Browsing by Author "Al-Qaisi, Muhammad K."

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    Optimized pulsing of high-intensity focused ultrasound for enhanced therapeutic window
    (2010-03) Al-Qaisi, Muhammad K.
    High intensity focused ultrasound (HIFU) provides a unique modality to perform non-invasive surgeries. The thermal ablation technique relies on focusing the non-ionizing acoustic wave within soft tissues to produce a small lesion. HIFU operations are typically attempted by continuous-wave (CW) applications of the beam intervened by wait periods to allow surrounding tissue to cool down. Large contiguous lesions are produced by raster-scanning the beam over the volume of the tumor; a procedure that requires up to three hours for a 2-cm diameter tumor. This is one of the main limitations of HIFU thermal therapy. As part of the ongoing research to accelerate the procedure, we investigate the role of pulsed-HIFU (pHIFU) parameters in the enhancement of the therapeutic gain within the HIFU focus. A therapeutic gain is observed when high duty cycle pHIFU is pulsed at the mechanical resonance of the medium. Up to 50% increase in temperature was measured in lab-prepared tissue mimicking phantoms. The therapeutic gain achieved by pHIFU over cwHIFU is attractive as no modifications on the currently used applicators are required.
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    Polarization-sensitive optical coherence tomography using polarization-maintaining fibers
    (2010-12) Al-Qaisi, Muhammad K.
    Optical Coherence Tomography (OCT) is a sensitive imaging technique that generates cross-sectional images of turbid tissues with a micrometer-scale resolution. Polarization-Sensitive (PS) OCT adds additional contrast to OCT by detecting polarization alterations within tissues, and provides accurate OCT images in polarization-altering tissues. Common approaches to build PSOCT are either: simple but difficult to incorporate in clinics and laboratories, or fiber-based and flexible but expensive, sophisticated, and computationally demanding. We have developed a new approach to build PSOCT using Polarization-Maintaining Fibers (PMF). A single depth scan is sufficient to calculate reflectivity, retardance, and axis orientation information using computationally-inexpensive algorithms. We present novel PMF-based PSOCT systems and demonstrate sensitivity figures larger than 100 dB, equivalent to common approaches. The developed PMF-based interferometers are used to measure minute Faraday rotations in tissue-mimicking phantoms, and the polarization properties of unmyelinated nerves. A novel algorithm is also developed to correct for errors calculating the birefringence of samples, and generate interpretable PSOCT images.