Evolution of Quantification in Clinical Nuclear Medicine: A Brief Overview of Salient Uses and Upcoming Trends

Since the inception of Nuclear Medicine, the field strove to not only understand pathology through the qualitative evaluation of physiologic and molecular based processes, but also to quantify them to further differentiate normal from abnormal findings. Whereas the former has been well achieved and has evolved into the field of Molecular Imaging, the latter continues to evolve with a goal to provide a definite incremental improvement in diagnostic and clinical management of patients over that provided by the former alone. Quantification is found ubiquitously in Nuclear Medicine, such as in Renal, Thyroid, and Cardiac imaging, to therapies such as Thyroid Diseases and Y-90 microspheres (SIRT). This has also evolved with technology, starting from the simplest probes, static planar imaging, and cine planar and tomographic imaging, now extended to more absolute quantification with modern Positron Emission Tomography (PET-CT and PET-MR) machines, and further with the evolution of quantitative Single Photon Emission Computed Tomography (SPECT and SPECT-CT). This evolution is also a product of other developments in acquisition standardization, imaging methodologies, and understanding of radiotracer physiology. This article summarizes some of the more common procedures relying on quantification, and which direction the newer generation of quantitative based imaging developments promise to provide in the field.