Hironori Ueki

Near-infrared finger vein patterns for personal identification

We have demonstrated a personal identification system that is based on near-infrared finger vein patterns. Finger vein patterns of 678 volunteers are acquired by transmitting near-infrared light through a finger and capturing the image with a CCD camera. These vein patterns are enhanced by a background-reduction filter. The similarity between two patterns is then quantified by use of the normalized maximum of the cross correlation of the two images after correction of the tilt angle. The enhanced finger vein pattern enabled 678 persons to be successfully identified.

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.

Two-dimensional aortographic coronary arteriography with above-K-edge monochromatic synchrotron radiation

RATIONALE AND OBJECTIVES The diagnostic potential of two-dimensional aortographic coronary arteriography with synchrotron radiation was examined in dogs. METHODS The experiment was performed at a wiggler beam line by using a silicon monocrystal, fluorescent plate, and avalanche-type camera. The x-ray energy was adjusted to just above the iodine K-edge to obtain the highest contrast. Quantitative densitometry was used to compare intravenous coronary arteriography with aortographic coronary arteriography. RESULTS Aortographic coronary arteriography clearly depicted the branches of the coronary arteries such as the left anterior descending coronary artery, circumferential coronary artery, and right coronary artery to sizes of less than 0.2 mm without major overlap of coronary arteries. Intravenous coronary arteriography depicted only the branches of the left anterior descending coronary artery and right coronary artery with poor image quality. The ratio of contrast material dilution was about 2.4 to 3.4 in aortographic procedures, whereas in intravenous procedures it ranged widely from 7.7 to 15.6. CONCLUSION These preliminary investigations indicate that two-dimensional aortographic coronary arteriography with synchrotron radiation promises to be a minimally invasive and easily repeatable method of clearly imaging the coronary arteries.

High-spatial-resolution and real-time medical imaging using a high-sensitivity HARPICON camera

A HARPICON(TM) camera has been applied to a digital angiography system with fluorescent-screen optical-lens coupling. It uses avalanche multiplication in the photoconductive layer for high-sensitivity imaging. The limiting spatial resolutions in the 1050 scanning-line mode of the camera are about 30 and 50 micro m at input field sizes of 20 x 20 and 50 x 50 mm on the screen, respectively. For high-speed imaging, the 525 scanning-line mode at a rate of 60 images s(-1) can be selected. High-quality images of coronary arteries in dogs were obtained by intra-aortic coronary angiography and superselective coronary angiography using a single-energy X-ray above the iodine K-edge energy.

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.

Iodine-Filter Imaging System for Subtraction Angiography and Its Improvement by Fluorescent-Screen Harpicon Detector

Our initial studies in animal experiments using K-edge energy subtraction transvenous coronary angiography at the Photon Factory were undertaken using an iodine filter for energy switching combined with an X-ray image intensifier. In vivo subtracted images of coronary arteries in dogs were obtained in the form of motion pictures. However, the image quality was not good for medical examinations because the contrast material was highly diluted. A new image detector with a fluorescent-screen lens-coupling approach has been developed to take high quality images. By using the new detector in place of the X-ray image intensifier, image quality has markedly increased in coronary angiography.

Development of optimized segmentation map in dual energy computed tomography

Dual energy computed tomography (DECT) has been widely used in clinical practice and has been particularly effective for tissue diagnosis. In DECT the difference of two attenuation coefficients acquired by two kinds of X-ray energy enables tissue segmentation. One problem in conventional DECT is that the segmentation deteriorates in some cases, such as bone removal. This is due to two reasons. Firstly, the segmentation map is optimized without considering the Xray condition (tube voltage and current). If we consider the tube voltage, it is possible to create an optimized map, but unfortunately we cannot consider the tube current. Secondly, the X-ray condition is not optimized. The condition can be set empirically, but this means that the optimized condition is not used correctly. To solve these problems, we have developed methods for optimizing the map (Method-1) and the condition (Method-2). In Method-1, the map is optimized to minimize segmentation errors. The distribution of the attenuation coefficient is modeled by considering the tube current. In Method-2, the optimized condition is decided to minimize segmentation errors depending on tube voltagecurrent combinations while keeping the total exposure constant. We evaluated the effectiveness of Method-1 by performing a phantom experiment under the fixed condition and of Method-2 by performing a phantom experiment under different combinations calculated from the total exposure constant. When Method-1 was followed with Method-2, the segmentation error was reduced from 37.8 to 13.5 %. These results demonstrate that our developed methods can achieve highly accurate segmentation while keeping the total exposure constant.

MO-D-330A-06: Development of the X-Ray Detector with Sequential Readout Circuits for Multidetector-Row Computed Tomography

Purpose: To develop a low‐cost X‐ray detector with sequential readout circuits, to realize enough low noise for multidetector‐row computed tomography(MDCT), and to evaluate image quality. Method and Materials: We have developed an X‐ray detector that has a MOS‐switch for each pixel, connects many pixels of a common column with the electric readout circuit, and outputs the signals of these pixels from one circuit by turning on lines of switches in order. It has fewer readout circuits than a conventional MDCT detector, but new design is necessary to realize enough low noise for MDCT. First, to make the required noise specific, we simulated the relation of the detectornoise and imagenoise (simulation(A)). Second, to consider how to realize it, we simulated the detectornoise with the circuit noise model (simulation(B)). Third, we constructed the detector in order to evaluate its noise. Last, we developed a test CTsystem with these detectors to evaluate imagenoise with phantoms. Results: The result of the simulation(A) indicated that detectornoise had to be less than about 10‐k rms electrons, and we found to be able to achieve it by optimizing the circuit parameters of the low pass filter and the data line as a result of the simulation(B). We constructed the detectors with these parameters to evaluate these noise, and it turned out that it was about 10.5‐k rms electrons and the required noise was achieved. Moreover, the result to evaluate the noise from images with phantoms indicated that the main was X‐ray quantum noise and the detectornoise was low enough to be ignored when the object was a cylindrical water‐filled phantom less than about 30 cm in diameter and the slice thickness of the images was 0.625 mm. Conclusion: We developed a low‐noise X‐ray detector with sequential readout circuits for MDCT.

Method using a Monte Carlo simulation database for optimizing x-ray fluoroscopic conditions

To improve image quality (IQ) and reduce dose in x-ray fluoroscopy, we have developed a new method for optimizing x-ray conditions such as x-ray tube voltage, tube current, and gain of the detector. This method uses a Monte Carlo (MC)-simulation database for analyzing the relations between IQ, x-ray dose, and x-ray conditions. The optimization consists of three steps. First, a permissible dose limit for each object thickness is preset. Then, the MC database is used to calculate the IQ of x-ray projections under all the available conditions that satisfy this presetting. Finally, the optimum conditions are determined as the ones that provide the highest IQ. The MC database contains projections of an estimation phantom simulated under emissions of single-energy photons with various energies. By composing these single-energy projections according to the bremsstrahlung energy distributions, the IQs under any x-ray conditions can be calculated in a very short time. These calculations show that the optimum conditions are determined by the relation between quantum noise and scattering. Moreover, the heat-capacity limit of the x-ray tube can also determine the optimum conditions. It is concluded that the developed optimization method can reduce the time and cost of designing x-ray fluoroscopic systems.

Synchrotron Radiation Coronary Angiography with Aortographic Approach

Two-dimensional synchrotron radiation (SR) coronary arteriography (CAG) with aortographic contrast injection was considered theoretically and animal experiments were performed to examine its diagnostic ability. This system consisted of a silicon monocrystal, fluorescent plate, avalanche-type pickup tube camera, and image acquisition system. The experiment was performed at synchrotron sources in the Photon Factory in Tsukuba. The x-ray energy was adjusted to just above the iodine K-edge.