PURPOSE:Radiographic measurement of TLC is useful when Pulmonary Function Testing (PFTs) are not available or when PFT results require verification. In 1972 Reger published a method of doing this from chest radiographs (CXR) using an equation derived from a conical lung model. This method is accurate and simple and has been used in all institutions in which I’ve worked. Computer programs have been developed for this task using Thoracic Computed Tomograms (CTs), but the software is cumbersome and expensive. This investigation uses Reger’s model to develop an equation for measurement of TLC from chest CTs.
METHODS:1) Design:á Retrospective review was performed on PFTs, CXRs, CTs and patient charts of 43 consecutive patients who had had all 3 studies within 5 day periods. 2) TLC was determined in each from CXR and CT by Reger’s equation utilizing centimeter measurements of the width, depth and altitude of the apical and basal conical sections of the lungs. These were compared with TLC by PFT. 3) Values for TLC were compared using Student’s T test. Their paired relationship was quantitated by rectilinear plotting and fitting of a Least Squares line.
RESULTS:1) The patients were 16/23 male/female, age 58±5yr. Their diseases included COPD, asthma, IPF, RA, cancer, pneumonia and OSA. 2) TLCs from CXR and PFT differed by less than 8% in any individual. 3) When TLC from CXR was plotted against TLC from CT, a close linear relationship was found with an R value of 0.93 for the Least Squares line. This line passed through the origin and had a slope of TLC(CXR)=1.2TLC (CT). 4) When this relationship was used to adjust the TLCs from CT, the resultant values were all within 10% of the matched TLCs by CXR and within 8% of the matched TLC by PFT.
CONCLUSION:Reger’s method of TLC determination can be utilized with chest CTs with a simple modification of his original equation.
CLINICAL IMPLICATIONS:This method can be used when neither PFTs nor PA/Lateral CXRs are available.
DISCLOSURE:William Marino, No Financial Disclosure Information; No Product/Research Disclosure Information