Poster Abstracts: Clinical MRI—Vascular Disease 374. Clinical Peripheral Magnetic Resonance Angiography: Comparison of Hybrid Technique Versus Sequential Stepping-Table Approach

Introduction: Lower extremity contrast enhanced peripheral MR Angiography (pMRA) is used routinely to triage patients with peripheral vascular disease to percutaneous intervention or surgery.A sequential stepping-table 3-station technique (bolus-chase) is routinely used for pMRA, risking either poor enhancement of run-off vessels or venous contamination. Purpose: The purpose of our study was to evaluate the efficacy of a ‘‘hybrid’’ dual timing/dual injection pMRA technique with separate preceding calf acquisition and compare it to a conventional bolus-chase pMRA technique. Methods: 155 consecutive patients underwent pMRA on a Magnetom Quantum scanner (Siemens Medical Systems, Malvern, PA) using a 3D gradient echo pulse sequence (TR/TE: 3.5/1.2; a: 25 ) and dedicated peripheral vascular coil. Angiographic correlation was available in 61 patients. The first 34 patients underwent bolus chase pMRA with a single 2 ml Gad-DTPA timing run followed by an automated sequential, 3-station bolus chase, stepping-table technique. Bolus-chase infusion was a graduated single infusion of Gad-DPTA: the first 20 ml at 2 ml/s followed by the remaining 28–40 ml (maximum weight based dose 0.3 mmol/kg) at 0.8 ml/s. The next 121 patients underwent hybrid pMRA with 2 separate axial timing runs centered in the calves and pelvis. Calf single-station MRA was performed first with the infusion of 20 ml Gad-DPTA at 2 ml/s. Subsequently, pelvis-thigh stepping-table MRA was carried out with a second injection of Gad-DPTA: 20 ml at 2 ml/s followed by 10–16 ml (maximum weight based total 0.3 mmol/kg) at 0.8 ml/s. Two independent observers reviewed partition, MIP and volume-rendered data. Arterial vessels were divided into 29 anatomic segments per patient and the most severe stenosis per segment was graded by 10% increments. Qualitative measures of venous contamination and diagnostic confidence per station were also obtained. Digital subtraction angiograms were assessed separately in a similar fashion for lesion severity by anatomic segment. Results: Sensitivity and specificity for the hybrid technique at each MR station were as follows: 97% and 98% respectively for pelvis, 93% and 97% for thigh, and 96% and 99% for calf; versus 85% and 92% for pelvis, 87% and 91% for thigh, and 83 and 90% for calf stations for the bolus-chase technique. Venous contamination in the calves was significantly more severe for bolus-chase pMRA. Diagnostic quality of the calf vessels was significantly higher with the hybrid technique. All p values above were significant (p<0.05). Conclusions: While increasing exam length slightly, the addition of a second timing run and separate calf acquisition significantly reduces venous contamination. This fact coupled with improved spatial resolution and diagnostic image quality make the hybrid approach superior to conventional bolus-chase, stepping-table techniques.