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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).MethodsMagnetic 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.ConclusionsThe 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.
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Objective:To optimize the injection protocol of contrast medium for contrast-enhanced MRA (CEMRA) of pulmonary artery and to evaluate the diagnostic value of CEMRA and pulmonary perfusion imaging (PPI) in an experimental model of acute pulmonary embolism. Methods:CEMRA and PPI were performed in 6 normal pigs with different doses of gadolinium contrast agent (5ml, 10ml, 15ml, 20ml and 25ml) at an injection rate of 3ml/s, and 3 pulmonary embolism models were injected with 20 ml contrast agent at 3 ml/s. DSA was also performed for comparison. Results:The signal intensities and the signal to noise ratios of the pulmonary arteries kept increasing with the dose increase of the contrast agent, but the best angio-pulmonary contrast dose was 10-15ml (0.25-0.375mmol/kg), while the optimal dose for PPI was 15-20ml (0.375-0.5mmol/kg). Although CEMRA demonstrated less obstructed pulmonary arteries than DSA (5/10 vs 8/10)did, it detected all obstructions when combined with PPI. The pulmonary infarction zones showed wedge-shaped perfusion defects on the PPI images, with the signal intensities lower than those of the normal areas (137.86±45.32 vs 330.14±46.52, P<0.001). Conclusion:It is suggested that the optimal dose of the contrast agent is 0.25mmol/kg to 0.375mmol/kg for CEMRA, and 0.375mmol/kg to 0.5mmol/kg for lung perfusion. CEMRA combined with PPI may be better than DSA in demonstrating pulmonary embolism.
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Objective:To investigate the influence of lung inflation on MR perfusion imaging of human lung using an arterial spin labeling sequence called flow sensitive alternating inversion recovery(FAIR).Methods:Coronal perfusion-weighted images were obtained at different respiratory phases from 10 healthy volunteers on a 1.5T whole body scanner(GE medical system)using FAIR sequence.The changes of tagging efficiency of pulmonary parenchyma(?SI %),pulmonary blood flow and area of the scanning slice of different respiratory phases were analyzed.Results:(1)Significant difference was found in ?SI% between different respiratory phases(right lung P=0.021 5,left lung P=0.008 4),with that at end expiration greater than that at end inspiration.(2)Significant difference was also found in pulmonary blood flow at different respiratory phases(right lung P=8.92?10-5,left lung P=0.000 2),with that at end expiration higher than that at end inspiration.(3)The areas of the scanning slice were also significantly different at different respiratory phases(right lung P=2.94?10-5,left lung P=0.000 5),with that at end inspiration larger than that at end expiration.Conclusion:Pulmonary blood flow during expiration is higher than that during inspiration,which might be due to the decreased lung volume and increased vascular density during expiration.