[en] This paper presents an experiential summary of the developing technique for automated ultrasonic testing system that consists of an ultrasonic tester, mechanical moving and fixing parts, controller and testing software. The application knowledges and limitations on these items are helpful to prevent the misoperation, the unadequate test result analysis and to build up the own test system.

[en] This study is to report experience with Fractionated Stereotactic Radiation Therapy (FSRT) for locally recurrent nasopharynx cancer after curative conventional radiation therapy. Three patients with locally recurrent and symptomatic nasopharynx cancer were given FSRT as reirradiation method between the period of September of 1995 and August of 1996. For two patients, application of FSRT is their third radiation therapy directed to the nasopharynx. Two patients were given low dose chemotherapy as radiation sensitizer concurrently with FSRT. Authors used 3-dimensional coordinate system by individually made, relocatable Gill-Thomas-Cosman (GTC) stereotactic frame and multiple non-coplanar arc therapy dose planning was done using XKnife-3. Total of 45 Gy/18 fractions or 50 Gy/20 fractions were given. Authors observed satisfactory symptomatic improvement and remarkable objective tumor size decrease by follow-up MR images taken 1 month post-FSRT in all three patients, while no neurologic side effect attributable to reirradiation was noticed. Two died at 7 and 9 months with loco-regional and distant seeding outside FSRT field, while one patient is living for 4 month. Authors experienced satisfactory therapeutic effectiveness and safety of FSRT as reirradiation method for locally recurrent nasopharynx cancer. Development of more effective systemic chemotherapeutic regimen is desired for distant metastasis. (author)

[en] The purpose of this study is to design an indirect photon-counting detector using a GAGG scintillator with Monte Carlo simulation and to evaluate the efficacy of the result using an energy weighted subtraction method. Factors to validate the efficacy of energy weighted subtraction were the type of scintillator and the profile of the x-ray spectrum. Images were obtained using GAGG and CsI scintillators with incident x-ray spectra split from continuous x-rays and were processed using energy weighted subtraction and energy subtraction. The composition of the phantom for image acquisition consisted of calcium embedded in the breast tissue, and the phantom images were analyzed by comparing the contrast-to-noise ratio (CNR). Based on the simulation results, GAGG demonstrates improved CNR compared to CsI, and the energy weighted subtraction method yields similar or higher CNR values compared to the energy subtraction method except in the case of using the CsI detector in a continuous x-ray spectrum. Moreover, the CNR values were higher for split x-rays than for continuous x-rays. In conclusion, GAGG detectors, the energy weighted subtraction method, and a split spectrum can be used to enhance the contrast of images while augmenting the fine calcification of simulated breast images.

[en] A large-angle gamma camera was developed for imaging small animal models used in medical and biological research. The simulation study shows that a large field of view (FOV) system provides higher sensitivity with respect to a typical pinhole gamma cameras by reducing the distance between the pinhole and the object. However, this gamma camera suffers from the degradation of the spatial resolution at the periphery region due to parallax error by obliquely incident photons. We propose a new method to measure the depth of interaction (DOI) using three layers of monolithic scintillators to reduce the parallax error. The detector module consists of three layers of monolithic CsI(Tl) crystals with dimensions of 50.0 × 50.0 × 2.0 mm³, a Hamamatsu H8500 PSPMT and a large-angle pinhole collimator with an acceptance angle of 120°. The 3-dimensional event positions were determined by the maximum-likelihood position-estimation (MLPE) algorithm and the pre-generated look up table (LUT). The spatial resolution (FWHM) of a Co-57 point-like source was measured at different source position with the conventional method (Anger logic) and with DOI information. We proved that high sensitivity can be achieved without degradation of spatial resolution using a large-angle pinhole gamma camera: this system can be used as a small animal imaging tool.

[en] The new method to correct a parallax error and the loss of coincidence counts caused by the gap between modules was developed for a small animal PET scanner. We proposed the TraPET scanner composed of 6 dual-layer phoswich detector modules. Each detector module consists of a 5.0 mm-thick trapezoidal-shaped monolithic LSO crystal and a 23 x 23 array of GSO crystal. The layer of interaction is identified by the pulse shape discrimination method. One detector module was built and the algorithm for layer identification was optimized. The dual-layer crystals were optically coupled to a Hamamatsu H8500 position-sensitive PMT and a resistive charge divider was used to multiplex 64-channel anode outputs into 4-channel position signals. The 4 signals have been sampled continuously by 14-bit ADC at a sampling rate of 105 MHz and the pulse shape discrimination algorithm was achieved through FPGA programming. The detector module was irradiated with a Na-22 point source from the side of the crystals to obtain flood images of each layer and two layers were clearly identified, thus verifying the DOI capability. The TraPET detector proved to be a reliable design for correcting the parallax error and improving the sensitivity simultaneously in the small animal PET.