IEEE Winter Workshop on Nonlinear Digital Signal Processing, 1993
This paper explores the application of nonlinear filtering techniques in volume rendering of medi... more This paper explores the application of nonlinear filtering techniques in volume rendering of medical ultrasound data. Volume rendering methods based on an initial probabilistic classification have been used with success on Computed Tomography and Mag- netic Resonance data, but have shown to fail in ultra- sonic studies. Several considerations have to be made in ultrasound imaging, because of a substantial
ABSTRACT In ultrasound Color Doppler imaging, a grayscale B-mode image and a Doppler image repres... more ABSTRACT In ultrasound Color Doppler imaging, a grayscale B-mode image and a Doppler image representing velocities are overlaid to produce a color coded image of e.g. blood flow or myocardial movement. Normally, the B-mode and Doppler images are acquired at the same rate, resulting in trade offs between B-mode image quality and Doppler frame rate. In this work, we present a new scan sequencing technique for Color Doppler imaging, where the B-mode image is acquired at a lower frame rate than the Doppler scan. This is achieved by splitting the B-mode image in subscans which are acquired in between multiple scans of the entire Doppler image. In this way, a full width B-mode image with high spatial resolution is kept while the temporal resolution of the velocity information is increased. In this paper, application of the new technique in Tissue Velocity Imaging (TVI), is discussed, showing the potential for improving lateral beam density or temporal resolution in Color Doppler imaging.
Proceedings., International Conference on Image Processing, 1995
This paper presents an approach to volume rendering based on real-time and interactive data reduc... more This paper presents an approach to volume rendering based on real-time and interactive data reduction prior to volume visualization. The underlying hardware design of a PCI based search engine is introduced including the architecture of a full custom VLSI chip that based on combinations of general range queries performs a real-time classification/opacity assignment of the multi-spectral voxel data. Various image
Computers in Cardiology 1998. Vol. 25 (Cat. No.98CH36292), 1998
This article describes an off-line software for extended analysis of tissue myocardial ultrasound... more This article describes an off-line software for extended analysis of tissue myocardial ultrasound Doppler information acquired at high temporal resolution. The software contains four main modalities for improved objective analysis of myocardial wall motion. (1) The possibility to extract velocity curves from multiple points in any pixel. (2) Color-coded 2-D images from mathematically processed velocity curves. (3) The possibility to analyze directional and velocity changes along any pre-defined line or curve (C-line) and then present these in analogue to the M-Mode (C-Mode). (4) Strain rate imaging (SRI)-by calculating the relative movement inside the tissue as distances between discrete points information about internal velocities i.e. compression or contraction and expansion, can be presented in a color-coded image both in 2D or C-mode
We introduce a method for automatic detection and tracking of the apex and two landmarks defining... more We introduce a method for automatic detection and tracking of the apex and two landmarks defining the atrioventricular plane in apical views of the left ventricle. The method is based on using tissue Doppler to track a set of candidate points in a cardiac cycle. Each candidate point is given a score based on the gray-scale, the velocity, and the
A new estimator, Bandwidth Imaging, related to the bandwidth of the ultrasound Doppler signal is ... more A new estimator, Bandwidth Imaging, related to the bandwidth of the ultrasound Doppler signal is proposed as a classification function of blood and tissue signal in transthoracial echocardiography of the left ventricle. An in vivo experiment is presented, where the apparent error rate of Bandwidth Imaging is compared with the apparent error rate of Second-Harmonic Imaging on 15 healthy men. The apparent error rates are calculated from the 16 myocardial wall segments defined in . A hypothesis test of Bandwidth Imaging having lower apparent error rate than Second-Harmonic Imaging is proved for a p-value of 0.94 in 3 segments in end diastole and in 1 segment in end systole. When data was averaged by a structural element of 5 radial, 3 lateral and 4 temporal samples the numbers of segments increased to 9 in end diastole and to 6 in end systole. This experiment indicates that Bandwidth Imaging can supply additional information for automatic border detection routines on endocardium.
Extraction of the endocardial boundary of the left ventricle is a key challenge in cardiac ultras... more Extraction of the endocardial boundary of the left ventricle is a key challenge in cardiac ultrasound imaging. The cardiac anatomy may be difficult to determine automatically without incorporating knowledge of both wall shape and intensity signature into the detection algorithm. The aim of this study is to establish a framework for knowledge based extraction of the left ventricular endocardial boundary.
In this paper, we present a new method for simple acquisition of dynamic three-dimensional (3-D) ... more In this paper, we present a new method for simple acquisition of dynamic three-dimensional (3-D) ultrasound data. We used a magnetic position sensor device attached to the ultrasound probe for spatial location of the probe, which was slowly tilted in the transthoracic scanning position. The 3-D data were recorded in 10-20 s, and the analysis was performed on an external PC within 2 min after transferring the raw digital ultrasound data directly from the scanner. The spatial and temporal resolutions of the reconstruction were evaluated, and were superior to video-based 3-D systems. Examples of volume reconstructions with better than 7 ms temporal resolution are given. The raw data with Doppler measurements were used to reconstruct both blood and tissue velocity volumes. The velocity estimates were available for optimal visualization and for quantitative analysis. The freehand data reconstruction accuracy was tested by volume estimation of balloon phantoms, giving high correlation with true volumes. Results show in vivo 3-D reconstruction and visualization of mitral and aortic valve morphology and blood flow, and myocardial tissue velocity. We conclude that it was possible to construct multimodality 3-D data in a limited region of the human heart within one respiration cycle, with reconstruction errors smaller than the resolution of the original ultrasound beam, and with a temporal resolution of up to 150 frames per second.
... Email: mari.thune @nr.no. ... L[] = twodimensional array of size N*MP[]l] = twodimensional ar... more ... Email: mari.thune @nr.no. ... L[] = twodimensional array of size N*MP[]l] = twodimensional array of size N*M fOr j= 1.... NL[j][0] = SL[0][j] for k = 1.... ML[t][k] = oo for k = 1..... M forj = N ..... 2 in for i = minLength...., jminLength mO = MAX(m, Lli][kll + SL[i][j] if (too m hypoTestOk ...
Locating content in existing video archives is both a time and bandwidth consuming process since ... more Locating content in existing video archives is both a time and bandwidth consuming process since users might have to download and manually watch large portions of superfluous videos. In this paper, we present two novel prototypes using an Internet based video composition and streaming system with a keyword-based search interface that collects, converts, analyses, indexes, and ranks video content. At user requests, the system can automatically sequence out portions of single videos or aggregate content from multiple videos to produce a single, personalized video stream on-the-fly.
Journal of the American Society of Echocardiography, 2000
The goals of this study were to examine peak systolic strain as an index of regional function in ... more The goals of this study were to examine peak systolic strain as an index of regional function in an animal model of inotropic stress and ischemia, and to compare these results with peak systolic myocardial tissue Doppler velocity (MDV). Background: Myocardial tissue Doppler velocity is an objective measure of regional left ventricular responses to inotropic stimulation and ischemia, but it is affected by tethering from adjacent segments and translational movement. Myocardial Doppler strain (ε, relative change in length) is a more local measure of contractility, which can now be derived noninvasively from MDV. Methods: Eight dogs underwent graded dobutamine infusion followed by coronary occlusion. Epicardial 2-dimensional echocardiography and color MDV of the left ventricle were obtained and digitized from the short-axis view at baseline and with dobutamine doses of 2, 4, and 8 µg/kg per minute. These were repeated 0, 10, 20, 45, and 90 seconds after occlusion of the left anterior descending artery (LAD) (n = 3) or circumflex coronary artery (n = 5). Dobutamine was continued at 8 µg/kg per minute during coronary occlusion. The peak systolic radial MDV (cm/s) and systolic strain (ε s , percent thickening) in the anterior and posterior walls were measured off-line at each stage. Results: Dobutamine caused an increase in MDV (P = .0001) and ε s (P = .09) above baseline values. Coronary occlusion caused a reduction in wall motion; after 45 seconds, all nonperfused segments were hypokinetic. There was a corresponding decrease in MDV and ε s , but this occurred earlier for ε s , and the difference between ischemic and nonischemic segments was greater for ε s than for MDV (P < .03). Nonischemic regions trended to an increase in ε s (compensatory hyperkinesis), whereas MDV trended downward, probably reflecting the global decrease in left ventricular function. Conclusion: Both MDV and ε s increase with dobutamine and decrease during ischemia. ε s appears to respond to local ischemia earlier than MDV, perhaps because it is a more local measure. Thus ε s may prove to be an accurate parameter for the clinical recognition of regional ischemia. (J Am Soc Echocardiogr 2000;13:731-7.)
Journal of the American Society of Echocardiography, 1998
A new color Doppler myocardial imaging (CDMI) system with high spatial and temporal resolution an... more A new color Doppler myocardial imaging (CDMI) system with high spatial and temporal resolution and novel postprocessing modalities has been developed that could allow quantifiable stress echocardiography. The purpose of this study was to determine whether regional myocardial systolic velocities could be accurately and reproducibly measured both at rest and during bicycle ergometry by using CDMI. Thirty normal subjects were examined with CDMI at rest, and peak mean systolic myocardial velocities (MSV) were measured for 34 predetermined left ventricular myocardial segments. Interobserver variability and intraobserver variability were established for all segments. Submaximal bicycle ergometry was performed in 20 normal subjects by using standardized weight-related increases in workload. MSV were measured at each step of exercise for 16 left ventricular stress echo segments. At rest, a base-apex gradient in regional MSV was recorded with highest longitudinal shortening velocities at the base. A similar pattern was noted for circumferential shortening MSV. Measurements were predictable and highly reproducible with low interobserver and intraobserver variability for 26 of 34 segments. Reproducibility was poor for basal anteroseptal segments in all views and mid anterior, anteroseptal, and septal segments in the short-axis views. During exercise, mid and basal segments of all walls showed a significant increase of MSV between each workload step and for apical segments between alternate steps. The resting base-apex velocity gradient observed at rest remained in all walls throughout ergometry. Thus a CDMI system with improved spatial and temporal resolution and postprocessing analysis modalities provided reproducible and accurate quantification of segmental left ventricular circumferential and longitudinal contraction both at rest and during exercise.
Abstmct-In this paper we explore the application of volume rendering in medical ultrasonic imagin... more Abstmct-In this paper we explore the application of volume rendering in medical ultrasonic imaging. Several volume rendering methods have been developed for X-ray Computed Tomography (X-CT), Magnetic Resonance Imaging (MRI) and Positron Emission Tomography (PET). Limited research has been done on applications of volume rendering techniques in medical ultrasound imaging because of a general lack of adequate equipment for 3D acquisitions. Severe noise sources and other limitations in the imaging system make volume rendering of ultrasonic data a challenge compared to rendering of MRI and X-CT data. Rendering algorithms that rely on an initial classification of the data into different tissue categories have been developed for high quality X-CT and MR-data. So far, there is a lack of general and reliable methods for tissue classification in ultrasonic imaging. This paper focuses on volume rendering methods which are not dependent on any classication into different tissue categories. Instead, features are extracted from the original 3D data-set, and projected onto the view plane. We found that some of these methods may give clinically useful information which is very difficult to get from ordinary 2D ultrasonic images, and in some cases renderings with very fine structural details. We have applied the methods to 3D ultrasound images from fetal examinations. The methods are now in use as clinical tools at the National Center of Fetal Medicine in 'kondheim, Norway.
Abstrucf-We consider the problem of partitioning a sequence of n real numbers into p intervals su... more Abstrucf-We consider the problem of partitioning a sequence of n real numbers into p intervals such that the cost of the most expensive interval, measured with a cost functionfis minimized. This problem is of importance for the scheduling of jobs both in parallel and pipelined environments. We develop a straightforward and practical dynamic programming algorithm that solves this problem in time O@(np ) ) , which is an improvement of a factor of log p compared to the previous best algorithm. A number of variants of the problem are also considered.
Tissue velocity information (TVI) is acquired by sampling of tissue Doppler velocity values at di... more Tissue velocity information (TVI) is acquired by sampling of tissue Doppler velocity values at discrete points. The information is stored in an interfoiled format with gray scale imaging during one or several cardiac cycle at a high temporal resolution, &amp;amp;gt; 60 Hz, giving signals that tolerate mathematical processing as derivation, integration and Fourier analysis of velocity profiles without distortions. The software enables the possibility to analyze multiple velocity profiles from any localization within the acquired scanned sector. The myocardial tissue velocity direction and color-coded numerical value can be computed along any chosen curve form (C-line) and be presented as a spatial function of velocities against time (C-mode). The velocity curves can also be presented in several new functional modes as color-coded running cineloops: phase imaging, time delay imaging, amplitude imaging, acceleration imaging, instantaneous phase imaging, wrapped phase imaging. The software also allows color or C-mode presentation of tissue contraction and expansion. This facilitates the differentiation between active and passive myocardial tissue movements, thus improving the ability to differentiate between healthy and diseased myocardial tissue. This article presents several applications of the software in normals and in cardiac patients.
Computer Methods and Programs in Biomedicine, 2008
A new imaging method, Bandwidth Imaging, which is related to the bandwidth of the ultrasound Dopp... more A new imaging method, Bandwidth Imaging, which is related to the bandwidth of the ultrasound Doppler signal is proposed as a classification function for blood and tissue signal in transthoracial echocardiography in the left ventricle. An in vivo experiment is presented, where the apparent error rate of Bandwidth Imaging is compared with the apparent error rate of Second-Harmonic Imaging on 15 healthy men. The apparent error rates are calculated from the 16 myocardial wall segments defined in . A hypothesis test of Bandwidth Imaging having lower apparent error rate than Second-Harmonic Imaging is proved for a p-value of 0.94 in 3 segments in end diastole and in 1 segment in end systole. When data was averaged by a structural element of 5 radial, 3 lateral and 4 temporal samples the numbers of segments increased to 9 in end diastole and to 6 in end systole. This experiment indicates that Bandwidth Imaging can supply additional information for automatic border detection routines on endocardium.
Computer Methods and Programs in Biomedicine, 2009
c o m p u t e r m e t h o d s a n d p r o g r a m s i n b i o m e d i c i n e 9 6 ( 2 0 0 9 ) 12-... more c o m p u t e r m e t h o d s a n d p r o g r a m s i n b i o m e d i c i n e 9 6 ( 2 0 0 9 ) 12-24 Echocardiography Doppler signal Endocardial detection Ejection fraction Likelihood ratio function a b s t r a c t A parametric model for the ultrasound signals from blood and tissue is developed and a new imaging method, knowledge-based imaging, is defined. This method utilizes the likelihood ratio function to classify blood and tissue signals. The method separates blood and tissue signals by the difference in movement patterns in addition to the difference in powers. The prior information about the levels of expected system white noise and clutter noise are utilized to enhance the image quality. The implementation of knowledge-based imaging is outlined, and some knowledge-based images with different parameter settings are visually compared with a second-harmonic image, a fundamental image and a bandwidth image. In order to understand the parameter estimation process a computer simulation is introduced to outline the differences between the imaging methods. The apparent error rates are calculated in any reasonable tissue to blood signal ratio, tissue to white noise ratio and clutter to white noise ratio. A discussion of further development of knowledge-based imaging is also described in this paper.
IEEE Winter Workshop on Nonlinear Digital Signal Processing, 1993
This paper explores the application of nonlinear filtering techniques in volume rendering of medi... more This paper explores the application of nonlinear filtering techniques in volume rendering of medical ultrasound data. Volume rendering methods based on an initial probabilistic classification have been used with success on Computed Tomography and Mag- netic Resonance data, but have shown to fail in ultra- sonic studies. Several considerations have to be made in ultrasound imaging, because of a substantial
ABSTRACT In ultrasound Color Doppler imaging, a grayscale B-mode image and a Doppler image repres... more ABSTRACT In ultrasound Color Doppler imaging, a grayscale B-mode image and a Doppler image representing velocities are overlaid to produce a color coded image of e.g. blood flow or myocardial movement. Normally, the B-mode and Doppler images are acquired at the same rate, resulting in trade offs between B-mode image quality and Doppler frame rate. In this work, we present a new scan sequencing technique for Color Doppler imaging, where the B-mode image is acquired at a lower frame rate than the Doppler scan. This is achieved by splitting the B-mode image in subscans which are acquired in between multiple scans of the entire Doppler image. In this way, a full width B-mode image with high spatial resolution is kept while the temporal resolution of the velocity information is increased. In this paper, application of the new technique in Tissue Velocity Imaging (TVI), is discussed, showing the potential for improving lateral beam density or temporal resolution in Color Doppler imaging.
Proceedings., International Conference on Image Processing, 1995
This paper presents an approach to volume rendering based on real-time and interactive data reduc... more This paper presents an approach to volume rendering based on real-time and interactive data reduction prior to volume visualization. The underlying hardware design of a PCI based search engine is introduced including the architecture of a full custom VLSI chip that based on combinations of general range queries performs a real-time classification/opacity assignment of the multi-spectral voxel data. Various image
Computers in Cardiology 1998. Vol. 25 (Cat. No.98CH36292), 1998
This article describes an off-line software for extended analysis of tissue myocardial ultrasound... more This article describes an off-line software for extended analysis of tissue myocardial ultrasound Doppler information acquired at high temporal resolution. The software contains four main modalities for improved objective analysis of myocardial wall motion. (1) The possibility to extract velocity curves from multiple points in any pixel. (2) Color-coded 2-D images from mathematically processed velocity curves. (3) The possibility to analyze directional and velocity changes along any pre-defined line or curve (C-line) and then present these in analogue to the M-Mode (C-Mode). (4) Strain rate imaging (SRI)-by calculating the relative movement inside the tissue as distances between discrete points information about internal velocities i.e. compression or contraction and expansion, can be presented in a color-coded image both in 2D or C-mode
We introduce a method for automatic detection and tracking of the apex and two landmarks defining... more We introduce a method for automatic detection and tracking of the apex and two landmarks defining the atrioventricular plane in apical views of the left ventricle. The method is based on using tissue Doppler to track a set of candidate points in a cardiac cycle. Each candidate point is given a score based on the gray-scale, the velocity, and the
A new estimator, Bandwidth Imaging, related to the bandwidth of the ultrasound Doppler signal is ... more A new estimator, Bandwidth Imaging, related to the bandwidth of the ultrasound Doppler signal is proposed as a classification function of blood and tissue signal in transthoracial echocardiography of the left ventricle. An in vivo experiment is presented, where the apparent error rate of Bandwidth Imaging is compared with the apparent error rate of Second-Harmonic Imaging on 15 healthy men. The apparent error rates are calculated from the 16 myocardial wall segments defined in . A hypothesis test of Bandwidth Imaging having lower apparent error rate than Second-Harmonic Imaging is proved for a p-value of 0.94 in 3 segments in end diastole and in 1 segment in end systole. When data was averaged by a structural element of 5 radial, 3 lateral and 4 temporal samples the numbers of segments increased to 9 in end diastole and to 6 in end systole. This experiment indicates that Bandwidth Imaging can supply additional information for automatic border detection routines on endocardium.
Extraction of the endocardial boundary of the left ventricle is a key challenge in cardiac ultras... more Extraction of the endocardial boundary of the left ventricle is a key challenge in cardiac ultrasound imaging. The cardiac anatomy may be difficult to determine automatically without incorporating knowledge of both wall shape and intensity signature into the detection algorithm. The aim of this study is to establish a framework for knowledge based extraction of the left ventricular endocardial boundary.
In this paper, we present a new method for simple acquisition of dynamic three-dimensional (3-D) ... more In this paper, we present a new method for simple acquisition of dynamic three-dimensional (3-D) ultrasound data. We used a magnetic position sensor device attached to the ultrasound probe for spatial location of the probe, which was slowly tilted in the transthoracic scanning position. The 3-D data were recorded in 10-20 s, and the analysis was performed on an external PC within 2 min after transferring the raw digital ultrasound data directly from the scanner. The spatial and temporal resolutions of the reconstruction were evaluated, and were superior to video-based 3-D systems. Examples of volume reconstructions with better than 7 ms temporal resolution are given. The raw data with Doppler measurements were used to reconstruct both blood and tissue velocity volumes. The velocity estimates were available for optimal visualization and for quantitative analysis. The freehand data reconstruction accuracy was tested by volume estimation of balloon phantoms, giving high correlation with true volumes. Results show in vivo 3-D reconstruction and visualization of mitral and aortic valve morphology and blood flow, and myocardial tissue velocity. We conclude that it was possible to construct multimodality 3-D data in a limited region of the human heart within one respiration cycle, with reconstruction errors smaller than the resolution of the original ultrasound beam, and with a temporal resolution of up to 150 frames per second.
... Email: mari.thune @nr.no. ... L[] = twodimensional array of size N*MP[]l] = twodimensional ar... more ... Email: mari.thune @nr.no. ... L[] = twodimensional array of size N*MP[]l] = twodimensional array of size N*M fOr j= 1.... NL[j][0] = SL[0][j] for k = 1.... ML[t][k] = oo for k = 1..... M forj = N ..... 2 in for i = minLength...., jminLength mO = MAX(m, Lli][kll + SL[i][j] if (too m hypoTestOk ...
Locating content in existing video archives is both a time and bandwidth consuming process since ... more Locating content in existing video archives is both a time and bandwidth consuming process since users might have to download and manually watch large portions of superfluous videos. In this paper, we present two novel prototypes using an Internet based video composition and streaming system with a keyword-based search interface that collects, converts, analyses, indexes, and ranks video content. At user requests, the system can automatically sequence out portions of single videos or aggregate content from multiple videos to produce a single, personalized video stream on-the-fly.
Journal of the American Society of Echocardiography, 2000
The goals of this study were to examine peak systolic strain as an index of regional function in ... more The goals of this study were to examine peak systolic strain as an index of regional function in an animal model of inotropic stress and ischemia, and to compare these results with peak systolic myocardial tissue Doppler velocity (MDV). Background: Myocardial tissue Doppler velocity is an objective measure of regional left ventricular responses to inotropic stimulation and ischemia, but it is affected by tethering from adjacent segments and translational movement. Myocardial Doppler strain (ε, relative change in length) is a more local measure of contractility, which can now be derived noninvasively from MDV. Methods: Eight dogs underwent graded dobutamine infusion followed by coronary occlusion. Epicardial 2-dimensional echocardiography and color MDV of the left ventricle were obtained and digitized from the short-axis view at baseline and with dobutamine doses of 2, 4, and 8 µg/kg per minute. These were repeated 0, 10, 20, 45, and 90 seconds after occlusion of the left anterior descending artery (LAD) (n = 3) or circumflex coronary artery (n = 5). Dobutamine was continued at 8 µg/kg per minute during coronary occlusion. The peak systolic radial MDV (cm/s) and systolic strain (ε s , percent thickening) in the anterior and posterior walls were measured off-line at each stage. Results: Dobutamine caused an increase in MDV (P = .0001) and ε s (P = .09) above baseline values. Coronary occlusion caused a reduction in wall motion; after 45 seconds, all nonperfused segments were hypokinetic. There was a corresponding decrease in MDV and ε s , but this occurred earlier for ε s , and the difference between ischemic and nonischemic segments was greater for ε s than for MDV (P < .03). Nonischemic regions trended to an increase in ε s (compensatory hyperkinesis), whereas MDV trended downward, probably reflecting the global decrease in left ventricular function. Conclusion: Both MDV and ε s increase with dobutamine and decrease during ischemia. ε s appears to respond to local ischemia earlier than MDV, perhaps because it is a more local measure. Thus ε s may prove to be an accurate parameter for the clinical recognition of regional ischemia. (J Am Soc Echocardiogr 2000;13:731-7.)
Journal of the American Society of Echocardiography, 1998
A new color Doppler myocardial imaging (CDMI) system with high spatial and temporal resolution an... more A new color Doppler myocardial imaging (CDMI) system with high spatial and temporal resolution and novel postprocessing modalities has been developed that could allow quantifiable stress echocardiography. The purpose of this study was to determine whether regional myocardial systolic velocities could be accurately and reproducibly measured both at rest and during bicycle ergometry by using CDMI. Thirty normal subjects were examined with CDMI at rest, and peak mean systolic myocardial velocities (MSV) were measured for 34 predetermined left ventricular myocardial segments. Interobserver variability and intraobserver variability were established for all segments. Submaximal bicycle ergometry was performed in 20 normal subjects by using standardized weight-related increases in workload. MSV were measured at each step of exercise for 16 left ventricular stress echo segments. At rest, a base-apex gradient in regional MSV was recorded with highest longitudinal shortening velocities at the base. A similar pattern was noted for circumferential shortening MSV. Measurements were predictable and highly reproducible with low interobserver and intraobserver variability for 26 of 34 segments. Reproducibility was poor for basal anteroseptal segments in all views and mid anterior, anteroseptal, and septal segments in the short-axis views. During exercise, mid and basal segments of all walls showed a significant increase of MSV between each workload step and for apical segments between alternate steps. The resting base-apex velocity gradient observed at rest remained in all walls throughout ergometry. Thus a CDMI system with improved spatial and temporal resolution and postprocessing analysis modalities provided reproducible and accurate quantification of segmental left ventricular circumferential and longitudinal contraction both at rest and during exercise.
Abstmct-In this paper we explore the application of volume rendering in medical ultrasonic imagin... more Abstmct-In this paper we explore the application of volume rendering in medical ultrasonic imaging. Several volume rendering methods have been developed for X-ray Computed Tomography (X-CT), Magnetic Resonance Imaging (MRI) and Positron Emission Tomography (PET). Limited research has been done on applications of volume rendering techniques in medical ultrasound imaging because of a general lack of adequate equipment for 3D acquisitions. Severe noise sources and other limitations in the imaging system make volume rendering of ultrasonic data a challenge compared to rendering of MRI and X-CT data. Rendering algorithms that rely on an initial classification of the data into different tissue categories have been developed for high quality X-CT and MR-data. So far, there is a lack of general and reliable methods for tissue classification in ultrasonic imaging. This paper focuses on volume rendering methods which are not dependent on any classication into different tissue categories. Instead, features are extracted from the original 3D data-set, and projected onto the view plane. We found that some of these methods may give clinically useful information which is very difficult to get from ordinary 2D ultrasonic images, and in some cases renderings with very fine structural details. We have applied the methods to 3D ultrasound images from fetal examinations. The methods are now in use as clinical tools at the National Center of Fetal Medicine in 'kondheim, Norway.
Abstrucf-We consider the problem of partitioning a sequence of n real numbers into p intervals su... more Abstrucf-We consider the problem of partitioning a sequence of n real numbers into p intervals such that the cost of the most expensive interval, measured with a cost functionfis minimized. This problem is of importance for the scheduling of jobs both in parallel and pipelined environments. We develop a straightforward and practical dynamic programming algorithm that solves this problem in time O@(np ) ) , which is an improvement of a factor of log p compared to the previous best algorithm. A number of variants of the problem are also considered.
Tissue velocity information (TVI) is acquired by sampling of tissue Doppler velocity values at di... more Tissue velocity information (TVI) is acquired by sampling of tissue Doppler velocity values at discrete points. The information is stored in an interfoiled format with gray scale imaging during one or several cardiac cycle at a high temporal resolution, &amp;amp;gt; 60 Hz, giving signals that tolerate mathematical processing as derivation, integration and Fourier analysis of velocity profiles without distortions. The software enables the possibility to analyze multiple velocity profiles from any localization within the acquired scanned sector. The myocardial tissue velocity direction and color-coded numerical value can be computed along any chosen curve form (C-line) and be presented as a spatial function of velocities against time (C-mode). The velocity curves can also be presented in several new functional modes as color-coded running cineloops: phase imaging, time delay imaging, amplitude imaging, acceleration imaging, instantaneous phase imaging, wrapped phase imaging. The software also allows color or C-mode presentation of tissue contraction and expansion. This facilitates the differentiation between active and passive myocardial tissue movements, thus improving the ability to differentiate between healthy and diseased myocardial tissue. This article presents several applications of the software in normals and in cardiac patients.
Computer Methods and Programs in Biomedicine, 2008
A new imaging method, Bandwidth Imaging, which is related to the bandwidth of the ultrasound Dopp... more A new imaging method, Bandwidth Imaging, which is related to the bandwidth of the ultrasound Doppler signal is proposed as a classification function for blood and tissue signal in transthoracial echocardiography in the left ventricle. An in vivo experiment is presented, where the apparent error rate of Bandwidth Imaging is compared with the apparent error rate of Second-Harmonic Imaging on 15 healthy men. The apparent error rates are calculated from the 16 myocardial wall segments defined in . A hypothesis test of Bandwidth Imaging having lower apparent error rate than Second-Harmonic Imaging is proved for a p-value of 0.94 in 3 segments in end diastole and in 1 segment in end systole. When data was averaged by a structural element of 5 radial, 3 lateral and 4 temporal samples the numbers of segments increased to 9 in end diastole and to 6 in end systole. This experiment indicates that Bandwidth Imaging can supply additional information for automatic border detection routines on endocardium.
Computer Methods and Programs in Biomedicine, 2009
c o m p u t e r m e t h o d s a n d p r o g r a m s i n b i o m e d i c i n e 9 6 ( 2 0 0 9 ) 12-... more c o m p u t e r m e t h o d s a n d p r o g r a m s i n b i o m e d i c i n e 9 6 ( 2 0 0 9 ) 12-24 Echocardiography Doppler signal Endocardial detection Ejection fraction Likelihood ratio function a b s t r a c t A parametric model for the ultrasound signals from blood and tissue is developed and a new imaging method, knowledge-based imaging, is defined. This method utilizes the likelihood ratio function to classify blood and tissue signals. The method separates blood and tissue signals by the difference in movement patterns in addition to the difference in powers. The prior information about the levels of expected system white noise and clutter noise are utilized to enhance the image quality. The implementation of knowledge-based imaging is outlined, and some knowledge-based images with different parameter settings are visually compared with a second-harmonic image, a fundamental image and a bandwidth image. In order to understand the parameter estimation process a computer simulation is introduced to outline the differences between the imaging methods. The apparent error rates are calculated in any reasonable tissue to blood signal ratio, tissue to white noise ratio and clutter to white noise ratio. A discussion of further development of knowledge-based imaging is also described in this paper.
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Papers by B. Olstad