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Medical Imaging > 0.3 - Ultrasound Basics > Flashcards

0.3 - Ultrasound Basics Flashcards

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USMLE® Step 1 flashcards
1
Q

What is ultrasound?

A

an acoustical frequency hundreds of times greater than humans can hear that is used in medical diagnostics

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2
Q

What is the piezoelectric effect?

A
  • direct effect: vibration/sound is converted into an electrical signal
  • reverse effect: applying an electrical signal produces vibration/sound

This is done by piezoelectric ceramics such as quartz crystals

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3
Q

How does the ultrasound probe work?

A
  • emits shot bursts of acoustical energy at a given frequency
  • it has a transmitter and receiver in one
  • between the pulses, the machine analyzes the sound waves reflected by tissues
  • the coupling gel eliminates air gaps by producing the best contact between the transducer and body surface
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4
Q

What does the creation of sonographic images depend on?

A
  1. production of high frequency sound waves
  2. reception of reflected waves
  3. conversion of that echo into the actual image
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5
Q

What is acoustic impedance?

A
  • it is the property in the tissue that determines the transmission or reflection of the sound waves
  • when acoustic impedance is high, most sound waves are reflected back
  • when acoustic impedance is low, most sound waves are transmitted forward
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6
Q

What are the types of ultrasound probes?

A
  • curvilinear probe: general OB and abdominal (3-5 MHz)
  • linear high frequency probe: vascular, small parts, musculoskeletal (7-10 MHz or higher)
  • endo-cavity probe: vaginal, rectal
  • cardiac probe: echocardiography application
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7
Q

Significance of the differences in probes

A
  • higher frequency results in better resolution
  • lower frequency has better penetrability
  • convex probes have a wider field of vision than linear probes
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8
Q

What is echogenicity?

A

Echogenicity is determined by the amount of sound waves the tissue reflects or transmits

  • hyperechoic: appears bright; tissue reflect more echo
  • anechoic: appears black; tissue transmits all echo
  • hypoechoic: appears darker; tissue reflects less echo
  • echodense: appears bright; tissue reflects all echo
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9
Q

What are the types of ultrasound?

A
  • A-mode
  • B-mode
  • M-mode
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10
Q

What is A-mode ultrasound?

A
  • simplest mode
  • there are spikes along a line that show the signal amplitude at certain depths
  • used in ophtalmology
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11
Q

What is B-mode ultrasound?

A
  • most often used in diagnostic imaging
  • each echo is depicted as a dot to provide a 2D tomographic image
  • can depict real-time motion
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12
Q

What is M-mode ultrasound?

A
  • used to visualize moving structures (ie. heart valves in echocardiography)
  • shows structure depth (vertical axis) as a function of time (horizontal axis)
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13
Q

What is the doppler effect?

A
  • change in frequency of a wave in relation to an observer who is moving relative to the sound wave source
  • higher frequency when closer to the observer and lower frequency at a distance
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14
Q

What is pulse wave doppler?

A
  • accurately measure the velocity of blood in a precise location and in real time
  • provides a quantitative measurement
  • shows blood velocity as a function of time
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15
Q

What is color doppler?

A
  • a color coded B-mode ultrasound that provides information about the frequency and/or amplitude of sound waves in a selected area
  • flow towards the transducer appears red
  • flow away from the transducer appears blue
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16
Q

What is a power doppler?

A
  • displays flow with no direction or velocity information
  • 7-8 times more sensitive than color doppler
  • demonstrates flow with low velocity (ie. vascularization of tumors)
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17
Q

What is the use of contrast enhanced ultrasound?

A
  • enhancement of circumscribed liver and kidney lesions
  • pediatrics: vesicoureteral reflux
  • gynecology: testing tubal patency
  • vascular surgery: control of aorta stet graft integrity to demonstrate any endo-leaks
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18
Q

What is the ultrasound contrast agent?

A

microbubbles are gas bubbles with a shell made of albumins, galactose, lipids and polymers
- about the size of RBC (1-4µm)
- 2-3mL is administered iv.
- eliminated by the lungs and not the kidneys so there is no nephrotoxicity (highly safe)
- modifies acoustic impedance to 100% reflection, and structures appear hyperechoic

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19
Q

What are the advantages of CEUS?

A
  • good resolution
  • real time tomographic scan
  • lack of ionizing radiation
  • complications are extremely rare
  • excreted through the lungs
  • reproducible
  • no need for patient preparation
20
Q

What are the disadvantages of CEUS?

A
  • high-end US
  • relatively expensive
  • limited fatty liver disease
  • operator-dependent
  • only one region/lesion can be scanned
21
Q

What is elastography?

A
  • detects change in elasticity
  • inflammation or malignancy can result in stiffer or less elastic tissue
  • high-end US is needed for sonoelastography
  • types: sonoelastography (using US) and MR-elastography
22
Q

What are the clinical applications of sonoelastography?

A
  • differentiating malignant and benign neoplams (especially in the breasts)
  • assessing liver fibrosis non-invasively and quantitatively
  • assessing liver steatosis
  • aiding in deciding the biopsy site more accurately
23
Q

What is endocavitary ultrasound?

A
  • special, high-frequency probes that provide high spatial resolution
  • many endocavitary sites of application: transrectal (prostate), intravaginal, transesophageal (heart, esophagus), endoscopic (GI tract, pancreas, liver, lymph nodes)
24
Q

What are the adverse effects or safety issues of ultrasonography?

A
  • no known long-term effects
  • should only be used when medically advised, FDA warns against unnecessary 3D and 4D US in pregnancies
25
Q

What are the advantages of ultrasonography?

A
  • lacks ionizing radiation
  • easily available and portable for bedside, ER, and ICU
  • lower cost
  • shorter waiting list compared to CT and MRI
26
Q

What are the disadvantages of ultrasonography?

A
  • cannot be used or limited in regions filled with air (lungs, meteoristic bowels) and regions covered by bone
  • operator dependent
  • limited in obese patients
  • limited use after surgery (bandages, catheters, drains)
27
Q

What is the clinical use of US for the liver?

A
  • primary method of detection for benign and malignant focal liver lesions, and diffuse parenchymal diseases (ie. fatty liver, fibrosis, cirrhosis)
  • sonoelastography and CEUS can be used for further diagnoses
28
Q

What are the causes of bile duct obstruction?

A
  • gallstones
  • pancreatic carcinoma
  • strictures
  • sclerosing cholangitis
  • cholangiocarcinoma
  • metastatic disease
29
Q

What is the clinical use of US for the biliary system?

A
  • US is used as the first choice to study biliary system diseases
  • CT is less sensitive than US for gall stone detection
  • evaluation of intrahepatic and extrahepatic bile duct and pancreatic duct
  • normal intrahepatic ducts are not visible but dilated biliary ducts appear as tubular structures without color Doppler signal
30
Q

What is the clinical use of US for the kidneys?

A
  • can be estimated accurately
  • renal sinuses usually appear bright (echogenic) due to fat content
  • calyces are not usually visible, pyramids are hypoechoic
  • kidney parenchyma is the same echogenicity as the liver, so hyperechoic renal parenchyma suggests renal disease
  • US is used primarily to evaluate the presence of hydronephrosis, because ureters are difficult to visualize on US, stone searches are conducted with CT
31
Q

What is the clinical use of US for the urinary bladder?

A
  • a full fluid-filled bladder is also used as an acoustic window to avoid image-degrading, air-filled bowel to assess the prostate in men and pelvic structures in women
  • US is the first choice modality to examine the urinary bladder
  • post void residual volume can also be estimated, which is helpful in the assessment of urinary incontinence and bladder outlet obstruction
  • helps rule out bladder tumors in patients with painless hematuria
32
Q

What is the clinical use of US for the bowels?

A
  • mostly utilized for follow-up examination of patients with inflammatory bowel diseases
  • preferably preprandially in the morning or after at least 4h fasting to reduce peristaltic movements and the amount of intraluminal air
  • visualization is impaired by the presence of gas and other intestinal content
33
Q

What is the clinical use of US for ascites?

A
  • primarily anechoic but if the fluid contains hemorrhage or pus it may contain echoes
  • large amount of ascites is easily identified in all four quadrants of the abdomen with US
  • smaller amounts may only be detectable in the right upper quadrant
  • image guidance for the safe removal of fluid
34
Q

What is the clinical use of US for the female pelvis?

A
  • uterine masses are solid while ovarian masses are cystic
  • first choice modality for pelvic pain or mass evaluation in women
  • full bladder is mandatory for good quality US study
  • for better spatial resolution, transvaginal US study is conducted
  • pelvic MRI is used as a 3D problem solving modality
35
Q

What is the clinical use of US for the scrotum?

A
  • useful for the differential diagnosis of acute scrotal pain
  • color doppler for the assessment of suspected torsion (elevated resistive index or no flow in torsed testes)
  • elevated flow is detected in inflammation
36
Q

What is the clinical use of US for the thyroid glands?

A
  • most sensitive modality for the thyroid
  • blood test and/or radioactive isotope uptake test is usually required to determine whether the gland is underactive, overactive or normal in function
  • thyroid volume, structure, vascularization and description of the nodules is determined by US
37
Q

What are the sonographic features of a malignant thyroid nodule?

A
  • hypoechoic
  • presence of microcalcifications
  • local invasion of surrounding structures
  • “taller than wide”
  • suspicious neck lymph nodes
  • intranodular blood flow
  • suspicious nodules (and lymph node) should undergo FNAB
  • lymphadenopathy with microcalcifications is almost 100% specific
38
Q
A
39
Q

What is doppler waveform?

A
  • doppler waveform is a graphic representation of the velocity of flow measured over time in a focused area
  • flow towards the transducer is displayed above the baseline and flow away is below the baseline
40
Q

What is considered a significant arterial stenosis?

A

luminal diameter is reduced by 50%

41
Q

What is the clinical use of US for abdominal aortic aneurysm?

A
  • US is the gold standard screening for asymptomatic, pulsatile abdominal mass
  • moving blood appears anechoic; thrombus in the wall of an aneurysm appears echogenic
  • size of aneurysm directly relates to risk of rupture: less than 4cm diameter has a less than 10% chance of rupture; 4-5cm rupture has almost 25% risk of rupture; aneurysms larger than 5cm require endovascular or surgical intervention
42
Q

What is the clinical use of US for pseudoaneurysms?

A
  • US is excellent to characterize circumscribed vascular problems
  • abnormal outpouching typically occurring when there is a breach in the vessel wall (trauma, iatrogenic injury), and blood is contained by the adventitia or surrounding perivascular tissue
  • due to turbulent forward and backward flow, there is a characteristic yin-yang sign in color doppler
43
Q

What is the clinical use of US for deep vein thrombosis?

A
  • venous vascular US for thrombosis of veins in the extremities
  • transducer needs to be able to systemically compress the deep veins
  • veins containing a thrombus will not completely collapse after compression and the echogenic thrombus can be visualized in gray-scale.
  • color doppler can be used to determine the presence or absence of flow in the vein or recanalization after therapy
44
Q

What are the US characteristics of portal flow in cirrhosis?

A
  • color doppler can examine direction of flow
  • liver fibrosis/cirrhosis can result in reversed portal flow due to the increase in presinusoidal resistance
45
Q

What is FAST examination?

A
  • focussed assessment with sonography in trauma
  • it is to identify any intraperitoneal bleeding, pleural effusion, pericardial blood, or pneumothorax
  • it searches for any blood or fluid in the most dependent regions of the abdominal cavity
  • it is a point of care (bedside) examination
46
Q

What is the clinical use of US for the lungs?

A
  • CT is the gold-standard for pneumothorax
  • in case of blunt trauma, thoracic ultrasound has more sensitivity than a supine chest radiograph
  • air rises to the anterior chest wall in supine position, so it will appear on FAST
  • on M mode:
    - normal lungs show the seashore sign (lung sliding movement)
    - pneumothorax have a barcode/stratosphere sign (no movement)
47
Q

What is the clinical use of US intraoperatively?

A
  • provides interactive and timely information during surgical intervention
  • high resolution imaging because the transducer is in direct contact with the organ examined
  • accurately localizes pathology, guides intraoperative biopsies, detects proper flow by doppler curves in transplanted organs and helps limit the extent of surgical resection

Medical Imaging (17 decks)

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