Assessment of regional myocardial oxygenation changes in the presence of coronary artery stenosis with balanced SSFP imaging at 3.0 T: Theory and experimental evaluation in canines

Department of Radiology, Northwestern University, Chicago, Illinois 60611, USA.
Journal of Magnetic Resonance Imaging (Impact Factor: 3.21). 05/2008; 27(5):1037-45. DOI: 10.1002/jmri.21345
Source: PubMed


To examine the dependence of steady-state free-precession (SSFP) -based myocardial blood-oxygen-level-dependent (BOLD) contrast on field strength using theoretical and experimental models.
Numerical simulations using a two-pool exchange model and a surgically prepared dog model were used to assess the SSFP-based myocardial BOLD signal changes at 1.5T and 3.0T. Experimental studies were performed in eight canines with pharmacological vasodilation under various levels of left circumflex coronary artery stenosis. Experimentally obtained BOLD signal changes were correlated against microsphere-based true flow changes.
Theoretical results showed that, at 3.0T, relative to 1.5T, a threefold increase in oxygen sensitivity can be expected. Experimental studies in canines showed near similar results-a 2.5 +/- 0.2-fold increase in BOLD sensitivity at 3.0T relative to 1.5T (P < 0.05). Based on the scatter gram of BOLD data and microsphere data, it was found that the minimum regional flow difference that can be detected with SSFP-based myocardial BOLD imaging at 1.5T and 3.0T were 2.9 and 1.6, respectively (P < 0.05).
This study demonstrated that SSFP-based myocardial BOLD sensitivity is substantially greater at 3.0T compared with 1.5T. The findings here suggest that SSFP-based myocardial BOLD imaging at 3.0T may have the necessary sensitivity to detect the clinically required minimum flow difference of 2.0.

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Available from: Debiao Li, Sep 22, 2014
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    • "Higher field strengths thus improve the sensitivity of MR to the BOLD effect. Data by Dharmakumar et al. indicate that the sensitivity to detect changes in myocardial oxygenation may increase by a factor of about 2.5 when moving from 1.5T to 3T [8]. "
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    ABSTRACT: Oxygenation-sensitive cardiovascular magnetic resonance (CMR) is a non-contrast technique that allows the non-invasive assessment of myocardial oxygenation. It capitalizes on the fact that deoxygenated hemoglobin in blood can act as an intrinsic contrast agent, changing proton signals in a fashion that can be imaged to reflect the level of blood oxygenation. Increases in O2 saturation increase the BOLD imaging signal (T2 or T2*), whereas decreases diminish it. This review presents the basic concepts and limitations of the BOLD technique, and summarizes the preclinical and clinical studies in the assessment of myocardial oxygenation with a focus on recent advances. Finally, it provides future directions and a brief look at emerging techniques of this evolving CMR field.
    Full-text · Article · May 2013 · Journal of Cardiovascular Magnetic Resonance
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    • "The ability to probe for changes in tissue oxygenation using T2* sensitized imaging/mapping offers the potential to address some of the spatial and temporal resolution constraints of conventional first pass perfusion imaging and holds the promise to obviate the need for exogenous contrast agents. Since microscopic susceptibility increases with field strength, thus making the BOLD effect due to (patho)physiology of interest more pronounced, T2* mapping at 7.0 T might be beneficial to address some of the BOLD sensitivity constraints reported for the assessment of regional myocardial oxygenation changes in the presence of coronary artery stenosis [60] or for the characterization of vasodilator-induced changes of myocardial oxygenation at 1.5 T and at 3.0 T [17]. "
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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.
    Full-text · Article · Dec 2012 · PLoS ONE
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    • "BOLD fMRI has been previously applied to measure local blood oxygenation to evaluate cerebral blood flow as well as skeletal muscle and myocardial perfusion [15]. In patients with peripheral artery occlusive disease, BOLD imaging can characterize post-ischemic hyperemia [16] and the effects of percutaneous transarterial angioplasty [17]. "
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    ABSTRACT: Nuclear magnetic resonance (NMR) imaging and spectroscopy have been applied to assess skeletal muscle oxidative metabolism. Therefore, in-vivo NMR may enable the characterization of ischemia-reperfusion injury. The goal of this study was to evaluate whether NMR could detect the effects of ischemic preconditioning (IPC) in healthy subjects. Twenty-three participants were included in two randomized crossover protocols in which the effects of IPC were measured by NMR and muscle force assessments. Leg ischemia was administered for 20 minutes with or without a subsequent impaired reperfusion for 5 minutes (stenosis model). IPC was administered 4 or 48 hours prior to ischemia. Changes in 31phosphate NMR spectroscopy and blood oxygen level-dependent (BOLD) signals were recorded. 3-Tesla NMR data were compared to those obtained for isometric muscular strength. The phosphocreatine (PCr) signal decreased robustly during ischemia and recovered rapidly during reperfusion. In contrast to PCr, the recovery of muscular strength was slow. During post-ischemic stenosis, PCr increased only slightly. The BOLD signal intensity decreased during ischemia, ischemic exercise and post-ischemic stenosis but increased during hyperemic reperfusion. IPC 4 hours prior to ischemia significantly increased the maximal PCr reperfusion signal and mitigated the peak BOLD signal during reperfusion. Ischemic preconditioning positively influenced muscle metabolism during reperfusion; this resulted in an increase in PCr production and higher oxygen consumption, thereby mitigating the peak BOLD signal. In addition, an impairment of energy replenishment during the low-flow reperfusion was detected in this model. Thus, functional NMR is capable of characterizing changes in reperfusion and in therapeutic interventions in vivo. NCT00883467.
    Full-text · Article · Jun 2011 · Journal of Cardiovascular Magnetic Resonance
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