Development of “virtual patient” models for simulation trials of the SPECT/CT method

A topical task of the single-photon emission computed tomography (SPECT) method combined with computed tomography (CT) is the development of a quantitative assessment of the obtained images of pathological areas and optimization of the protocol for examining patients using this method. Solving these problems requires a large number of studies. The development of a mathematical modeling method is a topical task in the field of nuclear medicine due to ethical restrictions due to radiation exposure. To solve this problem, it is necessary to create “virtual patient” models that describe the distribution of the administered radiopharmaceutical in organs and tissues, as well as its accumulation in pathological foci. The article presents approaches to creating mathematical models of patients (phantoms) for studying the diagnostic accuracy of the SPECT method combined with computed tomography (SPECT/CT). Two approaches to creating “virtual patient” models have been developed. The first approach, Constructive Solid Geometry (CSG), is based on the equations of analytical geometry and constructs models of an average patient. The second approach creates so-called "digital twins" based on segmentation of clinical SPECT/CT images of real patients. CSG phantoms have been successfully applied in simulation modeling aimed at studying and solving common problems of SPECT/CT imaging. Such problems include studying the optimal parameters of the data collection protocol, and the problem of false apical defect in nuclear cardiology. “Digital twins” allow the most accurate modeling of clinical cases and evaluation of errors in reconstructed images. Both approaches to creating “virtual patient” models have their own niche for research. Problems that require a large number of trials with variation of several anatomical parameters (e.g. patient habitus, angular orientation, wall thickness, and left ventricular myocardial size) are best investigated using geometric CSG models. “Digital twins” should be used in the study of real clinical cases, as well as for the verification of decisions and conclusions obtained in studies using CSG models.