AN INVITRO STUDY OF THE CHARACTERISTICS OF A COMPUTER-AIDED RADIOGRAPHIC EVALUATION (CARE) SYSTEM FOR LONGITUDINAL ASSESSMENT OF DENSITY CHANGES

In recent years, several systems for computerized analysis of radiogra phs have been introduced, most of which use digital conversion of the image followed by subtraction of consecutive images to assess changes. This paper introduces a computer-based qualitative and quantitative r adiographic evaluation system based on the CADIA algorithm. Problems a ssociated with computerized radiographic analysis are discussed and ev aluation criteria for this type of system are suggested. These criteri a include evaluation of system noise and threshold setting, reproducib ility, and establishment of the system working curve (validity). The C ARE system noise ranged from a - 10 to + 10 CADIA value and the thresh old was set on 13 for all measurements. The reproducibility was high, both for the radiographic technique and for repeated measurements. The working curve was established and showed the system's ability to dete ct small density changes of 0.048 O.D. which corresponds to 0.27 mm of aluminum thickness or compact bone equivalent. The linear range of th e curve was between 0.7 and 1.8 O.D. By controlling the exposure param eters it was possible to work within the linear range of the curve. Ba sed on these evaluation criteria, the CARE system can be used to quant itatively evaluate small density changes on sequential radiographs for early detection of caries and periodontal disease.