Akio Yoneyama

Vessel Imaging by Interferometric Phase-Contrast X-Ray Technique

Background—Phase-contrast x-ray imaging using an x-ray interferometer has great potential to reveal the structures inside soft tissues, because the sensitivity of this method to hydrogen, carbon, nitrogen, and oxygen is ≈1000 times higher than that of the absorption-contrast x-ray method. Imaging of vessels is very important to understand the vascular distribution of organs and tumors, so the possibility of selective angiography based on phase contrast is examined with a physiological material composed of low-atomic-number elements. Methods and Results—Phase-contrast x-ray imaging was performed with a synchrotron x-ray source. Differences in refractive index, d&dgr;, of physiological saline, lactated Ringer’s solution, 5% glucose, artificial blood such as pyridoxylated hemoglobin–polyoxyethylene conjugate, and perfluorotributylamine were measured. Because the d&dgr; of physiological saline has highest contrast, it was used for the phase-contrast x-ray imaging of vessel, and this was compared with absorption-contrast x-ray images. Vessels >0.03 mm in diameter of excised liver from rats and a rabbit were revealed clearly in phase-contrast x-ray imaging, whereas the vessel could not be revealed at all by the absorption-contrast x-ray image. Absorption-contrast x-ray images with iodine microspheres depicted only portal veins >0.1 mm in diameter with nearly the same x-ray dose as the present phase-contrast x-ray imaging. Conclusions—Phase-contrast x-ray imaging explored clear depiction of the vessels using physiological saline with small doses of x-rays.

Quantitative analysis of amyloid plaques in a mouse model of Alzheimer’s disease by phase-contrast X-ray computed tomography

Densely aggregated beta-amyloid peptides are believed to play a key role in the pathogenesis of Alzheimers disease. Amyloid plaques are a potential target for molecular imaging to determine the clinical status of Alzheimers disease. Phase-contrast X-ray imaging combined with computed tomography is a promising technique that can be used to visualize the physical density of structures in biological tissues non-invasively, and without the use of imaging agents. Using brain tissue isolated from a mouse model of Alzheimers disease, we show that beta-amyloid 40-positive/beta-amyloid 42-positive amyloid plaques, but not beta-amyloid 40-negative/beta-amyloid 42-positive amyloid plaques, exist as high-density aggregates that can be specifically detected by phase-contrast X-ray computed tomography. The phase-contrast X-ray computed tomography detected beta-amyloid 40-positive/beta-amyloid 42-positive amyloid plaques in three-dimensions with an extremely high sensitivity comparable to that of histological analysis, and also enabled the load of amyloid plaques to be quantified. Furthermore, the use of phase-contrast X-ray computed tomography reveals that the physical density of beta-amyloid 40-positive/beta-amyloid 42-positive amyloid plaques increases with age, and that the large volume, high-density, amyloid plaques that are specifically observed in aged Alzheimers disease mice are closely associated with neuritic dystrophy. These results demonstrate that phase-contrast X-ray computed tomography is a highly sensitive imaging technique for analyzing dense-cored amyloid plaques in postmortem samples, and is beneficial in elucidating amyloid pathophysiology in Alzheimers disease.

MPEG audio bit rate scaling on coded data domain

Formerly, once the audio data is compressed, transcoding is used to scale the bit rate, where decoding and re-encoding are taking place. Therefore, data manipulation of coded data has been very complex and time consuming work. We describe three algorithms for bit rate scaling in the coded MPEG data domain. One is a bandwidth limitation method cutting higher frequency components until the target data rate is satisfied. The other two use a re-quantization process where a quantization step in each subband is modified. One of them reflects the psychoacoustic model from bit allocation information obtained in the bitstream in order to improve the bit rate scaling efficiency. The simulation results show that the re-quantization process provides a very high conversion efficiency and a nearly equal sound quality can be obtained as directly coding from PCM by reflecting the psychoacoustic model. It is also shown that a very fast scaling (factor of six) have been achieved when compared with the transcoding method.

Phase-Contrast Tomographic Imaging Using an X-ray Interferometer

Apparatus for phase-contrast X-ray computed tomography using a monolithic X-ray interferometer is presented with some observational results for human breast tissues. Structures characteristic of the tissues were revealed in the phase-contrast tomograms. The procedure of image analysis consists of phase retrieval from X-ray interference patterns and tomographic image reconstruction from the retrieved phase shift. Next, feasibility of phase-contrast imaging using a two-crystal X-ray interferometer was studied aiming at in vivo observation in the future. In a preliminary study, the two-crystal X-ray interferometer was capable of generating fringes of 70% visibility using synchrotron X-rays.

A fast scene change detection on MPEG coding parameter domain

This paper proposes a very fast and accurate scene change detection algorithm on MPEG coding parameter domain. The fast operation can be obtained by spatio-temporally subsampling coding information and by exploiting only coding parameters extracted in variable length decoding (VLD) stage, while the accurate detection is accomplished by examining the statistical characteristics of various scene changes on the coding parameter domain. The computer simulation shows that the proposed algorithm can accomplish detection more than 5 times faster than that of real-time playback for MPEG-2 video sequences using a standard workstation. It is also shown that most of abrupt scene changes, dissolve transitions, and wipe transitions have been successfully detected.

MPEG encoding algorithm with scene adaptive dynamic GOP structure

Although a GOP (group of picture) length is often fixed in MPEG, this may not guarantee the best picture quality from the point of view of coding efficiency. Furthermore, it is also well known that P-picture interval M=3 does not provide the best quality for all sequences. We propose an MPEG encoding algorithm with scene adaptive dynamic GOP structure to enhance the picture quality in the cases mentioned above. Using macroblock characteristics such as luminance activity and simple motion compensation on the activity domain, N and M values are dynamically determined.

Moving-object detection from MPEG coded data

We describe a method of moving object detection directly from MPEG coded data. Since motion information in MPEG coded data is determined in terms of coding efficiency point of view, it does not always provide real motion information of objects. We use a wide variety of coding information including motion vectors and DCT coefficients to estimate real object motion. Since such information can be directly obtained from coded bitstream, very fast operation can be expected. Moving objects are detected basically analyzing motion vectors and spatio-temporal correlation of motion in P-, and B-pictures. Moving objects are also detected in intra macroblocks by analyzing coding characteristics of intra macroblocks in P- and B-pictures and by investigating temporal motion continuity in I-pictures. The simulation results show that successful moving object detection has been performed on macroblock level using several test sequences. Since proposed method is very simple and requires much less computational power than the conventional object detection methods, it has a significant advantage as motion analysis tool.

Operation of a separated-type x-ray interferometer for phase-contrast x-ray imaging

Aiming at large-area phase-contrast x-ray imaging, a separated-type x-ray interferometer system was designed and developed to produce 25×20 mm interference patterns. The skew-symmetric optical system was adopted because of the feasibility of alignment. The rotation between the separated crystal blocks was controlled within a drift of 0.06 nrad using a feedback positioning system. This interferometer generated a 25×15 mm interference pattern with 0.07 nm synchrotron x-rays. A slice of a rabbit’s kidney was observed, and its tubular structure could be revealed in a measured phase map.

In vivo physiological saline-infused hepatic vessel imaging using a two-crystal-interferometer-based phase-contrast X-ray technique

Using a two-crystal-interferometer-based phase-contrast X-ray imaging system, the portal vein, capillary vessel area and hepatic vein of live rats were revealed sequentially by injecting physiological saline via the portal vein. Vessels greater than 0.06 mm in diameter were clearly shown with low levels of X-rays (552 µGy). This suggests that in vivo vessel imaging of small animals can be performed as conventional angiography without the side effects of the presently used iodine contrast agents.

Observation of low-temperature object by phase-contrast x-ray imaging : Nondestructive imaging of air clathrate hydrates at 233 K

A cryochamber and a liquid cell that are designed for nondestructive three dimensional observations and arranged in a two-crystal x-ray interferometer expand the use of phase-contrast x-ray imaging that could only be performed at room temperature in previous studies to a new temperature range of 190K to room temperature. The methyl acetate in the liquid cell prevents undesirable sample outline contrasts and enables internal observations. Both a nondestructive observation and a highly accurate absolute density of the materials under low-temperature conditions can be obtained with a single measurement using this new technique. A three dimensional x-ray computed tomography (x-ray CT) of the air clathrate hydrate in the hexagonal ice drilled from Dome Fuji in Antarctica is shown, and the density of the air hydrate is estimated to be 0.937(3)g∕cm3 at 233K.