An Experimental 10-Port Microwave System for Brain Stroke Diagnosis-Potentials and Limitations

Abstract

Microwave imaging systems show potential as replacements for commonly used stroke diagnostic systems. We developed and tested a 10-port microwave system on a liquid head phantom with ischemic and hemorrhagic strokes of varying sizes and positions. This system allows for visualization of changes in dielectric parameters using the TSVD Born approximation, enabling recognition of stroke position and size from the resulting images. The SVM algorithm effectively distinguishes between ischemic and hemorrhagic strokes, achieving 98% accuracy on experimental data, with 99% accuracy in ischemic scenarios and 97% in hemorrhagic scenarios. Using the TSVD Born algorithm, it was possible to precisely image changes in the absolute permittivity of different stroke locations; however, changes in stroke size were more apparent in the variations of absolute permittivity than in the reconstructed stroke size within the antenna plane. Outside this plane, changes in the S-parameters decreased depending on the distance and size of the stroke, making detection and classification more difficult. One ring of antennas around the head proved insufficient, prompting us to focus on developing a system with antennas positioned around the entire head.

Keywords: SVM; TSVD Born approximation; brain stroke; microwave devices.

Figure 1

Numerical model of microwave system with 10 antennas in one plane: (a) top view and (b) side view.

Figure 2

H-slot antenna developed for brain imaging purposes: (a) numerical model and (b) fabricated antenna.

Figure 3

Stroke spherical phantoms of size 20, 30, and 40 mm in diameter.

Figure 4

The computer-controlled stroke position system to change the position of the stroke phantom on the x and y axes.

Figure 5

The 20 different x-y positions in the brain, indicated by white circles, where the stroke phantom was placed using the computer-controlled stroke positioning system. The z-axis position of the phantom was set to the center of the antennas.

Figure 6

Microwave imaging system with 10 antennas in one plane: (a) top view and (b) side view. (c) Measuring setup with VNA, switching matrix, antenna array, and computer; (d) complete system in its operational state (including liquid head phantom, stroke mounted in position system, and antenna array).

Figure 7

Confusion matrix for SVM classification for ischemic stroke, hemorrhagic stroke, and no-stroke scenario.

Figure 8

Result of TSVD Born imaging algorithm for (a,c) ischemic stroke and (b,d) hemorrhagic stroke of size 20 mm in diameter located (a,b) close to antennas at position (20, 30, 100) and located (c,d) deep in brain at position (10, 10, 100).

Figure 9

Result of TSVD Born imaging algorithm for (a,c) ischemic stroke and (b,d) hemorrhagic stroke of size 40 mm in diameter located (a,b) close to antennas at position (20, 30, 100) and located (c,d) deep in brain at position (10, 10, 100).

Figure 10

Result of TSVD Born algorithm for ischemic stroke of size 40 mm in diameter at position (20, 30, 70) located 30 mm under antenna plane. (a) XY view at stroke location (slice at Z = 70 mm), and (b) XZ view at corresponding Y-slice.