MEASURING THE PROGRESSION OF FOREIGN-BODY REACTION TO SILICONE IMPLANTS USING IN-VIVO MR MICROSCOPY

We used in vivo magnetic resonance (MR) microscopy to follow the growt h of fibrous capsule as a foreign body reaction to silicone implants i n rats. Anesthetized rats were imaged 1, 7, 14, and 28 days after sili cone-coated MR imaging coils were sutured to their neck muscles, On th e twenty-eighth day, rats were sacrificed and coils and adjacent tissu es were removed en bloc and fixed in formalin, reimaged,vith MR, and s ectioned for conventional histology, Three-dimensional (3-D) spin-echo [3DFT] acquisition gave in-plane resolution of 32 x 32 I-lm in viva a nd 16 x 16 mu m ex vivo. All MR images showed a diffuse band of elevat ed signal intensity between the silicone of the coil and adjacent tiss ue. The border of the hyperintense band was thin and not well defined at seven days post-implantation. From 7-28 days, the band showed relat ively homogeneous signal intensity and its thickness increased 44% on the rectus muscle side and 78% on the subcutaneous side. The capsule t hickness determined either by MR in vivo and ex vivo microscopy or con ventional histology was not significantly different, and there was a s ignificant correlation between thickness measurements among those meth ods. MR ire vivo microscopy provides sufficient resolution and spatial information to serially evaluate the growth of the foreign body fibro us capsule over time, thus achieving greater accuracy and consistency in measurements.