Pulse wave velocity and flow in the carotid artery versus the aortic arch: effects of aging.

PURPOSE: To explore differences in arterial stiffness of the aorta and carotid artery, assessed by pulse wave velocity (PWV), to evaluate the blood flow volume distribution towards the carotid circulation and to assess the effect of aging on the coupling between aortic and carotid PWV using velocity-encoded magnetic resonance imaging (MRI). MATERIALS AND METHODS: Sixteen adult younger volunteers (age <30 years) and 16 older volunteers (age >45 years) underwent 3T MRI examination to assess aortic and carotid flow volumes and PWV using the transit time method. RESULTS: Aortic versus carotid PWV-ratio was 1.2 for younger volunteers and 0.95 for older volunteers, demonstrating leveling of wall stiffness. Furthermore, flow volume per minute in the internal carotid artery was lower for older versus younger volunteers (mean volume 177 ± 42 mL/min/m(2) vs. 147 ± 32 mL/min/m(2), P = 0.028), whereas aorta and common carotid artery flow volumes were not different. Consequently, the fraction of blood flow volume towards the brain was smaller for older versus younger volunteers (61 ± 9% versus 71 ± 8%, P = 0.002). CONCLUSION: PWV-leveling between aorta and carotid artery at older age is associated with a reduction in blood flow volume towards the brain. Velocity-encoded MRI can be used to evaluate PWV and flow volume distribution in the aortic arch and the carotid circulation.

Coupling of vessel wall morphology and function in the aorta and the carotid artery: an evaluation with MRI.

To evaluate the regional association between vessel wall morphology [i.e. cross-sectional vessel wall area (VWA)] and function [i.e. wall stiffness expressed in the pulse wave velocity (PWV)] in both the aortic arch and the left carotid artery. Thirty-two healthy volunteers (mean age 41 ± 16 years) underwent 3T MRI examination to assess PWV and VWA of the aorta and the left carotid artery. PWV was determined by the transit-time method with velocity-encoded MRI recordings of the systolic blood flow propagation. VWA was assessed for both the aorta and the carotid artery, by detecting lumen and outer vessel wall contours in cross-sectional black blood images. Linear regression analyses were used to test associations between aortic and carotid vessel wall area and stiffness. Within the same vascular territory, correlation between PWV and VWA was stronger than across vascular territories. For the aorta, the correlation between PWVAO and VWAAO (r = 0.71, p < 0.0001) was stronger than between PWVAO and VWACA (r = 0.53, p = 0.002). For the carotid artery, the correlation between PWVCA and VWACA (r = 0.61, p < 0.0001) was stronger than between PWVCA and VWAAO (r = 0.46, p = 0.008). Morphologic and functional vessel wall properties assessed in the aortic arch and the left carotid artery are significantly stronger associated within the same vascular territory rather than across different vascular territories.

MRI-assessed regional pulse wave velocity for predicting absence of regional aorta luminal growth in marfan syndrome.

BACKGROUND: In patients with Marfan syndrome (MFS), increased aortic wall stiffening may lead to progressive aortic dilatation. Aortic Pulse Wave Velocity (PWV), a marker of wall stiffness can be assessed regionally, using in-plane multi-directional velocity-encoded MRI. This study examined the diagnostic accuracy of regional PWV for prediction of regional aortic luminal growth during 2-year follow-up in MFS patients. METHODS: In twenty-one MFS patients (mean age 36 ± 15 years, 11 male) regional PWV and aortic luminal areas were assessed by 1.5 T MRI. At 2-year follow-up, the incidence of luminal growth, defined as mean luminal diameter increase >2mm was determined for five aortic segments (S1, ascending aorta; S2, aortic arch; S3, thoracic descending aorta, S4, supra-renal and S5, infra-renal abdominal aorta). Regional PWV at baseline was considered increased when exceeding age-related normal PWV (healthy volunteers (n=26; mean age 30 ± 10 years, 15 male)) by two standard-errors. Sensitivity and specificity of regional PWV-testing for prediction of regional luminal growth were determined. RESULTS: Regional PWV at baseline was increased in 17 out of 102 segments (17%). Significant luminal growth at follow-up was reported in 14 segments (14%). The specificity of regional PWV-testing was ≥ 78% for all aortic segments, sensitivity was ≤ 33%. CONCLUSIONS: Regional PWV was significantly increased in MFS patients as compared to healthy volunteers within similar age range, in all aortic segments except the ascending aorta. Furthermore, regional PWV-assessment has moderate to high specificity for predicting absence of regional aortic luminal growth for all aortic segments in MFS patients.

Ultrahigh-field 7-T magnetic resonance carotid vessel wall imaging: initial experience in comparison with 3-T field strength.

OBJECTIVES: Magnetic resonance imaging (MRI) of the vessel wall enables determination of luminal area, vessel wall thickness, and atherosclerotic plaque characteristics. For clinical application, high spatial resolution, derived from optimal signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR), is paramount. Vessel wall MRI is expected to benefit from higher magnetic field strength. Therefore, the purposes of the present study were to develop an ultrahigh-field 7-T MRI hardware and protocols for vessel wall imaging of the carotid artery and to compare quantitative parameters of vessel wall morphology and image quality between 3-T and 7-T MRI. MATERIAL AND METHODS: Eighteen volunteers (11 men and 7 women; mean [SD] age, 29 [7] years) underwent MRI examinations at 7 T (using a custom-built surface transmit/receive coil of 15-cm diameter) and at 3 T (using a commercial phased-array coil with 2 flexible oval elements, 14 × 17 cm each). Magnetic resonance imaging of the left common carotid artery vessel wall was performed at 7 T with identical in-plane resolution as that of 3-T MRI (0.46 × 0.46 mm), providing transverse T1- and T2-weighted images. Blinded analysis of morphologic measurements (luminal area and vessel wall area), SNR for vessel wall (SNRVW), and the CNR between the lumen and the vessel wall were compared between 7 and 3 T. RESULTS: Morphologic carotid vessel wall measurements were comparable between 7 and 3 T for both T1-weighted images (luminal area: intraclass correlation [ICC], 0.81 and vessel wall area: ICC, 0.84) and T2-weighted images (luminal area: ICC, 0.97 and vessel wall area: ICC, 0.92). At 7 T, SNRVW and CNR were significantly higher compared with 3-T MRI for both T1- (P < 0.001) and T2-weighted images (P < 0.05), with gain factors ranging from 1.3 to 3.6. CONCLUSIONS: Ultrahigh-field 7-T MR carotid vessel wall imaging is feasible. 7-T MRI of the common carotid artery has comparable accuracy for determining luminal area and vessel wall area and has improved SNRVW and CNR compared with 3-T MRI. Therefore, ultrahigh-field 7-T vessel wall MRI may enable a more detailed assessment of plaque morphology.

Evaluation of sampling density on the accuracy of aortic pulse wave velocity from velocity-encoded MRI in patients with Marfan syndrome.

PURPOSE: To evaluate the effect of spatial (ie, number of sampling locations along the aorta) and temporal sampling density on aortic pulse wave velocity (PWV) assessment from velocity-encoded MRI in patients with Marfan syndrome (MFS). MATERIALS AND METHODS: Twenty-three MFS patients (12 men, mean age 36 ± 14 years) were included. Three PWV-methods were evaluated: 1) reference PWV(i.p.) from in-plane velocity-encoded MRI with dense temporal and spatial sampling; 2) conventional PWV(t.p.) from through-plane velocity-encoded MRI with dense temporal but sparse spatial sampling at three aortic locations; 3) EPI-accelerated PWV(t.p.) with sparse temporal but improved spatial sampling at five aortic locations with acceleration by echo-planar imaging (EPI). RESULTS: Despite inferior temporal resolution, EPI-accelerated PWV(t.p.) showed stronger correlation (r = 0.92 vs. r = 0.65, P = 0.03) with reference PWV(i.p.) in the total aorta, with less error (8% vs. 16%) and variation (11% vs. 27%) as compared to conventional PWV(t.p.) . In the aortic arch, correlation was comparable for both EPI-accelerated and conventional PWV(t.p.) with reference PWV(i.p.) (r = 0.66 vs. r = 0.67, P = 0.46), albeit 92% scan-time reduction by EPI-acceleration. CONCLUSION: Improving spatial sampling density by adding two acquisition planes along the aorta results in more accurate PWV assessment, even when temporal resolution decreases. For regional PWV assessment in the aortic arch, EPI-accelerated and conventional PWV assessment are comparably accurate. Scan-time reduction makes EPI-accelerated PWV assessment the preferred method of choice.

Positive remodeling on coronary computed tomography as a marker for plaque vulnerability on virtual histology intravascular ultrasound.

Coronary computed tomographic angiography allows direct evaluation of the vessel wall and thus positive remodeling, which is a marker of vulnerability. The purpose of this study was to assess the association between positive remodeling on computed tomography angiogram (CTA) and vulnerable plaque characteristics on virtual histologic intravascular ultrasound (VH IVUS) images. Forty-five patients (78% men, 58 ± 11 years old) underwent computed tomographic angiography followed by VH IVUS. On CTA, the remodeling index was determined for each lesion by a blinded observer using quantitative analysis. Positive remodeling was defined based on a remodeling index ≥1.0. Percent necrotic core and presence of thin-capped fibroatheroma (TCFA) were used as markers for plaque vulnerability on VH IVUS images. Ninety-nine atherosclerotic plaques were evaluated, of which 37 lesions (37.4%) were identified as having positive remodeling on CTA. Higher levels of plaque vulnerability were identified in lesions with positive remodeling compared to lesions without positive remodeling. Percent necrotic core was significantly higher in lesions with positive remodeling (15.7 ± 7.8%) compared to lesions without this characteristic (10.2 ± 7.2%, p <0.001). Furthermore, significantly more TCFA lesions were identified in positively remodeled lesions (n = 16, 43.2%) than in lesions without positive remodeling (n = 3, 4.8%, p <0.001). In conclusion, lesions with positive remodeling on CTA are associated with increased levels of plaque vulnerability on VH IVUS images including a higher percent necrotic core and a higher prevalence of TCFA. Thus evaluation of remodeling on CTA may provide a valuable marker for plaque vulnerability.