Rika Baba

Cone-Beam CT with Flat-Panel-Detector Digital Angiography System: Early Experience in Abdominal Interventional Procedures

We developed a cone-beam computed tomography (CBCT) system equipped with a large flat-panel detector. Data obtained by 200° rotation imaging are reconstructed by means of CBCT to generate three-dimensional images. We report the use of CBCT angiography using CBCT in 10 patients with 8 liver malignancies and 2 hypersplenisms during abdominal interventional procedures. CBCT was very useful for interventional radiologists to confirm a perfusion area of the artery catheter wedged on CT by injection of contrast media through the catheter tip, although the image quality was slightly degraded, scoring as 2.60 on average by streak artifacts. CBCT is space-saving because it does not require a CT system with a gantry, and it is also time-saving because it does not require the transfer of patients.

Comparison of flat-panel detector and image-intensifier detector for cone-beam CT

We evaluated a flat-panel detector (FPD) (scintillator screen and a-Si photo-sensor array) for use in a cone-beam computed tomography (CT) detector and compared it with an image-intensifier detector (IID). The FPD cone-beam CT system has a higher spatial resolution than the IID system. At equal pixel sizes, the standard deviation of noise intensity of the FPD system is equal to that of the IID system. However, the circuit noise of the FPD must be reduced, especially at low doses. Our evaluations show that the FPD system has a strong potential for use as a cone-beam CT detector because of high-spatial resolution.

Development of angiography system with cone-beam reconstruction using large-area flat-panel detector

A novel angiography system with cone-beam reconstruction using a large-area flat panel detector (FPD), with 40x30cm active area and 2048x1536 matrixes with a 194μm pixel pitch, has been developed. We present results on a basic performance, spatial resolution and contrast detectability obtained on this angiography system with cone-beam function using the FPD, and compare with a conventional angiography system with an image intensifier (I.I.) and charge-coupled device (CCD) camera. We’d achieved a fast acquisition, 15 seconds as for a subtraction mode by rotating a ceiling suspended C-arm at a speed of 40 degrees per second, and ensured a large reconstructed columnar volume, φ250mmx180mm, by using the large-area detector. As a result of the evaluation, the 3D image acquired from the FPD system has a high spatial resolution with no distortion and good contrast detectability.

Ellipsoid scan: chest cone-beam CT with a large ellipsoidal view field using a 16-in. x-ray image intensifier

We propose a cone-beam computed tomography (CT) system that has a large field of view and high image quality, and that can be applied to the chest imaging. This system uses a 16- inch x-ray image intensifier and a television camera. To enlarge the field of view, an ellipsoid-scan sequence is used, which requires the subject to be moved parallel to the transaxial plane during scanning. The contrast resolution is increased by applying a television camera with high sensitivity and non-linear efficiency. We tested this system using a stationary apparatus, and obtained an isotropic 3D image of a chest phantom which had 0.64 mm voxels and covered both lungs. This system attained better spatial resolution for coronal images and its contrast resolution in the transaxial images was only 3 to 7 times larger than conventional spiral-scan CT at the same x-ray dose. This system is promising for ling cancer screening, precise diagnosis and surgery.

Improving image quality of synchrotron CT by scattered X-ray correction

We developed a high-resolution CT system using synchrotron radiation. The system acquires high-quality CT images because the synchrotron CT has no beam-hardening effect that results from using monochromatic X-ray. It is said that X-ray scattering has no effects on the synchrotron CT images because a detector is set apart from a subject. However, the images have a disadvantage in non-uniformity caused by scattered X-rays owing to an area X-ray beam and a two-dimensional detector. The X-ray scattering decreased the accuracy of the CT number and increased the number of artifacts in CT images. We developed an accurate process for correcting scattered X-rays for the synchrotron CT. The correction process was applied for the synchrotron CT at 35-keV radiation. When a 10-mm-diameter 20%-hydroxyapatite homogeneous column phantom was used, the scattered X-rays led to a reduction of about 45% in the pixel values of CT images. With the correction, the pixel values were almost completely recovered.

A new x-ray imaging technique for radiography mode of flat-panel imager

A digital radiography system using a flat-panel imager, which has a novel imaging technique for a radiography mode, has been developed. A radiographic image captured by the new imaging technique has a wide dynamic range in comparison with conventional radiographic images. The purpose of this presentation is to show the basic performance of the image quality acquired by the new imaging technique and compare it with an image taken by a conventional technique. The flat-panel imager has a gain switching capability, normally used in a dynamic imaging mode for a cone-beam CT study. The gain switching method has two gain settings and switches between them automatically, depending on the incident dose to each pixel of flat-panel imager. As a result of the gain switching method, an image having wide dynamic range is achieved. In this study, we applied the gain switching method to the radiography mode, and achieved a radiographic image with wider dynamic range than a conventional radiograph. Furthermore, we have also developed an algorithm for calibration of the gain switching method in radiography mode.

Development of high-resolution x-ray CT system using parallel beam geometry

For fine three-dimensional observations of large biomedical and organic material samples, we developed a high-resolution X-ray CT system. The system consists of a sample positioner, a 5-μm scintillator, microscopy lenses, and a water-cooled sCMOS detector. Parallel beam geometry was adopted to attain a field of view of a few mm square. A fine three-dimensional image of birch branch was obtained using a 9-keV X-ray at BL16XU of SPring-8 in Japan. The spatial resolution estimated from the line profile of a sectional image was about 3 μm.

Feasibility study of a high-spatial resolution x-ray computed tomography using sub-pixel shift method

A high-spatial resolution X-ray computed tomography (CT) adopting a sub-pixel shift method has been developed. By calculating sectional images, using plural CT datasets obtained by scanning the X-ray imager, the spatial resolution can be reduced relative to the sub-pixel size of an X-ray imager. Feasibility observations of a biomedical sample were performed using 12-keV monochromatic synchrotron radiation and a photon-counting X-ray imager 174-μm pixels in size. Four CT measurements were performed to obtain datasets at different positions of the X-ray imager. Fine sectional images were obtained successfully, and the spatial resolution was estimated as 80-μm, which corresponds to just under half the pixel size of the imager. In addition, a fine 3D image was also obtained by scanning the imager two-dimensionally.