Digital subtraction radiography for longitudinal assessment of peri-implant bone change: method and validation

The purpose of this paper is to present a digital subtraction technique for the assessment of peri-implant bone change over time in vivo. Digital subtraction radiography may be used to detect areas of bony change that have occurred between radiographic examinations, and image processing algorithms have been developed which can relate the magnitude of the change on the subtraction image to a reference wedge, thereby allowing calculation of the mass of the lesion. This manuscript will present two algorithms for the assessment of osseous change. The method was validated in monkeys by means of small bony chips placed intra-orally prior to the first radiograph. The chips were removed, a second radiograph taken, and the images subtracted. Each algorithm was used to isolate the lesion and calculate change in bone mass. Overall, there was excellent correlation between the calculated lesion mass (in milligrams) and actual lesion mass (r2 > 0.9). The utility of the method was demonstrated by comparison of the results of subtraction radiography in successful implants and in implants that did not integrate during the healing phase.