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Takanori Tsunoo

Publications and source records attributed to Takanori Tsunoo.

10 recordsLinked to original sources
PubMed2006

Utility of 256-slice cone beam tomography for real four-dimensional volumetric analysis without electrocardiogram gated acquisition.

PURPOSE: Current ECG-gated multislice CT can reveal any cardiac phase data, including four-dimensional (4D) images, but cannot acquire the whole heart in one scanning, and arrhythmias impair the quality of the images. We used a prototype 256-slice cone beam CT (Athena, Sony Toshiba), with which the whole heart can be acquired in one scanning. MATERIALS AND METHODS: A pulsating device with contrast material (300 mgI/dl) diluted 10x with saline was moved at 5, 40, 60, 70, and 90 to-and-fro movements/min. Non-ECG-gated 256-slice cone beam CT with 256 x 0.5 mm slice thickness was performed during one to-and-fro motion at each rate. After acquisition, each to-and-fro motion was divided into 20 frames, and each volume was measured and volumetric curves were constructed. RESULTS: Even without ECG-gated acquisition, the configuration of the pulsating device at any rate continued to the through plane without any gaps, and the 4D movie of the pulsating device could be observed at any rate except 60 movements/min. Volumes of end-diastole (ED) and end-systole (ES), and ejection fraction (EF) at static state were 81.7, 17.5 ml, and 79% respectively. ED volumes were 81.7, 81.7, 70.3, 63.7, 68.3 and 65.9 ml, ES volumes were 17.5, 30.9, 39.8, 62.7, 55.0 and 43.2 ml, and EF was 79, 62, 43, 2, 19 and 34% at 0, 5, 40, 60, 70, and 90 to-and-fro movements/min, respectively. The ratios of ED volume, using the static state as the reference, were 100, 86, 78, 84 and 81%, those of ES volume were 177, 227, 358, 314 and 247%, and those of EF were 78, 54, 3, 24 and 43% at 5, 40, 60, 70, and 90 to-and-fro movements/min, respectively. From the configuration of volumetric curves, only 5/min could be evaluated. At 60 movements/min, the same device images without any motion were observed in 4D images during one to-and-fro motion. This may be because one to-and-fro time and one scanning time were the same (1 s). CONCLUSION: Even without ECG-gated acquisition, this new 256-slice cone beam CT achieved real 4D analysis of the pulsating device. The ED volume and the configuration of volumetric curve could only be evaluated up to 5 movements/min, but because of poor spatial resolution (1 s/rotation), even at 5 movements/min ES volume tended to be overestimated. As a result, EF tended to be underestimated, which may be improved in the next generation (0.5 s/rotation).

Cardiac Volume↗
PubMed2006

Superiority of synchrony of 256-slice cone beam computed tomography for acquiring pulsating objects. Comparison with conventional multislice computed tomography.

PURPOSE: A prototype 256-slice cone beam computed tomography (CT) provides complete volumetric data within a single gantry rotation (1 s/rotation) with 0.5 mm slice-thickness. MATERIALS AND METHODS: Calcified phantoms (200-400 HU) were attached to the balloon of a pulsating phantom and moved at a rate of 5-90/min. Acquisition was performed during one to-and-fro motion at each pulsation rate without electrocardiogram (ECG)-gating. Each period was divided into 10 phases, and compared to conventional multislice CT scanning without ECG-gating. RESULTS: At 5-20/min, the configuration of calcified phantoms continued to the through-plane without gaps. At 60/min, duplicated calcified phantoms at end-systole and end-diastole were observed without motion. At 90/min, motion could be observed without gaps but was more blurred, and total calcified volume, Agatston scores, mean and max CT values of three phantoms were almost equal compared with those at static state. However, at 60/min, total calcified volume, scores, mean and max CT values of three phantoms were decreased to 64%, 37%, 80% and 56%, respectively, compared with those at static state. In multislice CT, even at lower rates, there were gaps in the through-plane. At 60/min, total calcified volume, scores, mean and max CT values of three phantoms were decreased to only 8%, 3%, 79% and 53%, respectively, compared with static state. CONCLUSION: This new prototype's unique character (synchrony) enables the acquisition of pulsating objects. These can be acquired without gaps in the through-plane even in the absence of ECG-gating. However, its present temporal resolution only permits accurate quantitative evaluation of calcium up to 20/min.

Electrocardiography↗
PubMed2006

Properties of the prototype 256-row (cone beam) CT scanner.

We evaluated Feldkamp artifacts, which are specific to cone-beam computed tomography (CT), in phantom and clinical studies using the 256-multidetector-row CT (256MDCT), and compared the reconstruction accuracy of axial and helical scans. Image noise, slice sensitivity profile (SSP) and artifacts with the 256MDCT were evaluated using a phantom, and the results were compared to those of a 64MDCT. We also examined chest and abdomen scans produced with the 256MDCT in volunteers. For the axial scan, Feldkamp artifacts were visualized as high-frequency streak-like artifacts that are oriented horizontally at the edge of the scan region in the phantom study. Similar results were obtained with the volunteers in soft-tissue regions near either bony structures or air pockets. Feldkamp artifacts with the 256MDCT can lead to misdiagnosis if not correctly identified and minimized via helical scanning. Image noise was less for axial than helical scans, while SSP was better with helical than axial scans. Feldkamp artifacts observed in the 256MDCT images, however, did not generally affect the interpretation of images. The 256MDCT promises more accurate diagnosis, and will provide volumetric cine images of wider cranio-caudal coverage, enabling new applications of CT.

Adult↗
PubMed2006

Magnitude and effects of x-ray scatter in a 256-slice CT scanner.

We developed a prototype 256-slice CT scanner that employs continuous rotation of a cone-beam with a larger cone angle than conventional multidetector CTs (MDCT) to ensure a wide field of view. However, a larger cone angle may result in image deterioration due to increased x-ray scatter. Scattered radiation causes the detected signals to deviate from the true measurement of primary x-ray intensity and may result in artifacts (e.g., cupping and streak artifacts), quantitative inaccuracy in reconstructed CT number, and degradation of contrast-to-noise ratio (CNR). To reduce the effects of scatter, the 256-slice scanner incorporates an antiscatter collimator. Here, we estimated the magnitude of x-ray scatter in the prototype 256-slice CT scanner under clinical scan conditions and quantified the effects of this scatter on CT number accuracy, image noise, uniformity, and low contrast detectability. Although most experiments were performed with the antiscatter collimator, we also estimated the magnitude of x-ray scatter without the collimator to evaluate the scatter rejection efficiency of the collimator. The scatter-to-primary energy fluence ratio (SPR) without the collimator increased as cone angle increased, with estimated values of 49.7% for a 138 mm beam width with a phantom of 200 mm diameter, and 78.5% for a 320 mm diameter phantom. Estimated SPR was drastically decreased with the collimator, with an SPR reduction rate (ratio of SPR with and without the collimator) of 12.7% and 16.8% for the 200 and 320 mm diameter phantoms, respectively. The reduction in x-ray scatter by the collimator resulted in a considerable reduction in scatter effects. The measured uniformity was good and was independent of scatter amount. Although scatter still affected CT number accuracy, this could be corrected by rescaling. Further, although the CNR was decreased, in theory at least, the change was so subtle that it had no substantial effect on low-contrast detectability.

Algorithms↗
PubMed2005

Enlarged longitudinal dose profiles in cone-beam CT and the need for modified dosimetry.

In order to examine phantom length necessary to assess radiation dose delivered to patients in cone-beam CT with an enlarged beamwidth, we measured dose profiles in cylindrical phantoms of sufficient length using a prototype 256-slice CT-scanner developed at our institute. Dose profiles parallel to the rotation axis were measured at the central and peripheral positions in PMMA (polymethylmethacrylate) phantoms of 160 or 320 mm diameter and 900 mm length. For practical application, we joined unit cylinders (150 mm long) together to provide phantoms of 900 mm length. Dose profiles were measured with a pin photodiode sensor having a sensitive region of approximately 2.8 x 2.8 mm2 and 2.7 mm thickness. Beamwidths of the scanner were varied from 20 to 138 mm. Dose profile integrals (DPI) were calculated using the measured dose profiles for various beamwidths and integration ranges. For the body phantom (320-mm-diam phantom), 76% of the DPI was represented for a 20 mm beamwidth and 60% was represented for a 138 mm beamwidth if dose profiles were integrated over a 100 mm range, while more than 90% of the DPI was represented for beamwidths between 20 and 138 mm if integration was carried out over a 300 mm range. The phantom length and integration range for dosimetry of cone-beam CT needed to be more than 300 mm to represent more than 90% of the DPI for the body phantom with the beamwidth of more than 20 mm. Although we reached this conclusion using the prototype 256-slice CT-scanner, it may be applied to other multislice CT-scanners as well.

Head↗
PubMed2005

Cardiovascular circulation and hepatic perfusion of pigs in 4-dimensional films evaluated by 256-slice cone-beam computed tomography.

BACKGROUND: In both cardiac and hepatic disorders it is desirable to accurately visualize the direction and scale of blood flow in the whole organ in pulsating 3-dimensional (D) images, which are known as 4-D images. METHODS AND RESULTS: The present study used 256-slice cone-beam computed tomography (CT) (Athena, Sony-Toshiba) at one rotation per second and a section thickness of 0.5 mm to show the dynamics of cardiovascular circulation and hepatic perfusion by contrast injection in 4-D films of pigs. Four pigs (20 kg each) were anesthetized with isoflurane. The distal tips of the catheters were positioned in the inferior vena cava (IVC) (pigs 1-3) and in the proper hepatic artery (pig 4). Volumetric scanning and injection of contrast material were started simultaneously and continued for 25 s with image reconstruction at 1-s intervals. In pigs 1-3, 4-D filming revealed the dynamics of cardiovascular circulation, first in the IVC, followed by the right ventricle and pulmonary artery, then the left ventricle, left atrium, pulmonary vein, and finally, the right heart disappeared and only the left heart and aorta remained visible. In pig 4, the hepatic arterial trees, followed by the venous trees, could be easily visualized in turn on the 4-D images. CONCLUSIONS: This technology successfully demonstrated cardiovascular circulation and hepatic perfusion in 4-D and will have clinical applicability.

Animals↗
PubMed2004

Physical performance evaluation of a 256-slice CT-scanner for four-dimensional imaging.

We have developed a prototype 256-slice CT-scanner for four-dimensional (4D) imaging that employs continuous rotations of a cone-beam. Since a cone-beam scan along a circular orbit does not collect a complete set of data to make an exact reconstruction of a volume [three-dimensional (3D) image], it might cause disadvantages or artifacts. To examine effects of the cone-beam data collection on image quality, we have evaluated physical performance of the prototype 256-slice CT-scanner with 0.5 mm slices and compared it to that of a 16-slice CT-scanner with 0.75 mm slices. As a result, we found that image noise, uniformity, and high contrast detectability were independent of z coordinate. A Feldkamp artifact was observed in distortion measurements. Full width at half maximum (FWHM) of slice sensitivity profiles (SSP) increased with z coordinate though it seemed to be caused by other reasons than incompleteness of data. With regard to low contrast detectability, smaller objects were detected more clearly at the midplane (z = 0 mm) than at z = 40 mm, though circular-band like artifacts affected detection. The comparison between the 16-slice and the 256-slice scanners showed better performance for the 16-slice scanner regarding the SSP, low contrast detectability, and distortion. The inferiorities of the 256-slice scanner in other than distortion measurement (Feldkamp artifact) seemed to be partly caused by the prototype nature of the scanner and should be improved in the future scanner. The image noise, uniformity, and high contrast detectability were almost identical for both CTs. The 256-slice scanner was superior to the 16-slice scanner regarding the PSF, though it was caused by the smaller transverse beam width of the 256-slice scanner. In order to compare both scanners comprehensively in terms of exposure dose, noise, slice thickness, and transverse spatial resolution, K=Dsigma2ha3 was calculated, where D was exposure dose (CT dose index), sigma was magnitude of noise, h was slice thickness (FWHM of SSP), and a was transverse spatial resolution (FWHM of PSF). The results showed that the K value was 25% larger for the 16-slice scanner, and that the 256-slice scanner was 1.25 times more effective than the 16-slice scanner at the midplane. The superiority in K value for the 256-slice scanner might be partly caused by decrease of wasted exposure with a wide-angle cone-beam scan. In spite of the several problems of the 256-slice scanner, it took a volume data approximately 1.0 mm (transverse) x 1.3 mm (longitudinal) resolution for a wide field of view (approximately 100 mm long) along the zeta axis in a 1 s scan if resolution was defined by the FWHM of the PSF or the SSP, which should be very useful to take dynamic 3D (4D) images of moving organs.

Biophysical Phenomena↗
PubMed2003

Electron density measurement with dual-energy x-ray CT using synchrotron radiation.

Monochromatic x-ray computed tomography (CT) at two different energies provides information about electron density of human tissue without ambiguity due to the beam hardening effect. This information makes the treatment planning for proton and heavy-ion radiotherapy more precise. We have started a feasibility study on dual energy x-ray CT by using synchrotron radiation. A translation-rotation scanning CT system was developed for quantitative measurement in order to clarify what precision in the measurement was achieved. Liquid samples of solutions of K2HPO4 and solid samples of tissue equivalent materials were used to simulate human tissue. The experiments were carried out using monochromatic x-rays with energies of 40, 70 and 80 keV produced by monochromatizing synchrotron radiation. The solid samples were also measured in a complementary method using high-energy carbon beams to evaluate the electron densities. The measured electron densities were compared with the theoretical values or the values measured in the complementary method. It was found that these values were in agreement in 0.9% on average. Effective atomic numbers were obtained as well from dual-energy x-ray CT. The tomographic image based on each of the electron densities and the effective atomic number presents a different feature of the material, and its contrast drastically differs from that in a conventional CT image.

Connective Tissue↗
PubMedDate not supplied

Four-dimensional computed tomography (4D CT)--concepts and preliminary development.

Four-dimensional computed tomography (4D CT) is a dynamic volume imaging system of moving organs with an image quality comparable to that of conventional CT. 4D CT will be realized by several technical breakthroughs for dynamic cone-beam CT: (1) a large-area two-dimensional (2D) detector; (2) high-speed data transfer system; (3) reconstruction algorithms; (4) ultra-high-speed reconstruction computer; and (5) high-speed, continuously rotating gantry. Among these, development of the 2D detector is one of the main tasks because it should have as wide a dynamic range and as high a data acquisition speed (view rate) as present CT detectors. We are now developing a 4D CT scanner together with the key components. It will take one volume image in 0.5 sec with a 3D matrix of 512 x 512 x 512. This paper describes the concepts and designs of the 4D CT system, as well as preliminary development of the 2D detector.

Equipment Design↗