3D time-resolved MR angiography (MRA) of the carotid arteries with time-resolved imaging with stochastic trajectories: comparison with 3D contrast-enhanced Bolus-Chase MRA and 3D time-of-flight MRA

BACKGROUND AND PURPOSE: Time-resolved MR angiography (MRA) offers the combined advantage of large anatomic coverage and hemodynamic flow information. We applied parallel imaging and time-resolved imaging with stochastic trajectories (TWIST), which uses a spiral trajectory to undersample k-space, to perform time-resolved MRA of the extracranial internal carotid arteries and compare it to time-of-flight (TOF) and high-resolution contrast-enhanced (HR) MRA.MATERIALS AND METHODS: A retrospective review of 31 patients who underwent carotid MRA at 1.5T using TOF, time-resolved and HR MRA was performed. Images were evaluated for the presence and degree of ICA stenosis, reader confidence, and number of pure arterial frames attained with the TWIST technique.RESULTS: With a consensus interpretation of all sequences as the reference standard, accuracy for identifying stenosis was 90.3% for TWIST MRA, compared with 96.0% and 88.7% for HR MRA and TOF MRA, respectively. HR MRA was significantly more accurate than the other techniques (P < .05). TWIST MRA yielded datasets with high in-plane spatial resolution and distinct arterial and venous phases. It provided dynamic information not otherwise available. Mean diagnostic confidence was satisfactory or greater for TWIST in all patients.CONCLUSION: The TWIST technique consistently obtained pure arterial phase images while providing dynamic information. It is rapid, uses a low dose of contrast, and may be useful in specific circumstances, such as in the acute stroke setting. However, it does not yet have spatial resolution comparable with standard contrast-enhanced MRA.

Stroke has an estimated prevalence of 5.7 million (2.6%) adults in the United States, where it is the third most common cause of mortality.¹ Atherosclerotic carotid artery disease is an important risk factor for anterior circulation ischemic stroke. Imaging evaluation is essential for optimal management and stroke prevention, as demonstrated in studies of symptomatic^2,3 and asymptomatic populations.^4,5 Carotid dissection is another potential cause of anterior circulation ischemia, which also requires high-spatial-resolution imaging for definitive diagnosis.Digital subtraction angiography (DSA) remains the gold standard for assessment of the cervical vasculature,⁶ with excellent spatial and temporal resolution. However, risks include vascular injury, intracerebral complications, contrast nephrotoxicity, and exposure to ionizing radiation. Therefore, noninvasive techniques are typically used initially. Duplex Doppler sonography, CT angiography (CTA), and MR angiography (MRA) all have high but varying degrees of sensitivity and specificity, ranging from 70% to 99% for carotid stenosis detection.⁷ Although sonography provides excellent dynamic information and spatial resolution, insonation window limitations restrict anatomic coverage. Similarly, long imaging times with time-of-flight (TOF) MRA also limit anatomic coverage. CTA and conventional arterial contrast-enhanced MRA offer extensive coverage but provide no dynamic information and are dependent on accurate timing for optimal visualization of the arterial tree.3D time-resolved contrast-enhanced MR angiography (TR MRA) has been previously described.⁸ TR MRA offers combined anatomic and hemodynamic information and obtains pure arterial and venous phase images consistently and rapidly without a timing run. More recently, the technique has been specifically applied to the extracranial carotid arteries using parallel imaging or keyhole imaging techniques.^9,10 In this study, we report the diagnostic accuracy of TR MRA of the extracranial internal carotid artery (ICA) acquired with a combination of parallel imaging (generalized autocalibrating partially parallel acquisition [GRAPPA])¹¹ and time-resolved imaging with stochastic trajectories (TWIST), a new view-sharing technique, which undersamples the periphery of k-space depending on the radial distance from the center of k-space.^12,13 We compared TR MRA with 3D high-resolution contrast enhanced MRA (HR MRA) and 3D TOF MRA.     

Evaluation of contrast-enhanced magnetic resonance angiography (MRA) using Gd-DOTA compared with time-of-flight MRA in the diagnosis of clinically significant non-coronary arterial disease

Objectives

This trial assessed diagnostic accuracy of contrast-enhanced magnetic resonance angiography (MRA) with meglumine gadoterate (Gd-DOTA) at 3 Tesla (T) over unenhanced MRA at 3 T in non-coronary arterial diseases by comparing their accuracy with that of the gold standard, x-ray angiography.

Methods

Ninety-two patients with suspected non-coronary arterial disease underwent in fixed sequence unenhanced time-of flight (TOF) MRA, contrast-enhanced MRA using a Gd-DOTA bolus (intravenous bolus 0.1 mmol/kg) and x-ray angiography.

Results

Eighty-four patients (71 male, 13 female; median age 64.5 years) were included in an intent-to-treat efficacy analysis. Targeted vascular areas were aorto-iliac, calf, carotid, femoral, popliteal and renal. Within-patient accuracy was significantly higher with contrast-enhanced MRA using Gd-DOTA than with unenhanced MRA (p?=?0.0003). There was 84.4?±?17.5% agreement between contrast-enhanced MRA (Gd-DOTA) and x-ray angiography, compared with 76.8?±?20.4% between non-enhanced MRA and x-ray angiography. Sensitivity and specificity were also better with Gd-DOTA compared with non-enhanced MRA at the segment level. Duration of the MRA procedure was 3.5 times shorter with Gd-DOTA compared with non-enhanced MRA. Six patients reported six mild or moderate adverse events. No serious adverse events occurred.

Conclusions

Contrast-enhanced MRA using Gd-DOTA at 3 T was superior to unenhanced TOF MRA in the vascular territories investigated.     

ECG-Triggered Non-Contrast-Enhanced MR Angiography (TRANCE) versus Digital Subtraction Angiography (DSA) in patients with peripheral arterial occlusive disease of the lower extremities

Objective

To prospectively determine the diagnostic value of electrocardiography-triggered non-contrast-enhanced magnetic resonance angiography (TRANCE) of the lower extremities including the feet versus DSA.

Methods

All 43 patients with symptomatic peripheral arterial occlusive disease (PAOD) underwent TRANCE before DSA. Quality of MRA vessel depiction was rated by two independent radiologists on a 3-point scale. Arterial segments were graded for stenoses using a 4-point scale (grade 1: no stenosis; grade 2: moderate stenosis; grade 3: severe stenosis; grade 4: occlusion). Findings were compared with those of DSA.

Results

In the 731 vessel segments analysed, intra-arterial DSA revealed 283 stenoses: 33.6% moderate, 16.6% severe and 49.8% occlusions. TRANCE yielded a mean sensitivity, specificity, positive and negative predictive value and diagnostic accuracy to detect severe stenoses or occlusions of 95.6%, 97.4%, 87.2%, 99.2%, 97.1% for the thigh segments and 95.2%, 87.5%, 83.2%, 96.6%, 90.5% for the calf segments. Excellent overall image quality was observed for TRANCE in 91.4% versus 95.7% (DSA) for the thigh and in 60.7% versus 91.0% for the calves, while diagnostic quality of the pedal arteries was rated as insufficient.

Conclusion

TRANCE achieves high diagnostic accuracy in the thigh and calf regions, whereas the pedal arteries showed limited quality.     

Comparison between 64-row CT angiography and digital subtraction angiography in the study of lower extremities: personal experience

Purpose

This study was undertaken to evaluate the potential of 64-row multislice computed tomography (CT) versus digital subtraction angiography (DSA) in detecting significant lesions of lower-extremity inflow and runoff arteries.

Materials and methods

Fifty-three patients underwent 64-row multislice CT and DSA over a mean of 36 days. The vascular tree was divided into 33 segments. Three readers independently reviewed the axial CT scans and multiplanar oblique and two- and three-dimensional reconstructions (maximum intensity projection and volume rendering) images to assess degree of stenosis according to four categories: 1 (0%–49% stenosis); 2 (50%–99% stenosis); 3 (occluded); 4 (not evaluable). In all cases, DSA was performed by arterial catheterisation.

Results

In 53 patients, 1,440 segments were evaluated (infrarenal aorta and 16 arterial segments for each leg; 42 bilateral studies, 11 unilateral studies). Compared with DSA, CT angiography yielded 97.2% sensitivity, 97% specificity, 92.5% positive predictive value, 98.9% negative predictive value, 97.1% diagnostic accuracy and 95.4% concordance on the degree of stenosis.

Conclusions

Sixty-four-row multislice CT proved to be helpful in detecting haemodynamically significant lesions in peripheral arterial occlusive disease and improved the results obtained with 4- and 16-slice multidetector CT. In addition, owing to the high spatial resolution and rigorous technique, no variations in the data obtained below the knee were detected, overcoming a limitation of earlier generations of CT scanners.     

Optimisation of a high-resolution whole-body MR angiography protocol with parallel imaging and biphasic administration of a single bolus of Gd-BOPTA: preliminary experience in the systemic evaluation of atherosclerotic burden in patients referred for endovascular procedures

Purpose

This study was performed to validate a highresolution whole-body magnetic resonance angiography (MRA) protocol with parallel imaging and biphasic administration of a single bolus of contrast agent in the preliminary assessment of systemic atherosclerotic burden in patients referred for endovascular procedures.

Materials and methods

Forty patients referred for endovascular treatment of atherosclerotic disease of the carotid arteries (n=23), peripheral vessels (n=14) or aorta (n=3) on the basis of previous clinical and diagnostic examinations underwent high-resolution whole-body MRA at 1.5 T with 3D spoiled gradient recalled echo (GRE) sequences, featuring parallel imaging acquisition technique with ×2 acceleration factor. Sixty-eight surface coil elements and a four-station imaging protocol were employed. Biphasic intravenous administration of a paramagnetic contrast agent [gadolinium benzyloxyproprionic-tetraacetic acid (Gd-BOPTA)] was performed with the following protocol: 10 ml at a speed of 1 ml/s followed by further 10 ml at a speed of 0.5 ml/s. For image analysis, the arterial system was divided into 42 segments for evaluation. The presence or absence of atherosclerotic lesions was evaluated by two observers in consensus; segments were classified as having clinically significant disease (≥50% stenosis or an aneurysmal dilatation) or no significant disease (<50% stenosis). The presence of stenoocclusive disease, determined at all segments, was compared with findings on digital subtraction angiography (DSA), which were interpreted by a third independent reader. Sensitivity, specificity and concordance of whole-body MRA findings with DSA were calculated, and receiver operating characteristic (ROC) analysis was performed for all vascular territories.

Results

A total of 1,680 arterial segments was evaluated; 138 (8.3%) were affected by atherosclerotic alterations. Carotid lesions were confirmed in 23 patients (34 segments), involvement of peripheral vessels in 14 (57 segments) and abdominal aneurysms in three. Sensitivity and specificity of whole-body MRA were, respectively, 95%–97% for head and neck vessels, 100%-100% for thoracoabdominal vessels, 98%-97% for thigh vessels and 84%–88% for calf vessels; concordance with the DSA findings was significant (p<0.05). Subclinical atherosclerotic lesions were evidenced in 25 patients, involving carotid arteries (12 segments), peripheral vessels (21 segments) and abdominal aorta (one segment). All these lesions were confirmed by a second modality, and ten of these patients required further care.

Conclusions

High-resolution whole-body MRA with Gd-BOPTA may be considered a reliable modality for imaging systemic atherosclerosis in candidates for endovascular procedures. The subclinical detection of the total atherosclerotic burden has potential implications for secondary care in this population.     

Time‐resolved lower extremity MRA with temporal interpolation and stochastic spiral trajectories: Preliminary clinical experience

Purpose:

To assess added value of a new time‐resolved technique with temporal interpolation and stochastic spiral trajectory through k‐space and parallel imaging (TR‐MRA) to conventional bolus chase MRA (BC‐MRA) for infragenual peripheral artery evaluation.

Materials and Methods:

An institutional review board‐approved retrospective review of peripheral arterial disease patients was performed. Infragenual TR‐MRA and BC‐MRA were performed in 26 patients over four months. Two readers individually assessed image quality, diagnostic confidence, and stenosis severity and length in 13 defined below knee segments, first with BC‐MRA alone, and then with a combined BC‐MRA and TR‐MRA reading (BC+TR‐MRA). Perceived contribution of TR‐MRA was rated by each reader. The reference standard was a consensus reading of both sequences. Catheter angiographic (CA) correlation was available in 6 patients.

Results:

A total of 646 infragenual segments in 51 extremities were evaluated. Image quality and diagnostic confidence were superior for BC+TR‐MRA compared with BC‐MRA alone (P < 0.001). Adding TR‐MRA improved sensitivity (85.7% versus 80.7%; P < 0.05) and diagnostic accuracy (88.1% versus 85.4%; P < 0.05) for hemodynamically significant stenosis. Venous contamination (0% versus 13.1% segments) and motion (0.9% versus 8.0%) were decreased for BC+TR‐MRA versus BC‐MRA alone, P < 0.01. For BC+TR‐MRA, TR‐MRA was rated more useful than BC‐MRA in 30/51 legs (58.8%). TR‐MRA identified retrograde flow in 5 segments. Where available, there was high concordance between CA and BC+TR‐MRA (91.6%) for stenosis.

Conclusion:

Adding TR‐MRA with temporal interpolation and stochastic spiral trajectories to bolus chase MRA improves image quality, diagnostic confidence and accuracy. It provides hemodynamic information and minimizes venous contamination and patient motion. J. Magn. Reson. Imaging 2010;31:663–672. © 2010 Wiley‐Liss, Inc.     

Appropriate Minimal Dose of Gadobutrol for 3D Time-Resolved MRA of the Supra-Aortic Arteries: Comparison with Conventional Single-Phase High-Resolution 3D Contrast-Enhanced MRA

BACKGROUND AND PURPOSE:The development of nephrogenic systemic fibrosis and neural tissue deposition is gadolinium dose–dependent. The purpose of this study was to determine the appropriate minimal dose of gadobutrol with time-resolved MRA to assess supra-aortic arterial stenosis with contrast-enhanced MRA as a reference standard.MATERIALS AND METHODS:Four hundred sixty-two consecutive patients underwent both standard-dose contrast-enhanced MRA and low-dose time-resolved MRA and were classified into 3 groups; group A (a constant dose of 1 mL for time-resolved MRA), group B (2 mL), or group C (3 mL). All studies were independently evaluated by 2 radiologists for image quality by using a 5-point scale (from 0 = failure to 4 = excellent), grading of arterial stenosis (0 = normal, 1 = mild [<30%], 2 = moderate [30%–69%], 3 = severe to occlusion [≥70%]), and signal-to-noise ratio.RESULTS:The image quality of time-resolved MRA was similar to that of contrast-enhanced MRA in groups B and C, but it was inferior to contrast-enhanced MRA in group A. For the grading of arterial stenosis, there was an excellent correlation between contrast-enhanced MRA and time-resolved MRA (R = 0.957 for group A, R = 0.988 for group B, R = 0.991 for group C). The SNR of time-resolved MRA tended to be lower than that of contrast-enhanced MRA in groups A and B. However, SNR was higher for time-resolved MRA compared with contrast-enhanced MRA in group C.CONCLUSIONS:Low-dose time-resolved MRA is feasible in the evaluation of supra-aortic stenosis and could be used as an alternative to contrast-enhanced MRA for a diagnostic technique in high-risk populations.

Digital subtraction angiography remains the criterion standard for evaluation of supra-aortic steno-occlusive disease, with excellent spatial and temporal resolution. However, it is a time-consuming and invasive technique and is associated with several risks, including transient ischemic attack, permanent neurologic deficit, iodine contrast nephrotoxicity, and exposure to ionizing radiation.^1–3 Consequently, DSA has largely been reserved for interventions for extracranial and intracranial steno-occlusive disease or in cases of uncertain findings on noninvasive imaging studies.⁴ Noninvasive angiography techniques such as CTA and MRA are typically used for routine diagnostic procedures. Recently, 3D high-resolution contrast-enhanced MRA (CE-MRA) has become widely used as an excellent alternative imaging technique for the assessment of supra-aortic steno-occlusive disease.⁵Gadolinium-based contrast agents (GBCAs) were initially thought to be safe in patients with reduced renal function rather than iodine-based contrast agents.⁶ Recently, a positive association between nephrogenic systemic fibrosis and exposure to GBCAs in patients with renal failure has been described.⁷ Several studies showed a relationship between high doses of GBCAs and increased nephrogenic systemic fibrosis risk.^8–11 Also, in the past 2 years, several studies regarding gadolinium retention in intracranial neuronal tissues have been published.^12–14 The development of nephrogenic systemic fibrosis with exposure to GBCAs and gadolinium deposition in neuronal tissue is dose-dependent; therefore, caution has been advised when administering GBCAs.^13,15 There is increasing interest in dose-reduction strategies that maintain diagnostic image quality.¹⁶ Time-resolved MRA (TR-MRA) is used clinically to offer combined anatomic and hemodynamic information of the supra-aortic vessels, and another advantage of TR-MRA is the requirement for low-dose GBCAs.^2,3,16,17 Several studies have demonstrated that TR-MRA with low-dose GBCAs yields comprehensive anatomic and functional information with high sensitivity and negative predictive values.^2,3,17–20The purpose of this study was to determine the appropriate minimal dose for TR-MRA to assess supra-aortic arterial stenosis with CE-MRA as a reference standard.     

Contrast-enhanced time-resolved 4D MRA of congenital heart and vessel anomalies: image quality and diagnostic value compared with 3D MRA

Objectives

To evaluate time-resolved interleaved stochastic trajectories (TWIST) contrast-enhanced 4D magnetic resonance angiography (MRA) and compare it with 3D FLASH MRA in patients with congenital heart and vessel anomalies.

Methods

Twenty-six patients with congenital heart and vessel anomalies underwent contrast-enhanced MRA with both 3D FLASH and 4D TWIST MRA. Images were subjectively evaluated regarding total image quality, artefacts, diagnostic value and added diagnostic value of 4D dynamic imaging. Quantitative comparison included signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and vessel sharpness measurements.

Results

Three-dimensional FLASH MRA was judged to be significantly better in terms of image quality (4.0?±?0.6 vs 3.4?±?0.6, P?<?0.05) and artefacts (3.8?±?0.4 vs 3.3?±?0.5, P?<?0.05); no difference in diagnostic value was found (4.2?±?0.4 vs 4.0?±?0.4); important additional functional information was found in 21/26 patients. SNR and CNR were higher in the pulmonary trunk in 4D TWIST, but slightly higher in the systemic arteries in 3D FLASH. No difference in vessel sharpness delineation was found.

Conclusions

Although image quality was inferior compared with 3D FLASH MRA, 4D TWIST MRA yields robust images and added diagnostic value through dynamic acquisition was found. Thus, 4D TWIST MRA is an attractive alternative to 3D FLASH MRA.

Key Points

? New magnetic resonance angiography (MRA) techniques are increasingly introduced for congenital cardiovascular problems. ? Time-resolved angiography with interleaved stochastic trajectories (TWIST) is an example. ? Four-dimensional TWIST MRA provided inferior image quality compared to 3D FLASH MRA but without significant difference in vessel sharpness. ? Four-dimensional TWIST MRA gave added diagnostic value.     

Accuracy of 3 T MR angioraphy in vertebral artery stenosis and coincidence with other cerebrovascular stenoses

Introduction

Ostium of vertebral artery (VA) is a common site of pseudostenosis on contrast-enhanced MR angiography (CE-MRA). The purpose of this study was to determine the diagnostic accuracy of CE-MRA at 3 T in the evaluation of ostial stenosis of VA and to find associated coincidental stenoses using logistic regression analysis.

Methods

One hundred and thirty-five VA ostial regions from 72 patients who received CE-MRA of neck vessels, intracranial time of flight (TOF) MRA, and digital subtraction angiography (DSA) were retrospectively reviewed. The sensitivity and specificity of the CE-MRA in detection of ostial stenosis were calculated with reference standard of DSA. Ostial stenosis on MRA was correlated with coincidental lesions in intracranial and cervical arteries by logistic regression analysis.

Results

The sensitivity and specificity of the CE-MRA were 100% and 80.4% for detection of significant stenosis. In case of significant stenoses, CE-MRA showed a tendency of overestimation with a false-positive rate of 52.5%. Logistic regression analysis showed that the stenoses of middle cerebral artery (MCA) on TOF MRA was associated with significant stenoses of VA ostia (OR?=?5.84, 95% confidence intervals 1.41–24.17).

Conclusion

CE-MRA is sensitive in detection of VA ostial stenosis although it has high false-positive rate. True positive ostial stenosis should be considered in cases of coincidental stenoses of MCA on TOF MRA.     

Contrast-enhanced time-resolved 3-D MRA: applications in neurosurgery and interventional neuroradiology

Purpose

The decision-making process in the endovascular treatment of cranial dural AV fistulas and angiomas and their follow-up after treatment is usually based on conventional digital subtraction angiography (DSA). Likewise, acquiring the vascular and hemodynamic information needed for presurgical evaluation of meningiomas may necessitate DSA or different MR-based angiographic methods to assess the arterial displacement, the location of bridging veins and tumor feeders, and the degree of vascularization. New techniques of contrast-enhanced MR angiography (MRA) permit the acquisition of images with high temporal and spatial resolution. The purpose of this study was to evaluate the applicability and clinical use of a newly developed contrast-enhanced 3-D dynamic MRA protocol for neurointerventional and neurosurgical planning and decision making.

Methods

With a 3-T whole-body scanner (Philips Achieva), a 3-D dynamic contrast-enhanced (MultiHance, Bracco) MRA sequence with parallel imaging, and intelligent k-space readout (keyhole and “CENTRA” k-space filling) was added to structural MRI in patients with meningiomas, dural arteriovenous fistulas and pial arteriovenous malformations. The sequence had a temporal resolution of 1.3 s per 3-D volume with a spatial resolution of 0.566×0.566×1.5 mm per voxel in each 3-D volume and lasted 25.2 s. DSA was performed in selected patients following MRI.

Results

In patients with arteriovenous fistulas and malformations, MRA allowed the vascular shunt to be identified and correctly classified. Hemodynamic characteristics and venous architecture were clearly demonstrated. Larger feeding arteries could be identified in all patients. In meningiomas, MRA enabled assessment of the displacement of the cerebral arteries, depiction of the tumor feeding vessels, and evaluation of the anatomy of the venous system. The extent of tumor vascularization could be assessed in all patients and correlated with the histopathological findings that indicated hypervascularization.

Conclusion

High temporal and spatial resolution 3-D MRA may allow correct identification and classification of fistulas and angiomas and help to reduce the number of pre-or postinterventional invasive diagnostic angiograms. This sequence is also helpful for characterizing the degree of vascularization in preoperative evaluation of meningiomas and to select meningiomas suitable for embolization. Displacement of normal arteries and depiction of the venous anatomy can be achieved cost-effectively in a short period of time. The high spatial resolution also permits improved demonstration of the major feeding arteries, which helps to reduce the number of conventional angiograms required for meningioma evaluation.

     

Hybrid contrast-enhanced MR angiography of pelvic and lower extremity vasculature at 3.0 T: initial experience

Purpose

The objective of this study was to describe contrast-enhanced magnetic resonance angiography (MRA) of the lower extremities at 3.0 T system for assessment of high resolution images in patients with peripheral arterial occlusive disease (PAOD).

Material and methods

21 Patients with suspected PAOD were examined with four-station MRA at a 3.0 T MR system. The MRA protocol consisted of a hybrid technique with two contrast media injections, the first one for visualization of the calf and foot vasculature (non-moving-table technique), the second one for imaging the aortoiliacal and femoral arteries (moving-table technique). For the femoropopliteal and calf station a randomly segmented central k-space ordering (contrast-enhanced timing-robust angiography [CENTRA]) was used. MR-images were analyzed independently by two radiologists with regard to image quality, venous overlap and grade of stenosis. In 6 patients digital subtraction angiography was performed within the following 7 days and evaluated by two radiologists in consensus with regard to the grade of stenosis. The vasculature-tree of each leg was divided in 12 segments, and 3 anatomical regions (iliacal, femoropopliteal, calf/foot).

Results

490 and 488 of 495 arterial segments were visualized with diagnostic image quality by observer 1 and observer 2, respectively. Image quality was excellent in 470 and 457 arterial segments, respectively. Only 4 segments were rendered as non-diagnostic due to venous overlap. Relevant arterial stenoses (50–99%) were detected in 43 and 47 segments by observer 1 and observer 2, 66 and 65 arterial segments, respectively, were interpreted as occluded.

Conclusion

The hybrid MRA protocol at 3.0 T offers high diagnostic quality for the whole peripheral arterial tree without venous contamination at high spatial resolution.     

Preliminary experience with MRA in evaluating the degree of carotid stenosis and plaque morphology using high-resolution sequences after gadofosveset trisodium (Vasovist) administration: comparison with CTA and DSA

Purpose

The authors performed a preliminary study with blood-pool contrast-enhanced magnetic resonance angiography (MRA) in evaluating the degree of carotid artery stenosis and plaque morphology, comparing the diagnostic performance of first-pass (FP) and steady-state (SS) acquisitions with 64-slice computed tomography angiography (CTA) and using digital subtraction angiography (DSA) as the reference standard.

Materials and methods

Twenty patients with ≥50% carotid artery stenosis at Doppler sonography underwent blood-pool contrast-enhanced MRA, CTA and DSA. Two independent radiologists evaluated MRA and CTA examinations to assess the degree of stenosis and characterise plaque morphology. Accuracy, sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) were calculated for FP, SS and CTA. The McNemar and Wilcoxon tests were used to determine significant differences (p<0.05) between the diagnostic performance of the three modalities.

Results

Forty carotid bifurcations were studied. For stenosis grading, accuracy, sensitivity, specificity, PPV and NPV were 90%, 89%, 90%, 89% and 90%, respectively, at FP; 95%, 95%, 95%, 95% and 95%, respectively, at SS; and 97.5%, 95%, 100%, 100% and 95%, respectively, at CTA. SS and CTA were superior to FP for evaluating the degree of stenosis (p<0.05). For evaluating plaque morphology, accuracy, sensitivity, specificity, PPV and NPV were 87.5%, 89%, 86%, 85% and 90%, respectively, at FP; 97.5%, 100%, 95%, 95% and 100%, respectively, at SS; and 100%, 100%, 100%, 100% and 100%, respectively, at CTA. There were no significant differences between FP, SS and CTA for plaque assessment (p>0.05).

Conclusions

Blood-pool contrast-enhanced MRA with SS sequences allow improved diagnostic evaluation of the degree of carotid stenosis and plaque morphology compared with FP and is substantially equal to CTA and DSA.     

First-pass contrast-enhanced renal MRA at 7 Tesla: initial results

Objective

The aim of this study was to assess the feasibility of first-pass contrast-enhanced renal MR angiography (MRA) at 7 T.

Methods

In vivo first-pass contrast-enhanced high-field examinations were obtained in eight healthy subjects on a 7-T whole-body MRI. A custom-built body transmit/receive radiofrequency (RF) coil and RF system suitable for RF shimming were used for image acquisition. For dynamic imaging, gadobutrol was injected intravenously and coronal unenhanced, arterial and venous data sets using a T1-weighted spoiled gradient-echo sequence were obtained. Qualitative image analysis and assessment of artefact impairment were performed by two senior radiologists using a five-point scale (5 = excellent, 1 = non-diagnostic). SNR and CNR of the perirenal abdominal aorta and both main renal arteries were assessed.

Results

Qualitative image evaluation revealed overall high-quality delineation of all assessed segments of the unenhanced arterial vasculature (mean_unenhanced 4.13). Nevertheless, the application of contrast agent revealed an improvement in vessel delineation of all the vessel segments assessed, confirmed by qualitative (mean_unenhanced 4.13 to mean_{contrast-enhanced} 4.85) and quantitative analysis (SNR mean_unenhanced 64.3 to mean_{contrast-enhanced} 98.4).

Conclusion

This study demonstrates the feasibility and current constraints of ultra-high-field contrast-enhanced renal MRA relative to unenhanced MRA.

Key Points

? First-pass contrast-enhanced renal MRA at 7 T is technically feasible. ? Unenhanced renal MRA offers inherent hyperintense delineation of renal arterial vasculature. ? Contrast media application improves vessel assessment of renal arteries at 7 T.     

Pulmonary MRA: Differentiation of pulmonary embolism from truncation artefact

Purpose

Truncation artefact (Gibbs ringing) causes central signal drop within vessels in pulmonary magnetic resonance angiography (MRA) that can be mistaken for emboli, reducing diagnostic accuracy for pulmonary embolism (PE). We propose a quantitative approach to differentiate truncation artefact from PE.

Methods

Twenty-eight patients who underwent pulmonary computed tomography angiography (CTA) for suspected PE were recruited for pulmonary MRA. Signal intensity drops within pulmonary arteries that persisted on both arterial-phase and delayed-phase MRA were identified. The percent signal loss between the vessel lumen and central drop was measured. CTA served as the reference standard for presence of pulmonary emboli.

Results

A total of 65 signal intensity drops were identified on MRA. Of these, 48 (74 %) were artefacts and 17 (26 %) were PE, as confirmed by CTA. Truncation artefacts had a significantly lower median signal drop than PE on both arterial-phase (26 % [range 12–58 %] vs. 85 % [range 53–91 %]) and delayed-phase MRA (26 % [range 11–55 %] vs. 77 % [range 47–89 %]), p?<?0.0001 for both. Receiver operating characteristic (ROC) analyses revealed a threshold value of 51 % (arterial phase) and 47 % signal drop (delayed phase) to differentiate between truncation artefact and PE with 100 % sensitivity and greater than 90 % specificity.

Conclusion

Quantitative signal drop is an objective tool to help differentiate truncation artefact and pulmonary embolism in pulmonary MRA.

Key points

? Inexperienced readers may mistake truncation artefacts for emboli on pulmonary MRA ? Pulmonary emboli have non-uniform signal drop ? 51 % (arterial phase) and 47 % (delayed phase) cut-off differentiates truncation artefact from PE ? Quantitative signal drop measurement enables more accurate pulmonary embolism diagnosis with MRA     

Subtraction CT angiography for the diagnosis of iliac arterial steno-occlusive disease

Purpose

Accurate evaluation of stenosis in severely calcified arteries is a major challenge in conventional CT angiography (CTA) for peripheral arterial disease (PAD). The aim of this study was to evaluate the efficacy of subtraction CTA compared with conventional CTA and conventional angiography.

Materials and methods

175 arterial segments of 31 consecutive patients with PAD who underwent CTA and subsequent digital subtraction angiography (DSA) were evaluated. The percentage stenosis of diseased arteries was measured in iliac arteries with caliper methods on conventional CTA and subtraction CTA, and the concordance of each CTA method with DSA in the identification of >50 % stenosis was evaluated. Interpretation of CTA was always based only on maximum intensity projection (MIP).

Results

174 (99 %) segments were interpretable on subtraction CTA and showed a good correlation with DSA (R ² = 0.844), although 55 (31 %) segments were not evaluable on conventional CTA due to severe calcification. On subtraction CTA, the segmental accuracy, sensitivity, and specificity were 90.5, 78.9, and 80.0 %, respectively.

Conclusion

Subtraction CTA is an accurate diagnostic tool for the evaluation of PAD. It may be easier to interpret stenosis in the presence of calcifications using subtraction CTA rather than with the conventional CTA approach. Also, subtraction CTA using only MIP presented a similar accuracy to DSA.

     

Nonenhanced ECG-gated time-resolved 4D Steady-state free precession (SSFP) MR angiography (MRA) for assessment of cerebral collateral flow: comparison with digital subtraction angiography (DSA)

Objectives

To evaluate a nonenhanced time-resolved 4D SSFP MRA for dynamic visualization of intracranial collateral blood flow.

Methods

22 patients (59.0?±?11.8 years) with steno-occlusive disease of brain-supplying arteries were included in this study. 4D SSFP MRA of the intracranial arteries was acquired with 15 temporal phases and a temporal resolution of 115 ms using 1.5 T MR. Cerebral DSA served as the reference standard and was available in all patients.

Results

Nonenhanced 4D SSFP MRA allowed for detailed dynamic visualization of blood flow in the circle of Willis and its branches in 21 of 22 (95.5%) patients. Collateral flow was excluded with both 4D SSFP MRA and DSA in 4 patients. In 17 patients, DSA detected anterior collateral flow (n?=?8), posterior collateral flow via the right (n?=?8) and left (n?=?7) posterior communicating artery as well as patent EC-IC bypasses (n?=?8). 29 of 31 collateral flow pathways were visualized by 4D SSFP MRA. As compared to DSA, 4D SSFP MRA showed a high sensitivity (92.3%), specificity (100%), positive predictive value (100%) and negative predictive value (95.2%) for visualization of intracranial collateral flow.

Conclusions

4D SSFP MRA is a promising non-invasive imaging technique for dynamic visualization of intracranial collateral flow.     

Non-contrast-enhanced 4D MR angiography with STAR spin labeling and variable flip angle sampling: a feasibility study for the assessment of Dural Arteriovenous Fistula

Introduction

This study aimed to evaluate the feasibility of non-contrast-enhanced 4D magnetic resonance angiography (NCE 4D MRA) with signal targeting with alternative radiofrequency (STAR) spin labeling and variable flip angle (VFA) sampling in the assessment of dural arteriovenous fistula (DAVF) in the transverse sinus.

Methods

Nine patients underwent NCE 4D MRA for the evaluation of DAVF in the transverse sinus at 3 T. One patient was examined twice, once before and once after the interventional treatment. All patients also underwent digital subtraction angiography (DSA) and/or contrast-enhanced magnetic resonance angiography (CEMRA). For the acquisition of NCE 4D MRA, a STAR spin tagging method was used, and a VFA sampling was applied in the data readout module instead of a constant flip angle. Two readers evaluated the NCE 4D MRA data for the diagnosis of DAVF and its type with consensus. The results were compared with those from DSA and/or CEMRA.

Results

All patients underwent NCE 4D MRA without any difficulty. Among seven patients with patent DAVFs, all cases showed an early visualization of the transverse sinus on NCE 4D MRA. Except for one case, the type of DAVF of NCE 4D MRA was agreed with that of reference standard study. Cortical venous reflux (CVR) was demonstrated in two cases out of three patients with CVR.

Conclusion

NCE 4D MRA with STAR tagging and VFA sampling is technically and clinically feasible and represents a promising technique for assessment of DAVF in the transverse sinus. Further technical developments should aim at improvements of spatial and temporal coverage.     

Non-ECG-gated unenhanced MRA of the carotids: Optimization and clinical feasibility

Objectives

To optimise and assess the clinical feasibility of a carotid non-ECG-gated unenhanced MRA sequence.

Methods

Sixteen healthy volunteers and 11 patients presenting with internal carotid artery (ICA) disease underwent large field-of-view balanced steady-state free precession (bSSFP) unenhanced MRA at 3T. Sampling schemes acquiring the k-space centre either early (kCE) or late (kCL) in the acquisition window were evaluated. Signal and image quality was scored in comparison to ECG-gated kCE unenhanced MRA and TOF. For patients, computed tomography angiography was used as the reference.

Results

In volunteers, kCE sampling yielded higher image quality than kCL and TOF, with fewer flow artefacts and improved signal homogeneity. kCE unenhanced MRA image quality was higher without ECG-gating. Arterial signal and artery/vein contrast were higher with both bSSFP sampling schemes than with TOF. The kCE sequence allowed correct quantification of ten significant stenoses, and it facilitated the identification of an infrapetrous dysplasia, which was outside of the TOF imaging coverage.

Conclusions

Non-ECG-gated bSSFP carotid imaging offers high-quality images and is a promising sequence for carotid disease diagnosis in a short acquisition time with high spatial resolution and a large field of view.

Key Points

? Non-ECG-gated unenhanced bSSFP MRA offers high-quality imaging of the carotid arteries. ? Sequences using early acquisition of the k-space centre achieve higher image quality. ? Non-ECG-gated unenhanced bSSFP MRA allows quantification of significant carotid stenosis. ? Short MR acquisition times and ungated sequences are helpful in clinical practice. ? High 3D spatial resolution and a large field of view improve diagnostic performance.     

Comparison of remnant size in embolized intracranial aneurysms measured at follow-up with DSA and MRA

Introduction

The possibility of recanalization and the need for retreatment are the most important limitations of intracranial aneurysm embolization. The purpose of the study was to compare the size of aneurysm remnants measured at follow-up with three-dimensional digital subtracted angiography (3D-DSA) and magnetic resonance angiography (MRA).

Methods

Twenty-six aneurysms were found incompletely occluded in 72 consecutively examined patients at a follow-up after 3?months. The diameters and volume of aneurysm remnants were compared between 3D-DSA, time-of-flight MRA (TOF-MRA), contrast-enhanced TOF-MRA (CE-TOF-MRA), and contrast-enhanced MRA (CE-MRA) at 1.5?T.

Results

There was a significant correlation between remnant volumes calculated based on 3D-DSA and all MRA modalities. The intraobserver variability of the measurements ranged from 3.4 to 4.1?% and the interobserver variability from 5.8 to 7.3?%. There were no significant differences in the variability between the techniques. The mean residual filling volume ranged from 16.3?±?19.0?mm³ in TOF-MRA to 30.5?±?44.6?mm³ in 3D-DSA (P?<?0.04). Significant differences were found in the volumes measured with 3D-DSA and CE-MRA as compared to TOF-MRA and CE-TOF-MRA (P?<?0.01). There was a moderate significant correlation between the residual filling and the relative error of measurement in the case of TOF-MRA and CE-TOF-MRA.

Conclusions

TOF-MRA seems to underestimate the size of aneurysm remnants detected at follow-up and should not be used as a sole imaging method to decide on re-embolization.     

64-MDCT imaging of the coronary arteries and systemic arterial vascular tree in a single examination: optimisation of the scan protocol and contrast-agent administration

Purpose

The aim of this study was to validate a 64-row multidetector computed tomography (64-MDCT) acquisition protocol with biphasic administration of contrast medium for comprehensive assessment of the coronary and systemic arterial tree in a single examination.

Materials and methods

The scanning protocol comprised two acquisitions: an electrocardiograph (ECG)-gated scan at the level of the heart, followed by a total-body, low-dose scan of the systemic arterial circulation. Twenty patients were evaluated using two different strategies for contrast administration. In ten patients, the delay between the two acquisitions was set at 40 s, whereas in the remaining patients, it varied between 45 s and 65 s. For both strategies, the degree of systemic arterial opacification and the attenuation gradient between arterial and venous structures were quantitatively assessed at six extracoronary locations. Two observers evaluated in consensus the presence or absence of atherosclerosis and the degree of stenosis of arterial segments.

Results

Three hundred coronary segments were analysed. Arterial-wall changes were depicted in 155 (51%) segments, and in 35 (23%), the degree of stenosis was >50%. Of the 640 extracoronary arterial segments, 250 (39%) presented atherosclerotic wall alterations, in 50 (20%), the degree of stenosis was >50% and five were affected by aneurysmal dilatation. The magnitude of arterial opacification values and attenuation gradients between arterial and venous structures were significantly higher in patients scanned with the 40-s fixed-delay strategy.

Conclusions

Whole-body CT angiography with biphasic administration of contrast agent and fixed scan delay has been shown to be a feasible and reproducible technique. Comprehensive data on the global atherosclerotic burden potentially offer important therapeutic options for subclinical, high-risk segments.