Medical Imaging Technology
Online ISSN : 2185-3193
Print ISSN : 0288-450X
ISSN-L : 0288-450X
Volume 32, Issue 2
MEDICAL IMAGING TECHNOLOGY
Displaying 1-15 of 15 articles from this issue
The Frontier of Elastography
  • Mikio SUGA
    2014 Volume 32 Issue 2 Pages 61-62
    Published: 2014
    Released on J-STAGE: May 24, 2014
    JOURNAL FREE ACCESS
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  • Tsuyoshi SHIINA
    2014 Volume 32 Issue 2 Pages 63-68
    Published: 2014
    Released on J-STAGE: May 24, 2014
    JOURNAL FREE ACCESS
    Development of ultrasound elastography at the start of 1990s is aimed at the diagnosis of diseases which bring sclerotic change of tissues such as cancer, arteriosclerosis and cirrhosis. In 2003, the world's first practical system of ultrasound elastography was released in Japan. As the utility of ultrasound elastography for the clinical application such as breast cancer diagnosis has been proven, most of manufactures have produced equipment with ultrasound elastograpy as the third image mode behind the B-mode and Doppler method. At present, principles of ultrasound elastography are classified into two categories. One is strain imaging that uses strain generated by the tissue compression and the other is shear wave imaging that measures the speed of shear wave generated within the body. Displayed parameters and measurement methods are different between two imaging methods. In 2013, therefore, academic societies on medical ultrasound have started to establish the guidelines of ultrasound elastography practice.
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  • Naotaka NITTA
    2014 Volume 32 Issue 2 Pages 69-74
    Published: 2014
    Released on J-STAGE: May 24, 2014
    JOURNAL FREE ACCESS
    The usefulness of tissue elasticity for diagnosing lesions such as cancers has been recognized for many years. Recently, in the field of image diagnosis, various elastography techniques for imaging the tissue elasticity distribution in real time have been developed and put into practical use. Based on accumulations of clinical finding and efforts for establishing guidelines for diagnosis, the position of elastography in the clinical diagnosis is being established. The static ultrasound elastography was put into practical use for the first time among various elastography techniques and 10 years passed. Therefore, it can be considered that the static ultrasound elastography enters a mature phase technically. A principle of static ultrasound elastography is to measure the displacement distribution in tissues induced by applying the external force, and to calculate and image the strain distribution in real time. So far, various methods for applying external force and measuring the displacement and strain distribution by ultrasound have been developed. In this paper, based on the background of various developments, fundamentals of static ultrasound elastography are described.
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  • Makoto YAMAKAWA
    2014 Volume 32 Issue 2 Pages 75-80
    Published: 2014
    Released on J-STAGE: May 24, 2014
    JOURNAL FREE ACCESS
    In recent years, the ultrasonic tissue elasticity imaging equipments commoditized, and its validity has been verified clinically. As the ultrasonic tissue elasticity imaging method, there are a method based on the strain distribution and a method based on the shear wave speed. In this paper, we illustrate the principle of the method based on the shear wave speed. First, we describe the relation between the tissue elasticity and shear wave speed. Next, we describe the shear wave generating method, the shear wave propagation measuring method, the shear wave speed estimation method, and finally, we describe the tissue viscoelasticity estimation method based on the shear wave phase speed.
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  • Mikio SUGA
    2014 Volume 32 Issue 2 Pages 81-86
    Published: 2014
    Released on J-STAGE: May 24, 2014
    JOURNAL FREE ACCESS
    The viscoelasticity of tissue is related to numerous physiological and pathological states. Magnetic resonance elastography (MRE) is a phase-contrast technique that can noninvasively visualize shear wave patterns within tissue. The local quantitative tissue elasticity map, known as the elastogram, is reconstructed from the shear wave pattern using inversion algorithm. In order to generate and visualize shear waves within the tissue, various external drivers and pulse-sequence (MRI control program) have been developed. Furthermore, to obtain the quantitative elastogram from acquired shear wave images, various inversion algorithms are proposed. These three components are strongly dependent on each other. The purpose of this article is to summarize the current status and trend in research and development of MRE technology.
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  • Toshikatsu WASHIO
    2014 Volume 32 Issue 2 Pages 87-92
    Published: 2014
    Released on J-STAGE: May 24, 2014
    JOURNAL FREE ACCESS
    MR Elastography is noninvasive measurement of mechanical properties on organ. MR Elastography is a technology that is based on bi-polar gradient magnetic field technique and wave propagation. MR Elastography is taken with bi-polar gradient magnetic field and its synchronized forced shear oscillation and enables to measure wave propagation as information of phase image. Generally speaking, velocity of wave propagation is multiply wavelength and frequency of forced oscillation. Also, square of velocity is equal to modulus of rigidity divided by density of media. Modulus of rigidity on organ, therefore, is calculated from wavelength that is measured from phase image and frequency of oscillation is decided in advance with organ's density that is equal to water's one.
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  • Gen NAKAMURA
    2014 Volume 32 Issue 2 Pages 93-97
    Published: 2014
    Released on J-STAGE: May 24, 2014
    JOURNAL FREE ACCESS
    We will introduce mathematical methods to extract viscoelasticity or an indication of it from time harmonic viscoelastic waves propagatinng inside a human tissue or phantom measured by hardware of MR elastography. A method called the modified integral method is to identify the viscoelasticity of the human tissue or phamtom by modeling them as a viscoelastic medium. On the otherhand, the method using a continuous wavelet transform is to extract an indication of viscoelasticity.
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Special Issue on System Development for Medical Imaging Technology
  • Yukihiro NOMURA, Yoshitaka MASUTANI, Soichiro MIKI, Shouhei HANAOKA, M ...
    2014 Volume 32 Issue 2 Pages 98-108
    Published: 2014
    Released on J-STAGE: May 24, 2014
    JOURNAL FREE ACCESS
    The performance of computer-assisted detection (CAD) software depends on the quality and quantity of the dataset used for supervised learning. If the data characteristics differ in development and practical use, the performance of CAD software will be degraded. Therefore, it is necessary to continuously collect data for supervised learning in practical use, and to improve CAD software by retraining with the collected data. In this paper, we describe the development, clinical use, and continuous performance improvement of CAD software based on multi-institutional collaboration in teleradiology environment. We developed additional functions of the web-based CAD software processing and evaluation platform (CIRCUS CS) for implementing into teleradiology environment, and a multi-institutional study has been started since September 2011. We investigated the performance improvement of CAD software for each institution based on retraining through a simulation-based study. According to the results, the performance of CAD software for each institution was improved by retraining. These results suggest that the multi-institutional data collection has potential to accelerate development and clinical use of CAD software for various institutions.
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  • Ayako AKAZAWA, Yoshiyuki YAMAKAWA, Nobuya HASHIZUME, Tetsuya KOBAYASHI ...
    2014 Volume 32 Issue 2 Pages 109-115
    Published: 2014
    Released on J-STAGE: May 24, 2014
    JOURNAL FREE ACCESS
    3D list-mode PET image reconstruction using TOF information has advantages in size of acquisition data and accurate reflection of TOF information to image in comparison to 3D sinogram reconstruction. However, computation time of list-mode reconstruction increases in proportion to the number of events. In this work, we investigated acceleration of 3D list-mode image reconstruction using CUDA (Compute Unified Device Architecture), especially forward and back projections which were the dominant computational load. We sorted list-mode data by main direction (largest LOR's direction cosine) for efficient memory access, and used texture memory to store TOF kernel function for reducing calculation amount. The reconstructed images computed by both CPU (8-cores, MPI) and GPU are almost identical, while our approach runs 7.8 times faster than an equivalent CPU implementation.
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Papers
  • Comparing to Conventional Formalin-fixation
    Shogo KOKUBO, Thet-Thet- LWIN , Akio YONEYAMA, Kazuyuki HYODO, Hiroko ...
    2014 Volume 32 Issue 2 Pages 116-122
    Published: 2014
    Released on J-STAGE: May 24, 2014
    JOURNAL FREE ACCESS
    Phase contrast X-ray CT system using an X-ray interferometer has been developed. The phase contrast X-ray technique has approximately 1000 times higher sensitivity than conventional X-ray absorption technique for low-atomic number element, enables to detect the minute density difference within biomedical objects. In this study, the image quality of rat brain fixed by ethanol was examined comparing to conventional formalin fixed brain using Phase contrast X-ray CT system. The experiment was performed at the Photon Factory and X-ray energy was set at 35 keV. Rat brain fixed by 100% ethanol was imaged by phase-contrast X-ray CT, and high contrast brain image was obtained. It was possible to clearly depict the nerve plexus, and the white matter from corpus callosum was extracted well by using 3D image processing software.
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  • Satoshi ITO, Hiroaki HARADA, Yoshifumi YAMADA
    2014 Volume 32 Issue 2 Pages 123-131
    Published: 2014
    Released on J-STAGE: May 24, 2014
    JOURNAL FREE ACCESS
    MR multi-slice imaging is a technique which can reduce the total signal acquisition time by acquiring signals slice by slices sequentially. That imaging method is based on the two-dimensional (2D) imaging. However, the application of compressed sensing (CS) to three-dimensional (3D) objects is feasible by introducing an adequate signal acquisition trajectory and regarding a number of sliced images as three-dimensional objects. In this paper, comparison of image quality between multi-slice three-dimensional CS reconstruction and two-dimensional slice by slice CS reconstruction were performed using three MR model images by assuming that the same signal trajectories is used. Simulation experiments showed that the reconstruction error in multi-slice three-dimensional CS reconstruction reduces as the number of slice images increases, or the slice spacing decreases, which results in remarkable improvements in image quality compared to two-dimensional slice by slice CS reconstruction. In addition, 3D-FREBAS transform showed better performances than 3D-wavelet transform when they were used as a sparsifying transform function in CS reconstruction.
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Work-in-progress
  • Keisuke USUI, Chie KUROKAWA, Satoru SUGIMOTO, Shigeto KABUKI, Etsuo KU ...
    2014 Volume 32 Issue 2 Pages 132-142
    Published: 2014
    Released on J-STAGE: May 24, 2014
    JOURNAL FREE ACCESS
    To realize the accurate irradiation targeted to a small volume, confirmation of the target position is very important. A kilo-voltage cone-beam computed tomography (kV-CBCT) system mounted on a linear accelerator can improve the accuracy of irradiation by imaging the target just before the irradiation. However, the kV-CBCT system requires a long data acquisition time, therefore motion of a target causes the degradation of CT images. In this study, we proposed a method to reconstruct target motions in two directions from the projection images, and evaluated the feasibility of the method using the simulation and phantom studies with a dynamic phantom. In this method, we detected the target position in the two directions with the projection image using the template matching method. And a sonograms were constructed from projection data with the particular, and the images for each positions were reconstructed by the filtered backprojection method. The results showed that the blurring of the target caused by the motion was reduced, and we could obtained the reconstructed images incorporating the target motion.
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