Nuclear medicine and molecular imaging advances in the 21st century

Abstract

Currently, Nuclear Medicine has a clearly defined role in clinical practice due to its usefulness in many medical disciplines. It provides relevant diagnostic and therapeutic options leading to patients' healthcare and quality of life improvement. During the first two decades of the 21st^t century, the number of Nuclear Medicine procedures increased considerably.Clinical and research advances in Nuclear Medicine and Molecular Imaging have been based on developments in radiopharmaceuticals and equipment, namely, the introduction of multimodality imaging. In addition, new therapeutic applications of radiopharmaceuticals, mainly in oncology, are underway.This review will focus on radiopharmaceuticals for positron emission tomography (PET), in particular, those labeled with Fluorine-18 and Gallium-68. Multimodality as a key player in clinical practice led to the development of new detector technology and combined efforts to improve resolution. The concept of dual probe (a single molecule labeled with a radionuclide for single photon emission computed tomography)/positron emission tomography and a light emitter for optical imaging) is gaining increasing acceptance, especially in minimally invasive radioguided surgery. The expansion of theranostics, using the same molecule for diagnosis (γ or positron emitter) and therapy (β minus or α emitter) is reshaping personalized medicine.Upcoming research and development efforts will lead to an even wider array of indications for Nuclear Medicine both in diagnosis and treatment.

Figure 1.

Main fields of advances in Nuclear Medicine in the 21st century.

Figure 2.

Images of the physiologic distribution of PET radiopharmaceuticals used in clinical practice: ¹⁸F-FDG, ⁶⁸Ga-PSMA, ⁶⁸Ga-FAPI, ⁶⁸Ga-DOTANOC and ¹⁸F-Florbetaben. ¹⁸F-FDG, fludeoxyglucose; FAPI, fibroblast-activation-protein inhibitor; PET, positron emmision tomogrpahy.

Figure 3.

Illustration of the TOF principle. Annihilation of the positron originates two 511 kev photon that are detected by PET detectors. Taking the time difference between detection and speed of light, annihilation distance difference to both detectors can be easily computed ( $d_1-d_2=\left(t_1-t_2\right)\times c$ , where $c$ is the speed of light and $t_1$ and $t_2$ are the times of the detection). If the time measurements had no error, the exact position of the annihilation in the LOR could be computed, assuming the two photons describe exactly a 180° angle. Uncertainty of the time measurements is modulated by the TOF probability distribution. LOR, line of response; PET, positron emmision tomography; TOF,

Figure 4.

Evolution sequence of radioguided surgery (adapted from Van Oosterom et al). Both γ and positron emitting radiopharmaceuticals can be used.