Positron emission tomography with additional γ -ray detectors for multiple-tracer imaging

Abstract

Purpose: Positron emission tomography (PET) is a useful imaging modality that quantifies the physiological distributions of radiolabeled tracers in vivo in humans and animals. However, this technique is unsuitable for multiple-tracer imaging because the annihilation photons used for PET imaging have a fixed energy regardless of the selection of the radionuclide tracer. This study developed a multiisotope PET (MI-PET) system and evaluated its imaging performance. Methods: Our MI-PET system is composed of a PET system and additional c-ray detectors. The PET system consists of pixelized gadolinium orthosilicate (GSO) scintillation detectors and has a ring geometry that is 95 mm in diameter with an axial field of view of 37.5 mm. The additional detectors are eight bismuth germanium oxide (BGO) scintillation detectors, each of which is 50 9 50 9 30 mm 3 , arranged into two rings mounted on each side of the PET ring with a 92-mminner diameter. This system can distinguish between different tracers using the additional c-ray detectors to observe prompt c-rays, which are emitted after positron emission and have an energy intrinsic to each radionuclide. Our system can simultaneously acquire double-(two annihilation photons) and triple-(two annihilation photons and a prompt c-ray) coincidence events. The system's efficiency for detecting prompt de-excitation c-rays was measured using a positron-c emitter, 22 Na. Dual-radionuclide ( 18 F and 22 Na) imaging of a rod phantom and a mouse was performed to demonstrate the performance of the developed system. Our system's basic performance was evaluated by reconstructing two images, one containing both tracers and the other containing just the second tracer, from list-mode data sets that were categorized by the presence or absence of the prompt c-ray. Results: The maximum detection efficiency for 1275 keV c-rays emitted from 22 Na was approximately 7% at the scanner's center, and the minimum detection efficiency was 5.1% at the edge of the field of view. Dual-radionuclide imaging of the point sources and rod phantom revealed that our system maintained PET's intrinsic spatial resolution and quantitative nature for the second tracer. We also successfully acquired simultaneous double-and triple-coincidence events from a mouse containing 18 F-fluoro-deoxyglucose and 22 Na dissolved in water. The dual-tracer distributions in the mouse obtained by our MI-PET were reasonable from the viewpoints of physiology and pharmacokinetics. Conclusions: This study demonstrates the feasibility of multiple-tracer imaging using PET with additional c-ray detectors. This method holds promise for enabling the reconstruction of quantitative multiple-tracer images and could be very useful for analyzing multiple-molecular dynamics.

Radiolabelling of nanomaterials for medical imaging and therapy

“…These can be detected with additional gammaray detectors allowing the detection of multiple PET isotopes within the same system. 43 Despite its lower global availability, there are an increasing number of PET scanners and radiotracers becoming available in clinics worldwide, due to the superior sensitivity and spatial resolution. Finally, the recent breakthrough in the PET imaging field of the clinical total-body scanner technology should be highlighted.…”

Nuclear imaging of liposomal drug delivery systems: A critical review of radiolabelling methods and applications in nanomedicine

“…In PET, however, all photons emitted during positron annihilation have the same 511 keV energy, making multi-radionuclide imaging not currently possible with standard scanners. Interestingly, many PET radionuclides also emit characteristic gamma rays, and it is therefore possible to simultaneously detect multiple PET isotopes with additional gamma-ray detectors by locating triple-coincidence events [16].…”

Positron range-free and multi-isotope tomography of positron emitters

“…A second method is simultaneous imaging of a pure positron emitter and a positron emitter coemitting prompt gammas (Andreyev and Celler 2011, Gonzalez et al 2011, Andreyev et al 2014. The development of a small-animal multi-isotope PET based on this principle was reported recently (Fukuchi et al 2017). This method has the disadvantage that it requires modifications to the scanner's electronics to detect three gammas in coincidence and that a large number of quite bulky additional gamma detectors need to be added to reach a reasonable sensitivity for the scarce triple coincidences.…”