Assessment of Myocardial Blood Flow (MBF) in Humans Using Arterial Spin Labeling (ASL): Feasibility and Noise Analysis

Ming Hsieh Department of Electrical Engineering, Viterbi School of Engineering, University of Southern California, Los Angeles, California 90089-2564, USA.
Magnetic Resonance in Medicine (Impact Factor: 3.57). 10/2009; 62(4):975-83. DOI: 10.1002/mrm.22088
Source: PubMed


Arterial spin labeling (ASL) is a powerful tool for the quantitative measurement of tissue blood flow, and has been extensively applied to the brain, lungs, and kidneys. ASL has been recently applied to myocardial blood flow (MBF) measurement in small animals; however, its use in humans is limited by inadequate signal-to-noise ratio (SNR) efficiency and timing restrictions related to cardiac motion. We present preliminary results demonstrating MBF measurement in humans, using cardiac-gated flow-sensitive alternating inversion recovery (FAIR) tagging and balanced steady-state free precession (SSFP) imaging at 3T, and present an analysis of thermal and physiological noise and their impact on MBF measurement error. Measured MBF values in healthy volunteers were 1.36 +/- 0.40 ml/ml/min at rest, matching the published literature based on quantitative (13)N-ammonia positron emission tomography (PET), and increased by 30% and 29% with passive leg elevation and isometric handgrip stress, respectively. With thermal noise alone, MBF can be quantified to within +/- 0.1 ml/ml/min with 85.5% confidence, for 3.09 cm(3) regions averaged over 6 breath-holds. This study demonstrates the feasibility of quantitative assessment of myocardial blood flow in humans using ASL, and identifies SNR improvement and the reduction of physiological noise as key areas for future development.

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    • "The reference ASL scan was implemented as described previously by Zun et al.[12,15]. All image acquisitions had 3.2 ms TR, 1.5 ms TE, 50˚ prescribed flip angle, 62.5 kHz receiver bandwidth, and 24–26 cm isotropic field-of-view (FOV). "
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    ABSTRACT: : Background Myocardial arterial spin labeling (ASL) is a noninvasive MRI based technique that is capable of measuring myocardial blood flow (MBF) in humans. It suffers from poor sensitivity to MBF due to high physiological noise (PN). This study aims to determine if the sensitivity of myocardial ASL to MBF can be improved by reducing image acquisition time, via parallel imaging. Methods Myocardial ASL scans were performed in 7 healthy subjects at rest using flow-sensitive alternating inversion recovery (FAIR) tagging and balanced steady state free precession (SSFP) imaging. Sensitivity encoding (SENSE) with a reduction factor of 2 was used to shorten each image acquisition from roughly 300 ms per heartbeat to roughly 150 ms per heartbeat. A paired Student’s t-test was performed to compare measurements of myocardial blood flow (MBF) and physiological noise (PN) from the reference and accelerated methods. Results The measured PN (mean ± standard deviation) was 0.20 ± 0.08 ml/g/min for the reference method and 0.08 ± 0.05 ml/g/min for the accelerated method, corresponding to a 60% reduction. PN measured from the accelerated method was found to be significantly lower than that of the reference method (p = 0.0059). There was no significant difference between MBF measured from the accelerated and reference ASL methods (p = 0.7297). Conclusions In this study, significant PN reduction was achieved by shortening the acquisition window using parallel imaging with no significant impact on the measured MBF. This indicates an improvement in sensitivity to MBF and may also enable the imaging of subjects with higher heart rates and imaging during systole.
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    ABSTRACT: In subtractive imaging modalities, the differential longitudinal magnetization decays with time, necessitating signal-efficient scanning methods. Balanced steady-state free precession pulse sequences offer greater signal strength than conventional spoiled gradient echo sequences, even during the transient approach to steady state. Although traditional balanced steady-state free precession requires that each excitation pulse use the same flip angle, operating in the transient regimen permits the application of variable flip angle schedules that can be tailored to optimize certain signal characteristics. A computationally efficient technique is presented to generate variable flip angle schedules efficiently for any optimization metric. The validity of the technique is shown using two phantoms, and its potential is demonstrated in vivo with a variable angle schedule to increase the signal-to-noise ratio (SNR) in myocardial tissue. Using variable flip angles, the mean SNR improvement in subtractive imaging of myocardial tissue was 18.2% compared to conventional, constant flip angle, balanced steady-state free precession (P = 0.0078).
    Magnetic Resonance in Medicine 02/2010; 63(2):537-42. DOI:10.1002/mrm.22255 · 3.57 Impact Factor
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