Effect of gravity and lung volume on MR perfusion imaging of human lung

Objective To investigate the effect of gravity and lung volume on MR perfusion imaging of human lung using an arterial spin labeling sequence called flow sensitive alternating inversion recovery(FAIR).Methods Magnetic resonance imaging of lung perfusion was performed in supine position in ten healthy volunteers on a 1.5 T whole body scanner(GE medical system).Five sequentially coronal slices with the gap of 3cm from dorsal to ventral(labeled as P3,P6,P9,P12,P15,respeectivly)were obtained on end respiration and the relative pulmonary blood flow(rPBF)was measured.Another coronal perfusion-weighted image of P3 slice was obtained on end inspiration.Tagging efficiency of pulmonary parenchyma with IR(⊿SI%),the rPBF and area of the P3 slice were analyzed.respectively.Paired Student's t test was used for statistical analysis.Results (1)In the direction of gravity,an increase in rPBF of the gravity-dependent lung was found.rPBF of right lung from dorsal to ventral were 100.57±18.22,79.57±12.36,61.65±11.15,48.92±9.96,41.20±9.88,respectively；and that of left lung were 106.61±26.99,78.89±11.98,64.00±13.64,51.27±8.95,43.04±12.18.No statistical differences between P12 and P15,there were significant statistic differences of any other two coronal planes.But along an isogravitational plane,no statistical difference was observed.Regression coefficients of right and left lung were -4.98 and -5.16,respectively.This means the rPBF of right lung falls by 4.98 for each centimeter above the dorsal and that of left lung falls by 5.16.(2)For(⊿)SI%,rPBF and area,there were significant statistic differences at different respiratory phases(P＜0.05).(⊿)SI%,rPBF,area at expiration phase vs.inspiration phase were 1.12±0.31 vs 0.71±0.18,90.78±17.35 vs 52.85±8.75,(12.59±3.23)×103mm2 vs (17.77±4.24)×103mm2 for right lung;and 1.01±0.24 vs 0.70±0.11,91.08±18.68 vs 54.58±10.70,(12.34±3.08)×103mm2 vs(17.34±4.98)×103mm2 for left lung.Greater (⊿)SI%and increased perfusion were observed on end expiration than on end inspiration.The area was larger on end inspiration than on end expiration.Conclusions The FAIR is sensitive to perfusion changes in the gravity-dependent lung.Pulmonary blood flow is less in a state of high lung inflation than in a low state(inspiration vs.expiration).Positioning the patient so that the area of interest is down-gravity and breath-hold on end expiration may improve visibility of perfusion defects. Key words: Pulmonary circulation;  Vascular capacitance;  Magnetic resonance imaging; Perfusion