Demonstration of pulmonary perfusion heterogeneity induced by gravity and lung inflation using arterial spin labeling

To evaluate the effect of gravity and lung inflation on pulmonary perfusion heterogeneity in human lung using an arterial spin labeling (ASL) sequence called flow sensitive alternating inversion recovery (FAIR).

Magnetic resonance imaging of lung perfusion using arterial spin labeling sequence was performed in supine position in ten healthy volunteers on a 1.5T whole body scanner (GE Healthcare). Five coronal slices at an interval of 3cm from dorsal to ventral (labeled as P3, P6, P9, P12, P15, sequently) were obtained when the volunteers performed breath holding on end expiration and the relative pulmonary blood flow (rPBF) was measured. Then, another coronal perfusion-weighted image of P3 slice was obtained on end inspiration. Tagging efficiency of pulmonary parenchyma with IR (DeltaSI), rPBF and area of the P3 slice were analyzed.

(1) Along the direction of gravity, a gradient was visually perceived as a vertical increase in rPBF. There were significant statistic differences in rPBF between any two coronal planes except that between P12 and P15. In supine position, regression coefficients of right and left lung were -4.98 and -5.16, respectively. This means that rPBF decreased 4.98 (right) and 5.16 (left) for each centimeter above the dorsal. No statistical difference was seen between ROIs placed along iso-gravitational plane. (2) For a same slice, there were significant statistic differences in DeltaSI, rPBF and area at different respiratory phases (P<0.05). Greater DeltaSI and more perfusion were observed on end expiration than on end inspiration. The area was larger on end inspiration than on end expiration.

Both gravity and respiratory phase are important determinants of pulmonary perfusion heterogeneity. FAIR is sensitive to demonstrate gravity- and respiratory phase-dependent differences in lung perfusion. Positioning the patient so that the area of interest is down-gravity and asking patient to hold breath on end expiration may help in detection of perfusion defects.