 In such cases it is more accurate to use a body plethysmograph.A simplified helium dilution technique may be used as an alternative to quantitative CT scans to assess end-expiratory lung volumes (EELV) among patients who are on mechanical ventilation with diagnosis of ALI/ARDS according to a cross-sectional study.The results show a good correlation [EELV(He)=208+0.858xEELV(CT), r=0.941, p<0.001] between the two methods, and the helium dilution technique offers the advantages of lower cost, decreased transportation of critically ill patients, and reduced radiation exposure.