A method for the determination of proximal pulmonary vein size using contrast-enhanced magnetic resonance angiography.

OBJECTIVES: We sought to develop a reproducible method for characterizing the anatomy of the proximal pulmonary veins. BACKGROUND: Contrast-enhanced three-dimensional magnetic resonance angiography (CE-MRA) is a commonly requested test before and after radiofrequency ablation for the treatment of atrial fibrillation. While CE-MRA readily visualizes the pulmonary veins, there is no standardized method for determining their size and cross-sectional anatomy. METHODS: Data for 24 consecutive patients referred for pulmonary vein CE-MRA before an elective ablation procedure for the treatment of atrial fibrillation were analyzed. Detailed measurements of the pulmonary vein diameter, circumference, and cross-sectional area were obtained at three locations: the juncture of the pulmonary vein with the left atrium (LA) (position 1J), the narrowest segment within 5 mm of the juncture (position 2(5mm)), and at the location in the sagittal plane at which the pulmonary veins separate from the LA and from each other (position 3Sag). Intraobserver and interobserver variabilities were also determined for each method. RESULTS: The left lower pulmonary vein was significantly smaller than the other pulmonary veins at positions 1J and 2(5mm) (p<0.05). The right upper pulmonary vein was significantly larger than the other pulmonary vein at position 3Sag (p<0.05). At positions 1J and 2(5mm), the diameter had a low correlation with the circumference and cross-sectional area. At position 3Sag, the major and minor axis dimensions had a very high correlation with the circumference and cross-sectional area. The intraobserver and interobserver variabilities were substantially lower (better) for position 3Sag. CONCLUSIONS: Pulmonary vein diameter measurements are highly variable and do not reflect true anatomic variation in cross-sectional anatomy. A sagittal method of determining pulmonary vein size was highly reproducible and may therefore be advantageous for use in patients likely to need serial examinations.     

Free breathing contrast-enhanced time-resolved magnetic resonance angiography in pediatric and adult congenital heart disease

Background

Contrast enhanced magnetic resonance angiography (MRA) is generally performed during a long breath-hold (BH), limiting its utility in infants and small children. This study proposes a free-breathing (FB) time resolved MRA (TRA) technique for use in pediatric and adult congenital heart disease (CHD).

Methods

A TRA sequence was developed by combining spiral trajectories with sensitivity encoding (SENSE, x4 kx-ky and x2 kz) and partial Fourier (75% in kz). As no temporal data sharing is used, an independent 3D data set was acquired every ~1.3s, with acceptable spatial resolution (~2.3x2.3x2.3mm). The technique was tested during FB over 50 consecutive volumes. Conventional BH-MRA and FB-TRA data was acquired in 45 adults and children with CHD. We calculated quantitative image quality for both sequences. Diagnostic accuracy was assessed in all patients from both sequences. Additionally, vessel measurements were made at the sinotubular junction (N = 43), proximal descending aorta (N = 43), descending aorta at the level of the diaphragm (N = 43), main pulmonary artery (N = 35), left pulmonary artery (N = 35) and the right pulmonary artery (N = 35). Intra and inter observer variability was assessed in a subset of 10 patients.

Results

BH-MRA had significantly higher homogeneity in non-contrast enhancing tissue (coefficient of variance, P <0.0001), signal-to-noise ratio (P <0.0001), contrast-to-noise ratio (P <0.0001) and relative contrast (P = 0.02) compared to the FB-TRA images. However, homogeneity in the vessels was similar in both techniques (P = 0.52) and edge sharpness was significantly (P <0.0001) higher in FB-TRA compared to BH-MRA. BH-MRA provided overall diagnostic accuracy of 82%, and FB-TRA of 87%, with no statistical difference between the two sequences (P = 0.77). Vessel diameter measurements showed excellent agreement between the two techniques (r = 0.98, P <0.05), with no bias (0.0mm, P = 0.71), and clinically acceptable limits of agreement (-2.7 to +2.8mm). Inter and intra observer reproducibility showed good agreement of vessel diameters (r>0.988, P<0.0001), with negligible biases (between -0.2 and +0.1mm) and small limits of agreement (between -2.4 and +2.5mm).

Conclusions

We have described a FB-TRA technique that is shown to enable accurate diagnosis and vessel measures compared to conventional BH-MRA. This simplifies the MRA technique and will enable angiography to be performed in children and adults whom find breath-holding difficult.

Electronic supplementary material

The online version of this article (doi:10.1186/s12968-015-0138-9) contains supplementary material, which is available to authorized users.     

Towards highly accelerated Cartesian time-resolved 3D flow cardiovascular magnetic resonance in the clinical setting

Background

The clinical applicability of time-resolved 3D flow cardiovascular magnetic resonance (CMR) remains compromised by the long scan times associated with phase-contrast imaging. The present work demonstrates the applicability of 8-fold acceleration of Cartesian time-resolved 3D flow CMR in 10 volunteers and in 9 patients with different congenital heart diseases (CHD). It is demonstrated that accelerated 3D flow CMR data acquisition and image reconstruction using k-t PCA (principal component analysis) can be implemented into clinical workflow and results are sufficiently accurate relative to conventional 2D flow CMR to permit for comprehensive flow quantification in CHD patients.

Methods

The fidelity of k-t PCA was first investigated on retrospectively undersampled data for different acceleration factors and compared to k-t SENSE and fully sampled reference data. Subsequently, k-t PCA with 8-fold nominal undersampling was applied on 10 healthy volunteers and 9 CHD patients on a clinical 1.5 T MR scanner. Quantitative flow validation was performed in vessels of interest on the 3D flow datasets and compared to 2D through-plane flow acquisitions. Particle trace analysis was used to qualitatively visualise flow patterns in patients.

Results

Accelerated time-resolved 3D flow data were successfully acquired in all subjects with 8-fold nominal scan acceleration. Nominal scan times excluding navigator efficiency were on the order of 6 min and 7 min in patients and volunteers. Mean differences in stroke volume in selected vessels of interest were 2.5 ± 8.4 ml and 1.63 ± 4.8 ml in volunteers and patients, respectively. Qualitative flow pattern analysis in the time-resolved 3D dataset revealed valuable insights into hemodynamics including circular and helical patterns as well as flow distributions and origin in the Fontan circulation.

Conclusion

Highly accelerated time-resolved 3D flow using k-t PCA is readily applicable in clinical routine protocols of CHD patients. Nominal scan times of 6 min are well tolerated and allow for quantitative and qualitative flow assessment in all great vessels.     

Role of contrast-enhanced 3D magnetic resonance portography in evaluating portal venous system compared with color Doppler ultrasonography

Aim The purpose of this study was to evaluate the capability of contrast-enhanced three-dimensional (3D) MR portography in detecting abnormal findings associated with the portal venous system compared with the results of color Doppler ultrasonography (CDUS). Materials and methods MR portography findings were retrospectively compared with the results of CDUS examinations in 161 patients, who were suspected of having portal venous system abnormalities. Portal venous vessels were divided into main 5 groups including the main portal vein, its left and right intrahepatic branches, splenic vein and superior mesenteric vein. Imaging findings were classified as normal, occluded, or partially thrombosed. Results of clinical and imaging follow-up examinations including CDUS, MR portography or angiography, if available, were used as a proof of final diagnosis. The potential sites of varicose veins and collateral vessels were also examined by both imaging methods. Results Vascular abnormalities were identified in 79 of 161 patients. There was a statistically significant agreement between the results of MR portography and CDUS in evaluating portal venous system (κ = 0.871, P < 0.05). The sensitivity of MR portography was slightly superior to CDUS in detecting partially thrombosis and occlusion in the main portal venous vessels. In addition, MR portograms were superior to CDUS in the management of patients with portal hypertension by identifying portosystemic collaterals more adequately, and clearly demonstrated portal venous vessels that cannot be visualized at CDUS. Conclusion Results of present study indicates that contrast-enhanced 3D MR portography is well suited and superior to CDUS in the management of patients with portal hypertension.     

Validation of contrast-enhanced time-resolved magnetic resonance angiography in pre-ablation planning in patients with atrial fibrillation: comparison with traditional technique

Bolus timing is critical to optimal magnetic resonance angiography (MRA) acquisitions but can be challenging in some patients. Our purpose was to evaluate whether contrast-enhanced time-resolved magnetic resonance angiography (TR-MRA), a dynamic multiphase sequence that does not rely on bolus timing, is a viable alternative method to conventional 3D fast-long angle shot contrast-enhanced magnetic resonance angiography (CE-MRA). Coronal subtracted conventional CE-MRA images in 50 consecutive patients presenting for pre-atrial fibrillation ablation pulmonary venous (PV) mapping were compared with 50 TR-MRA images performed in 50 subsequent patients. The TR-MRA protocol was modified to optimize spatial resolution with slightly reduced temporal resolution (6.1 s scan time). Three experienced readers evaluated each scan’s image quality and relative left atrial (LA) opacification based on a 4-point scale and diagnostic PV visualization in a binary fashion. Additionally, LA signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and PV dimensions were measured for both techniques. TR-MRA had significantly higher overall image quality (3.10?±?0.69 vs. 2.42?±?0.69, p?<?0.0001), and LA opacification scores (3.33?±?0.70 vs. 2.15?±?1.13, p?<?0.0001) compared to CE-MRA. The proportion of diagnostically visualized pulmonary veins was 137/150 (91%) in the CE-MRA group vs. 147/150 (98%) with TR-MRA (p?=?0.010). Both SNR and CNR were higher with TR-MRA vs. CE-MRA (277.9?±?48.9 vs. 106.8?±?41, p?=?0.002 and 100.3?±?41.7 vs. 70.7?±?48.0, p?=?0.002, respectively). Inter-reader variance of individual PV measurements for each of the MR techniques ranged between 0.62 and 1.47 mm and the ICC for vein measurements was higher with TR-MRA (range: 0.62–0.81) compared to CE-MRA (range: 0.47–0.64). TR-MRA, modified to maximize spatial resolution, offers an alternative method for performing high quality MRA examinations in patients with AF. TR-MRA offers greater overall image quality, PV visualization, and similarly reproducible PV measurements compared to traditional CE-MRA, without the challenges of proper bolus timing.     

Reproducibility of free-breathing cardiovascular magnetic resonance coronary angiography.

OBJECTIVE: Contemporary free-breathing non contrast enhanced cardiovascular magnetic resonance angiography (CMRA) was qualitatively and quantitatively evaluated to ascertain the reproducibility of the method for coronary artery luminal dimension measurements. SUBJECTS AND METHODS: Twenty-two healthy volunteers (mean age 32 +/- 7 years, 12 males) without coronary artery disease were imaged at 2 centers (1 each in Europe and North America) using navigator-gated and corrected SSFP CMRA on a commercial whole body 1.5T System. Repeat images of right (RCA, n = 21), left anterior descending (LAD, n = 14) and left circumflex (LCX, n = 14) coronary arteries were obtained in separate sessions using identical scan protocol and imaging parameters. True visible vessel length, signal-to-noise (SNR), contrast-to-noise ratios (CNR) and the average luminal diameter over the first 4 cm of the vessel were measured. Intra-observer, inter-observer and inter-scan reproducibility of coronary artery luminal diameter were determined using Pearson's correlation, Bland-Altman analysis and intraclass correlation coefficients (ICC). RESULTS: CNR, SNR and the mean length of the RCA, LAD and LCX imaged for original and repeat scans were not significantly different (all p > 0.30). There was a high degree of intra-observer, inter-observer and inter-scan agreements for RCA, LAD and LCX luminal diameter respectively on Bland-Altman and ICC analysis (ICC's for RCA: 0.98. 0.98 and 0.86; LAD: 0.89, 0.89 and 0.63; LCX: 0.95, 0.94 and 0.79). CONCLUSION: In a 2-center study, we demonstrate that free-breathing 3D SSFP CMRA can visualize long continuous segments of coronary vessels with highly reproducible measurements of luminal diameter.     

Comparison of gadolinium-enhanced cardiovascular magnetic resonance angiography with high-resolution black blood cardiovascular magnetic resonance for assessing carotid artery stenosis.

PURPOSE: Carotid angiography is used to assess stroke risk, but it cannot reliably characterize plaque burden because the vessel remodels during plaque formation. High-resolution black blood cardiovascular magnetic resonance (BBCMR) depicts the outer wall thereby providing a truer estimate of plaque size. We compared carotid stenosis by gadolinium enhancement cardiovascular magnetic resonance angiography (CMRA) versus high-resolution BBCMR. METHODS: Twenty-four subjects (M:F = 20:4; ages 57-83 years) with carotid atherosclerosis underwent CMRA and transaxial BBCMR through the stenosis. Area and diameter stenosis measurements by NASCET criteria using CMRA images were compared to area stenosis measurements based on outer wall and lumen contours drawn on corresponding BBCMR images. RESULTS: Area stenosis by CMRA correlated with area stenosis by BBCMR (r = 0.77; 95% CI: 0.58, 0.89). BBCMR values exceeded corresponding CMRA area measurements in 20 of 24 cases, with the remainder being highly stenotic (> 90%). CONCLUSION: CMRA yields lower estimates of luminal narrowing compared to BBCMR, which delineates the outer wall and accounts for vascular remodeling. BBCMR could serve as a new measure of narrowing to guide management, but prospective studies are needed to better understand the clinical implications of this new scale of disease.     

Mapping right ventricular myocardial mechanics using 3D cine DENSE cardiovascular magnetic resonance

Background

The mechanics of the right ventricle (RV) are not well understood as studies of the RV have been limited. This is, in part, due to the RV''s thin wall, asymmetric geometry and irregular motion. However, the RV plays an important role in cardiovascular function. This study aims to describe the complex mechanics of the healthy RV using three dimensional (3D) cine displacement encoding with stimulated echoes (DENSE) cardiovascular magnetic resonance (CMR).

Methods

Whole heart 3D cine DENSE data were acquired from five healthy volunteers. Tailored post-processing algorithms for RV mid-wall tissue tracking and strain estimation are presented. A method for sub-dividing the RV into four regions according to anatomical land marks is proposed, and the temporal evolution of strain was assessed in these regions.

Results

The 3D cine DENSE tissue tracking methods successfully capture the motion and deformation of the RV at a high spatial resolution in all volunteers. The regional Lagrangian peak surface strain and time to peak values correspond with previous studies using myocardial tagging, DENSE and strain encoded CMR. The inflow region consistently displays lower peak strains than the apical and outflow regions, and the time to peak strains suggest RV mechanical activation in the following order: inflow, outflow, mid, then apex.

Conclusions

Model-free techniques have been developed to study the myocardial mechanics of the RV at a high spatial resolution using 3D cine DENSE CMR. The consistency of the regional RV strain patterns across healthy subjects is encouraging and the techniques may have clinical utility in assessing disrupted RV mechanics in the diseased heart.     

小腿远端动脉CE MRA成像参数的优化

周围血管闭塞性疾病患者要实施远端动脉分流术挽救缺血肢体,就必须获得高质量的小腿远端动脉图像。作为无创而实用的方法,CE MRA技术是评价周围远端小血管有价值的手段。但由于远端动脉管径小，对比剂到达所需时间长，应用团注跟踪连续三站CE MRA成像时，小腿远端动脉图像难以获得最佳质量。本研究通过应用高分辨率矩阵、减影和零填充技术，对小腿远端动脉图像质量进行评价。     

磁共振增强血管成像检测扫描延迟时间的探讨

目的 探讨磁共振增强血管成像(CEMRA)检测扫描延迟时间的可行性及其临床应用价值.方法 20例健康成人志愿者行循环时间(TT)和主动脉强化峰值持续时间(DPE)血管成像扫描时间测试,对注射速度时间TT.主动脉峰值信号(SPE)和DPE与延迟注射时间(TI)的差值(△T),分别获取不同注射速度及延迟注射时间CEMRA原始图信噪比及CEMRA影像.同时对18例主动脉病变患者行三维稳态快速激发序列(3DFISP)CEMRA.结果 20例健康成人组CEMRA图像清晰.主动脉走向显示清楚.18例主动脉病变组CEMRA图像清晰,对大动脉炎.颈动脉变窄,腹主动脉管腔扩张,走行扭曲,主动脉弓和胸主动脉内膜撕裂,胸腹主动瘤,主动脉病变大小,范围及主动脉各大分支动脉显示清楚.结论 磁共振灌注血管成像检测扫描延迟时间在理论、技术上有较高价值,充分满足影像诊断及临床应用.     

Whole-body contrast-enhanced magnetic resonance angiography: new advances at 3.0 T

During the past decade, technical improvements and numerous advances in scanner hardware and software have significantly improved image quality, speed, and reliability of 3-dimensional (3-D) contrast-enhanced magnetic resonance angiography (CE-MRA). The accuracy of CE-MRA is now comparable with that of computed tomography angiography or even conventional catheter angiography.Peripheral vascular disease (PVD) accounts for 50,000 to 60,000 cases of percutaneous transluminal angioplasty and for about 100,000 cases of amputation annually in the United States. Proper treatment of the arterial disease requires a comprehensive assessment of the underlying vascular morphology because it is crucial to localize and gauge the severity of arterial lesions for further therapeutic decision making.Contrast-enhanced magnetic resonance angiography has been widely implemented in noninvasive evaluation of PVD with high diagnostic accuracy. The lack of ionizing radiation and the use of contrast agent with relatively small potential nephrotoxicity in population of PVD with high prevalence of renal impairment are the appealing features for broad acceptance of CE-MRA in initial diagnosis and repeated follow-up studies of patients with PVD.The minimum anatomical coverage for evaluation of PVD comprises the aortic bifurcation to the ankles; however, because of the systemic nature of atherosclerosis hypertension, renal or cerebrovascular disease frequently coexist. Thus, many clinicians regard evaluation of the whole-body arterial vasculature as desirable.     

Evaluation of coronary arterial stenoses using 2D magnetic resonance coronary angiography

This study investigated the usefulness and limitations of magnetic resonance coronary angiography (MRCA). MRCA was performed with an electrocardiographically gated gradient echo sequence with k-space segmentation. Coronary angiography (CAG) was performed using a conventional system. We had three protocols. In protocol one, 160 consecutive patients (279 coronary arteries) who underwent initial CAG for diagnosing coronary artery disease were enrolled. Out of the 279 coronary arteries, 235 arteries (84.2%) were visualised with an image quality suitable for further analysis. In these 235 arteries, the validity for diagnosing over 75% arterial stenosis was 98%, and sensitivity and specificity was 79%. In protocol two, 48 stenoses were evaluated for restenosis after balloon angioplasty. The validity for diagnosing restenosis by MRCA was 93% in sensitivity and 33% in specificity. In protocol three, comprising 18 coronary arteries with total obstruction, the presence of collaterals was evaluated. The development of collateral circulation improved MRCA findings in the distal portion of obstructed coronary arteries. We conclude that MRCA provides useful information with acceptable sensitivity and specificity before balloon angioplasty. However, MRCA has a tendency to over-estimate restenosis after balloon angioplasty.     

Cardiothoracic magnetic resonance angiography.

At the current state of the art, cardiothoracic MR angiography offers the clinician information that is supplemental to that provided by other noninvasive imaging techniques. Indeed, in some areas MR angiography will likely surpass currently used methods as the technique of choice. Specifically, measurement of cardiac output, pulmonary blood flow, and lung perfusion can be performed relatively accurately and simply during a brief MR examination. Both standard spin-echo and angiographic evaluation of the thoracic aorta provide qualitative images with superior resolution. Additionally, development of pulmonary artery angiography is progressing rapidly and may soon be clinically useful. Phase incoherence caused by complex flow and resulting in a signal void is useful for location and qualitative assessment of abnormal flow jets induced by stenoses. However, this phenomenon represents the major limitation to quantitative assessment of flow abnormalities. Methods to increase signal to noise and/or reduce phase incoherence must be developed before MR angiography can be used effectively to assess abnormal flow conditions.     

The capability of inflow inversion recovery magnetic resonance compared to contrast-enhanced magnetic resonance in renal artery angiography

Purpose

To assess the capability of inflow inversion recovery (IFIR) magnetic resonance angiography (MRA), compared with contrast-enhanced MRA (CE-MRA) as reference standard, in evaluating renal artery stenosis (RAS).

Methods

Seventy-two subjects were examined by IFIR MRA with respiratory-gated, prior to CE-MRA with a 1.5-T scanner. Two readers evaluated the quality of IFIR MRA images and renal artery depiction on artery-by-artery basis. The agreement of two methods to assess RAS was analyzed using the Kappa test. The relationship between image quality of IFIR MRA and respiratory rate was analyzed by ANOVA test.

Results

The visibility of renal artery branch vessels was significantly higher using IFIR MRA than CE-MRA (p < 0.05). A good agreement of two methods in evaluating stenosis grade, and a near-perfect inter-observer agreement for IFIR MRA (Kappa value 0.98) and CE-MRA (Kappa value 0.93), were demonstrated. As RAS ≥50%, the sensitivity and specificity of IFIR MRA were 92 and 98% in reader 1, 93 and 98% in reader 2, respectively. The image quality was significantly better in patients with stable respiration (p < 0.01).

Conclusions

IFIR MRA in patients with stable respiration has higher visibility of renal artery branch vessels than CE-MRA, and a good agreement with CE-MRA in evaluating stenosis grade. It could be used to evaluate RAS for screening, and monitoring treatment.

     

Effect of rosiglitazone on progression of atherosclerosis: insights using 3D carotid cardiovascular magnetic resonance

Background

There is recent evidence suggesting that rosiglitazone increases death from cardiovascular causes. We investigated the direct effect of this drug on atheroma using 3D carotid cardiovascular magnetic resonance.

Results

A randomized, placebo-controlled, double-blind study was performed to evaluate the effect of rosiglitazone treatment on carotid atherosclerosis in subjects with type 2 diabetes and coexisting vascular disease or hypertension. The primary endpoint of the study was the change from baseline to 52 weeks of carotid arterial wall volume, reflecting plaque burden, as measured by carotid cardiovascular magnetic resonance. Rosiglitazone or placebo was allocated to 28 and 29 patients respectively. Patients were managed to have equivalent glycemic control over the study period, but in fact the rosiglitazone group lowered their HbA1c by 0.88% relative to placebo (P < 0.001). Most patients received a statin or fibrate as lipid control medication (rosiglitazone 78%, controls 83%). Data are presented as mean ± SD. At baseline, the carotid arterial wall volume in the placebo group was 1146 ± 550 mm³ and in the rosiglitazone group was 1354 ± 532 mm³. After 52 weeks, the respective volumes were 1134 ± 523 mm³ and 1348 ± 531 mm³. These changes (-12.1 mm³ and -5.7 mm³ in the placebo and rosiglitazone groups, respectively) were not statistically significant between groups (P = 0.57).

Conclusion

Treatment with rosiglitazone over 1 year had no effect on progression of carotid atheroma in patients with type 2 diabetes mellitus compared to placebo.     

Carebolus与testbolus两种测试方法在磁共振CE-MRA中的应用比较

目的 比较Carebolus与testbolus两种测试方法在CEMRA中的有效性。方法 搜集行CE-MRA的病例64例，其中头颈部26例，胸腹部18例，四肢20例。均在行CE—MRA前先进行Careb01us（51例）或testb01us（13例）测试。结果 用Carebolus测试的有5例显示不满意；用testbolus测试的有1例不满意。其余CE—MRA效果均满意。结论 Carebolus与testbolus两种测试方法各有优缺点，临床上应根据不同的成像血管和不同的血流动力学特点进行选择。     

4D flow cardiovascular magnetic resonance consensus statement

Pulsatile blood flow through the cavities of the heart and great vessels is time-varying and multidirectional. Access to all regions, phases and directions of cardiovascular flows has formerly been limited. Four-dimensional (4D) flow cardiovascular magnetic resonance (CMR) has enabled more comprehensive access to such flows, with typical spatial resolution of 1.5×1.5×1.5 – 3×3×3 mm³, typical temporal resolution of 30–40 ms, and acquisition times in the order of 5 to 25 min. This consensus paper is the work of physicists, physicians and biomedical engineers, active in the development and implementation of 4D Flow CMR, who have repeatedly met to share experience and ideas. The paper aims to assist understanding of acquisition and analysis methods, and their potential clinical applications with a focus on the heart and greater vessels. We describe that 4D Flow CMR can be clinically advantageous because placement of a single acquisition volume is straightforward and enables flow through any plane across it to be calculated retrospectively and with good accuracy. We also specify research and development goals that have yet to be satisfactorily achieved. Derived flow parameters, generally needing further development or validation for clinical use, include measurements of wall shear stress, pressure difference, turbulent kinetic energy, and intracardiac flow components. The dependence of measurement accuracy on acquisition parameters is considered, as are the uses of different visualization strategies for appropriate representation of time-varying multidirectional flow fields. Finally, we offer suggestions for more consistent, user-friendly implementation of 4D Flow CMR acquisition and data handling with a view to multicenter studies and more widespread adoption of the approach in routine clinical investigations.     

Fluorine cardiovascular magnetic resonance angiography in vivo at 1.5 T with perfluorocarbon nanoparticle contrast agents.

While the current gold standard for coronary imaging is X-ray angiography, evidence is accumulating that it may not be the most sensitive technique for detecting unstable plaque. Other imaging modalities, such as cardiovascular magnetic resonance (CMR), can be used for plaque characterization, but suffer from long scan and reconstruction times for determining regions of stenosis. We have developed an intravascular fluorinated contrast agent that can be used for angiography with cardiovascular magnetic resosnace at clinical field strengths (1.5 T). This liquid perfluorocarbon nanoparticle contains a high concentration of fluorine atoms that can be used to generate contrast on 19F MR images without any competing background signal from surrounding tissues. By using a perfluorocarbon with 20 equivalent fluorine molecules, custom-built RF coils, a modified clinical scanner, and an efficient steady-state free procession sequence, we demonstrate the use of this agent for angiography of small vessels in vitro, ex vivo, and in vivo. The surprisingly high signal generated with very short scan times and low doses of perfluorocarbon indicates that this technique may be useful in clinical settings when coupled with advanced imaging strategies.     

非对比剂增强磁共振血管成像评价门静脉血流动力学的可行性研究

目的探讨利用多反转空间标记脉冲非对比剂增强磁共振血管成像(non-contrast-enhanced magnetic resonance angiography using spatial labeling with multiple inversion pulses,SLEEK-MRA)评估门静脉血流动力学的可行性。材料与方法纳入25例门静脉高压患者先后行SLEEK-MRA和彩色多普勒超声(color doppler ultrasonograohy,CDUS)检查,SLEEK-MRA序列采用不同血流抑制反转时间(blood suppression inversion time,BSP TI):600、900、1200、1500 ms。对门静脉分支显示情况进行评级并与通过与CDUS血流速度测定结果进行相关性分析。依据CDUS所测流速将患者分组,并比较各组患者分支显示评级情况以及BSPTI参数应用情况。结果门静脉左、右支在全部BSPTI设定时SLEEK-MRA的分支显示评级均与CDUS所测得血流速度呈现出显著相关性。在门静脉流速明显减慢组患者,分支评级明显低于流速正常或轻度减慢组,应用BSP TI值明显高于流速正常或轻度减慢组。结论 SLEEK-MRA在提供高质量门静脉形态学成像同时,具有提示门静脉血流动力学变化的潜力,通过SLEEK-MRA获取血流动力学信息是可行的。     

3D contrast-enhanced MR angiography using fluoroscopic triggering and an elliptical centric view order

Although a variety of timing techniques and data acquisition strategies have been used for three-dimensional contrast-enhanced MR angiography, many are still limited by inadequate overall reliability, limited spatial resolution, or complexity. A technique is presented in this work in which contrast arrival is detected in the targetted vasculature in real time using MR fluoroscopy. Upon detection the operator triggers a 3D MR angiographic acquisition which uses an elliptical centric view order. It is shown that the view order intrinsically provides a high degree of venous suppression which in turn allows acquisition times of 30seconds or longer, permitting high spatial resolution. The reliability of fluoroscopic triggering in bolus detection is shown to be over 90%. The technique provides high quality contrast-enhanced MR angiograms for many vascular regions.