Diagnostic accuracy of film-based, TIFF, and wavelet compressed digital temporomandibular joint images

The purpose of this research was to determine if digitization and the appli cation of various compression routines to digital images of temporomandibul ar joint (TMJ) radiographs would diminish observer accuracy in the detectio n of specific osseous characteristics associated with TMJ degenerative join t disease (DJD). Nine observers viewed 6 cropped hard-copy radiographic fil ms each of 34 TMJs (17 radiographic series). Regions of interest measuring 2 in x 2 in were digitized using an 8-bit scanner with transparency adapter at 300 dpi. The images were placed into a montage of 6 images and stored a s tagged image file format (TIFF), compressed at 4 levels (25:1, 50:1, 75:1 , and 100:1) using a wavelet algorithm, and displayed to the observers on a computer monitor. Their observations regarding condylar faceting, sclerosi s, osteophyte formation, erosion, and abnormal shape were analyzed using RO C. Kappa values were determined for relative condylar size and condylar pos ition within the glenoid fossa. Indices were compared using ANOVA at a sign ificance level of P < .05. Although significant and substantial observer va riability was demonstrated, there were no statistically significant differe nces between image modalities, except for condylar position, in which TIFF and wavelet (at ail compression ratios) performed better than the original image. For faceting, wavelet 100:1 performed better than radiographic film images. Little actual image file reduction was achieved at compression rati os above 25:1. Copyright (C) 2000 by W.B. Saunders Company.