Evaluation of qualitative and quantitative data of Y-90 imaging in SPECT/CT and PET/CT phantom studies

Abstract

Introduction We aimed to assess the feasibility of SPECT and PET Y-90 imaging, and to compare these modalities by visualizing hot and cold foci in phantoms for varying isotope concentrations. Materials and methods The data was acquired from the Jaszczak and NEMA phantoms. In the Jaszczak phantom Y-90 concentrations of 0.1 MBq/ml and 0.2 MBq/ml were used, while higher concentrations, up to 1.0 MBq/ml, were simulated by acquisition time extension with respect to the standard clinical protocol of 30 sec/projection for SPECT and 30 min/bed position for PET imaging. For NEMA phantom, the hot foci had concentrations of about 4 MB/ml and the background 0.1 or 0.0 MBq/ml. All of the acquired data was analysed both qualitatively and quantitatively. Qualitative assessment was conducted by six observers asked to identify the number of visible cold or hot foci. Inter-observer agreement was assessed. Quantitative analysis included calculations of contrast and contrast-to-noise ratio (CNR), and comparisons with the qualitative results. Results For SPECT data up to two cold foci were discernible, while for PET four foci were visible. We have shown that CNR (with Rose criterion) is a good measure of foci visibility for both modalities. We also found good concordance of qualitative results for the Jaszczak phantom studies between the observers (corresponding Krippendorf’s alpha coefficients of 0.76 to 0.84). In the NEMA phantom without background activity all foci were visible in SPECT/CT images. With isotope in the background, 5 of 6 spheres were discernible (CNR of 3.0 for the smallest foci). For PET studies all hot spheres were visible, regardless of the background activity. Conclusions PET Y-90 imaging provided better results than Bremsstrahlung based SPECT imaging. This indicates that PET/CT might become the method of choice in Y-90 post radioembolization imaging for visualisation of both necrotic and hot lesions in the liver.

New Radionuclides and Technological Advances in SPECT and PET Scanners

“…One challenging aspect with Y-90 dosimetry is imaging quantification. Y-90 SPECT imaging is based on collecting Bremsstrahlung photons generated as a result of the interaction between the electrons originating from the β − decay and the tissue [ 36 ]. Due to this indirect imaging, various disadvantages are observed, such as its low spatial resolution (up to 15 mm) that depends on energy window width, collimator choice and image processing [ 36 ]; attenuation correction, since it depends on the density of the objects through which the photon passes, as well as the photon’s energy [ 37 ]; and overall quantification capability translating into an inaccurate dose-response analysis, despite the possible compensation techniques for attenuation, scatter and collimator detector response [ 38 , 39 ].…”

“…The limited positron-branching ratio is overcome with the improved sensitivity of new digital devices and TOF technology, which enables the acquisition of the annihilation photons, thus obtaining improved resolution images of the microsphere biodistribution. Moreover, Y-90 PET images have been proven to be suitable for quantification and, thus, potential use for post-SIRT dosimetry [ 36 ]. A recently published work, written by an international collaboration of experts, strongly recommends the use of Y-90 PET for post-therapy evaluation, due to its superior quantification capabilities in comparison to Bremsstrahlung SPECT [ 40 ].…”

Post Yttrium-90 Imaging

“…2). [25][26][27] This superiority is due in large part to the improved spatial resolution of PET compared with SPECT. Standard gamma SPECT imaging has a spatial resolution of around 10 mm (which is even worse when imaging bremsstrahlung radiation), as compared with the roughly 2-mm spatial resolution on most clinical PET scanners.…”

Frozen Hybrid Kernelised Expectation Maximisation For Bremsstrahlung SPECT Reconstruction

“…3 Christie Medical Physics and Engineering (CMPE), The Christie NHS Foundation Trust, Manchester, UK. 4 The University of Manchester, Manchester, UK. 5 Department of Medical Physics, Royal Surrey NHS Foundation Trust, Guildford, UK.…”

“…The microspheres lodge in the blood capillaries of the tumour, delivering a high localised absorbed dose while minimising the dose absorbed by the healthy liver parenchyma. [4,5].…”