Magnetic Resonance Imaging, commonly called MRI, is a non-invasive imaging test that uses a strong magnetic field, radiofrequency signals and computer processing to create detailed images of organs and tissues. Unlike CT and X-ray, MRI does not use ionising radiation.
MRI provides particularly detailed views of soft tissues and may be used to assess cancers affecting the brain, spine, head and neck, breasts, liver, pancreas, pelvis, prostate, rectum, female reproductive organs, bones and other parts of the body. Specialised techniques can also provide information about tissue cellularity, blood flow and other tumour characteristics.
MRI scanners are commonly available at magnetic field strengths of 1.5 Tesla and 3 Tesla, abbreviated as 1.5T and 3T. Both can produce high-quality cancer imaging, and the most appropriate scanner depends on the body area, clinical question, imaging protocol, patient factors and compatibility of any implanted devices.
Role in Cancer Care
What to Expect
Before the Test
Preparation varies according to the body area and imaging protocol. You can usually eat, drink and take regular medicines unless the care team provides different instructions.
Before the scan, inform the team if you:
Have a pacemaker, defibrillator, cochlear implant, neurostimulator, medicine pump or other implanted device
Have aneurysm clips, vascular stents, surgical clips or metal implants
May have metal fragments, bullets or shrapnel in your body, particularly near the eyes
Have undergone previous surgery or implantation of a medical device
Are pregnant or may be pregnant
Are breastfeeding
Have kidney disease or reduced kidney function
Have previously reacted to an MRI contrast agent
Experience claustrophobia or have difficulty remaining still
Have tattoos, medicine patches or wearable medical devices
Are taking prescription medicines, non-prescription medicines or supplements
Bring information identifying any implant or device, including its model and MRI safety documentation, if available. Many modern implants are MR Conditional, meaning MRI may be performed only under specified conditions, which can include the permitted field strength. The MRI team must confirm compatibility before you enter the scanning area.
If gadolinium contrast is planned, a kidney-function blood test may be required, particularly if you have known kidney disease or relevant risk factors. Remove jewellery, watches, hearing aids, removable dental work, mobile phones, cards and other metallic or electronic items as instructed.
Tell the team in advance if you are anxious in enclosed spaces. Additional preparation, a wider-bore scanner or sedation may be considered when appropriate. If sedation is planned, you will receive fasting instructions and must arrange for someone to accompany you home.
During the TestÂ
You will lie on a motorised table, and a specialised receiving coil may be placed around or near the body area being examined. Padding and supports may be used to help you remain comfortable and still.
The table moves into the MRI scanner, which is shaped like a tunnel. The machine produces loud knocking, tapping and buzzing sounds while images are acquired. You will be given earplugs or headphones for hearing protection.
It is important to remain still, as movement can blur the images. For some examinations, you may be asked to hold your breath briefly. The technologist will be able to see, hear and communicate with you throughout the scan, and you will be given a call device to request assistance.
If contrast is required, a cannula will be inserted into a vein in the hand or arm. Images may be taken before, during and after the contrast injection.
MRI is painless, although remaining in one position or being inside the scanner may cause discomfort or anxiety. The area being examined may feel slightly warm. Tell the technologist immediately if you experience excessive heating, burning, pain, dizziness, breathing difficulty or another unusual sensation.
Most MRI examinations take approximately 30 to 60 minutes, but specialised or multiparametric studies may take longer.
After the Test
If you have not received sedation, no recovery period is usually required. You can generally return to normal activities and resume your usual diet immediately.
If contrast was administered, the cannula will be removed before you leave. You may be advised to drink fluids unless you are on fluid restriction or have received different instructions.
If you received sedation, you will be monitored until it is safe to leave. You must not drive, operate machinery or make important decisions until the effects have worn off, as advised by the care team.
A radiologist will examine the images, compare them with previous studies and prepare a report. The findings will be considered together with pathology results, clinical information and other investigations.
Potential Benefits
- Detailed soft-tissue imaging: MRI can distinguish between different types of soft tissue and show tumour boundaries.
- Multiplanar views: Images can be acquired or reconstructed in different planes without repositioning the patient.
- No ionising radiation: MRI uses magnetic fields and radiofrequency signals rather than X-rays.
- Local staging: It can help assess involvement of nearby organs, muscles, nerves, blood vessels and other structures.
- Specialised tumour assessment: Diffusion, perfusion, contrast-enhanced and multiparametric techniques can provide additional information about tumour characteristics.
- Treatment planning: MRI may support surgery, radiation therapy, biopsy and selected image-guided treatments.
- Response monitoring: Changes in tumour size and imaging characteristics can help assess treatment response.
- Versatile field strengths: Both 1.5T and 3T systems can support high-quality oncology imaging using protocols selected for the individual patient and clinical question.
