Check the position of the ultrasound beam relation to the direction of flow. If the angle greater than 60 degrees, then the velocity is not being accurately calculated, and an abnormal waveform is created.35
 
Little or No Doppler Signal in an Artery
The spectral waveform shows apparent low systolic flow and minimal diastolic flow. This may be because of:
  • There may be a severe obstruction proximal to this area and in an area too difficult to evaluate with the ultrasound beam (e.g., origin of the common carotid artery)
  • This patient may have diminished cardiac output
  • The sample volume (gate) may not be placed where maximum flow is present
  • The sample volume is too large for the small amount of flow
  • The wall filters level is set too high.
Correction Technique
  • Do not depend solely on the visualization of the vessel
  • Color flow highlights the higher velocities in the artery and helps in gate placement, but a keen ear is more sensitive
  • A higher velocity may be evident as the sound beam is angled slightly off the center of the stream
  • A larger sample size may be needed when scanning to locate the site of flow, but to obtain a more precise flow measurement within an artery, decrease the gate size
  • The wall filter should be set at the lowest setting that does not introduce artifacts, especially when scanning a vein (a low-flow state)
Try the following maneuvers before giving up:
  • Change to another acoustic window or different incident angle
  • Open up the gate setting
  • Lower the velocity’ range36
  • Use a lower frequency transducer. The patient may be too obese for a higher frequency transducer.
 
A High-resistance Waveform in a Low-resistance Bed
 
Explanation
There may be soft plaque distal to this area. If the B-scan gain is too low, soft plaque may be missed. Use color flow to outline the true patent lumen.
 
Aliasing
A tight stenosis causes such high velocities at the site of flow and immediately distal to the narrowed area that flow is seen above the baseline and at the lower edge of the spectral display. When color is used, there may be peaks of color from the other end of the spectrum. A chirping sound may be heard as you angle through the stenotic area.
This may be due to the fact that, the velocity is so high that the signal wraps around itself, and peak velocities are displayed below the baseline. This problem arises because the selected PRF is too low to accurately pick up the high velocities that are occurring.
 
Correction Techniques
  • Place the baseline at its lowest site to allow the systolic peaks to be displayed
  • Increase the PRF (velocity range)
  • Some units allow the B-scan image to be frozen while the Doppler signal is obtained. This will also widen the measurable velocity range37
  • Increase the Doppler angle, but do not exceed 60 degrees
  • Decrease the insonating frequency. Most units offer a choice of several Doppler frequencies for each transducer. Otherwise, change to a lower frequency transducer
  • Change to CW (not widely available on most current machines).
 
Inadequate Venous Signal
Venous flow is difficult to detect even when the vessel is clearly demonstrated. This may be due to:
  • There may be little venous flow at rest
  • The vein may be compressed by patient position
  • The B-scan gain may be too low to demonstrate the clot within the vein.
 
Correction Technique
  • Respiration affects venous flow. With inspiration and the descent of the diaphragm, pressure increases in the abdomen. Ask the patient to perform a Valsalva maneuver. As the breath is released, venous flow increases, and the venous signal will become more pronounced
  • Ask the patient to flex the leg slightly and re-evaluate. Use color flow’ in these instances to accentuate subtle flow
  • Increase the gain and apply gentle compression to see if the vein collapses.
 
Audible Signal but Vessel not Seen
A venous signal can be heard, but a patent vessel cannot be visualized.
The vein may be subtotally occluded, or the presence of adjacent collaterals may cause the audible signal.38
 
Correction Technique
Color flow will demonstrate the smaller collateral vessels as well as a small amount of residual flow in an almost occluded vessel.
 
Spectral Broadening
Apparent spectral broadening may be caused by too much gain or by scanning too close to the vessel wall, picking up lower velocities.
 
Correction Technique
Make sure the supposed spectral broadening reflects true pathology and is not just noise by comparing it to an area known to be normal.
 
A Flickering Image
Sometimes, it is difficult to evaluate color flow when obtaining a pulsed Doppler signal because the image flickers.
A large amount of data is being processed to generate the image for each frame of information when obtaining the Doppler signal or color flow. Therefore, the frame rate is lowered, and a flicker may occur.
 
Correction Technique
To reduce this flicker, evaluate one mode at a time (e.g. use color flow only) or reduce the width of the color flow box.
 
Color Misregistration Artifact (Color Flash)
If the transducer is rapidly moved, a flash of color related to transducer movement and not to vascular flow may develop.39
 
Correction Technique
Use the filter to reduce noise and move the transducer slowly, using caution not to remove real vascular flow from the image.
 
Tissue Vibration or Transmitted Pulsation
In the region of a highly pulsatile structure such as an artery, neighboring structures may move, causing some color artifact in the surrounding tissues.
 
Correction Technique
Scan from a different axis if possible.
 
Active Peristalsis
Active peristalsis may induce a color flow artifact.
 
Undue Color Gain
The outline of vessels may be misregistered owing to excessive gain, so the flow appears to fill in some of the surrounding tissues (color bleed).
 
Correction Technique
Decrease gain so the color image corresponds to the vessel outline.
 
EQUIPMENT CARE AND QUALITY CONTROL
Ultrasound systems are precision instruments that require careful handling and regular maintenance to ensure optimum performance.40
 
Preventive Maintenance
  • Liquids other than contact gel should not be stored on the equipment
  • The hand used to adjust control settings should be kept clean to ensure that contact gel does not affect the trackball or other functions
  • Cables and transducers should be visually inspected for worn areas or cracks
  • Careless placement of the transducer and cable on the machine can cause cable damage
  • Transducers should be placed in proper holders to avoid stress on cables
  • When taking ultrasound equipment to wards, it should be moved carefully to avoid sudden impact, which may dislodge printed circuit boards from their connectors, resulting in failure of operation
  • Many ultrasound systems have cooling fans with overlying air filters to prevent deposition of dust and particles on circuit boards within the unit. These should be cleaned periodically (weekly), especially if used in carpeted areas
  • Error messages should be noted and recorded for referral to service personnel.
 
Transducer Care
Transducers are delicate instruments and require careful handling. Transducers that have been dropped or treated roughly may have “dead” elements that no longer transmit or receive signals (due to debonding of electrodes from crystal elements).
Each time a transducer is removed from its cradle, ensure that the transducer cable is not snagged on part of 41the ultrasound system (such as the wheel support). The compromised length of cable may result in the transducer being pulled out of the hand as it is moved toward the patient.
Transducers should be cleaned after each patient with an alcohol sponge or transducer disinfectant, particularly if the patient has an open wound or a skin problem. Plastic freezer bags are an inexpensive means of covering the transducer to avoid contact with open wounds and to avoid contamination. Some transducers can be immersed in Cidex up to the handle for sterilization. Approximately 10 minutes of immersion is required for adequate sterilization.
Use a commercial water-soluble coupling gel to ensure good acoustic contact between the transducer and patient. Thick, high-viscosity gels are desirable when scanning the patient in an erect position because they don't slide off easily. Thicker gels are also helpful for obstetric patients with large abdomens.
Use disposable gloves when scanning a patient to avoid the risk of infection. Spread the gel around the abdomen with the transducer rather than by hand. Do not handle the controls with gel on your hand or glove.
 
Quality Assurance
Quality assurance tests may be tedious to perform but are worthwhile because it may be difficult or even impossible to detect calibration and measurement distortions from examination of the images alone. Clearly, major clinical problems may result if erroneous measurement data are produced. Quality assurance checks should be performed on a quarterly basis with most systems or more often if a problem a suspected, e.g., if a transducer has been dropped or measurements are consistently higher or lower than expected.42
 
Quality Control Tests
The standard tests performed to ensure that the system is working satisfactorily are:
  • Aspect ratio and calibration tests
  • Resolution tests (both axial and lateral)
  • A comparative power output test that equates to a depth of penetration measurement.
All these tests are performed on a tissue-equivalent phantom.
 
Aspect Ratio and Calibration Test
The aspect ratio and calibration test measures whether distances are accurate in both directions—horizontal and vertical directions and whether these measurements are displayed accurately on a hard-copy device transducer.
 
Resolution
Axial and lateral resolution capability can be determined using closely spaced pins in a phantom.
 
Comparative Power Output
The test for comparative power output determines whether the sound beam emitted by the transducer can reach a depth adequate to see deep structures. The test is performed at full power output, and the time gain compensation is set at maximum at the area of depth visualization. The comparative power output can be calculated as follows:
Attenuation factor (0.7) × Depth (7.35) × Transducer frequency (5) = 25.725 dB
This number is recorded in the quality control logbook as the output for this transducer using this phantom. Repeat tests should give the same result. For the comparison of results to 43be valid, all settings must be the same each time the test is undertaken. This is a useful test to see whether transmitter and/or receiver characteristics are changing over time.
 
Malfunction
Modem ultrasound systems are very reliable but occasionally can malfunction, resulting in disruption of images.
This is rare in modem systems, but when it occurs, it is usually obvious with clear disruption of the images.
The disruption may relate to circuitry for a specific transducer, so the equipment may still be usable with different transducers until the problem can be rectified. Occasionally, a transducer that has been selected may not initialize correctly, or its connection to the ultrasound system may be fault, but can be corrected by disconnecting and reconnecting the transducer so that it re-initializes.
Software errors occasionally occur and can often be rectified by switching the ultrasound unit off and on again, allowing the system to reboot. It may be necessary to wait 30 seconds before switching the system on again to allow time for correction of the software error.
 
MALPRACTICE AND ULTRASOUND
 
Causes of Malpractice
Legally malpractice as it relates to ultrasound comes in two forms:
  1. Battery injury: The patient is injured during the examination by assault or inadequate care (e.g., falls off the table). Failure to obtain informed consent is another type of “battery” injury.44
  2. Negligence: The examination is performed in a fashion that is “below the standard of care.”
Standard of care is defined as the way in which a “reasonable and prudent” physician or sonographer would act under the same circumstances. In our court system, the standard of care is established in several inherent ways:
  • Expert witnesses testify as to the standard of care
  • Guidelines such as the American Institute of Ultrasound in Medicine (AIUM) “Practice Guidelines for the Performance of an Antepartum Obstetric Ultrasound Examination” or American Congress of Obstetricians and Gynecologists technical bulletins set national standards. There are no such laid down in our country
  • Local hospital, radiology, or obstetric department policy statements also set the standard of care.
 
Responsibilities of the Physician or Sonographer Reporting the Study
  • The physician or sonographer reporting the study is required to accurately describe the findings on the examination, including pertinent negative findings with a clinical conclusion about the presence or absence of an abnormality
  • Suggestions about additional procedures or follow-up studies may be required
  • Problems in the performance of the study, such as obesity or suboptimal patient position, should be covered in the narrative portion of the report
  • A preliminary report is not considered legally hazardous as long as the sonographer does not attempt to make a diagnosis45
  • If a sonographer is working for a sonologist, the sonographer is not responsible for errors in the study, provided that the study is performed according to standards set by the sonologist, even if the study is of poor quality
  • The sonographer is not liable if he or she uses a technique that creates an image that looks like pathology but is not
  • Some examples of misleading findings or wrong techniques that are not the sonographers legal responsibility if uncorrected by the sonologist are the following:
    • Pseudohydronephrosis as the result of a full urinary bladder
    • Sludge-filled gallbladder due to an overgained image
    • Not following up on a pathologic finding, such as missing hydronephrosis with a pelvic mass
    • Missing a pancreatic mass by not trying different scanning techniques, such as erect scanning or having the patient drink to fill the stomach to create an acoustic window
    • Missing stones in the gallbladder or kidneys due to a failure to use a high-frequency transducer.
Although the sonographer is not held legally responsible for these errors, there is still the moral and ethical element to consider.
 
Responsibilities of the Physician or Sonographer Performing the Examination
  • The primary responsibility is to perform a comprehensive examination that conforms to the national standards
  • One should care for the patient and make sure that the patient comes to no harm by rough treatment or carelessness
  • Confidentiality must be observed.46
Some examples of situations in which a sonographer is liable are:
  • Physically molesting the patient
  • Letting a patient fall, causing injury
  • Giving the patient or accompanying doctor a wrong diagnosis
  • Revealing confidential information about the contents of the sonogram or disclosing any information that has adverse effects on the patient
 
Legally Hazardous Situations
 
Emergency Studies
Emergency ultrasound studies often modify clinical management from conservative to aggressive, and because any management changes hinge on the sonographic findings, the examination may be legally hazardous.
Litigation is common when a wrong diagnosis leads to immediate consequences.
Some examples of emergency situations often followed by litigation are as follows:
  • Failure to recognize ectopic pregnancy; Few ectopic pregnancies now require immediate surgery because many are now treated with methotrexate. This has created a new risk: misdiagnosis of a normal pregnancy as an ectopic pregnancy with subsequent methotrexate treatment with survival of a deformed but viable intrauterine pregnancy
  • Failure to diagnose ovarian torsion
  • Misdiagnosis of fetal death: Wrongly diagnosing fetal death with the subsequent delivery of a live but damaged infant can occur47
  • Failure to diagnose abruptio placenta
  • Failure to diagnose a fetal anomaly: Fetal abnormalities are a common cause of litigation because the monetary award for a missed anomaly is so large. Litigation related to obstetric ultrasound is many times more frequent than for all other types of ultrasound combined
  • The common missed fetal abnormalities resulting in litigation are as follows:
    • Missed spina bifida
    • Hypoplastic left heart syndrome
    • Absent limb or limbs
    • Down syndrome signs
    • Hydrocephalus.
Often, the litigation concerns a basic level obstetric study in which there is a possibility of an abnormality and no recommendation is made for referral for a targeted or referral study to be performed at a specialized center.
 
Failure to Diagnose Major Obstetric Findings
Some obstetric ultrasound findings that have been overlooked and that have serious consequences to pregnancy management are as follows:
  • Twins or triplets: Failure to diagnose twins or triplets can lead to severe long-term disability if the presence of twins is first discovered at delivery.
  • Unrecognized placenta previa during a sonographic examination may lead to a major bleed at delivery.
  • Breast cancer that is misdiagnosed as merely a breast cyst: Failure to diagnose breast cancer is the most common cause of imaging litigation. Most suits relate to mammography, but breast cancer ultrasound cases are occurring increasingly.48
 
Substandard Reporting of the Ultrasound Study
  • Dating an obstetric study in the third trimester: The range of possible dates for a series of obstetric measurements such as the biparietal diameter, head circumference, femur length, and abdominal circumference in the third trimester is ± three to four weeks, so accurate dating if the patient presents in the third trimester is not possible. This error is so well known that the obstetrician and radiologist share responsibility if delivery is performed before fetal viability under these circumstances
  • Dating or weight estimation with unsatisfactory measurement data: It is not always possible to obtain a quality abdominal circumference or fetal head measurements with an unusual fetal position. Problems of this type should be noted in the report. Not reporting these problems may result in wrong clinical decisions about delivery or the presence of intrauterine growth restriction (IUGR)
  • Failure to compare the dates or weight on the current examination with earlier sonographic studies may mean a failure to diagnose IUGR. Data from earlier sonograms should be obtained if later examinations are performed at another facility.
 
Tardy Reporting
  • Delayed reporting of an ultrasound study or delayed transmission of an ultrasound report to the referring doctor can lead to litigation.49
  • Findings that change management, such as the discovery of an ectopic pregnancy or a low biophysical profile score of 0 to 2, require immediate notification to the managing physician.
  • Some examples of serious consequences of a delayed report are as follows:
    • Failure to relay a report of a placenta previa resulted in the loss of the pregnancy in a patient with heavy vaginal bleeding
    • Two week delay in transmitting a report of IUGR resulting in the loss of that pregnancy.
Failure to Perform an Appropriate Ultrasound Study when a Patient Presents with a Family History of a Malformation Or a Drug History predisposing to a Malformation.
A common indication of an ultrasound study is a family history of fetal malformations or when the patient is taking drugs like valproic acid, that causes the fetal malformations. Specific views of potential malformations such as the lumbar spine with valproic acid or the face with a family history of cleft lip and palate, need to be obtained and reported.
 
Interventional Guidance Problems
Amniocentesis for chromosomal abnormality or to establish fetal lung maturity is still commonly performed and is standardly performed under ultrasound guidance. Suits related to fetal damage or fetal death due to the procedure still occur. Documentation of the amniocentesis site and of fetal viability after the procedure and a written report of the way in which the procedure was performed are helpful in avoiding litigation and defending complaints. By convention, 50only two passes are made if aspiration of amniotic fluid is unsuccessful.
 
MALPRACTICE INSURANCE: WHO NEEDS IT?
Any sonographer performing freelance work should invest in malpractice insurance. Sonographers employed by a hospital or other institution do not generally need to purchase insurance because they are covered by the hospital's or clinic's policy.