Changes in proton relaxation times of the rat spleen during adjuvant-induced immunologic reaction

Possible changes in magnetic resonance (MR) relaxation times resulting from an immune reaction were evaluated in the rat spleen by means of in vitro proton spectroscopy and an established model of immune disease. Heat-killed Mycobacterium butyricum in Freund's adjuvant was injected intradermally into the tail of 28 rats. Ten normal rats served as controls. At different times following the injection of adjuvant (day 7, day 10, day 12, day 14, or day 22), the spleens were removed and weighed, and proton T1 and T2 relaxation times were measured with a 0.25-T spectrometer (10.7 MHz). Water content was also determined. Specimens of each spleen were histologically examined; this included Prussian-blue staining for detection of hemosiderin. In 22 of the 28 adjuvant-injected rats, spleen T1 values increased significantly, from a mean value of 451 msec +/- 23 S.D. (control rats) to a maximum mean value of 571 +/- 15 S.D., which occurred on day 12; this T1 increase paralleled an increase in weight and water content and a histologic appearance of granulomatous inflammation. In these rats, T2 changes were not significant. In the other six adjuvant-injected rats, spleen T2 relaxation time significantly decreased from a mean value of 42 msec +/- 5 S.D. to a mean value of 32 msec +/- 1 S.D. Histologic evaluation indicated that the origin of this T2 decrease was probably the presence of hemosiderin in the spleens of only these six rats. Mean T1 of these spleens decreased slightly, but not significantly.