Your FREE SPI Flashcards 2026 – 200+ Cards

A tissue's resistance to sound: Z = density × propagation speed. Differences in impedance at a boundary create reflections.

Describes refraction — the bending of a transmitted beam at an interface when it strikes obliquely and the two media have different propagation speeds.

Assumed average of 1,540 m/s (1.54 mm/μs). The machine uses this constant to place echoes by depth.

Wavelength = propagation speed ÷ frequency. In soft tissue, λ (mm) ≈ 1.54 ÷ f (MHz). Higher frequency means shorter wavelength.

Higher frequency improves resolution but attenuates faster, so it penetrates less. Lower frequency penetrates deeper but with poorer resolution.

The progressive weakening of the ultrasound beam (reflection, scattering, and absorption) as it travels through tissue. Increases with depth and frequency.

About 0.5 dB per cm per MHz. Total attenuation (dB) ≈ 0.5 × frequency (MHz) × path length (cm).

The conversion of acoustic energy into heat — the largest single contributor to attenuation in soft tissue.

The distance a single pulse occupies = number of cycles in the pulse × wavelength. Shorter SPL means better axial resolution.

Multiple equally spaced echoes from sound bouncing back and forth between two strong reflectors, appearing as parallel lines descending into the image.

A large, smooth interface (e.g., diaphragm, organ capsule) that reflects sound strongly in a single direction; brightest when the beam strikes it perpendicularly.

A small or rough interface that redirects sound in many directions; produces weaker, angle-independent echoes (e.g., the parenchyma of organs).

Scattering from reflectors much smaller than the wavelength (e.g., red blood cells); intensity is strongly frequency-dependent.

The fraction (or percent) of time the system is actually transmitting sound. In imaging it is very small (<1%); in CW Doppler it is 100%.

The acoustic power in the beam divided by the beam's cross-sectional area (W/cm²). It varies across the beam and over the pulse.

The time for one cycle to occur. Period = 1 ÷ frequency; it is the reciprocal of frequency and is determined by the source.

The number of cycles per second (Hz). Diagnostic ultrasound uses 2–15 MHz. Determined by the sound source, not the operator's depth/gain settings.

A gel-filled spacer placed between transducer and skin to move very superficial structures into the focal zone and reduce near-field reverberation.

Gel applied to the skin to displace air and reduce the large impedance mismatch between transducer and tissue, allowing sound to enter the body.

The process of ensuring the patient understands the procedure, its purpose, and any risks before it is performed.

Designing the workspace and scanning posture to reduce strain and prevent work-related musculoskeletal injury to the sonographer.

Bending of the transmitted beam at an oblique interface between media of different propagation speeds; can cause edge shadowing and lateral mispositioning.

The fraction of intensity reflected at a boundary; it grows as the difference in acoustic impedance between the two media increases.

How brightly a structure reflects sound: hyperechoic (bright), hypoechoic (dark), anechoic (echo-free, e.g., simple fluid), and isoechoic (same as surroundings).

Producing no internal echoes (appears black), characteristic of simple fluid such as a cyst, urine, or blood in a vessel lumen.

Brighter than surrounding tissue — strong reflectors such as bone surfaces, calcifications, fat, or gas.

Gas-filled microbubbles injected to increase the reflectivity of blood, enhancing vascular and perfusion imaging; imaged with low MI to avoid bubble destruction.

Sweeping the transducer to stitch many frames into one wide composite image of a structure larger than the footprint.

Acquisition of a volume of data displayed as a rendered three-dimensional image (static volume).

Real-time 3D — a continuously updating volume that adds motion over time (e.g., a moving fetal face).

Electronically angling the beam (via timed element firing) to direct it off-axis, used in sector formation and color-box and trapezoidal imaging.

The basis of imaging: the system sends a pulse, times the round trip of the echo, and uses 1,540 m/s to compute the reflector's depth.

Depth = (propagation speed × round-trip time) ÷ 2. The factor of 2 accounts for the down-and-back path of the pulse.

The actual time the transducer transmits in one pulse = number of cycles × period. Determined by the source, not the operator.

Each point on a wavefront acts as a source of secondary wavelets; their interference shapes the ultrasound beam and explains diffraction.

At diagnostic pressures the wave distorts as it travels, generating harmonic frequencies in tissue — the basis of tissue harmonic imaging.

A logarithmic ratio used for gain, attenuation, and dynamic range. −3 dB = half intensity; −6 dB = one-quarter (and ~half amplitude).

The tissue thickness that reduces the beam's intensity by half (−3 dB); thinner for higher frequencies because they attenuate faster.

Verifying the ordered exam is appropriate, matches the clinical question, and follows the established protocol before scanning.

Comparing with previous studies tailors the protocol, focuses the exam, and helps correlate findings over time.

Recording representative images and a preliminary worksheet so the interpreting physician has a complete record of the exam.

Verifying patient identity, the ordered exam, and the correct site before beginning, to prevent wrong-patient or wrong-exam errors.

Raising frequency shortens wavelength and SPL (better axial) and narrows the beam (better lateral) — at the cost of penetration.

Specular reflectors return the most echo to the transducer when the beam strikes them at 90°, giving the brightest interface.

Protecting patient privacy and health information during and after the exam is a core patient-care and professional responsibility.

The central SPI trade-off — higher frequency buys better resolution but less penetration; the sonographer selects frequency to balance the two for each exam.

The conversion of electrical voltage into mechanical vibration (transmit) and returning sound pressure back into voltage (receive) by the transducer's active element.

A layer on the transducer face whose impedance is between the element and skin; it reduces the impedance mismatch so more sound is transmitted into the body.

Material behind the active element that shortens the pulse (reduces ringing), improving axial resolution but widening the bandwidth and lowering sensitivity.

The range of frequencies in the pulse. A heavily damped (short) pulse has a wide bandwidth and low Q-factor.

A measure of how 'pure' (narrow-band) a transducer's frequency is. Imaging transducers are low-Q (broad bandwidth, short pulse); CW Doppler uses high-Q.

A transducer with elements in a row, fired in groups to make a rectangular image. High-frequency linear arrays image superficial structures (vascular, small parts).

A convex array that produces a wide, sector-like field; lower frequency for deeper abdominal and obstetric imaging.

A small-footprint transducer whose elements are fired with timing delays to electronically steer and focus the beam, producing a sector image (e.g., cardiac).

The transducer component that focuses the beam in the elevational (slice-thickness) plane to improve out-of-plane resolution.

The piezoelectric (PZT) element that converts electrical and mechanical energy; its thickness sets the operating frequency (thinner = higher frequency).

The temperature above which a piezoelectric element loses its polarization and stops working — why transducers must not be autoclaved with heat.

The region from the transducer face to the focus where the beam narrows. Its length increases with larger aperture and higher frequency.

The region beyond the focus where the beam diverges. A larger aperture and higher frequency reduce divergence.

The spreading of the beam in the far field, which worsens lateral resolution at depth. Reduced by a larger aperture or higher frequency.

The size of the active transducer face. A larger aperture gives a longer near zone and less far-field divergence.

Firing array elements with timed delays to converge the beam at a selected depth, narrowing beam width and improving lateral resolution there.

Short pulses needed for good axial resolution contain a wide range of frequencies, so a broadband (low-Q) transducer is required.

Because heat above the Curie point depolarizes the element, transducers are chemically (not heat) disinfected.

Set by the element thickness and propagation speed of the element material: thinner elements resonate at higher frequencies.

Varying the excitation across array elements to reduce the amplitude of side lobes and grating lobes, lowering those artifacts.

Cutting array elements into smaller sub-elements to suppress grating lobes caused by element spacing.

Ring-shaped elements that focus the beam symmetrically in both lateral and elevational planes but must be steered mechanically.

An array with several rows of elements, allowing some electronic focusing in the elevational plane to improve slice-thickness resolution.

A dedicated probe (e.g., pencil/Pedoff) with separate transmit and receive crystals for continuous-wave Doppler only, with no 2D image.

Choose the highest frequency that still penetrates to the structure of interest, to maximize resolution without sacrificing penetration.

Harmonic imaging requires a broadband transducer able to transmit a fundamental frequency and receive its higher harmonics.

Broader bandwidth allows shorter pulses, which improves axial resolution — the reason imaging transducers are damped/broadband.

CW Doppler uses a high-Q (narrow-band) crystal to transmit a steady pure tone, unlike the broadband elements used for imaging.

The ability to resolve two structures along the beam's path. Determined by spatial pulse length; equal to SPL ÷ 2. Shorter pulses (higher frequency) improve it.

The ability to resolve two structures side-by-side, perpendicular to the beam. Determined by beam width; best at the focal zone.

An operator control that boosts the amplitude of echoes returning from greater depth to compensate for attenuation, giving uniform brightness top to bottom.

The number of pulses the system sends per second. Higher PRF raises the Nyquist limit (less aliasing) but limits maximum imaging depth.

A duplicate of a structure displayed deeper than (on the far side of) a strong reflector such as the diaphragm, caused by the beam reflecting off it.

A dark band deep to a highly attenuating or strongly reflecting structure (bone, stone, calcification) where little sound reaches the tissue beyond.

Increased brightness deep to a weakly attenuating structure such as a fluid-filled cyst, because the beam there is less attenuated than at the sides.

Transmits at one (fundamental) frequency and forms the image from the higher harmonic frequencies generated within tissue, reducing clutter and improving contrast.

The time from the start of one pulse to the start of the next. PRP = 1 ÷ PRF; the two are reciprocals.

The ratio of the largest to smallest echo a system displays, in dB. Narrowing it increases contrast (fewer grays); widening it shows more shades of gray.

Receiver amplification applied to all returning echoes. Increasing gain brightens the whole image (signal and noise) without changing acoustic output.

Combines frames acquired from several steering angles into one image, reducing speckle and angle-dependent artifacts at the cost of lower temporal resolution.

The ability to display events in time accurately — set by frame rate. Improved by shallower depth, narrower sector, fewer focal zones, and lower line density.

Frame rate falls as imaging depth, sector width, line density, or number of focal zones increases. Each costs time per frame.

The region of narrowest beam width where lateral resolution is best. Placing the focus at the region of interest sharpens it; multiple focal zones lower frame rate.

A short, bright trail of closely spaced echoes deep to a small strong reflector (e.g., metal, cholesterol crystal) — a form of reverberation.

A continuous bright line or band deep to gas bubbles, caused by resonant vibration of trapped fluid/gas — distinct from but resembling reverberation.

Off-axis low-energy beams that place a real reflector's echo at the wrong lateral location, often as a curved line within an anechoic structure.

Array-specific off-axis energy from regular element spacing that produces a faint duplicate of a strong reflector to the side of its true position.

The granular texture in the image from interference of scattered echoes. It is not true anatomy; spatial/frequency compounding reduces it.

Angle dependence of echogenicity in ordered tissues (tendons, nerves): they look bright when insonated perpendicularly and dark when the angle changes.

Echoes from structures just off the scan plane are displayed within it (e.g., debris in a cyst), caused by finite beam thickness in the elevational plane.

Misregistration of a reflector's depth or a split appearance because tissue speed differs from the assumed 1,540 m/s.

Motion mode: displays the depth of reflectors along a single line over time, giving very high temporal resolution for moving structures like heart valves.

Amplitude mode: a one-dimensional display of echo amplitude versus depth along a single line; the earliest display format.

Brightness mode: echo amplitudes are mapped to dot brightness to build the standard two-dimensional gray-scale image.

A post-processing step that compresses the wide range of echo amplitudes into the limited gray-scale range the display and eye can show.

A post-processing technique that sharpens boundaries between structures to improve the perceived definition of edges.

Read zoom magnifies stored pixels (no new detail). Write zoom rescans the region of interest, increasing line density and true resolution.

The number of scan lines per frame. Higher density improves spatial detail but lowers frame rate (temporal resolution).

Averaging successive frames to reduce noise/speckle; it smooths the image but blurs rapidly moving structures and lowers temporal resolution.

Resolution in the slice-thickness (out-of-plane) dimension, set by the beam thickness; improved by an acoustic lens or a 1.5D array.

Output power changes the actual acoustic energy into the patient (affects bioeffects). Gain only amplifies returning echoes and does not change patient exposure.

Combining images formed from different frequency bands of the returning echoes to reduce speckle.

Applying a color map to gray-scale brightness values to aid perception; it does not add flow information (that is color Doppler).

Greater depth forces a lower PRF because the system must wait longer for deep echoes, which lowers the Nyquist limit and frame rate.

Preprocessing changes the data before it is stored (e.g., TGC, dynamic range) and cannot be undone on a frozen image; postprocessing alters the stored image.

Narrowing the imaging sector reduces the number of scan lines per frame, raising the frame rate (temporal resolution).

Wide dynamic range gives a smooth, low-contrast image with many grays; narrow gives a high-contrast, more black-and-white image.

All are repeating-echo artifacts: reverberation = equally spaced lines; comet tail = short tapering trail; ring-down = continuous band from gas.

Spatial combines frames from different angles; frequency combines images from different frequency bands. Both reduce speckle.

An imaging mode that maps tissue stiffness (elasticity), helping distinguish stiff (often malignant) from soft tissue.

A measure of how well contrast-enhanced signal is separated from background tissue signal during contrast imaging.

The maximum Doppler shift a pulsed system can display without aliasing — equal to one-half the pulse repetition frequency (PRF ÷ 2). Shifts above it alias.

The change in the frequency of reflected sound when the source and reflector move relative to each other — the basis for measuring blood-flow velocity.

The difference between the transmitted frequency and the received frequency caused by moving reflectors. Positive shift = flow toward the transducer.

The angle between the Doppler beam and the direction of flow. Velocity accuracy depends on its cosine; keep it at or below 60°.

cos(90°) = 0, so the calculated Doppler shift becomes zero. A beam perpendicular to flow detects no flow.

A pulsed-Doppler artifact occurring when the Doppler shift exceeds the Nyquist limit; high velocities wrap around and display in the wrong direction.

Uses separate transmit and receive elements running continuously. No aliasing and no peak-velocity limit, but no range resolution (range ambiguity).

Sends pulses and listens for echoes from a chosen sample volume, giving range (depth) resolution. Limited by the Nyquist limit, so it can alias.

Overlays mean velocity and direction as color on the 2D image. It encodes flow direction (toward/away) and is subject to aliasing.

Encodes the strength (amplitude) of the Doppler signal, not velocity or direction. More sensitive to slow flow and does not alias, but shows no direction.

Removes low-frequency, high-amplitude Doppler signals from slow-moving vessel walls. Set too high, it can erase true low-velocity (venous/diastolic) flow.

An artifact in PW/imaging when a too-high PRF sends the next pulse before deep echoes return, so the system mislocates them at the wrong depth.

Estimates the pressure gradient across a stenosis: pressure gradient (mmHg) = 4 × (peak velocity)². A 4 m/s jet gives 4 × 16 = 64 mmHg.

A widening (filling-in) of the spectral Doppler waveform indicating a broad range of velocities — a sign of turbulent or post-stenotic disordered flow.

The clear space under the systolic peak of a normal spectral waveform, indicating most cells move at similar (laminar) velocities; it fills in with turbulence.

Smooth, orderly flow in which cells in the center move fastest and those near the wall slowest; produces a narrow spectral band with a clear window.

The region in PW Doppler from which flow is sampled, set by depth and gate size. A gate ~two-thirds of the vessel reduces artifactual spectral broadening.

Tilting the color/Doppler sample region on a linear array to create a more favorable beam-to-flow angle for accurate velocity encoding.

A setting that decides whether a pixel displays color (flow) or gray-scale (tissue) based on echo amplitude thresholds, controlling color 'bleed.'

The number of pulses per color scan line. A larger packet improves color velocity accuracy/sensitivity but lowers frame rate.

Doppler optimized for the low-velocity, high-amplitude motion of tissue (e.g., myocardial walls) rather than blood flow.

A measure of downstream vascular resistance from a spectral waveform: (peak systolic − end diastolic velocity) ÷ mean velocity.

A resistance index: (peak systolic − end diastolic velocity) ÷ peak systolic velocity. Higher RI indicates greater distal resistance.

Moving the spectral or color zero-velocity baseline to allocate more scale to the dominant flow direction, expanding displayable velocity without raising PRF.

Raise the PRF/velocity scale, shift the baseline, lower the transducer frequency, or increase the Doppler angle — each raises or fits the displayable velocity.

Simultaneous display of B-mode gray-scale imaging and pulsed Doppler from a chosen sample volume, combining anatomy with flow information.

The reflector both receives a shifted frequency and re-emits another shift, so the Doppler equation includes a factor of 2 for the moving target.

In color Doppler, lighter shades indicate higher mean velocities and darker shades lower velocities; abrupt color reversal indicates aliasing.

A sudden burst of color filling the image from transducer or patient (e.g., breathing) motion; reduced with motion-discrimination filters.

Too much color gain produces random color that bleeds beyond vessel walls; reduce gain until color fills only true flow.

Controls the brightness/sensitivity of the spectral display. Too high adds noise and artifactual broadening; too low hides low-amplitude flow.

In diastolic cardiac assessment, the ratio of early (E) to late/atrial (A) mitral inflow velocities, used to evaluate ventricular filling.

The highest velocity during systole on a spectral waveform; elevated PSV is a key indicator of arterial stenosis severity.

The velocity at end of diastole on a spectral waveform; used with PSV in resistance/stenosis indices.

By continuity, flow speeds up through a narrowing; a high-grade stenosis produces a high-velocity jet and post-stenotic turbulence.

A lower transmit frequency produces a smaller Doppler shift for the same velocity, so a high velocity may fit under the Nyquist limit.

PW Doppler's advantage over CW: it samples flow from a specific depth (the gate), so the velocity is localized to one vessel.

It can measure very high velocities (no Nyquist limit), making it ideal for high-velocity stenotic or valvular jets.

Raising PRF in PW Doppler allows higher measurable velocities but introduces extra sample gates (range ambiguity).

Erases genuine low-velocity flow (e.g., venous or diastolic), producing a false 'no-flow' or truncated diastolic appearance.

Keep the angle at or below 60°; above 60° small angle errors cause large velocity errors because cosine changes rapidly.

The reference bar showing which colors/velocities correspond to flow toward and away from the transducer and the current velocity scale (PRF).

The color scale directly sets the color Nyquist limit; raising it lets faster flow display without color aliasing.

Volume flow is constant along a vessel, so as cross-sectional area decreases (stenosis), velocity must increase. Basis for grading stenosis by velocity.

Color encodes direction and mean velocity and can alias; power encodes signal strength, is more sensitive to slow flow, and shows no direction.

A spectral waveform with delayed systolic upstroke and low amplitude, seen downstream of a significant proximal arterial stenosis.

The normal peripheral arterial pattern: sharp forward systolic peak, brief early-diastolic reversal, then late forward flow.

The velocity scale (PRF) of the spectral display; set high enough to fit peak velocities under the Nyquist limit without aliasing.

Aligning the on-screen cursor with the true flow direction so the system applies the correct cosine and reports accurate velocity.

Selecting the depth and size of the sample volume so only echoes from that region are analyzed for the Doppler shift.

CW Doppler does not sample discretely (continuous transmit/receive), so there is no Nyquist limit and no aliasing, but it loses depth information.

The simplified form drops the proximal velocity term because it is small relative to the high downstream jet velocity.

Temporal averaging of color frames that smooths the flow display but can blur rapid changes — the color equivalent of gray-scale persistence.

A small gate samples a focal point of flow with less spectral broadening; a large gate captures the whole lumen but adds broadening.

As Low As Reasonably Achievable — use the lowest acoustic output and shortest scan time that still yields a diagnostic image, to minimize potential bioeffects.

An on-screen estimate of the likelihood of non-thermal (cavitation) bioeffects: MI = peak rarefactional pressure ÷ √(frequency). Higher MI = greater cavitation risk.

An on-screen estimate of potential tissue heating: the ratio of the acoustic power used to the power needed to raise tissue temperature by 1 °C. Variants: TIS (soft tissue), TIB (bone), TIC (cranial).

A non-thermal bioeffect: the formation/oscillation/violent collapse of gas bubbles driven by the peak rarefactional (negative) pressure. Estimated by the MI.

The acoustic intensity at the spatial peak averaged over time; the parameter most relevant to thermal bioeffects (tissue heating).

The FDA/AIUM/NEMA standard requiring the TI and MI be shown on screen so the operator can monitor and minimize potential bioeffects in real time.

Hand hygiene before and after contact, glove use, and cleaning/disinfecting the transducer between patients per CDC guidelines.

Required for transducers contacting mucous membranes or non-intact skin (e.g., endocavitary probes), beyond the low-level cleaning used for intact-skin probes.

A QA device with known targets used to test resolution, depth/distance accuracy, dead zone, and low-contrast (lesion) detectability of the system.

Sensitivity = the proportion of true positives correctly identified; specificity = the proportion of true negatives correctly identified.

The highest acoustic intensity in space measured at the peak of the pulse in time — the largest of the intensity descriptors.

Tissue heating from absorbed acoustic energy; greatest concern at bone (high absorption) and with Doppler/long dwell times. Tracked by the TI.

Effects from pressure rather than heat — chiefly cavitation and radiation force/streaming. Tracked by the MI.

Bulk movement of fluid produced by the radiation force of the sound beam — a non-thermal mechanical effect.

Diagnostic ultrasound is regulated so derated ISPTA stays below about 720 mW/cm² for most applications, balancing image quality and safety.

First-trimester and fetal scanning use the soft-tissue TI (TIS) and keep TI and MI low with short dwell times, especially with spectral Doppler.

Performing hand hygiene before and after every patient contact is the single most effective measure to prevent healthcare-associated infection (CDC).

Inspecting the probe face, housing, and cable for cracks or damage that could harbor pathogens or cause electrical hazard, as part of QA.

The shallowest region near the transducer face where structures cannot be imaged; assessed during phantom QA testing.

A QA test confirming the system places reflectors at correct depths, using a phantom with targets at known distances.

A QA test verifying correct side-to-side measurement using phantom targets at known horizontal spacing.

A QA measure of the smallest difference in echogenicity the system can resolve, tested with low-contrast phantom targets.

A clinical safety concern: damaged cables or housings can pose electric-shock risk; transducers are inspected and removed from service if compromised.

Intensity averaged over both the beam area and time — the lowest of the intensity descriptors, relevant to total energy delivered.

Two established mechanisms of potential harm: thermal (heating) and mechanical (cavitation). Both are kept low by ALARA and the displayed TI/MI.

After contacting mucous membranes, endocavitary transducers require high-level disinfection (per manufacturer and CDC guidance) before reuse.

Recording routine QA results (resolution, accuracy, uniformity) creates a baseline to detect equipment drift or failure over time.

Thermal-index variants for differing exposures: TIS (soft tissue, early pregnancy), TIB (bone in focus, late pregnancy), TIC (cranial/transcranial).

Because MI = peak rarefactional pressure ÷ √frequency, a lower frequency at the same pressure gives a higher MI (greater cavitation potential).