Assessment of whole brain blood flow changes in multiple sclerosis: phase contrast MRI versus ASL
Yulin Ge1, Olga Marshall1, Ilya Kister1, Jean-Christophe Brisset1, Louise Pape1, Jacqueline Smith1, and Robert I Grossman1

1Radiology, New York University School of Medicine, New York City, NY, United States

Synopsis

Cerebral blood flow (CBF) is an important characteristic of the brain since it reflects the availability of blood to enable healthy neuronal function. Previous studies in multiple sclerosis (MS) have shown regional hemodynamic changes indicating a state of both increased or decreased perfusion, which may reflect underlying neuroinflammatory activity and impaired vascular perfusion of the disease, respectively. However, it is still unclear how the whole brain blood supply or blood flow changes in MS. This study was to investigate whether global CBF levels are effected in MS compared to controls, while evaluating with two different imaging techniques to confirm the findings.

PURPOSE

Cerebral blood flow (CBF) is an important characteristic of the brain since it reflects the availability of blood to enable healthy neuronal function. Previous studies (1,2,3) in multiple sclerosis (MS) have shown regional hemodynamic changes indicating a state of both increased or decreased perfusion, which may reflect underlying neuroinflammatory activity and impaired vascular perfusion of the disease, respectively. In addition, chronic cerebrospinal venous insufficiency (CCSVI) (4) has also been previously reported, however, it is still unclear how the whole brain blood supply or blood flow changes in MS. This study was to investigate whether global CBF levels are effected in MS compared to controls, while evaluating with two different imaging techniques to confirm the findings.

METHODS

70 controls (39 male, 31 female, 37.6±12.4 years old) and 81 MS patients (30 male, 51 female, 41.6±11.0 years old) patients underwent MRI scans to assess whole brain CBF measured by single-slice phase-contrast (PC) (5) (Figure 1) or pseudocontinuous arterial spin labeling (pCASL) 6 perfusion MRI (Figure 2) or both.

  • - pCASL was acquired to cover the whole brain with 5mm thickness and 32 slices.

  • - PC with a single imaging slice was placed above the carotid artery bifurcation oriented perpendicular to the internal carotid (ICA) and vertebral arteries (VA) determined based on a time-of-flight angiogram, to simultaneously assess the four arteries.

  • - A high resolution anatomical T1 image was acquired for image co-registration and segmentation.

  • - Whole brain CBF (mL/100g/min) was measured from the PC data as the total blood flow through the arteries (bilateral ICA, VA, and ICA+VA) divided by the total brain parenchyma volume.

  • - CBF maps were generated from the pCASL data according to a previously described method (6) and whole brain CBF was calculated as the average of all gray and white matter voxels, excluding the cerebellum.

  • - CBF values acquired by both methods were compared between the patient and control group using a two-sample t-test, with a p<0.05 considered significant.


RESULTS

Whole brain CBF comparison showed lower value of using PC-based method compared with pCASL-based method. We did not find significantly decreased global CBF using either method (Figure 3). The PC-based global CBF (ml/100g tissue/min) was 49.0 ±9.5 (mean ± SD) in controls versus 50.2±9.5 in patients (p=0.48), and the pCASL-based global CBF was 54.2±11.3 in controls versus 58.9±14.0 in patients. The slightly high global CBF in MS was probably mainly due to higher blood flow in VA system in patients compared to controls (p=0.02) using PC-based technique for individual vessel calculation. A significant correlation (R = 0.43, p < 0.0001) is seen between whole brain CBF values as calculated using PC MRI and calculated using pCASL.

CONCLUSIONS

Although previous studies have shown significant regional perfusion changes in MS brains (1,2,3), our data showed no significant change of global CBF in MS using either ASL- or PC-based whole brain method. Such data suggest flow-related abnormalities cannot be detected at global level from the blood supply side. This is likely to reflect both regional decreased and increased perfusion (e. increased perfusion in the posterior circulation of VA system). Such global findings may also have value when other global structural and metabolic measures are interpreted.

Acknowledgements

This work was supported in part by NIH Grants (NS029029-20S1 and NS076588) and National Multiple Sclerosis Society (NMSS) research grant (RG 4707A1), this study was also performed under the rubric of the Center for Advanced Imaging Innovation and Research (CAI2R, www.cai2r.net), a NIBIB Biomedical Technology Resource Center (NIH P41 EB017183).

References

1. Wuerfel J, Bellmann-Strobl J, Brunecker P et al. Changes in cerebral perfusion precede plaque formation in multiple sclerosis: a longitudinal perfusion MRI study. Brain. 2004 Jan;127(Pt 1):111-9.

2. Ge Y, Law M, Johnson G et al. Dynamic susceptibility contrast perfusion MR imaging of multiple sclerosis lesions: characterizing hemodynamic impairment and inflammatory activity. AJNR Am J Neuroradiol. 2005 Jun-Jul;26(6):1539-47.

3. Rashid W, Parkes LM, Ingle GT et al. Abnormalities of cerebral perfusion in multiple sclerosis. J Neurol Neurosurg Psychiatry. 2004 Sep;75(9):1288-93.

4. Zamboni P, Galeotti R, Menegatti E, Malagoni AM, Chronic cerebrospinal venous insufficiency in patients with multiple sclerosis. J Neurol Neurosurg Psychiatry. 2009 Apr;80(4):392-9

5. Xu F, Ge Y, Lu H. Noninvasive quantification of whole-brain cerebral metabolic rate of oxygen (CMRO2) by MRI. Mag Reson Med. 2009 Jul;62(1):141-8.

6. Wu WC, Wong EC. Feasibility of velocity selective arterial spin labeling in functional MRI. J Cereb Blood Flow Metab. 2007 Apr;27(4):831-8.

Figures

Phase contrast (PC) is a well-established MRA technique based on velocity-encoded phase map, which is used to estimate blood flow . In this study, we calculated the whole brain blood flow (total flow from 4 vessels) using PC at the C2~C3 cervical vertebral level that include bilateral internal carotid arteries (ICA) and vertebral arteries (VA). The total flow (ml/min) was then normolized by the intracranial brain tissue (GM+WM) volume with total brain CBF calculated as ml/100g tissue/min.

Arterial spin labeling (ASL) is a novel perfusion MRI technique to measure CBF by taking advantages of arterial water as a moving and freely diffusible tracer, which can be labeled at the level of neck and measured in brain tissues (above left). Whole brain CBF was calculated on a voxel-by-voxel basis from all slices covering the whole brain (above right), in which total CBF (also in unit of ml/100g tissue/ min) was used for comparison between patients and controls.

Comparison between MS & control groups of average whole brain CBF (mL/100g/min) based on the PC (MS: N=68, NC: N=64) and pCASL images (N=38). There was no significant difference of global CBF using either PC-based (p=0.48) or pCASL-based (P=0.11) method.

Correlation of whole brain CBF as measured using the pCASL method with CBF as measured with the PC method in controls as well as MS patients (R = 0.43, p < 0.0001) (MS: N=62, NC: N=34).



Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)
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