Digital correction of computed X-radiographs for coral densitometry

The recent increase in sea surface temperature and ocean acidification raises major concerns about the evolution of the coral calcification rate. Digitized X-radiographs have been used for coral skeleton density measurements since the 1980s. The main limitation of coral densitometry from digitized X-radiographs is the X-ray intensity heterogeneity due to spherical spreading (inverse square law) and heel effect. Until now, extra X-ray images or aluminum standards have been used to correct X-radiographs. However, such corrective methods may be constraining when working with a high number of coral samples. Here, we present an inexpensive, straightforward, and accurate digital detrending (DD) method to correct the heterogeneities of the X-ray irradiation that affect X-radiographs. The X-radiograph is corrected against the irradiation imprint recorded by its own background using a kriging interpolation method, thus allowing reliable optical density measurements directly on the corrected X-ray image. This digital detrending (DD) method was validated using skeletal bulk density measurements and computerized tomography (CT). Coral densitometry using DD corrected X-radiographs does not require the destruction of the coral sample and provides high-resolution measurements. Since DD does not require extra aluminum standards to correct X-radiographs, this method optimizes the working space available on the X-ray image. Moreover, it corrects the entire X-radiograph, thus larger samples or numerous samples can be X-rayed at the same time. (C) 2012 Elsevier B.V. All rights reserved.