Comparing MRI, CT, and PET Scans: How They Work and When They’re Used

UNC Health Appalachian offers imaging services in the Schaefer Family Patient Care Tower on the campus of Watauga Medical Center in Boone and Cannon Memorial Hospital in Linville. We offer three advanced technologies – Magnetic Resonance Imaging (MRI), Computed Tomography (CT), and Positron Emission Tomography (PET) – each offer unique benefits and insights into the human body, aiding in the diagnosis and treatment of various conditions. MRI leverages magnetic fields and radio waves to produce high-resolution images of soft tissues, making it invaluable for neurological and musculoskeletal assessments. CT scans provide detailed cross-sectional images using X-rays, ideal for visualizing bone structures and detecting trauma. PET scans, use radioactive tracers to visualize metabolic activity in real-time, allowing for early detection of diseases such as cancer and evaluating organ function. This article explores the distinct features, advantages, and applications of MRI, CT, and PET scans, helping to clarify how each contributes to comprehensive patient care.

MRI

What is it and how does it work?

An MRI (magnetic resonance imaging) scan is a painless procedure that provides detailed images of the organs and structures inside your body. An MRI passes an electric current through coiled wires to create a temporary magnetic field in your body. A transmitter/receiver in the machine then sends and receives radio waves. The computer then uses these signals to make digital images of the scanned area of your body.

What does it show?

Healthcare providers can view and evaluate several different structures inside your body including:

• Brain and surrounding nerve tissue
• Organs in your chest and abdomen, including your heart, liver, biliary tract, kidneys, spleen, bowel, pancreas and adrenal glands
• Breast tissue
• Spine and spinal cord
• Pelvic organs, including your bladder and reproductive organs (uterus, ovaries and prostate gland)
• Blood vessels
• Lymph nodes

What should I expect during?

A radiology technologist typically performs the MRI scan. After the scan, a radiologist will analyze the MRI results and provide a report to your referring physician. The MRI scan generally takes between 30 to 50 minutes, though the exact time can vary depending on the specific type of MRI and the area being examined. While the scan is painless, some people find it challenging to stay still for the duration. The enclosed nature of the MRI machine can also cause discomfort or anxiety for those who are claustrophobic. MRI machines can be quite noisy, often producing loud tapping or thumping sounds during the scan.

Pros

• MRI scans are safe since they don’t use the damaging ionizing radiation of X-rays.
• MRI scans also take much clearer pictures of your brain, spinal cord, nerves, muscles, ligaments and tendons than regular X-rays and CT scans.
• Can be used with contrast to improve the diagnostic images.

Cons

• A very slight risk of an allergic reaction if your MRI requires the use of contrast material. These reactions are usually mild and controllable by medication.
• Not everyone can undergo an MRI. The magnetic field of MRI can displace metal implants or affect the function of devices such as pacemakers and insulin pumps. If this is the case, a CT scan is the next best option.
• MRI scanning is usually more expensive than X-ray imaging or CT scanning.
• Healthcare providers generally don’t perform gadolinium contrast-enhanced MRIs on pregnant patients due to unknown risks to the developing baby unless it’s necessary.¹

CT

What is it and how does it work?

A CT (computed tomography) scan takes multiple X-ray images from different angles around the body. These images are then processed by a computer to create cross-sectional views of the body. Unlike a single X-ray image, which provides a 2D view, a CT scan combines these multiple images to produce detailed 3D images. This allows for a clearer and more precise visualization of internal structures, including bones, organs, and soft tissues.

What does it show?

A CT scan takes pictures of your:

• Bones
• Muscles
• Organs
• Blood vessels

What should I expect during?

A radiology technologist typically performs the CT scan. After the scan, a radiologist will analyze the CT results and provide a report to your referring physician. The actual scan usually takes about 10 to 15 minutes. However, preparation time can be longer, around an hour, depending on factors like the need for contrast material or specific instructions given by your healthcare provider. It’s crucial to hold still during the scan, and you may also need to hold your breath for short periods (typically 15 to 20 seconds) to avoid blurring the images. Unlike an MRI scan, a CT scan is silent. During the scan, you’ll lie on a table that moves through a large, doughnut-shaped machine. The machine rotates around you, taking X-ray images from various angles. The table may move in and out of the scanner during the procedure.

Pros

• Painless and noninvasive
• Very little risk
• Help providers detect a wide range of health conditions
• Can be used with contrast to highlight certain areas

Cons

• Like X-rays, CT scans use a small amount of ionizing radiation to capture images.
• Some people develop minor side effects from contrast materials, which may include nausea and vomiting, headaches and dizziness
• If you’re pregnant or think you might be pregnant, you should tell your provider. CT scans of your pelvis and abdomen can expose the developing fetus to radiation, but it’s not enough to cause harm. CT scans in other parts of your body don’t put the fetus at any risk.²

PET

What is it and how does it work?

Positron emission tomography (PET) scans detect early signs of cancer, heart disease and neurological disorders. They provide information about the metabolic activity of tissues, which can be crucial for diagnosing and evaluating the progression or response to treatment. The procedure involves injecting a small amount of a radioactive tracer (radiotracer) into your bloodstream to detect diseased cells. The scanner detects diseased cells that absorb large amounts of the radiotracer, which indicates a potential health problem.

What does it show?

Your healthcare provider may order a PET scan to check for signs of:

• Cancer, including breast cancer, lung cancer and thyroid cancer
• Coronary artery disease, heart attack or other heart problems
• Brain disorders, such as brain tumors, epilepsy, dementia and Alzheimer’s disease

What should I expect during?

A radiology technologist typically performs the PET scan. After the scan, a radiologist will analyze the PET results and provide a report to your referring physician. The entire PET scan process takes about two hours. It will take up to 60 minutes for your body to absorb the injected radiotracer. During that time, you will need to sit quietly and limit movements. The actual imaging portion of the PET scan usually takes about 30 minutes. During this time, you’ll lie on a table that moves slowly through the PET scanner, which is shaped like a large doughnut. The table will move in and out of the scanner as the machine captures images. The doughnut-shaped tunnel open is typically about 30 inches in diameter. While this is spacious, some people may still feel a bit enclosed. If you have concerns about claustrophobia, let the technologist know beforehand, as they may offer strategies to help you feel more comfortable. It’s crucial to stay as still as possible during the scan to avoid blurring the images. The scanner may make buzzing or clicking sounds as it takes pictures. These noises are normal and are part of the scanning process.

Pros

• A very useful imaging test that healthcare providers use to assess cancer, heart issues and brain conditions

Cons

• The amount of radiation in the radioactive tracer is very low. It doesn’t stay in your body for long. You should drink lots of water after a PET scan to help flush the radioactive drug from your body.
• People who are pregnant, or breastfeeding should not get PET scans.
• Some people have an allergic reaction to PET scan radioactive tracers. These allergic reactions are infrequent and usually mild.
• People with diabetes may not absorb the sugar in the radiotracer, which can affect scan results.³

What’s the difference between an MRI, CT scan, and PET scan?³

MRI scans use magnets and radio waves. CT scans use X-rays. Both produce still images of organs and body structures. PET scans use a radioactive tracer to show how an organ is functioning in real time. PET scan images can detect cellular changes in organs and tissues earlier than MRI and CT scans. A PET scan and CT scan can be performed simultaneously (PET/CT) and produce 3D images that allow for a more accurate diagnosis. Each type of imaging has its strengths and is chosen based on the specific clinical needs. Combining these technologies can offer a more comprehensive view, helping healthcare providers make more accurate diagnoses and tailor treatment plans effectively.³

New imaging service offered at Watauga Medical Center

The uMI® 550 is an all-digital, first-of-its-kind PET/CT platform that delivers an unparalleled increase in sensitivity while maintaining the highest specificity. When you need answers, the uMI® 550 PET/CT exam helps inform the next steps in your care.

• Greater Sensitivity
• Enhanced Workflow
• Increased Accessibility

These imaging technologies ensure accurate and timely diagnoses, which are crucial for effective treatment planning. To access these specialized imaging services, a referral from your healthcare provider is required. This referral ensures that the appropriate imaging study is chosen based on your specific medical needs, enabling us to deliver targeted and effective care.

We are dedicated to delivering exceptional care by utilizing state-of-the-art imaging services and advanced technology in the High Country. Our commitment to excellence is reflected in our continuous efforts to provide the highest quality diagnostic imaging while maintaining a compassionate and patient-centered approach.

1. https://my.clevelandclinic.org/health/diagnostics/4876-magnetic-resonance-imaging-mri
2. https://my.clevelandclinic.org/health/diagnostics/4808-ct-computed-tomography-scan
3. https://my.clevelandclinic.org/health/diagnostics/10123-pet-scan