How Does PET Compare With Other Imaging Modalities?

Positron Emission Tomography (PET) provides physicians with unique diagnostic information which may alter patient management and reduce the total cost of patient care. It produces images of molecular-level physiological function which can be used to measure many vital processes, including glucose metabolism, blood flow and perfusion, and oxygen utilization. With these images, physicians can identify normal and abnormal states.

This exciting technology extends the capabilities of other advanced imaging modalities. Like MR and CT, for example, it uses proven tomographic algorithms to display data as cross-sectional images in any plane. And like nuclear medicine, these images represent the distribution of internal radiotracers.

But that's where PET's resemblance to other imaging modalities ends.

Clinical Example:

A female with history of breast cancer. Chest radiographs and CT scans showed no detectable disease in the lung bases.

The PET exam, performed at the same time as the chest radiograph and CT, was the only procedure to show abnormal areas, including her right axilla, and several areas of the chest (lung bases), representing metastatic disease. Several months after the inital PET exam the patient underwent additional chest radiograph and CT exams and the metastases were then visible.

As a result of the PET examination the patient underwent new chemotherapy.

How is PET Unique?

Unlike anatomical imaging modalities, such as CT and MR, PET permits assessment of chemical and physiological changes related to metabolism. This is important because functional change often predates structural changes in tissues. PET images may therefore demonstrate pathological changes long before they would be revealed by modalities like CT and MR.

Unlike traditional nuclear medicine, PET uses unique radiopharmaceuticals, or "tracers," labeled with isotopes which are the basic elements of biological substrates. These isotopes mimic natural substrates such as sugars, water, proteins, and oxygen. As a result, PET will often reveal more about the cellular-level metabolic status of a disease than other types of imaging modalities.

PET also stands alone in its ability to quantify physiological and biochemical measurements in vivo. Although a simplified qualitative mode is available, PET images can be acquired quantitatively to reflect the actual amounts of tracer in the regions of interest.

PET is already making critical contributions to more cost-effective patient management in three primary medical disciplines: oncology, cardiology and neurology. As researchers use PET to explore the basic physiology underlying disease processes, additional clinical applications are likely to evolve.

PET has the unique ability to cross the boundaries of specialties, adding new dimensions to a physician's ability to:

• Diagnose disease before structural changes become detectable with anatomical imaging techniques, potentially improving the prognosis.
• Manage patient therapy by monitoring response to a given regimen and providing early feedback on its efficacy. This can help reduce or avoid the cost of ineffective treatments or unnecessary hospitalization.
• In some cases, replace multiple diagnostic procedures with a single exam.
• Help predict the prognosis for surgical procedures, to eliminate those that won't benefit the patient, thus significantly reducing the cost of healthcare delivery.
• Identify distant, occult metastases that may affect the course of treatment and therefore change patient management.