Ultrasound and Sonography Glossary
80 terms from the ARDMS, ARRT and CCI registry exams, defined in plain English: what each one means, and how it shows up on the exam.
Definitions are written in our own words from the explanations in Prepry's registry question bank, not quoted from any source. References under each term point to where the facts can be checked.
Ultrasound Physics and Instrumentation
The parameters, transducer behavior and machine controls that the ARDMS SPI exam and the physics sections of every registry exam are built on.
- Acoustic impedance
Acoustic impedance is a tissue's resistance to the passage of sound, measured in Rayls, and it equals the tissue's density multiplied by the propagation speed of sound through it. At a boundary struck straight on, reflection depends on how much the impedance of the two tissues differs: identical impedances transmit all the sound, and a larger mismatch reflects more of it back to the transducer. This is why a soft tissue to bone or air interface reflects so strongly.
On the exam: SPI questions test that reflection strength depends on the size of the impedance mismatch at a boundary, and that identical impedances transmit sound completely.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound. (p. 38)
- Propagation speed
Propagation speed is how fast sound travels through a medium, and it depends only on the medium's stiffness and density, not on the transducer. Speed rises with stiffness and falls with density, so sound travels fastest in bone, around 3,500 m/s, and slowest in air, while soft tissue is assumed to average 1,540 m/s. The machine uses that assumed value, together with echo return time, to calculate the depth of a reflector.
On the exam: SPI questions use the 1,540 m/s assumption to test depth calculation, and ask which tissue property, stiffness or density, produces the fastest or slowest propagation speed.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound.
- Attenuation
Attenuation is the progressive weakening of an ultrasound beam as it travels through tissue, from absorption, scattering, and reflection. In soft tissue the attenuation coefficient in dB/cm equals half the frequency in MHz, and total attenuation in decibels equals that coefficient multiplied by the path length in cm. Because the coefficient rises with frequency, higher-frequency transducers and deeper structures both lose more signal, which is why raising frequency trades penetration for resolution.
On the exam: SPI questions give a frequency and depth and ask you to solve for the attenuation coefficient or the total attenuation in decibels.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound. (p. 85)
- Axial resolution
Axial resolution is the ability to display two structures lying one behind the other, along the beam's path, as two separate echoes. It is determined entirely by spatial pulse length, since axial resolution equals spatial pulse length divided by two, so shorter pulses give better, smaller-number resolution. Raising frequency or damping the transducer more heavily shortens the pulse and improves it. The depth of the reflector itself has no effect on axial resolution.
On the exam: SPI questions test that axial resolution depends only on spatial pulse length, not on how deep the reflector lies.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound.
- Lateral resolution
Lateral resolution is the ability to display two structures lying side by side, perpendicular to the beam, as two separate echoes, and it is set by the width of the ultrasound beam at a given depth. It is best at the focus, where the beam is narrowest, and worsens in the near and far fields where the beam is wider. Raising frequency and properly placing the focal zone at the depth of interest both narrow the beam and improve lateral resolution.
On the exam: SPI questions test that lateral resolution is best at the focal zone, where the beam is narrowest, not a fixed value like axial resolution.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound.
- Elevational resolution
Elevational resolution, also called slice-thickness resolution, is how well the system separates structures across the slice, the dimension at right angles to the scan plane, and it depends on how thick the beam is rather than how wide or how short the pulse is. It is fixed by the transducer's acoustic lens or elevation focus and cannot be adjusted at the console. A beam thicker than the structure being imaged pulls in echoes from outside the true plane, which can make a simple cyst appear to contain debris.
On the exam: SPI questions test that poor elevational resolution can make an anechoic structure like a cyst falsely appear to contain internal echoes.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound.
- Temporal resolution
Temporal resolution is how accurately a system displays motion over time, and in practice it is the frame rate: faster frame rates give better temporal resolution. Frame rate rises when pulse repetition frequency increases and falls when the system must acquire more information per frame, so increasing imaging depth, sector width, line density, or the number of focal zones all lower the frame rate and worsen temporal resolution.
On the exam: SPI questions ask what happens to frame rate, and therefore temporal resolution, when depth, sector width, line density, or focal zones increase.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound.
- Frequency
Frequency is the number of complete sound wave cycles per second, measured in Hertz, and diagnostic ultrasound uses roughly 2 to 18 MHz. It is set by the transducer and stays constant as sound crosses into a new medium, unlike wavelength, which changes with propagation speed. Higher frequency shortens wavelength and improves resolution, but it also raises scattering and attenuation, which is why higher frequencies penetrate less deeply.
On the exam: SPI questions give a transmitted, fundamental frequency and ask for the second harmonic, which is always double it.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound.
- Wavelength
Wavelength is the physical length that one complete cycle of a sound wave occupies, equal to propagation speed divided by frequency. Because frequency is fixed by the transducer, wavelength changes only when propagation speed changes, such as when sound crosses into a different medium; a faster medium stretches the wavelength and a slower one shortens it. In soft tissue, wavelength in millimeters is roughly 1.54 divided by frequency in MHz.
On the exam: SPI questions ask you to solve for wavelength in soft tissue using the 1.54 shortcut, and to recognize that wavelength, not frequency, changes when sound enters a new medium.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound.
- Period
Period is the time required to complete one full cycle of a sound wave, usually measured in microseconds, and it equals one divided by frequency. Like frequency, period is fixed by the sound source and does not change when the wave enters a different medium, even though wavelength does. A 5 MHz transducer, for example, produces a period of 0.2 microseconds. Pulse repetition frequency and pulse repetition period are separate, related quantities describing how often pulses are sent.
On the exam: SPI questions test which quantities, like period and frequency, stay constant across media, unlike wavelength, which changes with propagation speed.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound.
- Pulse repetition frequency
Pulse repetition frequency, or PRF, is the number of ultrasound pulses the transducer sends out each second, and it has a reciprocal relationship with pulse repetition period. PRF is largely set by imaging depth, since the system must wait for echoes to return from the deepest structure before firing the next pulse, so deeper imaging requires a lower PRF. PRF also sets the Nyquist limit, equal to half of PRF, and pushing PRF very high to raise that limit can cause range ambiguity.
On the exam: SPI and vascular questions test that raising imaging depth lowers PRF and the Nyquist limit, while pushing PRF too high to avoid aliasing risks range ambiguity instead.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound.
- Pulse repetition period
Pulse repetition period, or PRP, is the time from the start of one pulse to the start of the next, and it equals one divided by pulse repetition frequency. PRP is made up of pulse duration, the brief transmit time, plus the much longer listening time spent waiting for echoes to return. Increasing imaging depth lengthens PRP because the system must wait longer for the deepest echoes, while decreasing depth shortens it.
On the exam: SPI questions ask you to calculate PRP from a given PRF, or to identify how imaging depth changes PRP.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound.
- Spatial pulse length
Spatial pulse length, or SPL, is the physical length of space that one ultrasound pulse occupies, equal to the number of cycles in the pulse multiplied by wavelength. It is set entirely by the transducer and the medium, not by the sonographer or imaging depth, and typically ranges from 0.1 to 1.0 mm clinically. SPL is the only variable that directly sets axial resolution, since axial resolution equals SPL divided by two, so fewer cycles or a shorter wavelength both shorten it.
On the exam: SPI questions ask what happens to spatial pulse length, and therefore axial resolution, when frequency rises or cycles per pulse are reduced through damping.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound.
- Duty factor
Duty factor is the fraction of time the transducer spends actively transmitting sound rather than listening for echoes, equal to pulse duration divided by pulse repetition period, expressed as a percentage. Pulsed imaging has a duty factor under 1 percent because most of each cycle is spent listening, while continuous wave Doppler transmits constantly and has a duty factor of 100 percent. Increasing imaging depth lengthens listening time and lowers duty factor.
On the exam: SPI questions use duty factor to compare bioeffect risk between pulsed imaging, spectral Doppler, and continuous wave Doppler, since higher duty factor means more transmitted energy.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound.
- Damping
Damping is the reduction of ringing in a piezoelectric element after it is excited, done with a backing material bonded to the back of the crystal that absorbs excess vibration. Heavier damping shortens the pulse and spatial pulse length, which improves axial resolution and widens bandwidth, at the cost of reduced sensitivity. A detached or failing backing layer is a recognized cause of an enlarged dead zone on quality assurance testing.
On the exam: SPI questions describe backing material shortening the pulse to improve axial resolution, and identify a failing damping layer as a cause of an enlarged dead zone.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound. (p. 117)
- Q factor
Q factor, or quality factor, describes how pure a range of frequencies a transducer's pulse contains, and it equals operating frequency divided by bandwidth, so it is inversely related to bandwidth. A high Q factor means a long, narrow-bandwidth pulse, typical of an undamped continuous wave transducer. Diagnostic imaging transducers use heavy backing material to lower Q factor, which widens bandwidth and shortens the pulse for better axial resolution.
On the exam: SPI questions connect a low Q factor to heavy damping, wide bandwidth, and improved axial resolution in imaging transducers.
- Bandwidth
Bandwidth is the spread of frequencies a pulse carries instead of one pure tone, measured in Hertz as the difference between the pulse's highest and lowest frequency. Shorter, heavily damped pulses contain a wider range of frequencies and so have wider bandwidth, which goes along with a short spatial pulse length and good axial resolution. Continuous wave transducers, by contrast, have a narrow bandwidth and a high Q factor.
On the exam: SPI questions link wide bandwidth to short, heavily damped pulses used in imaging, and narrow bandwidth to the single-frequency pulse of continuous wave Doppler.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound. (p. 118)
- Piezoelectric effect
The piezoelectric effect is the property of certain crystals, such as lead zirconate titanate, that lets mechanical deformation from a returning echo generate an electrical signal on receive. Applying a voltage to the same crystal deforms it and produces sound on transmit, a process some textbooks call the reverse piezoelectric effect. Together these two conversions, electrical to mechanical and mechanical to electrical, let a single transducer both send and receive ultrasound.
On the exam: SPI questions ask you to identify the piezoelectric effect as the mechanism converting electrical energy to sound on transmit and echoes back into an electrical signal on receive.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound. (p. 113)
- Focal zone
The focal zone is the region of the beam surrounding the focus where it is narrowest, giving the best lateral resolution available at that depth, with roughly half the zone in the distal near field and half in the proximal far field. Sonographers place it at or just below the structure of interest to sharpen lateral resolution there. Using a single focal zone rather than several also keeps frame rate, and therefore temporal resolution, higher.
On the exam: SPI questions test that lateral resolution is best within the focal zone, and that adding more focal zones improves image detail but lowers frame rate.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound.
- Near fieldalso called Fresnel zone
The near field, or Fresnel zone, is the part of the beam between the transducer face and the focus, where the beam converges and narrows. Its length grows with a larger transducer diameter or a higher frequency, which lets the focus sit deeper and can improve resolution further from the skin. Structures too shallow for a clear image can be pushed into the near field's useful range with an acoustic standoff pad.
On the exam: SPI questions ask how increasing transducer diameter or frequency lengthens the near zone and moves the focus deeper.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound.
- Far fieldalso called Fraunhofer zone
The far field, or Fraunhofer zone, is the part of the beam beyond the focus, where it diverges and spreads with increasing depth. A small, low-frequency transducer spreads the most; a large, high-frequency one spreads the least, and less spread means better lateral resolution out here. Because the beam is wider here than at the focus, lateral resolution steadily worsens the farther a structure lies past the focal zone.
On the exam: SPI questions test that a large-diameter, high-frequency transducer gives the least beam divergence, and therefore the best lateral resolution, in the far field.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound. (p. 187)
- Time gain compensationalso called TGC
Time gain compensation, or TGC, also called depth gain compensation, amplifies returning echoes according to the depth they came from, boosting deeper echoes more than shallow ones to counteract attenuation. Without it, structures of equal true brightness would look progressively dimmer with depth simply because more sound was lost getting there and back. TGC lets the sonographer adjust this depth-dependent amplification to produce a uniformly bright image.
On the exam: SPI questions test that TGC is a receiver function equalizing brightness by depth, not an adjustment to overall transmit power or gain.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound.
- Dynamic range
Dynamic range is the ratio between the largest and smallest echo amplitudes a system can process and display, expressed in decibels. A wide dynamic range shows many shades of gray, a softer-looking, lower-contrast image, while a narrow dynamic range shows fewer shades and higher contrast. Compression shrinks that ratio before display: apply 50 dB of compression to a 90 dB signal and 40 dB reaches the screen.
On the exam: SPI questions ask how widening or narrowing dynamic range changes the number of gray shades, and how much compression lowers the final dynamic range.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound.
- Harmonic imaging
Harmonic imaging forms the image from harmonic frequencies generated as sound distorts while traveling through tissue, rather than from the reflected fundamental frequency. The second harmonic used is exactly twice the transmitted frequency. Because harmonic energy builds up gradually with depth and is weakest in the off-axis side lobes, tissue harmonic imaging reduces near-field reverberation clutter and lobe artifact compared with fundamental imaging, improving contrast resolution in technically difficult patients.
On the exam: SPI questions ask why harmonic imaging reduces reverberation and lobe artifact by relying on energy generated deeper in tissue and mainly along the main beam.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound.
Artifacts and Image Optimization
What the machine displays that is not really there, why it happens, and the controls that clean it up.
- Reverberation
Reverberation is an artifact caused by sound bouncing back and forth repeatedly between two strong, closely spaced reflectors, or between the transducer face and a reflector, before finally returning. Each bounce adds travel time, so the machine displays a series of equally spaced parallel echoes at increasing depth, fading in brightness with each successive line as energy is lost. It is a recognized sign of free air, such as pneumoperitoneum next to the diaphragm.
On the exam: SPI and abdomen questions ask you to identify reverberation from its ladder of equally spaced, fading parallel echoes, including as a sign of free intraperitoneal air.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound.
- Comet tail artifact
Comet tail artifact is a form of reverberation seen as a single, tapering, bright line of echoes trailing behind a small, strongly reflective structure, such as a metal clip, cholesterol crystals, or gas. The reflectors are so closely spaced that the individual reverberation echoes merge into one narrowing, tail-like streak instead of staying as separate parallel lines. It is the classic sign of adenomyomatosis of the gallbladder wall and of pneumobilia after ERCP.
On the exam: SPI and abdomen questions use comet tail artifact as a recognized sign of adenomyomatosis and, in the biliary tree, of pneumobilia.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound. (p. 358)
- Ring-down artifact
Ring-down artifact is a continuous, solid vertical band of echoes extending posteriorly from a small collection of gas bubbles, rather than the separate lines of typical reverberation. It is caused by fluid trapped between adjacent gas bubbles resonating at the transmitted frequency and re-emitting sound of their own, producing a sustained signal instead of discrete echoes. It is a recognized sign of gas, such as in the gastrointestinal tract, and differs from comet tail artifact, which tapers and is tied to metal or crystals.
On the exam: SPI questions distinguish ring-down's continuous vertical band, caused by resonating gas bubbles, from comet tail's discrete tapering line, tied to metal or crystals.
Reference: Grogan, S. P., & Mount, C. A. Ultrasound Physics and Instrumentation. StatPearls, NCBI Bookshelf.
- Acoustic shadowing
Acoustic shadowing is an artifact appearing as a dark band deep to a structure that strongly reflects or attenuates sound, such as a gallstone, calcification, or bone. Most of the beam stops at that structure, so the tissue underneath receives almost nothing, sends back almost nothing, and paints dark on the screen. It is the opposite of posterior acoustic enhancement, which brightens tissue behind a weak attenuator.
On the exam: SPI and abdomen questions pair shadowing behind stones, calcifications, and bone with enhancement behind cysts as opposite attenuation-based artifacts.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound. (p. 359)
- Posterior acoustic enhancement
Posterior acoustic enhancement is an artifact appearing as an unusually bright band deep to a structure, such as a simple cyst, that attenuates sound less than the surrounding tissue. Because time gain compensation assumes typical soft tissue attenuation and the fluid absorbs less sound than that, more energy actually reaches tissue beyond it, making that deeper tissue look falsely brighter. It is a helpful sign that a well-defined anechoic lesion, like a breast, splenic, or ganglion cyst, is fluid-filled rather than solid.
On the exam: Abdomen and breast questions use posterior enhancement behind a well-defined anechoic lesion as supporting evidence that it is a simple, fluid-filled cyst rather than solid.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound. (p. 359)
- Mirror image artifact
Mirror image artifact is a duplicate of a real structure displayed deeper than it truly is, produced when sound reflects off a strong, curved specular reflector, classically the diaphragm, continues to the real structure, and bounces back by the same path before returning to the transducer. Because the machine assumes a straight path, it places the copy along the beam but at the greater depth matching the extra travel time. A related form, crosstalk, mirrors a spectral waveform across the baseline.
On the exam: SPI and abdomen questions use liver lesions mirrored above the diaphragm as the classic example, and always place the artifact deeper than the true structure.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound.
- Refraction artifactalso called edge shadowing
Refraction artifact occurs when the beam bends at a boundary between two media with different propagation speeds, struck at an oblique angle, following Snell's law. This can duplicate a structure so it appears just to the side of its true position, or produce edge shadowing, a thin, clean shadow at the lateral margins of a curved structure like a cyst, gallbladder, or carotid artery, where the beam grazes the surface and bends away instead of returning.
On the exam: SPI questions ask you to tell edge shadowing, caused by refraction at a curved border, apart from shadowing caused by attenuation.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound.
- Side lobe artifact
Side lobe artifact is a false-echo artifact caused by the weaker secondary beams, called side lobes, that a transducer emits off-axis in addition to its main beam. When a side lobe strikes a strong reflector outside the main beam, such as bowel gas, the returning echo is displayed as though it came from directly along the main axis, placing false echoes inside a structure that should be anechoic, like the gallbladder or urinary bladder.
On the exam: SPI questions ask you to recognize side lobe artifact as the explanation for artifactual echoes filling in an otherwise anechoic structure like the bladder or gallbladder.
- Speed error artifactalso called speed displacement artifact
Speed error artifact is the mispositioning of a reflector that results from the machine always assuming sound travels at a constant 1,540 m/s to calculate depth, even when the true speed in a specific tissue, such as fat or a breast implant, is different. If the actual speed is slower than assumed, the extra travel time makes the machine place the reflector too deep; if it is faster, the reflector displays too shallow.
On the exam: SPI questions ask whether a structure displays too deep or too shallow depending on whether the true tissue speed is slower or faster than 1,540 m/s.
Reference: Radiopaedia.org: Speed Displacement Artifact (Ultrasound)
- Spatial compounding
Spatial compounding combines several real-time frames of the same tissue, acquired by steering the beam to different angles, into one averaged composite image. Because random speckle and angle-dependent artifacts like edge shadowing appear differently at each angle, averaging cancels much of that noise while true tissue boundaries reinforce, improving border definition. The trade-off is a lower frame rate, since the system must acquire and combine more frames for each displayed image, reducing temporal resolution.
On the exam: SPI questions test that spatial compounding reduces speckle and angle-dependent artifact like edge shadowing, at the cost of lower frame rate and temporal resolution.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound.
Doppler and Hemodynamics
How ultrasound measures moving blood, and the numbers reported from a spectral waveform.
- Doppler shift
Doppler shift is the difference between the frequency a transducer transmits and the frequency it receives back, caused by relative motion between the transducer and a moving reflector such as red blood cells. It is directly proportional to flow velocity and to transducer frequency, and is largest at a 0 degree angle of incidence and smallest near 90 degrees. Flow moving toward the transducer raises the received frequency, a positive shift, and flow moving away lowers it, a negative shift.
On the exam: SPI and vascular questions ask how doubling velocity or transducer frequency doubles the Doppler shift, and why a 90 degree angle minimizes it.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound.
- Doppler angle
Doppler angle is the angle between the ultrasound beam and the direction of blood flow, and it should be kept at 60 degrees or less, and consistent between measurements, for an accurate velocity estimate. Because the Doppler equation includes the cosine of this angle, error increases sharply beyond 60 degrees, so small inconsistencies in angle correction produce large velocity errors; at 90 degrees, cosine equals zero and no shift is measured regardless of true flow. Tortuous vessels can make holding 60 degrees difficult.
On the exam: SPI and vascular questions test that error rises sharply above a 60 degree Doppler angle, and that a 90 degree angle produces zero measurable shift.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound.
- Nyquist limit
The Nyquist limit is the highest Doppler shift frequency that pulsed wave or color Doppler can sample and display correctly, equal to half the pulse repetition frequency. A true shift greater than this limit cannot be sampled often enough to display accurately and will alias. Because PRF is tied to depth, decreasing the depth of the sample volume raises PRF and therefore the Nyquist limit, one way to resolve aliasing at high velocities.
On the exam: SPI questions ask you to calculate the Nyquist limit from a given PRF and predict whether a stated velocity will alias.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound.
- Aliasing
Aliasing is a display error in pulsed wave and color Doppler where a true velocity exceeding the Nyquist limit is shown incorrectly, wrapping around to appear as flow in the opposite direction. On a spectral waveform the peaks above the limit appear cut off at the top and wrapped to the bottom; on color Doppler it appears as an abrupt switch from one flow color to its opposite. It can be corrected by raising PRF or lowering the baseline; continuous wave Doppler does not alias.
On the exam: SPI and vascular questions ask you to recognize aliasing on a waveform or color image and pick a correct fix, such as raising PRF or lowering the baseline.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound.
- Spectral broadening
Spectral broadening is the filling-in of the normally clear window beneath a spectral Doppler waveform, because a wide range of velocities is present in the sample volume at the same instant. It most often signals turbulent flow, such as at or just past a stenosis, but a sample volume that is too large, a Doppler angle that is too steep, or excessive spectral gain can produce it artificially without any true flow disturbance.
On the exam: Vascular questions ask you to interpret spectral broadening as a sign of turbulence while ruling out technical causes like excessive gain or an oversized sample volume.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound.
- Peak systolic velocityalso called PSV
Peak systolic velocity, or PSV, is the highest blood flow velocity recorded during the systolic upstroke of the cardiac cycle on a spectral Doppler waveform. Because velocity must rise as a vessel narrows to keep the same volume of flow moving through a smaller area, PSV is the primary value used to grade arterial stenosis severity, with published thresholds such as greater than 230 cm/s for a 70 percent or greater internal carotid artery stenosis under NASCET criteria.
On the exam: Vascular exam questions apply PSV thresholds, such as the Society of Radiologists in Ultrasound consensus criteria for the internal carotid artery, to grade percent diameter stenosis.
Reference: Abuhamad, A., & Chaoui, R. (2016). A Practical Guide to Fetal Echocardiography: Normal and Abnormal Hearts (3rd ed., p. 351). Wolters Kluwer.
- End-diastolic velocityalso called EDV
End-diastolic velocity, or EDV, is the blood flow velocity measured at the end of diastole, just before the next systolic upstroke, on a spectral Doppler waveform. It reflects how much forward flow continues through a vessel during the resting phase of the cardiac cycle, which depends on downstream vascular resistance, and it rises alongside peak systolic velocity as an arterial stenosis worsens toward a pre-occlusive lesion. EDV is combined with PSV to calculate the resistive index.
On the exam: Vascular exam questions pair a rising EDV with a rising PSV, such as EDV greater than 100 cm/s in a 70 to 99 percent internal carotid stenosis, to grade severity.
- Resistive indexalso called RI
Resistive index, or RI, is a Doppler measurement of downstream resistance to flow, calculated as peak systolic velocity minus end-diastolic velocity, divided by peak systolic velocity. A higher RI reflects greater downstream resistance with little or no diastolic flow, while a lower RI reflects a low-resistance bed with substantial forward flow through diastole. The normal renal artery RI is roughly 0.47 to 0.70, and a renal transplant RI above about 0.8 raises concern for transplant dysfunction.
On the exam: Abdomen and vascular questions give PSV and EDV and ask you to calculate RI, then compare it to a threshold such as 0.8 for renal transplant dysfunction.
Reference: Drose, J. D. (2016). Fetal Echocardiography (p. 82). Woodlands, TX: ESP, Inc.
- Pulsatility indexalso called PI
Pulsatility index, or PI, is a Doppler measurement of flow resistance, calculated as peak systolic velocity minus end-diastolic velocity, divided by the mean velocity averaged over the cardiac cycle. A higher PI reflects greater downstream resistance, as seen when clenching a fist raises distal resistance in a radial artery waveform, while a lower PI reflects vasodilation, as in the fetal middle cerebral artery brain-sparing response to hypoxia. PI stays defined even with reversed diastolic flow, unlike resistive index.
On the exam: OB and vascular questions use a falling middle cerebral artery PI as the sign of fetal brain-sparing vasodilation in growth restriction.
- Laminar flow
Laminar flow is the normal pattern of blood movement in a healthy, unobstructed vessel, with concentric layers moving in parallel, fastest at the center and progressively slower toward the vessel wall due to friction. It occurs when the Reynolds number, a unitless value based on flow speed, vessel diameter, density, and viscosity, stays below about 1,500. On a spectral Doppler waveform it produces a narrow band of velocities at each instant, leaving a clear window beneath the waveform.
On the exam: Vascular questions ask you to recognize a narrow spectral waveform with a clear window, and a Reynolds number below about 1,500, as evidence of normal laminar flow.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound. (p. 336)
- Turbulent flow
Turbulent flow is a disorganized pattern in which blood moves in multiple directions and at many velocities at the same location and instant, rather than in smooth parallel layers. It develops when the Reynolds number rises above roughly 2,000, commonly distal to a stenosis, vessel wall irregularity, or high-velocity jet. On a spectral waveform it fills in the window as spectral broadening, and on color Doppler it can appear as a mosaic of mixed colors within the lumen.
On the exam: Vascular questions link turbulent flow, and a Reynolds number above about 2,000, to spectral broadening and a color mosaic pattern as indirect signs of stenosis.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound.
- Bernoulli principle
The Bernoulli principle states that as a flowing fluid's velocity increases, the pressure it exerts decreases, so total energy stays roughly constant when frictional losses are small. Blood speeds up as it crosses a narrowed vessel segment or stenotic valve to maintain the same volume of flow, so pressure drops at that point and rises again just past it. A simplified version of the equation, pressure gradient equals 4 times velocity squared, converts a measured peak velocity into an estimated pressure gradient.
On the exam: Echo questions use the simplified Bernoulli equation, pressure gradient equals 4 times velocity squared, to estimate pressure gradients across stenotic or regurgitant heart valves from Doppler velocities.
- Continuous wave Doppler
Continuous wave Doppler uses two separate piezoelectric elements, one continuously transmitting and one continuously receiving, so it can measure very high velocities accurately without a Nyquist limit or aliasing. Its major limitation is range ambiguity: because it samples along the entire beam at once rather than in pulses, it cannot localize the depth at which a given Doppler signal arose, giving it the poorest axial resolution of any Doppler mode. It still reports both flow speed and direction.
On the exam: Echo questions test that continuous wave Doppler is chosen over pulsed wave to measure high velocities, such as across a stenotic valve, without aliasing.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound.
- Color Doppler
Color Doppler overlays a real-time, color-coded map of blood flow direction and mean velocity onto a grayscale image, using pulsed wave Doppler sampled at many points at once rather than the Fast Fourier Transform used for spectral display. By convention, flow toward the transducer is one color, typically red, and flow away is another, typically blue, with brighter shades showing higher mean velocity. It shares the same Nyquist limit and aliasing behavior as pulsed wave spectral Doppler.
On the exam: SPI and vascular questions test the toward-red, away-blue convention and that raising the color scale, which raises the Nyquist limit, can eliminate aliasing.
Reference: Edelman, S. K. (2012). Understanding Ultrasound Physics. ESP Ultrasound.
Abdominal Sonography
Anatomy, measurements and pathology from the abdominal portion of the ARDMS Abdomen and ARRT Sonography exams.
- Portal hypertension
Portal hypertension is elevated pressure in the portal venous system, defined as a portal pressure gradient above 5 mm Hg. Cirrhosis is the most common cause in the United States. Ultrasound findings include splenomegaly, ascites, portosystemic collaterals and a portal vein wider than about 13 mm, though width alone is unreliable. Flow direction tells the story: blood normally runs toward the liver (hepatopetal), and reversed flow away from it (hepatofugal) indicates portal hypertension. A serious complication is acute variceal bleeding.
On the exam: Registry questions test hepatofugal versus hepatopetal flow direction as the classic Doppler sign of portal hypertension, along with splenomegaly as its most dependable clinical indicator.
Reference: StatPearls: Portal Hypertension, NCBI Bookshelf; Radiopaedia: Portal hypertension
- Cholelithiasis
Cholelithiasis is the presence of gallstones within the gallbladder, the most common cause of biliary disease. On ultrasound, stones typically appear as highly reflective foci that cast a posterior acoustic shadow and roll with gravity when the patient repositions. A gallbladder packed with stones gives the wall-echo-shadow sign. Gallbladder sludge is also mobile and gravity-dependent but does not shadow. A twinkling artifact can appear behind small stones on color Doppler, but it is not itself diagnostic criteria for a stone.
On the exam: Exams test the shadowing and mobility that separate a stone from sludge, and that twinkling artifact supports but does not confirm the diagnosis.
Reference: StatPearls: Gallstones (Cholelithiasis), NCBI Bookshelf
- Acute cholecystitis
Acute cholecystitis is inflammation of the gallbladder, most often from a stone obstructing the cystic duct. Look for a wall thicker than 3 mm, stones or sludge in the lumen, fluid tracking around the gallbladder, distension, and a positive sonographic Murphy sign, where transducer pressure over the gallbladder reproduces the patient's pain. Emphysematous cholecystitis, a gas-forming form seen more often in diabetics, is a surgical emergency.
On the exam: Exams pair wall thickening with a positive sonographic Murphy sign as the core diagnostic combination, and test emphysematous cholecystitis as the diabetic-associated emergency variant.
- Sonographic Murphy sign
The sonographic Murphy sign is maximal tenderness elicited by pressing the transducer directly over the sonographically visualized gallbladder, distinct from the clinical Murphy sign obtained by manual palpation. A positive sign localizes pain specifically to the gallbladder rather than the right upper quadrant generally, and it points to local inflammation. Combined with a thickened wall or fluid around the gallbladder, acute cholecystitis is the usual answer.
On the exam: Exams distinguish this transducer-elicited sign from the manual clinical Murphy sign and pair it with wall thickening as diagnostic criteria for cholecystitis.
Reference: Sonographic Murphy sign, Radiopaedia
- Common bile duct
The common bile duct carries bile from the liver and gallbladder into the duodenum, formed by the union of the common hepatic duct and cystic duct and joining the pancreatic duct at the ampulla of Vater. It normally measures less than 6 mm in diameter, and its normal caliber tends to increase somewhat with age. Dilation beyond about 8 mm suggests distal obstruction from a stone or mass.
On the exam: The normal size cutoff and the dilation threshold that suggests obstruction are frequently tested numeric thresholds on the Abdomen exam.
- Hepatic steatosisalso called fatty liver
Hepatic steatosis, commonly called fatty liver, is fatty infiltration of the liver in which triglycerides accumulate within hepatocytes. Sonographically the liver appears diffusely more echogenic than the adjacent renal cortex, with increased attenuation that reduces penetration to the deep liver and diaphragm. It is commonly linked to alcohol use, diabetes, and obesity, and can progress toward cirrhosis if the underlying cause persists.
On the exam: The liver-to-kidney echogenicity comparison and reduced posterior penetration are the classic sonographic clues tested for diffuse liver disease.
Reference: StatPearls: Liver Imaging, NCBI Bookshelf
- Abdominal aortic aneurysmalso called AAA
An abdominal aortic aneurysm is a focal dilation of the abdominal aorta, most often located below the renal arteries, defined as an outer-wall-to-outer-wall diameter of 3.0 cm or greater. More than 85 percent occur infrarenal, and the aneurysm is typically fusiform, ballooning uniformly on all sides. Mural thrombus commonly lines the wall. Ultrasound measures the aorta in transverse and longitudinal planes to confirm true dilation.
On the exam: The 3.0 cm diagnostic threshold and outer-to-outer wall measurement technique are standard, frequently tested facts on the Abdomen exam.
Reference: StatPearls: Abdominal Aortic Aneurysm Imaging, NCBI Bookshelf
- Splenomegaly
Splenomegaly is enlargement of the spleen beyond its normal size, generally taken as a length above 13 cm in an adult, with thickness above 5 cm as a second measure; some references use 12 cm, and true upper limits vary with patient height. Causes include portal hypertension, hematologic disease, infection, and infiltrative disorders. Sonographic assessment is made in the longitudinal plane, typically from a coronal or intercostal approach that captures the full length of the spleen.
On the exam: The 13 cm length threshold is a standard measurement question, often linked back to portal hypertension as a cause.
Reference: StatPearls: Splenomegaly, NCBI Bookshelf
- Hydronephrosis
Hydronephrosis is dilation of the renal collecting system, seen sonographically as anechoic fluid that separates and fills the central renal sinus echoes. A normal adult renal pelvis measures less than 10 mm in anteroposterior diameter; beyond this, dilation of the pelvis and calyces is considered hydronephrosis. A distended bladder can mimic it, so post-void images are obtained to confirm the finding does not resolve after voiding.
On the exam: Exams test the false-positive trap of a full bladder alongside the renal pelvis and calyceal dilation that defines true hydronephrosis.
Reference: StatPearls: Hydronephrosis and Hydroureter, NCBI Bookshelf
- Acute pancreatitis
Acute pancreatitis is acute inflammation of the pancreas, most often caused by pancreatic duct obstruction from gallstones, followed by alcohol use. Sonographically the gland is often diffusely enlarged and hypoechoic from edema, sometimes heterogeneous, with an indistinct margin against surrounding fat. Amylase and lipase are both elevated, though lipase remains elevated longer. Overlying bowel gas often limits visualization, so a nonvisualized pancreas does not rule out the diagnosis.
On the exam: Questions often test that bowel gas obscuring the pancreas is an expected limitation and does not exclude pancreatitis, along with lipase outlasting amylase.
Reference: StatPearls: Pancreas Imaging, NCBI Bookshelf
- Testicular torsion
Testicular torsion is twisting of the spermatic cord that cuts off blood supply to the testicle, a surgical emergency. The bell clapper deformity, which leaves the testis abnormally mobile, increases the risk. Grayscale findings can be subtle early on, but color and spectral Doppler showing absent or markedly decreased flow compared with the asymptomatic side is the key finding. Surgical salvage rates are highest when treatment occurs within 6 hours.
On the exam: Exams contrast torsion's absent Doppler flow and 6-hour salvage window with epididymitis, which shows increased flow instead.
Reference: Laquerre JN. Lange Review: The Fundamentals of Pediatric Sonography: A Registry Review and Protocol Guide. 1st ed. New York, NY: McGraw Hill LLC; 2022.
- Ascites
Ascites is free fluid within the peritoneal cavity. On ultrasound it appears as anechoic fluid that collects in dependent spaces, most prominently the hepatorenal recess, also called Morison pouch, as well as the pelvis and around loops of bowel. Common causes include cirrhosis and portal hypertension, along with heart failure, infection, and malignancy. In a fetus, ascites is one of the fluid collections used to diagnose hydrops when found in at least two body compartments.
On the exam: Exams test Morison pouch as a key dependent collection site for adult ascites, and the two-compartment rule that defines fetal hydrops.
Reference: StatPearls: Ascites, NCBI Bookshelf
OB/GYN Sonography
Obstetric and gynecologic findings, measurements and terminology used across first, second and third trimester scanning.
- Gestational sac
The gestational sac is the earliest sonographic sign of an intrauterine pregnancy, appearing as a small anechoic fluid collection within the endometrium as early as four and a half to five weeks gestation. It grows roughly 1 mm per day. Failure of a pregnancy is diagnosed when the sac reaches a mean diameter of 25 mm or more without a visible embryo.
On the exam: Exams test the mean sac diameter cutoff for a failed pregnancy alongside the sac's expected daily growth rate.
Reference: StatPearls: Early Pregnancy Loss (Spontaneous Abortion), NCBI Bookshelf
- Yolk sac
The yolk sac is the first structure visualized within a gestational sac, confirming a true intrauterine pregnancy before an embryo is seen. It looks like a small bright ring around a dark middle, normally no more than 6 mm across, and should be found once the mean sac diameter reaches roughly 13 mm. A yolk sac larger than about 7 mm, or one that is calcified, thickened, or irregular in shape, is a poor prognostic sign for the pregnancy.
On the exam: The yolk sac's role as the first confirmatory structure inside a gestational sac, along with its size limits, is a standard early first-trimester exam question.
Reference: StatPearls: First-Trimester Ultrasonography, NCBI Bookshelf
- Crown-rump lengthalso called CRL
Crown-rump length is the longest straight-line measurement of the embryo or fetus from the top of the head to the bottom of the torso, excluding the limbs and yolk sac. It is the most accurate method for dating a pregnancy, used from the time a fetal pole is visible up to a crown-rump length of about 84 mm, roughly 13 weeks 6 days, after which biparietal diameter becomes the more accurate measurement.
On the exam: CRL is tested as the single most accurate dating measurement in pregnancy, and its accuracy is why an early ultrasound date should not be revised later in pregnancy.
Reference: StatPearls: Gestational Age Assessment, NCBI Bookshelf
- Biparietal diameteralso called BPD
Biparietal diameter is a transverse measurement of the fetal head taken at the transthalamic plane, which shows the thalami, cavum septum pellucidum, and midline falx, with calipers placed from the outer edge of the near skull table to the inner edge of the far skull table. It is one of four standard fetal biometric parameters, along with head circumference, abdominal circumference, and femur length, and is most accurate for dating between 14 and 24 weeks.
On the exam: The exact skull table caliper placement and landmark level are commonly tested measurement technique details.
Reference: StatPearls: Estimated Date of Delivery, NCBI Bookshelf
- Amniotic fluid indexalso called AFI
The amniotic fluid index is a semiquantitative estimate of amniotic fluid volume, found by splitting the uterus into four quadrants around the umbilicus, measuring the deepest vertical fluid pocket in each one that holds no cord or fetal parts, and adding the four numbers. Roughly 5 to 24 cm is normal; at or below 5 cm is oligohydramnios, and at or above 24 cm is polyhydramnios.
On the exam: The four-quadrant technique and the 5 cm and 24 cm cutoffs are standard, frequently tested AFI thresholds.
Reference: StatPearls: Sonographic Evaluation of Amniotic Fluid, NCBI Bookshelf
- Oligohydramnios
Oligohydramnios is too little amniotic fluid: an amniotic fluid index at or below 5 cm, or a deepest pocket shallower than 2 cm. It can show up in any trimester. Causes include ruptured membranes, placental insufficiency, fetal renal anomalies that reduce urine output, and post-term pregnancy. It is often seen with intrauterine growth restriction and, when prolonged, is associated with pulmonary hypoplasia.
On the exam: Exams pair the numeric AFI and single-pocket cutoffs with fetal renal causes and growth restriction as a classic scenario question.
Reference: StatPearls: Oligohydramnios, NCBI Bookshelf
- Polyhydramnios
Polyhydramnios is too much amniotic fluid: an amniotic fluid index at or above 24 cm, or one pocket deeper than 8 cm. It is associated with fetal anomalies that impair swallowing, such as esophageal or duodenal atresia and cervical teratoma, as well as maternal diabetes and multiple gestation. In twin-to-twin transfusion syndrome, the recipient twin develops polyhydramnios while the donor develops oligohydramnios.
On the exam: Exams commonly link polyhydramnios to swallowing-related fetal anomalies and to the recipient twin in twin-to-twin transfusion syndrome.
Reference: StatPearls: Polyhydramnios, NCBI Bookshelf
- Placenta previa
Placenta previa is a condition in which the placenta implants over or near the internal cervical os. Placental tissue within 2 cm of the os without covering it is a low-lying placenta; touching but not covering the os is marginal previa; partially covering it is partial previa; and completely covering it is complete previa. Transvaginal ultrasound gives the best resolution for confirming the placental edge relative to the os. Placenta previa is a classic cause of painless third-trimester bleeding.
On the exam: Exams test the precise 2 cm cutoff and terminology that separate low-lying, marginal, and complete previa.
Reference: StatPearls: Placenta Previa, NCBI Bookshelf
- Nuchal translucency
Nuchal translucency is the fluid-filled space at the back of the fetal neck, measured in the first trimester between 11 and 14 weeks gestation, when the crown-rump length falls between 45 and 84 mm, as part of aneuploidy screening. Measurement requires a strict midsagittal view with calipers on the inner borders of the nuchal line. Anything over 3 mm counts as abnormal, and at 3.5 mm or more the fetus is referred for echocardiography.
On the exam: The precise gestational age and crown-rump length window for a valid measurement are heavily tested technique details, along with the referral threshold for fetal echocardiography.
Reference: Abuhamad, A., & Chaoui, R. (2022). A Practical Guide to Fetal Echocardiography: Normal and Abnormal Hearts (4th ed., p. 4). Wolters Kluwer.; StatPearls: Prenatal Genetic Screening, NCBI Bookshelf
- Endometrial stripe
The endometrial stripe is the sonographic measurement of the endometrium, taken as the thickest anteroposterior distance from one basal layer to the other on a midline sagittal view of the uterus, excluding any fluid within the cavity. Its normal thickness changes with the menstrual cycle and thins after menopause. In a postmenopausal woman with bleeding, a stripe greater than 4 mm warrants further evaluation such as biopsy.
On the exam: The postmenopausal bleeding threshold and correct measurement technique excluding fluid are standard GYN exam questions.
Reference: StatPearls: Postmenopausal Bleeding, NCBI Bookshelf
- Adenomyosis
Adenomyosis is a condition in which endometrial glands and stroma grow within the myometrium, most often affecting the posterior wall and causing diffuse uterine enlargement. The uterus looks globular, the myometrium echotexture is uneven, small cysts of about 1 to 7 mm sit within the muscle, borders stay indistinct instead of forming a discrete mass, and thin striations run beneath the endometrium. Patients often present with heavy periods and long-standing pain in the pelvis.
On the exam: Exams test the ill-defined, globular appearance of adenomyosis against the well-circumscribed masses typical of fibroids.
Reference: StatPearls: Adenomyosis, NCBI Bookshelf
- Ectopic pregnancy
Ectopic pregnancy is a pregnancy that implants outside the endometrial cavity, most commonly within the ampullary portion of the fallopian tube, which accounts for more than 90 percent of cases. Sonographic clues include an empty uterus with a positive pregnancy test, a complex adnexal mass separate from the ovary, a tubal ring surrounding a sac within the tube, and often a ring of fire pattern of peripheral vascularity. A corpus luteum can show the same ring, but it sits within the ovary, so location separates the two.
On the exam: This is one of the highest-stakes OB diagnoses tested, since location outside the ovary is the key feature separating a true ectopic from a corpus luteum cyst.
Vascular Sonography
Arterial and venous findings from vascular technology scanning, including the terms the RVT and RVS exams lean on.
- Deep vein thrombosisalso called DVT
Deep vein thrombosis is a blood clot within a deep vein, most often in the lower extremity, that can embolize to the lungs if untreated. Virchow's triad describes the contributing factors, of which venous stasis is the predominant cause, with clots typically forming around the valve leaflets. The primary diagnostic criterion is loss of vein compressibility with transducer pressure. Severe iliofemoral DVT with compromised arterial inflow, called phlegmasia cerulea dolens, threatens the limb.
On the exam: Noncompressibility is the single most tested diagnostic criterion for DVT, and phlegmasia cerulea dolens is tested as its limb-threatening complication.
Reference: StatPearls: Deep Venous Thrombosis, NCBI Bookshelf
- Peripheral arterial diseasealso called PAD
Peripheral arterial disease is narrowing or occlusion of arteries outside the heart and brain, most often from atherosclerosis in the lower extremities. True intermittent claudication is reproducible pain in a large muscle group brought on by walking and relieved by rest or quiet standing; pain at rest, relieved by dangling the leg, signals more severe disease. Diagnosis relies on the ankle-brachial index and duplex ultrasound, with angiography as the gold standard.
On the exam: PAD questions often connect claudication symptoms to the ankle-brachial index as the standard first-line diagnostic tool.
Reference: StatPearls: Peripheral Arterial Disease, NCBI Bookshelf
- Ankle-brachial indexalso called ABI
The ankle-brachial index screens for peripheral arterial disease by dividing the highest ankle systolic pressure by whichever arm systolic pressure is higher. A value below 0.9 is abnormal and indicates arterial insufficiency; 0.5 to 0.8 suggests single-level disease and below 0.5 suggests multilevel disease. A value above 1.4 suggests noncompressible, calcified vessels that make the result unreliable, often seen in diabetic patients.
On the exam: The calcified-vessel pitfall above 1.4 and the calculation method are standard numeric thresholds tested on both the RVT and RVS vascular exams.
- Intimal flap
An intimal flap is a mobile piece of the innermost arterial layer that has separated from the vessel wall, the defining sign of arterial dissection. On ultrasound it appears as a thin, echogenic line that may flutter with the pulse, separating true and false lumens, with color Doppler often showing different flow patterns on either side. After carotid endarterectomy, a flap longer than 2 mm on B-mode is considered significant enough to warrant surgical revision.
On the exam: Exams test recognition of an intimal flap as the defining sonographic sign of dissection, and the 2 mm threshold for revision after carotid endarterectomy.
- Pseudoaneurysm
A pseudoaneurysm is a contained collection of blood outside the arterial wall that communicates with the artery through a defect, most often from arterial laceration at a catheterization or biopsy access site, held together by surrounding tissue rather than a true vessel wall. Color Doppler classically shows a swirling yin-yang pattern of flow within the sac, and spectral Doppler of the connecting neck shows a to-and-fro waveform as blood moves into the sac in systole and back in diastole.
On the exam: The yin-yang sac pattern and to-and-fro neck waveform are the two classic Doppler findings tested for pseudoaneurysm.
Reference: Laquerre JN. Lange Review: The Fundamentals of Pediatric Sonography: A Registry Review and Protocol Guide. 1st ed. New York, NY: McGraw Hill LLC; 2022.
- Carotid bifurcation
The carotid bifurcation is where the common carotid splits into its internal and external branches. Plaque forms here more than anywhere else in the neck, because the split disturbs flow and leaves pockets of low shear stress. The internal carotid artery is usually larger, runs posterolateral to the external carotid, has no branches in the neck, and shows a low-resistance waveform. A temporal tap, tapping the superficial temporal artery while scanning, can help confirm the external carotid.
On the exam: Distinguishing the internal from the external carotid by branching, waveform resistance, and the temporal tap maneuver is a core carotid duplex exam question.
Reference: Temporal tap manoeuvre, Radiopaedia
- Calf muscle pump
The calf muscle pump is the mechanism by which contraction of the calf muscles during walking compresses the deep veins and propels venous blood back toward the heart. During relaxation, falling pressure in the deep veins draws blood in from the superficial veins through the perforators, and competent valves prevent backflow. Dorsiflexion of the ankle activates the distal calf, or piston, pump. Failure of this system contributes to venous stasis and chronic venous insufficiency.
On the exam: Understanding the calf muscle pump explains why immobility raises DVT risk and why upper extremity DVT is less common, a physiology question on the vascular exam.
- Tardus parvus waveform
A tardus parvus waveform is an abnormal arterial Doppler waveform found downstream from a significant stenosis, with a slowed, delayed systolic upstroke, called tardus, and a blunted, low-amplitude peak, called parvus. It is classically described in the intrarenal arteries as an indirect sign of proximal renal artery stenosis, with the stenosis located on whichever side shows the abnormal waveform, though the same pattern can appear distal to a significant stenosis anywhere in the arterial system.
On the exam: This indirect Doppler sign of proximal stenosis is tested particularly in renal artery stenosis screening and in evaluating bypass grafts.
Reference: StatPearls: Renal Artery Stenosis, NCBI Bookshelf
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