In Vivo Proton MR Spectroscopic Change of Experimental Rat Brain Abscess Model

Lee, Chae Heuck; Lim, Kun Ho; Lee, Jung Hee; Kwun, Byung Duk

Abstract

OBJECTIVE
This study was designed to clarify the phasic changes and distinctive spectral features of the brain abscess in the in vivo proton MR spectroscopy during the processes of abscess formation in rats, in relation to MR images.
METHODS
Staphylococcus aureus was stereotactically inoculated into the predetermined location of the right frontal brain of SPF controlled Sprague-Dawley female rats(200-250gm). T1 weighted image(WI), T2WI and gadolinium enhanced image(CEMR) were obtained serially prior to each MR spectroscopy in order to visualize the infected lesions. RESULT: Three characteristic peaks, from proton MR spectroscopy, were found. A dominant peak was shown at 1.3ppm, which was due to the high concentration of mobile lipid or lactate, and smaller two peaks were shown at 0.8-1.0ppm and 1.9ppm, due to the small concentration of aminoacid(leucine, isoleucine. valine) and acetate, respectively. The lactate peak has increased during the stage of cerebritis and started to decrease in its early capsulation stage, finally invisible in its late capsulation stage(p=0.0001). The change of lactate peak was conspicuous at the early stage of cerebritis while the change of MR image was rather subtle. The aminoacids peak remained small throughout all stages. The acetate peak was shown in the late stage of cerebritis. However, it's peak area of integration was not exactly measured because of overlapping on the N-acetylaspartate peak. On the other hand, the peak of N-acetylaspartate and creatines, which could be observed in normal brain, remained at low level after sharp decrease in the early stage of cerebritis(p=0.004, p=0.005). The cholines peak decreased in the early stage of cerebritis, but it was not statistically significant(p=0.124).
CONCLUSION
From this study, we were able to observe the characteristic MR spectroscopic features of each stage even from such a small volume of abnormal lesions with a 2X2X3mm 3 voxel size. Furthermore, based on our results that inflammatory change could be detected earlier by MR spectroscopy than by MR images, MR spectroscopy may be applied for early diagnosis of the brain abscess.