Comparison of scandium-44\u2009g with other PET radionuclides in pre-clinical PET phantom imaging

Simon Ferguson,Hans-Sonke Jans,Terence Riauka,Frank Wuest,Melinda Wuest

doi:10.1186/s40658-019-0260-0

Abstract

PurposeThe decay characteristics of radionuclides in PET studies can impact image reconstruction. 44gSc has been the topic of recent research due to potential theranostic applications and is a promising radiometal for PET imaging. In this study, the reconstructed images from phantom measurements with scandium in a small-animal PET scanner are compared with 18F and two prominent radiometals: 64Cu and 68GaMethodsThree phantoms filled with 18F, 64C, 68Ga, and 44gSc were imaged in the Siemens Inveon PET scanner. The NEMA image quality phantom was used to determine the recovery coefficients (RCs), spill-over ratios (SORs), and noise (%SD) under typical pre-clinical imaging conditions. Image contrast was determined using a Derenzo phantom, while the coincidence characteristics were investigated using an NEC phantom. Three reconstruction algorithms were used, namely filtered back projection (FBP), ordered subset expectation maximization (OSEM), and maximum a-posteriori (MAP).ResultsImage quality parameters were measured for 18F, 64Cu, 68Ga, and 44gSc respectively; using FBP, the %SD are 5.65, 5.88, 7.28, and 7.70; the RCs for the 5-mm rod are 0.849, 1.01, 0.615, and 0.825; the SORs in water are 0.0473, 0.0595, 0.141, 0.0923; and the SORs in air are 0.0589, 0.0484, 0.0525, and 0.0509. The contrast measured in the 2.5-mm rods are 0.674, 0.637, 0.196, and 0.347. The NEC rate with 44gSc increased at a slower rate than 18F and 68Ga as a function of activity in the field of view.Conclusion44gSc demonstrates intermediate behavior relative to 18F and 68Ga with regard to RC and contrast measurements. It is a promising radionuclide for preclinical imaging.

Highlights

The physical properties of the radionuclide used in a PET study affect the quality of the reconstructed image and the quantification of reconstructed activity
Spill-over ratio, and recovery coefficient The percentage standard deviation (%SD) is a measure for noise in the reconstructed image, and the measured values are shown in Fig. 3
The spill-over ratio (SOR) is a measure for activity falsely assigned to regions in the reconstructed image in which no radioactivity was present during image acquisition

Summary

Introduction

The physical properties of the radionuclide used in a PET study affect the quality of the reconstructed image and the quantification of reconstructed activity. Some newly proposed radionuclides possess high-energy co-emitted gammas (i.e., prompt gammas) which negatively interfere with the detection of positron annihilation photon pairs [10]; added image noise, owing to the increased the rate of spurious coincidences, has been reported [11, 12] and is not directly accounted for in conventional PET corrections. Prompt gamma corrections have been proposed to increase the accuracy of quantitative imaging, but are often radionuclide specific and require further investigation before being applied to novel radionuclides [13,14,15,16,17,18,19]

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Results

Discussion

Conclusion