Yoshiyuki Nyui

Development of a multi-pinhole brain SPECT system with CdZnTe semiconductor detectors

The purpose of our research is to develop a new brain single photon emission CT (SPECT) system with semiconductor detectors. The gamma camera with semiconductor detectors with multi-pinhole enables us to make a compact brain SPECT system. In this paper we evaluated the performance of the proposed data acquisition system by simulations in terms of the number of data acquisition angles including the wobbling of the gantry with pinhole collimators. Moreover, we developed a prototype system with three semiconductor detector units to evaluate the proposed method experimentally. In this system, we used three pinhole collimators on the three surfaces of the hexagonal gantry around a targeted object. In front of three surfaces with pinhole collimators, we located three detector units that consisted of ten (5 × 2) CdZnTe modules. The size of a module was 39 × 39 mm2 (16 × 16 pixels) and the thickness of the CdZnTe crystal was 5 mm. The results obtained with the simulations confirmed the validity of the proposed brain SPECT system. And the results of the preliminary experiment validated our proposed system.

A novel approach to the visualization of four-dimensional cerebral angiography with cine angiography data measured at several views

Intracranial arteriovenous malformation (AVM) has a very complex shape, so it is very difficult to decide the targeted region accurately. Intracranial AVM causes convulsion and cerebral hemorrhage, and is therefore a deadly disease. At the present time, as a treatment for AVM, stereotactic radiosurgery is more useful than surgical treatment or chemotherapy. In this radiation therapy, the accuracy of radiosurgical treatment planning for intracranial AVM relies on requiring accurate information of the three dimensional shape and size of the AVM nidus. In conventional radiosurgical treatment planning for intracranial AVM, irradiation fields are determined with dynamic X-ray CT images or angiography of the brain. However, intracranial AVM is complicated in structure, so it is usually very difficult to determine the AVM nidus accurately. The purpose of this study is to clarify the AVM nidus accurately. In order to clarify its region, we proposed a novel method with a cardio-vascular X-ray system with flat panel detector. Our proposed method uses cine angiography measured at several views, and reconstructs a four- dimensional image with these projection data. Also, we tried to reconstruct images with several iterative reconstruction algorithms for transmission tomography. In this paper, we proposed this novel method and showed the validity of our proposed method with some simulations and fundamental experiments.

Acquiring localization of permanent radioactive sources (1-125) in prostate brachytherapy

Prostate brachytherapy has become an increasingly popular treatment for early stage prostate cancer. The accuracy of treatment planning for prostate brachytherapy depends on how accurately the radioactive seed sources are localized. In order to make an accurate treatment plan, the positions of the radioactive seed sources must be accurate. The proposed method of this study was to accurately acquire localization of the seed sources from little projection data (6, 9, and 18 views) with iterative reconstruction algorithms for transmission tomography. The results obtained by experimental study showed that the locations of dummy seeds were accurately observed with a reconstructed image with little projection data (about 9 views) and overlapping seeds were completely separated.

Dose planning for prostate cancer with a three-dimensional image

Treatment planning for ultrasound-guided transperineal I-125 permanent prostatic implants is a time consuming task, because this treatment uses many seeds (e.g. 50-80) and there are many solutions (seed positions) for optimizing the dose distribution. In conventional treatment planning for brachytherapy the locations of sources are usually input into a computer manually with reference to two X-ray films. We use so many sources in this treatment planning that we can hardly obtain accurate location of each source. That is, the identification of each seed with two X-ray films is very difficult. Even though we can use X-ray CT images for deciding on the source position, there are artifacts due to the high attenuation material. This paper proposes a method for obtaining accurate locations of radioactive sources from a few projection data (e.g. RPO 60, 30, LPO 60, 30 and 0 deg.) with a reconstruction method. In our method for obtaining actual source positions we use iterative image reconstruction techniques. With these source positions we made a treatment planning system with a personal computer. In this paper we show our preliminary results obtained with the proposed system.