Impact of incorporating visual biofeedback in 4D MRI

Precise radiation therapy (RT) for abdominal lesions is complicated by respiratory motion and suboptimal soft tissue contrast in 4D CT. 4D MRI offers improved contrast although long scan times and irregular breathing patterns can be limiting. To address this, visual biofeedback (VBF) was introduced into 4D MRI. Ten volunteers were consented to an IRB‐approved protocol. Prospective respiratory‐triggered, T2‐weighted, coronal 4D MRIs were acquired on an open 1.0T MR‐SIM. VBF was integrated using an MR‐compatible interactive breath‐hold control system. Subjects visually monitored their breathing patterns to stay within predetermined tolerances. 4D MRIs were acquired with and without VBF for 2‐ and 8‐phase acquisitions. Normalized respiratory waveforms were evaluated for scan time, duty cycle (programmed/acquisition time), breathing period, and breathing regularity (end‐inhale coefficient of variation, EI‐COV). Three reviewers performed image quality assessment to compare artifacts with and without VBF. Respiration‐induced liver motion was calculated via centroid difference analysis of end‐exhale (EE) and EI liver contours. Incorporating VBF reduced 2‐phase acquisition time ([Formula: see text] and [Formula: see text] with and without VBF, respectively) while reducing EI‐COV by [Formula: see text]. For 8‐phase acquisitions, VBF reduced acquisition time by [Formula: see text] and EI‐COVs by [Formula: see text] despite breathing rate remaining similar ([Formula: see text] breaths/min with vs. [Formula: see text] without). Using VBF yielded higher duty cycles than unguided free breathing ([Formula: see text] vs. [Formula: see text] , respectively). Image grading showed that out of 40 paired evaluations, 20 cases had equivalent and 17 had improved image quality scores with VBF, particularly for mid‐exhale and EI. Increased liver excursion was observed with VBF, where superior–inferior, anterior–posterior, and left–right EE‐EI displacements were [Formula: see text] , [Formula: see text] , and [Formula: see text] , respectively, with VBF compared to [Formula: see text] , [Formula: see text] , and [Formula: see text] without. Incorporating VBF into 4D MRI substantially reduced acquisition time, breathing irregularity, and image artifacts. However, differences in excursion were observed, thus implementation will be required throughout the RT workflow. PACS number(s): 87.55.‐x, 87.61.‐c, 87.19.xj