ARDMS SPI Exam Prep
The SPI tests whether you can apply ultrasound physics, not just recite it. Use this free ARDMS SPI exam prep guide for physics review, 16 original practice questions, and a 4-week study plan.
Start your next 20 minutes
- 5 minutes: Without notes, write what happens to wavelength when frequency doubles and the speed of sound stays the same. Commit to an answer.
- 7 minutes: Work through the example right below. Check every unit conversion.
- 8 minutes: Answer Question 1 on echo depth using the same sound speed, then write down whether any mistake came from the relationship, the arithmetic, or the units.
Worked example 1: Frequency and wavelength
Wavelength is speed divided by frequency: λ = c ÷ f. Use the soft-tissue average the scanner assumes, c = 1,540 m/s.
- At 5 MHz: λ = 1,540 ÷ 5,000,000 = 0.000308 m = 0.308 mm
- At 10 MHz: λ = 1,540 ÷ 10,000,000 = 0.000154 m = 0.154 mm
Doubling the frequency halved the wavelength. The speed didn't change — speed depends on the medium, not on the transducer's frequency. A shortcut that saves time on the exam: in soft tissue, λ (mm) = 1.54 ÷ f (MHz). AIUM defines the wavelength relationship; the 1,540 m/s assumption is described in this AAPM research abstract.
Jump to: Physics review · Doppler · 4-week study plan · Formula sheet · Exam facts
Understand the physics behind the controls
On the current ARDMS content outline (Version 24.1), Doppler and image optimization together make up 60% of the exam. Give them substantial review time, while using your misses to decide where you need more work.
| Domain (current V24.1 outline) | Weight | What you need to be able to do |
|---|---|---|
| Apply Doppler Concepts | 34% | Reason through angle, aliasing and the Nyquist limit, PW vs. CW, color and power Doppler, wall filter, gate, scale, and spectral waveforms |
| Optimize Sonographic Images | 26% | Tell axial, lateral, elevational, and temporal resolution apart; use focus, gain, TGC, depth, harmonics, and processing controls correctly |
| Perform Ultrasound Examinations | 23% | Explain sound–tissue interactions, gray-scale artifacts, bioeffects, and patient care during the exam |
| Provide Clinical Safety & Quality Assurance | 10% | Apply infection control, QA checks and phantoms, and sensitivity/specificity |
| Manage Ultrasound Transducers | 7% | Choose and adjust transducers; understand construction, frequency, and array types |
Weights from the official SPI content outline, Version 24.1, page 1.
Each section below explains the relationships the SPI asks about, then gives you original practice questions on that domain. The 16 questions on this page are written by Castleport. They are unofficial and are not ARDMS exam questions. This is a starter set, not a full-length exam or coverage of every blueprint task. Pick an answer before you open the explanation.
1. Sound, artifacts, and the exam itself (23%)
Sound in tissue. Ultrasound is a pressure wave above the range of human hearing. Frequency is set by the transducer; propagation speed is set by the tissue. Conventional scanners assume 1,540 m/s and use the time an echo takes to come back to place it on the screen (AAPM: assumed sound speed; AIUM: echo ranging). Because the pulse goes out and back, sound needs about 13 µs per centimeter of depth (2 cm of travel ÷ 1.54 mm/µs ≈ 13 µs).
Losing energy with depth. Attenuation is the loss of amplitude as sound travels, mostly from absorption and scattering. It's quoted as an attenuation coefficient in dB per centimeter for a given frequency (AIUM glossary, A). In soft tissue, higher frequencies generally attenuate faster, which is why high-frequency probes give detail but have less penetration.
Artifacts. The scanner assumes sound travels in a straight line at 1,540 m/s and that every echo comes straight back. When those assumptions fail, the image shows things that aren't there or hides things that are:
- Shadowing: reduced echoes behind a strongly attenuating object such as a stone.
- Enhancement: brighter echoes behind something that attenuates little, such as fluid.
- Reverberation: sound bouncing between a strong reflector and the transducer, shown as equally spaced lines.
- Mirror image: a duplicate structure on the far side of a strong, smooth reflector.
- Refraction (edge) shadow: a dark line at the edge of a curved structure where the beam bends.
Sources: AIUM: enhancement and acoustic shadow, reverberation and refraction, and mirror image artifact.
Bioeffects and ALARA. The mechanical index (MI) relates to mechanical effects such as cavitation; the thermal indices (TI) relate to heating. AIUM's ALARA statement asks you to use correct presets, set power to the lowest level that still gives a diagnostic image, monitor MI and TI, reduce dwell time, and keep scan time to what the exam needs (AIUM ALARA principle, reapproved August 17, 2026).
The exam itself. Domain 1 also covers the human side of scanning: verifying the patient and order, reviewing history and prior imaging, protecting privacy, using sound ergonomic technique, and documenting preliminary findings (V24.1 outline, tasks 1.A–1.N).
Check yourself: Domain 1
Question 1 (SPI-PREP-01 · Task 1.C)
In soft tissue, an echo returns 104 µs after the pulse leaves the transducer. Assume a sound speed of 1,540 m/s. Approximately how deep is the reflector?
Show answer and explanation
Answer: C. 8 cm. At 1,540 m/s, each centimeter of depth takes about 13 µs round trip, so 104 ÷ 13 = 8 cm. Choosing 16 cm (D) means you used the full out-and-back distance as the depth. 4 cm (B) divides by two twice. 1.3 cm (A) is a unit slip.
Sources: AIUM: echo ranging; AAPM: range equation, PDF page 1.
Question 2 (SPI-PREP-02 · Task 1.C)
A hypothetical uniform material has an attenuation coefficient of 1 dB/cm at the operating frequency. A reflector is 4 cm deep. Ignoring reflection and beam spreading, how much attenuation occurs over the trip to the reflector and back?
Show answer and explanation
Answer: C. 8 dB. The sound travels 4 cm out and 4 cm back, so the path is 8 cm: 1 dB/cm × 8 cm = 8 dB. 4 dB (B) counts only the outgoing trip. 2 dB (A) halves the one-way answer. 16 dB (D) doubles a number that was already round trip. Because the coefficient is given for the operating frequency, you don't multiply by frequency again. The 1 dB/cm value is invented for this problem, not a tissue constant.
Sources: AIUM: attenuation coefficient.
Question 3 (SPI-PREP-03 · Task 1.D)
Several equally spaced, parallel bright lines appear deep to a strong, smooth reflector near the skin. Which artifact is this?
Show answer and explanation
Answer: B. Reverberation. Sound bouncing back and forth between a strong reflector and the transducer face returns repeated echoes at regular intervals, which the scanner draws as evenly spaced lines at increasing depth. Refraction shadows (A) are dark lines at the edges of curved structures. A mirror image (C) duplicates an actual structure across a strong reflector instead of drawing a series of lines. Shadowing (D) is a dark band, not repeated bright lines.
Sources: AIUM: reverberation and refraction; mirror image artifact; shadowing.
Question 4 (SPI-PREP-04 · Task 1.F)
Which displayed index is intended to indicate the potential for mechanical (nonthermal) bioeffects such as cavitation?
Show answer and explanation
Answer: C. Mechanical index. MI relates to mechanical effects such as cavitation. The thermal indices (A, B) relate to tissue heating. Duty factor (D) is the fraction of time the transducer is actively transmitting (AIUM glossary, D); it describes the pulse sequence and isn't a bioeffect index. ALARA asks you to watch both MI and TI.
Sources: AIUM: mechanical index; thermal index; duty factor; ALARA.
2. Transducers and pulse formation (7%)
A transducer converts electrical energy into sound and back again using piezoelectric elements. For a given sound speed, the operating frequency sets wavelength. Damping, including the effect of the backing layer, removes energy so the pulse rings for fewer cycles, giving a shorter pulse and better axial resolution, usually at the cost of sensitivity (AIUM: damping; backing layer).
Array type is about geometry and job. Linear arrays produce a rectangular image suited to superficial work; phased arrays steer from a small footprint, which helps between ribs; curvilinear arrays give a wide field for deeper abdominal imaging (SAEM: transducers). Choose frequency for the depth you need: higher for detail near the skin, lower for penetration.
Check yourself: Domain 2
Question 5 (SPI-PREP-05 · Task 2.A)
Which tradeoff generally follows greater damping in an otherwise comparable pulsed transducer?
Show answer and explanation
Answer: B. Damping shortens the pulse by reducing ringing, which improves axial resolution, usually at some cost to sensitivity. A reverses the ringing change. C pairs shorter ringing with the wrong bandwidth trend — a shorter pulse contains a wider range of frequencies. D confuses the transducer's behavior with the receiver's amplification.
Sources: AIUM: damping; backing layer and bandwidth.
3. Image optimization: resolution, brightness, and timing (26%)
Four kinds of resolution.
| Resolution | Direction | What controls it |
|---|---|---|
| Axial | Along the beam | Spatial pulse length (SPL): approximately SPL ÷ 2 in the ideal pulse-echo model |
| Lateral | Side to side, across the beam | Beam width, narrowest at the focus |
| Elevational | Slice thickness | Beam thickness perpendicular to the image plane |
| Temporal | Over time | Frame rate |
SPL equals wavelength × the number of cycles in the pulse. At fixed sound speed and cycles per pulse, higher frequency shortens SPL; stronger damping shortens ringing (AIUM: wavelength; damping). Lateral resolution is best at the focal zone, where the beam is narrowest (AIUM: lateral resolution; focal length). The SPL ÷ 2 estimate comes from the ideal short-pulse model (AAPM: Axial Resolution, PDF page 2).
Brightness: three controls that aren't interchangeable. Overall gain amplifies all returning echoes. Time gain compensation (TGC) amplifies echoes by depth to offset attenuation. Output power changes how much sound goes into the patient. Gain and TGC act on the received signal; output power changes exposure, which is why ALARA tells you to use the lowest output that still gives a diagnostic image (AIUM: TGC; overall gain and output power; ALARA).
Timing. In conventional sequential B-mode imaging, each scan line has to wait for echoes from the deepest point before the next pulse goes out. Deeper settings, more scan lines, a wider sector at fixed line density, and extra transmit focal zones increase acquisition time per frame. They can therefore lower frame rate; actual timing also depends on the system (AAPM: Frame Rate Limitation, PDF page 1; AIUM: multifocusing).
Processing and modes to know by name. Dynamic range (compression) controls the range of echo amplitudes mapped into gray shades and therefore affects contrast (AIUM: dynamic-range compression). Harmonic imaging builds the image from echoes at multiples of the transmitted frequency, which can improve resolution and reduce some artifacts (AIUM: harmonic imaging; ASE: Harmonic Imaging, PDF page 7). Persistence averages frames to smooth noise. Spatial compounding combines views from several beam angles. Pre-processing (write) magnification acquires the region of interest before image storage, while post-processing (read) magnification enlarges data already stored. M-mode records motion along one line over time and has very high temporal resolution.
Sources: AIUM: persistence and processing, spatial compounding, M-mode, and Siemens technical explanation of write versus read zoom.
Control → effect → tradeoff
| Change | What it does | What to remember |
|---|---|---|
| Raise frequency | Shortens wavelength at fixed sound speed; shortens SPL if cycles per pulse stay fixed | More attenuation, less penetration; speed of sound doesn't change |
| Raise overall gain | Amplifies all received echoes | Amplifies noise too; doesn't add transmitted energy |
| Adjust TGC | Amplifies echoes by depth | Can't recover a signal that was never received |
| Move the focus to the target | Narrows the beam there | Improves lateral, not axial, resolution |
| Increase depth | Longer listening time per line | Can lower frame rate in conventional line-by-line imaging |
| Raise conventional PW Doppler PRF (scale) | Raises the Nyquist limit | Limited by sample depth when unambiguous ranging is required |
| Raise the wall filter | Removes low-frequency signal | Can erase real slow flow |
| Lower output power | Reduces patient exposure | Goal is the lowest setting that's still diagnostic |
Check yourself: Domain 3
Question 6 (SPI-PREP-06 · Task 3.B)
Two small reflectors sitting side by side at 6 cm depth blur into one dot. The transmit focus is set at 2 cm. Which adjustment best separates them?
Show answer and explanation
Answer: B. Side-by-side separation is lateral resolution, which depends on beam width. The beam is narrowest at the focus, so placing the focus at the reflectors' depth gives the best lateral resolution there. More gain (A) makes both echoes brighter and can merge them further. Dynamic range (C) changes contrast, not beam width. Extra depth (D) does not narrow the beam at the reflectors and can reduce frame rate in conventional line-by-line imaging.
Sources: AIUM: lateral resolution; focal length; AAPM: frame-rate model, PDF page 1.
Question 7 (SPI-PREP-07 · Task 3.A)
An ultrasound pulse has a spatial pulse length of 1.2 mm. In the ideal pulse-echo model, what is the axial-resolution limit?
Show answer and explanation
Answer: D. 0.6 mm. The ideal axial-resolution limit is approximately SPL ÷ 2 = 1.2 ÷ 2 = 0.6 mm. In this model, reflectors along the beam closer than that blur together. B forgets to halve, C doubles, and A halves twice. A smaller number means better axial resolution.
Sources: AAPM: Axial Resolution, PDF page 2.
Question 8 (SPI-PREP-08 · Tasks 3.D, 3.O)
You're imaging a fast-moving structure with conventional line-by-line B-mode imaging, and frame rate is limited by echo-return time. The region of interest ends at 8 cm, but the depth is set to 16 cm. Which adjustment raises the possible frame rate without reducing line density? Assume other settings stay unchanged.
Show answer and explanation
Answer: A. Each line waits about 13 µs per centimeter of depth. At 16 cm that's roughly 208 µs per line; at about 8 cm, roughly 104 µs — so the propagation-limited frame-rate ceiling is nearly doubled when the other settings stay fixed. Actual frame rate may also be limited by other acquisition and processing requirements. A second focal zone (B) adds a pulse per line and slows things down. A wider sector (C) adds lines to every frame at unchanged line density. More depth (D) makes each line take longer.
Sources: AAPM: Frame Rate Limitation, PDF page 1; AIUM: multifocusing.
Question 9 (SPI-PREP-09 · Task 3.F)
On an abdominal image, the near field is well balanced but the deep half is uniformly too dark. Adequate deep echoes are present above the noise floor, and the focus is already at the region of interest. Which adjustment increases deep brightness without increasing acoustic output?
Show answer and explanation
Answer: A. TGC amplifies returning echoes by depth to compensate for attenuation. It works on the received signal, so it doesn't raise patient exposure. Because usable deep echoes are already present, a depth-specific receiver adjustment addresses the stated problem without increasing output power (B). Moving the focus into the near field (C) does not provide depth-selective receiver amplification. Dynamic range (D) changes contrast, not depth-dependent receiver gain.
Sources: AIUM: time-gain compensation; overall gain and output power; AAPM: gain versus power, PDF page 2.
4. Doppler: sampling and display choices (34%)
This is the biggest domain, and most of it comes down to keeping four quantities straight: the transmitted frequency (f₀), the Doppler shift (the change in frequency caused by moving blood), the pulse repetition frequency (PRF, how often pulses are sent), and the angle between the beam and the flow.
The Doppler equation. Doppler shift = 2 × f₀ × v × cos θ ÷ c, where v is blood velocity, θ is the angle between the beam and the flow, and c is the speed of sound (AAPM: Doppler demonstrations, PDF pages 6–7). Three things follow:
- The shift gets bigger with higher transmitted frequency and faster flow.
- cos 0° = 1, cos 60° = 0.5, and cos 90° = 0. Flow running perpendicular to the beam produces little or no shift.
- When you set the angle-correction marker, the machine uses that angle to turn the measured shift into a velocity. For angle-corrected vascular velocity measurements, angles above 60° amplify the effect of angle errors. The marker should follow the actual flow direction; changing the marker alone does not change the detected shift.
Aliasing and the Nyquist limit. Pulsed-wave (PW) Doppler samples the signal once per pulse. With a centered bidirectional display, the Nyquist limit is half the PRF (AIUM glossary, N). Above that, the signal aliases: on a spectral display it wraps to the other side of the baseline; on color it flips to the opposite color. Ways to reduce it include raising the scale (PRF), using a lower transmitted frequency, or using a shallower acoustic window that still samples the target and permits a higher PRF. Switching to continuous-wave (CW) Doppler avoids the PW sampling limit but gives up selected-depth information (AIUM: pulsed Doppler; CW Doppler; AAPM: Doppler equation). Shifting the baseline changes how the display is split between directions; it doesn't raise the Nyquist limit (AIUM: baseline shift).
PW vs. CW. Conventional PW uses a gate to sample one chosen depth but has the PRF/2 Nyquist ceiling. CW uses separate elements to transmit and receive continuously, so it can measure very high velocities but can't tell you what depth they came from (AIUM: PW; CW).
Color, power, and the other controls.
- Color Doppler shows the mean frequency shift in each pixel, with direction coded by the color map. Red is not automatically an artery; the map can be inverted (AIUM: color flow imaging; Siemens: color-map inversion).
- Conventional power Doppler shows signal strength instead of frequency. It's less angle-dependent and sensitive to slow flow, but shows no direction or velocity. Directional power Doppler variants also encode flow direction (AIUM: power Doppler; Siemens: power Doppler angle dependence, workbook page 111; directional power Doppler).
- Wall filter rejects low-frequency signal from moving vessel walls and tissue (AIUM glossary, W). Set too high, it also removes real slow flow.
- Doppler gain too high can cause color noise outside the vessel or noise in the spectrum; too low can hide real flow (ASE: spectral and color gain, PDF pages 12 and 17).
- Sample gate size and position matter. With a parabolic laminar velocity profile, a gate spanning the whole lumen collects both fast central flow and slower flow near the walls, which can fill in the spectral window even in a normal vessel (AAPM: Gate Size and Gate Position, PDF page 7).
Spectral waveforms and hemodynamics. A spectral Doppler trace displays the range of detected shifts or calculated velocities over time. Spectral broadening means that range has widened; disturbed flow can cause it, but so can sampling a broader range of velocities. Broadening alone does not establish disease (AIUM: spectral Doppler and spectral broadening).
Volume flow is the amount of blood passing per unit time; velocity is the speed of that blood. In a simple resistance model, volume flow = pressure difference ÷ resistance. At fixed resistance, a larger pressure difference increases flow. At fixed pressure difference, greater resistance reduces flow. Do not substitute a peak Doppler velocity for a volume-flow measurement (AIUM: flow rate and fluid resistance).
Tissue Doppler measures tissue motion toward or away from the transducer, rather than blood-flow velocity (AIUM: tissue Doppler imaging).
Try it: If pressure difference stays fixed and resistance doubles in the simple model, what happens to volume flow? It halves. If a larger gate broadens a spectrum, what should you reconsider before attributing that change to disease? The range of velocities included by the gate.
Worked example 2: Depth sets a ceiling on PRF
Assume one pulse in flight at a time and c = 1,540 m/s, neglecting pulse duration and other timing overhead.
- Reflector at 15.4 cm: round trip = 2 × 0.154 m ÷ 1,540 m/s = 200 µs. The theoretical ceiling is 1 ÷ 200 µs = 5,000 Hz.
- Reflector at 30.8 cm: round trip = 400 µs, so the ceiling drops to 2,500 Hz.
Doubling the depth halves the maximum PRF. Check it with the shortcut: 15.4 cm × 13 µs/cm ≈ 200 µs. Real systems may run lower because of other timing needs (AAPM: range and timing equations, PDF page 1).
Worked example 3: PRF and aliasing
A separate setup from example 2: conventional PW Doppler, baseline centered, and a sample depth that allows both PRFs. The Doppler shift is 3 kHz.
| PRF | Nyquist limit (PRF ÷ 2) | Does a 3 kHz shift alias? |
|---|---|---|
| 5 kHz | 2.5 kHz | Yes — it exceeds the limit |
| 8 kHz | 4 kHz | No — it fits under the limit |
Raising the PRF solved it here only because the sample depth allowed 8 kHz. At the 15.4 cm depth in example 2, 8 kHz wouldn't be possible under that one-pulse-in-flight model.
Check yourself: Domain 4
Question 10 (SPI-PREP-10 · Tasks 4.F, 4.Q)
A PW Doppler system uses a PRF of 6 kHz with the baseline centered. Which Doppler shift will alias?
Show answer and explanation
Answer: D. 4 kHz. The Nyquist limit is 6 ÷ 2 = 3 kHz, and only 4 kHz is above it. The 2.5 kHz shift (C) is close but still fits. If you thought nothing here aliases, you probably compared the shift with the full 6 kHz PRF instead of half of it.
Sources: AIUM: Nyquist limit.
Question 11 (SPI-PREP-11 · Task 4.A)
Same vessel, same flow, same transducer and unchanged transmit frequency, but the actual angle between the beam and the flow changes from 0° to 60°. What happens to the detected Doppler shift?
Show answer and explanation
Answer: A. The shift is proportional to cos θ. Cos 0° = 1 and cos 60° = 0.5, so the shift halves. It would drop to zero (D) only at 90°. That's why a vessel running straight across the beam can look empty on color Doppler.
Sources: AAPM: Doppler equation and gate angle, PDF pages 6–7.
Question 12 (SPI-PREP-12 · Task 4.F)
During a PW Doppler exam, peak systolic velocities wrap around below the baseline. The scale is already at its maximum for this gate depth, and you need to keep sampling at that exact depth. With flow and actual Doppler angle unchanged, which change most directly reduces the aliasing? Assume a lower Doppler transmit frequency is available.
Show answer and explanation
Answer: C. With the PRF maxed out, the remaining lever on this list is the size of the shift. The shift is proportional to the transmitted frequency, so at unchanged PRF a lower frequency produces a smaller shift that can fit under the Nyquist limit. Gain (A) changes brightness, not the limit. The wall filter (B) removes low-velocity signal near the baseline. Lowering the scale (D) lowers the Nyquist limit and makes aliasing worse. Shifting the baseline can redistribute the displayed range without raising the Nyquist limit. CW avoids the PW sampling limit but loses selected-depth information, so it does not meet this question's requirement.
Sources: AAPM: Doppler equation, PDF pages 6–7; AIUM: baseline shift; wall filter; CW Doppler.
Question 13 (SPI-PREP-13 · Task 4.G)
A narrow, high-velocity jet still aliases on PW Doppler after you maximize the scale and shift the baseline. You switch to CW Doppler. What do you give up?
Show answer and explanation
Answer: D. CW transmits and receives continuously with separate elements, so it is not limited by PW Doppler's PRF/2 aliasing threshold and can measure very high velocities — the opposite of A. The cost is range ambiguity: it receives motion signals from the overlapping transmit and receive beam regions and can't say where a velocity originated. B is wrong because CW transmits and receives simultaneously; PW alternates transmitting and listening. C is false; the Doppler equation, including cos θ, still applies.
Sources: AIUM: continuous-wave Doppler; pulsed Doppler; AAPM: Doppler angle, PDF pages 6–7.
Question 14 (SPI-PREP-14 · Task 4.B)
Color Doppler doesn't fill a vein with slow flow. The vessel segment is entirely inside the color box, the insonation angle is appropriate, and probe pressure is not compressing it. The color scale is already low, and the color gain is set just below where noise appears. Which setting is most likely removing the venous signal?
Show answer and explanation
Answer: A. The wall filter rejects low-frequency signal so wall and tissue motion don't clutter the display. A filter doesn't know which low frequencies are useful, so set too high it removes real slow flow too. A low scale (B) can cause aliasing if the shift exceeds its Nyquist limit; it does not itself filter out slow flow. Gain that's too high (C) causes color noise, and the stem says gain is below that point. A color box that excluded the vessel could omit its signal, but the stem rules that out.
Sources: AIUM: wall filter; high-pass filter; ASE: color region and gain, PDF page 17; Siemens: color scale.
5. Clinical safety and quality assurance (10%)
Infection control. How you reprocess a transducer depends on what it touched. AIUM's 2025 guideline says external transducers used on clean, intact skin need cleaning and low-level disinfection between patients, while internal transducers (transvaginal, transrectal, transesophageal) need high-level disinfection between patients and a single-use cover during each exam. A cover doesn't change that requirement, because covers can fail. Clean first, follow the manufacturer's instructions for compatible disinfectants, and follow your facility's protocol (AIUM transducer cleaning guideline, July 2, 2025; CDC: Spaulding classification).
Equipment QA. Inspect transducers regularly — connector, cable, housing, and lens. Damaged elements can reduce resolution and penetration and introduce Doppler errors, and imaging a tissue-mimicking phantom can reveal that kind of degradation (AIUM guideline above). Phantom tests check things like uniformity, how accurately the calipers measure known distances, and how deep the system can still detect targets (ACR: ultrasound quality control, revised April 9, 2025).
Test statistics. These describe how well a diagnostic test performs against a reference standard (FDA: diagnostic-test reporting guidance, Appendix 7.1 and glossary):
- Sensitivity = true positives ÷ (true positives + false negatives). Of the people who have the condition, how many tested positive?
- Specificity = true negatives ÷ (true negatives + false positives). Of the people who don't, how many tested negative?
- Positive predictive value = true positives ÷ all positive results. Negative predictive value = true negatives ÷ all negative results.
Check yourself: Domain 5
Question 15 (SPI-PREP-15 · Task 5.A)
An endovaginal transducer was used with a single-use cover, and the cover looked intact when removed. What is the minimum reprocessing before the next patient?
Show answer and explanation
Answer: B. Internal transducers contact mucous membranes, which makes them semicritical devices that require high-level disinfection between patients, after cleaning. An intact-looking cover doesn't lower that requirement, since covers can fail. Low-level disinfection (A) is for external transducers on clean, intact skin. C and D skip disinfection entirely.
Sources: AIUM: transducer preparation, Section I; CDC: Semicritical Items.
Question 16 (SPI-PREP-16 · Task 5.F)
A new ultrasound protocol is compared with a reference standard in 150 patients:
| Test result | Condition present | Condition absent |
|---|---|---|
| Test positive | 40 | 15 |
| Test negative | 10 | 85 |
What is the specificity?
Show answer and explanation
Answer: C. 85%. Specificity = true negatives ÷ (true negatives + false positives) = 85 ÷ (85 + 15) = 85%. The other choices are the other three classic measures: 80% is sensitivity (40 ÷ 50), 72.7% is positive predictive value (40 ÷ 55), and 89.5% is negative predictive value (85 ÷ 95).
What your score on these 16 questions means
It tells you how you did on these 16 items — nothing more. ARDMS reports a scaled score from 300 to 700, and a short original set can't estimate it. Use your misses to decide where to start:
| Missed questions | Start here |
|---|---|
| 1–4 | Section 1 and Week 1 of the plan |
| 5 | Section 2 |
| 6–9 | Section 3 and Week 2 |
| 10–14 | Section 4 and Week 3 |
| 15–16 | Section 5 and Week 4 |
Keep a short error log. Writing down why you missed something gives you a specific mistake to repair.
| Question or concept | What I thought | What actually decides the answer | When I'll review it |
|---|---|---|---|
| Example: Question 1, echo depth | I used the whole travel time as the depth | The echo time covers the trip out and back, so divide by two | Rework example 2 tomorrow without notes |
Your 4-week SPI study plan
Assumes: you've had a sonography physics course and can study six 1-hour sessions a week (24 hours total, with the seventh day for rest or catch-up). This is our editorial plan, not an ARDMS requirement. If physics is new to you, give the foundations more time.
Every session: 10 minutes recalling the last session without notes → 25 minutes on the new topic → 15 minutes on its example or questions → 10 minutes updating your error log.
| Week · Session | Focus | What to finish |
|---|---|---|
| 1 · 1 | Frequency and wavelength | Worked example 1; explain unit conversions out loud |
| 1 · 2 | Echo timing | Question 1; draw the out-and-back path and the 13 µs rule |
| 1 · 3 | Attenuation and tissue interactions | Question 2; explain why higher frequency penetrates less |
| 1 · 4 | Artifacts | Question 3; sketch shadowing, enhancement, reverberation, mirror, and edge shadow |
| 1 · 5 | Bioeffects, ALARA, and patient care | Question 4; list the AIUM ALARA steps from memory |
| 1 · 6 | Transducers | Question 5; compare linear, curvilinear, and phased arrays by footprint and depth |
| 2 · 1 | Axial and lateral resolution | Questions 6–7; draw both directions on one beam diagram |
| 2 · 2 | Elevational and temporal resolution | Question 8; list everything that lowers frame rate |
| 2 · 3 | Gain, TGC, and output power | Question 9; explain which ones change patient exposure |
| 2 · 4 | Processing | Write one sentence each for dynamic range, harmonics, compounding, persistence, and pre- vs. post-processing |
| 2 · 5 | M-mode and review | Rebuild the control → effect → tradeoff table without looking |
| 2 · 6 | Domains 1–3 retrieval | Redo Questions 1–9 cold; log every miss |
| 3 · 1 | The Doppler equation | Explain what each term does to the shift; memorize cos 0°, 60°, 90° |
| 3 · 2 | Angle and angle correction | Question 11; explain why 60° or less is the target for angle-corrected vascular velocity measurements |
| 3 · 3 | PRF, Nyquist, and aliasing | Worked examples 2 and 3; Question 10 |
| 3 · 4 | Fixing aliasing; PW vs. CW | Questions 12–13; list every aliasing fix and its cost |
| 3 · 5 | Color, power, wall filter, gain, gate | Question 14; explain each control as "what it changes → what you see → what you give up" |
| 3 · 6 | Doppler retrieval | Redo Questions 10–14 cold; explain why each wrong option is wrong |
| 4 · 1 | Infection control | Question 15; explain the difference between external and internal transducer reprocessing |
| 4 · 2 | QA and test statistics | Question 16; build your own 2×2 table and calculate all four measures |
| 4 · 3 | Spectral waveforms and hemodynamics | Work through the on-page hemodynamics review; explain gate-related broadening and solve the pressure/resistance check |
| 4 · 4 | Mixed practice | All 16 questions in random order, no notes; treat it as retrieval practice, not a readiness test |
| 4 · 5 | Error repair | Rework your three weakest concepts from the error log; change one number in a worked example and solve again |
| 4 · 6 | Final review and logistics | Rebuild the formula sheet from memory; confirm your appointment, ID, and test-center details |
Adapting the plan
- 30-minute sessions: split each session in two and take 8 weeks.
- Three sessions a week: keep the same 24 sessions over 8 weeks.
- Only 2 weeks: do two sessions a day, six days a week — only if the material is already familiar.
- A concept still isn't clicking: add a session on it. Don't skip it because a practice score looked fine.
SPI formula sheet
| Relationship | Formula or value | Notes |
|---|---|---|
| Speed of sound, soft tissue (assumed) | 1,540 m/s = 1.54 mm/µs | Depends on the medium, not the frequency |
| Wavelength | λ = c ÷ f | Soft tissue: λ (mm) = 1.54 ÷ f (MHz) |
| Period | T = 1 ÷ f | Inverse of frequency |
| Depth from echo time | depth = (c × round-trip time) ÷ 2 | About 13 µs per cm of depth |
| Spatial pulse length | SPL = wavelength × cycles per pulse | Higher frequency shortens SPL at fixed sound speed and cycles per pulse; damping reduces ringing |
| Axial resolution | Approximately SPL ÷ 2 | Ideal short-pulse model; smaller number = better |
| Pulse repetition period | PRP = 1 ÷ PRF | Greater depth raises the minimum PRP in conventional unambiguous pulse-echo ranging |
| Nyquist limit | PRF ÷ 2 | Conventional PW, centered bidirectional display; shifts above it alias |
| Doppler shift | 2 × f₀ × v × cos θ ÷ c | Bigger with higher f₀ and faster flow |
| Cosines | cos 0° = 1 · cos 60° = 0.5 · cos 90° = 0 | |
| Decibels | +3 dB ≈ double the intensity; −3 dB ≈ half | |
| Duty factor | Fraction of time the transducer is transmitting | Pulse duration ÷ PRP for a periodic pulse train |
| Sensitivity | TP ÷ (TP + FN) | |
| Specificity | TN ÷ (TN + FP) | |
| PPV / NPV | TP ÷ (TP + FP) · TN ÷ (TN + FN) |
Sources: AIUM: wavelength, period and pulse repetition, decibels and duty factor, Nyquist limit, AAPM: timing and axial resolution, Doppler equation, and FDA: diagnostic-test formulas. The decibel shortcuts above refer to intensity, not pressure amplitude.
SPI exam facts
| Item | Current official detail |
|---|---|
| Who runs it | ARDMS, part of Inteleos; delivered through Pearson VUE |
| Format | About 110 multiple-choice questions. ARDMS lists a two-hour exam and a five-minute survey. |
| Content outline | Version 24.1 — Doppler 34%, image optimization 26%, performing exams 23%, safety and QA 10%, transducers 7% |
| Scoring | Pass/fail on a 300–700 scale; 555 or higher passes. Scores aren't percentages and aren't curved. |
| Results | Score report at the test center right after the exam; posted to your Pearson and Inteleos accounts within a week |
| Fee | $275, including a $100 non-refundable processing fee; an extra non-refundable $50, paid at scheduling, for test centers outside the U.S., Canada, and Mexico |
| Availability | Applications and testing are year-round |
| Retake | Reapply after 72 hours; you must wait 60 days before retaking, and that wait can't be waived |
| Five-year rule | SPI and your specialty exam must both be passed within five years of each other, counted by calendar year. Pass your first exam on June 6, 2026, and you have until December 31, 2031, to pass the second. |
| After you pass | You don't retake SPI to add more ARDMS credentials, as long as your status stays active |
| Historical pass rates | 2025 global SPI administrations: 74% first-time, 47% repeat, 68% overall. These cohort rates do not predict an individual result. |
Sources: Inteleos SPI exam page, fee schedule, passing standard, notification of results, retake guidelines, five-year rule, 2025 global exam performance report, SPI row. Last verified October 28, 2026.
Passing SPI alone does not earn an ARDMS credential: the corresponding specialty exam and eligibility requirements also apply (Pearson: ARDMS credentials and examinations). ARDMS certification is not a state license; scope of practice also depends on applicable law and employer policy (Inteleos: scope of practice).
Common questions
Can I take the SPI before I graduate? Often, yes. The SPI Requirement – Early Entry pathway qualifies you for the SPI only, not a specialty exam. You need either a graded college, post-secondary, or higher-education physics course with "Physics," "Physical Principles," or "Instrumentation" in the title and a grade of C or above (unofficial transcripts are accepted), or at least 12 ARDMS-accepted CME credits from a physics seminar, review course, or correspondence course earned within two years before you apply. No Clinical Verification form is required. If SPI is your first ARDMS exam and you already qualify under a full prerequisite pathway, ARDMS recommends using that one because later applications process faster. Check the SPI and specialty prerequisites chart and the Inteleos Prerequisite Prep Tool — prerequisites can change.
My review book lists "Ultrasound Transducers 16%" and "Doppler Imaging Concepts 31%." Is it outdated? Those percentages do not match the current Version 24.1 outline. The underlying physics relationships can still be useful, but check the material against current coverage and safety guidance. Plan your time around the current V24.1 weights, where Doppler is 34% and transducers are 7%.
Where can I preview the test interface for free?
The Pearson ARDMS program page links an official Inteleos (ARDMS/APCA) tutorial under “Sample testing.” Use that route to become familiar with the computer-testing environment; keep the physics practice and study plan on this page.
Are "real SPI exam questions" sold online legitimate? Treat any site claiming to sell confidential live SPI questions as a red flag. Inteleos's exam security policy prohibits taking or offering review courses that claim to include live questions and acquiring or using unauthorized materials. Officially released sample material is different from leaked or recalled exam content.
Next steps
When you're ready to book, confirm your pathway with the prerequisites chart, then apply through the Inteleos portal. If you need testing accommodations, request them when you apply and follow the approved letter's scheduling instructions. After approval, schedule through Pearson within the eligibility period in your Exam Confirmation Letter. Until then, the best next step is on this page: pick up the 4-week plan at the session that matches your weakest domain.
Sources
Official exam sources (ARDMS / Inteleos and Pearson)
- Sonography Principles and Instrumentation (SPI) exam page — format, survey, and credentials
- SPI Content Outline, Version 24.1, pages 1–3
- Exam Fee Schedule — SPI row and fee notes
- Passing Standard
- Retake and reapply guidelines
- 5-Year Rule
- SPI Requirement & Specialty Examination Prerequisites, pages 1 and 3
- Prerequisites and Prerequisite Prep Tool
- Notification of Results and Scoring
- 2025 Global Exam Performance Summary — January 1–December 31, 2025, SPI row
- Exam Statistics index
- Pearson ARDMS program page — credentials, ID, and Sample testing tutorial route
- Schedule or Change an Exam
- Exam Accommodations
- Scope of Practice
- Exam Security
Physics, safety, and statistics references
- AIUM, Recommended Ultrasound Terminology: A: wavelength, attenuation, enhancement, axial resolution, B: backing layer and baseline shift, C: color/CW Doppler and compression, D: damping, decibels and duty factor, E: echo ranging, F: flow, resistance, filters, focus, H: harmonic imaging, L: lateral resolution, M: mechanical index, mirror artifact, M-mode, N: Nyquist limit, O: overall gain and output power, P: pulses, persistence, processing, power Doppler, R: refraction, reverberation, temporal resolution, S: spatial compounding and spectral Doppler, T: TGC, thermal index, tissue Doppler, W: wall filter.
- AAPM, Zheng F. Lu: QA/QC of Ultrasound Imagers, August 13, 2003 — pages 1–2 for stable range, frame-rate, gain/output, axial-resolution, and Doppler relationships.
- AAPM, Randell L. Kruger: Understanding and Teaching Ultrasound Physics, 2001 — pages 6–7 for the Doppler equation, angle correction, and gate size/position.
- AAPM abstract 15441: Speed of sound aberration correction in quantitative ultrasound-aided image guided radiotherapy — conventional 1,540 m/s assumption.
- ASE: Guidelines for Performing a Comprehensive Transthoracic Echocardiographic Examination in Adults — PDF pages 7, 12 and 17, harmonic imaging and spectral/color gain; hosted copy carries 2018 copyright.
- SAEM: Introduction to Bedside Ultrasound, updated 2023 — transducer types.
- Siemens Healthineers technical teaching: write versus read zoom, color controls and directional power Doppler, and power Doppler angle dependence, workbook page 111.
- AIUM: As Low As Reasonably Achievable (ALARA) Principle, reapproved August 17, 2026.
- AIUM: Guidelines for Cleaning and Preparing External- and Internal-Use Ultrasound Transducers, July 2, 2025 revision.
- CDC: A Rational Approach to Disinfection and Sterilization, from the 2008 guideline; page dated November 28, 2023.
- ACR: Quality Control — Ultrasound and Breast Ultrasound, revised April 9, 2025; phantom test purposes.
- FDA: Statistical Guidance on Reporting Results from Studies Evaluating Diagnostic Tests, March 13, 2007; Appendix 7.1 and statistical glossary.
Developed with AI assistance. Sources and calculations were checked for this version; no credentialed professional review is claimed. This guide is for exam preparation, not a substitute for clinical training or patient-care protocols. See how we create study material.
Castleport Test Prep is an independent exam prep publisher. We are not affiliated with, endorsed by, or approved by ARDMS or Inteleos. The practice questions on this page are original and unofficial. ARDMS, SPI, RDMS, RDCS, RVT, RMSKS, and related names are used to identify the exams and credentials they describe; trademarks belong to their respective owners.