Tatsuya Nagano

Initial evaluation of linear and spatially oriented planar images from a new dental panoramic system based on tomosynthesis

OBJECTIVE The purpose of this study was to describe a newly developed dental panoramic system based on the tomosynthesis method and to validate the accuracy of linear and spatially oriented planar images. STUDY DESIGN An original robotic mechanism incorporating a new high-speed cadmium-telluride (CdTe) semiconductor detector was fabricated to acquire panoramic images (raw data). The shift-and-add tomosynthesis method was applied to facilitate changes in the depth of the panoramic imaging layer. Using the texture mapping method, planar and spatially oriented images were reconstructed along a custom curved imaging plane. Using a custom phantom and dry skulls, the accuracy of selected linear measurements was evaluated. RESULTS Preliminary measurements demonstrated acceptable linear accuracy in reconstructed panoramic images with variations <5%. CONCLUSIONS This preliminary investigation demonstrates that dental panoramic images acquired by a novel robotic mechanism and CdTe detector using a tomosynthesis method provides planar and spatially oriented images with an image quality that may be acceptable for dental practice.

Development of mammography system using CdTe photon counting detector for the exposure dose reduction

We propose a new mammography system using a cadmium telluride (CdTe) photon-counting detector for exposure dose reduction. In contrast to conventional mammography, this system uses high-energy X-rays. This study evaluates the usefulness of this system in terms of the absorbed dose distribution and contrast-to-noise ratio (CNR) at acrylic step using a Monte Carlo simulation. In addition, we created a prototype system that uses a CdTe detector and automatic movement stage. For various conditions, we measured the properties and evaluated the quality of images produced by the system. The simulation result for a tube voltage of 40 kV and tungsten/barium (W/Ba) as a target/filter shows that the surface dose was reduced more than 60% compared to that under conventional conditions. The CNR of our proposal system also became higher than that under conventional conditions. The point at which the CNRs coincide for 4 cm polymethyl methacrylate (PMMA) at the 2-mm-thick step corresponds to a dose reduction of 30%, and these differences increased with increasing phantom thickness. To improve the image quality, we determined the problematic aspects of the scanning system. The results of this study indicate that, by using a higher X-ray energy than in conventional mammography, it is possible to obtain a significant exposure dose reduction without loss of image quality. Further, the image quality of the prototype system can be improved by optimizing the balance between the shift-and-add operation and the output of the X-ray tube. In future work, we will further examine these improvement points.

Accuracy of linear attenuation coefficients measured with a photon counting CT system

The purpose of our research is to develop a photon counting CT system with a semiconductor detector. The photon counting CT system enables us to decompose materials, and this information is useful to diagnose diseases. We developed a new CdTe detector that was able to measure x-rays with the count rate of 107 counts/sec/mm2 with four energy windows. The size of a CdTe detector module was 8×8 mm2, and that of a pixel was 0.2 × 0.2 mm2. The thickness of the detector was 1 mm. The active area of our detector was 8 × 144 mm2. We evaluated the performance of the photon counting CT images in terms of the accuracy of reconstructed linear attenuation coefficients. In addition, we compared these reconstructed images with those acquired with the energy integration detector with the CdTe semiconductor detector. The results showed that our detector could reconstruct linear attenuation coefficients with the error ratio of less than 3 % compared with the theoretical value.

Advantages of Energy-Binned Photon Counting Detector

We developed an energy-binned photon counting (EBPC) detector with a CdTe crystal, in which we can measure photons with four energy windows. The data acquired with the detector have information about the energy of x-rays that pass through the object, so that we can make a desired image by adding EBPC images after multiplying an appropriate weight to an image acquired with each energy window. With this energy weighting image we can improve the image contrast and reduce the beam hardening effects. This paper compared two data acquisition methods: one is an energy integration method and the other is the EBPC method. To compare these two methods we conducted Monte Carlo simulations and experiments with our newly developed EBPC detector. The results showed that the EBPC detector could improve the dynamic rage of acquired images.