3-DIMENSIONAL IMAGING OF TRABECULAR BONE USING THE COMPUTER NUMERICALLY CONTROLLED MILLING TECHNIQUE

Although various techniques exist for high-resolution, three-dimension al imaging of trabecular bone, a common limitation is that resolution depends on specimen size. Most techniques also have limited availabili ty due to their expense and complexity. We therefore developed a simpl e, accurate technique that has a resolution that is independent of spe cimen size. Thin layers are serially removed from an embedded bone spe cimen using a computer numerically controlled (CNC) milling machine, a nd each exposed cross section is imaged using a low-magnification digi tal camera. Precise positioning of the specimen under the camera is ac hieved using the programmable feature of the CNC milling machine. Larg e specimens are imaged without loss of resolution by moving the specim en under the camera such that an array of field-of-views spans the ful l cross section. The images from each field-of-view are easily assembl ed and registered in the postprocessing. High-contrast sections are ac hieved by staining the bone black with silver nitrate and embedding it in whitened methylmethacrylate. Due to the high contrast nature and h igh resolution of the images, thresholding at a single value yielded e xcellent predictions of morphological parameters such as bone volume f raction (mean +/- SD percent error = 0.70 +/- 4.28%). The main limitat ions of this fully automated ''CNC milling technique'' are that the sp ecimen is destroyed and the process is relatively slow. However, becau se of its accuracy, independence of image resolution from specimen siz e, and ease of implementation, this new technique is an excellent meth od for ex situ imaging of trabecular architecture, particularly when h igh resolution is required. (C) 1997 by Elsevier Science Inc. All righ ts reserved.