Quasistatic zooming of FDTD E-field computations : the impact of down-scaling techniques

• Published in: Physics in medicine & biology Vol. 46; no. 5; pp. 1539 - 1551
• Main Authors: VAN DE KAMER, J. B, KROEZE, H, DE LEEUW, A. A. C, LAGENDIJK, J. J. W
• Format: Journal Article
• Language: English
• Published: Bristol Institute of Physics 01.05.2001
• Subjects: Anisotropy; Biological and medical sciences; Computer Simulation; Humans; Hyperthermia, Induced; Image Processing, Computer-Assisted; Medical sciences; Phantoms, Imaging; Radiotherapy. Instrumental treatment. Physiotherapy. Reeducation. Rehabilitation, orthophony, crenotherapy. Diet therapy and various other treatments (general aspects); Static Electricity; Technology. Biomaterials. Equipments. Material. Instrumentation; Therapy, Computer-Assisted; Quasistatic problem; Electric field; Field distribution; Time domain method; Computer simulation; Dielectric properties; Low resolution; Hyperthermia; Treatment planning; Geometrical factor; Finite difference method; Test object
• ISSN: 0031-9155; 1361-6560
• DOI: 10.1088/0031-9155/46/5/314

Due to current computer limitations, regional hyperthermia treatment planning (HTP) is practically limited to a resolution of 1 cm, whereas a millimetre resolution is desired. Using the centimetre resolution E-field distribution, computed with, for example, the finite-difference time-domain (FDTD) method and the millimetre resolution patient anatomy it is possible to obtain a millimetre resolution SAR distribution in a volume of interest (VOI) by means of quasistatic zooming. To compute the required low-resolution E-field distribution, a low-resolution dielectric geometry is needed which is constructed by down-scaling the millimetre resolution dielectric geometry. In this study we have investigated which down-scaling technique results in a dielectric geometry that yields the best low-resolution E-field distribution as input for quasistatic zooming. A segmented 2 mm resolution CT data set of a patient has been down-scaled to 1 cm resolution using three different techniques: 'winner-takes-all', 'volumetric averaging' and 'anisotropic volumetric averaging'. The E-field distributions computed for those low-resolution dielectric geometries have been used as input for quasistatic zooming. The resulting zoomed-resolution SAR distributions were compared with a reference: the 2 mm resolution SAR distribution computed with the FDTD method. The E-field distribution for both a simple phantom and the complex partial patient geometry down-scaled using 'anisotropic volumetric averaging' resulted in zoomed-resolution SAR distributions that best approximate the corresponding high-resolution SAR distribution (correlation 97, 96% and absolute averaged difference 6, 14% respectively).