Comprehensive MR angiography of the lower limbs: a hybrid dual-bolus approach including the pedal arteries

Extra-vascular findings in patients undergoing magnetic resonance angiography of the abdomen, pelvis and lower extremities: A retrospective study of 352 patients

Background

The aim of this study was to assess the prevalence and clinical significance of extra-vascular findings in patients undergoing magnetic resonance angiography of the abdomen, pelvis and lower extremities.

Materials and methods

Three hundred fifty-two patients underwent abdominal, pelvic and lower extremity 1.5 T magnetic resonance angiography. Clinically relevant vascular and extra-vascular findings were identified. Relevant vascular findings were classified as stenosis, occlusion, aneurysm, sclerosis, dissection or vasculitis. Relevant extra-vascular findings were categorized as ‘safe’ (Group A), intermediate – requiring additional investigation – (Group B) and malignant/endangering – requiring change of therapy (Group C).

Results

A total of 2152 clinically relevant vascular findings was identified (6.1/patient). The most frequent vascular finding was femoral artery stenosis (10.6%). Four hundred fifty-one extra-vascular findings were observed (1.3/patient) and classified into Group A (78%), Group B (19.5%) and Group C findings (2.4%). The most frequent malignant findings were lung cancer, lymphoma, osteosarcoma, hepatocellular carcinoma and renal cell carcinoma (7/352 patients).

Conclusions

Extravascular findings are frequently encountered in magnetic resonance angiography performed for vascular indications. Clinically relevant findings are seen in a substantial part of patients and should prompt further diagnostic work-up.

Diagnostic performance of CE-MRA in grading stenosis and therapy planning with TASC II classification

Objectives

To assess to what extent results of CE-MRA coincide with DSA in grading of stenosis and planning of therapy in patients with PAOD.

Materials and methods

Retrospectively, images of 71 PAOD-patients were studied by three observers. For evaluation, the lower limb was subdivided into 31 segments and categorized with TASCII-score.

Results

In grading stenosis, both modalities agreed in 93.26%. CE-MRA achieved sensitivity of 92.69% and specificity of 96.87% (κ = 0.88). The concordance of TASCII-classification was almost perfect.

Conclusion

CE-MRA is an excellent method for the evaluation of PAOD with some tendency to overrate the grade of stenosis.

Time-resolved MR angiography of the legs at 3 T using a low dose of gadolinium: initial experience and contrast dynamics

OBJECTIVE

This article describes our initial clinical experience with time-resolved MR angiography (MRA) of the legs using the time-resolved imaging with stochastic trajectories (TWIST) technique with a half dose of gadolinium.

MATERIALS AND METHODS

Thirty-four patients underwent a TWIST examination of the legs at 3 T. Thirty-three patients also underwent a bolus-chase MRA examination in the same setting. Times elapsed between the start of contrast injection and the appearance of contrast material (t(A)) and peak enhancement of the arteries in the legs (t(B)) were analyzed. The number of patients with examinations affected by venous contamination was determined. The differences in t(A) and t(B) between cases in which venous contamination was present or absent were evaluated using a two-tailed Student t test.

RESULTS

The TWIST technique using a half dose of gadolinium provided diagnostic-quality images of all patients. The mean t(A) was 35.5 ± 8.8 (SD) seconds (range, 17.8-60.4 seconds), and the mean t(B) was 59.1 ± 15.1 seconds (range, 31-98.8 seconds). Venous contamination was observed in bolus-chase MRA images of 52.9% of patients. The relationship between venous contamination and t(A) was not statistically significant (p = 0.13). The incidence of venous contamination was higher in patients with lower values of t(B) (p = 0.01).

CONCLUSION

The described low-dose clinical experience with TWIST and the contrast dynamics information gained from this study could aid radiologists in planning protocols for leg MRA examinations.

Contrast-enhanced MRA of the renal and aorto-iliac-femoral arteries: comparison of gadobenate dimeglumine and gadofosveset trisodium

RATIONALE AND OBJECTIVES

Dedicated contrast agents are now available for contrast-enhanced magnetic resonance angiography (CE-MRA). This study retrospectively compares the safety and diagnostic performance data from Phase III regulatory trials performed to evaluate gadobenate dimeglumine (MultiHance(®)) and gadofosveset trisodium (Vasovist®)) for renal and peripheral CE-MRA.

MATERIALS AND METHODS

Similar examination and blinded assessment methodology was utilized in all studies to determine the safety and diagnostic performance of the agents for detection of significant (>50%) steno-occlusive disease. Digital Subtraction Angiography (DSA) was used as the standard of truth. Diagnostic performance data (sensitivity, specificity, predictive values [PVs], and likelihood ratios [LRs]) were compared (Chi-square test).

RESULTS

CE-MRA with gadobenate dimeglumine was more specific (92.4% vs. 80.5%, p < 0.0001) and accurate (83.6% vs. 77.1%, p = 0.022) than CE-MRA with gadofosveset in the detection of significant renal artery stenosis. The average sensitivity was higher for gadofosveset (74.4% vs. 67.3%, p = 0.011) in peripheral vessels although gadobenate dimeglumine was more specific (93.0% vs. 88.2%, p < 0.0001) with no difference in accuracy (86.6% vs. 86.3%, p = 0.66). PPVs were higher (p < 0.0001) for gadobenate dimeglumine in both vascular territories. Pre- to post-test shifts in the probability of detecting significant disease were greater after gadobenate dimeglumine. Adverse events in the renal and peripheral studies were reported by 9.2% and 7.7% of patients after gadobenate dimeglumine compared with 30.3% and 22.1% of patients after gadofosveset.

CONCLUSION

The diagnostic performance of CE-MRA for the detection of significant steno-occlusive disease is similar with gadofosveset and gadobenate dimeglumine although the rate of adverse events appears higher with gadofosveset.

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 > or = 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 kappa = 0.62 (0.44-0.67) and kappa = 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.

[MR angiography of peripheral arterial disease of the distal legs: is time resolved MRA (TRICKS) necessary?]

PURPOSE

To demonstrate the added diagnostic value of time-resolved imaging of contrast kinetics (TRICKS) in the evaluation of lower limb arteries compared to standard 3 level MRA with stepping table method.

PATIENTS AND METHODS

Forty patients (30% diabetics) with lower extremity peripheral arterial disease (87.5% with chronic ischemia) underwent standard contrast MRA including TRICKS of the distal arteries. Five arterial segments were defined per leg, and 395 arterial segments were compared (one patient with amputation). Two reviewers evaluated the quality of arterial imaging, presence of venous return and degree of stenosis per segment. The degree of interobserver agreement for arterial stenosis measurement was calculated.

RESULTS

More arterial segments could be analyzed on the TRICKS sequence (good or excellent analysis in 63.03%-66.32% of arterial segments compared to 41.51%-47.08% on routine MRA). There was less venous contamination on TRICKS images (25.57% to 27.60% gain). The degree of interobserver agreement was superior with TRICKS compared to standard MRA (kappa 0.85 vs 0.69).

CONCLUSION

The TRICKS sequence can be added to standard MRA for pre-therapeutic evaluation of distal arteries in patients with peripheral arterial disease, especially with chronic ischemic with rest pain and/or trophic changes.

MR angiography of the lower extremities

OBJECTIVE

Current MRI technology and postprocessing tools have enabled 3D contrast-enhanced MR angiography (MRA) to evolve into a first-line noninvasive diagnostic tool to evaluate vascular disorders.

CONCLUSION

In this article, 3D MRA techniques, bolus timing issues, new IV contrast agents allowing a steady-state acquisition, principals of postprocessing, and unenhanced MRA techniques are reviewed and how to effectively use 3D gadolinium-enhanced MRA for peripheral arterial imaging is described.

Whole-body MR angiography using variable density sampling and dual-injection bolus-chase acquisition

Conventional bolus-chase acquisition generates peripheral runoff images using a single injection of the contrast material. Low spatial resolution, small slice coverage and venous contamination are major problems especially in the distal stations. A technique is presented herein in which whole-body magnetic resonance angiography is performed using a dual-contrast-injection four-station acquisition protocol. Bolus sharing was performed between two stations: the abdomen and calf stations share the first bolus injection, while the thorax and thigh stations share the second bolus injection. The combination of variable density sampling and elliptical centric acquisition order was applied to the abdomen and thorax stations. The scan time was extended to generate high spatial resolution arterial phase images with broad slice coverage for the calf and thigh stations. The feasibility of this technique was demonstrated using phantom and in vivo human volunteer studies.

Effects of injection rate and dose on image quality in time-resolved magnetic resonance angiography (MRA) by using 1.0M contrast agents

In time-resolved MRA (TR MRA), injection parameters and contrast agent (CA) dose are important factors influencing image quality. In this study, three different injection schemes with different CA volumes were evaluated in 12 healthy volunteers. Injection rates between 0.2 and 0.8 ml/s were evaluated with CA volumes of 10 and 20 ml. To measure circulatory parameters, cine cardiac MRI was performed before each exam. Spatial resolution could be reduced to 2 x 1.4 x 2 mm3, temporal resolution was 2.25 s/frame. To exclude signal saturation at high CA concentrations, a phantom with fixed CA concentrations was placed in the field of view. SNR was measured, and the area under the curve of the arterial signal of the different injection schemes was calculated. Results showed the largest diagnostic window at a relatively slow injection rate of 0.4 ml/s and a CA volume of 10 ml. Circulatory parameters have an important impact on CA arrival, so delay times have to be set depending on these parameters.

[CTA and MRA in peripheral arterial disease--is DSA out?]

New developments in technique and postprocessing have led to further improvement in diagnosing and evaluating peripheral arterial disease (PAD) by noninvasive computed tomographic angiography (CTA) and magnetic resonance angiography (MRA). Under clinical conditions diagnostic conventional angiography (DSA) will be increasingly replaced by CTA and MRA. The radiologist has to become familiar with the field of indications, the different techniques, postprocessing tools, and effective visualization. In consideration of the current literature some methodological aspects and the role of CTA and MRA in PAD will be discussed.

The impact of the dosage of intravenous gadolinium-chelates on the vascular signal intensity in MR angiography

To show the effects of different concentrations of contrast agent on signal time curves and image contrast of abdominal aorta, vena cava and portal vein in comparison to each other as well as liver and spleen. Imaging was carried out in a 1.0 Tesla clinical scanner. Sixty patients were prospectively included and divided into three contrast agent (Gd-DTPA) dosage groups (0.1 mmol/kg, 0.2 mmol/kg and 0.3 mmol/kg). All patients were scanned using a time-resolved 3D FLASH sequence (58 phases) with a 3.75 second acquisition time per phase. Signal time curves and image contrast levels were evaluated. No significant differences were found for the maximum signal enhancement between the groups in the investigated vessels. Image masking, the subtraction of the baseline images, resulted in a substantial improvement in image contrast. However, statistically significant differences between the contrast agent dosage groups could only be found for vena cava and liver. Vessel conspicuity is not significantly improved with an increase of contrast agent dose. However, an increase in contrast agent dosage increases vessel contrast. Our findings suggest that a single dose single station investigation seems to be sufficient for high quality abdominal MRA.