The Sonography Principles and Instrumentation (SPI) exam is the physics exam every ARDMS candidate must pass, whether they are aiming for RDMS, RDCS, RVT or RMSKS. Many doctors and sonographers find it the hardest step because it tests physics rather than anatomy. This guide explains the format, what is tested and how to prepare.
SPI exam format at a glance
| Feature | Details |
|---|---|
| Questions | About 110 multiple-choice questions |
| Time | 2 hours |
| Fee | US$275 (as listed by Inteleos) |
| Passing score | 555 on a 300–700 scale |
| Retake | Reapply after 3 days; wait 60 days to re-sit |
| Time window | Pass SPI and a specialty within 5 years of each other |
| Delivery | Pearson VUE test centres, including selected international sites |
What the SPI tests
- Ultrasound physics: wave parameters, propagation speed, attenuation, impedance, reflection and refraction.
- Clinical safety: thermal and mechanical index, cavitation, ALARA.
- Instrumentation: the pulser, beam former, receiver functions (amplification, compensation, compression, demodulation, rejection) and display.
- Transducers: the piezoelectric effect, damping, matching layers, arrays and focusing.
- Image optimisation and artifacts: resolution, TGC, focal zones, reverberation, mirror image, refraction, side lobes and more.
- Doppler and haemodynamics: the Doppler equation, aliasing and the Nyquist limit, spectral, colour and power Doppler, Poiseuille and Bernoulli.
- Quality assurance: phantoms, test objects and preventive maintenance.
Ten formulas and rules you must know
| Rule | What to remember |
|---|---|
| Wavelength | λ (mm) = 1.54 ÷ frequency (MHz) |
| 13 µs rule | Each 1 cm of depth = 13 µs go-return time |
| Axial resolution | = spatial pulse length ÷ 2 |
| Nyquist limit | = PRF ÷ 2; above it the signal aliases |
| Decibels | +3 dB doubles intensity; +10 dB multiplies it by 10 |
| Attenuation | ≈ 0.5 dB/cm/MHz in soft tissue |
| Doppler shift | Δf = 2 f₀ v cos θ ÷ c |
| Bernoulli | ΔP = 4V² |
| Poiseuille | Resistance ∝ length × viscosity ÷ radius⁴ |
| Max PRF | PRF (Hz) = 77,000 ÷ depth (cm) |
Our free SPI flashcards cover these and more.
A 6-week SPI study plan
| Week | Focus |
|---|---|
| 1 | Waves, parameters, units and the range equation |
| 2 | Attenuation, impedance, reflection, refraction and decibels |
| 3 | Transducers, beams, focusing and resolution |
| 4 | Instrumentation, display, artifacts and quality assurance |
| 5 | Doppler, haemodynamics and bioeffects |
| 6 | Timed mock exams (110 questions in 2 hours) and weak areas |
1,000 SPI practice questions
The ARDMS Q Bank includes 1,000 SPI questions with calculations, artifacts and Doppler, plus 1,000 Abdomen and 1,000 OB/GYN, each fully explained.
Try free ARDMS questionsExam-day tips
- Pace yourself: about 65 seconds per question. Flag long calculations and return to them.
- Think in relationships: many questions ask what happens to one parameter when another changes. Know which are directly and inversely related.
- Know what the sonographer can change: output power, PRF and depth can be adjusted; frequency, period and propagation speed cannot be changed with the same transducer.
- Draw it: a quick sketch of the beam, pulse or Doppler angle prevents careless errors.
Frequently asked questions
How many questions are on the ARDMS SPI exam?
The SPI exam has approximately 110 multiple-choice questions to be answered in two hours. Inteleos lists the fee as US$275.
What score do I need to pass the SPI?
ARDMS exams are scored on a scale from 300 to 700, and a score of 555 or more is a pass. The score is not a simple percentage.
How long do I have between SPI and my specialty exam?
You must pass SPI and the matching specialty exam within five years of each other, in either order, to earn RDMS, RDCS, RVT or RMSKS.
What happens if I fail the SPI?
You can reapply after three days but must wait 60 days before sitting the exam again.
Can doctors from Pakistan take the SPI?
Yes. ARDMS has a physician prerequisite for MBBS, MD and DO holders with a current medical licence from any country and documented scanning experience. Check the current Inteleos prerequisites before applying.
What is the best way to study for SPI?
Learn the formulas and relationships first, then practise hundreds of exam-style questions, including calculations, artifacts and Doppler. Timed mock exams of 110 questions in 2 hours build pacing.