Free-breathing quantification of regional ventilation derived by phase-resolved functional lung (PREFUL) MRI

Purpose To test the feasibility of regional fully quantitative ventilation measurement in free breathing derived by phase-resolved functional lung (PREFUL) MRI in the supine and prone positions. In addition, the influence of T-2* relaxation time on ventilation quantification is assessed. Methods Twelve healthy volunteers underwent functional MRI at 1.5 T using a 2D triple-echo spoiled gradient echo sequence allowing for quantitative measurement of T-2* relaxation time. Minute ventilation (Delta V) was quantified by conventional fractional ventilation (FV) and the newly introduced regional ventilation (VR), which corrects volume errors due to image registration. Delta V-FV versus Delta V-VR and Delta V-VR versus Delta V-VR with T-2* correction were compared using Bland-Altman plots and correlation analysis. The repeatability and physiological plausibility of all measurements were tested in the supine and prone positions. Results On global and regional scales a strong correlation was observed between Delta V-FV versus Delta V-VR and Delta V-VR versus Delta V-VRT2* (r > 0.93); however, regional Bland-Altman analysis showed systematic differences (p < 0.0001). Unlike Delta V-VRT2*, Delta V-VR and Delta V-FV showed expected physiologic anterior-posterior gradients, which decreased in the supine but not in the prone position at second measurement during 3 min in the same position. For all quantification methods a moderate repeatability (coefficient of variation <20%) of ventilation was found. Conclusion A fully quantified regional ventilation measurement using Delta V-VR in free breathing is feasible and shows physiologically plausible results. In contrast to conventional Delta V-FV,V- volume errors due to image registration are eliminated with the Delta V-VR approach. However, correction for the T-2* effect remains challenging.