Naoki Sunaguchi

Crystal analyser-based X-ray phase contrast imaging in the dark field: implementation and evaluation using excised tissue specimens.

AbstractObjectivesWe demonstrate the soft tissue discrimination capability of X-ray dark-field imaging (XDFI) using a variety of human tissue specimens.MethodsThe experimental setup for XDFI comprises an X-ray source, an asymmetrically cut Bragg-type monochromator-collimator (MC), a Laue-case angle analyser (LAA) and a CCD camera. The specimen is placed between the MC and the LAA. For the light source, we used the beamline BL14C on a 2.5-GeV storage ring in the KEK Photon Factory, Tsukuba, Japan.ResultsIn the eye specimen, phase contrast images from XDFI were able to discriminate soft-tissue structures, such as the iris, separated by aqueous humour on both sides, which have nearly equal absorption. Superiority of XDFI in imaging soft tissue was further demonstrated with a diseased iliac artery containing atherosclerotic plaque and breast samples with benign and malignant tumours. XDFI on breast tumours discriminated between the normal and diseased terminal duct lobular unit and between invasive and in-situ cancer.ConclusionsX-ray phase, as detected by XDFI, has superior contrast over absorption for soft tissue processes such as atherosclerotic plaque and breast cancer.Key points• X-ray dark field imaging (XDFI) can dramatically increase sensitivity of phase detection. • XDFI can provide enhanced soft tissue discrimination. • With XDFI, abnormal anatomy can be visualised with high spatial/contrast resolution.

Characterization of nonlinearity of shear elasticity using local velocity mapping

The emerging technology of ultrasonic imaging of the soft tissue strain and elasticity, which aims at providing information about the mechanical properties of the tissues, has become a peer research issue since the 1990s. An elasticity imaging method using continuous shear wave excitation (CSWE) is expected to be a safe and quantitative technique. We have already proposed a local velocity mapping method for shear elasticity by reconstructing the small phase modulation components of the harmonic distortion in CSWE. In this paper, we propose a simple model of static hysteresis as the nonlinearity of shear elasticity. This model is based on the presence of harmonic phase modulation components in shear wave propagation. By using this model, we attempt to characterize the static hysteresis of shear elasticity. The relationship between the texture patterns of the local velocity map and the nonlinearity of the medium, which is measured by a rheometer, shows that the proposed model can be adopted for the imaging of the nonlinearity of shear elasticity.

Dual-energy fluorescent x-ray computed tomography system with a pinhole design: Use of K-edge discontinuity for scatter correction

We propose a pinhole-based fluorescent x-ray computed tomography (p-FXCT) system with a 2-D detector and volumetric beam that can suppress the quality deterioration caused by scatter components. In the corresponding p-FXCT technique, projections are acquired at individual incident energies just above and below the K-edge of the imaged trace element; then, reconstruction is performed based on the two sets of projections using a maximum likelihood expectation maximization algorithm that incorporates the scatter components. We constructed a p-FXCT imaging system and performed a preliminary experiment using a physical phantom and an I imaging agent. The proposed dual-energy p-FXCT improved the contrast-to-noise ratio by a factor of more than 2.5 compared to that attainable using mono-energetic p-FXCT for a 0.3 mg/ml I solution. We also imaged an excised rat’s liver infused with a Ba contrast agent to demonstrate the feasibility of imaging a biological sample.

Multi-pinhole fluorescent x-ray computed tomography for molecular imaging

We propose a multi-pinhole fluorescent x-ray computed tomography (mp-FXCT) technique for preclinical molecular imaging that can provide the complete data necessary to produce 3-D tomographic images during anaesthesia. In this method, multiple projections are simultaneously acquired through a multi-pinhole collimator with a 2-D detector and full-field volumetric beam to accelerate the data acquisition process and enhance the signal-to-noise ratios of the projections. We constructed a 15-pinhole mp-FXCT imaging system at beamline ARNE-7A at KEK and performed preliminary experiments to investigate its imaging properties using physical phantoms and a non-radioactive I imaging agent. The mp-FXCT system could detect an I concentration of 0.038 mg/ml, the minimum required for in-vivo imaging, at a spatial resolution of about 0.3 mm during a data acquisition time of 90 min, which is less than the time for which anaesthesia is effective and suggests that preclinical molecular imaging is feasible with mp-FXCT.

Limited view reconstruction for differential phase-contrast computed tomography.

This paper describes an algebraic reconstruction algorithm that uses total variation (TV) regularization for differential phase contrast computed tomography (DPC-CT) using a limited number of views. In order to overcome over-flattening inherent in TV regularization, a two-step reconstruction process is used: we first reconstruct tomographic images of gradient refractive index from differential projections with TV regularization; these images are then used to compute tomographic images of refractive index by solving the Poisson equation. We incorporate TV regularization in the reconstruction process because the distribution of gradient refractive index is much more flattened than the refractive index. Simulations of the proposed method demonstrate that it can achieve satisfactory image quality from a much smaller number of projections than is required by the Nyquist sampling theorem. We experimentally prove the feasibility of the proposed method using dark field imaging optics at PF-14C beamline at the Photon Factory, KEK. The differential phase contrast projection data was experimentally acquired from a biological sample and DPC-CT images were reconstructed. We show that far fewer projections are needed when the proposed algorithm is used.

Imaging with ultra-small-angle X-ray scattering using a Laue-case analyzer and its application to human breast tumors

PURPOSE In this study, we demonstrate a novel imaging technique, based on ultra-small-angle X-ray scattering (USAXS) that uses a Laue-case Si wafer as the angle analyzer. METHODS We utilized the (1 1 1) diffraction plane of a 356 μm thick, symmetrically cut Si wafer as the angle analyzer, denoted by A[L]. With this device, we performed USAXS imaging experiments using 19.8 keV synchrotron X-rays. The objects we imaged were formalin-fixed, paraffin-embedded breast tumors (an invasive carcinoma and an intraductal papilloma). During image acquisition by a charge-coupled device (CCD) camera, we varied the rotation angle of the analyzer in 0.02″ steps from -2.40″ to +2.40″ around the Bragg angle. The exposure time for each image was 2 s. We determined the amount of ultra-small-angle X-ray scattering from the width of the intensity curve obtained for each local pixel during the rotation of the analyzer. RESULTS We acquired USAXS images of malignant and benign breast tumor specimens using the A[L] analyzer; regions with larger USAXS form brighter areas in the image. We varied the sensitivity of the USAXS image by changing the threshold level of the object rocking curve. CONCLUSIONS The USAXS images can provide information about the internal distribution of closely packed scattering bodies in a sample with reasonable sensitivity. This information differs from that obtainable through refraction-contrast imaging. Although further validation studies will be necessary, we conclude that USAXS imaging using a Laue-case analyzer may have significant potential as a new diagnosis technique.

Shear Wave Imaging of Breast Tissue by Color Doppler Shear Wave Elastography

Shear wave elastography is a distinctive method to access the viscoelastic characteristic of the soft tissue that is difficult to obtain by other imaging modalities. This paper proposes a novel shear wave elastography [color Doppler shear wave imaging (CD SWI)] for breast tissue. Continuous shear wave is produced by a small lightweight actuator, which is attached to the tissue surface. Shear wave wavefront that propagates in tissue is reconstructed as a binary pattern that consists of zero and the maximum flow velocities on color flow image (CFI). Neither any modifications of the ultrasound color flow imaging instrument nor a high frame rate ultrasound imaging instrument is required to obtain the shear wave wavefront map. However, two conditions of shear wave displacement amplitude and shear wave frequency are needed to obtain the map. However, these conditions are not severe restrictions in breast imaging. This is because the minimum displacement amplitude is

Dark-Field Imaging: Recent developments and potential clinical applications

16~\mu \text{m}

An efficient reconstruction algorithm for differential phase-contrast tomographic images from a limited number of views

for an ultrasonic wave frequency of 12 MHz and the shear wave frequency is available from several frequencies suited for breast imaging. Fourier analysis along time axis suppresses clutter noise in CFI. A directional filter extracts shear wave, which propagates in the forward direction. Several maps, such as shear wave phase, velocity, and propagation maps, are reconstructed by CD SWI. The accuracy of shear wave velocity measurement is evaluated for homogeneous agar gel phantom by comparing with the acoustic radiation force impulse method. The experimental results for breast tissue are shown for a shear wave frequency of 296.6 Hz.

Improvement in microhollow production using bubble cloud cavitation by dual-frequency ultrasonic wave irradiation

This paper describes an X-ray phase contrast imaging technique using analyzer-based optics called X-ray Dark-Field Imaging that has been under development for the past 10years. We describe the theory behind XDFI, the X-ray optics required for implementing it in practice, and algorithms used for 2D, 2.5D, and 3D image reconstruction. The XDFI optical chain consists of an asymmetrically cut, Bragg-type monochromator-collimator that provides a planar monochromatic X-ray beam, a positioning stage for the specimens, a Laue-case angle analyzer, and one or two cameras to capture the dark and bright field images. We demonstrate the soft-tissue discrimination capabilities of XDFI by reconstructing images with absorption and phase contrast. By using a variety of specimens such as breast tissue with cancer, joints with articular cartilage, ex-vivo human eye specimen, and others, we show that refraction-based contrast derived from XDFI is more effective in characterizing anatomical features, articular pathology, and neoplastic disease than conventional absorption-based images. For example, XDFI of breast tissue can discriminate between the normal and diseased terminal duct lobular unit, and between invasive and in-situ cancer. The final section of this paper is devoted to potential future developments to enable clinical and histo-pathological applications of this technique.