Evaluation of collateral circulation through the Circle of Willis in internal carotid artery occlusion using non-contrast 4D-MRA: a comparative analysis of 4D-PACK, 4D-S-PACK, TOF-MRA, CE-MRA, and DSA

OBJECTIVES: This study aimed to evaluate the accuracy of non-contrast 4D-MRA techniques (4D-PACK and 4D-S-PACK) in assessing collateral circulation via the Circle of Willis (CoW) in patients with internal carotid artery occlusion (ICAO), using digital subtraction angiography (DSA) as the reference standard. METHODS: In this prospective study, patients with ICAO underwent multi-contrast MRA (3D TOF-MRA, CE-MRA, 4D-PACK, and 4D-S-PACK) and DSA within one week. Using DSA as the reference, the diagnostic accuracy of each MRA technique was independently assessed for ICAO occlusion, CoW anatomy, and collateral pathway patterns. The 4D-MRA acquisitions included time points of 100, 200, 500, 800, 1200, 1600, and 2000 milliseconds. Additionally, the optimal 4D-S-PACK protocol and its capacity to determine CoW flow direction were evaluated. RESULTS: A total of 19 patients with 21 ICAOs were included. Combined 4D-MRA (4D-PACK plus 4D-S-PACK) demonstrated high diagnostic accuracy for detecting ICAO (100.0%) and CoW anatomy (98.2%). In assessing collateral pathways, combined 4D-MRA (sensitivity 95.2%, specificity 100.0%, accuracy 98.2%) outperformed TOF-MRA (sensitivity 85.7%, specificity 86.1%, accuracy 86.0%) and CE-MRA (sensitivity 100.0%, specificity 86.1%, accuracy 91.2%). Using three time points (200, 800, and 2000 msec), 4D-S-PACK significantly reduced scan time while maintaining accurate flow direction assessment. CONCLUSIONS: Combined non-contrast 4D-PACK and 4D-S-PACK is a promising, non-invasive alternative for comprehensively evaluating ICAO, CoW morphology, and collateral circulation. ADVANCES IN KNOWLEDGE: This study establishes that a combined non-contrast 4D-MRA protocol surpasses standard MRA techniques in collateral pathway accuracy, providing a viable, non-invasive alternative to DSA.