Characterization and Evaluation of High Spatio-Temporal Resolution Aspects of X-ray Detectors in Medical Imaging
Shankar P.A., Alok
MetadataShow full item record
Minimally invasive endovascular image guided intervention (EIGI) is the preferred treatment procedure for stroke and allied vascular diseases. To achieve better treatment accuracy and efficacy, an imaging detector with higher performance in terms of spatio-temporal resolution and sensitivity is always desired. This dissertation reports the investigation of an x-ray detector for the next-generation EIGI imaging technology, and also a study of an image processing technique through physical sensors– the apodized aperture pixel (AAP) design. The impact of AAP technique on imaging performance was assessed through simulation and experiments. With AAP, images are acquired with smaller pixel sensors, such as 25 µm and processed to provide images at larger pixel dimensions at 50 µm or greater, with reduced signal and noise aliasing, while maintaining high resolution needs of x-ray detectors. Studies with standard pixel binning schemes, such as 2x and 3x binning, were compared to low pass filters, and the AAP design. AAP achieved advantages with resolution and reduced aliasing using simulations and experimentally measured modulation transfer functions (MTF) for MAF CCD and HRF-CMOS with 35 µm and 50 µm pixel pitch respectively. The main body of this dissertation is about a thorough characterization and evaluation of the x-ray imaging performance of a Cadmium Telluride (CdTe) photon counting detector (PCD) for EIGI. The PCD has a 100 µm pixel pitch and dual energy acquisition and four data acquisition modes including a high sensitivity with anti-coincidence on (ACC-On), which has a built in anti-charge sharing correction. The characterization study included assessment of detector’s linearity, instrumentation noise, dark field counts, and the calibration of energy thresholds using spectrum from an x-ray tube as well as a radioactive button source. The evaluation also includes dual energy material separation applications using a simulated setup for various attenuation profiles mimicking bone, soft tissue and contrast using the ACC-On mode. With this PCD’s unique 1000 frames per second imaging capability incorporated into a cone beam computed tomography (CBCT) setup, the mitigation of motion blur related to gantry rotation and ability to perform CBCT at high spatio-temporal resolution were demonstrated. The high spatio-temporal resolution of PCD could also be leveraged to implement rapid sequence angiography (RSA) to monitor flow rates and patterns in aneurysms, stenosis or arterio venous malformations (AVM). The performance and unique features of the energy resolved PCD such as spectroscopic and photon counting capabilities were tested and confirmed. High resolution in spatial and temporal domain have provided pioneering applications such as RSA and Rapid CBCT. In summary, this work demonstrated the feasibility and certain advantages of using a next generation energy resolved PCD for EIGI imaging.