TORONTO, CanadaThe combination of positron emission tomography (PET) and computed tomography (CT) has proved particularly advantageous in the diagnosis and treatment of cancer of the head and neck, Carolyn Cidis Meltzer, MD, said at the 48th Annual Meeting of the Society of Nuclear Medicine (abstract 133).
Dr. Meltzer reported on the application of a combined PET/CT scanner developed at the University of Pittsburgh School of Medicine by David Townsend, PhD, professor of radiology, Dr. Meltzer, and their colleagues. Dr. Meltzer is associate professor of radiology and psychiatry, and medical director of the University of Pittsburgh Medical Center’s PET facility.
With the new instrument, the CT scan can be followed immediately by a PET scan in the same imaging session. When the images are combined, the results are superior to those obtained by using either imaging technique on its own. The Pittsburgh prototype PET/CT machine has received FDA approval for marketing as the Biograph (CTI/Siemens).
PET measures the rate of metabolic activity in different regions of the body, by detecting the rate of accumulation of radiolabeled fluorodeoxyglucose (FDG). Because malignant cells often show enhanced glucose metabolism, the resulting PET scan can differentiate between cancer cells and normal tissue, and can even distinguish between benign and malignant tumors.
The interpretation of PET images can sometimes be complicated, however, since enhanced FDG uptake can also occur in a variety of normal tissues, including striated muscle, bone marrow, lymphoid tissue, salivary glands, and brain.
Not only are these various tissues in close proximity to each other in the head and neck, but variable uptake in normal tissues can occur asymmetrically, giving rise to the sort of localized signal that could be misinterpreted as coming from a malignant tumor.
Limitations of CT