The Optimization of Scan Timing for Contrast-Enhanced Magnetic Resonance Angiography

Objective

To determine the optimal scan timing for contrast-enhanced magnetic resonance angiography and to evaluate a new timing method based on the arteriovenous circulation time.

Materials and Methods

Eighty-nine contrast-enhanced magnetic resonance angiographic examinations were performed mainly in the extremities. A 1.5T scanner with a 3-D turbo-FLASH sequence was used, and during each study, two consecutive arterial phases and one venous phase were acquired. Scan delay time was calculated from the time-intensity curve by the traditional (n = 48) and/or the new (n = 41) method. This latter was based on arteriovenous circulation time rather than peak arterial enhancement time, as used in the traditional method. The numbers of first-phase images showing a properly enhanced arterial phase were compared between the two methods.

Results

Mean scan delay time was 5.4 sec longer with the new method than with the traditional. Properly enhanced first-phase images were found in 65% of cases (31/48) using the traditional timing method, and 95% (39/41) using the new method. When cases in which there was mismatch between the target vessel and the time-intensity curve acquisition site are excluded, erroneous acquisition occurred in seven cases with the traditional method, but in none with the new method.

Conclusion

The calculation of scan delay time on the basis of arteriovenous circulation time provides better timing for arterial phase acquisition than the traditional method.     

门脉高压的三维增强磁共振血管成像

目的 探讨上腹部磁共振对比增强三维血管成像技术(three-dimensional contrast-enhanced MR angiography,3D CE-MRA),对显示门脉高压所致血管改变及血流改变的应用价值.方法 对60例门脉高压患者,运用GE Signa 1.5T超导磁共振扫描仪进行3D CE-MRA 和2D CE-MRA成像,分析门脉高压的MRA表现.结果 (1)门静脉纤细狭窄18例.(2)门静脉闭塞、海绵样变11例.(3)食管下段、胃底静脉曲张43例.(4)腔静脉狭窄、闭塞 11例.(5)奇静脉、半奇静脉开放4例.(6)脐静脉开放4例.结论 3D CE-MRA是诊断门脉高压所致门脉系统血管及血流改变的可靠方法.     

Whole-Body Magnetic Resonance Angiography with Additional Steady-State Acquisition of the Infragenicular Arteries in Patients with Peripheral Arterial Disease

The purpose of this investigation was to determine if addition of infragenicular steady-state (SS) magnetic resonance angiography (MRA) to first-pass imaging improves diagnostic performance compared with first-pass imaging alone in patients with peripheral arterial disease (PAD) undergoing whole-body (WB) MRA. Twenty consecutive patients with PAD referred to digital-subtraction angiography (DSA) underwent WB-MRA. Using a bolus-chase technique, first-pass WB-MRA was performed from the supra-aortic vessels to the ankles. The blood-pool contrast agent gadofosveset trisodium was used at a dose of 0.03 mmol/kg body weight. Ten minutes after injection of the contrast agent, high-resolution (0.7-mm isotropic voxels) SS-MRA of the infragenicular arteries was performed. Using DSA as the “gold standard,” sensitivities and specificities for detecting significant arterial stenoses (≥50% luminal narrowing) with first-pass WB-MRA, SS-MRA, and combined first-pass and SS-MRA were calculated. Kappa statistics were used to determine intermodality agreement between MRA and DSA. Overall sensitivity and specificity for detecting significant arterial stenoses with first-pass WB-MRA was 0.70 (95% confidence interval 0.61 to 0.78) and 0.97 (0.94 to 0.99), respectively. In first-pass WB-MRA, the lowest sensitivity was in the infragenicular region, with a value of 0.42 (0.23 to 0.63). Combined analysis of first-pass WB-MRA and SS-MRA increased sensitivity to 0.81 (0.60 to 0.93) in the infragenicular region, with specificity of 0.94 (0.88 to 0.97). Sensitivity and specificity for detecting significant arterial stenoses with isolated infragenicular SS-MRA was 0.47 (0.27 to 0.69) and 0.86 (0.78 to 0.91), respectively. Intermodality agreement between MRA and DSA in the infragenicular region was moderate for first-pass WB-MRA (κ = 0.49), fair for SS-MRA (κ = 0.31), and good for combined first-pass/SS-MRA (κ = 0.71). Addition of infragenicular SS-MRA to first-pass WB MRA improves diagnostic performance.     

MR增强血管成像在颅内动脉狭窄及闭塞诊断中的价值

目的 探讨MR增强血管成像(3D CE-MRA)在颅内动脉狭窄及闭塞诊断中的价值及准确性.方法 选择103例脑血管疾病患者行3D CE-MRA检查,其中41例并行三维飞越法MR血管造影(3D TOF-MRA)检查,35例行DSA检查.对35例同时行3D CE-MRA、3D TOF-MRA和DSA检查者在显示动脉闭塞及狭窄能力上的优劣进行比较.结果总计发现217处不同程度的动脉狭窄或闭塞病变.3种检查方法在发现动脉狭窄或闭塞的支数及程度间存在显著性差异(χ2=13.418,P＜0.001);3D TOF-MRA与3D CE-MRA或DSA在发现动脉狭窄或闭塞程度及支数间存在差异(χ2=4.389,P＜0.05;χ2=11.22,P＜0.01),3D CE-MRA或DSA间比较没有显著性差异(χ2=3.101,P＞0.05).结论 3D CE-MRA具有快速、有效、无创等特点,在诊断颅内动脉闭塞及狭窄方面有着独特的价值.     

Whole-Body Magnetic Resonance Angiography at 3 Tesla Using a Hybrid Protocol in Patients with Peripheral Arterial Disease

The purpose of this study was to determine the diagnostic performance of 3T whole-body magnetic resonance angiography (WB-MRA) using a hybrid protocol in comparison with a standard protocol in patients with peripheral arterial disease (PAD). In 26 consecutive patients with PAD two different protocols were used for WB-MRA: a standard sequential protocol (n = 13) and a hybrid protocol (n = 13). WB-MRA was performed using a gradient echo sequence, body coil for signal reception, and gadoterate meglumine as contrast agent (0.3 mmol/kg body weight). Two blinded observers evaluated all WB-MRA examinations with regard to presence of stenoses, as well as diagnostic quality and degree of venous contamination in each of the four stations used in WB-MRA. Digital subtraction angiography served as the method of reference. Sensitivity for detecting significant arterial disease (luminal narrowing ≥ 50%) using standard-protocol WB-MRA for the two observers was 0.63 (95%CI: 0.51–0.73) and 0.66 (0.58–0.78). Specificities were 0.94 (0.91–0.97) and 0.96 (0.92–0.98), respectively. In the hybrid protocol WB-MRA sensitivities were 0.75 (0.64–0.84) and 0.70 (0.58–0.8), respectively. Specificities were 0.93 (0.88–0.96) and 0.95 (0.91–0.97). Interobserver agreement was good using both the standard and the hybrid protocol, with κ = 0.62 (0.44–0.67) and κ = 0.70 (0.59–0.79), respectively. WB-MRA quality scores were significantly higher in the lower leg using the hybrid protocol compared to standard protocol (p = 0.003 and p = 0.03, observers 1 and 2). Distal venous contamination scores were significantly lower with the hybrid protocol (p = 0.02 and p = 0.01, observers 1 and 2). In conclusion, hybrid-protocol WB-MRA shows a better diagnostic performance than standard protocol WB-MRA at 3 T in patients with PAD.     

Intracranial Aneurysms Treated by Flow-Diverting Stents: Long-Term Follow-Up with Contrast-Enhanced Magnetic Resonance Angiography

Purpose

Long-term data on aneurysm treatment with flow-diverting stents are still sparse, and follow-up protocols differ widely between institutions. We present long-term results, with a focus on the usefulness of contrast-enhanced MR angiography (ceMRA).

Materials and Methods

Interventions and follow-up imaging of patients with aneurysms treated by flow-diverting stents (“Pipeline,” “Silk” and “FRED” models) without additional coiling were analyzed. All MRI scans included dedicated two-phase ceMRA. Aneurysm occlusion rates, size of the aneurysmal sac and complications were evaluated on MRI and digital subtraction angiography (DSA), where available. The ability of ceMRA to depict aneurysm occlusion and stent patency was graded on a three-point scale.

Results

Twenty-five patients with 102 MRI scans were included. The median duration of follow-up was 830 days. Aneurysm occlusion rates were 52% at 3 months (10 of 19 patients), 72% at 6 months (18/25) and 84% overall (21/25). Shrinkage of the aneurysmal sac was found in 19 patients (76%) and in 12 cases to <50% of the original size (48%). CeMRA assessability of aneurysmal occlusion was graded as good in all cases. When compared to DSA (18 cases), ceMRA had a sensitivity of 100% and specificity of 91% regarding aneurysm remnant detection. Assessability of the stent lumen varied and was limited in most cases.

Conclusions

Flow-diverter treatment achieves high occlusion rates and can cause major aneurysm shrinkage. CeMRA is highly valuable regarding imaging of the aneurysmal sac. There are limitations regarding the assessability of the stent lumen on ceMRA.

Level of Evidence

Level 4, Case Series.

     

Value of Single-Dose Contrast-Enhanced Magnetic Resonance Angiography Versus Intraarterial Digital Subtraction Angiography in Therapy Indications in Abdominal and Iliac Arteries

The objective of the study was to prove the value of single-dose contrast-enhanced magnetic resonance angiography [three-dimensional (3D) ceMRA] in abdominal and iliac arteries versus the reference standard intra-arterial digital subtraction angiography (i.a.DSA) when indicating a therapy. Patients suspected of having abdominal or iliac artery stenosis were included in this study. A positive vote of the local Ethics Committe was given. After written informed consent was obtained, 37 patients were enrolled, of which 34 were available for image evaluation. Both 3D ceMRA and i.a. DSA were performed for each patient. The dosage for 3D ceMRA was 0.1 mmol/kg body weight in a 1.5-T scanner with a phased-array coil. The parameters of the 3D-FLASH sequence were as follows: TR/TE 4.6/1.8 ms, effective thickness 3.5 mm, matrix 512 × 200, flip angle 30°, field of view 420 mm, TA 23 s, coronal scan orientation. Totally, 476 vessel segments were evaluated for stenosis degree by two radiologists in a consensus fashion in a blinded read. For each patient, a therapy was proposed, if clinically indicated. Sensitivity, specificity, positive and negative predictive values, and accuracy for stenoses ≥50% were 68%, 92%, 44%, 97%, and 90%, respectively. In 13/34 patients, a discrepancy was found concerning therapy decisions based on MRA findings versus therapy decisions based on the reference standard DSA. The results showed that the used MRA imaging technique of abdominal and iliac arteries is not competitive to i.a. DSA, with a high rate of misinterpretation of the MRAs resulting in incorrect therapies.     

Intracranial Magnetic Resonance Angiography

Intraarterial angiography remains the "gold standard" for the evaluation of the intracranial vasculature, but it carries with it the risks of local vascular damage, systemic reactions, transient neurologic deficits, permanent neurologic compromise, and even death. To date, magnetic resonance angiography (MRA) has been applied to a variety of different manifestations of intracranial vascular disease. Presently, MRA studies and flow measurement techniques serve to compliment the more traditional spin-echo evaluation of patients with small aneurysms, arterial and venous occlusions, vascular malformations, and in some cases of neoplastic vascular invasion. Practically, the limitations of these techniques must be taken into account such that the appropriate method is applied to answer a specific clinical question and the acquisition parameters are chosen to maximize the sensitivity and specificity of the study. The intent of this review is to summarize the technical approaches, clinical role, pitfalls, and potential improvements in the MRA techniques as they apply to the intracranial circulation.     

对比增强磁共振冠状动脉成像对冠状动脉狭窄的诊断效能分析

目的探讨对比增强磁共振冠状动脉成像(CE CMRA)诊断冠状动脉明显狭窄(≥50%)的临床应用价值。资料与方法 21例疑似冠状动脉粥样硬化性心脏病患者与23名自愿者分别行CE CMRA及不使用对比剂磁共振冠状动脉成像(CMRA),经Soap-Bubble软件重组后处理获得左、右冠状动脉图像,比较其血管锐利度差异;其中行CE CMRA患者与其选择性冠状动脉造影(CAG)检查对照,按冠状动脉解剖节段进行配对比较,评价CE CM-RA对冠状动脉明显狭窄的诊断效能。结果 CE CMRA与CMRA分别获得20例、22例有效图像数据;CE CMRA与CMRA的冠状动脉血管锐利度分别为:RCA(63±12)%、(55±10)%;LCA(LM+LAD)(57±12)%、(47±16)%;LCX(47±13)%、(37±16)%;两者间差异均有统计学意义(P<0.05)。以CAG为参照标准,CE CMRA诊断冠状动脉明显狭窄的敏感性、特异性、准确性分别为79.3%、91.6%、89.4%,阳性预测值和阴性预测值分别为67.6%和95.2%。结论 CE CMRA可定性评价冠状动脉明显狭窄,尤其适用于冠状动脉明显狭窄的排除性诊断,...     

Differential Subsampling with Cartesian Ordering Contrast-Enhanced Magnetic Resonance Angiography for the Preoperative Assessment of Anterolateral Thigh Flap

ObjectiveTo investigate the clinical application of differential subsampling with Cartesian ordering (DISCO) contrast-enhanced (CE) magnetic resonance angiography for anterolateral thigh (ALT) flap transplantation, using operative findings as a reference.Materials and MethodsThirty patients (21 males and nine females; mean age ± standard deviation, 45.5 ± 15.6 years) who were scheduled to undergo reconstruction with ALT flaps between June 2020 and June 2021 were included in the prospective study. Before ALT flap transplantation, patients were scanned using CE-DISCO imaging. All acquired DISCO images of the 60 lower limbs (both sides from each patient) were analyzed using maximum intensity projection and volume rendering methods. Two experienced radiologists were employed to examine the patterns of the lateral circumflex femoral artery (LCFA), its branches, and perforators and their skin termini, which were compared with the operative findings.ResultsUsing CE-DISCO, the patterns of the LCFA and its branches were clearly identified in all patients. Four different origins of the LCFA were found among the 60 blood vessels: type I (44/60, 73.3%), type II (6/60, 10.0%), type III (8/60, 13.3%), and type IV (2/60, 3.3%). Owing to a lack of perforators entering the skin, two patients did not undergo ALT flap transplantation. For the remaining 28 patients, the ALT flaps in 26 patients were successfully operated without flap re-selection during the operation, while the remaining two patients underwent other surgical procedures due to the thin diameter of the perforator or injury of the perforator during the operation. The success rate of flap transplantation was 92.8% (26/28). All transplanted flaps exhibited good blood supply and achieved primary healing without infection or delayed healing.ConclusionCE-DISCO imaging can be an effective method for preoperative perforator imaging before ALT flap transplantation.     

Instrumentation for Magnetic Resonance Angiography

Magnetic resonance angiography (MRA) places high demands on instrumentation capabilities. Magnetic gradient strength capabilities, main magnetic field strength and homogeneity, and eddy current compensation all play a role in determining the quality of the flow studies. In addition, radiofrequency coil design and use is governed by the specific vascular territories of interest. Once the instrumentational and pulse sequence considerations have been optimized, the postprocessing and display of the acquired three-dimensional data sets is of key importance. Great strides have been made in addressing instrumentation needs for MRA, but further improvements are anticipated.     

Extracranial Carotid Magnetic Resonance Angiography

This article reviews early experience in the evaluation of the extracranial carotid artery with magnetic resonance angiography (MRA). A historical context is provided, with a brief review of the previously available noninvasive methods used for cervical carotid artery screening. The clinical context within which MRA must play its role is also briefly discussed. Finally, early clinical experience with MRA and several pitfalls are illustrated.     

Selective Magnetic Resonance Angiography of the Head

Selective magnetic resonance angiography (MRA) is a combination of two- or three-dimensional MRA with radiofrequency presaturation pulses. Presaturation pulses can be applied over user-defined regions. They reduce or eliminate signals within the presaturation slab. As a result, blood flowing within or through the presaturation slab turns dark whereas blood flowing outside and not through the presaturation slab still appears bright. Using this technique, flow direction and origin of flow can be determined and flowing blood can be differentiated from stationary bright tissues such as thrombus. Arteries and veins can be imaged selectively due to their usually opposite flow direction. The intracranial collateral circulation about the circle of Willis can be shown, and vessels feeding or draining arteriovenous malformations can be identified more accurately. In conclusion, selective MRA can provide functional information about the cerebrovascular system, which cannot be obtained from conventional MR imaging (MRI) or MRA alone.     

Magnetic Resonance Angiography of the Abdominal Aorta

Magnetic resonance angiography (MRA) of the abdominal aorta was performed in 36 patients using the "bright-blood" technique on the basis of a series of flow-compensated breath-hold 2 D-GE pulse sequences. Diverse diseases included complete occlusion, stenosis, atherosclerotic or dissecting aneurysm and renal artery stenosis. Coronal and axial projection angiograms [maximum intensity projection (MIP) algorithm] and individual GE images were compared with DSA and contrast-enhanced computed tomography (CT). Our data showed a good correlation of MR and digital subtraction arteriography (DSA) or CT resp. in all cases, when both rotating MIP angiograms and individual GE images were analyzed. Thus, MR is suggested to be a useful noninvasive diagnostic method for the abdominal aorta, particularly in preoperative staging of aneurysms, aortic occlusive disease, and stenosis of the proximal main renal artery. Drawbacks of the method are a signal loss in slow or turbulent flow conditions, and unsatisfactory spatial resolution in small vessels.     

Comparison Between Contrast-Enhanced Computed Tomography and Contrast-Enhanced Magnetic Resonance Imaging With Magnetic Resonance Cholangiopancreatography for Resectability Assessment in Extrahepatic Cholangiocarcinoma

ObjectiveTo compare the diagnostic performance and interobserver agreement between contrast-enhanced computed tomography (CECT) and contrast-enhanced magnetic resonance imaging (CE-MRI) with magnetic resonance cholangiopancreatography (MRCP) for evaluating the resectability in patients with extrahepatic cholangiocarcinoma (eCCA).Materials and MethodsThis retrospective study included treatment-naïve patients with pathologically confirmed eCCA, who underwent both CECT and CE-MRI with MRCP using extracellular contrast media between January 2015 and December 2020. Among the 214 patients (146 males; mean age ± standard deviation, 68 ± 9 years) included, 121 (56.5%) had perihilar cholangiocarcinoma. R0 resection was achieved in 108 of the 153 (70.6%) patients who underwent curative-intent surgery. Four fellowship-trained radiologists independently reviewed the findings of both CECT and CE-MRI with MRCP to assess the local tumor extent and distant metastasis for determining resectability. The pooled area under the receiver operating characteristic curve (AUC), sensitivity, and specificity of CECT and CE-MRI with MRCP were compared using clinical, surgical, and pathological findings as reference standards. The interobserver agreement of resectability was evaluated using Fleiss kappa (κ).ResultsNo significant differences were observed between CECT and CE-MRI with MRCP in the pooled AUC (0.753 vs. 0.767), sensitivity (84.7% [366/432] vs. 90.3% [390/432]), and specificity (52.6% [223/424] vs. 51.4% [218/424]) (P > 0.05 for all). The AUC for determining resectability was higher when CECT and CE-MRI with MRCP were reviewed together than when CECT was reviewed alone in patients with discrepancies between the imaging modalities or with indeterminate resectability (0.798 [0.754–0.841] vs. 0.753 [0.697–0.808], P = 0.014). The interobserver agreement for overall resectability was fair for both CECT (κ = 0.323) and CE-MRI with MRCP (κ = 0.320), without a significant difference (P = 0.884).ConclusionCECT and CE-MRI with MRCP showed no significant differences in the diagnostic performance and interobserver agreement in determining the resectability in patients with eCCA.     

Basic Principles of Magnetic Resonance Angiography

The flow of blood through magnetic field gradients and radiofrequency fields produces signal changes that can be used to distinguish blood vessels from surrounding stationary tissue. The field of magnetic resonance (MR) angiography attempts to overcome this limitation by creating images that depict blood vessels in a projective format similar to a conventional invasive angiogram, but without the need for ionizing radiation or a contrast agent. This article reviews basic concepts involved in MR angiography, including signal changes from time-of-flight and phase effects, maximum intensity projection algorithm for postprocessing of two-dimensional (2D) and three-dimensional (3D) image sets, and methods for flow quantification. Potential problems with MR angiography are considered, as well as means to overcome them.