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      Quantification of global myocardial oxygenation in humans: initial experience

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          Abstract

          Purpose

          To assess the feasibility of our newly developed cardiovascular magnetic resonance (CMR) methods to quantify global and/or regional myocardial oxygen consumption rate (MVO2) at rest and during pharmacologically-induced vasodilation in normal volunteers.

          Methods

          A breath-hold T2 quantification method is developed to calculate oxygen extraction fraction (OEF) and MVO2 rate at rest and/or during hyperemia, using a two-compartment model. A previously reported T2 quantification method using turbo-spin-echo sequence was also applied for comparison. CMR scans were performed in 6 normal volunteers. Each imaging session consisted of imaging at rest and during adenosine-induced vasodilation. The new T2 quantification method was applied to calculate T2 in the coronary sinus (CS), as well as in myocardial tissue. Resting CS OEF, representing resting global myocardial OEF, and myocardial OEF during adenosine vasodilation were then calculated by the model. Myocardial blood flow (MBF) was also obtained to calculate MVO2, by using a first-pass perfusion imaging approach.

          Results

          The T2 quantification method yielded a hyperemic OEF of 0.37 ± 0.05 and a hyperemic MVO2 of 9.2 ± 2.4 μmol/g/min. The corresponding resting values were 0.73 ± 0.05 and 5.2 ± 1.7 μmol/g/min respectively, which agreed well with published literature values. The MVO2 rose proportionally with rate-pressure product from the rest condition. The T2 sensitivity is approximately 95% higher with the new T2 method than turbo-spin-echo method.

          Conclusion

          The CMR oxygenation method demonstrates the potential for non-invasive estimation of myocardial oxygenation, and should be explored in patients with altered myocardial oxygenation.

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          Most cited references 25

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          Coronary Angiography with Magnetization-PreparedT2 Contrast

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            Quantitative assessment of blood flow, blood volume and blood oxygenation effects in functional magnetic resonance imaging.

            The ability to measure the effects of local alterations in blood flow, blood volume and oxygenation by nuclear magnetic resonance has stimulated a surge of activity in functional MRI of many organs, particularly in its application to cognitive neuroscience. However, the exact description of these effects in terms of the interrelations between the MRI signal changes and the basic physiological parameters has remained an elusive goal. We here present this fundamental theory for spin-echo signal changes in perfused tissue and validate it in vivo in the cat brain by using the physiological alteration of hypoxic hypoxia. These experiments show that high-resolution absolute blood volume images can be obtained by using hemoglobin as a natural intravascular contrast agent. The theory also correctly predicts the magnitude of spin-echo MRI signal intensity changes on brain activation and thereby provides a sound physiological basis for these types of studies.
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              Intravascular susceptibility contrast mechanisms in tissues.

              The factors affecting the rate of loss of transverse magnetization in gradient echo and spin-echo pulse sequences have been quantified using computer modeling for media containing arrays of susceptibility variations. The results are particularly relevant for describing the signal losses that occur in tissues containing capillaries of altered intrinsic susceptibility from the administration of exogenous contrast agents or arising from changes in blood oxygenation. The precise magnitudes and relationship of gradient echo and spin-echo decay rates depend on geometrical factors such as the sizes and spacings of the inhomogeneities, the rate of water diffusion, field strength, and echo times. The conventional separation of contributions to transverse decay rates arising from so-called static field effects and diffusion is shown to be inappropriate for many situations of practical interest because diffusion introduces a motional averaging of the static field even in gradient echo sequences. The result of diffusion in some regimes is to reduce the decay rate from field inhomogeneities in gradient echo sequences, so that T2* is longer in media such as tissue where water diffuses reasonably rapidly, than would be the case for stationary nuclei. The effects of different types of contrast agent and the implications for functional imaging based on the effects of deoxyhemoglobin in brain tissue are considered.
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                Author and article information

                Affiliations
                [1]Mallinckrodt Institute of Radiology, Washington University School of Medicine, 510 S. Kingshighway Blvd, St. Louis, MO 63110, USA
                Contributors
                Journal
                J Cardiovasc Magn Reson
                Journal of Cardiovascular Magnetic Resonance
                BioMed Central
                1097-6647
                1532-429X
                2010
                2 June 2010
                : 12
                : 1
                : 34
                2890683
                1532-429X-12-34
                20525217
                10.1186/1532-429X-12-34
                Copyright ©2010 McCommis et al; licensee BioMed Central Ltd.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                Categories
                Technical notes

                Cardiovascular Medicine

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