Abstract
The presence of deoxygenated hemoglobin (Hb) results in a drop in T2 and T2* in magnetic resonance imaging (MRI), known as the blood oxygenation level-dependent (BOLD-)effect. The purpose of this study was to investigate if deoxygenated myoglobin (Mb) exerts a BOLD-like effect. Equine Met-Mb powder was dissolved and converted to oxygenated Mb. T1, T2, T2*-maps and BOLD-bSSFP images at 3Tesla were used to scan 22 Mb samples and 12 Hb samples at room air, deoxygenation, reoxygenation and after chemical reduction. In Mb, T2 and T2* mapping showed a significant decrease after deoxygenation (− 25% and − 12%, p < 0.01), increase after subsequent reoxygenation (+ 17% and 0% vs. room air, p < 0.01), and finally a decrease in T2 after chemical reduction (− 28%, p < 0.01). An opposite trend was observed with T1 for each stage, while chemical reduction reduced BOLD-bSSFP signal (− 3%, p < 0.01). Similar deflections were seen at oxygenation changes in Hb. The T1 changes suggests that the oxygen content has been changed in the specimen. The shortening of transverse relaxation times in T2 and T2*-mapping after deoxygenation in Mb specimens are highly indicative of a BOLD-like effect.
Highlights
Ogawa et al first described the utility of sequences exploiting the blood oxygen level-dependent (BOLD) effect in brain magnetic resonance imaging (MRI) scans for functional imaging[1]
At 0.4% oxygen concentration the characteristic double-peak spectrum of MbO2 has vanished, and only the single peak spectrum remains, which is characteristic for deoxygenated Mb (dMb), demonstrating that no M bO2 remained in these specimens
blood oxygenation level-dependent (BOLD-)MRI and Mb-magnetic resonance spectroscopy (Mb-Magnetic Resonance Spectroscopy (MRS)) studies have been performed in humans, interrogating the skeletal muscle[13,17,18,19]
Summary
Ogawa et al first described the utility of sequences exploiting the blood oxygen level-dependent (BOLD) effect in brain magnetic resonance imaging (MRI) scans for functional imaging[1]. The presence of the paramagnetic dHb results in microscopic magnetic field inhomogeneities, which alters the bulk susceptibility of the solvent medium. This will lead to a decrease in T2 and T2* relaxation times or a reduction in signal intensity (SI) in sequences sensitive to this BOLD effect. In cases of vascular dysfunction, if an increase in workload and oxygen consumption cannot be matched by an increased blood supply, local deoxygenation occurs reducing BOLD based SI. This study aimed to assess if Mb has a BOLD-effect that can be detected by clinical cardiovascular magnetic resonance parametric mapping sequences
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