What the SPI exam is, what it covers, how it fits into earning a credential, and the timing rule that surrounds it.
The SPI exam — Sonography Principles and Instrumentation — is the physics exam at the center of ARDMS certification. Every primary credential from the American Registry for Diagnostic Medical Sonography (ARDMS) requires passing it, whatever the specialty (ARDMS). It is also the exam prospective sonographers worry about most, because it covers the physics and machine principles behind the images rather than the anatomy of any one specialty.
What the SPI covers
The SPI tests the science of how ultrasound works: the physics of sound waves, how transducers create and receive them, how the machine builds an image, how Doppler measures blood flow, the factors that affect image quality, the safety principles that keep exposure low, and the quality-assurance checks that keep equipment accurate. It is the shared foundation under every specialty — the abdominal, cardiac, and vascular exams all assume a sonographer understands this material.
How it fits with a specialty exam
Passing the SPI alone does not grant a credential. An ARDMS credential requires the SPI plus a specialty exam — for example, SPI plus Abdomen to earn the RDMS, or SPI plus a cardiac exam to earn the RDCS (ARDMS). The two exams can be taken in either order. Some students take the SPI first to clear the physics early; others take the specialty exam first.
The five-year rule
The two exams are linked by timing. Once an applicant passes the first of the two — whether it is the SPI or the specialty exam — the second must be passed within five years (ARDMS). Missing that window means the first result no longer counts toward the credential. This is why many students plan the two exams close together rather than spacing them far apart.
Cost and preparation
The SPI exam fee is $275, which includes a $100 non-refundable processing fee; ARDMS also offers paid practice tests at $50 each (ARDMS, 2026). The physics material is a common source of test anxiety, and practice exams are widely used to prepare. Prerequisites — usually completion of an accredited program — must be met before sitting; Accreditation covers why.
Last verified: 2026-06-14. Exam fees and content outlines change; confirm current details with ARDMS before registering. This page is informational and does not recommend a preparation product or program.