QUANTITATION OF GALACTOSEMIC CATARACTS IN DOGS USING MAGNETIZATION-TRANSFER CONTRAST-ENHANCED MAGNETIC-RESONANCE-IMAGING

Purpose. Magnetic resonance imaging (MRI) is becoming increasingly imp ortant for the diagnosis and characterization of ocular pathologies. A drawback to this technique is that image contrast between different r egions of tissue can be obscured because of the similarity of their nu clear magnetic resonance relaxation parameters. This problem is addres sed by magnetization transfer contrast (MTC) enhancement, a MRI techni que that generates high-contrast images based on characteristic tissue differences resulting from the interaction of water and macromolecule s. The purpose of this study was to investigate the feasibility-of usi ng MTC-enhanced imaging to monitor quantitatively the lens changes ass ociated with sugar cataract formation in galactose-fed dogs. Methods. Male beagles fed a diet containing 30% galactose were periodically exa mined by MRI for changes in tissue character. Each examination include d a gradient recalled echo image (M(0)), an MTC-enhanced gradient reca lled echo image (M(s)), a T-1 image determined from a one-shot T-1 ima ging sequence, and a T-1-weighted image taken from the raw T-1 data. A verage values were obtained for several regions of interest and tabula ted. These were correlated with cataractous stages visually observed b y slit lamp biomicroscopy and retroillumination photography. Results. Enhanced image details of the lens and anterior segment that documente d osmotic changes from initial cortical vacuole formation to cortical and nuclear changes associated with advanced sugar cataracts were char acterized from measurements of parameters obtained from M(0), M(s), T- 1-weighted, and T-1 images. Changes in the cross-sectional areas of le nses during sugar cataract formation also were documented. The magneti c resonance images showed visible changes from the onset of cortical v acuole formation. Region of interest (ROI) analysis of the images show ed tissue changes occurring throughout the cataract progression. Concl usions. The MTC-enhanced MRI technique is well suited to detecting len s changes associated with cataractogenesis. All but the earliest chang es were readily apparent from the images with no further analysis. Gra phic ROI analysis was able to detect regional changes associated the c ataract progression for all degrees of severity. Furthermore, the imag es demonstrated changes in size and shape that would not be detectable by visual inspection.