Tsuyoshi Mitake

Real-time Virtual Sonography for navigation during targeted prostate biopsy using magnetic resonance imaging data.

Objectives:  To evaluate the effectiveness of the medical navigation technique, namely, Real‐time Virtual Sonography (RVS), for targeted prostate biopsy.

Non-Invasive Evaluation of Hepatic Fibrosis for Type C Chronic Hepatitis

Objective: The aim of this study was to investigate liver fibrosis using non-invasive Real-time Tissue Elastography® (RTE) and transient elastography (FibroScan®) methods. Methods: RTE, FibroScan and percutaneous liver biopsy were all performed on patients with chronic liver disease, particularly hepatitis C, to investigate liver fibrosis. Results: FibroScan and RTE were compared for fibrous liver staging (F stage), which was pathologically classified using liver biopsy. In FibroScan, significant differences were observed between F1/F3 and F2/F4, but no such differences were observed between F1/F2, F2/F3 and F3/F4. In RTE, significant differences were observed between F1/F2, F2/F3 and F2/F4. But for F3/F4, no significant differences were observed. Conclusion: FibroScan and RTE correlated well with F staging of the liver. In particular RTE was more successful than FibroScan in diagnosing the degree of liver fibrosis.

A single mediaprocessor-based programmable ultrasound system

We have developed a programmable ultrasound imaging system using a single commercially available mediaprocessor. We have efficiently mapped all of the necessary B-mode processing algorithms on the underlying processor architecture, including envelope detection, dynamic range compression, lateral and axial filtering, persistence processing, and scan conversion. Our system can handle varying specifications ranging from 128 vectors and 512 samples per vector to more than 256 vectors and 1024 samples per vector. For an image size of 330 vectors and 512 samples per vector, it can process 30 frames per second using a 300-MHz MAP-CA mediaprocessor from Hitachi/Equator Technologies. This programmable ultrasound machine will not only offer significant advantages in terms of low cost, portability, scalability, and reduced development time, but also provide a flexible platform for developing and deploying new clinical applications to aid the clinicians and improve the quality of healthcare to patients.

High-speed Freehand Tissue Elasticity Imaging for Breast Diagnosis

Tissue elasticity imaging technology is expected to be a new technique for breast disease diagnosis. In clinical measurement, high-speed and freehand manipulation of the probe is required for a practical system. Thus, we developed a tissue elasticity imaging system which performs a stable strain measurement with freehand tissue compression based on the extended combined autocorrelation method. The method enables us to obtain tissue strain distribution at high-speed and suppressing errors due to lateral slip of the probe caused by freehand compression. The developed method can estimate the strain images at about 5 frames/s and was applied to breast disease measurement in vivo. Consequently, it is shown that the system is effective not only for the diagnosis of tissue hardness but also to determine the disease expansion area. It is also confirmed that the method can stably estimate the strain during the breast measurement in vivo.

Diagnostic results for breast disease by real-time elasticity imaging system

We have previously reported our real-time elasticity imaging system and a preliminary application to breast tissue diagnosis. We now propose several post processing algorithms to stabilize the elasticity imaging, introduce a method for scoring its clinical usefulness, and report the current status of the scoring method on breast tissue diagnosis. Our newly implemented post processing algorithms are: (1) frame-to-frame smoothing; (2) adaptive contrast optimization; (3) noisy-frame rejection; (4) noisy-region reduction. Using these algorithms, more than 20% of intensity fluctuations (SD) in strain images can be reduced. Our newly introduced scoring method is based on the imaging pattern of the low-strain region inside the hypoechoic region in the B-mode image. We classify 5 grades of elasticity score ranging from 1 (no strain-zero brightness region; benign) to 5 (broader strain-zero brightness region; malignant). As the result of applying 137 patients with breast diseases, this method provides a sensitivity of 87%, a specificity of 91%, and an accuracy of 89%.

Mechanical Model Analysis for Quantitative Evaluation of Liver Fibrosis Based on Ultrasound Tissue Elasticity Imaging

Precise evaluation of the stage of chronic hepatitis C with respect to fibrosis has become an important issue to prevent the occurrence of cirrhosis and to initiate appropriate therapeutic intervention such as viral eradication using interferon. Ultrasound tissue elasticity imaging, i.e., elastography can visualize tissue hardness/softness, and its clinical usefulness has been studied to detect and evaluate tumors. We have recently reported that the texture of elasticity image changes as fibrosis progresses. To evaluate fibrosis progression quantitatively on the basis of ultrasound tissue elasticity imaging, we introduced a mechanical model of fibrosis progression and simulated the process by which hepatic fibrosis affects elasticity images and compared the results with those clinical data analysis. As a result, it was confirmed that even in diffuse diseases like chronic hepatitis, the patterns of elasticity images are related to fibrous structural changes caused by hepatic disease and can be used to derive features for quantitative evaluation of fibrosis stage.

Measurement of elastic property of breast tissue for elasticity imaging

It is necessary to investigate detailed elastic property of human tissue as a foundation for developing objective and quantitative elasticity imaging (elastography). In this paper, we present our elasticity measurement method based on direct compression test for surgically-resected breast tissues. In addition, we discuss the feasibility of our approach to quantitative elastography by comparing the results of elastography obtained in vivo with those confirmed in direct compression test after extirpative surgery.

Clinical assessment of real-time, freehand elasticity imaging system based on the combined autocorrelation method

Various techniques for tissue elasticity imaging have been proposed in the last decade. For clinical applications, real-time and freehand manipulation of a probe is required. In a previous study, we developed the combined autocorrelation method (CAM), which produces an elasticity image with high-speed processing and accuracy, and achieves a wide dynamic range for strain estimation. In the current study, we extended the CAM clinical uses to be robust for tissue sideslip and suited to freehand compression. We achieved this imaging system by adopting its algorithm and using a commercial ultrasonic scanner and a PC. The echo signals are captured in real time and the strain image frame rate was 10 frames/s. Strain images are superimposed on B-mode images with a translucent color scale. In the clinical measurement, elasticity images for breast and prostate cancer were obtained from more than 50 subjects. Some results yielded an elasticity image, that is, a visualization of the tumor area and detected a non-invasive ductal carcinoma. These results demonstrate that the system can provide high-quality and stable elasticity images in clinical measurement.

Programmable ultrasound scan conversion on a media-processor-based system

Scan conversion is an important ultrasonic processing stage that maps the acquired polar coordinate data to Cartesian coordinates for display. This requires computationally expensive square root and arctangent calculations for geometric transformation. Previously, we developed an algorithm for implementing scan conversion for gray-scale images using pre-computed lookup tables. In a clinical setting, however, interactive changes of scan conversion parameters, e.g., zoom and sector angle, require these table to be recomputed often. In this paper, we describe a fast lookup table generation algorithm and its implementation on Hitachi/Equators MAP-CA mediaprocessor architecture. In addition, we have extended the gray-scale scan conversion algorithm for color images, which requires interpolation between angular data. For a 600x420 output image, gray- scale scan conversion takes 12 ms while color scan conversion takes 20.3 ms on a 300 MHz MAP-CA. Interactive parameter changes take 102.5 ms for table regeneration. We believe that this high performance is an important step towards making software-based ultrasound programmable systems using mediaprocessors a reality. Such a system would provide more flexibility and improved cost/performance in the future than the existing hardwired solutions.

Ultrasonic contrast medium imaging apparatus and method

An ultrasonic enhanced-contrast imager includes an ultrasonic probe for transmitting an ultrasonic wave to an organism and receiving an ultrasonic wave from the organism, a transmitting section for transmitting an ultrasonic signal to the ultrasonic probe, a receiving section for processing a response signal ultrasonic wave received by the ultrasonic probe, a filter for extracting a specific frequency component from the processed response signal, a setting control section for setting a pass frequency band of the filter on the basis of a frequency band of the response signal from a contrast medium injected to the organism, and a control section for controlling the operation of the filter in the set pass band.