Why buy a PET/MR for high end research?

Recently, in a discussion, Alex Margulis, maybe the most prominent radiologist of the late 20th century, said to me: “it is a shame when Radiology and Nuclear Medicine do not work together well because the future of Radiology is the TRACERS,” in other words: the future of Radiology is Nuclear Medicine! At first sight, this may sound a bit surprising. On second thought, there may be important truths in this statement. Looking over the emerging imaging technologies in the past 50 years, the computer afforded us with the cross-sectional techniques spanning from ultrasound to MR and PET; and these techniques are still being refined and further developed. However, around the year 2000, it became evident to most imaging specialists that the contrast media sensitivity attainable in MR and even more so in CT was not high enough to really probe in vivo human molecular biology. Low molecular weight contrast agents have to be given at least in micromolar quantities to generate a visible contrast on MR images, and even higher doses are needed with CT contrast agents. Contrast agents based on super-paramagnetic particles may be given in lower molar doses, but are too large to pass through vessel walls and cell membranes to participate in metabolic or receptor processes in the cells. And there are no new imaging modalities in sight that could provide such information using anything else than those based on the tracer principle. It is important for this reason that PET became a clinical reality: the insight, that PET (and Nuclear Medicine in general) can provide contrast visible at nanoto picomolar concentrations. As most molecular processes operate at these low concentrations, PET and NM are the true clinical molecular imaging modalities. Even hyperpolarized MR will not be able to match neither the molecular sensitivity nor flexibility of PET-tracers, even though it may provide interesting research insights. Why are Nuclear Medicine, and—more importantly—PET with its much higher spatial resolution so important for research? As we get more and more into personalized medicine, specific molecular imaging information is needed, and this can be provided with unique sensitivity and usually very high contrast by PET imaging. A spectrum spanning from FDG, the workhorse tracer of PET, to perfusion tracers, such as water and ammonia, amino acid tracers such as F-18 ethyl tyrosine and C-11 methionine, F-18 labeled choline and thymidine, F-18 Fluoride for bone scanning and to amyloid plaque tracers and receptor markers for various receptor systems are now available, and with the ever increasing installed base of PET scanners, companies start to become interested in providing tracers as well, thereby multiplying the potential uses of PET. So an important part of the imaging future IS the tracers! Hybrid imaging modalities are the result of the recognition that both function and morphology are key to understanding a patients’ disease. This recognition has led to the situation, that all PET today is “hybridized” with CT and in the future also with MR. This fact has an interesting side effect: if forces the Radiologists and Nuclear Physicians to work together in one or another way. Thus the possibility of addressing various disease entities with new more specific tracers increases every day. Clinical Alzheimer plaque imaging is just around the corner. In oncology, many tumors become more “chronic” with partly successful therapy, and here only molecular imaging with hybrid PET can differentiate the aggressiveness of various tumor metastases within the same patient. Combining PET with CT has been a dramatic success story and requires knowledge both in Nuclear Medicine and cross-sectional imaging. The potential of PET/MR is yet unfathomed. There is major clinical research necessary to understand how to use PET/ MR and this will occupy researchers at least for another decade. Two areas seem to be particularly relevant: