Volume viewer software

Two experienced nuclear medicine physicians reviewed all ¹⁸F-FDG PET/CT images for initial staging on a dedicated workstation (GE Advantage Workstation 4.4). Metabolic and volumetric parameters were measured using Volume Viewer software (GE Healthcare, Milwaukee, WI, USA), which provides an automatically delineated VOI using an isocontour threshold method based on the SUV (Fig. 1). MTV was defined as the total tumor volume segmented by the threshold SUV [17 (link)]. Mediastinal blood pool (MBP) activity [23 (link)] was used as a threshold for determining the VOI boundary. To determine the threshold using MBP, a VOI consisting of 5×5×1 voxels was manually drawn at the aortic arch. Mean standardized uptake value (SUV_mean) plus two standard deviations of the VOI in the aortic arch was adopted as the threshold SUV for the primary tumor. Using the threshold SUV, VOIs of the primary tumor were automatically generated. Experienced nuclear medicine physicians manually adjusted VOIs of the primary tumor to exclude adjacent lymph nodes. The software calculated the maximum standardized uptake value (SUV_max), SUV_mean, and MTV of the entire primary tumor. TLG was obtained by multiplying the SUV_mean by the number of voxels.

All PET/CT images were reconstructed and reviewed using Volume Viewer software on Workstation AW 4.5 (GE Healthcare) by two experienced radiologists and a nuclear medicine physician who were blinded to the clinical information. Visual assessment and semi-quantitative analysis were used for image analysis. Tumor contours covering the entire lesion volume in axial, coronal and sagittal images were delineated automatically or manually as and when necessary, and then the quantitative parameters such as maximum standardized uptake value (SUVmax), mean standardized uptake value (SUVmean), metabolic tumor volume of the maximum lesion (MTVmax), sum of the metabolic tumor volume (MTVsum), total lesion glycolysis of the maximum lesion (TLGmax), sum of total lesion glycolysis (TLGsum), maximum diameter of the maximum lesion (Dmax) were measured or calculated. MTV was measured with a threshold of 40% SUVmax. TLG was the product of MTV and SUVmean.