BackgroundFluorodeoxyglucose (18F-FDG) positron emission tomography/computed tomography (PET/CT) is an important method for detecting tumours, planning radiotherapy treatment, and evaluating treatment responses. However, using the standardized uptake value (SUV) threshold with PET imaging may be suitable not to determine gross tumour volume but to determine biological target volume (BTV). The aim of this study was to extract internal target volume of BTV from PET images.MethodsThree spherical densities of 18F-FDG were employed in a phantom with an air or water background with repetitive motion amplitudes of 0–30 mm. The PET data were reconstructed with attenuation correction (AC) based on CT images obtained by slow CT scanning (SCS) or helical CT scanning (HCS). The errors in measured SUVmax and volumes calculated using SUV threshold values based on SUVmax (THmax) in experiments performed with varying extents of respiratory motion and AC were analysed.ResultsA partial volume effect (PVE) was not observed in spheres with diameters of ≥ 28 mm. When calculating SUVmax and THmax, using SCS for AC yielded smaller variance than using HCS (p < 0.05). For spheres of 37- and 28-mm diameters in the phantom with either an air or water background, significant differences were observed when mean THmax of 30-, 20-, or 10-mm amplitude were compared with the stationary conditions (p < 0.05). The average THmax values for 37-mm and 28-mm spheres with an air background were 0.362 and 0.352 in non-motion, respectively, and the mean THmax values for 37-mm and 28-mm spheres with a water background were 0.404 and 0.387 in non-motion and 0.244 and 0.263 in motion, respectively. When the phantom background was air, regardless of sphere concentration or size, THmax was dependent only on motion amplitude.ConclusionsWe found that there was no PVE for spheres with ≥ 28-mm diameters, and differences between SUVmax and THmax were reduced by using SCS for AC. In the head-and-neck and the abdomen, the standard values of THmax were 0.25 and 0.40 with and without respiratory movement, respectively. In the lungs, the value of THmax became the approximate expression depending on motion amplitude.

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A kA-class fault current limiting unit (FCL unit) with YBCO thin films has been developed. The size of the YBCO film on a sapphire substrate with a metal shunt layer is 3 cm in width and 10 cm in length. The kA class unit consists of eight films in parallel. A polygonal arrangement of the YBCO films selected to keep the current distribution uniform. Moreover, the return pass of the current is set at the center axis of the unit. The model, connected to two units in series, was tested for normal operation and current limitation. The model carried 1 kA for 1 hour and 1.2 kA for 5 min without quench at normal operation, and the current distribution between the films was uniform. The short circuit tests were performed against a power line that has a prospective fault current of 8.9 kA. A total of eight tests were successfully carried out at 200 V, 3.5 cycles, and the model limited the fault current to 1.2 kA.

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