Takumi Hamaguchi

Measurement of effective atomic numbers using energy-resolved computed tomography

For ion radiation therapy, the measurement of effective atomic numbers, Zeff, is necessary to know the material distribution in a human body; the range of ions entering the human body is influenced by the material distribution along their paths. Zeff, however, cannot be measured at hospitals because monochromatic X-rays with different energies are necessary and are used only at synchrotron facilities. To make Zeff measurements at hand, we propose energy-resolved computed tomography (CT) using a “transXend detector”. By assigning two narrow energy ranges in the unfolding process of the data obtained by the transXend detector, Zeff for acrylic and aluminum can be estimated by energy-resolved CT. The estimated Zeff are compared with those obtained by dual-energy and monochromatic X-ray CT.

Response function estimation with fine energy bins for the energy-resolved computed tomography using a transXend detector

ABSTRACT A new ‘transXend’ detector system has been developed for energy-resolved computed tomography (CT). It consists of several segmented detectors that measure X-rays as electric currents. Response functions of segmented detectors are estimated using component materials of a body under inspection to unfold X-ray spectra. To avoid material-dependent measurements, response functions inherent to segmented detectors are evaluated by Monte Carlo calculations. CT was performed for a phantom consisting of five resins and was analyzed by the estimated response functions. The linear attenuation coefficients for the five resins have excellent agreement with database values.

Two-dimensional “transXend” detector with band structure absorbers for third-generation energy-resolved computed tomography with improved spatial resolution

ABSTRACT Energy-resolved computed tomography (CT) is a method that can generate multiple CT images reconstructed by the X-rays in specific energy ranges. We have previously discussed a lattice absorber type of X-ray detector for energy-resolved CT. We have now developed a band absorber type detector with the aim of improving spatial resolution. We compare spatial resolution and contrast-to-noise ratios for the two types of detectors.

Metal artifact reduction by filter-based dual-energy cone-beam computed tomography on a bench-top micro-CBCT system: concept and demonstration

Abstract We evaluated two dual-energy cone-beam computed tomography (DE-CBCT) methodologies for a bench-top micro-CBCT system to reduce metal artifacts on reconstructed images. Two filter-based DE-CBCT methodologies were tested: (i) alternative spectral switching and (ii) simultaneous beam splitting. We employed filters of 0.6-mm-thick tin and 0.1-mm-thick tungsten to generate high- and low-energy spectra from 120 kVp X-rays, respectively. The spectral switching method was imitated by two half scans with different filters (pseudo-switching). Filters were placed and between the X-ray tube and a phantom (‘1-u,’ ‘2-u’), a phantom and a flat panel detector (‘1-d,’ ‘2-d’), and compared with (iii) two half scans at 80 and 140 kVp [pseudo-(80,140)]. For the splitting method, two half-width filters were aligned along a rotating axis. Projections were separated into halves and merged with corresponding areas of opposed projections after one full rotation. A solid 30-mm-diameter acrylic phantom and an acrylic phantom with four 5-mm-diameter titanium rods were used. DE images were generated by weighted summation of the high- and low-energy images. The blending factor was changed from 0 to +5 in increments of 0.01. Relative errors (REs) of the linear attenuation coefficients of the two phantoms and the contrast-to-noise ratios (CNRs) between the titanium and acrylic regions were compared. All methods showed zero REs except for the method (2-d). CNRs for pseudo-switching with upstream placement were 1.4-fold larger than CNRs for the pseudo-(80,140) method. CNRs for the downstream placements were small. It was concluded that the pseudo-switching method with upstream placement is appropriate for reducing metal artifacts.

Performance improvement of the filter-type ‘transXend’ energy-resolving detector by considering noise sensitivity

ABSTRACT The filter-type ‘transXend’ detector is an energy-resolving X-ray detector consisting of an energy-integrating flat-panel detector and multiple filters. In our previous studies, we have shown the effectiveness of the transXend detector, but the filters used were not optimized. To obtain better performance, the filters, especially their thickness and material, should be considered. In this paper, we present a method that can preliminarily estimate filter performance by comparing their noise sensitivity before carrying out numerous experiments. Two kinds of filter sets, Cu–Sn and W–Ag, with various thicknesses were evaluated. The results suggest that to image a 20-cm-thick object with 120-kV X-rays, an unfiltered channel and a channel filtered with 0.5-mm-thick Sn or 0.4-mm-thick Ag may be the best combination. The optimal filter thickness will be smaller if the object is thinner and the tube voltage is lower. For applications that require a wide dynamic range of detector response, a channel with a W filter may be better than an unfiltered channel. To verify the calculation results, computed tomography imaging experiments with a 3-cm-diameter phantom were also performed, and the experimental results showed good agreement with the calculation results.