Positron Emission Tomography (PET) is one of the most sensitive clinical tools for early detections of small tumours, but its performance is dependent on multiple factors including image quality and human perception. Current methods relying on physical and numerical image quality phantoms are inadequate for evaluating clinical task-based performance, such as limits of lesion detection, due to lack of physiologic realism of the images.In this work, we describe development and validation of the Lesion Synthesis Toolbox, easy-to-use software to synthetize well-characterized, user-defined lesions in real patient PET data prior to image reconstruction and in corresponding Computed Tomography (CT) images on GE Discovery line of PET/CT scanners.We employ synthetic lesions in a preliminary perception study to estimate the limits-of-detection (LOD) in representative clinical setting. Finally, we describe a custom developed, web-based tool for conducting perception studies using synthetic lesions of varying parameters to characterize the LOD. We conclude with a discussion of how these tools can be employed in future studies to compare LOD between imaging methods, image generation algorithms, observers, display types, and computer-based lesion detection solutions.ii

Dynamic contrast‐enhanced (DCE)‐MRI is a technique for obtaining tissue hemodynamic information (e.g. tumours). Despite widespread clinical application of DCE‐MRI, the technique suffers from a lack of standardization and accuracy, especially with respect to the concentration‐versus‐time of gadolinium (Gd) in feeding arteries (the input function, IF). MR phase has a linear quantitative relationship with Gd concentration ([Gd]), making it ideal for measuring the first‐pass of the IF, but is not considered accurate in the steady‐state washout. Modified Look‐Locker Inversion Recovery (MOLLI) is a fast and accurate method to measure T1 and has been validated to quantify typical [Gd] ranges experienced in the washout of the IF. Two different methods to measure the IF for DCE‐MRI were compared: 1) conventional phase‐versus‐time (“Phase‐only”) and 2) phase‐versus‐time combined with pre‐ and post‐DCE MOLLI T1 measurements (“Phase+MOLLI”). The IF obtained from Phase+MOLLI was calculated from MOLLI T1 values and known relaxivity, then added to the Phase‐only acquisition with the washout IF subtracted. A significant difference was observed between IF values for [Gd] between the Phase‐only and Phase+MOLLI acquisitions (P = 0.03). To ensure the IFs from MOLLI T1s were accurate, it was compared to [Gd] obtained from “gold‐standard” inversion recovery (IR). MOLLI showed excellent agreement with IR when imaged in static phantoms (r2 = 0.997, P = 0.001). The Phase+MOLLI IF was more accurate than the Phase‐only IF in measuring the washout. The Phase+MOLLI acquisition may therefore provide a DCE‐MRI reference standard that could lead to better clinical diagnoses.