Magnetic resonance imaging (MRI) has proven to be a very important tool for discovering many forms of cancer. From diagnosis to evaluating the efficacy of treatment, visualizing a tumor allows physicians to gather real-time information about the behavior of a specific cancer.
Magnetic resonance imaging uses magnets and radio waves to move electrons in human tissue which allows the tissue to be visualized. As each tissue in the body has a specific frequency that can be detected, each tissue produces a specific resonance that can be collected and formed into an image. Fatty tissues and muscular tissues produce different frequencies when placed in a magnetic field, so each of these tissues will have a distinct pattern of resonance. Those patterns are transformed into an image by converting these frequencies into visual patterns. This also allows normal tissues to be differentiated from abnormal tissues. Normal bone and muscles will appear dissimilar than those with tumors. As there is no radiation with an MRI, these tests can be performed as often as needed without affecting a patient’s overall body exposure to radiation. This can be very important in those patients that may be utilizing radiation for the treatment of their tumor.
Some tumors have a specific appearance on an MRI that allows physicians to make a diagnosis immediately. These diagnostic criteria may relate to the visual patterns of the tissue or to the specific location of the tumor in an organ. MRI scans provide a more accurate diagnostic tool for soft-tissue tumors than does x-ray imaging or CT scanning. Tumors that evolve purely from muscles, tendons or nerves will be seen on a CT scan as a mass, while the MRI is able to show the nature of the mass and distinguish the mass from the surrounding tissues. In cases where the tumor has leaked from a bone structure, the MRI will provide visual images of the extent of the tumor into the soft-tissues surrounding the bone. These images give the physician more accurate information about the expansion of a tumor from its original site. Soft-tissue sarcomas, lipomas, blood vessel tumors and nerve tumors are well-visualized on an MRI. The MRI may also help to determine if the tumor is benign or malignant by its pattern or growth.
MRI is very helpful in differentiating tumors from fractures in bone by their specific patterns of fat and water content. As patients with cancers can lose their bone mass, making the bones more fragile. Fractures may occur from minor incidents, like coughing or sitting down too hard and sometimes patients cannot remember a specific incident. Patients with cancer can develop pain in bones from either a fracture or a new tumor. Defining whether a finding on an x-ray or CAT scan is a new tumor or a fracture can be done with an MRI. Generally, tumors are seen where there is good blood supply in the bone. Knowing the location of the arteries that supply nutrition to the bones helps to determine the most likely pattern of a tumor deposited there. Particularly in metastatic tumors, if some of the tumor’s cells are able to enter the bloodstream, they will travel to portions of the body that filter the blood. At these filter areas, tumor cells will get stuck and start to form a new site for the original tumor (metastasis). As this pattern of spread is blood-flow related, these new tumors will grow in those areas where the greatest blood flow occurs. Fractures however, occur where the bone is weakest. This pattern is where the blood flow is least, or the least amount of nutrition is getting to the bone. These patterns allow physicians to make a determination about the likelihood of a specific finding on an MRI to be related to a tumor or a fracture.
MRI has long been used in orthopaedics for diagnosis and treatment of bone, tendon and cartilage disorders. This technology can also be very beneficial to the diagnosis and treatment of tumors that arise from any tissue in the body, from brain to bone. Because it adds a more accurate picture of the tissue in a particular mass, MRI is not just for orthopedics anymore.