Electromagnetically induced focused heat in the treatment of surgically created aneurysm models.

A hand-held radiofrequency (rf) probe of a novel design based on the principle of the induced current convergence was used to treat aneurysm models using focused hyperthermia. Aneurysms were created surgically in rats by a side-to-side anastomosis between the inferior vena cava and the abdominal aorta or by grafting a donor abdominal aorta from one rat onto the abdominal aorta of another rat. Aneurysms were treated by inserting the 0.3-mm diameter probe tip into the fundus and applying the power for brief periods (0.5-1.5 sec) using a foot pedal. Collapse of the fundus was observed as the result of the heat-induced thrombosis. Thermal distribution in the immediate vicinity of the probe as well as the heating rate were measured in a uniformly dielectric phantom and in rat vessels. The aneurysms were histologically examined immediately, three days, and three weeks after the treatment. Complete obliteration of the aneurysms and patency of the parent arteries were confirmed. Partial integrity of the vessels around the lesion was also confirmed.

Electromagnetic field focusing (EFF) probe--a new neurosurgical tool.

The electromagnetic field focusing (EFF) probe is capable of producing well circumscribed, intense heat at the point of contact with the tissue. Experimental studies were carried out to assess this probe as a neurosurgical tool using 38 rats and 4 mice with mammary carcinoma. The study on the rats included study of the cutting, coagulating and vaporizing effect on brain tissue including study of blood brain barrier disruption and heat dissipation. The study on the mice included the study of vaporizing property of the probe on solid tumours. The probe proved to be an excellent tool for cutting, coagulating and vaporizing purposes with very minimal disruption of blood brain barrier and demonstrated well circumscribed heating pattern. The study indicates that this tool combines the beneficial effect of both the YAG and CO2 laser.

Electromagnetic field focusing (EFF) probe in aneurysm thrombosis. Preliminary report.

Due to its capability of producing a well localized intense heat field of predictable dimensions, the electromagnetic field focusing probe was evaluated experimentally as a surgical tool in aneurysm thrombosis. Aneurysm models were created by anastomosing a segment of vein to the abdominal aorta. Seventy-five such aneurysms were created in seventy-five animals. The aneurysms were then placed under the solenoidal radiofrequency coil and the tip of the field focusing probe was inserted into them. Intense heat was delivered with well defined, effective and quick thrombosis and shrinkage of the aneurysm. Nineteen of the aneurysms were followed for up to one week. Histological studies were conducted showing complete thrombosis of the aneurysm with good preservation of the aorta. With further refinement of this technique, it is hoped that stereotaxic aneurysm thrombosis might be possible.

Noninvasive tumor volume measurement using magnetic resonance (MR) imaging and an open sided saddle coil.

A magnetic resonance (MR) imaging scanner operated at 0.5 T with a specially constructed receiving coil was used to measure volumes of primary spontaneous tumors in rats and guinea pigs. The coil was used to improve the signal to noise ratio (S/N) of the MR images of tumors in these small animals. The tumor volume was determined by the summation of the volume of contiguous slices or ellipsoid approximation. The accuracy of the volume measurement was better when the numerical integration was used in calculating the slice volume. The open sided saddle (OSS) coil used as the receiving coil gave better S/N than that of the standard head coil.