Ryo Imamura

A Current-Mode Detector for Unfolding X-ray Energy Distribution

To turn the advantage of energy measurement in x-ray transmission diagnosis into practice, we propose a novel detector for the estimation of x-ray energy distribution. This detector consists of several segment detectors arrayed in the direction of x-ray incidence. Each segment detector measures x-rays as current. With unfolding measured currents, the x-ray energy distribution is obtained. The practical application of this detector was verified by estimating the iodine thickness in an acryl phantom.

Unfolding Method with X-ray Path Length-Dependant Response Functions for Computed Tomography Using X-ray Energy Information

The computed tomography (CT) values obtained by the energy subtraction method with a transXend detector, which measured X-rays as current and gave the corresponding X-ray energy information, show the disadvantage that the CT values are dependent on the thickness of a homogeneous phantom. In order to obtain constant CT values for a uniform material, a new unfolding method is proposed using variable response functions of the transXend detector according to the X-ray path length in the phantom. The CT values measured using the new unfolding method are discussed with respect to the energy range used in the unfolding process, the number of segment detectors, and the substrate of the segment detectors.

Using energy-resolved X-ray computed tomography with a current mode detector to distinguish materials

In conventional X-ray computed tomography (CT), X-rays are measured as electric current. Materials inside a subject are described by the linear attenuation coefficients averaged by the energy spectrum of the X-rays. A CT image cannot distinguish materials such as iodine and calcium, because the linear attenuation coefficient is not inherent to a material, but the product of X-ray mass attenuation coefficient and the density of the material. Materials such as iodine and calcium can be distinguished using an energy-resolved CT technique, with a current-mode detector system, using segment detectors aligned in the direction of X-ray incidence: the energy-resolved CT images are reconstructed by the X-rays with the energy of interest, by unfolding electric currents measured by the segment detectors.

Low dose exposure diagnosis with a transXend detector aiming for iodine-marked cancer detection

The energy resolved computed tomography (CT), which had advantage over conventional CT (twofold higher CT value for iodine contrast agent and being free from beam hardening effect), was shown practical by employing the transXend detector: it measured X-rays as electric current and gave energy distribution of incident X-rays after analysis. This article shows a new application of the transXend detector for estimating the thicknesses of acrylic, iodine, and aluminum in a phantom. For this purpose, the responses of the segment detectors in the transXend detector are changed intentionally with inserting filters. With previously obtained two-dimensional maps for acrylic–iodine and acrylic–aluminum thicknesses, which are shown by the ratios of electric currents measured by the segment detectors, the thickness of materials on the path of the X-rays are obtained by a transmission measurement.

Using X-ray Energy Information in CT Measurement of a Phantom with an Al Region

X-ray computed tomography (CT) using X-ray energy information has been studied by the present authors on acrylic phantoms containing an iodine contrast medium. To observe a human body, however, it is necessary to consider the bone. In this paper, CT measurements were made on a phantom with regions of both iodine and aluminum, which was used as a substitute for the bone. A filtered back-projection method and a maximum likelihood-expectation maximization method were employed for image reconstruction.

Advantages of Response Function Change in a transXend Detector with Various Scintillators as Substrates of Segment Detectors

To enable practical computed tomography (CT) that uses the energy information of X-rays, the “transXend detector” was developed to provide energy information about incident X-rays by measuring them as an electric current. The transXend detector requires a spectrum survey method in the unfolding process for measuring the energy distribution of incident X-rays, when the response functions of segment detectors have nearly the same behavior. When employing various scintillators with different effective atomic numbers and densities as the substrates of the segment detectors, better convergence is obtained in the unfolding process by using only one initial guess spectrum. Additionally, less dose exposure is possible when using the transXend detector with various segment detectors, compared with the transXend detector that consists of the segment detectors with the same substrate.

Simulation Study on Unfolding Methods for Diagnostic X-rays and Mixed Gamma Rays

A photon detector operating in current mode that can sense X-ray energy distribution has been reported. This detector consists of a row of several segment detectors. The energy distribution is derived using an unfolding technique. In this paper, comparisons of the unfolding techniques among error reduction, spectrum surveillance, and neural network methods are discussed through simulation studies on the detection of diagnostic X-rays and gamma rays emitted by a mixture of 137Cs and 60Co. For diagnostic X-ray measurement, the spectrum surveillance and neural network methods appeared promising, while the error reduction method yielded poor results. However, in the case of measuring mixtures of gamma rays, the error reduction method was both sufficient and effective.