Olaf T. von Ramm

Angle Independent Ultrasonic Detection of Blood Flow

We present a new technique for blood velocity imaging based on tracking the motion of the speckle pattern produced by blood. Unlike Doppler velocity determinations, these are angle independent. Initial in vivo experiments yield promising results.

Explososcan: A parallel processing technique for high speed ultrasound imaging with linear phased arrays

The data acquisition rate in medical ultrasonic imaging devices is limited by the acoustic propagation velocity in the tissues. Typically in such machines the image lines are produced sequentially one line per transmitted pulse. A parallel processing scheme has been implemented which enables the data acquisition rate to increase by a factor of four through the simultaneous acquisition of four B‐mode image lines from each individual broadened transmit pulse. The higher data rate can be used to increase the image frame rate to produce independent images that can be averaged in the image frame to reduce noise, or to produce a conventional image at standard video frame rates while reducing patient exposure. Alternatively, the field of view can be increased over that of a normal scan without sacrificing frame rate. These advantages are achieved with little reduction in the measured resolution. The design and performance of this device are described. A sample in vivo image is included.

Beam Steering with Linear Arrays

The principles and techniques of real-time imaging with phased array ultrasound scanners are reviewed. Topics include 1) the geometric optics of beam steering and focusing with a linear array in the transmit and receive modes; 2) limitations on image data acquisition due to ultrasound propagation velocity; 3) optical diffraction theory for linear arrays including effects of amplitude grating lobes. Limitations on the image quality of phased array imaging systems are also discussed, including 1) nonideal response of array transducers; 2) target ambiguities caused by phase error grating lobes; 3) refraction errors; 4) delay line design. Finally, an analysis is presented of current techniques for improving ultrasound image quality using phased array methods including phase compensation, spatial compounding, frequency compounding, and parallel processing.

Frequency Compounding for Speckle Contrast Reduction in Phased Array Images

Frequency compounding is investigated as one technique for reducing the speckle contrast in phased array ultrasonic images. The degree of speckle contrast reduction was found to be inversely proportional to the bandwidth of the transmitted acoustic burst. The speckle pattern was also found to be anisotropic in its response to frequency compounding. Increases in the speckle pattern signal-to-noise ratios of 26 percent were found in B-mode images and increases as high as 84 percent were found in A-mode images.

Real-Time, Three-Dimensional Echocardiography: Feasibility and Initial Us

The purpose of this article is to review new approaches to three‐dimensional acquisition and presentation ofechocardiographic data. New three‐dimensional phased‐array devices hold great promise for the development and application of new descriptors for left ventricular performance, myocardial perfusion, and other important indices of cardiac function. (ECHOCARDIOGRAPHY, Volume 8, January 1991)

Real-time three-dimensional echocardiography for measurement of left ventricular volumes

Left ventricular (LV) volumes are important prognostic indexes in patients with heart disease. Although several methods can evaluate LV volumes, most have important intrinsic limitations. Real-time 3-dimensional echocardiography (RT3D echo) is a novel technique capable of instantaneous acquisition of volumetric images. The purpose of this study was to validate LV volume calculations with RT3D echo and to determine their usefulness in cardiac patients. To this end, 4 normal subjects and 21 cardiac patients underwent magnetic resonance imaging (MRI) and RT3D echo on the same day. A strong correlation was found between LV volumes calculated with MRI and with RT3D echo (r = 0.91; y = 20.1 + 0.71x; SEE 28 ml). LV volumes obtained with MRI were greater than those obtained with RT3D echo (126 +/- 83 vs 110 +/- 65 ml; p = 0.002), probably due to the fact that heart rate during MRI acquisition was lower than that during RT3D echo examination (62 +/- 11 vs 79 +/- 16 beats/min; p = 0.0001). Analysis of intra- and interobserver variability showed strong indexes of agreement in the measurement of LV volumes with RT3D echo. Thus, LV volume measurements with RT3D echo are accurate and reproducible. This technique expands the use of ultrasound for the noninvasive evaluation of cardiac patients and provides a new tool for the investigational study of cardiovascular disease.

Three-dimensional imaging system

An acoustic pulse echo imaging system capable of producing an image of a three-dimensional object utilizing a two-dimensional display having perspective capabilities is described. In the system angular relationships of targets at all ranges are maintained for display. The system uses a two-dimensional transducer array of piezoelectric elements; the array is steered to assume transmit and receive orientations in both azimuth and elevation by producing (1) a directed transmit pulse and many similarly directed receive orientations or (2) a non-directed transmit pulse and many directed receive orientations. For each transmit pulse a parallel processing system produces several unique image points whose locations in the image correspond to the tangents of the angles of the receive orientations in the azimuth and elevation planes. The brightness of each image point is the weighted integral of the echo data received along each receive path. As an option, range discrimination capability is provided by means of a range dependent gain control, brightness shading as a function of range or a color display in which data originating from different ranges is displayed in different hues.

Real-time, three-dimensional echocardiography : Feasibility of dynamic right ventricular volume measurement with saline contrast

BACKGROUND The asymmetry and complex shape of the right ventricle have made it difficult to determine right ventricular (RV) volume with 2-dimensional echocardiography. Three-dimensional cardiac imaging improves visualization of cardiac anatomy but is also complex and time consuming. A newly developed volumetric scanning system holds promise of obviating past limitations. METHODS Real-time, transthoracic 3-dimensional echocardiographic images of the right ventricle were obtained with a high-speed volumetric ultrasound system that uses a 16:1 parallel processing schema from a 2.5 MHz matrix phased-array scanner to interrogate an entire pyramidal volume in real time. The instrumentation was used to measure RV volume in 8 excised canine hearts; dynamic real-time 3-dimensional images were also obtained from 14 normal subjects. RESULTS Three-dimensional images were obtained in vitro and in vivo during intravenous hand-agitated saline injection to determine RV volumes. The RV volumes by real-time 3-dimensional echocardiography are well correlated with those of drained in vitro (y = 1.26x - 9.92, r = 0.97, P <.0001, standard error of the estimate = 3.26 mL). For human subjects, the end-diastolic and end-systolic RV volumes were calculated by tracing serial cross-sectional, inclined C scans; functional data were validated by comparing the scans with conventional 2-dimensional echocardiographic indexes of left ventricular stroke volume. CONCLUSIONS These data indicate that RV volume measurements of excised heart by real-time 3-dimensional echocardiography are accurate and that beat-to-beat RV quantitative measurement applying this imaging method is possible. The new application of real-time 3-dimensional echocardiography presents the opportunity to develop new descriptors of cardiac performance.

Real-time volumetric echocardiography: the technology and the possibilities.

The heart is a dynamic organ with complexities in its shape. As such, it places special demands on three‐dimensional techniques for reconstruction. Real‐time volumetric echocardiography, which is based on phased array and parallel processing principles to enhance line density within a scan volume, provides rapid image acquisition. We introduce the principle, potential clinical importance, current limitations, and future of volumetric imaging methods.

Multi-dimensional real-time ultrasonic blood flow imaging apparatus and method

An ultrasonic diagnostic apparatus and method for real-time multi-dimensional blood flow imaging with enhanced sensitivity to lateral blood flow. The apparatus constitutes an improvement on the ultrasonic diagnostic apparatus of the type wherein an ultrasonic pulse beam is repeatedly transmitted into the subject under examination at a fixed pulse rate and the reflected echoes are picked up, amplified and displayed. The improvement comprises an ultrasonic transducer means comprising a phased array transducer which is electronically and/or mechanically divided into two or more independently controlled sub-apertures and adapted for transmitting ultrasonic pulse beams from one of the two or more sub-apertures and for receiving the reflected echoes with at least two of the two or more sub-apertures. Optionally, the apparatus and method further comprises signal processing means including quadrature detection circuitry comprising sampling means for sampling the echo signals or a downward shifted version of echo signals and Hilbert transform means for filtering the signals so as to obviate the need for mixers, low-pass filters (LPF) and quadrature reference frequencies utilized in conventional ultrasonic blood flow imaging.