- ALARA
- As Low As Reasonably Achievable — use the lowest acoustic output and shortest scan time that still yields a diagnostic image, to minimize potential bioeffects.
- Mechanical index (MI)
- An on-screen estimate of the likelihood of non-thermal (cavitation) bioeffects: MI = peak rarefactional pressure ÷ √(frequency). Higher MI = greater cavitation risk.
- Thermal index (TI)
- 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).
- Nyquist limit
- 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.
- Acoustic impedance (Z)
- A tissue's resistance to sound: Z = density × propagation speed. Differences in impedance at a boundary create reflections.
- Snell's law
- Describes refraction — the bending of a transmitted beam at an interface when it strikes obliquely and the two media have different propagation speeds.
- Propagation speed in soft tissue
- Assumed average of 1,540 m/s (1.54 mm/μs). The machine uses this constant to place echoes by depth.
- Wavelength equation
- Wavelength = propagation speed ÷ frequency. In soft tissue, λ (mm) ≈ 1.54 ÷ f (MHz). Higher frequency means shorter wavelength.
- Piezoelectric effect
- The conversion of electrical voltage into mechanical vibration (transmit) and returning sound pressure back into voltage (receive) by the transducer's active element.
- Frequency vs. penetration
- Higher frequency improves resolution but attenuates faster, so it penetrates less. Lower frequency penetrates deeper but with poorer resolution.
- Attenuation
- The progressive weakening of the ultrasound beam (reflection, scattering, and absorption) as it travels through tissue. Increases with depth and frequency.
- Attenuation coefficient (soft tissue)
- About 0.5 dB per cm per MHz. Total attenuation (dB) ≈ 0.5 × frequency (MHz) × path length (cm).
- Absorption
- The conversion of acoustic energy into heat — the largest single contributor to attenuation in soft tissue.
- Axial resolution
- 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.
- Lateral resolution
- The ability to resolve two structures side-by-side, perpendicular to the beam. Determined by beam width; best at the focal zone.
- Spatial pulse length (SPL)
- The distance a single pulse occupies = number of cycles in the pulse × wavelength. Shorter SPL means better axial resolution.
- Time gain compensation (TGC)
- An operator control that boosts the amplitude of echoes returning from greater depth to compensate for attenuation, giving uniform brightness top to bottom.
- Doppler effect
- 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.
- Doppler shift
- The difference between the transmitted frequency and the received frequency caused by moving reflectors. Positive shift = flow toward the transducer.
- Doppler angle (angle of insonation)
- The angle between the Doppler beam and the direction of flow. Velocity accuracy depends on its cosine; keep it at or below 60°.
- Why velocity is inaccurate at 90°
- cos(90°) = 0, so the calculated Doppler shift becomes zero. A beam perpendicular to flow detects no flow.
- Aliasing
- A pulsed-Doppler artifact occurring when the Doppler shift exceeds the Nyquist limit; high velocities wrap around and display in the wrong direction.
- Continuous wave (CW) Doppler
- Uses separate transmit and receive elements running continuously. No aliasing and no peak-velocity limit, but no range resolution (range ambiguity).
- Pulsed wave (PW) Doppler
- Sends pulses and listens for echoes from a chosen sample volume, giving range (depth) resolution. Limited by the Nyquist limit, so it can alias.
- Color Doppler
- Overlays mean velocity and direction as color on the 2D image. It encodes flow direction (toward/away) and is subject to aliasing.
- Power Doppler
- 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.
- Pulse repetition frequency (PRF)
- The number of pulses the system sends per second. Higher PRF raises the Nyquist limit (less aliasing) but limits maximum imaging depth.
- Wall filter (high-pass filter)
- Removes low-frequency, high-amplitude Doppler signals from slow-moving vessel walls. Set too high, it can erase true low-velocity (venous/diastolic) flow.
- Reverberation artifact
- Multiple equally spaced echoes from sound bouncing back and forth between two strong reflectors, appearing as parallel lines descending into the image.
- Mirror-image artifact
- 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.
- Acoustic shadowing
- A dark band deep to a highly attenuating or strongly reflecting structure (bone, stone, calcification) where little sound reaches the tissue beyond.
- Acoustic enhancement (through transmission)
- 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.
- Cavitation
- A non-thermal bioeffect: the formation/oscillation/violent collapse of gas bubbles driven by the peak rarefactional (negative) pressure. Estimated by the MI.
- Spatial peak temporal average intensity (SPTA)
- The acoustic intensity at the spatial peak averaged over time; the parameter most relevant to thermal bioeffects (tissue heating).
- Output display standard (ODS)
- 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.
- Specular reflector
- A large, smooth interface (e.g., diaphragm, organ capsule) that reflects sound strongly in a single direction; brightest when the beam strikes it perpendicularly.
- Diffuse (scatter) reflector
- A small or rough interface that redirects sound in many directions; produces weaker, angle-independent echoes (e.g., the parenchyma of organs).
- Rayleigh scattering
- Scattering from reflectors much smaller than the wavelength (e.g., red blood cells); intensity is strongly frequency-dependent.
- Harmonic imaging
- Transmits at one (fundamental) frequency and forms the image from the higher harmonic frequencies generated within tissue, reducing clutter and improving contrast.
- Duty factor
- 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%.
- Intensity
- 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.
- Period
- The time for one cycle to occur. Period = 1 ÷ frequency; it is the reciprocal of frequency and is determined by the source.
- Frequency
- 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.
- Pulse repetition period (PRP)
- The time from the start of one pulse to the start of the next. PRP = 1 ÷ PRF; the two are reciprocals.
- Matching layer
- 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.
- Backing (damping) material
- Material behind the active element that shortens the pulse (reduces ringing), improving axial resolution but widening the bandwidth and lowering sensitivity.
- Bandwidth
- The range of frequencies in the pulse. A heavily damped (short) pulse has a wide bandwidth and low Q-factor.
- 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.
- Linear (sequential) array
- 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).
- Curvilinear (curved) array
- A convex array that produces a wide, sector-like field; lower frequency for deeper abdominal and obstetric imaging.
- Phased array
- 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).
- Acoustic lens
- The transducer component that focuses the beam in the elevational (slice-thickness) plane to improve out-of-plane resolution.
- Dynamic range
- 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.
- Gain
- Receiver amplification applied to all returning echoes. Increasing gain brightens the whole image (signal and noise) without changing acoustic output.
- Spatial compounding
- Combines frames acquired from several steering angles into one image, reducing speckle and angle-dependent artifacts at the cost of lower temporal resolution.
- 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 trade-offs
- Frame rate falls as imaging depth, sector width, line density, or number of focal zones increases. Each costs time per frame.
- Focal zone
- 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.
- Range ambiguity
- 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.
- Simplified Bernoulli equation
- Estimates the pressure gradient across a stenosis: pressure gradient (mmHg) = 4 × (peak velocity)². A 4 m/s jet gives 4 × 16 = 64 mmHg.
- Spectral broadening
- A widening (filling-in) of the spectral Doppler waveform indicating a broad range of velocities — a sign of turbulent or post-stenotic disordered flow.
- Spectral window
- 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.
- Laminar flow
- 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.
- Sample volume (gate)
- 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.
- Standoff pad
- A gel-filled spacer placed between transducer and skin to move very superficial structures into the focal zone and reduce near-field reverberation.
- Coupling gel
- Gel applied to the skin to displace air and reduce the large impedance mismatch between transducer and tissue, allowing sound to enter the body.
- Universal precautions / infection control
- Hand hygiene before and after contact, glove use, and cleaning/disinfecting the transducer between patients per CDC guidelines.
- High-level disinfection
- Required for transducers contacting mucous membranes or non-intact skin (e.g., endocavitary probes), beyond the low-level cleaning used for intact-skin probes.
- Tissue-mimicking phantom
- A QA device with known targets used to test resolution, depth/distance accuracy, dead zone, and low-contrast (lesion) detectability of the system.
- Sensitivity vs. specificity
- Sensitivity = the proportion of true positives correctly identified; specificity = the proportion of true negatives correctly identified.
- Informed consent
- The process of ensuring the patient understands the procedure, its purpose, and any risks before it is performed.
- Ergonomics in sonography
- Designing the workspace and scanning posture to reduce strain and prevent work-related musculoskeletal injury to the sonographer.
- Refraction
- Bending of the transmitted beam at an oblique interface between media of different propagation speeds; can cause edge shadowing and lateral mispositioning.
- Reflection coefficient
- The fraction of intensity reflected at a boundary; it grows as the difference in acoustic impedance between the two media increases.
- Comet-tail artifact
- A short, bright trail of closely spaced echoes deep to a small strong reflector (e.g., metal, cholesterol crystal) — a form of reverberation.
- Ring-down artifact
- A continuous bright line or band deep to gas bubbles, caused by resonant vibration of trapped fluid/gas — distinct from but resembling reverberation.
- Side-lobe artifact
- 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.
- Grating-lobe artifact
- 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.
- Speckle
- The granular texture in the image from interference of scattered echoes. It is not true anatomy; spatial/frequency compounding reduces it.
- Anisotropy
- Angle dependence of echogenicity in ordered tissues (tendons, nerves): they look bright when insonated perpendicularly and dark when the angle changes.
- Slice-thickness (partial-volume) artifact
- 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.
- Propagation-speed (speed) error artifact
- Misregistration of a reflector's depth or a split appearance because tissue speed differs from the assumed 1,540 m/s.
- M-mode
- Motion mode: displays the depth of reflectors along a single line over time, giving very high temporal resolution for moving structures like heart valves.
- A-mode
- Amplitude mode: a one-dimensional display of echo amplitude versus depth along a single line; the earliest display format.
- B-mode
- Brightness mode: echo amplitudes are mapped to dot brightness to build the standard two-dimensional gray-scale image.
- Logarithmic compression
- A post-processing step that compresses the wide range of echo amplitudes into the limited gray-scale range the display and eye can show.
- Edge enhancement
- A post-processing technique that sharpens boundaries between structures to improve the perceived definition of edges.
- Read zoom vs. write zoom
- Read zoom magnifies stored pixels (no new detail). Write zoom rescans the region of interest, increasing line density and true resolution.
- Line density
- The number of scan lines per frame. Higher density improves spatial detail but lowers frame rate (temporal resolution).
- Persistence (frame averaging)
- Averaging successive frames to reduce noise/speckle; it smooths the image but blurs rapidly moving structures and lowers temporal resolution.
- Elevational 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.
- Color box steering
- Tilting the color/Doppler sample region on a linear array to create a more favorable beam-to-flow angle for accurate velocity encoding.
- Color priority (over gray scale)
- A setting that decides whether a pixel displays color (flow) or gray-scale (tissue) based on echo amplitude thresholds, controlling color 'bleed.'
- Packet size (ensemble length)
- The number of pulses per color scan line. A larger packet improves color velocity accuracy/sensitivity but lowers frame rate.
- Tissue Doppler imaging (TDI)
- Doppler optimized for the low-velocity, high-amplitude motion of tissue (e.g., myocardial walls) rather than blood flow.
- Pulsatility index (PI)
- A measure of downstream vascular resistance from a spectral waveform: (peak systolic − end diastolic velocity) ÷ mean velocity.
- Resistive index (RI)
- A resistance index: (peak systolic − end diastolic velocity) ÷ peak systolic velocity. Higher RI indicates greater distal resistance.
- Baseline shift (to fix aliasing)
- Moving the spectral or color zero-velocity baseline to allocate more scale to the dominant flow direction, expanding displayable velocity without raising PRF.
- Ways to correct aliasing
- Raise the PRF/velocity scale, shift the baseline, lower the transducer frequency, or increase the Doppler angle — each raises or fits the displayable velocity.
- Duplex Doppler
- Simultaneous display of B-mode gray-scale imaging and pulsed Doppler from a chosen sample volume, combining anatomy with flow information.
- Crystal (active element)
- The piezoelectric (PZT) element that converts electrical and mechanical energy; its thickness sets the operating frequency (thinner = higher frequency).
- Curie point (depoling)
- The temperature above which a piezoelectric element loses its polarization and stops working — why transducers must not be autoclaved with heat.
- Near zone (Fresnel zone)
- The region from the transducer face to the focus where the beam narrows. Its length increases with larger aperture and higher frequency.
- Far zone (Fraunhofer zone)
- The region beyond the focus where the beam diverges. A larger aperture and higher frequency reduce divergence.
- Beam divergence
- The spreading of the beam in the far field, which worsens lateral resolution at depth. Reduced by a larger aperture or higher frequency.
- Aperture
- The size of the active transducer face. A larger aperture gives a longer near zone and less far-field divergence.
- Multi-element electronic focusing
- Firing array elements with timed delays to converge the beam at a selected depth, narrowing beam width and improving lateral resolution there.
- Transmit power (output) vs. gain
- Output power changes the actual acoustic energy into the patient (affects bioeffects). Gain only amplifies returning echoes and does not change patient exposure.
- Echogenicity
- How brightly a structure reflects sound: hyperechoic (bright), hypoechoic (dark), anechoic (echo-free, e.g., simple fluid), and isoechoic (same as surroundings).
- Anechoic
- Producing no internal echoes (appears black), characteristic of simple fluid such as a cyst, urine, or blood in a vessel lumen.
- Hyperechoic
- Brighter than surrounding tissue — strong reflectors such as bone surfaces, calcifications, fat, or gas.
- Contrast agents (microbubbles)
- Gas-filled microbubbles injected to increase the reflectivity of blood, enhancing vascular and perfusion imaging; imaged with low MI to avoid bubble destruction.
- Panoramic (extended field-of-view) imaging
- Sweeping the transducer to stitch many frames into one wide composite image of a structure larger than the footprint.
- 3D imaging
- Acquisition of a volume of data displayed as a rendered three-dimensional image (static volume).
- 4D imaging
- Real-time 3D — a continuously updating volume that adds motion over time (e.g., a moving fetal face).
- Beam steering
- Electronically angling the beam (via timed element firing) to direct it off-axis, used in sector formation and color-box and trapezoidal imaging.
- Spatial peak temporal peak intensity (SPTP)
- The highest acoustic intensity in space measured at the peak of the pulse in time — the largest of the intensity descriptors.
- Thermal bioeffects
- Tissue heating from absorbed acoustic energy; greatest concern at bone (high absorption) and with Doppler/long dwell times. Tracked by the TI.
- Non-thermal (mechanical) bioeffects
- Effects from pressure rather than heat — chiefly cavitation and radiation force/streaming. Tracked by the MI.
- Acoustic streaming
- Bulk movement of fluid produced by the radiation force of the sound beam — a non-thermal mechanical effect.
- FDA acoustic-output limit (SPTA)
- Diagnostic ultrasound is regulated so derated ISPTA stays below about 720 mW/cm² for most applications, balancing image quality and safety.
- Obstetric scanning 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.
- Bandwidth and short pulses
- Short pulses needed for good axial resolution contain a wide range of frequencies, so a broadband (low-Q) transducer is required.
- Curie temperature and disinfection
- Because heat above the Curie point depolarizes the element, transducers are chemically (not heat) disinfected.
- Frequency compounding
- Combining images formed from different frequency bands of the returning echoes to reduce speckle.
- Colorized (color) B-mode
- Applying a color map to gray-scale brightness values to aid perception; it does not add flow information (that is color Doppler).
- Imaging depth and PRF
- Greater depth forces a lower PRF because the system must wait longer for deep echoes, which lowers the Nyquist limit and frame rate.
- Preprocessing vs. postprocessing
- 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.
- Sector width and frame rate
- Narrowing the imaging sector reduces the number of scan lines per frame, raising the frame rate (temporal resolution).
- Pulse-echo principle
- 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.
- Range equation
- Depth = (propagation speed × round-trip time) ÷ 2. The factor of 2 accounts for the down-and-back path of the pulse.
- Why the Doppler factor of 2
- 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.
- Color saturation (hue/shade)
- In color Doppler, lighter shades indicate higher mean velocities and darker shades lower velocities; abrupt color reversal indicates aliasing.
- Flash artifact
- A sudden burst of color filling the image from transducer or patient (e.g., breathing) motion; reduced with motion-discrimination filters.
- Color noise from excessive gain
- Too much color gain produces random color that bleeds beyond vessel walls; reduce gain until color fills only true flow.
- Spectral Doppler gain
- Controls the brightness/sensitivity of the spectral display. Too high adds noise and artifactual broadening; too low hides low-amplitude flow.
- E/A ratio
- In diastolic cardiac assessment, the ratio of early (E) to late/atrial (A) mitral inflow velocities, used to evaluate ventricular filling.
- Peak systolic velocity (PSV)
- The highest velocity during systole on a spectral waveform; elevated PSV is a key indicator of arterial stenosis severity.
- End-diastolic velocity (EDV)
- The velocity at end of diastole on a spectral waveform; used with PSV in resistance/stenosis indices.
- Hemodynamics: stenosis and velocity
- By continuity, flow speeds up through a narrowing; a high-grade stenosis produces a high-velocity jet and post-stenotic turbulence.
- Lowering frequency to reduce aliasing
- A lower transmit frequency produces a smaller Doppler shift for the same velocity, so a high velocity may fit under the Nyquist limit.
- Range resolution of PW Doppler
- PW Doppler's advantage over CW: it samples flow from a specific depth (the gate), so the velocity is localized to one vessel.
- CW Doppler advantage
- It can measure very high velocities (no Nyquist limit), making it ideal for high-velocity stenotic or valvular jets.
- High-PRF trade-off
- Raising PRF in PW Doppler allows higher measurable velocities but introduces extra sample gates (range ambiguity).
- Wall filter set too high
- Erases genuine low-velocity flow (e.g., venous or diastolic), producing a false 'no-flow' or truncated diastolic appearance.
- Optimal Doppler angle for vessels
- Keep the angle at or below 60°; above 60° small angle errors cause large velocity errors because cosine changes rapidly.
- Color map / scale
- The reference bar showing which colors/velocities correspond to flow toward and away from the transducer and the current velocity scale (PRF).
- Color scale (PRF) for aliasing
- The color scale directly sets the color Nyquist limit; raising it lets faster flow display without color aliasing.
- Hand hygiene
- Performing hand hygiene before and after every patient contact is the single most effective measure to prevent healthcare-associated infection (CDC).
- Transducer integrity check
- Inspecting the probe face, housing, and cable for cracks or damage that could harbor pathogens or cause electrical hazard, as part of QA.
- Dead zone
- The shallowest region near the transducer face where structures cannot be imaged; assessed during phantom QA testing.
- Depth (vertical distance) accuracy
- A QA test confirming the system places reflectors at correct depths, using a phantom with targets at known distances.
- Horizontal (lateral) distance accuracy
- A QA test verifying correct side-to-side measurement using phantom targets at known horizontal spacing.
- Low-contrast detectability
- A QA measure of the smallest difference in echogenicity the system can resolve, tested with low-contrast phantom targets.
- Electrical safety hazard
- A clinical safety concern: damaged cables or housings can pose electric-shock risk; transducers are inspected and removed from service if compromised.
- Continuity equation (flow)
- Volume flow is constant along a vessel, so as cross-sectional area decreases (stenosis), velocity must increase. Basis for grading stenosis by velocity.
- Spatial average temporal average (SATA) intensity
- Intensity averaged over both the beam area and time — the lowest of the intensity descriptors, relevant to total energy delivered.
- Bioeffects: confirmed mechanisms
- Two established mechanisms of potential harm: thermal (heating) and mechanical (cavitation). Both are kept low by ALARA and the displayed TI/MI.
- Pulse duration
- The actual time the transducer transmits in one pulse = number of cycles × period. Determined by the source, not the operator.
- Operating (resonant) frequency
- Set by the element thickness and propagation speed of the element material: thinner elements resonate at higher frequencies.
- Apodization
- Varying the excitation across array elements to reduce the amplitude of side lobes and grating lobes, lowering those artifacts.
- Subdicing
- Cutting array elements into smaller sub-elements to suppress grating lobes caused by element spacing.
- Annular array
- Ring-shaped elements that focus the beam symmetrically in both lateral and elevational planes but must be steered mechanically.
- 1.5D array
- An array with several rows of elements, allowing some electronic focusing in the elevational plane to improve slice-thickness resolution.
- Nonimaging (CW Doppler) transducer
- A dedicated probe (e.g., pencil/Pedoff) with separate transmit and receive crystals for continuous-wave Doppler only, with no 2D image.
- Selecting transducer frequency
- Choose the highest frequency that still penetrates to the structure of interest, to maximize resolution without sacrificing penetration.
- Bandwidth and harmonic imaging
- Harmonic imaging requires a broadband transducer able to transmit a fundamental frequency and receive its higher harmonics.
- Huygens' principle
- Each point on a wavefront acts as a source of secondary wavelets; their interference shapes the ultrasound beam and explains diffraction.
- Nonlinear propagation
- At diagnostic pressures the wave distorts as it travels, generating harmonic frequencies in tissue — the basis of tissue harmonic imaging.
- Decibel (dB)
- A logarithmic ratio used for gain, attenuation, and dynamic range. −3 dB = half intensity; −6 dB = one-quarter (and ~half amplitude).
- Half-value (half-intensity) layer
- The tissue thickness that reduces the beam's intensity by half (−3 dB); thinner for higher frequencies because they attenuate faster.
- Imaging protocol / appropriateness
- Verifying the ordered exam is appropriate, matches the clinical question, and follows the established protocol before scanning.
- Reviewing prior imaging
- Comparing with previous studies tailors the protocol, focuses the exam, and helps correlate findings over time.
- Documenting preliminary findings
- Recording representative images and a preliminary worksheet so the interpreting physician has a complete record of the exam.
- Patient identification (time-out)
- Verifying patient identity, the ordered exam, and the correct site before beginning, to prevent wrong-patient or wrong-exam errors.
- Gray-scale (B-mode) dynamic range
- Wide dynamic range gives a smooth, low-contrast image with many grays; narrow gives a high-contrast, more black-and-white image.
- Color Doppler vs. power Doppler (summary)
- Color encodes direction and mean velocity and can alias; power encodes signal strength, is more sensitive to slow flow, and shows no direction.
- Tardus-parvus waveform
- A spectral waveform with delayed systolic upstroke and low amplitude, seen downstream of a significant proximal arterial stenosis.
- Triphasic arterial waveform
- The normal peripheral arterial pattern: sharp forward systolic peak, brief early-diastolic reversal, then late forward flow.
- Spectral Doppler scale
- The velocity scale (PRF) of the spectral display; set high enough to fit peak velocities under the Nyquist limit without aliasing.
- Angle correction
- Aligning the on-screen cursor with the true flow direction so the system applies the correct cosine and reports accurate velocity.
- Range gating (PW)
- Selecting the depth and size of the sample volume so only echoes from that region are analyzed for the Doppler shift.
- Reverberation vs. comet tail vs. ring-down
- All are repeating-echo artifacts: reverberation = equally spaced lines; comet tail = short tapering trail; ring-down = continuous band from gas.
- Compound (spatial) vs. frequency compounding
- Spatial combines frames from different angles; frequency combines images from different frequency bands. Both reduce speckle.
- Elastography
- An imaging mode that maps tissue stiffness (elasticity), helping distinguish stiff (often malignant) from soft tissue.
- Contrast-to-tissue ratio (CTR)
- A measure of how well contrast-enhanced signal is separated from background tissue signal during contrast imaging.
- Bandwidth vs. axial resolution
- Broader bandwidth allows shorter pulses, which improves axial resolution — the reason imaging transducers are damped/broadband.
- Higher frequency improves both resolutions
- Raising frequency shortens wavelength and SPL (better axial) and narrows the beam (better lateral) — at the cost of penetration.
- Why CW has no aliasing
- CW Doppler does not sample discretely (continuous transmit/receive), so there is no Nyquist limit and no aliasing, but it loses depth information.
- Bernoulli: ignoring proximal velocity
- The simplified form drops the proximal velocity term because it is small relative to the high downstream jet velocity.
- Color persistence/smoothing
- Temporal averaging of color frames that smooths the flow display but can blur rapid changes — the color equivalent of gray-scale persistence.
- Doppler sample volume size
- A small gate samples a focal point of flow with less spectral broadening; a large gate captures the whole lumen but adds broadening.
- Why perpendicular beams maximize gray-scale
- Specular reflectors return the most echo to the transducer when the beam strikes them at 90°, giving the brightest interface.
- Endocavitary probe disinfection
- After contacting mucous membranes, endocavitary transducers require high-level disinfection (per manufacturer and CDC guidance) before reuse.
- QA documentation
- Recording routine QA results (resolution, accuracy, uniformity) creates a baseline to detect equipment drift or failure over time.
- TIS, TIB, TIC
- Thermal-index variants for differing exposures: TIS (soft tissue, early pregnancy), TIB (bone in focus, late pregnancy), TIC (cranial/transcranial).
- MI and frequency relationship
- Because MI = peak rarefactional pressure ÷ √frequency, a lower frequency at the same pressure gives a higher MI (greater cavitation potential).
- Confidentiality / HIPAA
- Protecting patient privacy and health information during and after the exam is a core patient-care and professional responsibility.
- Bandwidth of CW Doppler signal
- CW Doppler uses a high-Q (narrow-band) crystal to transmit a steady pure tone, unlike the broadband elements used for imaging.
- Overall summary: resolution vs. penetration
- The central SPI trade-off — higher frequency buys better resolution but less penetration; the sonographer selects frequency to balance the two for each exam.
