Compressed sensing based optimization of electromagnetic field measurements required for quality assurance of hyperthermia applicators

Objective:

Quality assurance of hyperthermia applicators can be a cumbersome task. Periodic validation of the fields generated by the applicator is crucial for ensuring proper device performance, but the required measurements are very time-consuming. While most clinics use heating rate as a parameter of interest, consensus exists that spatial variation of the electromagnetic field in three dimensions (3D) would be much more insightful. Unfortunately, such 3D coverage would require measurements at many locations.

Approach:

To address this challenge, we propose a compressed sensing based methodology that enables accurate E-field and specific absorption rate (SAR) reconstruction from significantly reduced sampling densities. Using a Lucite Cone Applicator (LCA) and a homogeneous tissue-mimicking phantom, E-field measurements were obtained via a robotic scanning system equipped with an isotropic EM field probe (EX3DV4, SPEAG). Field maps were reconstructed using a discrete cosine transform (DCT)-based compressed sensing algorithm and evaluated using peak signal-to-noise ratio (PSNR), structural similarity index (SSIM), and the area under 50\%-iso-field contour overlap error. This error refers to the computational reconstruction accuracy of the compressed sensing algorithm when benchmarked against a densely sampled high-resolution reference scan.

Main results:

Results demonstrated that accurate field reconstruction can be achieved using only 8\% of the full measurements, reducing acquisition time from 135 minutes to just 11 minutes, while maintaining clinically relevant precision (SSIM = 0.9, PSNR = 27 dB, 50\%-iso-field contour overlap error is within ± 2.5\%).

Significance:

In this way, the need for extensive measurements is reduced while validation reliability is maintained. This approach delivers a faster solution, enhancing information content while significantly reducing the time required for quality assurance in hyperthermia clinics.