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S N Hornsleth

Publications and source records attributed to S N Hornsleth.

5 recordsLinked to original sources
PubMed1994

Radio-frequency ring applicator: energy distributions measured in the CDRH phantom.

SAR distributions were measured in the CDRH phantom, a 1 cm fat-equivalent shell filled with an abdomen-equivalent liquid (sigma = 0.4-1.0 S m-1; dimensions 22 x 32 x 57 cm) to demonstrate the feasibility of the ring applicator to obtain deep heating. The ring electrodes were fixed in a PVC tube; diameter 48 cm, ring width 20 cm and gap width between both rings 31.6 cm. Radio-frequency energy was fed to the electrodes at eight points. The medium between the electrodes and the phantom was deionised water. The SAR distribution in the liquid tissue volume was obtained by a scanning E-field probe measuring the E-field in all three directions. With equal amplitude and phase applied to all feeding points, a uniform SAR distribution was measured in the central cross-section at 30 MHz. With RF energy supplied to only four adjacent feeding points (others were connected to a 50 omega load), the feasibility to perform amplitude steering was demonstrated; SAR values above 50% of the maximum SAR were measured in one quadrant only. SAR distributions obtained at 70 MHz showed an improved focusing ability; a maximum at the centre exists for an electric conductivity of the abdomen-equivalent tissue of 0.6 and 0.4 S m-1.

Electromagnetic Fields↗
PubMed1994

Deep heating using a movable applicator phased array hyperthermia system. A preclinical feasibility study.

A preclinical evaluation of the 'movable applicator phased array hyperthermia system' was performed. The system employs four coherent applicators enabling power steering by amplitude and phase control. This concept has already been used in other systems, but the combination with a compact applicator design and easy movement of applicators has not been used before. The paper contains a description of the system and a verification of its performance using quality assurance tests with scanned E-field measurements. A clinical simulation was performed in pig to address the clinical feasibility of the system. The target volume was the left kidney. Two heating sessions, with and without occluded blood-flow to the kidney, were performed. In the low-flow experiments a temperature of 48 degrees C and 46 degrees C was obtained in the upper and lower pole of the kidney respectively. For the high-flow experiment the temperature in the upper pole was 48 degrees C.

Animals↗
PubMedDate not supplied

Multi-applicator hyperthermia system description using scattering parameters.

Hyperthermia systems using electromagnetic phased arrays have often been investigated from a SAR distribution point of view. One of the problems in these systems is that the achieved SAR distribution is different from the intended one because of changes in the generator signals due to mutual coupling between applications. The use of circuit theory and S-parameters in the description of an N-applicator phased array system is introduced in this paper, and a compact matrix equation giving excitation as a function of generator signals is derived. Measurement of the S-parameters is discussed using a phased array deep heating system (Danish Hyperthermia Foundation (DHF)) as an example. In a phantom experiment a significant improvement in the SAR distribution is demonstrated when the developed method is applied.

Electromagnetic Phenomena↗
PubMedDate not supplied

Quality assurance for radiofrequency regional hyperthermia.

Today most treatments with regional hyperthermia are applied using radiofrequency systems with 'focus' steering by amplitude and phase control. This paper deals with quality assurance procedures developed to ensure controlled and safe treatments in such systems. Our results show how the deviations between requested and observed phase and amplitude vary with frequency, and how these deviations depend on both the geometry of the object (phantom) inside the system and the power level applied. The results also indicate that the investigated systems' internal quality assurance procedures were inadequate and that additional procedures should be applied. Since the system parameters depend on patient and treatment specific conditions it is concluded that there is a need for QA measurements before or during treatment. This paper deals specifically with the commercial BSD-2000 system from BSD Medical Corp. in Salt Lake City, Utah, as installed in Bergen, but the procedure outlined can be applied to other phase and amplitude-controlled RF-RHT systems with only minimal adjustments.

Calibration↗