Magnetic resonance imaging (MRI) scan
Like CT scans, MRI scans give detailed images of soft tissues in the body. But MRI scans use radio waves and strong magnets instead of x-rays to create pictures. A contrast material might be injected, just as with CT scans, but is used less often.
MRI scans are very helpful in looking at the brain and spinal cord.
MRI scans take longer than CT scans – often up to an hour – and are a little more uncomfortable. You may have to lie inside a narrow tube, which is confining and can upset people with a fear of enclosed spaces. Newer, more open MRI machines can sometimes be used instead, but the images might not be as sharp in some cases. The MRI machine also makes loud buzzing noises, so some places provide earplugs to help block this noise out.
Positron emission tomography (PET) scan
A PET scan can help show if the cancer has spread to lymph nodes or other parts of the body. It is most useful in people with more advanced stages of melanoma – it is not usually done in people with early-stage melanoma.
For this test, you are injected with a radioactive substance (usually a type of sugar related to glucose, known as FDG). The amount of radioactivity used is very low and will pass out of the body over the next day or so. Because cancer cells in the body are growing quickly, they absorb more of the radioactive sugar. After about an hour, you are moved onto a table in the PET scanner. You lie on the table for about 30 minutes while a special camera creates a picture of areas of radioactivity in the body. The picture is not detailed like a CT or MRI scan, but it can provide helpful information about your whole body.
Many centers have special machines that can do both a PET and CT scan at the same time (PET/CT scan). This lets the doctor compare areas of higher radioactivity on the PET scan with the more detailed appearance of that area on the CT scan.
For more information on these imaging tests, see our document Imaging (Radiology) Tests.
Blood tests
Blood tests aren’t used to diagnose melanoma, but some tests may be done before or during treatment, especially for more advanced melanomas.
Doctors often test blood for levels of a substance called lactate dehydrogenase (LDH) before treatment. If the melanoma has spread to distant parts of the body, a high LDH level is a sign that the cancer may be harder to treat. This affects the stage of the cancer (see “How is melanoma skin cancer staged?”).
Other tests of blood cell counts and blood chemistry levels may be done in a person who has advanced melanoma to see how well the bone marrow (where new blood cells are made), liver, and kidneys are working during treatment.
