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Image Resolution Improvement in a Photoacoustic Imaging System based on Beamforming

Amjadian, Mohammad Reza | 2022

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 55375 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Kavehvash, Zahra
  7. Abstract:
  8. The fast-growing development of engineering and medical sciences leads to the diagnosis and treatment of diseases with higher accuracy and in the early stages of the disease. Medical imaging systems are considered as a crucial and effective tool in this field that based on the principle of technology used, are able to image various tissues with high quality. In recent years, photoacoustic imaging has attracted the attention of many researchers and engineers, because it able to image different tissues with good resolution and penetration depth non-invasively and without the use of ionizing radiation. The photoacoustic system response is a low-pass filter that passes only low-frequency components and filters higher frequencies. Therefore, the system resolution is limited to this filter response because the received photoacoustic signal does not include the high frequency contents of the object being imaged. Structured illumination implemented in ultrasound and optical systems improves system resolution. In this method, the light beam is formed by an optical modulator. Modulated light is illuminated to the target of imaging, and the generated photoacoustic signal is received by an ultrasonic transducer. In this manner, the target frequency spectrum to be imaged is shifted to lower frequencies, and as a result, higher frequencies can pass through the system response filter. By combining the high and low frequency components, the frequency bandwidth received from the target is increased, which leads to improved system resolution. In the optical resolution photoacoustic microscopy system, by mathematically modeling the frequency response of the system in different optical, thermal and ultrasound phases, we have been able to investigate the effect of the structured illumination on the lateral resolution and imaging speed. In the Monte Carlo simulation results, the lateral resolution improves from 2.86 to 2.26 µm compared to the conventional structure, and the imaging depth of field has improved from 50 µm to 1.8 mm. In the next step, in an acoustic resolution photoacoustic microscopy system by using structured illumination, the lateral resolution has been improved in the depth range of 1.5 mm. The lateral resolution in the conventional acoustic resolution photoacoustic microscopy system is equal to 45.8 µm, which the structured illumination improves and reaches a uniform resolution of 23 µm in different depths. To prove the capability of the mentioned system, imaging targets such as mouse ear and liver have been used to demonstrate the system's superiority to image real tissues
  9. Keywords:
  10. Synthetic Aperture ; Structured Illumination ; Fourier Domain ; Fourier Domain Image Reconstruction ; Photoacoustic Microscopy Imaging System ; Image Resolution

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