Introduction Hyperpolarised 3He MRI provides high resolution images of lung ventilation and is more sensitive than spirometry to early changes in lung ventilation in cystic fibrosis (CF). Lung clearance index (LCI) is a global measure of ventilation heterogeneity which is also sensitive to early changes in the lungs in CF before spirometry. The aim of this study was to investigate the capability of hyperpolarised 3He MRI and LCI to detect ventilation changes in children with mild CF.
Methods 4 CF patients (FEV1 78 110% predicted) and 4 healthy volunteers have been assessed so far. 3He ventilation images were acquired at breath-hold following inhalation of hyperpolarised 3He, with 2.7x2.7x10mm resolution and full lung coverage using a 1.5T MRI system. The percentage of lung ventilated (VV%) was calculated as 3He ventilated volume divided by total lung volume segmented from 1H MR images. LCI was measured using 0.2% SF6 and a modified Innocor gas analyser. LCI was performed sitting and repeated supine to mimic the position adopted for MRI scanning. Spirometry and plethysmography were also performed. Gas trapping was calculated as% difference in plethysmographic versus washout FRC.
Results Healthy volunteers had a mean (standard deviation) age of 8.8(1.5) years, FEV1% predicted = 97(10) and gas trapping = 4.4(9.1)%. LCI sitting was 6.9,7.3,6.6 and 6.9, LCI supine was 7.3,7.5,6.8 and 6.4. Healthy volunteers had homogeneous ventilation in 3He ventilation images e.g. Fig1(a), and VV% = 94.5(2.8). CF patients had an age of 11.8(2.9) years, FEV1% predicted = 95(13), and gas trapping = 8.7(11.0). LCI sitting was 7.7,6.6,6.6 and 9.1, LCI supine was 7.8,7.3,7.1 and 11.8. Ventilation abnormalities were observed using 3He MRI in all four CF patients scanned (Fig 1(b-e), with order corresponding to the LCI values given), and VV% = 89.2(2.6). 2 of the 4 CF patients had normal sitting and supine LCI and 2 of 3 had no evidence of gas trapping, but 3He MRI showed clear focal ventilation defects in all patients (b-d).
Conclusions High quality 3He MRI images can be produced in young children. Preliminary results suggest that hyperpolarised 3He ventilation MRI may be more sensitive to early ventilation changes in CF than LCI or conventional lung function tests.
Acknowledgements CF Trust funding
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