X-ray, ultrasound, CT, MRI, PET-CT: what each scan does

By Dr. Mark Bekhit, Radiologist · Last updated July 2026

Short answer: X-ray and ultrasound are the everyday scans — most radiology clinics offers both, and ultrasound uses no radiation at all. CT is a detailed, three-dimensional X-ray done at most larger clinics and hospitals. MRI (magnets, no radiation) is listed by about 486 Australian clinics, and PET-CT (a tracer scan showing how tissue functions) by about 140, as at July 2026. One reliable rule: a clinic providing Medicare MRI or PET must also run X-ray, ultrasound and CT — the advanced sites do everything.

• What does each scan actually show?
• Which clinics can do which scans?
• Which scans use radiation, and how much?
• Who can refer you for each scan?
• How to use this when you book
• Common questions about the five scan types
• How we know: sources and method

What does each scan actually show?

Each of the five common scans makes its picture a different way, and that physics decides what it is good at.

MRI and PET-CT numbers are clinic listings in our directory as at July 2026; the other three are offered so widely that a count adds nothing.

X-ray: the fast first look

An X-ray beam passes through the body; bone absorbs a lot of it and shows up light, soft tissue absorbs little and shows up dark. That makes X-ray the right first test for fractures, arthritis, pneumonia, heart failure and bowel blockage, and it is quick — a chest X-ray can take under a minute, the whole visit usually under 15 (InsideRadiology, healthdirect).

Ultrasound: sound, not radiation

A sonographer slides a probe over gelled skin; the echoes of high-frequency sound waves become a live moving image. It uses no radiation and is considered safe even in pregnancy, so it is the workhorse for obstetrics, abdominal organs, tendons and muscles, breast lumps and blood-flow studies (InsideRadiology, healthdirect). Because it images movement, it is also the preferred test for babies and children.

CT: an X-ray in fine slices

A CT scanner rotates an X-ray beam around you and rebuilds slices — often thinner than 1 mm — into three-dimensional pictures of the head, chest, abdomen or spine (InsideRadiology). It is fast and detailed, which makes it the emergency department’s favourite tool, and many CTs use an injected iodine contrast dye to show blood vessels and organs. The trade-off is a higher radiation dose than a plain X-ray (healthdirect).

MRI: magnets for soft-tissue detail

MRI builds its image from a strong magnet and radio waves — no X-rays at all — and is often the best test for the brain, spine, knee and other joints, and anything where soft-tissue detail decides the diagnosis (InsideRadiology, healthdirect). The catch is practical: the scan is slower, the tunnel is noisy, and certain pacemakers and implants rule it out, so every MRI starts with a safety questionnaire.

PET-CT: function, not just structure

A PET-CT is the odd one out: you are injected with a mildly radioactive sugar tracer, and cells that are metabolically active — cancer, most importantly — light up. As healthdirect puts it, a PET scan shows how the body is working, unlike other scans, which only show its structure. The CT half pinpoints exactly where the activity is. Our PET-CT guide covers the eligible cancers, costs and scan day in detail.

Which clinics can do which scans?

Radiology clinics sit on a capability ladder, and the rungs are predictable. X-ray equipment is widely available in hospitals, X-ray clinics and other locations, even in remote areas — a small suburban practice with one X-ray room can handle most referrals for bones and chests (InsideRadiology). Ultrasound sits alongside it: it is done in hospitals and private radiology practices, and because the equipment is portable and inexpensive to operate it can be carried out in a variety of places (InsideRadiology). CT sits one rung up: it is carried out at most hospitals and private radiology practices in Australia, though specialised versions — heart (coronary) CT, CT colonography, scans of babies and young children — are not offered everywhere (InsideRadiology).

MRI and PET-CT are where availability genuinely narrows. About 486 clinics list MRI in our directory and about 140 list PET-CT, as at July 2026 — and PET-CT sites cluster around hospitals and specialised centres (healthdirect). The Department of Health publishes the official lists of Medicare-eligible MRI and PET locations, which is worth checking for MRI because not every machine is Medicare-eligible yet; our MRI and Medicare guide explains the eligibility rules and what changes on 1 July 2027.

Here is the rule that makes the ladder useful when you are choosing where to book. Medicare requires both MRI and PET to be provided at what the regulations call a comprehensive practice — “a medical practice, or a radiology department of a hospital, that provides X-ray, ultrasound and computed tomography services”. That definition sets the eligible sites for MRI (MBS MRI equipment factsheet) and for PET (MBS, item 61563 notes). In practice: a clinic advertising Medicare MRI or PET-CT can also do your X-ray, ultrasound and CT on the same site. The reverse is not true — plenty of excellent clinics stop at CT.

Which scans use radiation, and how much?

Two of the five use no ionising radiation at all: ultrasound and MRI (InsideRadiology). That is why they are preferred for children, who are more sensitive to radiation, whenever they can answer the referrer’s question.

For the others, the useful yardstick is background radiation: living in Australia exposes you to an estimated 2 millisieverts a year — roughly the equivalent of 100 chest X-rays (InsideRadiology). A single plain X-ray adds a small fraction of that. CT delivers more than plain X-ray or mammography, which is why your doctor weighs it rather than ordering it reflexively (healthdirect). PET-CT adds a tracer dose on top of its CT component, and the tracer makes you slightly radioactive for a short time afterwards — a nuclear-medicine feature X-ray and CT never have, since those scans leave no radiation in your body (InsideRadiology).

The honest framing for all of them: the added cancer risk from a diagnostic dose is small, and usually smaller than the risk of leaving a real problem undiagnosed. If a CT or PET-CT has been requested for you, the question worth asking your referrer is not “is there radiation?” but “what will this scan change about my treatment?” — a scan that changes nothing is the one to skip.

Who can refer you for each scan?

For X-ray, ultrasound and CT, any doctor — including your GP — can write the request (MBS note IN.0.6). This is why these three feel so accessible: same-week appointments on a GP referral are normal.

MRI is different. Most adult MRI items require a specialist or consultant physician request; a GP referral earns a Medicare rebate only for a short list of items (MBS note IN.0.18). The clearest example: a GP can request a rebatable knee MRI after acute trauma only for patients aged 16–49 with signs of an acute meniscal or ACL tear (item 63560). PET is stricter still — Medicare-rebatable PET requires a specialist or consultant physician request, full stop (MBS).

Whether Medicare pays, and how much, is its own topic with per-modality rules; our guide to which scans Medicare covers works through requester rights, rebates and bulk billing modality by modality. And if your real question is whether you need an MRI or a CT for the same body part, that decision has its own logic — see MRI vs CT: which do you need?

How to use this when you book

Plan your time around the modality. An X-ray visit is usually under 15 minutes. An ultrasound runs about 20 to 30 minutes and is appointment-based (healthdirect, InsideRadiology). A CT spends under 10 minutes in the scanner but the preparation often takes longer than the scan. MRI runs from about 10 minutes to over an hour depending on the body part. PET-CT is a half-day: about 90 minutes resting after the tracer injection, then a 15–20 minute scan (healthdirect).

Preparation follows the same pattern. X-ray needs none. Ultrasound depends on the scan — commonly 8 hours fasting for an abdominal study, or 750 mL of water an hour beforehand for a pelvic or kidney scan; our ultrasound preparation guide covers each type. Contrast CT usually means 2–4 hours of fasting, and the clinic will ask about kidney function and diabetes before injecting the dye (InsideRadiology). MRI means completing the safety questionnaire honestly — pacemakers, aneurysm clips, cochlear implants and metal fragments in the eye all matter, and paperwork about your implant speeds everything up.

Two more things worth knowing. First, a referral form printed with one company’s logo does not bind you: as Services Australia puts it, “You are free to choose your own provider as long as they offer the scan you need.” Compare CT clinics in Melbourne or PET-CT clinics in Brisbane the way you would any other service. Second, providers set their own fees — so when you book, ask the clinic two specific things: is the item on my referral bulk billed here, and if not, what will I pay on the day?

Common questions about the five scan types

Is ultrasound safer than an X-ray?

Ultrasound uses sound waves and no ionising radiation, so there is no radiation dose to weigh at all. An X-ray’s dose is real but small — for scale, background radiation in Australia is about 2 mSv a year, roughly 100 chest X-rays’ worth (InsideRadiology). Both are considered safe tests; they answer different questions.

Why did my GP order an X-ray instead of an MRI?

Usually because it is the right sequence, not a compromise. X-ray answers most bone and chest questions in minutes at nearly any clinic, while most adult MRI items need a specialist request before Medicare contributes (MBS note IN.0.18). A normal or clear X-ray often makes the MRI unnecessary.

Can I swap my CT referral for an MRI?

Not on your own — the referral names a specific test and Medicare item, and the two scans answer different questions. If you would rather avoid radiation or think MRI suits your problem better, raise it with your referrer, who can reissue the request if it is clinically right. The trade-offs are worked through in our MRI-versus-CT guide.

Will a PET-CT make me radioactive?

Slightly, and briefly. PET is a nuclear-medicine test: the injected tracer makes you weakly radioactive for a short time after the scan, unlike X-ray and CT, which leave no radiation in your body (InsideRadiology). Clinics give specific after-scan instructions — our PET-CT guide covers scan day in full.

Does every MRI or PET clinic also do X-ray, ultrasound and CT?

If it provides those scans under Medicare, yes. The MBS requires both MRI (MBS MRI factsheet) and PET (MBS item 61563) to be provided at a comprehensive practice — “a medical practice, or a radiology department of a hospital, that provides X-ray, ultrasound and computed tomography services”. So the most advanced clinic near you can handle your simplest scan too.

Related reading: Which scans does Medicare cover? · MRI vs CT: which do you need? · Radiology wait times: public vs private

How we know: sources and method

The clinical descriptions of each scan come from InsideRadiology (the Royal Australian and New Zealand College of Radiologists’ patient site) and healthdirect, cross-checked against each other; the referral and comprehensive-practice rules are quoted from the Medicare Benefits Schedule; and the choose-your-provider and fee facts come from Services Australia. All sources were accessed on 7 July 2026. The MRI (about 486) and PET-CT (about 140) figures are clinic listings published in our directory as at July 2026 — a reliable guide to where each scan is offered, not a guarantee that every item is rebatable at a given site.

• InsideRadiology — Plain radiograph/X-ray (accessed 7 July 2026)
• InsideRadiology — Ultrasound (accessed 7 July 2026)
• InsideRadiology — Computed tomography (CT) (accessed 7 July 2026)
• InsideRadiology — Magnetic resonance imaging (MRI) (accessed 7 July 2026)
• InsideRadiology — Radiation risk of medical imaging (accessed 7 July 2026)
• healthdirect — X-rays; Ultrasound; CT scan; MRI scan; PET scan (accessed 7 July 2026)
• MBS item 61563 and associated notes; item 63560; note IN.0.6; note IN.0.18; MBS factsheet — Medicare eligibility for MRI equipment (accessed 7 July 2026)
• Department of Health — Medicare-eligible MRI and PET locations (accessed 7 July 2026)
• Services Australia — Screening tests and scans covered by Medicare (accessed 7 July 2026)

Whichever scan you end up needing, you can compare the clinics that offer it near you: radiology clinics in Sydney, Melbourne, Brisbane and Perth.

This article is general information, not personal medical advice. Availability, Medicare eligibility, billing and preparation can change — confirm the specifics with your referrer and the clinic.

Author: Dr. Mark Bekhit

Dr Mark Bekhit (MBChB, FRANZCR) is a musculoskeletal radiologist practising in Brisbane and an AHPRA-registered specialist in diagnostic radiology (MED0002920947). He spends as much time building software as reading scans: he founded Imaging Finder (Australia) and Radiology Clinics NZ to make imaging easier to find, and builds radiology dictation and pain-tracking tools with one aim — better patient outcomes and a smoother reporting workflow. Outside the reading room he's usually training, bringing the same performance mindset to imaging.