Correction for heart rate variability during 3D whole heart MR coronary angiography

PURPOSE: To evaluate the effect of a real-time adaptive trigger delay on image quality to correct for heart rate variability in 3D whole-heart coronary MR angiography (MRA). MATERIALS AND METHODS: Twelve healthy adults underwent 3D whole-heart coronary MRA with and without the use of an adaptive trigger delay. The moment of minimal coronary artery motion was visually determined on a high temporal resolution MRI. Throughout the scan performed without adaptive trigger delay, trigger delay was kept constant, whereas during the scan performed with adaptive trigger delay, trigger delay was continuously updated after each RR-interval using physiological modeling. Signal-to-noise, contrast-to-noise, vessel length, vessel sharpness, and subjective image quality were compared in a blinded manner. RESULTS: Vessel sharpness improved significantly for the middle segment of the right coronary artery (RCA) with the use of the adaptive trigger delay (52.3 +/- 7.1% versus 48.9 +/- 7.9%, P = 0.026). Subjective image quality was significantly better in the middle segments of the RCA and left anterior descending artery (LAD) when the scan was performed with adaptive trigger delay compared to constant trigger delay. CONCLUSION: Our results demonstrate that the use of an adaptive trigger delay to correct for heart rate variability improves image quality mainly in the middle segments of the RCA and LAD.     

全心冠状动脉磁共振成像初步探讨

目的：探讨自由呼吸导航全心冠状动脉磁共振成像（CMRA）心率对成像效果的影响。方法：对28例正常者,用自由呼吸导航触发3D-TFE序列行全心冠状动脉成像,用＂Soap Bubble＂软件进行冠状动脉曲面重建;以显示冠状动脉的节段数及图像质量为评价指标,分析比较不同心率对成像效果的影响。结果：28例中显示冠状动脉112支208段。不同心率冠状动脉显示节段数差异有统计学意义,当心率〈70次/min时各支冠状动脉主干近、中、远段均可良好显示。图像质量一级17例,二级5例,三级3例,四级2例,五级1例。不同心率的图像质量差异有统计学意义（P〈0.05）,当心率〈70次/min时图像质量较好。结论：自由呼吸导航全心CMRA的成像效果与心率有关,心率慢时,冠状动脉各支、段显示较完整,图像质量也较好。     

导航技术三维对比剂增强磁共振冠状动脉成像

目的评价导航技术三维对比剂增强磁共振冠状动脉成像的应用价值。方法应用导航技术三维对比剂增强磁共振血管成像方法,对20例受检者分别进行左、右冠状动脉成像,经后处理获得左、右冠状动脉血管图像。应用信噪比和对比噪声比评价增强前后的冠状动脉图像,并对冠状动脉主干及其主要分支的显示情况进行评价。结果(1)对获得成功的18例冠状动脉图像进行评价,增强前冠状动脉图像的信噪比为26.37±7.02,对比噪声比为14.76±6.97;增强后冠状动脉图像的信噪比为38.87±11.62,对比噪声比为33.72±10.80,经统计学比较,信噪比和对比噪声比增强前后的差异有统计学意义(t=2.91,4.62;P<0.05)。(2)对比剂增强后左、右及左回旋支冠状动脉近中段的显示率为100%,远侧段的显示率分别为94.4%、88.8%、77.8%。结论导航技术三维对比剂增强磁共振冠状动脉成像有较高的信噪比和对比噪声比,应用于临床尚需进一步的对照研究。     

32通道线圈在3.0 T MR对比增强全心冠状动脉成像中的初步应用

目的 评价32通道线圈高并行采集加速3.0 T MR对比增强全心冠状动脉成像(CECMRA)技术的临床应用价值.方法 对拟诊冠心病的60例患者进行32通道线圈3.0 T CE CMRA检查,成像采用心电门控、呼吸导航、扰相位梯度回波序列,加用非选择性反转回波抑制心肌信号,TT为200 ms.以全心覆盖和并行采集方式获取图像数据.增强扫描采用钆贝葡胺(Gd-BOPTA,0.15 mmoL/kg)慢速静脉注射(0.3 ml/s).以X线冠状动脉造影结果作为参考标准,采用四格表χ2检验,评价CE CMRA诊断冠状动脉≥50%狭窄的诊断准确性.结果 60例患者中56例成功完成3.0 T CE CMRA,平均扫描时间为(6.0±1.3)min.CE CMRA在28例患者正确检出至少1个有意义狭窄,其诊断敏感性为93.3%.在26例CAG除外冠心病的患者中,CMRA正确排除了23例,其诊断特异性为88.5%.结论 应用32通道相控阵线圈行高并行采集加速3.0 T CE CMRA检查,可以在减少对比剂用量的同时缩短扫描时间,提高诊断准确性.     

Correlation of 3D MR coronary angiography with selective coronary angiography: feasibility of the motion-adapted gating technique

The aim of this study was to verify the feasibility of a respiratory motion compensation technique (motion-adapted gating, MAG) for visualization of coronary arteries (CA) by correlation with selective coronary angiography (SCA). Fifteen subjects (11 patients, mean age 61.3 years, age range 41-73 years; and 4 healthy volunteers, mean age 32.3 years, age range 31-35 years) were investigated. A Philips Gyroscan ACS-NT was used, operating at 1.5 T, was combined with the PowerTrak 6000 gradient system. An ECG-triggered, respiratory motion-gated 3D turbo field echo sequence was used. The real-time algorithm utilized the concept of k-space weighting in combination with automatic analysis of respiratory motion. The main CA were investigated. Qualitative analysis was performed by three blinded investigators. Visibility was graded on a five-point scale (0=not visualized, 1=insufficient, 2=sufficient, 3=good, 4=excellent). Segments graded 2-4 were defined as adequately visualized. Sixty-two of 88 assessable CA segments in patient, and 22 of 32 in volunteer group were adequately visualized. Visibility of CA was classified as excellent for proximal RCA (avg. 3.6+/-0.5), good for LM, proximal LAD, proximal LCX, middle RCA and sufficient for middle LAD. Sensitivity, specificity, positive and negative predictive values for coronary MRA in detection of CA stenoses with luminal narrowing >/=50% were 88, 94, 83, and 96%, respectively. Magnetic resonance imaging in combination with MAG has proven to be a promising technique for noninvasive imaging of CA due to good image quality and a patient convenient free-breathing technique.     

Intraindividual comparison of 3D coronary MR angiography and coronary CT angiography

RATIONALE AND OBJECTIVES: To compare the diagnostic value of magnetic resonance (MR) and computed tomography (CT) for the detection of coronary artery disease (CAD) with special regard to calcifications. MATERIALS AND METHODS: Twenty-seven patients with known CAD were examined with a targeted, navigator-gated, free-breathing, steady-state free precession MR angiography sequence (repetition time = 5.6 milliseconds, echo time = 2.8 milliseconds, flip angle 110 degrees ) and 16-slice coronary CT angiography. Segment-based sensitivity, specificity, and accuracy for the detection of stenoses larger than 50% were determined as defined by the gold standard catheter coronary angiography along with the subjective image quality (Grade 1-4). The degree of calcifications in each segment was quantified using a standard calcium scoring tool. RESULTS: Of 115 possible segments, 7% had to be excluded in MR imaging because of poor image quality. In CT, 3% were nondiagnostic because of image quality and 15% were not evaluable because of calcifications. Values for the detection of relevant coronary artery stenoses in the evaluated segments were: sensitivity: MR imaging 85% versus CT 96%; specificity: 88% versus 96%; accuracy: 87% versus. 96%. Average subjective image quality was 1.8 for MR imaging and 1.6 for CT. Of the 15% of segments that had to be excluded from CT evaluation because of calcifications, MR imaging provided the correct diagnosis segments in 67%. CONCLUSIONS: CT provided a better image quality with superior accuracy for the detection of CAD. Despite its overall inferiority, MR imaging proved to be helpful method in interpreting coronary stenosis in severely calcified segments.     

Correction for heart rate variability improves coronary magnetic resonance angiography

PURPOSE: To address degradation of coronary MR angiography (MRA) image quality due to heart rate variability (HRV)-associated variations in coronary artery position and motion. MATERIALS AND METHODS: Free-breathing navigator-gated and -corrected coronary MRA using subject-specific trigger delays and acquisition windows was combined with a real-time HRV correction algorithm, such as commonly used in left ventricular wall motion studies. Ten healthy adults underwent free-breathing navigator-gated and -corrected coronary MRA with and without HRV correction. Signal-to-noise (SNR), contrast-to-noise (CNR), vessel length, diameter, sharpness, and subjective image quality (on a five-point scale) were compared in a blinded fashion. RESULTS: Vessel sharpness improved significantly for both the left (LCA) and right (RCA) coronary artery systems (P = 0.016 and P = 0.015, respectively) with the use of HRV correction. Subjective image quality also improved significantly when HRV correction was used (P = 0.003). There were no significant differences with regard to SNR and CNR (P > 0.1). CONCLUSIONS: Preliminary results suggest that HRV correction improves objective and subjective image quality in coronary MRA. Continued studies in patients with known or suspected coronary artery disease are warranted to investigate the clinical impact of this technique.     

单纯含服硝酸甘油对全心导航冠状动脉MRA成像参数及图像质量影响的自身对照研究

目的:探讨单纯舌下含服硝酸甘油对全心自由呼吸导航三维采样冠脉MRA的成像参数和图像质量的影响.方法:使用自由呼吸导航三雏采样全心MR冠状动脉成像序列,对17例志愿者完成基础状态以及舌下含服硝酸甘油的MRA扫描,并进行自身对照研究,分析含服硝酸甘油对成像参数和图像质量的影响.结果:服用硝酸甘油前后受试者的心率分别为(68...     

Head and neck haemangiomas: contrast-enhanced three-dimensional MR angiography

We evaluated the clinical effectiveness of contrast-enhanced three-dimensional (3D) magnetic resonance angiography (MRA) for diagnosing head and neck haemangiomas. We studied six patients using a magnetization prepared rapid acquisition gradient-echo (MP-RAGE) sequence on a 1.5-T system. Conventional T1- and T2-weighted and contrast-enhanced images were also obtained. The images were compared with histological findings. In four cavernous haemangiomas, a mass was partially visible as an enhancing lesion on the early phase of MRA, and was completely visible as a larger enhancing lesion in the late phase, showing slow blood flow. In two capillary haemangiomas, a mass was completely visible in the early phase showing fast flow. In all patients, MRA clearly showed both the haemangiomas and the external carotid artery branches. MRA allowed assessment of the relationship between the haemangiomas and the feeding arteries, and of the haemodynamics. Received: 17 April 1998 Accepted: 5 June 1998     

The detection of coronary stiffness in cardiac allografts using MR imaging

Objective

To test the hypothesis that biomechanical changes are quantitatively related to morphological features of coronary arteries in heart transplant (HTx) recipients.

Materials and methods

With IRB approval, three-dimensional (3D) magnetic resonance (MR) angiography and two-dimensional (2D) black-blood stead-state free precession (SSFP) MR imaging were performed to image coronary arteries of 36 HTx patients. Contours of coronary wall were manually drawn. For each coronary segment, coronary wall thickness, wall area, lumen area (in systole and diastole) were acquired. Coronary distensibility index (CDI) and the percent of the coronary wall occupying the vessel area (PWOV) were calculated.

Results

There are totally 98 coronary segments eligible for quantitative analysis from 27 HTx patients. The CDI is 4.90 ± 2.44 mmHg⁻¹. The mean wall thickness is 1.49 ± 0.24 mm and the PWOV is 74.6% ± 7.5%. CDI has moderate correlations with wall thickness (r = −0.531, P < 0.001) and with PWOV (R = −0.435, P < 0.001).

Conclusions

Detected with coronary MR imaging, CDI is quantitatively correlated with the morphological features of the coronary artery in HTx patients. Coronary stiffness has the potential to become an alternative imaging biomarker for the quantitative assessment of the status of cardiac allografts.     

Improved bulk myocardial motion suppression for navigator-gated coronary magnetic resonance imaging

PURPOSE: To evaluate the impact of a new, cross-correlation based method for compensation of respiratory induced motion of the heart using an individually adapted three-dimensional (3D) translation or affine transformation approach. MATERIALS AND METHODS: A total of 32 patients underwent a routine cardiac MR examination. In each patient, a calibration scan was performed during free-breathing to register breathing-related motion within a 3D ellipsoid registration kernel covering the entire heart. Three navigators were employed for all three spatial dimensions (feet-head, anterior-posterior, and left-right) and the optimal translatory correction factors for each spatial dimension were determined. In addition, the cross-correlations for different motion models (no compensation, fixed 1D-translation, adapted 3D-translation, and affine transformation) were calculated. RESULTS: The mean correction factor for the feet-head direction was 0.45 +/- 0.13. Though the mean correction factors for the anterior-posterior and left-right direction were nearly zero (-0.01 +/- 0.08 and 0.02 +/- 0.09, respectively), the correction factors exceeded the amount of 0.1 in 12 (19%) and in 19 patients (30%), respectively. All motion compensation models showed significantly higher cross-correlations when compared to "no compensation" (P < 0.05). In particular, the affine transformation algorithm achieved the highest cross-correlation values (88.3 +/- 5.1%) with a significant increase compared to fixed 1D translation (84.7 +/- 6.5%, P < 0.05). CONCLUSION: A considerable number of patients demonstrated relevant breathing-related movement of the heart in the anterior-posterior or left-right direction in addition to the predominant breathing-related movement in the feet-head direction. Thus, it is recommended to compensate for all three spatial dimensions. The affine transformation algorithm combined with three navigators significantly improved breathing-related cardiac motion compensation when compared to the conventionally applied 1D translation with a fixed correction factor.     

Acute chest pain: The role of MR imaging and MR angiography

MR imaging (MRI) and MR angiography (MRA) have gained a high level of diagnostic accuracy in cardiovascular disease. MRI in cardiac disease has been established as the non-invasive standard of reference in many pathologies. However, in acute chest pain the situation is somewhat special since many of the patients presenting in the emergency department suffer from potentially life-threatening disease including acute coronary syndrome, pulmonary embolism, and acute aortic syndrome. Those patients need a fast and definitive evaluation under continuous monitoring of vital parameters. Due to those requirements MRI seems to be less suitable compared to X-ray coronary angiography and multislice computed tomography angiography (CTA). However, MRI allows for a comprehensive assessment of all clinically stable patients providing unique information on the cardiovascular system including ischemia, inflammation and function. Furthermore, MRI and MRA are considered the method of choice in patients with contraindications to CTA and for regular follow-up in known aortic disease. This review addresses specific features of MRI and MRA for different cardiovascular conditions presenting with acute chest pain.     

前瞻性心电门控双源CT冠状动脉成像在高心率患者中应用的可行性研究

目的 探讨心率不低于91次/分(bpm)患者回顾性心电门控双源CT(DSCT)冠状动脉成像R-R间期的最佳重建时相,从扫描时相选择的角度分析前瞻性心电门控(简称前门控)应用的可行性.方法 分析232例行回顾性心电门控DSCT冠状动脉成像患者(体质量指数23～25 kg/m2,心率≥91 bpm)的图像,根据扫描过程中患者屏气时心电监控记录到的心率将其分为3组(A～C组),A组83例,心率91～95 bpm,B组68例,心率96～100 bpm,C组81例,心率≥101 bpm.每隔3%重建1个时相,分别由2名医师独立对横断面图像、薄层MIP、CPR、VRT图像质量采用5分法进行综合评估,按照15段分段法,选出每个节段的R-R间期的最佳重建时相及范围.采用Kappa检验,评价2名医师对冠状动脉图像评分的一致性.结果 232例患者中,可评价冠状动脉节段共3343个,其图像最佳重建时相范围集中在81%～61%和51%～31%.3组冠状动脉节段与之相对应的节段数百分比:A组(91～95 bpm,83例的1183个节段)分别为5.49%、94.51%;B组(96-100 bpm,68例986个节段)分别为0.20%、99.80%;C组(≥101 bpm,81例1174个节段)分别为0.17%、99.83%.232例患者的3343个冠状动脉节段中3274个节段(97.94%)最佳重建时相范围集中在以41%为中心的51%～31%R-R间期范围内.2名医师对232例患者的3343个冠状动脉节段图像质量的评分结果得到了较高的一致性(Kappa值=0.883,P<0.05).结论 具有稳定的窦性心律,且屏气时平均心率≥91 bpm患者,冠状动脉节段的最佳重建时相集中于以R-R间期41%为中心的51%～31%,从扫描时相选择的角度考虑,可以对稳定高心率(≥91 bpm)患者行前门控横断面扫描,并且预设41%为曝光时间窗,成功把握较大.     

烟雾病MRI和MRA诊断价值(附16例报告)

目的；评价MRI和MRA对烟雾病的诊断价值。方法：分析16例烟雾病患者的MRI、MRA表现和临床资料。MRA采用三维时间飞跃法。结果：16例患者MRA检查均显示不同程度的颈内动脉分叉以上狭窄或闭塞，其中17支后交通动脉增粗，4支眼动脉增粗；16例显示基底节区异常血管网，其中6例同时显示后部异常血管网；10例显示软脑膜吻合支增多；MRI显示脑出血或脑梗塞等脑实质改变，并能显示基底节区异常血管点状流空。结论：MRI和MRA是诊断烟雾病的有效非创伤性检查方法。对该病的诊断、筛选、随访和外科5一的评价有较大价值。     

The importance of adjusting for differences in proximal and distal contrast bolus arrival times in contrast-enhanced iliac artery magnetic resonance angiography

We tested the hypothesis that differences in proximal and distal contrast bolus arrival times may result in insufficient vascular signal in the distal part of the aortoiliofemoral territory with routinely used timing techniques. The difference in arrival time of the contrast medium bolus between the aorta and the common femoral arteries was measured in 14 patients undergoing magnetic resonance angiography of the aortoiliac arteries. A dual-station test bolus technique adjusting for this difference was evaluated. The variation coefficient of the signal intensity in six defined locations and signal intensities (SI) normalised to fat were calculated. Comparisons were made with findings in 13 patients examined with a fluoroscopically triggered timing technique (BolusTrak, Philips Medical Systems, Best, The Netherlands). The difference in bolus arrival time between proximal and distal vessels was 0–7 s. In 3 of 14 patients it was 5.6–7 s. There was a tendency towards a lower mean variation coefficient in the dual-station group (p=0.10). With both techniques, significantly lower SIs were measured in the femoral arteries compared with SIs in the superior part of the abdominal aorta. In two cases in the BolusTrak group, a distal vessel could not be delineated but was shown to be patent on a delayed scan. Differences in contrast medium arrival time along the vessel may be large enough to preclude visualisation of distal vessels unless there is compensation. A dual-station test bolus technique taking this into account was found to be feasible. Electronic Publication     

三维对比剂增强MR血管成像诊断布加综合征的价值

目的观察三维对比剂增强MR血管成像（3DCEMRA）上布加综合征（BCS）的各种表现,并初步评价该项新技术的价值。方法33例BCS患者行3DCEMRA检查。23例为继发性BCS,分别继发于肝细胞癌（21例）、右肾上腺癌（1例）或血栓性静脉炎（1例）。10例为原发性BCS。观察肝静脉、下腔静脉（IVC）和门静脉的开放性,观察有无肝内外侧支、肝实质病变和门静脉一体静脉间曲张静脉。10例患者行下腔静脉造影术,2例行肝右静脉穿刺造影术,把3DCEMRA所获的诊断结果与造影相对照。结果3DCEMRA可显示BCS的各种表现。肝静脉表现包括：癌栓形成（19例）、肿瘤压迫（2例）、肝静脉未显示（4例）和局限性狭窄（4例）。IVC表现为严重狭窄或闭塞（10例）、肿瘤直接侵犯（2例）、癌栓形成（3例）、血栓性静脉炎（1例）和隔膜形成（3例）。9例显示肝内侧支形成,其中2例显示“蜘蛛网”征象。所见的肝外侧支包括扩张的奇静脉和半奇静脉（13例）,以及左肾一膈下一心包膈静脉侧支（2例）形成。2例患者发现门静脉左支闭塞,10例患者发生门静脉．体静脉间静脉曲张。3DCEMRA发现的肝实质病变有：尾叶增大（7例）、不均匀强化（18例）和并发肿瘤（18例）。12例3DCEMRA诊断结果均与造影结果一致。结论3DCEMRA能显示BCS的各种征象,并能帮助提供正确诊断。     

磁共振三维血流成像在小儿腹部疾病诊断中的价值

目的：探讨对比剂增强自动触发磁共振三维血流成像(3D CE MRA)技术在小儿腹部疾病诊断中的价值。方法：2001年3月～2003年6月对临床拟诊腹部实体肿瘤和腹腔大血管病变的46例患儿行常规MRI扫描和3D CEMRA检查，年龄生后1天～14岁，平均4．8岁。腹部实体肿瘤40例，腹腔大血管病变6例。全部患者检查前行肘静脉穿刺并保留静脉通道．镇静睡眠后注射2～3倍剂量非离子型对比剂。扫描采用Smart Prep Angio。对比剂智能捕捉技术。结果：本组检查成功率97．83％。40例实体肿瘤中,3D CEMRA显示肿瘤起源2例，肿瘤侵犯和包绕腹主动脉11例，下腔静脉闭塞3例，肾动静脉受侵蚀闭塞6例，肾蒂受肿瘤牵拉变细3例，腹腔动脉干、肠系膜上动静脉及睥静脉移位共12例，门静脉及其左右肝内分支受侵犯3例。腹部大血管病变6例。结论：3D CEMRA技术对巨大腹膜后肿瘤的起源定位具有诊断价值。结合多方位的断面图像不仅可以了解腹腔重要大血管被肿瘤浸润包裹和推挤移位情况，而且可对肾脏受浸润破坏情况进行术前评估，从而为临床制定恰当的治疗方案提供比较可靠的影像学依据。3D CEMRA是无创显示体腔大血管病变的有效方法。     

MR navigator-echo monitoring of temporal changes in diaphragm position: Implications for MR coronary angiography

Temporal changes in respiration could influence navigator-echo (NE)-gated MR coronary angiography (MRCA), but systematic investigation of the effects of such variations and how to limit them has not been performed. We addressed these issues by studying the influence of time in the magnet on diaphragm position and respiratory patterns using NE diaphragm monitoring in volunteers and a phantom model. NE diaphragm monitoring was performed at .5 T in 10 subjects over a total period of 35 minutes. The end-expiratory position was sustained for longer (1.1 vs .4 seconds, P < .001) and with greater position stability (SD 1.9 vs 5.9 mm, P = .01) than the end-inspiratory position. Drift of the end-expiratory position occurred over time, causing a fall in scan efficiency (44–28%, P = .01). Up-drift of the end-expiratory position was most common. Loss of scan efficiency was worse with up-drift because of loss of the end-expiratory pause from the NE window (up-drift 10% mm^?1, down-drift 7% mm^?1, both P = .03). Scan efficiency also was reduced during sleep (to a nadir of 0%), secondary to loss of the end-expiratory pause, periodic breathing with oscillating end-expiratory position, and periods of apnea. The phantom model used actual diaphragm traces to evaluate the artifact resulting from diaphragm motion during acquisition. Artifact was considerably reduced by NE adaptive motion correction compared with NE gating alone (ghosting ratio 2.0 vs 2.8, P < .01). Artifact also was significantly reduced with up-drift if scan efficiency was maintained above 35% (P = .05). For optimal NE-gated MRCA, the following features are important: the NE window should be placed around the end-expiratory position; subjects should not sleep; scan efficiency should be monitored and the NE window should be repositioned if scan efficiency falls below 35%; and adaptive motion correction should be used.