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CT scans, PET scans and MRIs are all advanced internal imaging techniques that provide healthcare providers with valuable information about the health and function of your internal structures and tissues. Often these imaging tests are used in conjunction, to provide as much visibility as possible.
This article will outline what each kind of imaging test is and how it works, when and why they’re used and how to access and understand your results.
A positron emission tomography (PET) scan is considered nuclear medicine because PET scans use a radioactive sugar substance, usually injected by IV, to create detailed internal images. The radiotracer gathers in cells that require a lot of energy, emitting positively charged particles. Powerful cameras in the PET scanner record the position of the positrons and compile the recordings into colorful images.
PET scans provide visibility into both how organs and tissues look and how well they are working. Doctors use them to track the progress of diseases and treatments and to assess the function of major organs like the brain and heart.
A computed tomography (CT) scan uses multiple low-dose X-rays to create cross-sectional images which are then digitally compiled into a detailed 360° image. Each image is taken from one of three planes: the coronal (front to back); sagittal (left side to right); or axial (top to bottom).
CT scans are more common and less expensive than other advanced imaging techniques, which is why doctors often use them to locate and diagnose illnesses and injuries. They provide particularly detailed views of the skeletal structure.
Magnetic resonance imaging (MRI) uses a magnetic field and radio waves to capture internal images. Powerful magnets temporarily disrupt the alignment of the body’s protons, then radio waves restore alignment. A computer measures the energy and time it takes for the protons to resume alignment and uses those measurements to create images.
MRIs provide very clear images of soft tissues like muscles, ligaments and tendons, which doctors use to diagnose illness or injury.
PET SCAN | CT SCAN | MRI | |
Uses | Used to assess function, detect disease and monitor treatment | Used to detect and locate internal illness and injuries | Used to identify illness and injury in soft tissues |
Noise | Not very loud | Not loud | Can be loud |
Enclosed? | Not fully enclosed | Not enclosed, but movement can be restricted | Fully enclosed |
Duration | Can be very time consuming (1.5 - 2 hours) | Very fast (10-15 minutes) | Time consuming (45 minutes - 1 hour) |
Radiation | Small amounts of radiation remain in the body | X-rays pass through your body, but radiation does not remain in the body | Does not involve radiation |
During pregnancy | Can be risky during pregnancy | Generally safe during pregnancy | Safe during pregnancy |
These imaging tests have complementary strengths, which is why they are often used together.
PET scans track function as well as appearance. They involve a higher dose of radiation, as a radiotracer is injected directly into the body. Not every hospital has access to PET scanner machines.
CT scans are faster to perform, and CT scanner machines are more widely available. They use low dose radiation and are excellent for skeletal imaging.
MRI machines are much louder and more enclosed than either PET or CT scanner machines. MRIs provide highly detailed images of soft tissues and can catch early signs of disease CT scans might miss. MRIs do not use radiation.
With Pockethealth, you can keep all your medical images and reports in one secure location, and access them on any device. My Care Navigator can provide you with a list of questions to ask for each kind of image and report you receive.
Left: PET/CT scan; Right: MRI
Doctors often refer patients for more than one type of imaging test, to get as much interior visibility as possible. In some cases, a PET scan is performed at the same time as a CT scan.
In a PET/CT scan, the two types of imaging tests are performed at the same time, in the same machine. The CT scan creates detailed images from multiple X-rays, while the PET scan uses a radiotracer to detect metabolic activity. When taken together, the two scans give doctors increased visibility into the nature and progression of disease and treatment.
PET/CT scans are often used to monitor the progression and treatment of cancer. Together, the two tests provide detailed information about the disease at the cellular level.
The preparation for a PET/CT scan is the same as for a regular PET scan. If you are breastfeeding or pregnant, or if you take insulin for diabetes, inform the hospital or imaging clinic when your appointment is booked.
Check ahead of time to find out if there are any specific protocols for your scan. For more details, see our pages on CT scan and PET scan preparation.
To better understand the progression and treatment of disease, doctors might order another type of hybrid imaging test: a PET/MRI scan.
A PET/MRI combines a PET scan with an MRI during the same scan session, on the same machine. The PET scan tracks cell activity and function while the MRI examines the detail and structure of soft tissues.
A PET/MRI is often used to track the progression and/or treatment of cancer, heart conditions or neurological issues. PET/MRIs deliver less radiation exposure than PET/CT scans, so they are also used more frequently for children.
Preparation for a PET/MRI scan is also very similar to prep for a regular PET scan. Again, it is important to inform the imaging clinic if you are breastfeeding, pregnant or taking insulin for diabetes. When your appointment is booked, as if there are any special requirements for your specific case.
Be sure to ask ahead of time if there are any special requirements, dietary or otherwise, for your scan. For more information, see our page on MRI scan preparation.
The technician who takes your scan is not allowed to discuss the results with you. They can, however, answer any questions you have about the process. The results will be delivered to your referring physician.
The imaging technician sends your images to the radiologist for analysis. The radiologist creates a report and sends it and the images to your doctor, who may discuss them with you at a follow up appointment. The process generally takes 3-5 days but can often take longer.
For faster access, you can use PocketHealth to view your scan results as soon as they are released by the radiologist. PocketHealth gives you secure early access to see, share and store your scan results.
A patient uses PocketHealth Report Reader to understand their report
Imaging scan reports contain detailed medical terminology. Pockethealth’s Report Reader provides easy-to-understand definitions of complex medical terms.
Although you should always confer with your doctor, PocketHealth has a guide to help you understand how to read a radiology report. We also have specific information pages to help you read your:
PocketHealth gives patients the tools and access they need to take control of their health. My Care Navigator creates a personalized list of questions to help frame your follow-up discussion with your doctor and highlights any recommendations your report contains.
PocketHealth empowers you with valuable insights into your health, enabling you and your healthcare team to work together more efficiently. The more you understand, the better prepared you are to be proactive about the next steps in your health journey.
