Poster — Thur Eve — 16: Four‐dimensional x‐ray computed tomography and hyperpolarized 3He magnetic resonance imaging of gas distribution in lung cancer

Dynamic imaging methods such as four‐dimensional computed tomography (4DCT) and static imaging methods such as noble gas magnetic resonance imaging(MRI) deliver direct and regional measurements of lung function even in lungcancer patients in whom global lung function measurements are dominated by tumour burden. The purpose of this study was to directly compare quantitative measurements of gas distribution from static hyperpolarized 3He MRI and dynamic 4DCT in a small group of lungcancer patients. MRI and 4DCT were performed in 11 subjects prior to radiation therapy.MRI was performed at 3.0T in breath‐hold after inhalation 1L of hyperpolarized 3He gas. Gas distribution in 3He MRI was quantified using a semi‐automated segmentation algorithm to generate percent‐ventilated volume (PVV), reflecting the volume of gas in the lung normalized to the thoracic cavity volume. 4DCT pulmonary function maps were generated using deformable image registration of six expiratory phase images. The correspondence between identical tissue elements at inspiratory and expiratory phases was used to estimate regional gas distribution and PVV was quantified from these images. After accounting for differences in lung volumes between 3He MRI (1.9±0.5L ipsilateral, 2.3±0.7 contralateral) and 4DCT (1.2±0.3L ipsilateral, 1.3±0.4L contralateral) during image acquisition, there was no statistically significant difference in PVV between 3He MRI (72±11% ipsilateral, 79±12% contralateral) and 4DCT (74±3% ipsilateral, 75±4% contralateral). Our results indicate quantitative agreement in the regional distribution of inhaled gas in both static and dynamic imaging methods. PVV may be considered as a regional surrogate measurement of lung function or ventilation.