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Assessment of cerebral venous outflow rates with 4D arterial spin labeling vessel-selective angiography1Facing Faces Institute/CHIMERE EA 7516, University of Picardy, Amiens, France, 2Radiology Department, University Hospital of Picardy, Amiens, France, 3Medical Image Processing Department, University Hospital of Picardy, Amiens, France
Synopsis
4D arterial spin labeling (ASL) angiography has gained attention in the diagnosis of cerebrovascular diseases. The aim of this study was to evaluate the feasibility for estimating blood flow rates of the cerebral drainage system using data obtained by a 4D ASL angiography sequence. Data of a 4D ASL angiography acquisition provided comparable flow measurements to those of a standard 2D phase-contrast MR imaging sequence in 12 subjects. We demonstrated that both detailed morphological information and flows rates can be obtained by using a single 4D ASL angiography acquisition.
INTRODUCTION
4D angiography based on arterial spin labeling (ASL) is a non-invasive technique allowing to assess information about dynamic filling by selectively looking at specific vessels. In cerebrovascular diseases, previous studies using this technique for evaluation of hemodynamic alterations were mainly focused on the arterial system. Because hemodynamic information of the cerebral drainage system is also important in idiopathic intracranial hypertension1 and hydrocephalus2,3, we aim to simultaneous assess vasculature information and quantitative volumetric blood flow rates by 4D ASL-based angiography in the venous sinus system.METHODS
Twelve volunteers receiving clinically indicated MR angiography and phase-contrast MR imaging (PC-MRI) underwent imaging at 3T (Philips Healthcare) using a 32-channel head coil, according to an IRB-approved protocol. Dynamic angiography was performed using an ASL sequence based on spin tagging with alternating radiofrequency (STAR) scheme4 and that allowed to measure the blood signal at multiples delays. Imaging parameters for this 4D ASL-based angiography sequence were as follows: TR/TE/FA = 7ms/3ms/10°, FOV = 210×210mm2, SENSE factor = 2.5, 70 slices and resulting spatial resolution= 0.7×0.7×2 mm3. These data were acquired with a total of 8 frames with a temporal resolution of 200 ms and a total acquisition time of 2.3 mn. Each angiogram map of each participant was manually segmented to extract volumetric measurements of the dynamic filling using the 3DSlicer software (www.slicer.org). The net blood volume of each frame was its segmented volume minus that of the first frame. Flow rates were obtained by dividing each net volume by the temporal delay. To validate our approach, the flow measurements from these data were compared with those obtained from a reference standard 2D PC-MRI sequence, which parameters included: FOV = 120×120 mm2, resulting spatial resolution = 0.5×0.5 mm2, TR/TE/FA = 10ms/6ms/30°, velocity encoding = 30 cm/s, cardiac phases = 32, scan time ~ 2 mn. For 2D PC-MRI analysis, a semi-automatic software tool was applied to quantify the flows using methods described previously5. The total outflow was calculated as the summation of flows measured in the two transverse sinuses. Comparison of flow measurements between the two techniques was performed using a Wicoxon’s signed-rank test.RESULTS
Figure 1 shows a representative velocity image and flow curve measured by the 2D PC-MRI sequence. Figure 2, examples of 4D ASL angiograms showing the label bolus passing through the intracranial drainage system. In this example, a narrowing in one transverse sinuses may be detected, as indicated by an arrow. Furthermore, for this subject, the dynamic filling was asymmetric between its two transverse sinuses. Individuals flow measurements obtained using the 4D ASL-based angiography acquisition were compared to those of the 2D PC-MRI acquisition, as shown in figure 3. Group mean flow was 422±170 cm3/mn for the data acquired with the 4D ASL sequence vs. 409±155 cm3/mn for the data from the 2D PC-MRI acquisition. There was no significant difference between these mean flows (P>0.17). Mean flow variability (in the group) was 40% for the data acquired with 4D ASL sequence and 38% for those of the 2D PC-MRI sequence.DISCUSSION
Overall, our results indicated a good agreement between the flows measured by the two sequences. However, the mean flows obtained with both sequences are relatively variables over the group. This was likely due to individual variability in flow dynamics. In addition, this work demonstrated the feasibility to obtain both morphological information and flow dynamics using a single 4D MR angiography acquisition. These information might be useful to characterize the resistance to drainage of the blood across the cerebral venous sinus system6. It is assumed that an increase in venous sinus flow resistance pathways may impact the cerebral hydrodynamics. One drawback of this approach is a relatively long segmentation time (2-3 hours) compared to that of the 2D PC-MRI data (~ 15 mn). Because, the segmentations of the 4D ASL images were manually performed. Further studies on flow phantom are required to evaluate flow measurements accuracy and reproducibility by 4D MR angiography technique compared to 2D standard PC-MRI.CONCLUSION
This approach may provide both qualitative and quantitative information about the dynamic filling of the cerebral drainage system.Acknowledgements
The authors thank the study volunteers.References
1-Bateman GA. Vascular hydraulics associated with idiopathic and secondary intracranial hypertension. AJNR Am J Neuroradiol. 2002;23(7):1180-1186.
2-Sainte-Rose C, LaCombe J, Pierre-Kahn A, Renier D, Hirsch JF. Intracranial venous sinus hypertension: cause or consequence of hydrocephalus in infants? J Neurosurg. 1984;60(4):727-736.
3-ElSankari S, Balédent O, van Pesch V, Sindic C, de Broqueville Q, Duprez T. Concomitant analysis of arterial, venous, and CSF flows using phase-contrast MRI: a quantitative comparison between MS patients and healthy controls. J Cereb Blood Flow Metab Off J Int Soc Cereb Blood Flow Metab. 2013;33(9):1314-1321.
4-Yan L, Sumei W, Zhuo Y, et al. Unenhanced dynamic MR angiography: high spatial and temporal resolution by using true FISP-based spin tagging with alternating radiofrequency. Radiology. 2010;256(1):270-279.
5-Balédent O, Henry-Feugeas MC, Idy-Peretti I. Cerebrospinal fluid dynamics and relation with blood flow: a magnetic resonance study with semiautomated cerebrospinal fluid segmentation. Invest Radiol. 2001;36(7):368-377.
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