Choosing the Right Imaging Test: X-Ray, Ultrasound, CT or MRI?

Different imaging tests work in very different ways and are suited to different parts of the body and clinical questions. Choosing the wrong test can mean missing a diagnosis, repeating an unnecessary scan, or paying more out of pocket than you need to.

Your doctor will usually tell you which test to get, but understanding the options helps you ask better questions and know what to expect. This guide covers the four most common tests: X-ray, ultrasound, CT scan, and MRI.

X-rays use ionising radiation to produce a 2D image. Dense structures like bone appear white; soft tissue appears grey.

Best for: • Suspected fractures or broken bones • Chest conditions - pneumonia, fluid on the lungs, heart size • Dental problems (OPG/panoramic X-ray) • Arthritis and joint degeneration • Quick screening when something is clearly wrong

Not ideal for: • Soft tissue injuries (tendons, ligaments, muscles, cartilage) • Brain, spinal cord, or nerve problems • Abdominal organs in detail

Typical cost with Medicare: $0-$50 Typical duration: 5-10 minutes Referral required: Yes (for Medicare rebate)

Ultrasound uses high-frequency sound waves to create real-time images. There is no radiation - making it the preferred choice for pregnancy and in children.

Best for: • Pregnancy and foetal development • Abdominal organs - gallbladder, liver, kidneys, pancreas • Pelvic organs - uterus, ovaries, prostate, bladder • Tendons, muscles, and small joints (shoulder, Achilles, wrist) • Thyroid, breast lumps, and lymph nodes • Vascular studies - blood clots, arterial disease

Not ideal for: • Bone detail • Brain or spinal cord (blocked by bone) • Lungs • Deep structures obscured by bowel gas

Typical cost with Medicare: $0-$100 Typical duration: 20-40 minutes Referral required: Yes (for Medicare rebate)

A CT scan uses X-rays from multiple angles processed by computer to create 3D cross-sectional images. It's faster than MRI and gives excellent detail across large body areas.

Best for: • Trauma and emergencies - internal bleeding, organ damage, complex fractures • Chest and lungs - pulmonary embolism, cancer staging, lung nodules • Abdominal organs - appendicitis, kidney stones, bowel obstruction • Blood vessels - aortic aneurysm, coronary arteries (CT angiography) • Head injuries and stroke (quick screening) • Cancer staging and monitoring

Not ideal for: • Repeated imaging over time (radiation accumulates) • Soft tissue detail in joints (MRI is superior) • Pregnancy (radiation risk)

Typical cost with Medicare: $0-$200 Typical duration: 15-30 minutes Referral required: Yes (for Medicare rebate)

MRI uses magnetic fields and radio waves - no radiation. It provides the most detailed images of soft tissue, the brain, and spinal cord.

Best for: • Brain and spinal cord - tumours, MS, stroke, disc herniation • Joints and musculoskeletal - torn ligaments (ACL, rotator cuff), meniscus, cartilage • Prostate, uterus, and pelvic organs • Breast imaging (high-risk screening) • Cardiac structure and function • Any situation where detailed soft-tissue contrast is needed without radiation

Not ideal for: • Claustrophobic patients (though open scanners exist) • Metal implants that are not MRI-safe • When speed is critical (CT is faster) • Bone detail (CT or X-ray is superior)

Typical cost with Medicare: $0-$400 (higher out-of-pocket than CT in Australia) Typical duration: 30-75 minutes Referral required: Yes (for Medicare rebate)

Test | Best for | Radiation | Speed | Typical cost* X-ray | Bones, chest | Low | 5-10 min | $0-$50 Ultrasound | Soft tissue, pregnancy | None | 20-40 min | $0-$100 CT scan | Emergencies, chest, abdomen | Moderate | 15-30 min | $0-$200 MRI | Brain, joints, spine | None | 30-75 min | $0-$400

*With a valid Medicare referral. Costs vary significantly between clinics and scan types. Use Radly to compare prices near you.

If you're unsure which test your referral is for, read our guide on how to read your imaging referral.

Before leaving your doctor's office, ask:

• Why this test specifically - what are you looking for? • Is there a lower-cost or lower-radiation alternative that would answer the same question? • Is this scan bulk-billed, or will I have an out-of-pocket cost? • Do I need to fast or prepare in any special way? • How long until I get results, and who do I follow up with? • If you have claustrophobia or implants: Is an open MRI or alternative available?

You can also use Radly to compare imaging clinics near you and find the best combination of price, bulk billing, and availability for the scan your doctor recommends.