The Experts below are selected from a list of 87498 Experts worldwide ranked by ideXlab platform

N Wilke - One of the best experts on this subject based on the ideXlab platform.

  • contrast enhanced first pass myocardial perfusion imaging correlation between myocardial blood flow in dogs at rest and during hyperemia
    1993
    Co-Authors: N Wilke, C Simm, Jianyi Zhang, Jutta M Ellermann, X Ya, Hellmut Merkle, G Path
    Abstract:

    The sensitivity of contrast-enhanced MR first pass perfusion imaging in detection and quantification of hypoperfused myocardium was evaluated using an instrumented, closed-chest dog model where graded regional hypoperfusion was induced by applying predetermined levels of stenosis to the left anterior descending artery (LAD). All measurements were performed at rest and under stress induced by dipyridamole (DIP). Myocardial perfusion was assessed both with MR and radiolabeled microspheres injected immediately before the administration of the MR contrast agent. Ultrafast MR imaging was performed using a Turbo FLASH sequence with a 180° inversion prepulse. A Gd-DTPA bolus was injected into the left atrium and T1-weighted images were acquired with every heart beat. Signal intensity measured from the images in regions of the LAD and left circumflex (LCx) perfusion beds was plotted against time to Generate Signal intensity versus time curves (SI time curve). Various flow indices were derived according to the indicator dilution theory, and compared with and without volume correction due to vasodilation to the myocardial blood flow (MBF) calculated from radiolabeled microspheres. Correlation of the MR and MBF data demonstrated that different transmural and regional myocardial perfusion levels can be easily visualized in the perfusion images and accurately monitored by the SI time curves. Detection of the impairment of myocardial perfusion improved significantly after administration of DIP. The inverse mean transit time calculated from the SI time curve was found to yield a linear correlation to absolute MBF derived from the microsphere data. These results suggest that with intracardiac injections of exogenous contrast agent, myocardial perfusion can be assessed parametrically with first pass contrast enhanced ultrafast MRI.

  • contrast enhanced first pass myocardial perfusion imaging correlation between myocardial blood flow in dogs at rest and during hyperemia
    1993
    Co-Authors: N Wilke, C Simm, Jianyi Zhang, Jutta M Ellermann, Hellmut Merkle, G Path, H Ludemann
    Abstract:

    The sensitivity of contrast-enhanced MR first pass perfusion imaging in detection and quantification of hypoperfused myocardium was evaluated using an instrumented, closed-chest dog model where graded regional hypoperfusion was induced by applying predetermined levels of stenosis to the left anterior descending artery (LAD). All measurements were performed at rest and under stress induced by dipyridamole (DIP). Myocardial perfusion was assessed both with MR and radiolabeled microspheres injected immediately before the administration of the MR contrast agent. Ultrafast MR imaging was performed using a Turbo FLASH sequence with a 180 degrees inversion prepulse. A Gd-DTPA bolus was injected into the left atrium and T1-weighted images were acquired with every heart beat. Signal intensity measured from the images in regions of the LAD and left circumflex (LCx) perfusion beds was plotted against time to Generate Signal intensity versus time curves (SI time curve). Various flow indices were derived according to the indicator dilution theory, and compared with and without volume correction due to vasodilation to the myocardial blood flow (MBF) calculated from radiolabeled microspheres. Correlation of the MR and MBF data demonstrated that different transmural and regional myocardial perfusion levels can be easily visualized in the perfusion images and accurately monitored by the SI time curves. Detection of the impairment of myocardial perfusion improved significantly after administration of DIP. The inverse mean transit time calculated from the SI time curve was found to yield a linear correlation to absolute MBF derived from the microsphere data. These results suggest that with intracardiac injections of exogenous contrast agent, myocardial perfusion can be assessed parametrically with first pass contrast enhanced ultrafast MRI.

C Simm - One of the best experts on this subject based on the ideXlab platform.

  • contrast enhanced first pass myocardial perfusion imaging correlation between myocardial blood flow in dogs at rest and during hyperemia
    1993
    Co-Authors: N Wilke, C Simm, Jianyi Zhang, Jutta M Ellermann, X Ya, Hellmut Merkle, G Path
    Abstract:

    The sensitivity of contrast-enhanced MR first pass perfusion imaging in detection and quantification of hypoperfused myocardium was evaluated using an instrumented, closed-chest dog model where graded regional hypoperfusion was induced by applying predetermined levels of stenosis to the left anterior descending artery (LAD). All measurements were performed at rest and under stress induced by dipyridamole (DIP). Myocardial perfusion was assessed both with MR and radiolabeled microspheres injected immediately before the administration of the MR contrast agent. Ultrafast MR imaging was performed using a Turbo FLASH sequence with a 180° inversion prepulse. A Gd-DTPA bolus was injected into the left atrium and T1-weighted images were acquired with every heart beat. Signal intensity measured from the images in regions of the LAD and left circumflex (LCx) perfusion beds was plotted against time to Generate Signal intensity versus time curves (SI time curve). Various flow indices were derived according to the indicator dilution theory, and compared with and without volume correction due to vasodilation to the myocardial blood flow (MBF) calculated from radiolabeled microspheres. Correlation of the MR and MBF data demonstrated that different transmural and regional myocardial perfusion levels can be easily visualized in the perfusion images and accurately monitored by the SI time curves. Detection of the impairment of myocardial perfusion improved significantly after administration of DIP. The inverse mean transit time calculated from the SI time curve was found to yield a linear correlation to absolute MBF derived from the microsphere data. These results suggest that with intracardiac injections of exogenous contrast agent, myocardial perfusion can be assessed parametrically with first pass contrast enhanced ultrafast MRI.

  • contrast enhanced first pass myocardial perfusion imaging correlation between myocardial blood flow in dogs at rest and during hyperemia
    1993
    Co-Authors: N Wilke, C Simm, Jianyi Zhang, Jutta M Ellermann, Hellmut Merkle, G Path, H Ludemann
    Abstract:

    The sensitivity of contrast-enhanced MR first pass perfusion imaging in detection and quantification of hypoperfused myocardium was evaluated using an instrumented, closed-chest dog model where graded regional hypoperfusion was induced by applying predetermined levels of stenosis to the left anterior descending artery (LAD). All measurements were performed at rest and under stress induced by dipyridamole (DIP). Myocardial perfusion was assessed both with MR and radiolabeled microspheres injected immediately before the administration of the MR contrast agent. Ultrafast MR imaging was performed using a Turbo FLASH sequence with a 180 degrees inversion prepulse. A Gd-DTPA bolus was injected into the left atrium and T1-weighted images were acquired with every heart beat. Signal intensity measured from the images in regions of the LAD and left circumflex (LCx) perfusion beds was plotted against time to Generate Signal intensity versus time curves (SI time curve). Various flow indices were derived according to the indicator dilution theory, and compared with and without volume correction due to vasodilation to the myocardial blood flow (MBF) calculated from radiolabeled microspheres. Correlation of the MR and MBF data demonstrated that different transmural and regional myocardial perfusion levels can be easily visualized in the perfusion images and accurately monitored by the SI time curves. Detection of the impairment of myocardial perfusion improved significantly after administration of DIP. The inverse mean transit time calculated from the SI time curve was found to yield a linear correlation to absolute MBF derived from the microsphere data. These results suggest that with intracardiac injections of exogenous contrast agent, myocardial perfusion can be assessed parametrically with first pass contrast enhanced ultrafast MRI.

Kjersti Engan - One of the best experts on this subject based on the ideXlab platform.

  • Optimized Signal expansions for sparse representation
    2001
    Co-Authors: S.o. Aase, John Hakon Husoy, J.h.h.k. Skretting, Kjersti Engan
    Abstract:

    Traditional Signal decompositions such as transforms, filterbanks, and wavelets Generate Signal expansions using the analysis-synthesis setting: the expansion coefficients are found by taking the inner product of the Signal with the corresponding analysis vector. In this paper, we try to free ourselves from the analysis-synthesis paradigm by concentrating on the synthesis or reconstruction part of the Signal expansion. Ignoring the analysis issue completely, we construct sets of synthesis vectors, which are denoted waveform dictionaries, for efficient Signal representation. Within this framework, we present an algorithm for designing waveform dictionaries that allow sparse representations: the objective is to approximate a training Signal using a small number of dictionary vectors. Our algorithm optimizes the dictionary vectors with respect to the average nonlinear approximation error, i.e., the error resulting when keeping a fixed number n of expansion coefficients but not necessarily the first n coefficients. Using Signals from a Gaussian, autoregressive process with correlation factor 0.95, it is demonstrated that for established Signal expansions like the Karhunen-Loeve transform, the lapped orthogonal transform, and the biorthogonal 7/9 wavelet, it is possible to improve the approximation capabilities by up to 30% by fine tuning of the expansion vectors.

  • design of Signal expansions for sparse representation
    2000
    Co-Authors: S.o. Aase, John Hakon Husoy, Karl Skretting, Kjersti Engan
    Abstract:

    Traditional Signal decompositions Generate Signal expansions using the analysis-synthesis setting: the expansion coefficients are found by taking the inner product of the Signal with the corresponding analysis vector. In this paper we try to free ourselves from the analysis-synthesis paradigm by concentrating on the synthesis or reconstruction part of the Signal expansion. Ignoring the analysis issue completely, we construct sets of synthesis vectors, denoted waveform dictionaries, for sparse Signal representation. The objective is to approximate a training Signal using a small number of dictionary vectors. Our algorithm optimize the dictionary vectors with respect to the average non-linear approximation error. Using Signals from a Gaussian, autoregressive process with correlation factor 0.95, it is demonstrated that for established Signal expansions like the Karhunen-Loeve transform, the lapped orthogonal transform, and the biorthogonal 7/9 wavelet, it is possible to improve the approximation capabilities by up to 30% by optimizing the expansion vectors.

G Path - One of the best experts on this subject based on the ideXlab platform.

  • contrast enhanced first pass myocardial perfusion imaging correlation between myocardial blood flow in dogs at rest and during hyperemia
    1993
    Co-Authors: N Wilke, C Simm, Jianyi Zhang, Jutta M Ellermann, X Ya, Hellmut Merkle, G Path
    Abstract:

    The sensitivity of contrast-enhanced MR first pass perfusion imaging in detection and quantification of hypoperfused myocardium was evaluated using an instrumented, closed-chest dog model where graded regional hypoperfusion was induced by applying predetermined levels of stenosis to the left anterior descending artery (LAD). All measurements were performed at rest and under stress induced by dipyridamole (DIP). Myocardial perfusion was assessed both with MR and radiolabeled microspheres injected immediately before the administration of the MR contrast agent. Ultrafast MR imaging was performed using a Turbo FLASH sequence with a 180° inversion prepulse. A Gd-DTPA bolus was injected into the left atrium and T1-weighted images were acquired with every heart beat. Signal intensity measured from the images in regions of the LAD and left circumflex (LCx) perfusion beds was plotted against time to Generate Signal intensity versus time curves (SI time curve). Various flow indices were derived according to the indicator dilution theory, and compared with and without volume correction due to vasodilation to the myocardial blood flow (MBF) calculated from radiolabeled microspheres. Correlation of the MR and MBF data demonstrated that different transmural and regional myocardial perfusion levels can be easily visualized in the perfusion images and accurately monitored by the SI time curves. Detection of the impairment of myocardial perfusion improved significantly after administration of DIP. The inverse mean transit time calculated from the SI time curve was found to yield a linear correlation to absolute MBF derived from the microsphere data. These results suggest that with intracardiac injections of exogenous contrast agent, myocardial perfusion can be assessed parametrically with first pass contrast enhanced ultrafast MRI.

  • contrast enhanced first pass myocardial perfusion imaging correlation between myocardial blood flow in dogs at rest and during hyperemia
    1993
    Co-Authors: N Wilke, C Simm, Jianyi Zhang, Jutta M Ellermann, Hellmut Merkle, G Path, H Ludemann
    Abstract:

    The sensitivity of contrast-enhanced MR first pass perfusion imaging in detection and quantification of hypoperfused myocardium was evaluated using an instrumented, closed-chest dog model where graded regional hypoperfusion was induced by applying predetermined levels of stenosis to the left anterior descending artery (LAD). All measurements were performed at rest and under stress induced by dipyridamole (DIP). Myocardial perfusion was assessed both with MR and radiolabeled microspheres injected immediately before the administration of the MR contrast agent. Ultrafast MR imaging was performed using a Turbo FLASH sequence with a 180 degrees inversion prepulse. A Gd-DTPA bolus was injected into the left atrium and T1-weighted images were acquired with every heart beat. Signal intensity measured from the images in regions of the LAD and left circumflex (LCx) perfusion beds was plotted against time to Generate Signal intensity versus time curves (SI time curve). Various flow indices were derived according to the indicator dilution theory, and compared with and without volume correction due to vasodilation to the myocardial blood flow (MBF) calculated from radiolabeled microspheres. Correlation of the MR and MBF data demonstrated that different transmural and regional myocardial perfusion levels can be easily visualized in the perfusion images and accurately monitored by the SI time curves. Detection of the impairment of myocardial perfusion improved significantly after administration of DIP. The inverse mean transit time calculated from the SI time curve was found to yield a linear correlation to absolute MBF derived from the microsphere data. These results suggest that with intracardiac injections of exogenous contrast agent, myocardial perfusion can be assessed parametrically with first pass contrast enhanced ultrafast MRI.

S.o. Aase - One of the best experts on this subject based on the ideXlab platform.

  • Optimized Signal expansions for sparse representation
    2001
    Co-Authors: S.o. Aase, John Hakon Husoy, J.h.h.k. Skretting, Kjersti Engan
    Abstract:

    Traditional Signal decompositions such as transforms, filterbanks, and wavelets Generate Signal expansions using the analysis-synthesis setting: the expansion coefficients are found by taking the inner product of the Signal with the corresponding analysis vector. In this paper, we try to free ourselves from the analysis-synthesis paradigm by concentrating on the synthesis or reconstruction part of the Signal expansion. Ignoring the analysis issue completely, we construct sets of synthesis vectors, which are denoted waveform dictionaries, for efficient Signal representation. Within this framework, we present an algorithm for designing waveform dictionaries that allow sparse representations: the objective is to approximate a training Signal using a small number of dictionary vectors. Our algorithm optimizes the dictionary vectors with respect to the average nonlinear approximation error, i.e., the error resulting when keeping a fixed number n of expansion coefficients but not necessarily the first n coefficients. Using Signals from a Gaussian, autoregressive process with correlation factor 0.95, it is demonstrated that for established Signal expansions like the Karhunen-Loeve transform, the lapped orthogonal transform, and the biorthogonal 7/9 wavelet, it is possible to improve the approximation capabilities by up to 30% by fine tuning of the expansion vectors.

  • design of Signal expansions for sparse representation
    2000
    Co-Authors: S.o. Aase, John Hakon Husoy, Karl Skretting, Kjersti Engan
    Abstract:

    Traditional Signal decompositions Generate Signal expansions using the analysis-synthesis setting: the expansion coefficients are found by taking the inner product of the Signal with the corresponding analysis vector. In this paper we try to free ourselves from the analysis-synthesis paradigm by concentrating on the synthesis or reconstruction part of the Signal expansion. Ignoring the analysis issue completely, we construct sets of synthesis vectors, denoted waveform dictionaries, for sparse Signal representation. The objective is to approximate a training Signal using a small number of dictionary vectors. Our algorithm optimize the dictionary vectors with respect to the average non-linear approximation error. Using Signals from a Gaussian, autoregressive process with correlation factor 0.95, it is demonstrated that for established Signal expansions like the Karhunen-Loeve transform, the lapped orthogonal transform, and the biorthogonal 7/9 wavelet, it is possible to improve the approximation capabilities by up to 30% by optimizing the expansion vectors.