Magnetic Resonance Imaging (MRI)
Additionally, the MRI provides greater contrast between the different soft tissues of the body than a CT scan. Thus, it is especially useful for imaging the brain, connective tissue, spine, muscles, and the inside of bones. To perform the scan the patient lies within a large device that creates magnetic field that aligns the magnetization of atomic nuclei in the body.
MRI tests are painless and there is no radiation involved. It takes much longer than a CT scan and is more expensive. Some patients report feelings of mild to severe anxiety and/or restlessness during the test. A mild sedative before the test can be administered to those who are claustrophobic or find it difficult to lie still for long periods of time. MRI machines produce loud banging, thumping, and humming sounds. Wearing earplugs can reduce the effect of noise.
CT of the head and neck showing a cystic lesion
PET scan is a nuclear medicine imaging test that creates a three-dimensional image or picture of the functional metabolic processes in the body. It uses a radioactive substance called a "tracer" that is administered through a vein to look for disease in the body. The tracer travels through the blood and collects in organs and tissues with high metabolic activity. A single PET scan can accurately image the cellular function of the entire human body.
It is also important to realize that these tests are not perfect and can miss a small tumor (less than one inch). A thorough physical examination should also accompany any scanning procedure.
PET and CT scans are often done in the same session and are performed by the same machine. While the PET scan demonstrates the biological function of the body, the CT scan provides information with respect to the location of any increased metabolic activity. By combining these two scanning technologies, a physician can more accurately diagnose and identify existing cancer.
The general recommendation is to perform fewer PET/CT scans the longer the elapsed time from the surgery that removed the cancer. Generally, PET/CT is performed every three to six months during the first year, then every six months during the second and then yearly throughout the fifth year. Some patients are followed yearly throughout life with PET/CT, and others undergo them if recurrence or a new malignancy is suspected. These recommendations, however, are not based on studies and are merely the opinion or consensus among the specialists. More scans are performed if there are concerns or suspicious findings. When scheduling a PET and/or CT scan any potential benefit gained by the information should be weighed against any potential deleterious effects of exposure to ionizing radiation and or X rays.
Sometimes physicians do not need a PET scan and only request a CT dedicated to the area in question. Such a CT is more precise compared to a combined PET/CT; the former can also include the injection of contrast material to assist in the diagnosis of the problem.
On occasion CT is not helpful, especially in those who had extensive dental work, including filings, crowns or implants that can interfere with the interpretation of the data. Not performing a CT spares the patient from receiving a substantial amount of radiation. Instead an MRI of the area can be done.
CT/PET showing left lesion in the left floor of the mouth and a spread to the lymph glands
When viewing the scans, radiologists compare the new scan(s) with the old ones to determine if there have been any changes. This can be useful in determining if there is new pathology.
Ultrasound image of a neck mass