Limits...
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.

Show MeSH

Related in: MedlinePlus

(A) Schematic sequence diagram. Note that the timing of the first global inversion pulse is constrained by the (vessel-encoded) pseudocontinuous arterial spin labeling ((VE)PCASL) pulse train; (B) Simulated longitudinal magnetization at the start of the echo planar imaging (EPI) readout for postlabeling delay (PLD)=1 second and optimum T1 (T1,opt)=390 ms. Tissues at T1,opt and 2T1,opt are ed perfectly but those with longer T1 values are also largely suppressed; (C) A Time-of-flight (TOF) axial slice through the neck showing a typical labeling plane. The four main brain-feeding arteries are circled in color: red=right internal carotid artery (RICA), green=left internal carotid artery (LICA), blue=right vertebral artery (RVA), and magenta=left vertebral artery (LVA). For VEPCASL, left–right encodings contrast vessels aligned with line A versus those at line B, anterior–posterior encodings contrast lines C and D and diagonal encodings contrast lines E and F. Note that F is shown twice due to the periodic nature of the encoding function.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3824178&req=5

fig1: (A) Schematic sequence diagram. Note that the timing of the first global inversion pulse is constrained by the (vessel-encoded) pseudocontinuous arterial spin labeling ((VE)PCASL) pulse train; (B) Simulated longitudinal magnetization at the start of the echo planar imaging (EPI) readout for postlabeling delay (PLD)=1 second and optimum T1 (T1,opt)=390 ms. Tissues at T1,opt and 2T1,opt are ed perfectly but those with longer T1 values are also largely suppressed; (C) A Time-of-flight (TOF) axial slice through the neck showing a typical labeling plane. The four main brain-feeding arteries are circled in color: red=right internal carotid artery (RICA), green=left internal carotid artery (LICA), blue=right vertebral artery (RVA), and magenta=left vertebral artery (LVA). For VEPCASL, left–right encodings contrast vessels aligned with line A versus those at line B, anterior–posterior encodings contrast lines C and D and diagonal encodings contrast lines E and F. Note that F is shown twice due to the periodic nature of the encoding function.

Mentions: A schematic of the ASL pulse sequence is shown in Figure 1A. Both standard PCASL and VEPCASL acquisitions were performed in each subject and shared a common labeling plane positioned ∼8 cm below the circle of Willis, through the proximal V3 segment of the vertebral arteries (VAs). In this plane, the four main brain-feeding arteries all run in the inferior–superior direction and form an approximately rectangular arrangement in the axial plane (Figure 1C). Other than the vessel-encoded preparation all parameters were kept constant between the two scans, as listed in Table 1. Pseudocontinuous ASL was achieved using 600 μs duration Gaussian RF pulses once per ms over the labeling duration (τ) of 1.4 seconds. A single-shot echo planar imaging readout was used with repetition time (TR)=4.05 seconds and echo time (TE)=14 ms. Slices were acquired sequentially from inferior to superior, giving whole brain coverage with voxel size=3.4 × 3.4 × 5 mm. Images were acquired in separate blocks for six PLDs, ranging from 0.25 to 1.5 seconds, giving a total acquisition time of 6.5 minutes.


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

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

(A) Schematic sequence diagram. Note that the timing of the first global inversion pulse is constrained by the (vessel-encoded) pseudocontinuous arterial spin labeling ((VE)PCASL) pulse train; (B) Simulated longitudinal magnetization at the start of the echo planar imaging (EPI) readout for postlabeling delay (PLD)=1 second and optimum T1 (T1,opt)=390 ms. Tissues at T1,opt and 2T1,opt are ed perfectly but those with longer T1 values are also largely suppressed; (C) A Time-of-flight (TOF) axial slice through the neck showing a typical labeling plane. The four main brain-feeding arteries are circled in color: red=right internal carotid artery (RICA), green=left internal carotid artery (LICA), blue=right vertebral artery (RVA), and magenta=left vertebral artery (LVA). For VEPCASL, left–right encodings contrast vessels aligned with line A versus those at line B, anterior–posterior encodings contrast lines C and D and diagonal encodings contrast lines E and F. Note that F is shown twice due to the periodic nature of the encoding function.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig1: (A) Schematic sequence diagram. Note that the timing of the first global inversion pulse is constrained by the (vessel-encoded) pseudocontinuous arterial spin labeling ((VE)PCASL) pulse train; (B) Simulated longitudinal magnetization at the start of the echo planar imaging (EPI) readout for postlabeling delay (PLD)=1 second and optimum T1 (T1,opt)=390 ms. Tissues at T1,opt and 2T1,opt are ed perfectly but those with longer T1 values are also largely suppressed; (C) A Time-of-flight (TOF) axial slice through the neck showing a typical labeling plane. The four main brain-feeding arteries are circled in color: red=right internal carotid artery (RICA), green=left internal carotid artery (LICA), blue=right vertebral artery (RVA), and magenta=left vertebral artery (LVA). For VEPCASL, left–right encodings contrast vessels aligned with line A versus those at line B, anterior–posterior encodings contrast lines C and D and diagonal encodings contrast lines E and F. Note that F is shown twice due to the periodic nature of the encoding function.
Mentions: A schematic of the ASL pulse sequence is shown in Figure 1A. Both standard PCASL and VEPCASL acquisitions were performed in each subject and shared a common labeling plane positioned ∼8 cm below the circle of Willis, through the proximal V3 segment of the vertebral arteries (VAs). In this plane, the four main brain-feeding arteries all run in the inferior–superior direction and form an approximately rectangular arrangement in the axial plane (Figure 1C). Other than the vessel-encoded preparation all parameters were kept constant between the two scans, as listed in Table 1. Pseudocontinuous ASL was achieved using 600 μs duration Gaussian RF pulses once per ms over the labeling duration (τ) of 1.4 seconds. A single-shot echo planar imaging readout was used with repetition time (TR)=4.05 seconds and echo time (TE)=14 ms. Slices were acquired sequentially from inferior to superior, giving whole brain coverage with voxel size=3.4 × 3.4 × 5 mm. Images were acquired in separate blocks for six PLDs, ranging from 0.25 to 1.5 seconds, giving a total acquisition time of 6.5 minutes.

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