Abstract
Based on the calculated attenuation numbers in computed tomograms (CT) of the chest, histographical analy of distributions in CT for 18 patients with cryptogenic fibrosing alveolitis was performed. For better clinical understanding, this histogram was correlated to the attenuation numbers of each type tissue and structure within the chest wall.
On histograms for normal subjects, four steep peaks were observed and the attenuation number of each peak ranged from -400 to -440 (peak A), -80 to -100 (peak B), -40 to -50 (peak C) and 10 and 20 (peak D) respectively (settled attenuation numbers of water and air, 0 and -500, respectively). Examination of the corresponding tissue or structure to each peak showed that lung parenchyma was included mostly in peak A, since attenuation numbers of lung parenchyma ranged from -360 to -470. Peak B was comparable to bean bags, peak C to fat tissue and peak D to soft tissues apart from fat. On the other hand, the pulmonary blood vessels distributed widely on histogram ranging from -40 to -360 and no corresponding peak was observed.
In patients with cryptogenic fibrosing alveolitis, the most characteristic change on histogram was found on peak A which tended to decrease in height and to shift widely to the range of higher attenuation numbers. In advanced cases, this shift was observed up to peak C range. These changes shown on histograms were attributed to a markedly high density area of the lung on CT, since the attenuation number for this area ranged from -200 to -100. Therefore, histographical presentation of attenuation numbers was considered to be clinically useful for quantitative evaluation of cryptogenic fibrosing alveolitis.
