title: Audiovisual biofeedback improves diaphragm motion reproducibility in MRI.
abstract: OBJECTIVE
  In lung radiotherapy, variations in cycle-to-cycle breathing results in four-dimensional computed tomography imaging artifacts, leading to inaccurate beam coverage and tumor targeting. In previous studies, the effect of audiovisual (AV) biofeedback on the external respiratory signal reproducibility has been investigated but the internal anatomy motion has not been fully studied. The aim of this study is to test the hypothesis that AV biofeedback improves diaphragm motion reproducibility of internal anatomy using magnetic resonance imaging (MRI).
  
  
  METHODS
  To test the hypothesis 15 healthy human subjects were enrolled in an ethics-approved AV biofeedback study consisting of two imaging sessions spaced ∼1 week apart. Within each session MR images were acquired under free breathing and AV biofeedback conditions. The respiratory signal to the AV biofeedback system utilized optical monitoring of an external marker placed on the abdomen. Synchronously, serial thoracic 2D MR images were obtained to measure the diaphragm motion using a fast gradient-recalled-echo MR pulse sequence in both coronal and sagittal planes. The improvement in the diaphragm motion reproducibility using the AV biofeedback system was quantified by comparing cycle-to-cycle variability in displacement, respiratory period, and baseline drift. Additionally, the variation in improvement between the two sessions was also quantified.
  
  
  RESULTS
  The average root mean square error (RMSE) of diaphragm cycle-to-cycle displacement was reduced from 2.6 mm with free breathing to 1.6 mm (38% reduction) with the implementation of AV biofeedback (p-value < 0.0001). The average RMSE of the respiratory period was reduced from 1.7 s with free breathing to 0.3 s (82% reduction) with AV biofeedback (p-value < 0.0001). Additionally, the average baseline drift obtained using a linear fit was reduced from 1.6 mm∕min with free breathing to 0.9 mm∕min (44% reduction) with AV biofeedback (p-value = 0.012). The diaphragm motion reproducibility improvements with AV biofeedback were consistent with the abdominal motion reproducibility that was observed from the external marker motion variation.
  
  
  CONCLUSIONS
  This study was the first to investigate the potential of AV biofeedback to improve the motion reproducibility of internal anatomy using MRI. The study demonstrated the significant improvement in diaphragm motion reproducibility using AV biofeedback combined with MRI. This system can potentially provide clinically beneficial motion management of internal anatomy in MRI and radiotherapy.
authors.affiliation: Radiation Physics Laboratory, Sydney Medical School, University of Sydney, Sydney, Australia.
authors.forename: Taeho
authors.initials: T
authors.lastname: Kim
authors.forename: Sean
authors.initials: S
authors.lastname: Pollock
authors.forename: Danny
authors.initials: D
authors.lastname: Lee
authors.forename: Ricky
authors.initials: R
authors.lastname: O'Brien
authors.forename: Paul
authors.initials: P
authors.lastname: Keall
mesh_terms: D000005:Abdomen / Q000502:physiology; D001676:Biofeedback, Psychology; D003964:Diaphragm / Q000502:physiology*; D006309:Hearing; D006801:Humans; D008175:Lung Neoplasms / Q000175:diagnosis / Q000503:physiopathology; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009068:Movement; D015203:Reproducibility of Results; D014785:Vision, Ocular