Tohru Takeda

Development of a two-dimensional imaging system for clinical applications of intravenous coronary angiography using intense synchrotron radiation produced by a multipole wiggler.

A two-dimensional clinical intravenous coronary angiography system, comprising a large-size view area produced by asymmetrical reflection from a silicon crystal using intense synchrotron radiation from a multipole wiggler and a two-dimensional detector with an image intensifier, has been completed. An advantage of the imaging system is that two-dimensional dynamic imaging of the cardiovascular system can be achieved due to its two-dimensional radiation field. This world-first two-dimensional system has been successfully adapted to clinical applications. Details of the imaging system are described in this paper.

High‐Spatial‐Resolution Medical‐Imaging System Using a HARPICON Camera Coupled with a Fluorescent Screen

A high-sensitivity HARPICON camera was developed for medical X-ray imaging using a fluorescent screen. It is an avalanche-multiplication-type image pick-up tube and is 32 times more sensitive than conventional tubes. The camera also has a wider dynamic range than conventional medical-imaging cameras because a maximum output signal current of 2.3 muA is obtained and, in high-illumination-intensity regions, photocurrent is not proportional to illumination intensity. The fluorescent screen is an intensifying screen of the type used for radiographic screen-film combinations in medical examination. An X-ray image on the screen is focused on the photoconductive layer of the pick-up tube using a coupling lens with f/0.65. Experiments were performed using monochromated X-rays at the Photon Factory. An image of a spatial resolution test chart was taken in a 525 scanning-line mode of the camera. The chart pattern of 5 line-pairs mm(-1 )(spatial resolution of 100 mum) was observed at an X-ray input field of 50 x 50 mm. Real-time digital images of the heart of a 12 kg dog were obtained at a frame rate of 60 images s(-1) after injection of a contrast medium into an artery. The images were stored in digital format at 512 x 480 pixels with 12 bits pixel(-1). High-spatial-resolution and high-contrast images of coronary arteries were obtained in aortography using X-rays with energy above that of the iodine K edge; the image quality was comparable with that of conventional selective coronary angiography.

Development of a fluorescent x‐ray source for medical imaging

A fluorescent x‐ray source for medical imaging, such as K‐edge subtraction angiography and monochromatic x‐ray CT, has been developed. Using a 6.5 GeV accumulation ring in Tsukuba, fluorescent x rays, which range from about 30 to 70 keV are generated by irradiating several target materials. Measurements have been made of output intensities and energy spectra for different target angles and extraction angles. The intensities of fluorescent x rays at a 30 mA beam current are on the order of 1–3×106 photons/mm2/s at 30 cm from the local spot where the incident beam is collimated to 1 mm2. A phantom which contains three different contrast media (iodine, barium, gadolinium) was used for the K‐edge energy subtraction, and element selective CT images were obtained.

Iodine K-edge dual-energy imaging for subtraction angiography using synchrotron radiation and a 2-dimensional detector

Abstract A 2-dimensional energy-subtraction imaging system using synchrotron radiation has been improved in a number of ways; especially the energy-switching mechanism in which a monochromator crystal is oscillated trapezoidally has been improved. These improvements have led to real-time imaging of the right coronary artery in a rabbit after an intravenous injection of a contrast agent. This artery has a diameter of about 0.5 mm. However, this system has limitations concerning the energy difference between two component exposures and the total time of acquiring two images. We have tested a new method. Since the crystal was too heavy to oscillate quickly, the next step was to make the energy switching faster than in the previous method by the use of lighter moving parts. An iodine filter is used in the new method. Filter-chopping of the X-ray beam switches the dual-energy imaging energies, because the iodine filter selectively absorbs high-energy X-rays rather than K-edge energy X-ray. Moreover, by the use of the iodine filter, the energy difference between two exposures can be decreased to less than half of that in the previous method. Preliminary studies on the new method were performed in rats.

Large-Area Phase-Contrast X-ray Imaging System Using a Two-Crystal X-ray Interferometer--Development of an Interference-Pattern-Based Feedback Positioning System

To more accurately suppress the phase fluctuation of the interference beams of a large‐area phase‐contrast X‐ray imaging system using a two‐crystal X‐ray interferometer, a new feedback positioning system (FPS) has been developed and applied. The motion of interference patterns replaces the intensity of the interference beam in a small region as the feedback signal used in controlling the rotation of crystal blocks relative to each other. This FPS kept the phase fluctuation of the interference beams within π/15 over more than six hours. Examples of high‐quality two and three‐dimensional images of biological samples obtained by the imaging system with the new FPS are given.

Integrated image presentation of transmission and fluorescent X-ray CT using synchrotron radiation

Abstract We have developed a computed tomography (CT) system with synchrotron radiation (SR) to detect fluorescent X-rays and transmitted X-rays simultaneously. Both SR transmission X-ray CT (SR-TXCT) and SR fluorescent X-ray CT (SR-FXCT) can describe cross-sectional images with high spatial and contrast resolutions as compared to conventional CT. TXCT gives morphological information and FXCT gives functional information of organs. So, superposed display system for SR-FXCT and SR-TXCT images has been developed for clinical diagnosis with higher reliability. Preliminary experiment with brain phantom was carried out and the superposition of both images was performed. The superposed SR–CT image gave us both functional and morphological information easily with high reliability, thus demonstrating the usefulness of this system.

Daily variations of ECG and left ventricular parameters at exercise in patients with anginal attacks but normal coronary arteriograms

In 21 patients with typical exercise-induced anginal pain but normal coronary arteriograms (group N) and in 14 patients with angiographically proved coronary stenosis (group C), symptom-limited ergometer exercise ECG and radionuclide angiocardiography were performed twice on two different days. Exercise-induced ST changes showed larger variations between the two exercise tests in group N than in group C ([delta ST1-delta ST2]: 0.07 +/- 0.06 mV in group N, 0.03 +/- 0.03 mV in group C, p less than 0.05). Rate pressure product and left ventricular ejection fraction at exercise also showed larger variations between the two tests in group N than in group C (p less than 0.001, p less than 0.05, respectively). However, substantial overlaps existed in some cases in the two groups. In conclusion, some of the patients with exercise-induced anginal pain but normal coronary arteriograms may have a variable threshold of exertional chest pain probably caused by variation in coronary vascular tone, and the other patients may have a fixed threshold of chest pain caused by other mechanisms.

Significance of ST-segment and T wave changes in the resting electrocardiograms of patients with exertional angina, studied by exercise radionuclide angiocardiograms*

In order to investigate the clinical significance of ST-T changes in resting ECG in angina pectoris, symptom-limited ergometer exercise radionuclide angiocardiography with ECG was performed in 60 patients with exertional angina. In those with normal ECG at rest (Group N), left ventricular ejection fraction (EF) did not change during exercise (71 +/- 5% to 71 +/- 6%). In those with only ST change at rest (Group ST) and those with only T change at rest (Group T), EF decreased significantly during exercise (68 +/- 5% to 63 +/- 7%, p less than 0.01; 68 +/- 6% to 61 +/- 7%, p less than 0.001). In those with ST and T changes at rest (Group ST + T), EF was low at rest (58 +/- 11%) and decreased further at exercise (52 +/- 8%, p less than 0.001). In those whose negative or flat T wave became more negative during exercise, EF was low both at rest and at exercise. In conclusion, ST and T changes at rest in patients with exertional angina might suggest a depressed reserve of myocardial function for exercise.

Fast algorithm for fluorescent X-ray CT reconstruction

Describes a fast algorithm for the fluorescent X-ray computed tomography (FXCT) reconstruction. The proposed FXCT reconstruction involves solving the algebraic equation system whose input is the measured FXCT projections. The system is described by a large-scale sparse matrix. First, the authors propose a fast algorithm for FXCT reconstruction using a conjugate gradient method (CGM) based on an efficient data handling routine. Next, the authors demonstrate the algorithms effectiveness by applying it to data obtained from simulations and from experiments. Finally, the authors show that optimization CGM is better than those of the performance of the other iterative solutions, such as the simultaneous iterative reconstruction technique (SIRT).

A coherent scatter computed tomography with scintillator-CCD system

A preliminary experiment has executed using a highly sensitive HPGe detector with spectral resolution, and it demonstrated that the subtraction of two images obtained from different scatter angles yielded a specific material distribution. To get a more exact image, a new system is designed with a scintillator-CCD detector which can correct the attenuation of incident and scattered beams by transmission CT obtained simultaneously. The proposed system can detect wide angle coherent scattered and transmitted X-rays with high spatial resolution by the same detector.