PET/MRI: The Blended-Modality Choice of the Future?

Abstract

This article addresses the emerging technology of PET coupled with MRI, or PET/MRI, which could become the technology of choice in the future for many reasons. Some of these reasons will be discussed, along with a historical account of the field of MRI and how this modality has evolved to include many aspects of molecular and functional imaging. After reading this article, nuclear medicine technologists should be able to provide an overview of the history of MRI, discuss PET and how it is mainly used today melded to CT as PET/CT, discuss how MRI is used diagnostically, explain how PET technology and MRI technology are able to function simultaneously together as PET/MRI, discuss some issues concerning who will operate these new units, and discuss the possibility that PET/MRI could be the blended technology of choice in the future. In the beginning, there was a chemical identification technology known as nuclear magnetic resonance (NMR) spectroscopy. This technology was in the form of tabletop units, which were standard issue in research organic chemistry laboratories. Essentially, researchers discovered that by putting organic chemicals in a strong magnetic field, hydrogen atoms would orient themselves along the strong magnetic field. When this magnetic field was switched off, hydrogen atoms would relax back to their equilibrium state and in the process give off a radiofrequency energy signal. The energy or spectral signatures of these signals could identify them as coming from hydrogen atoms attached to different molecules. Overall, these energy spectra were the basis of NMR spectroscopy and gave scientists the ability to detect unique fingerprints for different chemicals.In the 1970s, this same spectroscopic technology was expanded into the diagnostic imaging realm. Essentially, scientists developed the ability to apply the same NMR signal as is used in spectroscopy studies to a technology that was able to scan an entire organ system. This technology was first demonstrated in organic objects such as fruits and then in animal organ systems, and then it quickly was extended to humans.The initial technologic challenge was to build instruments large enough to scan a human yet robust enough to maintain strong and stable magnetic fields over long periods. This challenge was finally met with the advent of magnets constructed with materials able to operate in the superconductive realm (i.e., the realm in which electrical energy loss due to resistive losses is near zero). In the early to mid 1980s, when NMR first emerged as a widespread clinical imaging modality, it originally fell under the domain of nuclear medicine technology as an offshoot of nuclear medicine. Additionally, the very first NMR technologists were nuclear medicine technologists. Furthermore, some of the more progressive nuclear medicine technology educational programs taught NMR physics and provided students with opportunities to experience clinical rotations in NMR. Unfortunately, once the modality began to mature and after Medicare began to reimburse...

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