Detecting microcirculatory changes in blood oxygen state with steady‐state free precession imaging

Dharmakumar, Rohan; Qi, Xiuling; Hong, Juimiin; Wright, Graham A.

doi:10.1002/mrm.20911

Cited by 36 publications

(47 citation statements)

References 21 publications

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“…The fact that BOLD CMR shows a linear correlation to coronary sinus oxygen saturation is in agreement with the expected proportionality between the BOLD effect and the absolute tissue content of deoxygenated hemoglobin[13,19,20]. Importantly, a previous theoretical study by Dharmakumar et al demonstrated that the BOLD signal is blood volume-independent[21]. …”

Section: Discussionsupporting

confidence: 80%

Oxygenation-sensitive CMR for assessing vasodilator-induced changes of myocardial oxygenation

Vöhringer

Flewitt

Green

et al. 2010

Journal of Cardiovascular Magnetic Resonance

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BackgroundAs myocardial oxygenation may serve as a marker for ischemia and microvascular dysfunction, it could be clinically useful to have a non-invasive measure of changes in myocardial oxygenation. However, the impact of induced blood flow changes on oxygenation is not well understood. We used oxygenation-sensitive CMR to assess the relations between myocardial oxygenation and coronary sinus blood oxygen saturation (SvO2) and coronary blood flow in a dog model in which hyperemia was induced by intracoronary administration of vasodilators.ResultsDuring administration of acetylcholine and adenosine, CMR signal intensity correlated linearly with simultaneously measured SvO2 (r2 = 0.74, P < 0.001). Both SvO2 and CMR signal intensity were exponentially related to coronary blood flow, with SvO2 approaching 87%.ConclusionsMyocardial oxygenation as assessed with oxygenation-sensitive CMR imaging is linearly related to SvO2 and is exponentially related to vasodilator-induced increases of blood flow. Oxygenation-sensitive CMR may be useful to assess ischemia and microvascular function in patients. Its clinical utility should be evaluated.

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Section: Discussionsupporting

confidence: 80%

Oxygenation-sensitive CMR for assessing vasodilator-induced changes of myocardial oxygenation

Vöhringer

Flewitt

Green

et al. 2010

Journal of Cardiovascular Magnetic Resonance

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“…Blood gases were adjusted to a target paO 2 of 100 mmHg and a paCO 2 of 40 mmHg. Then, BOLD-sensitive steady-state-free-precession (SSFP) cine images were acquired in mid left-ventricular short axis views (slice thickness 10 mm, TE 2.78 ms, TR 5.56 ms, flip angle 90°, FOV 280×157.5, matrix 128×72) [9], [10]. Each cine was composed of 20 phases covering the entire cardiac cycle, obtained by retrospective ECG gating.…”

Section: Methodsmentioning

confidence: 99%

Impact of Intermittent Apnea on Myocardial Tissue Oxygenation—A Study Using Oxygenation-Sensitive Cardiovascular Magnetic Resonance

et al. 2013

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BackgroundCarbon dioxide (CO2) is a recognized vasodilator of myocardial blood vessels that leads to changes in myocardial oxygenation through the recruitment of the coronary flow reserve. Yet, it is unknown whether changes of carbon dioxide induced by breathing maneuvers can be used to modify coronary blood flow and thus myocardial oxygenation. Oxygenation-sensitive cardiovascular magnetic resonance (CMR) using the blood oxygen level-dependent (BOLD) effect allows for non-invasive monitoring of changes of myocardial tissue oxygenation. We hypothesized that mild hypercapnia induced by long breath-holds leads to changes in myocardial oxygenation that can be detected by oxygenation-sensitive CMR.Methods and ResultsIn nine anaesthetized and ventilated pigs, 60s breath-holds were induced. Left ventricular myocardial and blood pool oxygenation changes, as monitored by oxygenation-sensitive CMR using a T2*-weighted steady-state-free-precession (SSFP) sequence at 1.5T, were compared to changes of blood gas levels obtained immediately prior to and after the breath-hold. Long breath-holds resulted in an increase of paCO2, accompanied by a decrease of paO2 and pH. There was a significant decrease of blood pressure, while heart rate did not change. A decrease in the left ventricular blood pool oxygenation was observed, which was similar to drop in SaO2. Oxygenation in the myocardial tissue however, was maintained throughout the period. Changes in myocardial oxygenation were strongly correlated with the change in paCO2 during the breath-hold (r = 0.90, p = 0.010).ConclusionDespite a drop in blood oxygen levels, myocardial oxygenation is maintained throughout long breath-holds and is linearly correlated with the parallel increase of arterial CO2, a known coronary vasodilator. Breathing maneuvers in combination with oxygenation-sensitive CMR may be useful as a diagnostic test for coronary artery function.

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“…The flexibility in choosing the T R also allows control over the diffusion distance of the water molecules in between the excitations. As evidenced by earlier studies, with this contrast mechanism passband b-SSFP fMRI has the potential to generate spatial scale selectivity (12,15,16,19,20). For voxels mostly containing small vessels, most of the dephasing effects are expected to come from the extravascular components.…”

Section: Theorymentioning

confidence: 81%

“…While the detailed biophysics of passband b-SSFP functional signal source remains elusive, the most parsimonious explanation of the contrast mechanism for passband b-SSFP fMRI is the dephasing that is not refocused around the off-resonance created by the deoxyhemoglobin (12,15,16,19,20). The rapid refocusing mechanism in b-SSFP imaging allows for the refocusing of any large-scale off-resonance effects.…”

Section: Theorymentioning

confidence: 99%

Full‐brain coverage and high‐resolution imaging capabilities of passband b‐SSFP fMRI at 3T

Lee

Dumoulin

Sarıtaş

et al. 2008

Magnetic Resonance in Med

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Balanced-steady-state free precession (b-SSFP) imaging is an image acquisition technique that uses rapid RF excitation pulses combined with fully balanced gradient pulses during each excitation repetition interval (T R ) (1,2). Due to its short readout time and T R , b-SSFP provides distortionfree 3D imaging suitable for full-brain, high-resolution functional imaging.The first use of b-SSFP for functional MRI (fMRI) was proposed by Scheffler et al. (3), which used the steep magnitude transitional portion of the b-SSFP resonance spectrum to generate oxygen contrast based on the resonance frequency shift induced by deoxyhemoglobin. Another acquisition scheme using the steep phase transition of the b-SSFP off-resonance spectrum was subsequently proposed by Miller et al. (4) (Fig. 1b). We refer to these techniques as transition-band b-SSFP fMRI methods. Transition-band b-SSFP fMRI combines the advantages of b-SSFP imaging with a functional contrast mechanism sensitive to the deoxyhemoglobin frequency-shift following neuronal activations. In contrast, in conventional gradientecho (GRE) blood oxygenation level-dependent (BOLD) fMRI (5-7) using echo-planer imaging (EPI) with long echo time (T E ) and readout time, venous signal dephasing due to deoxygenation is both the source of functional signals, as well as the main source for signal dropouts and image distortions. Despite its potential for functional imaging, the use of the transition-band b-SSFP can be challenging. Transition-band b-SSFP methods produce oxygenationsensitive contrast only in a very narrow range of frequencies near resonance. This requires the use of multi-frequency acquisitions even for a small volume coverage (8).Here we describe an alternative approach, termed passband b-SSFP fMRI (9 -14), which has the potential to provide distortion-free, high-spatial-resolution fMRI studies. The passband b-SSFP fMRI utilizes the flat portion of the b-SSFP off-resonance profile instead of the steep transitional portion (see Fig. 1c). Here the rapid refocusing of b-SSFP imaging suppresses larger scale off-resonance effects. This refocusing degrades when the off-resonance is spatially in the scale of the water diffusion distances (compare Fig. 1e,f). The resulting dephasing is expected to produce oxygenation contrast predominantly in parenchymal regions near small vessels with steep off-resonance changes. This mechanism is assumed to be similar to that of spin-echo (SE)-based fMRI. The difference in contrast mainly comes from the signal augmenting stimulated echo pathways that exist in b-SSFP acquisitions. Imaging constraints such as acquisition speed, distortion properties, and signal-to-noise ratio (SNR) add further advantages for passband b-SSFP-based fMRI. Bowen et al. (13,14) demonstrated passband b-SSFP fMRI's potential to sensitize itself to signal changes arising from the smaller vessel size of interest, while proposed passband b-SSFP schemes combined with 3D imaging trajectories and multiple-acquisition techniques. The functional contrast mechanisms o...

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Detecting microcirculatory changes in blood oxygen state with steady‐state free precession imaging

Cited by 36 publications

References 21 publications

Oxygenation-sensitive CMR for assessing vasodilator-induced changes of myocardial oxygenation

Oxygenation-sensitive CMR for assessing vasodilator-induced changes of myocardial oxygenation

Impact of Intermittent Apnea on Myocardial Tissue Oxygenation—A Study Using Oxygenation-Sensitive Cardiovascular Magnetic Resonance

Full‐brain coverage and high‐resolution imaging capabilities of passband b‐SSFP fMRI at 3T

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