A methodology for correcting spatial distortions in planar images for small Field Of View (FOV) γ-Camera systems based on Position Sensitive Photomultiplier Tubes (PSPMT) and pixelated scintillation crystals is described. The process utilizes a correction matrix whose elements are derived from a prototyped planar image obtained through irradiation of the scintillation crystal by a 60 Co point source and without a collimator. The method was applied to several planar images of a SPECT experiment with a simple phantom construction at different detection angles. The tomographic images are obtained using the Maximum-Likelihood Expectation-Maximization (MLEM) reconstruction technique. Corrected and uncorrected images are compared and the applied correction methodology is discussed.
Objective: Simulated endoscopic training can be challenging and stressful for the novice trainee. The absence of a reliable stress detection method during simulated endoscopic training makes estimating trainees' mental stress difficult to quantify. This study concomitantly measures the responses of four saliva stress biomarkers and compares them to the video score (VS) achieved by novice endoscopists in a reproducibly stressful simulation environment. Methods: Thirty-six male endoscopy naïve surgery residents were enrolled. After an orientation phase, a saliva specimen was collected for cortisol (sC), alpha-amylase (sAA), Chromogranin A (sCgA), and immunoglobulin A (sIgA) measurements (baseline phase, BL). Thereafter, the simulation exercise phase (E) started, practicing in the Fundamentals of Endoscopic Surgery Skills module (GI-Bronch Mentor). Immediately after, a second saliva sample for measuring the above-cited biomarkers was collected. The whole experiment was videotaped, and the VS was calculated. The percentage (E-BL) diff of each of the four saliva biomarkers was calculated and examined for correlation to VS. Results: sCgA diff showed the best correlation with VS, followed by sAA diff . Conclusions: sCgA and sAA, are saliva stress biomarkers that are easy to collect non-invasively and showed the best correlation with novice endoscopist's performance in our simulation setting, and therefore, they could be used for monitoring stress.
The principal goal of this study is to characterize the width of the light distribution for a given number of initial optical photons and to try to express it as a function of the Depth of Interaction (DOI) in the crystal, where the initial optical photons are produced, the size of the initial volume the optical photons occupy before starting the transmission and the geometrical properties of the optical medium that guides the light to the photomultiplier surface. Monte Carlo runs based on the optical simulation package DETECT2000 have been performed.The results indicate that in the case of continuous crystal there is an apparent correlation of the DOI and the width of the light distribution. In the case of pixelated crystals the width of the light distribution seems to be independent of the DOI when the source is located deep in the crystal but there is a strong dependence as the source approaches the PSPMT's entrance window. This correlation of the DOI and the light distribution is not affected by the transverse dimensions of the continuous crystal but in the case of pixelated crystals this correlation is strongly depended on the crystal's aspect ratio. Through this study it also became clear that there is no dependence of the light distribution on the shape of the source.
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