A multi-element ultrasound hyperthermia system (Labthermics Technologies, Inc., Sonotherm 1000) was utilized to deliver energy to two relatively well-defined regions (3.8 X 3.8 cm) on the lateral aspect of the right rear leg of 22 dogs in 1, 2 and 3 weekly treatments to a target temperature of 42-43 degrees C, at a depth of 1 cm. The total treatment time was 30 min. One area heated on each dog was adjacent to the proximal femur and the other was 2-3 cm away from the distal aspect of the same bone. The system performed in an acceptably controlled manner and was able to deliver energy to a well-defined site. The mean temperature achieved, and rate of temperature rise in the heated regions, was independent of the region being treated. Little difference (0.12 degrees C) was noted between the mean temperatures of the heated regions, and the temperature bounds (42-43 degrees C) were exceeded by a small amount and for a relatively short period of time (out of range RMSE = 0.6 degrees C). Unheated regions showed much lower mean temperatures than did heated regions located 3.8 cm away, indicating that the energy was delivered in a well-defined manner. Superficial thermal injuries occurred in three of 22 dogs in the area heated 2-3 cm away from bone, and 11 of 22 dogs exhibited injuries in the tissue heated immediately adjacent to the femur.
Three-dimensional microscopic NMR images of spleen and liver specimens from rats injected with dextran magnetite particles and from controls were obtained at 4.7 T, using a specially designed probe in conjunction with a 3D filtered back projection reconstruction algorithm. All of the images were reconstructed as 64(3) arrays with (25 microns) 3 isotropic voxels. With the aid of the MR contrast agent, the red pulp and marginal zone of the spleen and the portal triad of the liver could be distinguished from the surrounding tissue in T2-weighted images. For mature rat spleen, natural contrast in T2-weighted images was found to distinguish the same features. Histological examinations of the tissues with and without contrast agent were also performed using an optical microscope. Microscopic NMR images, despite their lower resolution, clearly revealed many features seen in the optical images.
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