Wavelet compression on detection of brain lesions with magnetic resonance imaging

The purpose of this report is to assess clinically acceptable compression r atios on the detection of brain lesions at magnetic resonance imaging (MRI) . Four consecutive T-2-weighted and the corresponding T-1- weighted images obtained in 20 patients were studied for 109 anatomic sites including 50 wi th lesions and 59 without lesions. The images were obtained on a 1.5-T MR u nit with a pixel size of 0.9 to 1.2 x 0.47 mm and a section thickness of 5 mm. The image data were compressed by wavelet-based algorithm at ratios of 20:1, 40:1, and 60:1. Three radiologists reviewed these images on an intera ctive workstation and rated the presence or absence of a lesion with a 50 p oint scale for each anatomic site. The authors also evaluated the influence of pixel size on the quality of image compression. At receiver operating c haracteristic (ROC) analysis, no statistically significant difference was d etected at a compression ratio of 20:1. A significant difference was observ ed with 40:1 compressed images for one reader (P = .023), and with 60:1 for all readers (P = .001 to .012). A root mean squared error (RMSE) was highe r in 0.94- x 0.94-mm pixel size images than in 0.94- x 0.47-mm pixel size i mages at any compression ratio, indicating compression tolerance is lower f or the larger pixel size images. The RMSE, subjective image quality, and er ror images of 10:1 compressed 0.94- x 0.94-mm pixel size images were compar able with those of 20:1 compressed 0.94- x 0.47-mm pixel size images. Wavel et compression can be acceptable clinically at ratios as high as 20:1 for b rain MR images when a pixel size at image acquisition is around 1.0 x 0.5 m m, and as high as 10:1 for those with a pixel size around 1.0 x 1.0 mm. Cop yright (C) 2000 by W.B. Saunders Company.