Non-radiographic severity measurement of pectus excavatum

Background: To avoid the radiation exposure of CT imaging and the expense of CT or MRI studies, we sought to develop a non-radiographic severity measurement of pectus excavatum based on 3D photogrammetric imaging. Methods: Over 28 mo, ten consecutive patient volunteers with pectus excavatum underwent 3D stereophotogrammetric imaging. The surface width to surface depth ratio (Surface Lengths Pectus Index), the chest deformity's surface area to total chest surface area (Pectus Surface Area Ratio), and the chest deformity's volume to total chest volume (Pectus Volume Ratio) were calculated. Simple linear regression analysis compared the Surface Lengths Pectus Index, Pectus Surface Area Ratio, and Pectus Volume Ratio calculations each to the corresponding known CT pectus index. Results: The correlation between CT pectus index versus Surface Lengths Pectus Index yielded an R-squared value of 0.7637 and a P value of 0.0013. A CT pectus index of 3.4 or greater (eight patients) corresponded to a Surface Lengths Pectus Index of 1.86 or greater (six patients). The CT pectus index versus Pectus Surface Area Ratio (R-squared = 0.4627, P = 0.0305) and the CT pectus index versus the Pectus Volume Ratio (R-squared = 0.3048, P = 0.0990) demonstrated less correlation. Conclusion: Surface Lengths Pectus Index corresponds to the CT pectus index and may be adequate to determine severity of pectus excavatum in some patients.