Computerized axial tomography, known as CAT scanning, became widely available nearly three decades ago. As compared to the then-standard imaging technologies, it was a stupendous leap forward. Physicians for the first time were able to view the internal anatomy in great detail without having to subject the patient to surgical exploration.
Since then, several generations of CAT scans have come into being. Each provided an incremental improvement in speed and clarity. The MRI (magnetic resolution imaging) became available more recently. It provided better images of bony structures, joints, spine and the brain. An added benefit was that it did not expose the patient to radiation. The disadvantage was that patients with metal prostheses could not be processed through the MRI, for obvious reasons. The major drawback of both CAT scans and MRI is that a benign abnormal lesion could not be differentiated from a malignant lesion. In other words, although they could show the anatomy clearly and accurately, the physiological or functional status of a given lesion could not be deciphered.
This is where positron emission tomography (PET) scans provide a clear advantage over CT and MRI. PET can tell the physicians whether an abnormal finding on a CT scan is likely to be benign or malignant. The PET images are obtained after injecting a radio-labeled glucose compound called radio-labeled flurodeoxyglucose. This substance is taken up by different tissues in the body. It is avidly accumulated within malignant tissues, since malignant cells have enhanced glucose metabolism. This substance being radio-labeled exhibits an intense glow on the PET image.
These PET images can be fused or superimposed onto a CT scan to detect the exact location of a possible malignancy. Because the CT and the PET are taken at different times, slight differences in the patient positioning can lead to moderate inaccuracies in the exact anatomic location of the lesion of interest, especially in a tightly packed area such as the head and the neck. A new device developed at the University of Pittsburg (PET/CT) can obtain both PET and CT images on the same machine in one single session, providing accurate anatomic and physiologic (functional) information. This helps the surgeon in avoiding unnecessary, unsuccessful biopsies and helps steer him to the site most likely to yield an accurate diagnosis. It also helps the radiation oncologist in delivery of the radiation doses to the tumor-bearing area and avoiding damaging radiation to nearby normal tissues.
No matter how good the scans are and how advanced the technology is, the end result is only as good as the person interpreting the scans. Fortunately for us in Citrus County, there are several experienced and expert radiologists. PET scanning is currently available at Citrus Memorial Hospital.
_ V. Upender Rao, MD, FACP, practices at the Cancer and Blood Disease Center in Lecanto.