Most of us have experienced a CT or MRI scan as a patient and know little information about the scans or what they do. A common question asked by patients is what is the difference between a Computed Tomography (CT) and Magnetic Resonance Imaging (MRI). Both modalities are commonly used as diagnostic imaging techniques that produce images of the body to assist with diagnosis. A qualified Radiographer will operate a CT and MRI machine, whilst a Radiologist will interpret the scan to provide an accurate diagnosis.
The following information summarises the modalities by outlining the main differences between a CT and MRI scan:
- What it does:
A CT scan combines a series of x-ray images from different angles around the body and uses computer processing to create cross-sectional images (slices).
An MRI uses powerful magnetic fields and radio frequency pulses to produce images. The machine produces three dimensional detailed – anatomical images without the use of radiation.
- When is it used:
A CT scan provides excellent details of bony structures and can take a diagnostic image of soft tissues, bones and blood vessels at the same time. A CT scan can see different levels of bone density and tissues inside a solid organ and can provide detailed information about the body.
An MRI are well suited to image the non-bony parts or soft tissues of the body. The brain, spinal cord, nerves, muscles ligaments and tendons are seen more clearly with an MRI than with a CT. For this reason, an MRI is often used to image knee and shoulder injuries. The machine is often used for disease detection, treatment monitoring and to collect additional information to other tests such as an x-ray or ultrasound.
- Timeframe of scan:
The time required for a CT will depend on the scan which means it could be a few seconds to several minutes. Some scans can take 15 – 30 minutes, however generally a CT scan has faster scanning times than an MRI.
An MRI may take half an hour to an hour depending on the type of scan being requested. An MRI is noisy which can be off putting for the patient however head phones can be used to minimise the noise.
Radiation is used in a CT however the scans have become quicker and x-ray exposure has decreased providing better images at lower radiation doses. For example, today’s CT scan exposes patients to less radiation than what an airline passenger receives on one long-haul flight.
An MRI is a safe procedure and does not have any ionizing radiation whatsoever. It is the imaging modality choice when frequent imaging is required for diagnosis or therapy. Due to the strong magnetic field patients must notify their doctors of any form of medical or implant prior to an MRI scan.
- Patient Claustrophobic:
CT scans are a lot more comfortable for patients who are claustrophobic. An MRI can be quite stressful and unsettling for patients who suffer from mild claustrophobia. Patients may find it difficult to tolerate long scan times, particularly if they need to keep still during the imaging process in order to not blur the image. Some imaging providers can assist with sedation however this service would include having an Anaesthetist and Registered Nurse on site.
CT’s can vary in cost however a majority of imaging providers in Australia offer a bulk billing service. A CT scan is generally cheaper than an MRI if a cost is involved.
MRI’s can also vary in cost from $0 to $600 depending on whether the scan is rebateable from Medicare. If an MRI machine holds a full Medicare licence, certain MRI services can be bulk billed if referred by a GP and the referral meets the Medicare requirements. Otherwise a cost is required for both public and private patients and this can vary depending on the imaging provider.