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Assessment of Pulsatility Index of Lenticulostriate Arteries using 2D PC-MRI with Dual-VENC in elderly adults at 7T: A Preliminary Study
Jianing Tang1,2, Tianrui Zhao1,2, Elizabeth Joe3, Helena Chui3, and Lirong Yan1,2
1Department of Radiology, Northwestern University, Chicago, IL, United States, 2Department of Biomedical Engineering, Northwestern University, Chicago, IL, United States, 3Department of Neurology, University of Southern California, Los Angeles, CA, United States

Synopsis

Keywords: Aging, High-Field MRI

Motivation: LSA plays an important role in the pathology of small vessel disease. Directly assessing LSA pulsatility may offer valuable insight into SVD pathology.

Goal(s): To assess the utility of 7T dual-VENC PC-MRI for the LSA pulsatility assessment in elderly adults by investigating its association with age and cognitive impairment.

Approach: LSA pulsatility was assessed using 7T PC-MRI using both dual- and single-VENC on 25 elderly participants. Cognitive tests including MMSE and MOCA were conducted.

Results: Our results showed that the LSA pulsatility was significantly correlated with upstream major arteries and increased LSA pulsatility was associated with aging, education level, and cognitive impairment.

Impact: Increased LSA pulsatility measured by dual-VENC PC-MRI shows a strong association with aging, education, and cognitive impairment. Compared to single-VENC, dual-VENC PC-MRI enhanced the detection and characterization of LSAs, providing a promising imaging tool for investigating vascular pathology of SVD.

Introduction

Small vessel disease (SVD) is characterized by pathological changes in cerebral perforating arteries within the basal ganglia, which serves as a common cause of both stroke and vascular dementia1. Arterial pulsatility, quantified by the pulsatility index (PI), is a well-established marker of vascular dysfunction. Elevated arterial pulsatility can lead to the transmission of excessive pulsatile energy into downstream microvasculature and tissue, resulting in endothelial dysfunction, injury, and vascular inflammation2. Therefore, directly assessing the pulsatility of perforating arteries offers valuable insight into the contribution of vascular dysfunction to the pathophysiology of SVD. Our recent 7T test-retest work has shown improved detection of LSA perforators and enhanced reliability of PI measurements using submillimeter-resolute dual-VENC phase-contrast MRI (PC-MRI) in comparison to the conventional PC-MRI with a single-VENC3. This study aims to evaluate the utility of 7T dual-VENC PC-MRI in the LSA pulsatility assessment by investigating its association with age and cognitive functions within an aged cohort.

Methods

Study Participants and Cognitive Assessments
Twenty-five elderly participants (13 female: 71 ± 9.2 years) were enrolled in the study after providing written informed consent. 23 out of 25 provided information about their education level. Cognitive assessments were conducted including 19 undergoing the Mini-Mental State Exam (MMSE) and 23 taking Montreal Cognitive Assessment (MoCA). Additionally, 2D PC-MRI scans on M1 segment of middle cerebral artery (MCA) and internal carotid artery (ICA) were performed on 13 of the participants.
MRI experiments
All MRI experiments were performed on a Siemens 7T MAGNETOM Terra MRI system using an 8-transmit/32-receive head coil. Retrospectively gated single-slice 2D PC-MRI sequences with VENCs of 20 cm/s and 40 cm/s were acquired (FOV = 180x200 mm2, slice thickness = 2 mm, voxel size = 0.2x0.2x2.0 mm3, flip angle = 50°, TE/TR= 9.72/95ms, 20 phases across a cardiac cycle). A 3D high-resolution TOF was performed on each subject prior to PC-MRI scans to locate the perforating arteries.
Image processing and statistical analysis
LSA masks were blindly generated for single-VENC of 40cm/s and dual-VENC data, respectively. Background phase correction and phase unwrapping were done before calculating the blood velocity and PI. In the dual-VENC image processing, high VENC phase maps were used to unaliase the phase wrapping in low VENC phase maps to ensure a proper velocity profile. Pearson correlation was used to evaluate the association between PI and age, education level, and cognitive measurements. A linear mixed-effects model was used to describe the linear relationship between the PI and cognitive measurements while accounting for the effects of age, gender, and education.

Results and Discussion

Flow velocity curves and PI values were successfully extracted and calculated from all 25 participants. An example is illustrated in Figure 1. Consistent with our previous findings in healthy young participants3, significantly more LSAs were detected using dual-VENC (p<0.001) compared to single-VENC of 40cm/s (Figure 2). No significant difference (p=0.19) was found in the PI values between single VENC (PI=0.94+/-0.23) and dual VENCs (PI=0.86+/-0.23) (Figure 2). The LSA PI values measured by both single and dual-VENC highly correlated with the PI values obtained from the proximal vessel segments including the ICA and the M1 of MCA (Figure 3). This finding further validates the reliability of the LSA PI measurement using PC-MRI with both single and dual-VENC. Moreover, the PI values with dual-VENC showed a slightly stronger correlation with those of ICA and MCA compared to those with single VENC (p=0.01 vs p=0.024, p=0.004 vs 0.053).
Consistent with the previous findings with single-VENC PC-MRI 3, LSA PI showed a significant correlation with age for both single and dual-VENC (p=0.01, 0.002 respectively). In addition, LSA PI measured by dual VENC showed a significant correlation with the education level (p=0.03), while no significant association was found with single VENC (p=0.25).
Increased PI was strongly associated with lower MMSE scores with (p = 0.028) and without correcting for age, gender, and educational level (p=0.048). A similar trend was observed between PI and MOCA scores, although there was no significance (p=0.18, 0.31). These findings suggest a strong association between LSA dysfunction and cognitive performance.

Conclusion

This study has demonstrated that elevated LSA pulsatility is associated with aging, education, and cognitive function. These findings indicate that LSA dysfunction may play an important role in aging and cognitive decline in elderly adults. Dual-VENC detects more LSAs compared to the single-VENC, which could provide more reliable measures from both larger and smaller LSAs, compared to single-VENC. The advantages of PC-MRI with dual-VENC will be further evaluated in a larger cohort in future work.

Acknowledgements

This work was partly supported by National Institute of Health (NIH) grants R01NS118019, RF1AG072490, and BrightFocus Foundation A20201411S

References

1. Wardlaw, Joanna M., Colin Smith, and Martin Dichgans. "Small vessel disease: mechanisms and clinical implications." The Lancet Neurology 18.7 (2019): 684-696.

2. Geurts, Lennart J., et al. "Higher pulsatility in cerebral perforating arteries in patients with small vessel disease related stroke, a 7T MRI study." Stroke 50.1 (2019): 62-68.

3. Tang,J et al. " Comparison of arterial pulsatility of cerebral perforating arteries between dual-VENC and single-VENC phase-contrast MRI at 7T." ISMRM Proceedings, 2023.

Figures

Figure 1. a. An example of PC-MRI structural image, in which LSAs in the basal ganglia region (orange box) are well delineated. b. The resulting velocity curve of detected LSAs from PC-MRI data. PI is calculated by dividing the difference between the maximum and minimum velocities by the mean velocity across a cardiac cycle.

Figure 2. a and b show an example of the zoomed-in PC-MRI magnitude images in the basal ganglia region with a single VENC of 40cm/s (a) and dual VENC (b). c and d are Box plots of the number of detected LSAs (c) and calculated PI values (d) across subjects with a single VENC and dual VENC.

Figure 3. Scatter plots of LSA PI measurements using dual-VENC (a) and single-VENC (b) with the PI measurements of ICA and MCA, respectively. LSA pulsatility with both single and dual-VENC is significantly associated with the pulsatility of the proximal arteries, i.e., ICA and MCA

Figure 4. Scatter plots of the LSA PI measurements with age (a) and educational level (b). Increased LSA pulsatility with both single and dual-VENC is strongly associated with age (p=0.01, 0.002) and educational level (p=0.25, 0.03).

Figure 5. Scatter plots of the LSA PI measurements with MMSE (a) and MOCA (b) scores. Increased LSA pulsatility is associated with cognitive decline (lower MMSE scores (p=0.048, 0.049) and lower MOCA scores (p=0.18, 0.31))

Proc. Intl. Soc. Mag. Reson. Med. 32 (2024)
3886
DOI: https://doi.org/10.58530/2024/3886