A Fully Automatic and Highly Efficient Navigator Gating Technique for High-resolution Free-breathing Acquisitions: Continuously Adaptive Windowing Strategy

A fully automatic and highly efficient free-breathing navigator gated technique, continuously adaptive windowing strategy (CLAWS), is presented. Using a novel and dynamic acquisition strategy that ensures all potential navigator acceptance windows are possible, CLAWS acquires an image with the highest possible efficiency regardless of variations in the respiratory pattern. Unnecessary prolongation of scan durations due to respiratory drift or navigator acceptance window adjustments are avoided. As CLAWS requires no setting of the acceptance window, nor monitoring of the navigator traces during the scan, operator dependence is minimized and ease of use improved. CLAWS was compared against a standard accept/reject algorithm (ARA) and an end-expiratory following ARA (EE-ARA) in 20 healthy subjects and 10 patients (ARA only). The respiratory efficiency was compared against the retrospectively determined best possible respiratory efficiency for each acquisition. On average, the difference between CLAWS scan times and best possible scan times was 0.6% (± 1.3%). For the ARA and EE-ARA techniques, mean differences were 14.4% (± 20.9%) and 32.6 ± 10.9%, respectively. Had the CLAWS algorithm been used with the ARA and EE-ARA traces, mean differences would have been 0.2% (± 1.1%) and 0.5% (± 1.7%), respectively. Image quality was the same for all techniques: respiratory gating, motion artifacts, navigator, and coronary artery imaging.