Images reconstructed from long wavelength holograms have aberrations as a result of large constru... more Images reconstructed from long wavelength holograms have aberrations as a result of large construction to reconstruction wavelength ratios. For many practical recording geometries, these aberrations of which spherical aberration is often the largest may seriously degrade image resolution.
Introduction: Deriving timing data from high frame rate ultrasound images can be difficult, as th... more Introduction: Deriving timing data from high frame rate ultrasound images can be difficult, as the image quality decreases as frame rate increases. However, higher temporal resolution increases the...
In spite of many previous research efforts, B-mode echoencephalography is not used clinically for... more In spite of many previous research efforts, B-mode echoencephalography is not used clinically for adults because of the poor quality of the images obtained with current, techniques. The intervening presence of the skull results in low sensitivity, reverberations, distortions in the range and lateral dimension, and, most importantly, poor lateral resolution (White, 1970). Lateral resolution, which can be described by the system point spread function (PSF), is a function of the relative phase variation introduced across the transducer aperture by the presence of the skull. A technique has been described (Phillips, et al., this volume) whereby this phase aberration can be measured by a secondary transducer and compensated for in a phased array imaging system, thus restoring the PSF to its unaberrated condition. An alternate technique will be described here which requires no such a priori knowledge of the skull phase variation. This is accompushed by optimizing the transducer frequency ...
The study describes a novel algorithm for deriving myocardial strain from an entire cardiac cycle... more The study describes a novel algorithm for deriving myocardial strain from an entire cardiac cycle using high-frame-rate ultrasound images. Validation of the tracking algorithm was conducted in vitro prior to the application to patient images. High-frame-rate ultrasound images were acquired in vivo from 10 patients, and strain curves were derived in six myocardial regions around the left ventricle from the apical four-chamber view. Strain curves derived from high-frame-rate images had a higher frequency content than those derived using conventional methods, reflecting improved temporal sampling.
Pulsed Doppler ultrasonic blood velocity imaging devices suffer from aliasing at high velocities ... more Pulsed Doppler ultrasonic blood velocity imaging devices suffer from aliasing at high velocities and sizable velocity errors resulting from a lack of knowledge of the angle between the acoustic propagation and blood velocity vectors. We describe a new velocity imaging technique which operates on the envelope-detected echo signal and uses a two-dimensional correlation search method. Several experiments were performed in
We have measured the rates of ultrasonic Bmode speckle pattern changes as a function of the chang... more We have measured the rates of ultrasonic Bmode speckle pattern changes as a function of the change in center frequency of the transmitted acoustical pulse under a variety of experimental conditions. Our experimental results agree with a previous theoretical description of this phenomenon. The results are then used to determine the optimal method of frequency compounding for speckle reduction in a fixed bandwidth imaging. Our analysis indicates that by dividing the available system bandwidth in half for the purpose of frequency compounding, the equivalent of 1.46 independent images may be averaged for speckle reduction. Further analysis indicates that frequency compounding does not improve diffuse target detectability in a fixed bandwidth system.
Since the initial development of B-mode ultrasonography, there have been many attempts (Fry et al... more Since the initial development of B-mode ultrasonography, there have been many attempts (Fry et al, 1974; Brinker & Taveras, 1966) to produce high quality cross-sectional images of the brain through the intact adult skull. Real time B-mode echo-encephalography was initially demonstrated by Somer in 1968 using phased array techniques. Despite these efforts, however, B-mode echoencephalography is not used clinically in the United States because of the poor quality of the images obtained with current techniques. The intervening presence of the skull results in poor signal to noise ratio, large reverberation artifacts, limited dynamic range and reduced lateral resolution.
Reports in the literature have implied or indicated that the normal pancreas cannot be visualized... more Reports in the literature have implied or indicated that the normal pancreas cannot be visualized. The reasons for this lack of visualization are: 1) the inconsistent location and appearance; 2) the increased number of echoes returning from the pancreatic structure causing it to be confused with surrounding areas and 3) technical inadequacy of previous scanning equipment. Since the normal pancreas has size and structure measurable at autopsy, it seemed logical that the pancreatic echoes were included in the normal echogram but not recognized. Taking the areas of known pancreatic location, special technique pancreatic echograms were performed and correlated with pancreatic duct cannulations in over twenty-five cases to confirm the ability to demonstrate the normal pancreas. The normal pancreas was demonstrated in over 90% of the cases.
25th AIPR Workshop: Emerging Applications of Computer Vision, 1997
We describe an active contour based on the elliptical Fourier series, and its application to matr... more We describe an active contour based on the elliptical Fourier series, and its application to matrix-array ultrasound. Matrix-array ultrasound is a new medical imaging modality that scans a 3D-volume electronically without physically moving the transducer, allowing for real-time continuous 3D imaging of the heart. Unlike other 3D ultrasound modalities which physically move a linear array, matrix array ultrasound is rapid enough to capture an individual cardiac cycle, yielding a temporal resolution of 22 volumetric scans per second. With the goal of automatically tracking the heart wall, an active contour has been developed using the elliptical Fourier series to find perpendicular lines intersecting an initial contour. The neighborhood defined by these perpendiculars is mapped into a rectangular space, called the 1D swath, whose vertical axis represents the inside-vs.-outside dimension of the contour (along the perpendicular), and whose horizontal axis represents parametric distance along the contour (tangent to the contour). A dynamic programming technique is then used to find the optimum error function traversing the rectangle horizontally, and this error function is mapped back into image space to yield a new contour. The method does not iterate, but rather simultaneously searches for the optimum contour within a limited domain. Results are presented applying the technique to 3D ultrasound images of in vivo hearts.
Matrix-array ultrasound is a new medical imaging modality that steers an ultrasound beam electron... more Matrix-array ultrasound is a new medical imaging modality that steers an ultrasound beam electronically in three dimensions. It is the first imaging modality that can view the heart in 3D in real time, making possible thevolumetricardiogram,'ie, continuous beat to beat ...
The application of the Thaumascan imaging system has been described in cardiology. This system ca... more The application of the Thaumascan imaging system has been described in cardiology. This system can also be utilized in producing high quality images of abdominal structures. High resolution, real-time, tomographic images are generated at the rate of 30 frames/sec. in a circular sector format by electronically phasing a linear array of ultrasound transducers. The small, hand held transducer can be placed on any portion of the abdomen and various tomographic sections can readily be obtained. The real-time feature of this imaging system aids in localizing specific anatomic structures by providing immediate visual feedback.
Southwest Symposium on Mixed-Signal Design, 2003., 2003
ABSTRACT In this paper we present a 64-channel ultrasound preamplifier device that is used to amp... more ABSTRACT In this paper we present a 64-channel ultrasound preamplifier device that is used to amplify and filter pulsed echo transducer signals sourced from a real time three dimensional (RT3DU) non-invasive ultrasound system. Schematics, simulation data, and layout for each of the broadband sub-circuit macros are described which include a high gain preamplifier, a linear output buffer, and bias circuits. This device was implemented using AMI Semiconductor's, 0.5 μm, double poly, triple level metal CMOS technology. The device floorplan, circuit schematics and layout, specifications and measured test data are presented.
Images reconstructed from long wavelength holograms have aberrations as a result of large constru... more Images reconstructed from long wavelength holograms have aberrations as a result of large construction to reconstruction wavelength ratios. For many practical recording geometries, these aberrations of which spherical aberration is often the largest may seriously degrade image resolution.
Introduction: Deriving timing data from high frame rate ultrasound images can be difficult, as th... more Introduction: Deriving timing data from high frame rate ultrasound images can be difficult, as the image quality decreases as frame rate increases. However, higher temporal resolution increases the...
In spite of many previous research efforts, B-mode echoencephalography is not used clinically for... more In spite of many previous research efforts, B-mode echoencephalography is not used clinically for adults because of the poor quality of the images obtained with current, techniques. The intervening presence of the skull results in low sensitivity, reverberations, distortions in the range and lateral dimension, and, most importantly, poor lateral resolution (White, 1970). Lateral resolution, which can be described by the system point spread function (PSF), is a function of the relative phase variation introduced across the transducer aperture by the presence of the skull. A technique has been described (Phillips, et al., this volume) whereby this phase aberration can be measured by a secondary transducer and compensated for in a phased array imaging system, thus restoring the PSF to its unaberrated condition. An alternate technique will be described here which requires no such a priori knowledge of the skull phase variation. This is accompushed by optimizing the transducer frequency ...
The study describes a novel algorithm for deriving myocardial strain from an entire cardiac cycle... more The study describes a novel algorithm for deriving myocardial strain from an entire cardiac cycle using high-frame-rate ultrasound images. Validation of the tracking algorithm was conducted in vitro prior to the application to patient images. High-frame-rate ultrasound images were acquired in vivo from 10 patients, and strain curves were derived in six myocardial regions around the left ventricle from the apical four-chamber view. Strain curves derived from high-frame-rate images had a higher frequency content than those derived using conventional methods, reflecting improved temporal sampling.
Pulsed Doppler ultrasonic blood velocity imaging devices suffer from aliasing at high velocities ... more Pulsed Doppler ultrasonic blood velocity imaging devices suffer from aliasing at high velocities and sizable velocity errors resulting from a lack of knowledge of the angle between the acoustic propagation and blood velocity vectors. We describe a new velocity imaging technique which operates on the envelope-detected echo signal and uses a two-dimensional correlation search method. Several experiments were performed in
We have measured the rates of ultrasonic Bmode speckle pattern changes as a function of the chang... more We have measured the rates of ultrasonic Bmode speckle pattern changes as a function of the change in center frequency of the transmitted acoustical pulse under a variety of experimental conditions. Our experimental results agree with a previous theoretical description of this phenomenon. The results are then used to determine the optimal method of frequency compounding for speckle reduction in a fixed bandwidth imaging. Our analysis indicates that by dividing the available system bandwidth in half for the purpose of frequency compounding, the equivalent of 1.46 independent images may be averaged for speckle reduction. Further analysis indicates that frequency compounding does not improve diffuse target detectability in a fixed bandwidth system.
Since the initial development of B-mode ultrasonography, there have been many attempts (Fry et al... more Since the initial development of B-mode ultrasonography, there have been many attempts (Fry et al, 1974; Brinker & Taveras, 1966) to produce high quality cross-sectional images of the brain through the intact adult skull. Real time B-mode echo-encephalography was initially demonstrated by Somer in 1968 using phased array techniques. Despite these efforts, however, B-mode echoencephalography is not used clinically in the United States because of the poor quality of the images obtained with current techniques. The intervening presence of the skull results in poor signal to noise ratio, large reverberation artifacts, limited dynamic range and reduced lateral resolution.
Reports in the literature have implied or indicated that the normal pancreas cannot be visualized... more Reports in the literature have implied or indicated that the normal pancreas cannot be visualized. The reasons for this lack of visualization are: 1) the inconsistent location and appearance; 2) the increased number of echoes returning from the pancreatic structure causing it to be confused with surrounding areas and 3) technical inadequacy of previous scanning equipment. Since the normal pancreas has size and structure measurable at autopsy, it seemed logical that the pancreatic echoes were included in the normal echogram but not recognized. Taking the areas of known pancreatic location, special technique pancreatic echograms were performed and correlated with pancreatic duct cannulations in over twenty-five cases to confirm the ability to demonstrate the normal pancreas. The normal pancreas was demonstrated in over 90% of the cases.
25th AIPR Workshop: Emerging Applications of Computer Vision, 1997
We describe an active contour based on the elliptical Fourier series, and its application to matr... more We describe an active contour based on the elliptical Fourier series, and its application to matrix-array ultrasound. Matrix-array ultrasound is a new medical imaging modality that scans a 3D-volume electronically without physically moving the transducer, allowing for real-time continuous 3D imaging of the heart. Unlike other 3D ultrasound modalities which physically move a linear array, matrix array ultrasound is rapid enough to capture an individual cardiac cycle, yielding a temporal resolution of 22 volumetric scans per second. With the goal of automatically tracking the heart wall, an active contour has been developed using the elliptical Fourier series to find perpendicular lines intersecting an initial contour. The neighborhood defined by these perpendiculars is mapped into a rectangular space, called the 1D swath, whose vertical axis represents the inside-vs.-outside dimension of the contour (along the perpendicular), and whose horizontal axis represents parametric distance along the contour (tangent to the contour). A dynamic programming technique is then used to find the optimum error function traversing the rectangle horizontally, and this error function is mapped back into image space to yield a new contour. The method does not iterate, but rather simultaneously searches for the optimum contour within a limited domain. Results are presented applying the technique to 3D ultrasound images of in vivo hearts.
Matrix-array ultrasound is a new medical imaging modality that steers an ultrasound beam electron... more Matrix-array ultrasound is a new medical imaging modality that steers an ultrasound beam electronically in three dimensions. It is the first imaging modality that can view the heart in 3D in real time, making possible thevolumetricardiogram,'ie, continuous beat to beat ...
The application of the Thaumascan imaging system has been described in cardiology. This system ca... more The application of the Thaumascan imaging system has been described in cardiology. This system can also be utilized in producing high quality images of abdominal structures. High resolution, real-time, tomographic images are generated at the rate of 30 frames/sec. in a circular sector format by electronically phasing a linear array of ultrasound transducers. The small, hand held transducer can be placed on any portion of the abdomen and various tomographic sections can readily be obtained. The real-time feature of this imaging system aids in localizing specific anatomic structures by providing immediate visual feedback.
Southwest Symposium on Mixed-Signal Design, 2003., 2003
ABSTRACT In this paper we present a 64-channel ultrasound preamplifier device that is used to amp... more ABSTRACT In this paper we present a 64-channel ultrasound preamplifier device that is used to amplify and filter pulsed echo transducer signals sourced from a real time three dimensional (RT3DU) non-invasive ultrasound system. Schematics, simulation data, and layout for each of the broadband sub-circuit macros are described which include a high gain preamplifier, a linear output buffer, and bias circuits. This device was implemented using AMI Semiconductor's, 0.5 μm, double poly, triple level metal CMOS technology. The device floorplan, circuit schematics and layout, specifications and measured test data are presented.
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Papers by Olaf Von Ramm