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Cerebral blood flow quantification using vessel-encoded arterial spin labeling.

Okell TW, Chappell MA, Kelly ME, Jezzard P - J. Cereb. Blood Flow Metab. (2013)

Bottom Line: Experimental results in healthy volunteers showed that there is no systematic bias in the CBF estimates produced by VEPCASL and that the signal-to-noise ratio of the two techniques is comparable.Although more complex acquisition and image processing is required and the potential for motion sensitivity is increased, VEPCASL provides comparable data to PCASL but with the added benefit of vessel-selective information.This could lead to more accurate CBF estimates in patients with a significant collateral flow.

View Article: PubMed Central - PubMed

Affiliation: Nuffield Department of Clinical Neurosciences, Centre for Functional Magnetic Resonance Imaging of the Brain, University of Oxford, Oxford, UK.

ABSTRACT
Arterial spin labeling (ASL) techniques are gaining popularity for visualizing and quantifying cerebral blood flow (CBF) in a range of patient groups. However, most ASL methods lack vessel-selective information, which is important for the assessment of collateral flow and the arterial supply to lesions. In this study, we explored the use of vessel-encoded pseudocontinuous ASL (VEPCASL) with multiple postlabeling delays to obtain individual quantitative CBF and bolus arrival time maps for each of the four main brain-feeding arteries and compared the results against those obtained with conventional pseudocontinuous ASL (PCASL) using matched scan time. Simulations showed that PCASL systematically underestimated CBF by up to 37% in voxels supplied by two arteries, whereas VEPCASL maintained CBF accuracy since each vascular component is treated separately. Experimental results in healthy volunteers showed that there is no systematic bias in the CBF estimates produced by VEPCASL and that the signal-to-noise ratio of the two techniques is comparable. Although more complex acquisition and image processing is required and the potential for motion sensitivity is increased, VEPCASL provides comparable data to PCASL but with the added benefit of vessel-selective information. This could lead to more accurate CBF estimates in patients with a significant collateral flow.

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Simulation results: (A) Example high signal-to-noise ratio (SNR) simulated data (circles) and fits (lines) for a voxel fed by two arteries. When the arrival times of the two components are the same, both vessel-encoded (VE) and standard pseudocontinuous arterial spin labeling (PCASL) estimate the cerebral blood flow (CBF) correctly (left). When there is an arrival time difference, PCASL begins to underestimate the CBF, by 25% in this case (right); (B) CBF errors (mean and standard deviation) for a voxel fed by two arteries using PCASL and VEPCASL techniques. The mean and standard deviation in the CBF error are shown for a range of bolus arrival time (BAT) differences, CBF ratios (see legend) and both high and low SNR data. PCASL systematically underestimates the CBF when the BAT difference is >0.25 second. When the SNR is high, VEPCASL gives very accurate CBF estimates. When the SNR is reduced, VEPCASL begins to underestimate the CBF from the late arriving bolus, which becomes submerged in the noise floor, but the mean errors remain smaller than PCASL.
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fig3: Simulation results: (A) Example high signal-to-noise ratio (SNR) simulated data (circles) and fits (lines) for a voxel fed by two arteries. When the arrival times of the two components are the same, both vessel-encoded (VE) and standard pseudocontinuous arterial spin labeling (PCASL) estimate the cerebral blood flow (CBF) correctly (left). When there is an arrival time difference, PCASL begins to underestimate the CBF, by 25% in this case (right); (B) CBF errors (mean and standard deviation) for a voxel fed by two arteries using PCASL and VEPCASL techniques. The mean and standard deviation in the CBF error are shown for a range of bolus arrival time (BAT) differences, CBF ratios (see legend) and both high and low SNR data. PCASL systematically underestimates the CBF when the BAT difference is >0.25 second. When the SNR is high, VEPCASL gives very accurate CBF estimates. When the SNR is reduced, VEPCASL begins to underestimate the CBF from the late arriving bolus, which becomes submerged in the noise floor, but the mean errors remain smaller than PCASL.

Mentions: Examples of results from the simulations are shown in Figure 3A. As expected, when the BATs of the two arterial components feeding the simulated voxel are equal, the PCASL perfusion signal (total) has the same shape as the two VEPCASL signals (components 1 and 2), resulting in an accurate estimation of CBF. However, when there is a difference in the BAT between the two components, an accurate CBF estimate can no longer be extracted from the PCASL data. For VEPCASL, the two components are fitted separately, so the total CBF estimate is unaffected and remains accurate.


Cerebral blood flow quantification using vessel-encoded arterial spin labeling.

Okell TW, Chappell MA, Kelly ME, Jezzard P - J. Cereb. Blood Flow Metab. (2013)

Simulation results: (A) Example high signal-to-noise ratio (SNR) simulated data (circles) and fits (lines) for a voxel fed by two arteries. When the arrival times of the two components are the same, both vessel-encoded (VE) and standard pseudocontinuous arterial spin labeling (PCASL) estimate the cerebral blood flow (CBF) correctly (left). When there is an arrival time difference, PCASL begins to underestimate the CBF, by 25% in this case (right); (B) CBF errors (mean and standard deviation) for a voxel fed by two arteries using PCASL and VEPCASL techniques. The mean and standard deviation in the CBF error are shown for a range of bolus arrival time (BAT) differences, CBF ratios (see legend) and both high and low SNR data. PCASL systematically underestimates the CBF when the BAT difference is >0.25 second. When the SNR is high, VEPCASL gives very accurate CBF estimates. When the SNR is reduced, VEPCASL begins to underestimate the CBF from the late arriving bolus, which becomes submerged in the noise floor, but the mean errors remain smaller than PCASL.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3824178&req=5

fig3: Simulation results: (A) Example high signal-to-noise ratio (SNR) simulated data (circles) and fits (lines) for a voxel fed by two arteries. When the arrival times of the two components are the same, both vessel-encoded (VE) and standard pseudocontinuous arterial spin labeling (PCASL) estimate the cerebral blood flow (CBF) correctly (left). When there is an arrival time difference, PCASL begins to underestimate the CBF, by 25% in this case (right); (B) CBF errors (mean and standard deviation) for a voxel fed by two arteries using PCASL and VEPCASL techniques. The mean and standard deviation in the CBF error are shown for a range of bolus arrival time (BAT) differences, CBF ratios (see legend) and both high and low SNR data. PCASL systematically underestimates the CBF when the BAT difference is >0.25 second. When the SNR is high, VEPCASL gives very accurate CBF estimates. When the SNR is reduced, VEPCASL begins to underestimate the CBF from the late arriving bolus, which becomes submerged in the noise floor, but the mean errors remain smaller than PCASL.
Mentions: Examples of results from the simulations are shown in Figure 3A. As expected, when the BATs of the two arterial components feeding the simulated voxel are equal, the PCASL perfusion signal (total) has the same shape as the two VEPCASL signals (components 1 and 2), resulting in an accurate estimation of CBF. However, when there is a difference in the BAT between the two components, an accurate CBF estimate can no longer be extracted from the PCASL data. For VEPCASL, the two components are fitted separately, so the total CBF estimate is unaffected and remains accurate.

Bottom Line: Experimental results in healthy volunteers showed that there is no systematic bias in the CBF estimates produced by VEPCASL and that the signal-to-noise ratio of the two techniques is comparable.Although more complex acquisition and image processing is required and the potential for motion sensitivity is increased, VEPCASL provides comparable data to PCASL but with the added benefit of vessel-selective information.This could lead to more accurate CBF estimates in patients with a significant collateral flow.

View Article: PubMed Central - PubMed

Affiliation: Nuffield Department of Clinical Neurosciences, Centre for Functional Magnetic Resonance Imaging of the Brain, University of Oxford, Oxford, UK.

ABSTRACT
Arterial spin labeling (ASL) techniques are gaining popularity for visualizing and quantifying cerebral blood flow (CBF) in a range of patient groups. However, most ASL methods lack vessel-selective information, which is important for the assessment of collateral flow and the arterial supply to lesions. In this study, we explored the use of vessel-encoded pseudocontinuous ASL (VEPCASL) with multiple postlabeling delays to obtain individual quantitative CBF and bolus arrival time maps for each of the four main brain-feeding arteries and compared the results against those obtained with conventional pseudocontinuous ASL (PCASL) using matched scan time. Simulations showed that PCASL systematically underestimated CBF by up to 37% in voxels supplied by two arteries, whereas VEPCASL maintained CBF accuracy since each vascular component is treated separately. Experimental results in healthy volunteers showed that there is no systematic bias in the CBF estimates produced by VEPCASL and that the signal-to-noise ratio of the two techniques is comparable. Although more complex acquisition and image processing is required and the potential for motion sensitivity is increased, VEPCASL provides comparable data to PCASL but with the added benefit of vessel-selective information. This could lead to more accurate CBF estimates in patients with a significant collateral flow.

Show MeSH
Related in: MedlinePlus