The SPI exam is the same for everyone — but it's only half of what you need. To earn an ARDMS credential, you also need to pass at least one specialty exam corresponding to that credential, and the four credential paths (RDMS, RDCS, RVT, and RMSKS) lead to meaningfully different careers. Here's how they break down.
A key structural point that applies to all four: you must pass the SPI exam and at least one corresponding specialty exam within five years of each other, and they can be taken in either order. Once you've earned one ARDMS credential, you can add additional specialties later without retaking the SPI exam, as long as your certification stays active.
RDMS — Registered Diagnostic Medical Sonographer
The broadest of the four credentials, covering general diagnostic ultrasound. RDMS pairs with several specialty exams, including Abdomen, Breast, Obstetrics & Gynecology, Fetal Echocardiography, and Pediatric Sonography. Most general sonographers working in hospital imaging departments, OB/GYN clinics, or outpatient imaging centers hold an RDMS with one or more of these specialties.
Good fit if: you're drawn to general diagnostic imaging — abdominal, pelvic, obstetric — and want the widest range of work settings. Many sonographers start here because the Abdomen and OB/GYN specialties are commonly offered and align closely with general sonography training programs.
RDCS — Registered Diagnostic Cardiac Sonographer
Focused on cardiac imaging. RDCS pairs with Adult Echocardiography, Pediatric Echocardiography, or Fetal Echocardiography. This is the credential path for echocardiography — imaging the heart's structure and function, often in cardiology departments or dedicated echo labs.
Good fit if: you're interested in cardiac anatomy and function specifically, and want to work in cardiology rather than general imaging. Adult Echocardiography is the most common entry point.
Note: Fetal Echocardiography (FE) can be pursued under either RDMS or RDCS — but once you take the FE exam under one credential area, it cannot be switched to the other.
RVT — Registered Vascular Technologist
Focused on vascular imaging. RVT pairs with the Vascular Technology (VT) specialty exam, covering arterial and venous studies — carotid duplex, venous duplex for DVT evaluation, abdominal vascular imaging, and peripheral arterial studies, among others.
Good fit if: you're interested in vascular physiology and want to work in a vascular lab, often within cardiology, surgery, or dedicated vascular diagnostic departments. Vascular sonography is also one of the more procedure-and-protocol-driven specialties, with a strong emphasis on standardized exam techniques.
RMSKS — Registered Musculoskeletal Sonographer
The newest and most specialized of the four, RMSKS pairs with the Musculoskeletal Sonographer (MSKS) exam, covering ultrasound imaging of tendons, ligaments, muscles, joints, and nerves — commonly used in orthopedics, sports medicine, rheumatology, and physical medicine settings.
Good fit if: you're working in or interested in orthopedic or sports medicine settings, where musculoskeletal ultrasound is increasingly used for both diagnosis and guided procedures (such as joint injections).
Side-by-side comparison
| Credential | Specialty exams available | Typical setting |
|---|---|---|
| RDMS | Abdomen, Breast, OB/GYN, Fetal Echo, Pediatric Sonography | General imaging, OB/GYN clinics, hospitals |
| RDCS | Adult Echo, Pediatric Echo, Fetal Echo | Cardiology departments, echo labs |
| RVT | Vascular Technology | Vascular labs, surgery, cardiology |
| RMSKS | Musculoskeletal Sonographer (MSKS) | Orthopedics, sports medicine, rheumatology |
What about the specialty exam itself?
Specialty exams are separate from the SPI and test clinical knowledge specific to that area — anatomy, pathology, scanning protocols, and image interpretation — rather than physics and instrumentation. They're generally longer than the SPI exam, commonly around 150 questions over roughly three hours, though the exact format can vary by specialty, so check the current details for your specific exam on the ARDMS website when you're ready to register.
Because SPI is shared across all four paths, many candidates take it first — while general physics concepts are still fresh — and then focus their specialty exam study on the clinical content specific to their chosen path. This is also why SonoPrep is built around the SPI: it's the common first step for every ARDMS credential, regardless of which specialty you eventually pursue.
Not sure which specialty fits your career plans? Talk to sonographers and program faculty in the settings you're considering — clinical exposure to a specialty during your training is often the best signal for whether you'll enjoy the day-to-day work, beyond just the exam content.