Demonstration of enhanced K-edge angiography using a cerium target x-ray generator

Fully digitalized triple-energy x-ray computed tomography with high spatial resolutions using beam hardening

To regulate the effective photon energy with a constant tube voltage and to perform enhanced K-edge x-ray imaging, we built a prototype fully digitalized triple-energy x-ray computed tomography (TECT) scanner utilizing beam hardening. An object on the turntable is irradiated by a 0.1-mm-focus x-ray tube at 1.4-time-magnification. 720 raw radiograms are obtained using a flat panel detector, and 512 tomograms are reconstructed. With an increasing digital amplification factor, the gray raw-density projections obtained using low-energy-photon absorption disappeared at a constant maximum raw density, and the effective energy was increased by x-ray beam hardening. TECT was performed at digital amplifier factors below 3.0, and the effective energy increased with increasing amplification factors. In particular, fine blood vessels were visible using gadolinium-K-edge CT.

Embossed x-ray computed tomography utilizing pixel-shifted dual-energy subtraction

To observe fine blood vessels as uneven tomographic images at a high contrast, we performed tentative experiments on embossed x-ray computed tomography (CT). We constructed a cone-beam CT scanner and carried out dual-energy CT with tube voltages of 60 and 100 kV. X-ray photons penetrating through an object were detected using an indirect-conversion flat panel detector, and radiograms were produced and sent to a personal computer to reconstruct tomograms. Embossed CT was performed using pixel-shifted dual-energy subtraction, and blood vessels filled with Gd medium were observed as uneven images at high contrast and spatial resolutions. Using 1.4-time magnification imaging in combination with a 0.1-mm-focus x-ray tube, the diameter of the object visible on the embossed CT was below 100 μm.

A rotating cerium anode X-ray system allows visualization of intramural coronary vessels after cardiac stem cell therapy for myocardial infarction

Conventional angiography is insufficient for evaluating the therapeutic effect of cardiac regeneration therapy. A microangiographic X-ray system using a cerium anode was developed. Cerium has a characteristic X-ray with a peak at 34.6 keV, which allows visualization of tiny amounts of iodine. The performance of the cerium anode X-ray system was evaluated in two excised normal canine hearts and in excised ischemic canine hearts treated with c-kit-positive cardiac stem cells (5 canines) or without cells (5 control canines). In the normal canines, branches penetrating from the left anterior descending artery into the myocardium were visualized, down to third-order branches. In just the treated hearts treated with stem cells, small vessels characterized by irregular vessel walls were observed. The cerium anode X-ray system allowed visualization of microvessels in excised ischemic canine hearts, and may evaluate the effect of cardiac stem cell therapy.

100 μA-100 kV Photon-counting X-ray Computed Tomography System Using an LSO-MPPC Detector and a High-Speed Comparator and its Application to Gadolinium Imaging

A high-sensitive x-ray computed tomography (CT) system is useful for decreasing absorbed dose for patients, and we performed preliminary experiments for first-generation photon-counting CT using a high-sensitive single detector. X-ray photons are detected using an LSO [Lu₂(SiO₄)O] single crystal scintillator and a multipixel photon counter (MPPC). The photocurrent from the MPPC is amplified by a current-voltage amplifier and an integrator, and the event pulse is sent to a high-speed comparator. Logical pulses are then produced by the comparator and are counted by a counter card. Tomography is accomplished by repeated linear scans and rotations of an object, and projection curves of the object are obtained by the linear scan. The count rate decreased with increase in lower level voltage of the comparator V_l, and the maximum count rate was 265 kcps at a V_l of 0.4 V. The exposure time for obtaining a tomogram was 10 minutes at a scan step of 0.5 mm and a rotation step of 1.0°. The image contrast of gadolinium medium slightly varied with change in V_l. We carried out low-dose-rate photon-counting CT at a tube current of 100 μA and a tube voltage of 100 kV. The energy-dispersive effect of the CT image was confirmed by selecting V_l. The absorbed dose for objects can be reduced using the linear detector consisting of plural LSO-MPPC detectors.

Demonstration of enhanced iodine K-edge imaging using an energy-dispersive X-ray computed tomography system with a 25 mm/s-scan linear cadmium telluride detector and a single comparator

An energy-dispersive (ED) X-ray computed tomography (CT) system is useful for carrying out monochromatic imaging. To perform enhanced iodine K-edge CT, we developed an oscillation linear cadmium telluride (CdTe) detector with a scan velocity of 25 mm/s and an energy resolution of 1.2 keV. CT is performed by repeated linear scans and rotations of an object. Penetrating X-ray photons from the object are detected by the CdTe detector, and event signals of X-ray photons are produced using charge-sensitive and shaping amplifiers. The lower photon energy is determined by a comparator device, and the maximum photon energy of 60 keV corresponds to the tube voltage. Rectangular-shaped comparator outputs are counted by a counter card. In the ED-CT, tube voltage and current were 60 kV and 0.30 mA, respectively, and X-ray intensity was 14.8 μGy/s at 1.0m from the source at a tube voltage of 60 kV. Demonstration of enhanced iodine K-edge X-ray CT for cancer diagnosis was carried out by selecting photons with energies ranging from 34 to 60 keV.

Embossed radiography utilizing energy subtraction

Currently, it is difficult to carry out refraction-contrast radiography by using a conventional X-ray generator. Thus, we developed an embossed radiography system utilizing dual-energy subtraction for decreasing the absorption contrast in unnecessary regions, and the contrast resolution of a target region was increased by use of image-shifting subtraction and a linear-contrast system in a flat panel detector (FPD). The X-ray generator had a 100-microm-focus tube. Energy subtraction was performed at tube voltages of 45 and 65 kV, a tube current of 0.50 mA, and an X-ray exposure time of 5.0 s. A 1.0-mm-thick aluminum filter was used for absorbing low-photon-energy bremsstrahlung X-rays. Embossed radiography was achieved with cohesion imaging by use of the FPD with pixel sizes of 48 x 48 microm, and the shifting dimension of an object in the horizontal direction ranged from 100 to 200 microm. At a shifting distance of 100 mum, the spatial resolutions in the horizontal and vertical directions measured with a lead test chart were both 83 microm. In embossed radiography of non-living animals, we obtained high-contrast embossed images of fine bones, gadolinium oxide particles in the kidney, and coronary arteries approximately 100 microm in diameter.