磁共振冠状动脉成像新技术及其临床应用

磁共振冠状动脉成像作为一项无创性检查冠状动脉的影像手段，近十年来，成像序列及方法不断突破和创新，正由研究阶段逐步进入临床应用。目前全球多中心研究的重点是如何消除心脏及呼吸运动伪影，增加信噪比和空间分辨力以及快速成像、缩短检查时间等，力求更精确显示冠状动脉及其狭窄以满足临床需要。     

Enhancement of phase-contrast MR angiography with superparamagnetic iron oxide

The effect of superparamagnetic iron oxide particles (AMI-227) was assessed in three-dimensional (3D) phase-contrast (PC) MR angiography (MRA), with various scanning parameters for rats at 1.5 T. The blood T1 and T2 before and after 20 μmol Fe/kg of AMI-227 injection were measured sequentially at .47 T. The visualization of abdominal aorta, renal artery, inferior vena cava, and portal vein was respectively evaluated before and after AMI-227 injection qualitatively by the four confidence levels and quantitatively by analysis of signal-to-noise ratio (SNR) of vessels. The blood T1 and T2 were sufficiently shortened for at least 1 hour after AMI-227 injection. The visualization of each vessel was improved by AMI-227 at various velocity encoding (VENC) value, suggesting the extended application of PC-MRA in various conditions. The optimal flip angle was increased from 20° to 30° in higher VENC after AMI-227 injection, resulting in higher signal from blood flow. Quantitative analyses showed that the optimal flip angle to achieve the maximum SNR seemed to be 20° in unenhanced images, but the optimal flip angle of the high speed flow was increased by contrast enhancement. The postcontrast PC-MRA provides the increased sensitivity of slow flow components, even with a high VENC gradient. AMI-227 can significantly improve SNR to blood vessels during 3D-PC-MRA with various scanning parameters.     

肠系膜上动、静脉病变64层螺旋CT血管成像探讨

目的探讨64层螺旋CT血管成像在肠系膜上动、静脉病变的诊断和临床应用价值。资料与方法回顾性分析经CT增强血管造影诊断肠系膜上动、静脉病变45例。采用Philips 64层螺旋CT容积扫描,增强扫描于注射对比剂后延迟25~30 s扫描动脉期、65~75 s扫描门静脉期。在工作站采用多平面重组(multi-planar reformat-ting,MPR)、最大密度投影(maximum intensity projection,MIP)及容积再现(volumetric rendering,VR)重组肠系膜上动、静脉图像,分析肠系膜上动、静脉血管成像对肠系膜血管病变的诊断价值。结果 45例患者均清晰显示肠系膜上动、静脉主干及其分支,共发现肠系膜上动、静脉病变49处,其中累及肠系膜上动脉23处,肠系膜上静脉13处,肠系膜上动、静脉同时累及13处。结论 64层螺旋CT血管成像能清楚显示肠系膜上动、静脉解剖结构,对肠系膜动、静脉病变有确诊价值,为临床诊断和治疗节省宝贵时间。     

Contrast-enhanced MR angiography utilizing parallel acquisition techniques in renal artery stenosis detection

Significant renal artery stenosis (RAS) is a potentially curable cause of renovascular hypertension and/or renal impairment. It is caused by either atherosclerosis or fibromuscular dysplasia. Correct and timely diagnosis remains a diagnostic challenge. MR angiography (MRA) as a minimally invasive method seems to be suitable for RAS detection, however, its diagnostic value widely differs in the literature (sensitivity 62-100% and specificity 75-100%). The aim of our prospective study was to compare the diagnostic value of contrast-enhanced MRA utilizing parallel acquisition techniques in the detection of significant RAS with digital subtraction angiography (DSA).A total of 78 hypertensive subjects with suspected renal artery stenosis were examined on a 1.5 Tesla MR system using a body array coil. Bolus tracking was used to monitor the arrival of contrast agent to the abdominal aorta. The MRA sequence parameters were as follows: TR 3.7 ms; TE 1.2 ms; flip angle 25°; acquisition time 18 s; voxel size 1.1 mm × 1.0 mm × 1.1 mm; centric k-space sampling; parallel acquisition technique with acceleration factor of 2 (GRAPPA). Renal artery stenosis of 60% and more was considered hemodynamically significant. The results of MRA were compared to digital subtraction angiography serving as a standard of reference.Sensitivity and specificity of MRA in the detection of hemodynamically significant renal artery stenosis were 90% and 96%, respectively. Prevalence of RAS was 39% in our study population.Contrast-enhanced MRA with high spatial resolution offers sufficient sensitivity and specificity for screening of RAS.     

肝静脉阻断下给药对门脉血药浓度的影响

目的 研究暂时性肝静脉(HV)阻断下经肠系膜上动脉(SMA)化疗及肝动脉(HA)化疗的价值。方法 10条犬,每犬均行4组实验并作自身对照。于灌注5-氟尿嘧啶(5-Fu)以后0．5、5、10、15、20、30、60min抽取门脉血各5ml,测定血药浓度,进行药动学分析。结果 阻断组5-Fu的峰浓度及药时曲线下的面积明显高于单纯组,药物总清除率阻断组低于单纯组。肝静脉阻断下肝动脉造影显示阻断区末梢分支增多,肝段浓染明显。结论 暂时性阻断肝静脉经肠系膜上动脉、肝动脉灌注5-Fu,可以提高门脉及局部肝组织的药物浓度,延长药物作用时间,增强抗肿瘤作用。     

Carotid stenosis: a comparison between MR and spiral CT angiography

We performed a preliminary study comparing three-dimensional time-of-flight (3 D TOF) magnetic resonance angiography (MRA) and spiral CT angiography (SCTA) in the detection and assessment of internal carotid artery stenosis. Digital subtraction angiography (DSA) was the reference examination. We examined 20 patients with signs of cerebrovascular insufficiency, who underwent MRA, SCTA and DSA within a 3 day period. Both internal carotid arteries were assessed by three blinded readers for degree of stenosis at two different levels (bulb and remaining section) giving a total of 80 assessments. Interobserver variability, sensitivity, specificity, diagnostic accuracy, concordance, overestimation and underestimation were assessed. Interobserver variability was not statistically significant. MRA showed higher sensitivity, specificity, diagnostic accuracy and concordance than SCTA (92.0 % vs 80.8 %, 98.2 % vs 96.4 %, 96.3 % vs 91.3 % and 96.0 % vs 88.0 %, respectively). MRA gave rise to a 5.0 % overestimation rate, whereas SCTA occasioned a 7.5 % underestimation rate. These differences are not statistically significant. These results suggest that MRA is a more useful, noninvasive modality for assessment of the internal carotid artery with a more than 70 % stenosis. Received: 8 August 1997 Accepted: 10 October 1997     

MR imaging and MR angiography in popliteal artery entrapment syndrome

Popliteal artery entrapment (PAE) syndrome is an uncommon congenital anomaly seen in young adults causing ischemic symptoms in the lower extremities. It is the result of various types of anomalous relationships between the popliteal artery and the neighboring muscular structures. The purpose of this study was to define the role of MR imaging combined with MR angiography in the diagnosis of PAE cases. Four cases with segmental occlusion and medial displacement of popliteal artery in digital subtraction angiography (DSA) examinations were diagnosed as PAE syndrome by MR imaging and MR angiography. The DSA and MRA images are compared. All of the cases showed various degrees of abnormal intercondylar insertion of the medial head of the gastrocnemius muscle. The MR images showed detailed anatomy of the region revealing the cause of the arterial entrapment. Subclassification of the cases were done and fat tissue filling the normal localization of the muscle was evaluated. The DSA and MRA images demonstrated the length and localization of the occluded segment and collateral vascular developments equally. It is concluded that angiographic evaluation alone in PAE syndrome might result in overlooking the underlying cause of the arterial occlusion, which in turn leads to unsuccessful therapy procedures such as balloon angioplasty. Magnetic resonance imaging combined with MR angiography demonstrates both the vascular anatomy and the variations in the muscular structures in the popliteal fossa successfully, and this combination seems to be the most effective way of evaluating young adults with ischemic symptoms suggesting PAE syndrome. Received 7 April 1997; Revision received 15 July 1997; Accepted 13 November 1997     

Time-resolved contrast-enhanced 3D MR angiography

An MR angiographic technique, referred to as 3D TRICKS (3D time-resolved imaging of contrast kinetics) has been developed. This technique combines and extends to 3D imaging several previously published elements. These elements include an increased sampling rate for lower spatial frequencies, temporal interpolation of k-space views, and zero-filling in the slice-encoding dimension. When appropriately combined, these elements permit reconstruction of a series of 3D image sets having an effective temporal frame rate of one volume every 2-6 s. Acquiring a temporal series of images offers advantages over the current contrast-enhanced 3D MRA techniques in that it i) increases the likelihood that an arterial-only 3D image set will be obtained, ii) permits the passage of the contrast agent to be observed, and iii) allows temporal-processing techniques to be applied to yield additional information, or improve image quality.     

Effects of intravoxel velocity distributions on the complex difference method of phase-contrast MR angiography

The complex difference method of phase-contrast MR angiography is affected not only by the degree of velocity encoding applied during the scan but also by the variance of the intravoxel velocity distribution. The reconstructed intensities of voxels with the same average flow rate but different variances of the velocity distribution can differ significantly. Mathematical analysis and scanner phantom experiments confirm this conclusion.     

MR imaging: acronyms and clinical applications

The intention of this article is to provide an overview of all MR imaging techniques that are accessible on most of commercially available scanners and have the potential to be used in routine clinical applications. The techniques implemented by the major vendors are briefly explained, including a comparison of the commonly used acronyms. A classification scheme is introduced which provides a reasonable illustration of similarities and differences between various techniques. The imaging techniques are divided into two main groups, the spin-echo and gradient-echo sequences. Within each group is the basic sequence, those which require a preparation of the magnetization, those which use multiple echoes to fill the k-space and those which are performed in a single shot. For each technique the typical clinical applications are listed or the potential applications which have been published. Received: 18 August 1998; Revision received: 3 November 1998; Accepted: 4 November 1998     

Comparison of phase-difference and complex-difference processing in phase-contrast MR angiography.

The two main phase-contrast reconstruction methods are phase difference and complex difference. The signal-to-noise ratio properties and relative advantages of the two techniques are discussed. It is argued that each processing method has applications in which it is superior, and guidelines are provided to determine those applications. It is demonstrated theoretically and experimentally that only the complex-difference method is well suited for processing phase-contrast slabs with use of a projection dephaser gradient.     

Use of giant steel coils in the therapeutic embolization of a superior mesenteric artery-portal vein fistula

The use of a series of giant steel coils is described for the therapeutic embolization of a posttraumatic arteriovenous fistula between the superior mesenteric artery and the portal vein.     

Three-dimensional time-of-flight MR angiography using selective inversion recovery RAGE with fat saturation and ECG-triggering: Application to renal arteries

A three-dimensional (3D), ECG-triggered, selective inversion recovery (SIR) rapid gradient-echo (RAGE) technique is proposed to obtain MR angiograms of the main renal arteries. By using the selective inversion recovery and fat saturation, the background is significantly suppressed while blood maintains a high signal intensity as compared with conventional 3D time-of-flight (TOF) MR angiography. The sequence is ECG-triggered so that blood in-flow is maximized during systole, and intravoxel dephasing and pulsatile flow artifacts are minimized by collecting data during diastole. As a result, vessel boundary blurring and ghosting artifacts due to background motion are dramatically reduced, and the conspicuity and lumen definition of the arteries are significantly improved. High-quality MR angiograms of the main renal arteries with excellent blood/tissue contrast and suppression of motion artifacts have been consistently obtained for normal volunteers, with the length of visualization being 51 ± 07 mm for the left, and 57 ± 06 mm for the right renal arteries, significantly greater than using conventional 3D TOF pulse sequences. Statistical analysis was performed by using a one-sided Student's t test. Key words: renal artery; MR angiography; three-dimensional MR imaging.     

Evaluation of renal arteries in living renal donors: comparison between MDCT angiography and gadolinium-enhanced 3D MR angiography

Purpose The purpose of this study was to clarify and compare the accuracy of contrast-enhanced computed tomography (CT) angiography using multidetector-row helical CT (MDCT angiography) and gadolinium-enhanced MR angiography using three-dimensional Fourier transformation gradient-echo sequence (3D MR angiography) for preoperative evaluation of renal arteries in living renal donors. Materials and methods A total of 42 living renal donor candidates underwent both MDCT angiography and 3D MR angiography before digital subtraction angiography (DSA). Each MDCT angiogram and 3D MR angiogram was prospectively interpreted, and the findings were compared with the DSA results. Results MDCT angiography identified all of the 12 supernumerary arteries detected by DSA, whereas 3D MR angiography identified only 8. MDCT angiography identified all of the 19 proximal arterial branches detected by DSA, whereas 3D MR angiography identified only 16. Conclusion A more accurate depiction of renal arteries in living renal donors can be achieved with MDCT angiography than with 3D MR angiography.     

Hemodynamics of ovarian veins: MR angiography in women with uterine leiomyomata

Purpose

The passive reflux into ovarian veins (OVs) is well known as a common finding in normal asymptomatic women. The purpose of this study was to investigate the hemodynamics of OVs in women with myomatous uterus.

Materials and methods

Thirty-two women with symptomatic uterine leiomyomata underwent time-of-flight MR (TOF-MR) angiography, including venography and arteriography, and contrast-enhanced MRI. The frequency of reflux into OVs on TOF-MR angiography was retrospectively assessed with uterine volume, and compared to that of normal women in previous publication. The statistical evaluation was performed using Fisher's exact test.

Results

The mean uterine volume was 932 ± 612 ml (range, 301–2627 ml). The reflux into left OVs was observed in 4 of 32 women (13%) and that into right OVs was noted in 0 of 32 women (0%). These rates were significantly lower than those of normal asyptomatic women in the previous publication (p < 0.05). The reflux into OVs was observed in 0 of 19 women (0%) with 600 ml or larger myomatous uterus, whereas it was noted in 4 of the remaining 13 women (31%) with less than 600 ml myomatous uterus, with significant difference between the two groups (p = 0.02).

Conclusions

We found that reflux into OVs was infrequent in the vast majority of women with myomatous uterus, especially those with larger uterus due to leiomyomata on the basis of TOF-MR angiography. These findings suggested myomatous uterus could affect the flow direction of OVs, and passive reflux into OVs might be prevented due to the influence of antegrade flow of OVs.     

Combination of 2D sensitivity encoding and 2D partial fourier techniques for improved acceleration in 3D contrast-enhanced MR angiography.

Sensitivity encoding (SENSE) and partial Fourier (PF) techniques both reduce MRI acquisition time. Two-dimensional SENSE uses coil sensitivities to unfold aliasing in the phase/slice-encoding plane. One-dimensional PF and homodyne reconstruction are routinely applied in the frequency/phase-encoding plane to compensate for nonsampled k-space of the presumed real magnetization. Recently, a modified 3D elliptical centric acquisition was proposed to facilitate 2D-PF and homodyne reconstruction on an undersampled phase/slice-encoding plane. In this work we hypothesized that this 2D-PF technique can be combined with 2D-SENSE to achieve a greater acceleration factor than what each method can provide separately. Reconstruction of data whereby SENSE and PF are applied along the same axes is described. Contrast-enhanced MR angiography (CE-MRA) results from experiments using four receiver coils in phantom and volunteer studies are shown. In 11 volunteer studies, the SENSE-PF-homodyne technique using sevenfold acceleration (4x SENSE, 1.7x PF) consistently provided high-diagnostic-quality images with near 1-mm isotropic resolution in acquisition times of <20 s.     

Contrast-enhanced three-dimensional MR angiography in the assessment of subclavian artery diseases

The purpose of this prospective study was to determine the potential diagnostic value of 3D breath-hold contrast-enhanced MRA (CEMRA) in the evaluation of subclavian artery pathology, and to compare CEMRA and digital subtraction angiography (DSA) findings. The study group included 50 patients with suspicion of subclavian artery pathology: 40 suspected steno-occlusive disease and 10 different vascular anomalies. The MRA examinations were performed on a 1.5-T system using fast 3D sequences. A fixed dose of 40 ml Gd-DTPA was administered at 2 ml/s after previous bolus tracking. Images were analyzed to assess: subclavian depiction; luminal changes; collateral branches; and feeders of arterial venous malformations (AVM). A multireader blinded fashion was used. The CEMRA revealed an optimal agreement with DSA findings in the different types of diseases. Sensitivity and specificity were 90 and 95 %, respectively, in detecting steno-occlusive disease (including functional and arteritic stenoses), and 100 and 100 %, respectively, in cases of vascular anomalies (dilation, kinking, anomalous origin and AVM). Contrast-enhanced MRA can be proposed as a non-invasive, robust technique for imaging subclavian pathologies with high diagnostic performance. Received: 18 May 1999; Revised: 5 January 2000; Accepted: 27 March 2000     

Multiple pulmonary aneurysms secondary to Hughes-Stovin syndrome: Demonstration by MR angiography

We report a case of a 41-year-old patient with multiple pulmonary aneurysms secondary to Hughes-Stovin syndrome. Conventional pulmonary angiography could not be performed, because thrombus in both the inferior and superior vena cavae prevented catheter passage. Contrast-enhanced three-dimensional (3D) MR angiography (MRA) showed two segmental pulmonary aneurysms in the right lung. The affected segments of the lung were resected successfully, predicated on the MRA findings.     

Mesenteric CT angiography: a discussion of techniques and selected applications

Sixty-four slice MDCT with advanced three-dimensional (3D) visualization software provides a unique opportunity for noninvasive evaluation of the mesenteric vasculature. Although standard axial computed tomography (CT) scanning has always allowed identification of the mesenteric arteries and veins, it is limited in its ability to adequately image small branches and complex anatomy. However, the submillimeter collimation possible with 64-slice CT scanners now allows the acquisition of true isotropic data and therefore high spatial resolution is now maintained in any imaging plane. This ability to visualize the mesenteric vasculature in real-time using 3D rendering and multiplanar reconstruction is crucial for comprehensive review of the complex mesenteric vessels. In this article, we discuss CT scanning protocols and 3D imaging techniques that can be utilized for CT angiography of the mesenteric vessels. Additionally, we will discuss several key conditions that illustrate the value of 3D imaging over standard axial images in mesenteric CT angiography.     

Clinical anatomy of hepatic vessels by computed tomography angiography: A minireview

The liver has a complex vascular anatomy with a unique dual blood supply. Clinical conditions of the liver vary widely and include disorders originating in the vascular and biliary systems as well as the parenchyma. In most vascular disorders, the effects on the liver are generally subclinical because of its abundant blood supply. However, early diagnosis of such vascular diseases can significantly reduce patient morbidity and mortality. Because imaging findings of vascular disease are not always readily apparent, diagnosis can be difficult. Computed tomography angiography is an excellent imaging modality for visualizing the vascular anatomy of patients for treatment planning. In this review article, we focus on the vascular anatomy of the liver and the imaging findings in some acute hepatic vascular diseases.