Date of Award
Electrical and Computer Engineering
M. Jamal Deen
In the past decades, great advances in biomedical imaging towards using less invasive and more sensitive imaging modalities have enabled early detection of diseases through timely diagnosis of patients. Positron emission tomography (PET) imaging, as one of the recent imaging technologies, provides imaging from cellular-level metabolic changes in tissues. This gives PET imaging a substantial lead in detecting disease in their very early stages. PET imaging provides high sensitivity and chemical specificity. However, it suffers from low resolution compared to other imaging methods. Time of Flight (ToF) PET imaging, one of the derivations of the PET, improves the imaging by exactly determining the position of the annihilation event using a time digital converter (TDC). By achieving the timing information of the incident anti-parallel photons coming from an event in ToF PET scanner, the TDC helps to determine the exact location of the event. So, it increases the resolution of the PET scanner.
A ToF PET custom-designed TDC has been proposed in this work. The designed TDC offers relatively high resolution and dynamic range (DR) to satisfy some PET imaging specifications. To increase the sensitivity and reduce the noise and latency, in-pixel design of TDC is desired. Therefore, a time digital converter that is specifically designed for ToF PET should follow a strict set of criteria in its design procedure. A three-staged hierarchical TDC was designed and implemented in 0.13μm standard CMOS technology to reduce the total number of delay elements for this area limitation issue. Also, a novel half-CLK period interpolation idea was proposed to reduce the total size of the TDC even more. A counter and half-CLK counter construct the coarse stage of the TDC. A delay locked loop (DLL) works as the first fine interpolator, while, the Vernier delay line (VDL) acts as the second fine interpolation stage.
A high resolution of 39ps was achieved with a relatively high DR of 1.28μs and the measured DNL and INL of 0.2TLSB and 0.4TLSB. Due to all area reduction techniques used, the final designed TDC measures for 0.11 mm2, which is much smaller than other similar TDCs with the same resolution and DR. As the amount of delay in the delay elements in the TDC are susceptible to any change in the environmental changes, a delay locking method was used to compensate for process, voltage and temperature (PVT) variations.
Nemati Hosseinabadi, Ebrahim, "IN-PIXEL TIME DIGITAL CONVERTER FOR TIME-OF-FLIGHT PET IMAGING" (2012). Open Access Dissertations and Theses. Paper 7531.
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