Measuring aortic pulse wave velocity using high-field cardiovascular magnetic resonance: comparison of techniques

Background

The assessment of arterial stiffness is increasingly used for evaluating patients with different cardiovascular diseases as the mechanical properties of major arteries are often altered. Aortic stiffness can be noninvasively estimated by measuring pulse wave velocity (PWV). Several methods have been proposed for measuring PWV using velocity-encoded cardiovascular magnetic resonance (CMR), including transit-time (TT), flow-area (QA), and cross-correlation (XC) methods. However, assessment and comparison of these techniques at high field strength has not yet been performed. In this work, the TT, QA, and XC techniques were clinically tested at 3 Tesla and compared to each other.

Methods

Fifty cardiovascular patients and six volunteers were scanned to acquire the necessary images. The six volunteer scans were performed twice to test inter-scan reproducibility. Patient images were analyzed using the TT, XC, and QA methods to determine PWV. Two observers analyzed the images to determine inter-observer and intra-observer variabilities. The PWV measurements by the three methods were compared to each other to test inter-method variability. To illustrate the importance of PWV using CMR, the degree of aortic stiffness was assessed using PWV and related to LV dysfunction in five patients with diastolic heart failure patients and five matched volunteers.

Results

The inter-observer and intra-observer variability results showed no bias between the different techniques. The TT and XC results were more reproducible than the QA; the mean (SD) inter-observer/intra-observer PWV differences were -0.12(1.3)/-0.04(0.4) for TT, 0.2(1.3)/0.09(0.9) for XC, and 0.6(1.6)/0.2(1.4) m/s for QA methods, respectively. The correlation coefficients (r) for the inter-observer/intra-observer comparisons were 0.94/0.99, 0.88/0.94, and 0.83/0.92 for the TT, XC, and QA methods, respectively. The inter-scan reproducibility results showed low variability between the repeated scans (mean (SD) PWV difference = -0.02(0.4) m/s and r = 0.96). The inter-method variability results showed strong correlation between the TT and XC measurements, but less correlation with QA: r = 0.95, 0.87, and 0.89, and mean (SD) PWV differences = -0.12(1.0), 0.8(1.7), and 0.65(1.6) m/s for TT-XC, TT-QA, and XC-QA, respectively. Finally, in the group of diastolic heart failure patient, PWV was significantly higher (6.3 ± 1.9 m/s) than in volunteers (3.5 ± 1.4 m/s), and the degree of LV diastolic dysfunction showed good correlation with aortic PWV.

Conclusions

In conclusion, while each of the studied methods has its own advantages and disadvantages, at high field strength, the TT and XC methods result in closer and more reproducible aortic PWV measurements, and the associated image processing requires less user interaction, than in the QA method. The choice of the analysis technique depends on the vessel segment geometry and available image quality.     

The relationship between modified pulse wave transit time and cardiovascular changes in isoflurane anesthetized dogs

Objective.To clarify the relationship between blood pressure andpulse wave transit time at the peripheral artery from the R wave of theelectrocardiogram (m-PWTT), the effects of cardiovascular interventions onthis relationship was evaluated. Methods.Ten mongrel dogs wereanesthetized by isoflurane inhalation, and catheter tip pressure transducerswere inserted into the ascending aorta and at the bifurcation of abdominalaorta to measure central and peripheral pulse wave arrival. Pulse wave arrivalat the ascending aorta from the R wave represents pre-ejection period (PEP)and pulse wave arrival between the ascending aorta and bifurcation of aortarepresents pulse wave transit time (PWTT), thus m-PWTT = PEP + PWTT.Hypertension was induced by the continuous infusion of dobutamine andphenylephrine, and hypotension was induced by deepening isoflurane anesthesia,acute blood loss and nitroglycerine infusion. The relationship between timingcomponents (PWTT, PEP, and m-PWTT) and blood pressure was recorded andanalyzed by using the least squares method. Results.The relationshipbetween timing components (PWTT, PEP and, m-PWTT) and blood pressure wassignificant and highly correlated. When the change in blood pressure was dueto the myocardial contractility, such as after dobutamine infusion, therelationship between all timing components and blood pressure was consistentand negative. However, when the change in blood pressure was due to thevasoactive agents, such as phenylephrine, the relationship between timingcomponents and blood pressure was dependent on the reflex change in PEP.Conclusions.Change in m-PWTT is a good parameter to predict bloodpressure changes, although the absolute blood pressure value cannot beobtained.     

Evaluation of aortic valve stenosis using cardiovascular magnetic resonance: comparison of an original semiautomated analysis of phase-contrast cardiovascular magnetic resonance with Doppler echocardiography

Background- Accurate quantification of aortic valve stenosis (AVS) is needed for relevant management decisions. However, transthoracic Doppler echocardiography (TTE) remains inconclusive in a significant number of patients. Previous studies demonstrated the usefulness of phase-contrast cardiovascular magnetic resonance (PC-CMR) in noninvasive AVS evaluation. We hypothesized that semiautomated analysis of aortic hemodynamics from PC-CMR might provide reproducible and accurate evaluation of aortic valve area (AVA), aortic velocities, and gradients in agreement with TTE. Methods and Results- We studied 53 AVS patients (AVA(TTE)=0.87±0.44 cm(2)) and 21 controls (AVA(TTE)=2.96±0.59 cm(2)) who had TTE and PC-CMR of aortic valve and left ventricular outflow tract on the same day. PC-CMR data analysis included left ventricular outflow tract and aortic valve segmentation, and extraction of velocities, gradients, and flow rates. Three AVA measures were performed: AVA(CMR1) based on Hakki formula, AVA(CMR2) based on continuity equation, AVA(CMR3) simplified continuity equation=left ventricular outflow tract peak flow rate/aortic peak velocity. Our analysis was reproducible, as reflected by low interoperator variability (<4.56±4.40%). Comparison of PC-CMR and TTE aortic peak velocities and mean gradients resulted in good agreement (r=0.92 with mean bias=-29±62 cm/s and r=0.86 with mean bias=-12±15 mm Hg, respectively). Although good agreement was found between TTE and continuity equation-based CMR-AVA (r>0.94 and mean bias=-0.01±0.38 cm(2) for AVA(CMR2), -0.09±0.28 cm(2) for AVA(CMR3)), AVA(CMR1) values were lower than AVA(TTE) especially for higher AVA (mean bias=-0.45±0.52 cm(2)). Besides, ability of PC-CMR to detect severe AVS, defined by TTE, provided the best results for continuity equation-based methods (accuracy >94%). Conclusions- Our PC-CMR semiautomated AVS evaluation provided reproducible measurements that accurately detected severe AVS and were in good agreement with TTE.     

Site-specific association between distal aortic pulse wave velocity and peripheral arterial stenosis severity: a prospective cardiovascular magnetic resonance study

Background

Vascular disease expression in one location may not be representative for disease severity in other vascular territories, however, strong correlation between disease expression and severity within the same vascular segment may be expected. Therefore, we hypothesized that aortic stiffening is more strongly associated with disease expression in a vascular territory directly linked to that aortic segment rather than in a more remote segment. We prospectively compared the association between aortic wall stiffness, expressed by pulse wave velocity (PWV), sampled in the distal aorta, with the severity of peripheral arterial occlusive disease (PAOD) as compared to atherosclerotic markers sampled in remote vascular territories such as PWV in the proximal aorta and the normalized wall index (NWI), representing the vessel wall thickness, of the left common carotid artery.

Methods

Forty-two patients (23 men; mean age 64±10 years) underwent velocity-encoded cardiovascular magnetic resonance (CMR) in the proximal and distal aorta, whole-body contrast-enhanced MR angiography (CE-MRA) and carotid vessel wall imaging with black-blood CMR in the work-up for PAOD. Strength of associations between aortic stiffness, carotid NWI and peripheral vascular stenosis grade were assessed and evaluated with multiple linear regression.

Results

Stenosis severity correlated well with PWV in the distal aorta (Pearson r_P=0.64, p<0.001, Spearman r_S=0.65, p<0.001) but to a lesser extent with PWV in the proximal aorta (r_P=0.48, p=0.002, r_S=0.22, p=0.18). Carotid NWI was not associated with peripheral stenosis severity (r_P=0.17, p=0.28, r_S=0.14, p=0.37) nor with PWV in the proximal aorta (r_P=0.22, p=0.17) nor in the distal aorta (r_P=0.21, p=0.18). Correlation between stenosis severity and distal aortic PWV remained statistically significant after correction for age and gender.

Conclusions

Distal aortic wall stiffness is more directly related to peripheral arterial stenosis severity than markers from more remote vascular territories such as proximal aortic wall stiffness or carotid arterial wall thickness. Site-specific evaluation of vascular disease may be required for full vascular risk estimation.     

Consistency of aortic distensibility and pulse wave velocity estimates with respect to the Bramwell-Hill theoretical model: a cardiovascular magnetic resonance study

Background

Arterial stiffness is considered as an independent predictor of cardiovascular mortality, and is increasingly used in clinical practice. This study aimed at evaluating the consistency of the automated estimation of regional and local aortic stiffness indices from cardiovascular magnetic resonance (CMR) data.

Results

Forty-six healthy subjects underwent carotid-femoral pulse wave velocity measurements (CF_PWV) by applanation tonometry and CMR with steady-state free-precession and phase contrast acquisitions at the level of the aortic arch. These data were used for the automated evaluation of the aortic arch pulse wave velocity (Arch_PWV), and the ascending aorta distensibility (AA_Distc, AA_Distb), which were estimated from ascending aorta strain (AA_Strain) combined with either carotid or brachial pulse pressure. The local ascending aorta pulse wave velocity AA_PWVc and AA_PWVb were estimated respectively from these carotid and brachial derived distensibility indices according to the Bramwell-Hill theoretical model, and were compared with the Arch_PWV. In addition, a reproducibility analysis of AA_PWV measurement and its comparison with the standard CF_PWV was performed. Characterization according to the Bramwell-Hill equation resulted in good correlations between Arch_PWV and both local distensibility indices AA_Distc (r = 0.71, p < 0.001) and AA_Distb (r = 0.60, p < 0.001); and between Arch_PWV and both theoretical local indices AA_PWVc (r = 0.78, p < 0.001) and AA_PWVb (r = 0.78, p < 0.001). Furthermore, the Arch_PWV was well related to CF_PWV (r = 0.69, p < 0.001) and its estimation was highly reproducible (inter-operator variability: 7.1%).

Conclusions

The present work confirmed the consistency and robustness of the regional index Arch_PWV and the local indices AA_Distc and AA_Distb according to the theoretical model, as well as to the well established measurement of CF_PWV, demonstrating the relevance of the regional and local CMR indices.     

Regional in vivo transit time measurements of aortic pulse wave velocity in mice with high-field CMR at 17.6 Tesla

Background

Transgenic mouse models are increasingly used to study the pathophysiology of human cardiovascular diseases. The aortic pulse wave velocity (PWV) is an indirect measure for vascular stiffness and a marker for cardiovascular risk.

Results

This study presents a cardiovascular magnetic resonance (CMR) transit time (TT) method that allows the determination of the PWV in the descending murine aorta by analyzing blood flow waveforms. Systolic flow pulses were recorded with a temporal resolution of 1 ms applying phase velocity encoding. In a first step, the CMR method was validated by pressure waveform measurements on a pulsatile elastic vessel phantom. In a second step, the CMR method was applied to measure PWVs in a group of five eight-month-old apolipoprotein E deficient (ApoE^(-/-)) mice and an age matched group of four C57Bl/6J mice. The ApoE^(-/-) group had a higher mean PWV (PWV = 3.0 ± 0.6 m/s) than the C57Bl/6J group (PWV = 2.4 ± 0.4 m/s). The difference was statistically significant (p = 0.014).

Conclusions

The findings of this study demonstrate that high field CMR is applicable to non-invasively determine and distinguish PWVs in the arterial system of healthy and diseased groups of mice.     

Bramwell-Hill modeling for local aortic pulse wave velocity estimation: a validation study with velocity-encoded cardiovascular magnetic resonance and invasive pressure assessment

Background

The Bramwell-Hill model describes the relation between vascular wall stiffness expressed in aortic distensibility and the pulse wave velocity (PWV), which is the propagation speed of the systolic pressure wave through the aorta. The main objective of this study was to test the validity of this model locally in the aorta by using PWV-assessments based on in-plane velocity-encoded cardiovascular magnetic resonance (CMR), with invasive pressure measurements serving as the gold standard.

Methods

Seventeen patients (14 male, 3 female, mean age ± standard deviation = 57 ± 9 years) awaiting cardiac catheterization were prospectively included. During catheterization, intra-arterial pressure measurements were obtained in the aorta at multiple locations 5.8 cm apart. PWV was determined regionally over the aortic arch and locally in the proximal descending aorta. Subsequently, patients underwent a CMR examination to measure aortic PWV and aortic distention. Distensibility was determined locally from the aortic distension at the proximal descending aorta and the pulse pressure measured invasively during catheterization and non-invasively from brachial cuff-assessment. PWV was determined regionally in the aortic arch using through-plane and in-plane velocity-encoded CMR, and locally at the proximal descending aorta using in-plane velocity-encoded CMR. Validity of the Bramwell-Hill model was tested by evaluating associations between distensibility and PWV. Also, theoretical PWV was calculated from distensibility measurements and compared with pressure-assessed PWV.

Results

In-plane velocity-encoded CMR provides stronger correlation (p = 0.02) between CMR and pressure-assessed PWV than through-plane velocity-encoded CMR (r = 0.69 versus r = 0.26), with a non-significant mean error of 0.2 ± 1.6 m/s for in-plane versus a significant (p = 0.006) error of 1.3 ± 1.7 m/s for through-plane velocity-encoded CMR. The Bramwell-Hill model shows a significantly (p = 0.01) stronger association between distensibility and PWV for local assessment (r = 0.8) than for regional assessment (r = 0.7), both for CMR and for pressure-assessed PWV. Theoretical PWV is strongly correlated (r = 0.8) with pressure-assessed PWV, with a statistically significant (p = 0.04) mean underestimation of 0.6 ± 1.1 m/s. This theoretical PWV-estimation is more accurate when invasively-assessed pulse pressure is used instead of brachial cuff-assessment (p = 0.03).

Conclusions

CMR with in-plane velocity-encoding is the optimal approach for studying Bramwell-Hill associations between local PWV and aortic distensibility. This approach enables non-invasive estimation of local pulse pressure and distensibility.     

Multidirectional flow analysis by cardiovascular magnetic resonance in aneurysm development following repair of aortic coarctation

Aneurysm formation is a life-threatening complication after operative therapy in coarctation. The identification of patients at risk for the development of such secondary pathologies is of high interest and requires a detailed understanding of the link between vascular malformation and altered hemodynamics. The routine morphometric follow-up by magnetic resonance angiography is a well-established technique. However, the intrinsic sensitivity of magnetic resonance (MR) towards motion offers the possibility to additionally investigate hemodynamic consequences of morphological changes of the aorta.We demonstrate two cases of aneurysm formation 13 and 35 years after coarctation surgery based on a Waldhausen repair with a subclavian patch and a Vosschulte repair with a Dacron patch, respectively. Comprehensive flow visualization by cardiovascular MR (CMR) was performed using a flow-sensitive, 3-dimensional, and 3-directional time-resolved gradient echo sequence at 3T. Subsequent analysis included the calculation of a phase contrast MR angiography and color-coded streamline and particle trace 3D visualization. Additional quantitative evaluation provided regional physiological information on blood flow and derived vessel wall parameters such as wall shear stress and oscillatory shear index.The results highlight the individual 3D blood-flow patterns associated with the different vascular pathologies following repair of aortic coarctation. In addition to known factors predisposing for aneurysm formation after surgical repair of coarctation these findings indicate the importance of flow sensitive CMR to follow up hemodynamic changes with respect to the development of vascular disease.     

Hemodynamic predictors of aortic dilatation in bicuspid aortic valve by velocity-encoded cardiovascular magnetic resonance

Background

Congenital Bicuspid Aortic Valve (BAV) is a significant risk factor for serious complications including valve dysfunction, aortic dilatation, dissection, and sudden death. Clinical tools for identification and monitoring of BAV patients at high risk for development of aortic dilatation, an early complication, are not available.

Methods

This paper reports an investigation in 18 pediatric BAV patients and 10 normal controls of links between abnormal blood flow patterns in the ascending aorta and aortic dilatation using velocity-encoded cardiovascular magnetic resonance. Blood flow patterns were quantitatively expressed in the angle between systolic left ventricular outflow and the aortic root channel axis, and also correlated with known biochemical markers of vessel wall disease.

Results

The data confirm larger ascending aortas in BAV patients than in controls, and show more angled LV outflow in BAV (17.54 ± 0.87 degrees) than controls (10.01 ± 1.29) (p = 0.01). Significant correlation of systolic LV outflow jet angles with dilatation was found at different levels of the aorta in BAV patients STJ: r = 0.386 (N = 18, p = 0.048), AAO: r = 0.536 (N = 18, p = 0.022), and stronger correlation was found with patients and controls combined into one population: SOV: r = 0.405 (N = 28, p = 0.033), STJ: r = 0.562 (N = 28, p = 0.002), and AAO r = 0.645 (N = 28, p < 0.001). Dilatation and the flow jet angle were also found to correlate with plasma levels of matrix metallo-proteinase 2.

Conclusions

The results of this study provide new insights into the pathophysiological processes underlying aortic dilatation in BAV patients. These results show a possible path towards the development of clinical risk stratification protocols in order to reduce morbidity and mortality for this common congenital heart defect.     

监测脉搏波传导时间的无线传感器网络系统术

随着无线传感器网络技术的出现,低负荷医学监测技术发生了革命性的变化.文章运用无线传感器网络技术设计了心电和脉搏波无线传感器组成整个监测系统,同步测量头部颞浅动脉脉搏波信号和体表心电信号,以及计算脉搏波传导时间.此心电和脉搏波无线传感器的体积小,且采用纽扣电池供电,彼此之间的时间同步精度小于l ms.计算出的脉搏波传导时间随缓慢深呼吸而相应变化.提示由具有体积小、功耗低和时间同步精度岛等特点的心电和脉搏波无线传感器组成的监测系统能够在作业条件下连续低负荷监测脉搏波传导时间.     

Regional assessment of carotid artery pulse wave velocity using compressed sensing accelerated high temporal resolution 2D CINE phase contrast cardiovascular magnetic resonance

Background

Cardiovascular magnetic resonance (CMR) allows for non-invasive assessment of arterial stiffness by means of measuring pulse wave velocity (PWV). PWV can be calculated from the time shift between two time-resolved flow curves acquired at two locations within an arterial segment. These flow curves can be derived from two-dimensional CINE phase contrast CMR (2D CINE PC CMR). While CMR-derived PWV measurements have proven to be accurate for the aorta, this is more challenging for smaller arteries such as the carotids due to the need for both high spatial and temporal resolution. In this work, we present a novel method that combines retrospectively gated 2D CINE PC CMR, high temporal binning of data and compressed sensing (CS) reconstruction to accomplish a temporal resolution of 4 ms. This enables accurate flow measurements and assessment of PWV in regional carotid artery segments.

Methods

Retrospectively gated 2D CINE PC CMR data acquired in the carotid artery was binned into cardiac frames of 4 ms length, resulting in an incoherently undersampled k_y-t-space with a mean undersampling factor of 5. The images were reconstructed by a non-linear CS reconstruction using total variation over time as a sparsifying transform. PWV values were calculated from flow curves by using foot-to-foot and cross-correlation methods. Our method was validated against ultrasound measurements in a flow phantom setup representing the carotid artery. Additionally, PWV values of two groups of 23 young (30?±?3 years, 12 [52%] women) and 10 elderly (62?±?10 years, 5 [50%] women) healthy subjects were compared using the Wilcoxon rank-sum test.

Results

Our proposed method produced very similar flow curves as those measured using ultrasound at 1 ms temporal resolution. Reliable PWV estimation proved possible for transit times down to 7.5 ms. Furthermore, significant differences in PWV values between healthy young and elderly subjects were found (4.7?±?1.0 m/s and 7.9?±?2.4 m/s, respectively; p?<?0.001) in accordance with literature.

Conclusions

Retrospectively gated 2D CINE PC CMR with CS allows for high spatiotemporal resolution flow measurements and accurate regional carotid artery PWV calculations. We foresee this technique will be valuable in protocols investigating early development of carotid atherosclerosis.

     

Monitoring of reactive hyperemia using photoplethysmographic pulse amplitude and transit time

Background: Peripheral arterial tonometry and Ultrasound measurement of flow mediated dilation have been the widely reported noninvasive techniques to assess vasodilation during reactive hyperemia (RH). Objective: Simultaneous monitoring of dilatation and tone of the vasculature during RH induced by venous occlusion (VO) and arterial occlusion (AO) has been presently attempted using simple noninvasive measures of photoplethysmography (PPG). Methods: Finger-PPG characteristics that include pulse timings, amplitude, upstroke-slope and pulse transit time (PTT) were studied before (1 min), post-VO (5 min) and post-AO (5 min) in 11 healthy volunteers. Results: PPG amplitude was significantly increased to maximum at 2nd min of post-AO (1.28±0.11 vs. 1.0 nu, P<0.05) as compared to the baseline; meanwhile, no significant changes (P>0.05) in PPG amplitude was observed during post-VO. Tremendous increase in PTT was evident at 1st min of post-AO (196.6±3.3 vs. 185.3±3.6 ms, P<0.0001) and was maintained significantly longer through 1–5 min of post-AO. Relatively small but significant increase in PTT was noticed only at 1st min of post-VO (193.9±6.8 vs. 189.6±6.2 ms, P<0.0001), followed by an immediate recovery to baseline by 2nd min of post-VO. The increase in PTT (i.e. ΔPTT) was higher at 1st min of post-AO (11.4±1.3 vs. 4.3±1.1 ms) as compared to post-VO. Conclusion: Results suggests that PTT response reflects the myogenic components in the early part of RH and PPG amplitude response reflects the metabolic component reinforcing the later course of RH. PPG amplitude and PTT can be used to quantify the changes in diameter and tone of the vessel wall, respectively during RH. The collective responses of PPG amplitude and PTT can be more appropriate to facilitate PPG technique for monitoring of vasodilation caused by RH.     

Unravelling cardiovascular disease using four dimensional flow cardiovascular magnetic resonance

Knowledge of normal and abnormal flow patterns in the human cardiovascular system increases our understanding of normal physiology and may help unravel the complex pathophysiological mechanisms leading to cardiovascular disease. Four-dimensional (4D) flow cardiovascular magnetic resonance (CMR) has emerged as a suitable technique that enables visualization of in vivo blood flow patterns and quantification of parameters that could potentially be of prognostic value in the disease process. In this review, current image processing tools that are used for comprehensive visualization and quantification of blood flow and energy distribution in the heart and great vessels will be discussed. Also, imaging biomarkers extracted from 4D flow CMR will be reviewed that have been shown to distinguish between normal and abnormal flow patterns. Furthermore, current applications of 4D flow CMR in the heart and great vessels will be discussed, showing its potential as an additional diagnostic modality which could aid in disease management and timing of surgical intervention.     

Assessment of mitral bioprostheses using cardiovascular magnetic resonance

Background

The orifice area of mitral bioprostheses provides important information regarding their hemodynamic performance. It is usually calculated by transthoracic echocardiography (TTE), however, accurate and reproducible determination may be challenging. Cardiovascular magnetic resonance (CMR) has been proven as an accurate alternative for assessing aortic bioprostheses. However, whether CMR can be similarly applied for bioprostheses in the mitral position, particularly in the presence of frequently coincident arrhythmias, is unclear. The aim of the study is to test the feasibility of CMR to evaluate the orifice area of mitral bioprostheses.

Methods

CMR planimetry was performed in 18 consecutive patients with mitral bioprostheses (n = 13 Hancock^®, n = 4 Labcore^®, n = 1 Perimount^®; mean time since implantation 4.5 ± 3.9 years) in an imaging plane perpendicular to the transprosthetic flow using steady-state free-precession cine imaging under breath-hold conditions on a 1.5T MR system. CMR results were compared with pressure half-time derived orifice areas obtained by TTE.

Results

Six subjects were in sinus rhythm, 11 in atrial fibrillation, and 1 exhibited frequent ventricular extrasystoles. CMR image quality was rated as good in 10, moderate in 6, and significantly impaired in 2 subjects. In one prosthetic type (Perimount^®), strong stent artifacts occurred. Orifice areas by CMR (mean 2.1 ± 0.3 cm²) and TTE (mean 2.1 ± 0.3 cm²) correlated significantly (r = 0.94; p < 0.001). Bland-Altman analysis showed a 95% confidence interval from -0.16 to 0.28 cm² (mean difference 0.06 ± 0.11 cm²; range -0.1 to 0.3 cm²). Intra- and inter-observer variabilities of CMR planimetry were 4.5 ± 2.9% and 7.9 ± 5.2%.

Conclusions

The assessment of mitral bioprostheses using CMR is feasible even in those with arrhythmias, providing orifice areas with close agreement to echocardiography and low observer dependency. Larger samples with a greater variety of prosthetic types and more cases of prosthetic dysfunction are required to confirm these preliminary results.     

Ultra-short echo time cardiovascular magnetic resonance of atherosclerotic carotid plaque

Background

Multi-contrast weighted cardiovascular magnetic resonance (CMR) allows detailed plaque characterisation and assessment of plaque vulnerability. The aim of this preliminary study was to show the potential of Ultra-short Echo Time (UTE) subtraction MR in detecting calcification.

Methods

14 ex-vivo human carotid arteries were scanned using CMR and CT, prior to histological slide preparation. Two images were acquired using a double-echo 3D UTE pulse, one with a long TE and the second with an ultra-short TE, with the same TR. An UTE subtraction (ΔUTE) image containing only ultra-short T2 (and T2*) signals was obtained by post-processing subtraction of the 2 UTE images. The ΔUTE image was compared to the conventional 3D T1-weighted sequence and CT scan of the carotid arteries.

Results

In atheromatous carotid arteries, there was a 71% agreement between the high signal intensity areas on ΔUTE images and CT scan. The same areas were represented as low signal intensity on T1W and areas of void on histology, indicating focal calcification. However, in 15% of all the scans there were some incongruent regions of high intensity on ΔUTE that did not correspond with a high intensity signal on CT, and histology confirmed the absence of calcification.

Conclusions

We have demonstrated that the UTE sequence has potential to identify calcified plaque. Further work is needed to fully understand the UTE findings.     

Impact of asymmetry on measurements of the aortic root using cardiovascular magnetic resonance imaging in patients with a bicuspid aortic valve

To assess the impact of aortic root asymmetry on the relationship between aortic dimensions derived from two-dimensional transthoracic echocardiography (TTE) as compared with cross-sectional cardiovascular magnetic resonance (CMR) imaging in adults with a bicuspid aortic valve (BAV). Maximal CMR cross-sectional aortic measurements at the level of the sinuses of Valsalva, including cusp–commissure, cusp–cusp diameters and aortic root areas, from 68 consecutive patients (65 % male) were retrospectively analyzed. The degree of aortic root asymmetry on CMR was expressed using the coefficient of variance of the root diameters in each dimension for an individual (CoeffVi) as compared with the median of the entire population (CoeffVp) and asymmetry was defined as CoeffVi > CoeffVp. Values obtained from CMR were compared with standard root measurements using TTE from contemporary studies (48 patients, 71 %). Reproducibility of CMR measurements was assessed using the intra-class correlation coefficient (ICC). Echocardiography systematically underestimated aortic root dimensions in comparison with CMR, particularly in asymmetric roots with cusp–cusp measurements in systole (bias: ?4.9 mm). Best agreement between modalities existed in symmetric roots with cusp–commissure measurements in diastole (bias: ?0.01 mm). CMR measurements showed excellent intra-reader (ICC ≥ 0.98) and moderate inter-reader (ICC range 0.37–0.95) reproducibility, particularly aortic root area (inter/intra-reader ICC ≥ 0.94). In comparison to cross-sectional CMR diameters, standard TTE measurements consistently underestimates maximum aortic root diameter in adults with a BAV and aortic root asymmetry further decreases the agreement between CMR and TTE. CMR-derived aortic root measurements are reproducible and aortic root area showed the best reproducibility.