Exploring the effects of coded excitations and pulse compression on the performance of magneto-acousto-electrical tomography with magnetic field measurements in mr magnet

Date

2024-12-06

Author

Gözü, Mehmet Soner

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This thesis investigates the effects of coded excitations and pulse compression techniques on the performance of Magneto-Acousto-Electrical Tomography (MAET) with magnetic field measurements in MR magnet. MAET maps conductivity distributions in biological tissues by utilizing the interaction of ultrasound waves and a static magnetic field, generating a velocity current density detectable via receiver coils. The effectiveness of linear frequency modulated (LFM), Barker coded, and Golay coded excitations in improving signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and image quality metrics is evaluated through numerical simulations and experimental studies. In numerical simulations, a linear phased array (LPA) transducer is used to generate acoustic waves and a specific coil configuration is employed to detect MAET signals. Breast models with tumor inclusions are utilized to simulate conductivity variations. The results of coded excitations at 0 degrees LPA steering angle and in reconstructed B-mode MAET images demonstrate significant improvements over single-cycle excitation. Golay and Barker codes exhibit superior SNR performance, with Golay code achieving the highest CNR and image quality metrics. In experimental studies, an LPA transducer, a Helmholtz coil, and phantoms composed of water, agar-gelatin, and graphite discs are utilized in a 1.5 T MR magnet. At 100 repetitions, the computed mean SNR improvements for LFM, Barker code, and Golay code in comparison with single-cycle excitation are 5.84, 7.42, and 7.72 dB, respectively. The corresponding mean CNR improvements are 1.47, 1.82, and 2.1 dB, respectively. The system achieves a 3 mm boundary separation for all excitations under noisy conditions, confirming its capability to resolve closely spaced boundaries. The results highlight the effectiveness of coded excitations, particularly Golay code, in improving signal detection and image quality metrics for MAET, with numerical results closely aligning with experimental outcomes.

Subject Keywords

Magneto-acousto-electrical tomography, Conductivity imaging, Pulse compression, Coded excitation

URI

https://hdl.handle.net/11511/112684

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Graduate School of Natural and Applied Sciences, Thesis