Background
Patients who are being evaluated to undergo fibula free flap transfer often do not have arterial disease. However a significant anatomical variant cannot be clinically excluded. Contrast enhanced magnetic resonance angiogram (CE-MRA) is commonly performed to identify the suitable side to harvest the flap and to exclude unsuitable infra-popliteal arterial anatomy. The aim of this study is to measure the quality and accuracy of a non-contrast MRA (NC-MRA) technique (Native SPACE = Non-contrast Angiography of the Arteries and Veins using Sampling Perfection with Application Optimized Contrast by using different flip angle Evolution) compared to CE-MRA.
Methods
Institutional review board approval was obtained for this study. Between October 2012 and August 2014, 16 patients underwent NC-MRA followed by CE-MRA to identify infra-popliteal arterial anatomy prior to fibular-free flap surgery. Clinically, none had symptoms of peripheral vascular disease. CE-MRA was performed in early and later arterial phases. After acquisition of one NC-MRA, it was repeated with different trigger delay at the discretion of the technologist to improve the quality. In this study, NC- and CE-MRA were randomly reviewed and their qualities were recorded on a 3- point scale for each leg: optimal (arteries and any significant disease are clearly detectable), suboptimal (arteries are detectable; however any significant disease cannot be excluded) and non-diagnostic (arteries are not detectable). Using CE-MRA as gold standard, sensitivity, specificity, positive and negative predictive values of NC-MRA in identifying the type of infra-popliteal arterial anatomy and significant disease (occlusion or >50% stenosis) was calculated.
Results
Compared to 2-phase CE-MRA, an average 1.94 (SD 0.97) number of NC-MRA acquisitions were performed per patient. CE-MRA was optimal in all the legs (n = 32) and NC-MRA was optimal in 75%. NC-MRA was suboptimal in 19% and non-diagnostic in 6%. NC-MRA correctly identified normal and variant anatomy in 100% of optimal and suboptimal groups. Among the optimal quality NC-MRA (12 patients/69 infra-popliteal arteries), 58% demonstrated no significant disease. Compared with CE-MRA, the sensitivity, specificity, positive and negative predictive values of NC-MRA in identifying significant disease was 100%, 89%, 30% and 100% respectively.
Conclusions
In patients undergoing MRA prior to fibular-free flap harvest, NC-MRA often provides optimal quality images of infra-popliteal arteries with high negative predictive value for significant disease. Administration of contrast to acquire CE-MRA should be reserved for those with suboptimal or non-diagnostic NC-MRA and when disease is suspected in an optimal quality NC-MRA.
Figure 1.
Maximum intensity projection image of the subtracted data of two CE-MRA sequences: One obtained before and one obtained after adminstration of Gadolinium based contrast agent timed to arterial phase.
Figure 2.
Maximum intensity projection image of the subtracted data of two acqusitions within a Native SPACE sequence obtained when blood flow is minimal and maximal using different ECG trigger times.