Quanwen Yu

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.

Phase-contrast X-ray imaging with a large monolithic X-ray interferometer

To increase the field of view for large objects in phase-contrast X-ray imaging, a large monolithic X-ray interferometer has been fabricated using an available silicon ingot of diameter 10 cm. A performance study of this interferometer has been carried out using a synchrotron X-ray source. The view size of the interference pattern obtained with this interferometer was 25 mm wide and 15 mm high and its visibility was 79%. Various structures of a sliced human hepatocellular carcinoma were identified as necrosis, hemorrhagic necrosis, normal liver tissue and blood vessel. The performance of this interferometer was sufficient for phase-contrast X-ray imaging.

Preliminary experiment of fluorescent X-ray computed tomography to detect dual agents for biological study

The simultaneous observation of various information, such as blood flow, tissue metabolism and distribution of receptors, is quite important in order to understand the functional state of biomedical objects. The simultaneous detectability of contrast agents by fluorescent X-ray computed tomography (FXCT) with synchrotron radiation is examined in this study. The system consisted of a silicon (111) double-crystal monochromator, an X-ray slit system, a scanning table, a PIN diode, a highly purified germanium detector and an X-ray charge-coupled device (CCD) camera. The monochromatic X-ray beam energy was adjusted to 37.0 keV and collimated into a pencil beam of 1 x 1 mm. The fluorescent spectra of the K alpha lines for iodine and xenon were detected simultaneously. FXCT could image the distribution of both iodine and xenon agents in a phantom clearly and the contrast ratio was significantly better than that of transmission X-ray computed tomography images.

Human thyroid specimen imaging by fluorescent x-ray computed tomography with synchrotron radiation

Fluorescent x-ray computed tomography (FXCT) is being developed to detect non-radioactive contrast materials in living specimens. The FXCT system consists of a silicon (111) channel cut monochromator, an x-ray slit and a collimator for fluorescent x ray detection, a scanning table for the target organ and an x-ray detector for fluorescent x-ray and transmission x-ray. To reduce Compton scattering overlapped on the fluorescent K(alpha) line, incident monochromatic x-ray was set at 37 keV. The FXCT clearly imaged a human thyroid gland and iodine content was estimated quantitatively. In a case of hyperthyroidism, the two-dimensional distribution of iodine content was not uniform, and thyroid cancer had a small amount of iodine. FXCT can be used to detect iodine within thyroid gland quantitatively and to delineate its distribution.

First experiment by two-dimensional digital mammography with synchrotron radiation

Two-dimensional digital mammography with synchrotron radiation was developed to obtain high-contrast images. The system consisted of a single-crystal monochromator with an asymmetrically reflecting silicon 〈311〉 crystal, an avalanche multiplication-type pick-up tube camera with a fluorescent plate and lens-coupling system, and a workstation. The preliminary experiment was carried out with a synchrotron light source at the Photon Factory, KEK, in Tsukuba. Breast phantom and human breast specimen were imaged using 20 keV monochromatic synchrotron X-rays. These images were compared with images obtained by a conventional mammography system. The minimal detectable diameter of microcalcification on the breast phantom was 165 µm by the two-dimensional synchrotron radiation imaging system and 196 µm by the conventional mammography system. In the breast specimens, microcalcification and soft-tissue masses were clearly imaged and their contrasts improved by about 18% and 38%, respectively, in the two-dimensional synchrotron radiation system. The entrance surface dose of the two-dimensional synchrotron radiation system was about 400 mR, which was almost the same value as the 420 mR delivered by the conventional mammography system. Two-dimensional synchrotron radiation digital mammography is considered to be a powerful imaging modality for diagnosing breast tumors.

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.

Medical imaging by fluorescent x-ray CT: its preliminary clinical evaluation

Fluorescent x-ray CT (FXCT) with synchrotron radiation (SR) is being developed to detect the very low concentration of specific elements. The endogenous iodine of the human thyroid and the non-radioactive iodine labeled BMIPP in myocardium were imaged by FXCT. FXCT system consists of a silicon (111) double crystal monochromator, an x-ray slit, a scanning table for object positioning, a fluorescent x-ray detector, and a transmission x-ray detector. Monochromatic x-ray with 37 keV energy was collimated into a pencil beam (from 1 mm to 0.025 mm). FXCT clearly imaged endogenous iodine of thyroid and iodine labeled BMIPP in myocardium, whereas transmission x-ray CT could not demonstrate iodine. The distribution of iodine was heterogeneous within thyroid cancer, and its concentration was lower than that of normal thyroid. Distribution of BMIPP in normal rat myocardium was almost homogeneous; however, reduced uptake was slightly shown in ischemic region. FXCT is a highly sensitive imaging modality to detect very low concentration of specific element and will be applied to reveal endogenous iodine distribution in thyroid and to use tracer study with various kinds of labeled material.

Optimization of air gap for two-dimensional imaging system using synchrotron radiation

Since synchrotron radiation (SR) has several excellent properties such as high brilliance, broad continuous energy spectrum and small divergence, we can obtain x-ray images with high contrast and high spatial resolution by using of SR. In 2D imaging using SR, air gap method is very effective to reduce the scatter contamination. However, to use air gap method, the geometrical effect of finite source size of SR must be considered because spatial resolution of image is degraded by air gap. For 2D x-ray imaging with SR, x-ray mammography was chosen to examine the effect of air gap method. We theoretically discussed the optimization of air gap distance suing effective scatter point source model proposed by Muntz, and executed experiment with a newly manufactured monochromator with asymmetrical reflection and an imaging plate.

Development of a multispectral autoradiography using a coded aperture

Autoradiography is a useful imaging technique to understand biological functions using tracers including radio isotopes (RIs). However, it is not easy to describe the distribution of different kinds of tracers simultaneously by conventional autoradiography using X-ray film or Imaging plate. Each tracer describes each corresponding biological function. Therefore, if we can simultaneously estimate distribution of different kinds of tracer materials, the multispectral autoradiography must be a quite powerful tool to better understand physiological mechanisms of organs. So we are developing a system using a solid state detector (SSD) with high energy- resolution. Here, we introduce an imaging technique with a coded aperture to get spatial and spectral information more efficiently. In this paper, the imaging principle is described, and its validity and fundamental property are discussed by both simulation and phantom experiments with RIs such as 201Tl, 99mTc, 67Ga, and 123I.

Two-dimensional aortographic coronary angiography with synchrotron radiation at aortic regurgitation state

At aortic regurgitation state, 2D synchrotron radiation (SR) coronary arteriography (CAG) with aortographic contrast injection was examined theoretically and animal experiments were performed to confirm 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 of Tsukuba. The x- ray energy was adjusted to just above the iodine K-edge. Theoretical calculation described that the coronary arteries overlapping on left ventricle could not be demonstrated well with a high signal-to-noise ratio by using the aortographic CAG with SR. The canine coronary arteries without overlap over the left ventricle were demonstrated clearly, however, the image quality appear to be reduced. The coronary artery overlapping over left ventricle could not be demonstrated well, however the transient reduction of left ventricular wall motion was revealed by transient stenotic procedure of left anterior descending coronary artery.