Single-dose time-resolved contrast enhanced hybrid MR angiography in diagnosis of peripheral arterial disease: Compared with digital subtraction angiography

Pulsatility index-adjusted doppler flow measurement of pedal arteries in peripheral artery disease patients

BACKGROUND

To examine the feasibility of using pulsatility index-adjusted (PI) flow equations to accurately characterize blood volume flow changes using Doppler technique in patients with peripheral artery disease (PAD) before and after percutaneous transluminal angioplasty (PTA).

METHODS

PTA was performed on 17 PAD patients (23 target vessels treated, 16 anterior tibial arteries, and 7 posterior tibial arteries). Arterial diameter, peak systolic velocity, PI, time-averaged mean velocity, and measured volume flow (MVF) of dorsalis pedis artery (DPA) and common plantar artery (CPA) were measured with duplex Doppler ultrasound before and after PTA. PI-adjusted volume flows (PIVF) were calculated as part of the MVF/PIVF relative percentage metric.

RESULTS

Significant changes (p < 0.001) of the MVF (mean: 33.0 mL/min, range: -20.9-102.2 mL/min) and MVF/PIVF relative percentages (mean: 51.8, range: 5.1-127.2%) in the DPA existed between before and after PTA, whereas no significant changes could be found in the CPA (mean:10.9 mL/min, p = 0.148 and mean: 21.3%, p = 0.146, respectively). Of the 7 treated posterior tibial arteries, the increments of the MVF/PIVF (mean: 60.4%, p = 0.033) was significant but not in the MVF (mean: 26.5 mL/min, p = 0.125). The ankle-brachial index also showed non-significant changes (p = 0.081). All PI-adjusted results matched clinical observations after blood flow restoration.

CONCLUSION

No conclusions can be drawn from the comparison of actual measured volume flow between before and after PTA. However, using the MVF/PIVF relative percentage allows for a more objective framework upon which to base clinical observations and provides clarity in situations where direct measurement provides a counter-intuitive or contradictory picture.

Diagnostic Performance of a Lower-dose Contrast-Enhanced 4D Dynamic MR Angiography of the Lower Extremities at 3 T Using Multisegmental Time-Resolved Maximum Intensity Projections

BACKGROUND

For peripheral artery disease (PAD), MR angiography (MRA) is a well-established diagnostic modality providing morphologic and dynamic information comparable to digital subtraction angiography (DSA). However, relatively large amounts of contrast agents are necessary to achieve this.

PURPOSE

To evaluate the diagnostic accuracy of time-resolved 4D MR-angiography with interleaved stochastic trajectories (TWIST-MRA) by using maximum intensity projections (MIPs) of dynamic images acquired with reduced doses of contrast agent.

STUDY TYPE

Retrospective.

POPULATION

Forty adult PAD patients yielding 1088 artery segments.

FIELD STRENGTH/SEQUENCE

A 3.0 T, time-resolved 4D MR-angiography with TWIST-MRA and MIP of dynamic images.

ASSESSMENT

DSA was available in 14 patients (256 artery segments) and used as reference standard. Three-segmental MIP reconstructions of TWIST-images after administration of 3 mL of gadolinium-based contrast agent (Gadoteridol/Prohance®, 0.5 M) per anatomical level (pelvis, thighs, and lower legs) yielded 256 artery segments for correlation between MRA and DSA. Three independent observers rated image quality (scale: 1 [nondiagnostic] to 4 [excellent]) and the degree of venous overlay (scale: 0 [none] to 2 [significant]) for all segments. Diagnostic accuracy for the detection of >50% stenosis and artery occlusion was calculated for all observers.

STATISTICAL TESTS

Binary classification test (sensitivity, specificity, positive/negative predictive values, diagnostic accuracy). Intraclass correlation coefficients (ICCs), logistic regression analysis with comparison of areas under the receiver-operating-characteristics (ROC) curves (AUCs) with the DeLong method. Bland-Altman-comparison.

RESULTS

High diagnostic performance was achieved for the detection of >50% stenosis (sensitivity 92.9% [84.3-99.9% (95%-CI)] and specificity 98.5% [95.7-99.8% (95%-CI)]) and artery occlusion (sensitivity 93.1% [77.2-99.2% (95%-CI)] and specificity 99.1% [96.9-99.9% (95%-CI)]). Inter-reader agreement was excellent with ICC values ranging from 0.95 to 1.0 for >50% artery stenosis and occlusion. Image quality was good to excellent for both readers (3.41 ± 0.72, 3.33 ± 0.65, and 3.38 ± 0.61 [mean ± SD]) with good correlation between observer ratings (ICC 0.71-0.81). No significant venous overlay was observed (0.06 ± 0.24, 0.23 ± 0.43 and 0.11 ± 0.45 [mean ± SD]).

DATA CONCLUSION

MIPs of dynamic TWIST-MRA offer a promising diagnostic alternative necessitating only reduced amounts (50%) of gadolinium-based contrast agents for the entire runoff vasculature.

EVIDENCE LEVEL

3 TECHNICAL EFFICACY: Stage 2.

MR Angiography at 3 T of Peripheral Arterial Disease: A Randomized Prospective Comparison of Gadoterate Meglumine and Gadobutrol

OBJECTIVE

This large-scale randomized study aimed to show the noninferiority in terms of diagnostic performance of gadoterate meglumine-enhanced versus gadobutrol-enhanced 3-T MR angiography (MRA) using digital subtraction angiography (DSA) as the reference standard in patients with peripheral arterial occlusive disease (PAOD).

SUBJECTS AND METHODS

In this prospective international randomized double-blind phase IV trial, 189 patients were enrolled. Of them, 156 could be included in the per-protocol population for on-site assessments and 154 for off-site readings. Subjects underwent peripheral MRA, after injection of 0.1 mmol/kg of either gadoterate meglumine or gadobutrol, and DSA within 30 days. The diagnostic accuracy was evaluated and compared using a noninferiority analysis. Secondary endpoints included sensitivity, specificity, diagnostic confidence, contrast-to-noise ratio, and signal-to-noise ratio evaluations.

RESULTS

The percentage agreement between MRA and DSA for stenosis detection was similar for on-site readings for both groups (mean ± SD, 80.6% ± 16.1% with gadoterate meglumine vs 77.1% ± 19.6% with gadobutrol; 3.5% difference), and the same was true for off-site readings (73.9% ± 16.9% with gadoterate meglumine vs 75.1% ± 13.8% with gadobutrol; 1.1% difference). The noninferiority of gadoterate meglumine to gadobutrol was shown for both on- and off-site readings. Sensitivity in detecting significant stenosis (> 50%) was 72.3% for gadoterate meglumine versus 70.6% for gadobutrol, whereas specificity (92.6% vs 92.3%), diagnostic confidence (87.0% vs 86.0%), signal-to-noise ratio (165.5 vs 161.0), and contrast-to-noise ratio (159.5 vs 155.3) did not differ statistically significantly between the two groups.

CONCLUSION

Gadoterate meglumine was found to be not inferior to gadobutrol in terms of diagnostic performance in patients with PAOD undergoing 3-T contrast-enhanced MRA. No statistically significant differences were detected between the two MRA groups.

Recent advances in 3D time-resolved contrast-enhanced MR angiography

Contrast-enhanced magnetic resonance angiography (CE-MRA) was first introduced for clinical studies approximately 20 years ago. Early work provided 3-4 mm spatial resolution with acquisition times in the 30-second range. Since that time there has been continuing effort to provide improved spatial resolution with reduced acquisition time, allowing high resolution 3D time-resolved studies. The purpose of this work is to describe how this has been accomplished. Specific technical enablers have been: improved gradients allowing reduced repetition times, improved k-space sampling and reconstruction methods, parallel acquisition, particularly in two directions, and improved and higher count receiver coil arrays. These have collectively made high-resolution time-resolved studies readily available for many anatomic regions. Depending on the application, ∼1 mm isotropic resolution is now possible with frame times of several seconds. Clinical applications of time-resolved CE-MRA are briefly reviewed.

Prospective comparison of cartesian acquisition with projection-like reconstruction magnetic resonance angiography with computed tomography angiography for evaluation of below-the-knee runoff

PURPOSE

To compare prospectively the assessment of stenosis and radiologist confidence in the evaluation of below-the-knee lower extremity runoff vessels between computed tomography (CT) angiography and contrast-enhanced magnetic resonance (MR) angiography in a cohort of 19 clinical patients.

MATERIALS AND METHODS

The study was compliant with the Health Insurance Portability and Accountability Act of 1996 and approved by the institutional review board. Imaging was performed in 19 consecutive patients with known or suspected peripheral arterial disease; both CT angiography and a more recently developed MR angiography technique were performed within 24 hours of each other and before any therapeutic intervention. Resulting images were randomized and interpreted in blinded fashion by four board-certified radiologists with expertise in CT angiography and MR angiography. Vasculature of the lower leg was apportioned into 22 segments, 11 for each leg. For each segment, degree of stenosis and confidence of diagnosis were determined using a 3-point scale. Differences between CT angiography and MR angiography were assessed for significance using pooled histograms that were analyzed using the Wilcoxon signed rank test.

RESULTS

For assessment of stenosis, there was no difference in CT angiography compared with MR angiography for 20 of 22 segments. For confidence of diagnosis, assessment of popliteal arteries was superior on CT angiography compared with MR angiography (P<.05). Confidence in assessment of both tibioperoneal trunks and the left proximal anterior tibial artery was not significantly different between CT angiography and MR angiography. Confidence in assessment of all other 17 segments was superior with MR angiography compared with CT angiography (P<.02).

CONCLUSIONS

MR angiography using the method described here is a promising technique for evaluating lower extremity arterial runoff. MR angiography had an overall superior performance in radiologist confidence compared with CT angiography for imaging runoff vessels below the knee.

Evaluation of the lower limb vasculature before free fibula flap transfer. A prospective blinded comparison between magnetic resonance angiography and digital subtraction angiography

Introduction The aim of this study was to compare magnetic resonance angiography (MRA) with digital subtraction angiography (DSA) in the preoperative assessment of crural arteries and their skin perforators prior to free fibular transfer. Patients and methods Fifteen consecutive patients, scheduled for free vascularized fibular flap transfer, were subjected to DSA as well as MRA of the crural arteries of both legs (n = 30). All DSA and MRA images were assessed randomly, blindly, and independently by two radiologists. Each of the assessors scored the degree of stenosis of various segments on a 5 point scale from 0 (occlusive) to 4 (no stenosis). The Cohen's Kappa coefficient was used to assess the agreement between DSA and MRA scores. In addition, the number of cutaneous perforators were scored and the assessors were asked if they would advise against fibula harvest and transplantation based on the images. Results A Cohen's Kappa of 0.64, indicating "substantial agreement of stenosis severity scores" was found between the two imaging techniques. The sensitivity of MRA to detect a stenosis compared with DSA was 79% (CI 95%:60-91), and a specificity of 98% (CI 95%: 97-99). In 53 out of 60 assessments, advice on suitability for transfer were equal between DSA and MRA. The median number of cutaneous perforators that perfuse the skin overlying the fibula per leg was one for DSA as well as MRA (P = 0.142).Conclusions A substantial agreement in the assessment of stenosis severity was found between DSA and MRA. The results suggest that MRA is a good alternative to DSA in the preoperative planning of free fibula flap transplantation.

Improved characterization of popliteal aneurysms using gadofosveset-enhanced equilibrium phase magnetic resonance angiography

Although standard magnetic resonance angiography (MRA) has many advantages in the evaluation of peripheral artery disease, it has poorer spatial resolution compared with computed tomographic angiography and digital subtraction angiography. The MRA blood pool contrast agents have an extended half-life. By allowing longer imaging times, MRA enables the acquisition of high-resolution images as well as providing simultaneous visualization of both arteries and veins. Two cases of popliteal artery aneurysm are presented, in which MRA with a blood pool contrast agent provided critical clues to the correct diagnosis: a traumatic pseudoaneurysm of the popliteal artery caused by a femoral osteochondroma and a large fusiform popliteal aneurysm compressing the adjacent popliteal vein, causing venous congestion and leg pain.

Time-resolved MR angiography of renal artery stenosis in a swine model at 3 Tesla using gadobutrol with digital subtraction angiography correlation

PURPOSE

To establish the minimum dose required for detection of renal artery stenosis using high temporal resolution, contrast enhanced MR angiography (MRA) in a porcine model.

MATERIALS AND METHODS

Surgically created renal artery stenoses were imaged with 3 Tesla MR and digital subtraction angiography (DSA) in 12 swine in this IACUC approved protocol. Gadobutrol was injected intravenously at doses of 0.5, 1, 2, and 4 mL for time-resolved MRA (1.5 × 1.5 mm(2) spatial resolution). Region of interest analysis was performed together with stenosis assessment and qualitative evaluation by two blinded readers.

RESULTS

Mean signal to noise ratio (SNR) and contrast to noise ratio (CNR) values were statistically significantly less with the 0.5-mL protocol (P < 0.001). There were no statistically significant differences among the other evaluated doses. Both readers found 10/12 cases with the 0.5-mL protocol to be of inadequate diagnostic quality (κ = 1.0). All other scans were found to be adequate for diagnosis. Accuracies in distinguishing between mild/insignificant (<50%) and higher grade stenoses (>50%) were comparable among the higher-dose protocols (sensitivities 73-93%, specificities 62-100%).

CONCLUSION

Renal artery stenosis can be assessed with very low doses (~0.025 mmol/kg bodyweight) of a high concentration, high relaxivity gadolinium chelate formulation in a swine model, results which are promising with respect to limiting exposure to gadolinium based contrast agents.

Usefulness of contrast-enhanced three-dimensional MR angiography using time-resolved imaging of contrast kinetics applied to description of Extracranial Arteriovenous Malformations: initial experience

PURPOSE

The purpose of this study was to evaluate the usefulness of contrast-enhanced three-dimensional MR angiography using time-resolved imaging of contrast kinetics (TRICKS-MRA) to demonstrate extracranial arteriovenous malformations (E-AVMs).

MATERIALS AND METHODS

TRICKS-MRA was performed in 33 patients (adults; n = 30, children; n = 3) with E-AVMs. Four different scan protocols were arranged based on the size of E-AVM, and serial images were acquired from the start of contrast injection with a time frame ranging from 1.2 to 7.1s. Demonstration of feeding arteries and drainage veins, and the extent of nidus was qualitatively graded using a three-point scale. In sixteen patients who underwent DSA 3 days to 15 months after TRICKS-MRA, the comparability of TRICKS-MRA to DSA was evaluated using a three-point scale. In each category, score of 3 or excellent was defined as the positive result.

RESULTS

Demonstration of the feeding arteries, the drainage veins, and the extent of nidus were graded as excellent in 68%, 65%, and 58% of the patients, respectively. Comparability of TRICKS-MRA to DSA was excellent in 75%, 88%, and 88% of the sixteen patients who underwent DSA.

CONCLUSION

TRICKS-MRA is a feasible and useful vascular imaging technique to provide time-resolved analysis of angioarchitecture of E-AVMs.