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Journal of the Academy of Hospital Administration

Positron Emission Tomography - Clinical and Administrative Dimensions

Author(s): Lt Col (Dr) Alok Kulsrestha

Vol. 16, No. 1 (2004-01 - 2004-06)

Introduction

Positron Emission Tomography, also called PET imaging or a PET scan, is a diagnostic examination that involves the acquisition of physiologic images based on the detection of positrons through non invasive molecular imaging technique. Positrons are tiny particles emitted from a radioactive substance administered to the patient. The subsequent views of the human body developed by this technique are used to evaluate a variety of diseases.

Need of Equipment

PET imaging is unique in that shows the functioning of organs & tissues, while other imaging techniques such as X-ray and CT show the structure, and may miss a cancer diagnosis if no physical change has taken place in these cells. The usefulness of PET extends into a variety of medical specialties, including heart and neurological disorders as well as many types of cancers. These are used most often to detect cancer and to examine the effects of cancer therapy by characterizing biochemical changes in the cancer tissue. These scans are performed on the whole body.

Procedure

PET is usually done on an outpatient basis. Before the examination begins, a radioactive substance is produced in a machine called a cyclotron and attached, or tagged, to a natural body compound, most commonly glucose, but sometimes water or ammonia. Once this substance is administered to the patient, the radioactivity localizes in the appropriate areas of the body and is detected by the PET scanner.

Patients who undergo a PET scan receive a radioactive tracer containing ingredients that act like water, sugar, proteins and oxygen, which are normally used in the body. Diseased tissues use these materials at different rates than surrounding normal tissues, so that a whole-body scan can produce images that point to the location, size and activity of abnormal tissues or tumors.

Different colours or degrees of brightness on a PET image represent different levels of tissue or organ function. For example, because healthy tissue uses glucose for energy, it accumulates some of the tagged glucose, which will show up on the PET images. However, cancerous tissue, which uses more glucose than normal tissue, will absorb more of the substance and appear brighter than normal tissue on the PET images. When a physician uses a PET tracer that mimics the way glucose is consumed in the body, cancer cells show up on a PET scan as a "hot spot" and the cancer can be detected at a very early stage.

PET scans also can accurately reveal the extent of a cancer and measure how most tumors respond to therapy, it helps doctors choose the best treatment for each patient. For example, information from PET scans can help doctors decide whether surgery is appropriate and, if so, help them plan the operation. PET scans also can be used to monitor a patient’s response to treatment and provide early feedback on whether a therapy is working. It can differentiate malignant from benign growth as well as spread of malignant tumours.

PET scans of the heart can be used to determine blood flow to the heart muscle and help evaluate signs of coronary artery disease. PET scans of the heart can also be used to determine if areas of the heart that show decreased function are alive rather than scarred due to a prior heart attack, called a myocardial infarction. Combined with a myocardial perfusion study, PET scans differentiate non-functioning heart muscle from heart muscle that would benefit from a procedure, such as angioplasty or coronary artery bypass surgery, which would re-establish adequate blood flow and improve heart function. PET scans of the brain are used to evaluate patients who have memory disorders of an undetermined cause; who have suspected or proven brain tumors; or who have seizure disorders that are not responsive to medical therapy and, therefore, are candidates for surgery, degenerative diseases like Alzheimer’s Huntington’s and Parkinson disease. Within first few weeks of stroke, PET may be useful in determining treatment therapies. It can help detect recurrent brain tumours, tumours of lungs, colon, breast, limph node, skin and other organs.

Importance

The medical importance of PET lies in the existence of isotopes like 11C, 13N, 15O and 18F, which are essential elements of all living systems, and their physiological processes. Hence, tissue-specific and chemistry-specific tracers can be synthesized and injected into human/animals to study the physiological functions of normal and pathological tissues in vivo. There is increasing recognition of the role of positron emission tomography (PET) in oncology, supplementing its established roles in the evaluation of myocardial viability and epilepsy. The radiopharmaceutical fluorine-18 fluorodeoxyglucose (FDG), an analogue of glucose, has high uptake in a wide range of tumours. FDG PET has been shown to be an accurate technique for tumour staging and for therapeutic monitoring

Advantages

No special preparation or change in the daily routine is required. As PET allows study of body function, it can help physicians detect alterations in biochemical processes that suggest disease before changes in anatomy are apparent on other imaging tests such as CT or MRI scans. T he radioactivity is very short-lived, the radiation exposure is extremely low. The substance amount is so small that it does not affect the normal processes of the body.

The radioactive substance may expose radiation to the fetus of patients who are pregnant or the infants of women who are breast-feeding. The risk to the fetus or infant should be considered related to the potential information gain from the result of the PET examination. Pregnant patient should inform the PET imaging staff before the examination is performed.

Disadvantages

PET can give false results if a patient's chemical balances are not normal. Specifically, test results of diabetic patients or patients who have eaten within several hours prior to the examination can be adversely affected because of blood sugar or blood insulin levels.

The radioactive substance decays quickly (half life of FDG 110 minutes)and is effective for a short period of time, it must be produced in a laboratory near the PET scanner. It is important to be on time for the appointment and to receive the radioactive substance at the scheduled time.

A radiologist who has specialized in nuclear medicine and has substantial experience with PET can do PET. Most large medical centers now have PET services available to their patients. Medicare and insurance companies cover many of the applications of PET, and coverage continues to increase.

Finally, the value of a PET scan is enhanced when it is part of a larger diagnostic work-up. This often entails comparison of the PET scan with other imaging studies such as CT or MRI.

Treatment Costs

PET scans also can lower treatment costs as they help avoid inappropriate or unnecessary surgeries and eliminate the need for multiple diagnostic tests and invasive biopsy procedures

However, the high establishment and operating costs of conventional PET facilities make economic justification more difficult than for cheaper imaging methods. Before funding new technologies, government and third-party payers increasingly require evidence of cost-effectiveness as well as diagnostic accuracy. High unit scanning costs demand substantially greater effectiveness. The development of lower-cost positron imaging systems over the past 10 years offers a realistic opportunity to expand the clinical availability of PET by improving this balance

Despite an increasing body of evidence supporting the accuracy of FDG PET in oncology, its high cost and limited cost-effectiveness data have militated against funding for routine clinical use. In certain western counties, FDG PET scanning has been shown to be a cost-effective alternative to conventional diagnostic methods of assessing solitary pulmonary nodules and staging non-small-cell lung cancer. Because of reduction in surgical procedures, cost-effectiveness of PET for lung cancer staging has been reported

Cost-benefit analyses to justify the use of FDG PET have shown significant savings even when based on costs derived from conventional PET facilities.

The ultimate cost of clinical PET scans depends on throughput of patients, availability and cost of radiopharmaceutical supplies, and the case mix of PET studies. Further evolution of lower-cost positron imaging devices and the development of production and distribution facilities to supply FDG to sites remote from a cyclotron have the potential to further reduce costs. If the cost of PET scans becomes more competitive, the merit of funding of PET for clinical use could be argued not on the basis of cost, but on its proven diagnostic and prognostic accuracy compared with standard investigations.

Resident Administrator, Department of Hospital Administration, AIIMS, New Delhi

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