How reliable are Hounsfield-unit measurements in forensic radiology?

Objective: To assess the reliability of computed tomography (CT) numbers, also known as Hounsfield-units (HU) in the differentiation and identification of forensically relevant materials and to provide instructions to improve the reproducibility of HU measurements in daily forensic practice. Materials and methods: We scanned a phantom containing non-organic materials (glass, rocks and metals) on three different CT scanners with standardized parameters. The t-test was used to assess the influence of the scanner, the size and shape of different types of regions-of-interest (ROI), the composition and shape of the object, and the reader performance on HU measurements. Intra-class correlation coefficient was used to assess intra- and inter-reader reliability. Results: HU values did not change significantly as a function of ROI-shape or -size (p > 0.05). Intra-reader reliability reached ICC values >0.929 (p < 0.001). Inter-reader reliability was also excellent with an ICC of 0.994 (p < 0.001). Four of seven objects yielded significantly different CT numbers at different levels within the object (p < 0.05). In 6/7 objects the HU changed significantly from CT scanner to CT scanner (p < 0.05). Conclusion: Reproducible CT number measurements can be achieved through correct ROI-placement and repeat measurements within the object of interest. However, HU may differ from CT-scanner to CT-scanner. In order to obtain comparable CT numbers we suggest that a dedicated Forensic Reference Phantom be developed. (c) 2012 Elsevier Ireland Ltd. All rights reserved.