The OpenPET and its real-time imaging capability have great potential for real-time tumor tracking in medical procedures such as biopsy and radiation therapy. For the real-time imaging system, we intend to use the one-pass list-mode dynamic row-action maximum likelihood algorithm (DRAMA) and implement it using general-purpose computing on graphics processing units (GPGPU) techniques. However, it is difficult to make consistent reconstructions in real-time because the amount of list-mode data acquired in PET scans may be large depending on the level of radioactivity, and the reconstruction speed depends on the amount of the list-mode data. In this study, we developed a system to control the data used in the reconstruction step while retaining quantitative performance. In the proposed system, the data transfer control system limits the event counts to be used in the reconstruction step according to the reconstruction speed, and the reconstructed images are properly intensified by using the ratio of the used counts to the total counts. We implemented the system on a small OpenPET prototype system and evaluated the performance in terms of the real-time tracking ability by displaying reconstructed images in which the intensity was compensated. The intensity of the displayed images correlated properly with the original count rate and a frame rate of 2 frames per second was achieved with average delay time of 2.1 s.

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Evaluation of biological chromophore levels is useful for detection of various skin diseases, including cancer, monitoring of health status and tissue metabolism, and assessment of clinical and physiological vascular functions. The major chromophores in the superficial layer of skin are oxygenated hemoglobin, deoxygenated hemoglobin, and melanin, which have distinct optical absorption properties in the visible wavelength range. Hemoglobin has two main derivatives, oxygenated and deoxygenated hemoglobin. The absorption spectra of oxygenated and deoxygenated hemoglobin are different. This is because the binding of oxygen to hemoglobin changes the light absorption spectrum of hemoglobin.¹ Varying the concentrations of oxygenated and deoxygenated hemoglobin will alter the diffuse reflectance spectrum. A continuous supply of oxygen is required for peripheral skin tissues and cells. Oxygen is delivered through the bloodstream. The delivery of oxygen to the peripheral skin tissues can be evaluated from the diffuse reflectance spectrum, which is based on the absorption spectra of oxygenated and deoxygenated hemoglobin. The percentage of oxygenated hemoglobin to total hemoglobin in a volume of tissue is referred to as tissue oxygen saturation (${\mathrm{StO}}_2$) or hemoglobin oxygen saturation.² It is a useful indicator to monitor peripheral tissue oxygen consumption, hypoperfusion, and cyanosis.