Satoshi Tamano

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%.

Ultrasonic doppler blood flow measuring apparatus

An ultrasonic Doppler blood flow measuring apparatus comprises a plurality of frame memories for storing information pieces about a blood flow speed in a unit of frame, circuits for comparing blood flow speed information pieces at corresponding addresses on the plurality of frame, memories and determining a speed difference, a circuit for comparing the speed difference with a predetermined threshold value and determining a blood flow at the corresponding address as an arterial flow when the speed difference exceeds the threshold value but as a venous flow when the speed difference is below the threshold value, and a circuit for displaying the determined arterial and venous flows in different colors.

Ultrasonic diagnosis apparatus for displaying the distribution of speed of movement of an internal part of a living body

An ultrasonic diagnosis apparatus comprises a probe means for transmitting an ultrasonic pulse beam toward an internal moving part of a living body and receiving the reflected wave therefrom, and a plurality of phasing circuits for simultaneously receiving and phasing the received signal in parallel in a plurality of channels. The received signals of plural channels are mixed with a set of complex reference signals having a complex relation therebetween, thereby converting the received signals into complex signals. Autocorrelators delay the complex signals computes the autocorrelation of the complex signals. Speed operators compute the speed of the internal moving part of the basis of the computed autocorrelation. The result of measurement of the distribution of the speed of the internal moving part is displayed on a display unit.

3D ultrasound imaging system using Fresnel ring array & high voltage multiplexer IC

In a previous report (Satoshi Tamano et al, Proc. IEEE Ultrason. Symp., p.1310-1313, 2003), a prototype 2D convex-convex shaped array probe and a real-time 3D ultrasound imaging prototype system was reported. This time, our convex-convex (40 mmR-40 mmR, 3.5 MHz center frequency) shaped 2D array probe is modified to include approximately 8,000 PZTs. Moreover, the scale of our custom multiplexer IC is enlarged from 8:1 with 8 channels to 32:1 with 32 channels. These high voltage multiplexer ICs are chip-on-board (COB) mounted on a PCB inside the 2D array probe. With this improved probe and multiplexer ICs, it is possible to bundle more than 3,000 active PZTs into 32 Fresnel rings. It is expected that our system will enable us to form a uniform beam in a 3D space by use of the Fresnel ring and to bundle a large number of PZTs into 32 to 64 channels.

Novel automatic first-arrival picking method for ultrasound sound-speed tomography

Ultrasound sound-speed tomography (USST) is a promising technique for breast cancer diagnosis that is currently under investigation. Compared with two-dimensional X-ray mammography, it not only provides three-dimensional images but also avoids radiation exposure. However, the image quality of USST is highly dependent on the accuracy of travel time map (TTM). To improve the accuracy, a novel automatic first-arrival picking method is proposed in this study. With this method, Akaike information criterion is used to obtain travel time roughly, then cross-correlation of neighboring traces is employed to correct the obtained travel time. Simulation, phantom, and ex vivo experiments are implemented. The simulation experiments showed that the absolute errors of the proposed method were 52 and 98 ns for simple and complex structure data, respectively. The phantom and ex vivo experiments demonstrated the feasibility of the proposed method. In this study, a novel and robust first-arrival picking method was proposed for USST.

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.

Real-time feedback control for high-intensity focused ultrasound system using localized motion imaging

High-intensity focused ultrasound (HIFU) is one of the noninvasive treatment for tumors. Visualizing the treated area inside the human body is necessary to control the HIFU exposure. Localized motion imaging (LMI) using ultrasound to induce and detect tissue deformation is one technique to detect a change in tissue stiffness caused by thermal coagulation. In experiments with porcine liver, LMI has shown to detect deformation with less than 20% accuracy. We have developed a prototype feedback control system using real-time LMI. In this system, coagulation size was measured every 1 s and controlled to correspond to a targeted size. The typical size error was reduced to 14% from 35%. LMI displacements in normal and coagulated tissues were sufficiently different to discriminate between coagulated areas and noncoagulated ones after HIFU sonication and to visualize treated areas after HIFU treatment.

3D ultrasound imaging system using Fresnel ring array

A real-time 3D ultrasound system using Fresnel ring array is proposed. We have developed a prototype of a convex-convex shaped 2D-array probe with curvature of 40 mm for both in the lateral-axis direction and the elevational (vertical)-axis direction, and the center frequency is 3.5MHz. As a result, a transmitted beam profile measured in water is in good accordance with the theoretical simulation using FEM. By using the convex-convex shaped 2D array probe including a newly developed multiplex-IC, the dynamic focusing is performed with Fresnel ring, so that a good isotropic beam for scan can be obtained. A preliminary real-time 3D image has been demonstrated.

Ultrasonic diagnosis apparatus for displaying speed or correlation between speed and speed dispersion by color change

An ultrasonic diagnosis apparatus comprises an ultrasonic probe for transmitting an ultrasonic pulse beam toward an internal moving member of a living body at a constant recurrence frequency, a converter for mixing the received high-frequency signal with a set of complex reference signals having a frequency n times as high as the recurrence frequency of the transmitted ultrasonic pulse beam and having a complex relation therebetween, thereby converting the high-frequency signal into complex signals, a speed operating circuit for computing the speed of the moving part on the basis of the complex signals, a speed deviation operating circuit for computing the deviation of the speed computed by the speed operator, and a display unit for displaying, by a color change, at least one of the speed, the speed dispersion, the speed and the speed deviation, and the correlation between the speed and the speed deviation. The display unit may display the reflected ultrasonic wave intensity by a luminance and may display the correlation between the reflected ultrasonic wave intensity and the speed and/or the speed deviation by a color change.