Are collimated low-dose digital radiographs valid for performing Delaire's architectural analysis?

Computed radiography (CR) provides the dynamic exposure range to reveal objects in film areas exposed by very low X-ray exposure. Conventional cephalometric radiographs are normally beam limited to the facial skeleton. The cranial vault and cervical vertebra are collimated and only exposed by extra-focal radiation and scatter. We hypothesize that, on conventional cephalometric radiographs obtained with CR, image data of collimated film areas can be enhanced for reliable performance of Delaire's cephalometric analysis of the entire skull. Therefore the aim of the present study was to compare the reproducibility of landmark placement on normal and underexposed film areas of CR images. Intra- and inter-observer reproducibility of landmark identification was evaluated on 200 randomly selected radiographs by calculating the error radius of repeated landmark placements. A paired-samples t-test revealed differences (P< 0.001) between intra- and inter-observer reproducibility. Intra-observer accuracy was influenced (P< 0.001) by variability of suture obliteration (bregma). Identification of landmarks in areas of extra-focal radiation showed no difference (P> 0.05) from that of landmarks inside the normally exposed area. CR offers the opportunity to perform of a full cranial analysis on a cephalometric radiograph collimated to the facial region.