Positron Emission Tomography in Clinical Medicine

Abstract

Introduction Positron emission tomography (PET) imaging is set to change the whole impact and role of Nuclear Medicine, not because it does everything better than conventional single photon imaging (planar and single photon emission computed tomography (SPECT)), but because it also has the impact and public relations of the fastest growing diagnostic speciality. PET is a powerful metabolic imaging technique utilising possibly the best radiopharmaceutical we have ever used [ 18 F]-fluorodeoxyglucose (FDG). However, in addition, it yields excellent quality images, the importance of which can be appreciated by non-nuclear medicine clinicians, and has an enormous clinical impact, as demonstrated in many well-conducted studies. Any on-cologist exposed to a good PET imaging service very quickly appreciates its value. Sitting in on routine clinical PET reporting sessions, it is easy to appreciate how patient after patient is having their management changed in a very significant way as a direct result of the new information provided by the PET scan. There is now an impressive body of data evaluating the impact of PET on patient management. These studies are showing that PET results alter management in a significant way in more than 25% of patients, with some as high as 40%[1]. Examples include changing decisions on surgical treatment for non-small cell lung cancer (both avoiding inappropriate surgery and enabling potentially curative resection), the staging and treatment of lymphoma, decisions on surgical resections for metastatic colo-rectal cancer, referral for revasculari-sation of high-risk coronary artery disease (CAD) patients and many others. This is a level of impact on patient care for common and life-threatening diseases not previously achieved by Nuclear Medicine. Nuclear Medicine has always improved patient care, but usually marginally, such that it has sometimes been difficult to argue that good medicine could not be practised without it. This has often resulted in limitations on the manpower and other resources being put into Nuclear Medicine, particularly in health care systems functioning at the lower end of gross national product (GNP) percentage investment, such as the National Health Service (NHS) in the United Kingdom. This is not true of PET. It is no longer possible to practice the highest standard of clinical oncology without access to PET, and it is clear that without it many patients are needlessly undergoing major surgical procedures and many are being denied potentially curative treatments. If PET and X-ray computed tomography (CT) were to be introduced simultaneously now for oncology staging, follow-up, assessment of tumour recurrence, evaluation of treatment response, etc, there would be no competition with PET proving vastly superior in these areas of cancer patient management. We therefore have in clinical PET a new imaging tool as part of Nuclear Medicine which has brought the speciality to the very heart of patient management, especially for Oncology, but also in Cardiology and Neuropsychiatry. Nuclear Medicine has always been excited by the potential for new ligands for clinical application and the study of patho-physiology. Although for many reasons the potential has not been fully delivered , it may be that the future role of PET ligands will be huge, especially as we are on the brink of molecular and genetic imaging. Furthermore, for PET to be the