重力和肺容积对MR肺灌注的影响

目的 用血流敏感性交替反转恢复(FAIR)序列评价重力和肺容积对MR肺灌注血流分布的影响.方法 应用GE 1.5 T MR系统,10名健康志愿者取仰卧位呼气末屏气时,用FAIR序列自背侧至腹侧每隔3 cm依次进行5个冠状面(依次标记为P3、P6、P9、P12、P15)扫描,之后再对P3层面在吸气末屏气时扫描.对5个冠状面的相对肺血流量(rPBF)进行方差分析,同一层面左、右肺rPBF间进行配对t检验,并对5个层面和rPBF进行线性回归分析;分析P3层面在不同呼吸相时反转脉冲标记前、后双肺信号强度变化率(⊿SI%)、rPBF及P3层面肺面积(Area)的变化情况,并进行配对t检验.结果 (1)5个不同冠状面:在重力方向上,右肺由后至前的rPBF依次为:100.57±18.22、79.57±12.36、61.65±11.15、48.92±9.96、41.20±9.88;左肺为:106.61±26.99、78.89±11.98、64.00±13.64、51.27±8.95、43.04±12.18;除P12与P15间差异无统计学意义外(P＞0.05),其余两两之间差异均有统计学意义(F值分别为27.43、15.83,P值均＜0.05),rPBF由后至前是逐渐减小的;在非重力方向上,即同一冠状面,左、右肺rPBF之间差异无统计学意义(P＞0.05);回归系数(r值)右肺为-4.98,左肺为-5.16.(2)P3层面在不同呼吸相时:右肺呼气相和吸气相的⊿SI%、rPBF、Area分别为1.12±0.31和0.71±0.18、90.78±17.35和52.85±8.75、(12.59±3.23)×103mm2和(17.77±4.24)×103mm2;左肺呼气相和吸气相的⊿SI%、rPBF、Area分别为1.01±0.24和0.70±0.11、91.08±18.68和54.58±10.70、(12.34±3.08)×103mm2和(17.34±4.98)×103mm2.不同呼吸相时⊿SI%、rPBF、Area间差异均有统计学意义(P＜0.05),呼气末的⊿SI%及rPBF明显高于吸气末;吸气末Area明显大于呼气末.结论 FAIR评价肺灌注在重力方向的灌注梯度是比较敏感的,不同呼吸相时肺灌注之间存在差异,所以检查时将感兴趣区置于重力依赖性区域,并在呼气末屏气可以提高灌注缺损的检出率.

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.