Speaker
Description
Objective
The upright position of patients is related to significant changes of geometry and spatial arrangement of abdominal organs relative to the conventional supine position. As respiration acts on this altered anatomy, posture and breathing jointly determine the resulting abdominal motion. So far, this posture-breathing interaction which is relevant for upright RT is insufficiently characterised [1]. This work presents a 4D MRI framework for characterising breathing-related abdominal organ motion in supine and upright positions.
Methods
A free-breathing 4D MRI acquisition protocol was implemented on the 0.5 T open MROPEN EVO system using a HASTE-CINE (Half-Fourier Acquisition Single-shot Turbo Spin Echo) sequence [2,4]. Healthy volunteers were imaged in supine and upright positions with a stack of sagittal slices from the spine to the right of the liver. An interleaved acquisition strategy was employed for approximately 10 minutes whereby a navigator slice through the diaphragm dome was acquired every second. All other slices were acquired sequentially in between to generate multiple positional updates of the complete volume with an interval of N slices times 1 second. Resolution and slice thickness reflect a balance of image sharpness and signal-to-noise ratio. Respiratory signals are extracted from the navigator slice using image-based template tracking of the liver dome boundary after initial localisation, providing a displacement-based surrogate for diaphragm motion [3]. Each volunteer was scanned in supine and sitting or standing position. Scans were repeated to simulate separate visits.
Results
Initial volunteer datasets show variation in breathing amplitude, frequency, and regularity between supine and upright acquisitions, together with clear posture-dependent differences in abdominal anatomy and organ shape. Liver-dome displacement ranged from 10.4 to 38.3 mm in the supine position and from 7.4 to 21.9 mm in the standing position. In a separate group scanned in the supine and sitting positions, the corresponding ranges were 8.3 to 11.1 mm and 8.8 to 11.7 mm, respectively. These values represent the 5th-to-95th percentile range of the tracked liver-dome position. The measurements demonstrate the feasibility of capturing breathing-related motion across different volunteers, acquisitions, and postures.
Outlook and Discussion
This work establishes the technical foundation for posture-dependent 4D MRI investigations within the UPLIFT project using an open MR scanner with 0.5 T field. Next steps include expanding the volunteer cohort, finalising the respiratory signal extraction pipeline, and defining quantitative motion metrics to compare supine and upright postures. The results indicate that a positional support or fixation of shoulders may become a potential requirement for extending further studies with multiple repetitions over several days, for example, to address deformation, motion reproducibility, and inter-session variability.
References
[1] Volz L, Korte J, Martire MC, et al. Opportunities and Challenges of Upright Patient Positioning in Radiotherapy. Physics in Medicine & Biology, 2024.
[2] Liu Y, Chang Z, Czito B, Bashir M, Yin FF, Cai J. 4D-MRI Using Sagittal Acquisition and Body Area as Respiratory Surrogate. International Journal of Radiation Oncology Biology Physics, 2013.
[3] Liu Y, Yin FF, Czito BG, Bashir MR, Palta M, Cai J. Retrospective Four-Dimensional Magnetic Resonance Imaging With Image-Based Respiratory Surrogate: A Sagittal-Coronal-Diaphragm Point of-Intersection Motion Tracking Method. Journal of Medical Imaging, 2017.
[4] Aljaafari L, Bird D, Buckley DL, Al-Qaisieh B, Speight R. A Systematic Review of 4D Magnetic Resonance Imaging Techniques for Abdominal Radiotherapy Treatment Planning. Physics and Imaging in Radiation Oncology, 2024.
Acknowledgements: The work was performed in scope of UPLIFT Project (EU grant agreementNo.101168955)