Correlation between low attenuation area (LAA) of the lungs in high-resolution computed tomography (HRCT) and mean CT number in bronchial asthma

The maximal percent low attenuation area < -950 HU (% LAA) among three anatomic lung levels on high resolution computed tomography (HRCT) was examined in patients with asthma, classified by the degree of % LAA, in relation to the mean CT number, % FVC of the predicted value, and FEV 1/FVC (FEV1%). 1 . The mean CT number was closely related to the degree of % LAA of the lungs. The mean CT number was significantly lower in patients with high % LAA (mean CT number-915.3HU, % LAA 37.6%) than in those with low % LAA (-852.9HU, 4.7%). 2. The FEV1% value was significantly lower in patients with high % LAA (47.8%) than in those with low % LAA (62.2%)(p<0.05). The % FVC value was also significantly lower in patients with high % LAA (77.1%) compared to the value in those with low % LAA (101.2%). The results suggest that a large volume of LAA<-950HU of the lungs can be observed in patients with asthma, and the % LAA is closely correlated with mean CT number and the values of FEV1% and % FVC.

HRCT (high resolution computed tomography)により,-950HU以下のlow attenuation area(LAA)を3つの高さの肺野レベルで観察し,そのなかの最も高い値をmaximal% LAAとして表し,この値と平均CT number, % FVCおよびFEV1.0%の値と比較検討した｡1.平均CT numberは,maximal% LAAと密接な関連を示した｡そして,平均CT numberは,% LAAが低い症例(% LAA :4.7%, mean CT number:-852.9HU)に比べ,% LAAが高い症例(% LAA :37.6%, mean CT number:-915.3HU)において低い傾向が見られた｡2.FEV1.0%値は,% LAA値が低い症例(62.2%)に比べ% LAA値が高い症例(47.8%)において有意に低い値を示した(P<0.05)。% FVC値も同様% LAA値が低い症例(101.2%)に比べ高い症例(77.1%)で低い値を示したが両群間に有意の差は見られなかった｡これらの結果より,気管支喘息においも,HRCT上肺野で-950HU以下のLow attenuation area(LAA)を示す症例が見られること,そして,% LAAは,mean CT number,FEV1.0%や% FVC値とある程度関連していることが示唆された｡