Background: SPECT/CT combines high resolution anatomical 3D computerized tomography (CT) and single\r\nphoton emission computerized tomography (SPECT) as functional imaging, which provides 3D information about\r\nbiological processes into a single imaging modality. The clinical utility of SPECT/CT imaging has been recognized in\r\na variety of medical fields and most recently in orthopaedics; however, clinical adoption has been limited due to\r\nshortcomings of analytical tools available. Specifically, SPECT analyses are mainly qualitative due to variation in\r\noverall metabolic uptake among patients. Furthermore, most analyses are done in 2D, although rich 3D data are\r\navailable. Consequently, it is difficult to quantitatively compare the position, size, and intensity of SPECT uptake\r\nregions among patients, and therefore difficult to draw meaningful clinical conclusions.\r\nMethods: We propose a method for normalizing orthopaedic SPECT/CT data that enables standardised 3D\r\nvolumetric quantitative measurements and comparison among patients. Our method is based on 3D localisation\r\nusing clinically relevant anatomical landmarks and frames of reference, along with intensity value normalisation\r\nusing clinically relevant reference regions. Using the normalised data, we describe a thresholding technique to\r\ndistinguish clinically relevant hot spots from background activity.\r\nResults: Using an exemplar comparison of two patients, we demonstrate how the normalised, 3D-rendered data\r\ncan provide a richer source of clinical information and allow quantitative comparison of SPECT/CT measurements\r\nacross patients. Specifically, we demonstrate how non-normalized SPECT/CT analysis can lead to different clinical\r\nconclusions than the normalized SPECT/CT analysis, and that normalized quantitative analysis can be a more\r\naccurate indicator of pathology.\r\nConclusions: Conventional orthopaedic frames of reference, 3D volumetric data analysis and thresholding are used\r\nto distinguish clinically relevant hot spots from background activity. Our goal is to facilitate a standardised\r\napproach to quantitative data collection and comparison of clinical studies using SPECT/CT, enabling more\r\nwidespread clinical use of this powerful imaging tool
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