Appearance and minimisation of respiratory motion artefacts in thoracic MRI images of prone patients

Introduction Prone positioning during magnetic resonance imaging (MRI) has been reported as advantageous, to reduce feelings of claustrophobia [1], to clarify and distinguish the appearance of specific anatomical structures [2] and so that consistent positioning of the patient and their internal anatomy can be achieved throughout the treatment planning and delivery process for prone radiotherapy [3]. Despite these advantages, prone positioning is declining in use during thoracic MRI imaging, with the adoption of triggered (respiratory-gated) MRI for supine patients [4]. This study involved the development of a method to perform triggered MRI imaging on prone patients, in order to evaluate and minimise the appearance of respiratory motion artefacts. Method T2-weigted turbo skin echo (TSE) MR images of the upper-thoracic spine of a healthy volunteer were obtained, while the volunteer was prone and free breathing. After first imaging without triggering, a process of trial-and-error was undertaken, to optimise the setup of the displacement transducer used to trigger MR image acquisition and refine the verbal instructions given to the volunteer. The final set of triggered MRI images was acquired throughout exhale, during normal free breathing with the displacement transducer strapped firmly to the volunteer’s back, beneath the body coils. Results The figures below exemplify the reduction of the streaking artefacts throughout the lungs and the improvement of the resolution of the spinal anatomy achieved using triggered MRI for imaging in the prone position. Conclusion For patients lying prone, the chest and abdomen are effectively fixed against the surface of the MRI couch, so the dorsal side of the patient rises and falls with respiration. This study has shown that triggered MRI imaging, with the displacement transducer carefully strapped to each patient’s back, has the potential to dramatically reduce the appearance of respiratory motion artefacts when acquiring thoracic images using the prone position.