Ryoichi Kanda

Image signal processing circuit for ultrasonic imaging apparatus

An image signal processing circuit for an ultrasonic imaging apparatus includes a frame correlation circuit for performing, in accordance with a predetermined correlation coefficient, a frame correlation process for an ultrasonic frame image signal output from an ultrasonic transmitter/receiver circuit, and a correlation coefficient output circuit for outputting a frame correlation coefficient corresponding to a difference between a current input frame image signal and an immediately preceding frame image signal, i.e., a coefficient which decreases as the difference increases to the frame correlation circuit.

An investigation of wavefront distortion correction: correction using averaged phase information and the effect of correction in one and two dimensions (medical US imaging)

A method for estimating arrival time fluctuation for wavefront distortion correction is proposed and compared with the cross-correlation method. The improvement of image quality achieved by these methods is almost the same under normal conditions. However, the proposed method underestimates phase aberration in the presence of increased severe noise, while estimates from the cross-correlation method fluctuate more than expected under the same condition. the effect of phase aberration on received signals has been confirmed experimentally to be a decrease in the similarity between signals. Beam patterns distorted by two-dimensional phase aberration are not improved by one-dimensional correction but are improved by two-dimensional correction.<<ETX>>

Visualization of clear echocardiographic images with near field noise reduction technique: experimental study and clinical experience.

BACKGROUND With transthoracic echocardiography, it is sometimes difficult to obtain a clear image of the apical portion of the heart because of noise near the transducer. To reduce this artifact, we have developed a new technique (near field noise reduction, NFNR) based on the digital filtering by using radiofrequency signals. This technique may be useful for the accurate measurement of the wall thickness of the myocardium in the near field. The objectives of these studies were (1) to determine the accuracy of this new technique for the measurement of wall thickness in the experimental study and (2) to determine whether the improvement in the image quality in the apical portion can be obtained in the clinical setting by using the NFNR technique. EXPERIMENTAL STUDY By using the NFNR technique, we measured wall thickness of three kinds of phantoms (wall thickness 9.0, 14.0, and 21.0 mm) moving at various velocities (5 to 80 mm/sec) in the water bath with artifact produced by a single probe. It was difficult to obtain clear echocardiographic images of the phantom and measure its wall thickness because of the artifact. By using the NFNR technique, on the other hand, the same phantom was clearly imaged. It was possible to measure the wall thickness of each phantom at each moving velocity with the NFNR technique. Mean differences between the echocardiographic measurement and actual value of wall thickness in each phantom model (9.0, 14.0, and 21.0 mm) were 0.04 +/- 0.58 mm, 0.09 +/- 0.58 mm, and -0.02 +/- 0.24 mm, respectively. CLINICAL STUDY We studied 25 initial patients in whom the near field was not clearly imaged in apical views by conventional echocardiography because of near field noise. Apical four-chamber or two-chamber views were obtained with and without the NFNR technique. Two observers independently graded endocardial visualization for the 50 segments by using a three-point scale (0 = endocardium not seen, 1 = seen in part but not all of the segment, 2 = endocardium seen along entire segment). The mean segment score in the imaging with the NFNR technique was significantly higher than that without the NFNR technique (observer 1: 1.8 +/- 0.7 vs 1.2 +/- 0.8, p < 0.01; observer 2: 1.6 +/- 0.7 vs 1.2 +/- 0.8, p < 0.01). CONCLUSIONS The newly developed NFNR technique provides clear echocardiographic images and accurate wall thickness measurement in the experimental model even when it is difficult to obtain clear images because of the artifact. This new technique will be useful in the reduction of near field noise in the clinical setting.

Accurate detection of regional contraction using angle-corrected tissue strain and displacement imaging combined with two-dimensional tissue doppler tracking technique

index remained unchanged in the AP group and on a lower level in the El group. In contrast during DI, systolic strain and stroke volume initially increased (5pg/kg/min: strain=77±6%, p<0.01), then progressively returned to baseline. During El, stroke volume and systolic strain decreased (strain=38±2%, p<0.001). Pacing also decreased stroke volume and systolic strain in the AP (180/min: strain=36±2%, p<0.001) and El groups (180/rain: strain =25±3%, p<0.001). Conclusions: For normal myocerdium, peak systolic strain rate may better reflect regional contractile function and is more independent of HR and stroke volume. In contrast systolic strain is mainly related to stroke volume and therefore reflects on a regional myocardial level changes in global hemodynamics.

Computational and experimental investigation of time‐shift estimation for compensation of wave‐front distortion in ultrasonic applications using scattered signals

Time‐shift compensation of wave‐front distortion that degrades images in medical ultrasound has been studied using computations and measurements. In the computations, wave‐front distortion was assumed to arise from a phase screen placed at various distances from the receiving aperture. Intensity patterns were determined from uncompensated data and from data compensated with time‐shift estimates made in the aperture. In the experiments, waveforms scattered by a wire target and randomly distributed particles were collected for a water path and for a tissue path. Images were reconstructed from uncompensated data, from data compensated with time‐shift estimates made in the receiving aperture, and from data compensated with time‐shift estimates made after a backpropagation step in which a waveform similarity factor was maximized. The results show the limitations of time‐shift estimation in the aperture for compensation of wave‐front distortion produced by a phase screen that is not close to the receiving apert...