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.
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 sound passing through it, and it determines how strongly an interface reflects sound back to the transducer. It equals density x propagation speed. When two adjacent tissues have very different impedances, like soft tissue and bone or soft tissue and air, most of the sound reflects at that boundary instead of continuing deeper, which is why gel is needed to remove the air gap at the skin.
On the exam: SPI questions ask you to rank interfaces by echo strength based on how large the impedance mismatch is between the two tissues.
- Propagation speed
Propagation speed is how fast sound travels through a medium, and it depends on the medium's stiffness and density, not on the ultrasound machine. The assumed average in soft tissue is 1,540 m/s, fastest in bone and slowest in air and lung. Using that constant, sound takes about 13 microseconds to make the round trip through 1 cm of soft tissue, which is how the machine calculates depth from echo return time.
On the exam: SPI problems use 1,540 m/s and the 13-microsecond rule to test whether you can calculate depth or transit time from a given scenario.
- Attenuation
Attenuation is the weakening of an ultrasound beam as it travels through tissue, caused by absorption, scattering, and reflection. In soft tissue it is estimated with the rule of thumb of about 0.5 dB per cm per MHz, so total attenuation in decibels equals the attenuation coefficient x path length in cm x frequency in MHz. Higher frequency and greater depth both increase attenuation, which is why higher frequencies penetrate less.
On the exam: SPI calculation questions give you frequency and depth and ask you to solve for total attenuation in decibels.
- Axial resolution
Axial resolution is the ability to separate two structures that lie one behind the other, along the direction of the beam, into two distinct echoes. It equals spatial pulse length divided by 2 (axial resolution = SPL / 2), so a shorter pulse gives better, smaller-number axial resolution. Because spatial pulse length depends on wavelength and cycles per pulse, raising frequency or using a heavily damped transducer improves it.
On the exam: SPI questions ask you to predict what happens to axial resolution when spatial pulse length or frequency changes.
- Lateral resolution
Lateral resolution is the ability to separate two structures that lie side by side, perpendicular to the beam, into two distinct echoes. It is determined by the width of the ultrasound beam at a given depth, so it is best at the focus, where the beam is narrowest, and worsens in the near field and far field where the beam is wider. Focusing narrows the beam and improves lateral resolution.
On the exam: SPI questions test whether you know that lateral resolution equals beam width and is best at the focal zone, not a fixed value like axial resolution.
- Elevational resolution
Elevational resolution, also called slice-thickness resolution, is the ability to resolve structures in the dimension perpendicular to the scan plane, controlled by the height of the beam rather than its width or pulse length. It is set by the transducer's fixed acoustic lens or elevational focus and cannot be adjusted by the sonographer at the console. A thick slice can cause partial volume artifact, making a structure look falsely filled in.
On the exam: SPI questions distinguish elevational resolution from axial and lateral resolution by testing that it is fixed by transducer design, not machine controls.
- Temporal resolution
Temporal resolution is how accurately a system displays motion over time, and it is really the frame rate. Faster frame rates give better temporal resolution and smoother-looking motion. Frame rate depends on pulse repetition frequency divided by the number of scan lines per frame, so anything that increases imaging depth, sector width, or line density lowers the frame rate and worsens temporal resolution.
On the exam: SPI questions ask what happens to frame rate, and therefore temporal resolution, when depth, sector width, or line density is increased.
- Frequency
Frequency is the number of complete cycles of a sound wave that occur per second, measured in Hertz. Diagnostic ultrasound uses frequencies in the megahertz range, roughly 2 to 18 MHz. Frequency is set by the transducer and is not changed by the medium the sound travels through, only propagation speed and wavelength change between media. Higher frequency improves resolution but reduces penetration because it attenuates faster.
On the exam: SPI questions test the tradeoff that raising frequency improves resolution but decreases the depth of useful penetration.
- Wavelength
Wavelength is the length of space that one complete cycle of a sound wave occupies. It equals propagation speed divided by frequency (wavelength = propagation speed / frequency), so in soft tissue, wavelength in millimeters is approximately 1.54 divided by frequency in MHz. Unlike frequency, wavelength changes when the medium changes, because propagation speed changes with the medium even though frequency stays fixed by the transducer.
On the exam: SPI calculation questions give frequency and ask you to solve for wavelength in soft tissue using the 1.54 shortcut.
- Period
Period is the time it takes to complete one full cycle of a sound wave, usually measured in microseconds. It equals 1 divided by frequency (period = 1 / frequency), so higher frequency means a shorter period. Like frequency, period is a property of the source and does not change when the sound wave moves into a different medium, even though propagation speed and wavelength do.
On the exam: SPI questions test which variables, like period and frequency, stay constant across media versus which ones, like wavelength, change.
- Pulse repetition frequency
Pulse repetition frequency, or PRF, is the number of ultrasound pulses sent out by the transducer per second. It is largely controlled by imaging depth, because the machine must wait for echoes to return from the deepest structure before sending the next pulse, so deeper imaging requires a lower PRF. PRF sets the Nyquist limit in pulsed Doppler and equals 1 divided by pulse repetition period.
On the exam: SPI and vascular questions ask how increasing imaging depth lowers PRF and, in turn, lowers the Nyquist limit and increases aliasing risk.
- Pulse repetition period
Pulse repetition period, or PRP, is the total time from the start of one pulse to the start of the next, and it equals 1 divided by pulse repetition frequency (PRP = 1 / PRF). PRP is made up of pulse duration, the brief time the transducer is transmitting, plus listening time, the much longer time it spends receiving returning echoes before the next pulse fires.
On the exam: SPI questions ask you to calculate PRP from a given PRF, or to identify which portion of PRP is pulse duration versus listening time.
- Spatial pulse length
Spatial pulse length, or SPL, is the physical length of space that one ultrasound pulse occupies. It equals the number of cycles in the pulse x wavelength (SPL = cycles x wavelength). SPL is the only variable that directly sets axial resolution, since axial resolution equals SPL divided by 2. Reducing the number of cycles per pulse, through heavier transducer damping, shortens SPL and improves axial resolution.
On the exam: SPI questions ask what happens to axial resolution when spatial pulse length is shortened by reducing cycles per pulse or raising frequency.
- Duty factor
Duty factor is the fraction of time the transducer spends actually transmitting sound rather than listening for returning echoes. It equals pulse duration divided by pulse repetition period (duty factor = pulse duration / PRP), expressed as a percentage or decimal. In pulsed imaging, duty factor is under 1 percent, since most of each cycle is spent listening; continuous wave Doppler has a duty factor of 100 percent.
On the exam: SPI questions use duty factor to compare bioeffect and intensity considerations between pulsed imaging and continuous wave Doppler.
- Damping
Damping is the process of reducing how long a piezoelectric element rings after being excited, done with a backing material bonded to the back of the crystal that absorbs excess vibration. Heavier damping shortens pulse duration and spatial pulse length, which improves axial resolution, at the cost of reduced sensitivity because less energy is available in each pulse. Damping also widens bandwidth and lowers Q factor.
On the exam: SPI questions describe the backing material's role in shortening the pulse to improve axial resolution while trading off sensitivity.
- Q factor
Q factor, or quality factor, describes how pure or narrow a range of frequencies a pulse contains. It equals operating frequency divided by bandwidth. A high Q factor means a long, narrow-bandwidth pulse, typical of undamped or lightly damped systems such as continuous wave Doppler. Diagnostic imaging transducers are heavily damped to produce a low Q factor, giving a wide bandwidth and a short pulse for good axial resolution.
On the exam: SPI questions ask you to connect a low Q factor to heavy damping, wide bandwidth, and better axial resolution in imaging transducers.
- Bandwidth
Bandwidth is the range of frequencies contained within an ultrasound pulse, rather than a single pure frequency. Shorter pulses, produced by heavy damping and fewer cycles, contain a wider range of frequencies and therefore have a wider bandwidth. Wide bandwidth is desirable in imaging because it goes along with a short spatial pulse length and good axial resolution, and it supports harmonic and multi-frequency transducer operation.
On the exam: SPI questions link wide bandwidth to short pulses and heavy damping, and narrow bandwidth to long pulses used in continuous wave Doppler.
- Piezoelectric effect
The piezoelectric effect is the property of certain crystals, such as lead zirconate titanate, that lets them convert electrical energy into mechanical vibration and convert mechanical vibration back into an electrical signal. Applying a voltage to the crystal on transmit makes it vibrate and produce sound, while returning echoes striking the crystal on receive generate the electrical signal the machine processes into an image. This two-way conversion is the basis of every ultrasound transducer.
On the exam: SPI questions ask you to identify the piezoelectric effect as the mechanism converting electrical energy to sound and back again inside the transducer.
- Focal zone
The focal zone is the region of the ultrasound beam surrounding the focus where the beam is narrowest, giving the best lateral resolution available at that depth. It extends a short distance above and below the true focal point rather than being a single point. Sonographers place the focal zone at or just below the depth of the structure of interest to optimize lateral resolution there.
On the exam: SPI and clinical scanning questions test that lateral resolution is best within the focal zone and worsens in the near and far fields.
- Near fieldalso called Fresnel zone
The near field, or Fresnel zone, is the part of the ultrasound beam between the transducer face and the focus, where the beam converges and narrows. Its length increases with a larger transducer diameter or a higher frequency, following near zone length equals diameter squared divided by four times the wavelength. A longer near zone lets the focus be placed deeper, which can improve resolution at greater depths.
On the exam: SPI questions ask how increasing transducer diameter or frequency lengthens the near zone and moves the focus deeper.
- Far fieldalso called Fraunhofer zone
The far field, or Fraunhofer zone, is the part of the ultrasound beam beyond the focus, where the beam diverges and spreads out with increasing depth. Because the beam is wider here than at the focus, lateral resolution steadily worsens the farther a structure lies into the far field. A longer near zone, from a larger transducer or higher frequency, pushes the start of the far field deeper.
On the exam: SPI questions test that lateral resolution degrades progressively in the far field as the beam diverges with depth.
- Time gain compensationalso called TGC
Time gain compensation, or TGC, is the machine function that amplifies returning echoes based on the depth they came from, boosting deeper echoes more than shallow ones to counteract attenuation. Without TGC, structures at equal true brightness would appear progressively dimmer with depth simply because more sound was lost getting there and back. TGC controls let the sonographer adjust this depth-dependent amplification manually to produce uniform brightness.
On the exam: SPI questions ask you to recognize TGC as a receiver function that compensates for attenuation, not a transmit power adjustment.
- Dynamic range
Dynamic range is the ratio between the largest and smallest echo amplitudes a system can detect and display, expressed in decibels. A wide dynamic range compresses that whole span into many shades of gray, producing a softer-looking image with more subtle detail, while a narrow dynamic range shows fewer, higher-contrast shades of gray, often called a harder-looking image. It is a receiver and display setting, not a transmit power control.
On the exam: SPI questions ask how widening or narrowing dynamic range changes the number of gray shades and overall image contrast.
- Harmonic imaging
Harmonic imaging forms the image from harmonic frequencies, typically twice the transmitted fundamental frequency, that are generated as sound distorts while traveling through tissue, rather than from the reflected fundamental frequency itself. Because harmonics build up gradually with depth and are weaker near the skin surface, this technique reduces near-field artifact and clutter and improves contrast resolution, especially in technically difficult body habitus patients.
On the exam: SPI questions ask why harmonic imaging reduces artifact and improves image quality compared to conventional fundamental imaging.
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 multiple times between two strong, closely spaced parallel reflectors, or between the transducer face and a reflector, before finally returning to the transducer. Each bounce adds extra travel time, so the machine displays a series of equally spaced, parallel echoes at increasing depth, with brightness decreasing at each successive line since some energy is lost with every bounce.
On the exam: SPI questions ask you to identify reverberation from its signature of equally spaced parallel bands decreasing in brightness with depth.
- Comet tail artifact
Comet tail artifact is a form of reverberation seen as a tapering series of closely spaced, discrete bright echoes trailing behind a small, strongly reflective structure, such as a metallic clip or cholesterol crystals in adenomyomatosis of the gallbladder wall. The reflectors causing it are so close together that the individual reverberation echoes appear to merge into a narrowing, tail-like streak rather than staying widely separated.
On the exam: SPI and abdominal questions use comet tail artifact as a recognized sign of adenomyomatosis and other tightly packed small reflectors.
- Ring-down artifact
Ring-down artifact appears as a continuous, solid band of echoes extending posteriorly from a small collection of gas bubbles, rather than the discrete separated lines of typical reverberation. It is caused by fluid trapped between adjacent gas bubbles resonating continuously as sound passes through, producing sustained sound that returns to the transducer as an unbroken streak. It is a recognized sign of gas, such as in the gastrointestinal tract.
On the exam: SPI questions distinguish ring-down's continuous band from comet tail's discrete tapering lines, both tied to small gas or crystal reflectors.
- Acoustic shadowing
Acoustic shadowing is an artifact appearing as a dark, anechoic band deep to a structure that strongly attenuates or reflects sound, such as a gallstone, calcification, or bone. Because that structure absorbs or reflects most of the incoming beam, very little sound energy reaches tissue directly beneath it, so few or no echoes return from that region and it is displayed as unusually dark on the image.
On the exam: SPI and abdominal questions ask you to identify shadowing behind highly attenuating structures like stones and calcifications.
- Posterior acoustic enhancement
Posterior acoustic enhancement is an artifact appearing as an unusually bright band deep to a structure that attenuates sound less than the surrounding tissue, such as a simple fluid-filled cyst. Because the machine's time gain compensation assumes typical soft tissue attenuation, and the fluid absorbs less sound than that assumption, more sound energy actually reaches tissue beyond it, making that deeper tissue appear falsely brighter than it truly is.
On the exam: SPI questions pair enhancement behind cysts with shadowing behind stones as opposite attenuation-based artifacts.
- Mirror image artifact
Mirror image artifact is a duplicate of a real structure that appears on the far side of a strong, highly reflective curved surface, classically the diaphragm. Sound reflects off the diaphragm toward the real structure, bounces back to the diaphragm, and returns to the transducer later than the direct echo, so the machine displays it as a second, deeper copy of the structure positioned symmetrically across the reflector.
On the exam: SPI and abdominal questions use liver lesions mirrored above the diaphragm as the classic teaching example of this artifact.
- Refraction artifactalso called edge shadowing
Refraction artifact occurs when the ultrasound beam bends as it crosses a boundary between two media with different propagation speeds, following Snell's law, causing a reflector to be displayed in the wrong lateral position or to be missed entirely. Edge shadowing is the specific thin, clean shadow seen at the lateral edges of a curved structure, like a cyst or vessel, 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.
- Side lobe artifact
Side lobe artifact happens because a transducer emits weaker secondary beams, called side lobes, radiating off-axis from the main ultrasound beam. When a side lobe strikes a strong reflector, the returning echo is displayed as if it came from directly along the main beam axis, placing artifactual echoes inside structures that should be anechoic, such as false-appearing debris inside a fluid-filled bladder or gallbladder.
On the exam: SPI questions ask you to recognize side lobe artifact as the explanation for artifactual echoes filling in an otherwise anechoic structure.
- Speed error artifactalso called speed displacement artifact
Speed error artifact results from the machine always assuming a constant propagation speed of 1,540 m/s to calculate depth, even when the sound is actually traveling through tissue at a different speed. If the true speed is slower than assumed, such as in fat, the reflector is displayed too deep; if the true speed is faster, the reflector is displayed too shallow, misplacing structures in the image.
On the exam: SPI questions ask whether a structure displays too deep or too shallow depending on whether the actual tissue speed is slower or faster than 1,540 m/s.
- Spatial compounding
Spatial compounding is an imaging technique that combines several real-time frames of the same tissue, acquired by electronically steering the beam to different angles, into one averaged composite image. Because random speckle and angle-dependent artifacts like refraction shadowing appear differently at each steering angle, averaging the frames cancels much of that noise while true tissue boundaries reinforce, improving border definition and overall contrast resolution.
On the exam: SPI questions ask you to identify spatial compounding as a technique that reduces speckle and angle-dependent artifact by averaging multiple steered frames.
Doppler and Hemodynamics
How ultrasound measures moving blood, and the numbers reported from a spectral waveform.
- Doppler shift
Doppler shift is the change in frequency between the sound a transducer transmits and the sound it receives back, caused by relative motion between the transducer and a moving reflector such as red blood cells. It is calculated as Doppler shift = (2 x transmitted frequency x velocity x cosine of the Doppler angle) / propagation speed. Flow moving toward the transducer raises the received frequency, and flow moving away lowers it.
On the exam: SPI and vascular questions give you frequency, velocity, and angle and ask you to solve the Doppler equation for the shift.
- Doppler angle
Doppler angle is the angle between the ultrasound beam and the direction blood is flowing, 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, accuracy drops sharply as the angle approaches 90 degrees, where cosine equals zero and no Doppler shift is detected even though flow is present.
On the exam: SPI and vascular questions test that a 90-degree Doppler angle produces zero measurable shift regardless of actual flow velocity.
- Nyquist limit
The Nyquist limit is the highest Doppler shift frequency that pulsed wave Doppler can measure correctly without aliasing. It equals half the pulse repetition frequency (Nyquist limit = PRF / 2). Any true Doppler shift greater than this limit cannot be sampled often enough to be displayed accurately and will alias. Raising PRF raises the Nyquist limit, which is one common way to resolve aliasing at higher 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.
- Aliasing
Aliasing is a display error in pulsed wave and color Doppler where a true velocity exceeding the Nyquist limit is displayed incorrectly, wrapping around to appear as flow in the opposite direction. On a spectral waveform, the peaks that exceed the limit appear cut off at the top and wrapped to the bottom of the baseline; on color Doppler, it appears as an abrupt change from one flow color straight to the opposite color.
On the exam: SPI and vascular questions ask you to recognize aliasing on a waveform or color image and select the correct fix, such as raising PRF.
- Spectral broadening
Spectral broadening is the filling-in of the normally clear window beneath a spectral Doppler waveform, caused by a wide range of velocities being present in the sample volume at the same instant. It commonly indicates disturbed or turbulent flow, such as downstream of a stenosis, but a sample volume that is too large or a Doppler angle that is too steep can also cause it artificially without true flow disturbance.
On the exam: Vascular and SPI questions ask you to interpret spectral broadening as a sign of turbulence while also recognizing technical causes.
- Peak systolic velocityalso called PSV
Peak systolic velocity, or PSV, is the highest blood flow velocity recorded during the systolic phase of the cardiac cycle on a spectral Doppler waveform, measured at the tallest point of each systolic upstroke. It is the primary value used to grade the severity of arterial stenosis, since velocity rises as a vessel narrows to maintain the same volume of flow through a smaller cross-sectional area.
On the exam: Vascular exam questions use PSV thresholds, along with velocity ratios across a stenosis, to grade percent diameter narrowing.
- End-diastolic velocityalso called EDV
End-diastolic velocity, or EDV, is the blood flow velocity measured at the end of diastole, immediately before the next systolic upstroke begins, 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 heavily on the resistance of the vascular bed downstream. EDV is combined with peak systolic velocity to calculate the resistive index.
On the exam: Vascular exam questions pair EDV with PSV to calculate resistive index and to grade the severity of a stenosis.
- Resistive indexalso called RI
Resistive index, or RI, is a Doppler measurement describing how much resistance to flow exists downstream of the sampling point. It is calculated as RI = (peak systolic velocity - end-diastolic velocity) / peak systolic velocity. A higher RI reflects higher downstream resistance, with little or no diastolic flow, while a lower RI reflects a low-resistance bed with substantial forward flow throughout diastole. Normal ranges vary by vascular bed.
On the exam: Vascular questions give PSV and EDV values and ask you to calculate RI and interpret it against a normal reference range.
- Pulsatility indexalso called PI
Pulsatility index, or PI, is another Doppler measurement of flow resistance, calculated as PI = (peak systolic velocity - end-diastolic velocity) / mean velocity averaged over the cardiac cycle. Unlike resistive index, PI remains a usable, defined value even when there is reversed flow in diastole, a situation where resistive index loses its meaning. Higher PI values indicate greater pulsatility and downstream resistance.
On the exam: Vascular questions ask when to use PI instead of RI, specifically when diastolic flow reversal makes RI less informative.
- Laminar flow
Laminar flow is the normal pattern of blood movement in a healthy, unobstructed vessel, where blood travels in smooth, parallel layers, fastest at the center of the vessel and progressively slower toward the vessel walls due to friction. On a spectral Doppler waveform, laminar flow produces a narrow band of velocities at each point in time, leaving a clear window visible underneath the waveform.
On the exam: Vascular questions ask you to recognize a narrow spectral waveform with a clear window as evidence of normal laminar flow.
- Turbulent flow
Turbulent flow is a disorganized flow pattern in which blood moves in multiple directions and at many different velocities at the same location and instant, rather than in smooth, parallel layers. It commonly develops distal to a stenosis, vessel wall irregularity, or high-velocity jet. On a spectral waveform it produces spectral broadening that fills the window, and on color Doppler it can appear as a mosaic of mixed colors within the vessel lumen.
On the exam: Vascular questions link turbulent flow to spectral broadening and color mosaic patterns as indirect signs of a stenosis.
- Bernoulli principle
The Bernoulli principle states that as the velocity of a flowing fluid increases, the pressure it exerts decreases, which is why blood speeds up as it passes through a narrowed vessel segment or a stenotic heart valve. A simplified version of the equation, pressure gradient = 4 x velocity squared, lets a measured peak velocity across a stenosis or valve be converted into an estimated pressure gradient across it.
On the exam: Echo questions use the simplified Bernoulli equation 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 any Nyquist limit or aliasing. Its major limitation is a lack of range resolution: because it samples along the entire length of the beam at once, it cannot tell the operator the specific depth from which a given Doppler signal originated, called range ambiguity.
On the exam: Echo questions test that continuous wave Doppler is chosen over pulsed wave specifically to measure high velocities, such as across a stenotic valve, without aliasing.
- Color Doppler
Color Doppler is an imaging mode that overlays a real-time, color-coded map of blood flow direction and mean velocity onto a grayscale image, using pulsed wave Doppler sampled across many points at once. By convention, flow toward the transducer is displayed in one color, typically red, and flow away from the transducer in another, typically blue, with brighter shades representing higher mean velocities. 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 color convention and that color Doppler aliases the same way pulsed wave Doppler does.
Abdominal Sonography
Anatomy, measurements and pathology from the abdominal portion of the ARDMS Abdomen and ARRT Sonography exams.
- Portal hypertension
Elevated pressure in the portal venous system, most often caused by cirrhosis. On ultrasound it is suggested by a portal vein diameter greater than 13 mm, loss of respiratory variation, slowed or reversed (hepatofugal) flow, splenomegaly, ascites, and portosystemic collaterals such as a recanalized paraumbilical vein. Doppler direction is the key finding: normal portal flow moves toward the liver, called hepatopetal flow.
On the exam: Registry questions often test hepatofugal versus hepatopetal flow direction and the portal vein diameter threshold as the classic Doppler sign of portal hypertension.
- Cholelithiasis
Gallstones within the gallbladder, the most common cause of biliary disease. Sonographically, stones appear as echogenic foci within the gallbladder lumen that produce posterior acoustic shadowing and move with changes in patient position, which distinguishes them from a fixed polyp. Small stones without shadowing can still be diagnosed by demonstrating gravity-dependent movement on repositioning.
On the exam: Exams test the combination of echogenic focus, posterior shadowing, and mobility as the criteria that separate a stone from a polyp or adenomyoma.
- Acute cholecystitis
Acute inflammation of the gallbladder, usually caused by a stone obstructing the cystic duct. Sonographic findings include gallbladder wall thickening beyond 3 mm, pericholecystic fluid, gallbladder distension, and a positive sonographic Murphy sign. Wall thickening alone is nonspecific and can also come from ascites, hepatitis, or hypoalbuminemia, so the full clinical and sonographic picture matters.
On the exam: This is a heavily tested diagnosis, often presented as a case combining right upper quadrant pain, a thickened gallbladder wall, and a positive Murphy sign.
- Sonographic Murphy sign
Focal tenderness elicited by pressing the transducer directly over the sonographically visualized gallbladder, rather than by manual palpation as in the classic clinical Murphy sign. The key differentiator is precise localization: a positive sonographic sign confirms that the maximal tenderness sits directly over the gallbladder itself, not just somewhere in the right upper quadrant. It is one of the most reliable individual findings for acute cholecystitis, especially when paired with gallbladder wall thickening or pericholecystic fluid.
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.
- Common bile duct
The duct that carries bile from the liver and gallbladder into the duodenum, formed by the union of the common hepatic duct and cystic duct. In an adult it normally measures up to about 6 mm, with an allowance of roughly 1 mm per decade of life after age 60, and it may measure larger after cholecystectomy. Dilation suggests distal obstruction from a stone or mass.
On the exam: The normal size cutoff and its adjustments for age and cholecystectomy are a frequently tested numeric threshold on the Abdomen exam.
- Hepatic steatosisalso called fatty liver
Fatty infiltration of the liver, commonly called fatty liver, in which triglycerides accumulate within hepatocytes. Sonographically the liver appears diffusely more echogenic, or brighter, than the adjacent right renal cortex, with increased attenuation that reduces penetration to the deep liver and diaphragm, and sometimes with focal areas of sparing near the gallbladder fossa or porta hepatis.
On the exam: The liver-to-kidney echogenicity comparison and reduced posterior penetration are the classic sonographic clues tested for diffuse liver disease.
- Abdominal aortic aneurysmalso called AAA
Focal dilation of the abdominal aorta, most often below the renal arteries, defined as an outer wall to outer wall diameter of 3.0 cm or greater, or a diameter at least 1.5 times the expected normal size. Ultrasound is the primary screening tool, measuring the aorta in both transverse and longitudinal planes to confirm true dilation rather than tortuosity.
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.
- Splenomegaly
Enlargement of the spleen beyond its normal size, generally accepted as a splenic length greater than 12 cm, though craniocaudal length varies with patient height. Causes include portal hypertension, hematologic disease, infection, and infiltrative disorders. Sonographic assessment is usually made from a coronal or intercostal approach that captures the full long axis of the spleen.
On the exam: The 12 cm length threshold is a standard measurement question, often linked back to portal hypertension as a cause.
- Hydronephrosis
Dilation of the renal collecting system, seen sonographically as anechoic, branching fluid filling and separating the central renal sinus echoes. It ranges from mild pelvicaliectasis to severe cases with cortical thinning. A distended bladder or extrarenal pelvis can mimic hydronephrosis, so re-scanning after the patient voids is a standard way to confirm true obstruction.
On the exam: Exams test the false-positive traps of a full bladder and extrarenal pelvis alongside grading of true hydronephrosis by severity.
- Acute pancreatitis
Acute inflammation of the pancreas, most commonly from gallstones or alcohol use. Sonographically the gland may appear diffusely enlarged and hypoechoic from edema, with an indistinct margin against the surrounding fat, and peripancreatic fluid may be present. Overlying bowel gas from ileus often limits visualization, so a nonvisualized pancreas does not rule out pancreatitis.
On the exam: Questions often test that bowel gas obscuring the pancreas is expected in pancreatitis and does not exclude the diagnosis.
- Testicular torsion
Twisting of the spermatic cord that cuts off blood supply to the testicle, a surgical emergency. 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 diagnostic finding, sometimes with a whirlpool pattern in the twisted cord. Salvage is time dependent, so this is urgent.
On the exam: Exams contrast torsion's absent Doppler flow with epididymitis, which shows increased flow, as a classic differentiating pair.
- Ascites
Free fluid within the peritoneal cavity. On ultrasound it appears as anechoic fluid that collects in dependent spaces such as the hepatorenal recess, also called Morison pouch, the pelvic cul-de-sac, and around loops of bowel, which may float freely within the fluid. Causes range from cirrhosis and portal hypertension to malignancy, heart failure, and infection.
On the exam: Morison pouch is tested as the most dependent space in the upper abdomen where right-sided fluid collects first, while the pelvis remains the most dependent space in the peritoneal cavity overall.
OB/GYN Sonography
Obstetric and gynecologic findings, measurements and terminology used across first, second and third trimester scanning.
- Gestational sac
The earliest sonographic sign of an intrauterine pregnancy, seen as a small anechoic fluid collection surrounded by an echogenic ring within the endometrium. A true gestational sac is eccentrically located within the decidua, distinguishing it from the centrally located pseudosac seen with an ectopic pregnancy. Absence of a yolk sac or embryo once the sac reaches 25 mm suggests a failed pregnancy.
On the exam: Exams test the eccentric location that separates a true gestational sac from an ectopic pregnancy's pseudosac, plus the 25 mm failed-pregnancy criterion.
- Yolk sac
The first structure visualized within a gestational sac, confirming a true intrauterine pregnancy before an embryo is seen. It provides early nutrition and blood cell formation for the developing embryo. A yolk sac that appears unusually large, thickened, calcified, or irregular in shape is considered a poor prognostic sign for the pregnancy, even when a heartbeat is still present.
On the exam: The yolk sac's role as the first confirmatory structure inside a gestational sac is a standard early first-trimester exam question.
- Crown-rump lengthalso called CRL
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, particularly in the first trimester, and is used up to about 13 to 14 weeks, after which biparietal diameter and other biometric measurements take over.
On the exam: CRL is tested as the single most accurate dating measurement in pregnancy, especially when it disagrees with menstrual dating.
- Biparietal diameteralso called BPD
A transverse measurement of the fetal head taken at the level of the thalami and cavum septum pellucidum, from the outer edge of the near skull table to the inner edge of the far skull table. It is one of the four standard fetal biometric parameters used for dating and growth assessment, alongside head circumference, abdominal circumference, and femur length.
On the exam: The exact skull table caliper placement, outer to inner, and landmark level are commonly tested measurement technique details.
- Amniotic fluid indexalso called AFI
A semiquantitative estimate of amniotic fluid volume calculated by dividing the uterus into four quadrants, measuring the deepest vertical fluid pocket free of cord or fetal parts in each, and summing the four measurements. A value below 5 cm defines oligohydramnios and a value above 24 cm defines polyhydramnios, with a normal range roughly in between.
On the exam: The four-quadrant technique and the 5 cm and 24 cm cutoffs are standard, frequently tested AFI thresholds.
- Oligohydramnios
Abnormally low amniotic fluid volume, generally defined as an amniotic fluid index below 5 cm or a single deepest pocket under 2 cm. Causes include ruptured membranes, placental insufficiency, fetal renal anomalies that reduce urine output, and post-term pregnancy. It is associated with pulmonary hypoplasia and limb positioning abnormalities when it occurs early and persists.
On the exam: Exams pair the numeric AFI and single-pocket cutoffs with fetal renal causes as a classic scenario question.
- Polyhydramnios
Abnormally high amniotic fluid volume, generally defined as an amniotic fluid index above 24 cm or a single deepest pocket over 8 cm. It is associated with maternal diabetes, fetal anomalies that impair swallowing such as esophageal or duodenal atresia, multiple gestation, and some fetal infections. Severe cases increase the risk of preterm labor and cord prolapse.
On the exam: Exams commonly link polyhydramnios to maternal diabetes and swallowing-related fetal anomalies as the tested causes.
- Placenta previa
A condition in which the placenta implants over or near the internal cervical os, ahead of the presenting fetal part. It is classified by how closely the placental edge approaches or covers the os and is best confirmed with a transvaginal or translabial scan, since an overfull maternal bladder on transabdominal imaging can falsely suggest previa. It is a cause of painless third-trimester bleeding.
On the exam: The overfull-bladder false positive and the need for transvaginal confirmation are classic exam traps for this diagnosis.
- Nuchal translucency
The fluid-filled space at the back of the fetal neck, measured between 11 weeks 0 days and 13 weeks 6 days gestation as part of first-trimester aneuploidy screening. Measurement requires a strict midsagittal view of the fetal profile with calipers placed on the inner borders of the nuchal line. A measurement of 3 mm or more is commonly taught as increased and raises the risk of chromosomal abnormality and cardiac defects.
On the exam: The precise gestational age window and strict view criteria for NT measurement are heavily tested technique details.
- Endometrial stripe
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 and appearance change with the menstrual cycle and menopausal status. In a postmenopausal woman with bleeding, a stripe greater than 4 mm warrants further evaluation.
On the exam: The postmenopausal bleeding threshold and correct measurement technique excluding fluid are standard GYN exam questions.
- Adenomyosis
A condition in which endometrial glands and stroma grow within the myometrium, causing the uterus to enlarge, most often affecting the posterior wall. Sonographic findings include a globular uterine shape, heterogeneous myometrial echotexture, poorly defined myometrial cysts, asymmetric wall thickening, and subendometrial linear striations. It is a common cause of chronic pelvic pain and heavy menstrual bleeding, and can coexist with fibroids.
On the exam: Exams test the distinction between adenomyosis, with its heterogeneous globular uterus, and the well-defined masses typical of fibroids.
- Ectopic pregnancy
A pregnancy that implants outside the endometrial cavity, most commonly within the ampullary portion of the fallopian tube. Sonographic clues include an empty uterus with a positive pregnancy test, a complex adnexal mass separate from the ovary, and a ring of fire pattern of peripheral vascularity on color Doppler, though this pattern can also be seen with a corpus luteum. It is a surgical emergency if it ruptures.
On the exam: This is one of the highest-stakes OB diagnoses tested, since a ruptured ectopic pregnancy is life threatening and must not be missed.
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
A blood clot within a deep vein, most often in the lower extremity, that can embolize to the lungs if untreated. The primary diagnostic criterion is loss of vein compressibility with transducer pressure in the transverse plane. An acute thrombus tends to be hypoechoic, spongy, and causes venous distension, while a chronic thrombus is more echogenic, contracted, and often shows collateral vessels.
On the exam: Noncompressibility in the transverse plane is the single most tested diagnostic criterion for DVT on the vascular exam.
- Peripheral arterial diseasealso called PAD
Narrowing or occlusion of arteries outside the heart and brain, most often from atherosclerosis in the lower extremities, causing reduced blood flow to the legs and feet. It commonly presents as claudication, pain with walking that resolves with rest. Diagnostic testing includes the ankle-brachial index, segmental pressures, and duplex ultrasound to localize and grade the severity of stenosis.
On the exam: PAD questions often connect claudication symptoms to the ankle-brachial index as the standard first-line diagnostic tool.
- Ankle-brachial indexalso called ABI
A ratio comparing the higher systolic pressure at the ankle to the higher systolic pressure in the arms, used to screen for peripheral arterial disease. A value below 0.9 is considered abnormal and indicates arterial insufficiency, while a value above 1.4 suggests noncompressible, calcified vessels that make the result unreliable, often seen in diabetic patients.
On the exam: The 0.9 and 1.4 cutoffs are standard numeric thresholds tested on both the RVT and RVS vascular exams.
- Intimal flap
A mobile piece of the innermost arterial layer that has separated from the vessel wall, classically seen in aortic or arterial dissection. On ultrasound it appears as a thin, echogenic, undulating line within the vessel lumen that divides true and false lumens, and color Doppler often shows different flow patterns or velocities on either side of the flap.
On the exam: Exams test recognition of an intimal flap as the defining sonographic sign of arterial dissection, separate from a simple plaque.
- Pseudoaneurysm
A contained collection of blood outside the arterial wall that communicates with the artery through a defect, most often at a catheterization access site, held together only by surrounding tissue rather than a true vessel wall. Color Doppler classically shows a yin-yang pattern of swirling flow within the sac, and spectral Doppler of the connecting neck shows a to-and-fro waveform.
On the exam: The yin-yang sac pattern and to-and-fro neck waveform are the two classic Doppler findings tested for pseudoaneurysm.
- Carotid bifurcation
The point where the common carotid artery divides into the internal and external carotid arteries, and a common site for atherosclerotic plaque formation. 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, while the external carotid has visible branches, a high-resistance waveform, and responds to a temporal tap.
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.
- Calf muscle pump
The mechanism by which contraction of the calf muscles during walking compresses the deep veins and propels venous blood back toward the heart against gravity. Competent venous valves prevent backflow between contractions. Failure of this pump, from valve incompetence or outflow obstruction, contributes to venous stasis, chronic venous insufficiency, and increased risk of clot formation.
On the exam: Understanding the calf muscle pump explains why immobility raises DVT risk, a common physiology question on the vascular exam.
- Tardus parvus waveform
An abnormal arterial Doppler waveform found downstream from a significant stenosis, characterized by 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 main renal artery stenosis, but the same pattern can appear distal to any significant stenosis in the arterial system.
On the exam: This indirect Doppler sign of proximal stenosis is tested particularly in the context of renal artery stenosis screening.
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