Tetsuya Yuasa

Refraction-based tomosynthesis: Proof of the concept

Tomosynthesis is a well known technique for imaging a plane in a target by blurring other planes in the target. Commonly, the tomosynthesis is based on the x-ray absorption contrast. Recently, methods for generating other x-ray contrasts were developed. One of them, the so-called refraction contrast, is extremely sensitive to soft tissues and small defects. It was used as the base for the computed tomography. However, a very promising application of this contrast in the tomosynthesis remains undeveloped. This letter is dedicated to this problem. It includes both theoretical background and experimental implementation of the idea.

Quantitative evaluation of myocardial function by a volume-normalized map generated from relative blood flow.

Our study aimed to quantitatively evaluate blood flow in the left ventricle (LV) of apical hypertrophic cardiomyopathy (APH) by combining wall thickness obtained from cardiac magnetic resonance imaging (MRI) and myocardial perfusion from single-photon emission computed tomography (SPECT). In this study, we considered paired MRI and myocardial perfusion SPECT from ten patients with APH and ten normals. Myocardial walls were detected using a level set method, and blood flow per unit myocardial volume was calculated using 3D surface-based registration between the MRI and SPECT images. We defined relative blood flow based on the maximum in the whole myocardial region. Accuracies of wall detection and registration were around 2.50 mm and 2.95 mm, respectively. We finally created a bulls-eye map to evaluate wall thickness, blood flow (cardiac perfusion) and blood flow per unit myocardial volume. In patients with APH, their wall thicknesses were over 10 mm. Decreased blood flow per unit myocardial volume was detected in the cardiac apex by calculation using wall thickness from MRI and blood flow from SPECT. The relative unit blood flow of the APH group was 1/7 times that of the normals in the apex. This normalization by myocardial volume distinguishes cases of APH whose SPECT images resemble the distributions of normal cases.

Fundamental study on subharmonic imaging by irradiation of amplitude-modulated ultrasound waves

The second harmonic and subharmonic components, the frequencies of which are twice and one half the fundamental frequency, are included in echoes from contrast agents. An imaging method, which employs a second harmonic (second harmonic imaging), is widely used in medical diagnoses. On the other hand, subharmonic is expected to provide a higher contrast between biological tissues and blood flow because echo signals are generated only from blood containing the contrast agents. However, the subharmonic component echo signal power from contrast agents is relatively low. This has resulted in little progress in the field of subharmonic imaging. In this study, a new imaging method is proposed using amplitude-modulated waves as transmitted waves combined with the pulse inversion method to enhance subharmonic echo signals. Two optimal frequencies are set, including the modulated waves, F(1) and F(2), so that the subharmonic frequency of F(1) and the second harmonic frequency of F(2) may result in the same value. This allows a more powerful signal at the frequency band because the second harmonic and subharmonic components are integrated. Furthermore, a B-mode ultrasound image of an agar phantom that imitated biological tissue and showed the effectiveness of our method was reconstructed. As a result, the echo power of the subharmonic component was enhanced by approximately 11.8 dB more than the conventional method and the signal to noise ratio showed an improvement of 7.6 dB.

Fusion imaging of fluorescent and phase-contrast X-ray computed tomography using synchrotron radiation in medical biology

We integrated fluorescent X-ray computed tomography (FXCT) and phase-contrast X-ray computed tomography (PCCT), and the feasibility of this fusion imaging was assessed for small animals. Brain tumor model of mouse and cardiomyopathic model of hamsters were examined. The brain and heart were extracted after intravenous injection of cerebral perfusion agent 127I-IMP and myocardial fatty acid metabolic agent 127I-BMIPP, respectively. Each target organ was fixed by formalin for FXCT and PCCT. Images were obtained three-dimensionally (3D), and the surface contour of brain and heart were determined from 3D-image after re-sampling for the description with the same spatial resolution. These images were fused interactively on displayed images by 3D image manipulation software. In FXCT, cerebral perfusion image with IMP and fatty acid metabolic image with BMIPP were clearly demonstrated at 0.5 mm and 0.2 mm spatial resolution, respectively. PCCT image with 0.03 mm spatial resolution depicted clearly the morphological structures of brain such as cerebral cortex, hippocampus, lateral ventricle and cerebellum, and for heart such as cardiac lumen, papillary muscle, left and right ventricle. On fusion image, localization and degree of abnormality of cerebral perfusion and myocardial fatty acid metabolism were easily recognized. Our results suggested that the integration of FXCT and PCCT is very useful to understand biological state corresponding to its anatomical localization even in small animal.

Application of x-ray computed tomography based on the refraction contrast to biomedicine

We have developed X-ray refraction based computed tomography (CT) which is able to visualize soft tissue in between hard tissue. The experimental system consists of Si(220) diffraction double-crystals called the DEI (diffraction-enhanced imaging) method, object locating in between them and a CCD camera to acquire data of 900 x-ray images. The x-ray energy used was 17.5 keV. The algorithm used to reconstruct CT images has been invented by A. Maksimenko et al.. We successfully visualized calcification and distribution of breast cancer nest which are the inner structure. It has much higher contrast which in comparison with the conventional absorption based CT system.

2D and 3D Refraction Based X‐ray Imaging Suitable for Clinical and Pathological Diagnosis

The first observation of micro papillary (MP) breast cancer by x‐ray dark‐field imaging (XDFI) and the first observation of the 3D x‐ray internal structure of another breast cancer, ductal carcinoma in‐situ (DCIS), are reported. The specimen size for the sheet‐shaped MP was 26 mm × 22 mm × 2.8 mm, and that for the rod‐shaped DCIS was 3.6 mm in diameter and 4.7 mm in height. The experiment was performed at the Photon Factory, KEK: High Energy Accelerator Research Organization. We achieved a high‐contrast x‐ray image by adopting a thickness‐controlled transmission‐type angular analyzer that allows only refraction components from the object for 2D imaging. This provides a high‐contrast image of cancer‐cell nests, cancer cells and stroma. For x‐ray 3D imaging, a new algorithm due to the refraction for x‐ray CT was created. The angular information was acquired by x‐ray optics diffraction‐enhanced imaging (DEI). The number of data was 900 for each reconstruction. A reconstructed CT image may include ductus lact...

Quantitative evaluation of heart disease by integration of MRI and SPECT images

We tried to evaluate the blood flow in left ventricle quantitatively by combining wall thickness obtained from cardiac magnetic resonance imaging (MRI) and myocardial perfusion from single-photon emission tomography (SPECT). Paired MRI and myocardial perfusion SPECT from 16 patients including apical hypertrophic cardiomyopathy (APH) and normal subjects were considered. Blood flow per unit myocardium volume was calculated by 3-D surface-based registration between MRI and SPECT images.

First attempt at 3d x-ray visualization of DCIS (ductal carcinoma in situ) due to refraction contrast – in good relation to pathological view

First 3D X-ray internal observation of DCIS (ductal carcinoma in-situ) is reported. Its rod shaped specimen with 3.6 mm in diameter and 4.7 mm in height was punched out to have successfully observed by using a newly made algorithm due to refraction for x-ray CT. Its data was acquired by the x-ray optics DEI (diffraction-enhanced imaging). Data of 900 projections with interval of 0.2 degrees was used at Photon Factory, KEK in Tsukuba. A reconstructed CT image may include clearly revealed ductus lactiferi, microcalcification and other structure. The voxel resolution is approximately 50 μm by the present instrumental condition. This modality could open up an x-ray pathological diagnosis.

First attempt of the medical application of the refraction-based computed tomography

In recent years, the X-ray refraction contrast was widely developed and applied in different fields of science which deal with the nondestructive observation methods. As it follows from the name, the refraction contrast is the distribution of the X-ray intensity dependent on the deflection angle of the X-ray beam. This property of the contrast provides certain advantages over other contrasts such as absorption and phase-shift. The refraction contrast can show tiny details of the inner structure which are invisible in other types of the X-ray imaging techniques. Another advantage of the X-ray refraction contrast is the sensitivity to the low Z materials. This property of the refraction contrast may be of great importance in the medical applications of the X-ray. The advantages provided by the refraction contrast allow one to expect the same advantages of the computed tomography (CT) from the refraction contrast. Therefore this report is dedicated to the realization of the refraction-based CT. It describes the theoretical background of the problem, experimental realization of the method and actual results of the reconstruction of the breast cancer sample. The experimental data were acquired using X-ray synchrotron source at Photon Factory (KEK, Japan). The energy of used in the experiment was 11.7keV. The spatial resolution of the reconstructed images is about 20 microns.

Physico-Mathematical Considerations on X-Ray Computed Tomography Based on Diffraction Enhanced Imaging

We consider x-ray computed tomography (CT) technique based on refractive effects, which has advantages for delineating biological weakly-absorbing soft-tissues over the conventional absorption-contrast CT (computed tomography) because of the use of phase sensitive detection. The refraction-based CT described here detects the angular deviation of the beam, refracted by a sample, from the incident beam in a cross-sectional plane of interest, based on the diffraction enhanced imaging (DEI) method using the Bragg-case analyzing crystal, which is arranged behind the sample on a positioning device for collecting projection data from various directions. The set of angular deviation data from various directions, which corresponds to the projection data in the conventional absorption-contrast CT, are used for reconstruction of the refractive-index gradient vector field. So far, some groups have proposed the distinct DEI-based CT protocols. We theoretically summarize and compare the algorithms from the viewpoint of geometrical optics.