Image artifacts during MRT hybrid hyperthermia--causes and elimination.

Purpose: Online MR-thermometry during hyperthermia can improve treatment control. It needs excellent image quality during hyperthermia treatment to get information from subtracted images.

Materials And Methods: For hybrid hyperthermia two high-frequency devices were used in combination working with different frequencies. The imaging was performed on a 1.5 T MR tomograph (Siemens Symphony, Quantum Gradienten, Maestro Class, Firma Siemens, Erlangen, Germany) at 64 MHz whereas hyperthermia was administered with a BSD 2000 3D unit utilizing a Sigma Eye applicator and a 12 channel DODECK transistor amplifier (BSD 2000, BSD-MC, Salt Lake City, Utah, USA) operating at 100 MHz. For analysing image artifacts a spectrum analyser (Hewlett Packard HP8591E) was used.

Results: Two different image artifacts, occurring during the use of this hybrid system, are described. The artifacts result from introduction of additional frequencies into the imager. Here we demonstrated the detection and elimination of these spurious frequencies in the context of two case studies.

Conclusion: Hybrid hyperthermia requires excellent imaging for optimal operation. Additional frequencies causing image artifacts can be identified by use of a spectrum analyser. Once identified, these interfering frequencies can be eliminated with appropriate RF filters. With MRI quality control for hyperthermia systems with different treatment frequencies is possible.