High Spatial Resolution and Temporally Resolved T2* Mapping of Normal Human Myocardium at 7.0 Tesla: An Ultrahigh Field Magnetic Resonance Feasibility Study

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Abstract

Myocardial tissue characterization using T ₂ ^* relaxation mapping techniques is an emerging application of (pre)clinical cardiovascular magnetic resonance imaging. The increase in microscopic susceptibility at higher magnetic field strengths renders myocardial T ₂ ^* mapping at ultrahigh magnetic fields conceptually appealing. This work demonstrates the feasibility of myocardial T ₂ ^* imaging at 7.0 T and examines the applicability of temporally-resolved and high spatial resolution myocardial T ₂ ^* mapping. In phantom experiments single cardiac phase and dynamic (CINE) gradient echo imaging techniques provided similar T ₂ ^* maps. In vivo studies showed that the peak-to-peak B ₀ difference following volume selective shimming was reduced to approximately 80 Hz for the four chamber view and mid-ventricular short axis view of the heart and to 65 Hz for the left ventricle. No severe susceptibility artifacts were detected in the septum and in the lateral wall for T ₂ ^* weighting ranging from TE = 2.04 ms to TE = 10.2 ms. For TE >7 ms, a susceptibility weighting induced signal void was observed within the anterior and inferior myocardial segments. The longest T ₂ ^* values were found for anterior (T ₂ ^* = 14.0 ms), anteroseptal (T ₂ ^* = 17.2 ms) and inferoseptal (T ₂ ^* = 16.5 ms) myocardial segments. Shorter T ₂ ^* values were observed for inferior (T ₂ ^* = 10.6 ms) and inferolateral (T ₂ ^* = 11.4 ms) segments. A significant difference (p = 0.002) in T ₂ ^* values was observed between end-diastole and end-systole with T ₂ ^* changes of up to approximately 27% over the cardiac cycle which were pronounced in the septum. To conclude, these results underscore the challenges of myocardial T ₂ ^* mapping at 7.0 T but demonstrate that these issues can be offset by using tailored shimming techniques and dedicated acquisition schemes.

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Most cited references 37

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Wietske van der Zwaag, Susan Francis, Kay E. Head … (2009)

Blood oxygenation level dependent (BOLD) signal changes occurring during execution of a simple motor task were measured at field strengths of 1.5, 3 and 7 T using multi-slice, single-shot, gradient echo EPI at a resolution of 1x1x3 mm(3), to quantify the benefits offered by ultra-high magnetic field for functional MRI. Using four different echo times at each field strength allowed quantification of the relaxation rate, R(2)* and the change in relaxation rate on activation, DeltaR(2)*. This work adds to previous studies of the field strength dependence of BOLD signal characteristics, through its: (i) focus on motor rather than visual cortex; (ii) use of single-shot, multi-slice, gradient echo EPI for data acquisition; (iii) co-registration of images acquired at different field strengths to allow assessment of the BOLD signal changes in the same region at each field strength. DeltaR(2)* was found to increase linearly with field strength (0.51+/-0.06 s(-1) at 1.5 T; 0.98+/-0.08 s(-1) at 3 T; 2.55+/-0.22 s(-1) at 7 T), while the ratio of DeltaR(2)*/R(2), which dictates the accessible BOLD contrast was also found to increase (0.042+/-0.002 at 1.5 T; 0.054+/-0.002 at 3 T; 0.084+/-0.003 at 7 T). The number of pixels classified as active, the t-value calculated over a common region of interest and the percentage signal change in the same region were all found to peak at TE approximately T(2)* and increase significantly with field strength. An earlier onset of the haemodynamic response at higher field provides some evidence for a reduced venous contribution to the BOLD signal at 7 T.

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Reproducible and accurate myocardial T2* measurements are required for the quantification of iron in heart tissue in transfused thalassemia. The aim of this study was to determine the best method to measure the myocardial T2* from multi-gradient-echo data acquired both with and without black-blood preparation. Sixteen thalassemia patients from six centers were scanned twice locally, within 1 week, using an optimized bright-blood T2* sequence and then subsequently scanned at the standardization center in London within 4 weeks, using a T2* sequence both with and without black-blood preparation. Different curve-fitting models (monoexponential, truncation, and offset) were applied to the data and the results were compared by means of reproducibility. T2* measurements obtained using the bright- and black-blood techniques. The black-blood data were well fitted by the monoexponential model, which suggests that a more accurate measure of T2* can be obtained by removing the main source of errors in the bright-blood data. For bright-blood data, the offset model appeared to underestimate T2* values substantially and was less reproducible. The truncation model gave rise to more reproducible T2* measurements, which were also closer to the values obtained from the black-blood data.

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Author and article information

Contributors

Wolfgang Rudolf Bauer: Role: Editor

Journal

Journal ID (nlm-ta): PLoS One

Journal ID (iso-abbrev): PLoS ONE

Journal ID (publisher-id): plos

Journal ID (pmc): plosone

Title: PLoS ONE

Publisher: Public Library of Science (San Francisco, USA )

ISSN (Electronic): 1932-6203

Publication date Collection: 2012

Publication date (Electronic): 14 December 2012

Volume: 7

Issue: 12

Electronic Location Identifier: e52324

Affiliations

[1 ]Berlin Ultrahigh Field Facility (B.U.F.F.), Max Delbrueck Center for Molecular Medicine, Berlin, Germany

[2 ]Experimental and Clinical Research Center, a Joint Cooperation between the Charité Medical Faculty and the Max Delbrueck Center for Molecular Medicine, Campus Berlin Buch, Berlin, Germany

[3 ]Department of Cardiology and Nephrology, HELIOS Klinikum Berlin Buch, Berlin, Germany

University Hospital of Würzburg, Germany

Author notes

* E-mail: Thoralf.Niendorf@ 123456mdc-berlin.de

Competing Interests: TN is founder of MRI.Tools GmbH. This does not alter the authors' adherence to all the PLOS ONE policies on sharing data and materials. The authors would also like to point out that there are no patents, products in development or marketed products to declare.

Conceived and designed the experiments: FH CT JSM TN. Performed the experiments: FH CT TN. Analyzed the data: FH JSM. Contributed reagents/materials/analysis tools: FH SW. Wrote the paper: FH CT SW JSM TN.

Article

Publisher ID: PONE-D-12-22596

DOI: 10.1371/journal.pone.0052324

PMC ID: 3522647

PubMed ID: 23251708

SO-VID: 24e1bac3-7d72-41f5-9bd5-f41bea199106

License:

This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

History

Date received : 23 July 2012

Date accepted : 16 November 2012

Page count

Pages: 14

Funding

This study was founded through institutional funding provided by the Max Delbrück Centrum for Molecular Medicine. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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