PET/CT Takes Aim

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Making A Difference in Cancer, Brain and Cardiac Imaging

When it comes to valuable imaging techniques, it is hard to beat the combination of positron emission tomography (PET) that reveals metabolic processes and cell function, and CT that provides detailed anatomic information. The latest versions of hybrid PET/CT machines merge high-resolution PET technology with multidetector CT scanners to produce fused images that improve various aspects of patient care in oncology, cardiology and neurology.

While clinicians involved in PET/CT imaging are quite impressed with the current capabilities of these systems, they eagerly await future applications now being developed as works in progress. With anticipated new radiotracers, they can only dream of potential benefit to patient care.

In centers around the country, PET/CT has become an accepted workhorse in oncology, but some centers have used this technology for a variety of clinical studies.

Multitalented technology

Marcelo F. Di Carli, MD, FACC, FAHA, chief of nuclear medicine/PET, co-director of cardiovascular imaging at Brigham and Women’s Hospital in Boston and associate professor of radiology and medicine at Harvard Medical School explains that they have been using their GE Healthcare Discovery VCT 64-slice PET/CT system for all applications in PET including oncology, brain and cardiac imaging since May 2006.

“We are looking at cardiac perfusion as a way to diagnose coronary artery disease as well as for CTA [angiography] in connection with the PET scan,” Di Carli says. Not only do they visualize the anatomic extent of coronary artery disease but also they gain instant access to the physiologic significance of that disease. “I say it is the one test that provides you with more than the sum of the parts.”

There are several instances where the PET/CT has proven valuable in analysis of specific neurologic conditions. They use FDG (flurodeoxyglucose) PET for selected circumstances with brain tumors, particularly differentiating radiation necrosis from viable tumor. In some patients who have undergone radiation treatment for a brain tumor, they will have equivocal MRI studies where it is unclear whether recurrence is a factor. The metabolic information from the PET study helps to differentiate tissue types.

Another approved use of FDG-PET is in early diagnosis of dementia, including Alzheimer’s disease. “PET is very sensitive to early changes in brain tissue function, even before clear-cut clinical manifestation such as those individuals with mild cognitive impairment,” says Di Carli. Some experts who study dementia suggest that early diagnosis may hold the key to slowing the progression of the disease.

“For epilepsy, PET has been very successful in both pediatric and adult patients for identifying epileptic foci within the brain,” Di Carli says. Particularly for those patients with intractable epilepsy and who are potential candidates for surgery, PET is specifically approved for that indication. Diagnostic information to identify whether there are either single or multiple foci given the electrical activation of an epileptic cascade is provided by PET used in conjunction with an EEG (electroencephalogram) recording. The CT component helps to identify specific anatomic landmarks.

In the future, Di Carli believes that the use of PET/CT for guiding interventions will emerge. For example, when a patient requires a needle-biopsy of a mass, PET can pinpoint the area that should be sampled. Many tumors have some sections that are necrotic while others contain viable cancer cells. The physiologic information from FDG-PET indicates the portions of the tumor which are most metabolically active and therefore should serve as the area of interest for the biopsy. While this technique is still under study, Di Carli expects that eventually PET will guide interventions such as radiofrequency (RF) ablation or cryoablation of tumors.

Ronald A. Korn, MD, PhD, director of PET/CT and research for Scottsdale Medical Imaging, Ltd. in Scottsdale, Ariz., and past chairman of radiology at Scottsdale Health Care works in a community based private-practice radiology group that provides imaging services in Phoenix and Scottsdale. He explains that their GE Discovery STE PET/CT plays a vital role in the healthcare of their oncology patients, and that they see a large demand for use of this technology in cardiac imaging and a lesser demand for neurologic disease. He considers that they provide the full