Design, Calibration, and Evaluation of Depth-of-Interaction-Capable PET Detector Modules

High-resolution, small-bore PET systems suffer from a tradeoff between system sensitivity, and image quality degradation. In these systems long crystals allow mispositioning of the line of response due to parallax error and this mispositioning causes resolution blurring, but long crystals are necessary for high system sensitivity. One means to allow long crystals without introducing parallax errors is to determine the depth of interaction (DOI) of the gamma ray interaction within the detector module. While DOI has been investigated previously, newly available solid state photomultipliers (SSPMs) well-suited to PET applications and allow new modules for investigation. Depth of interaction in full modules is a relatively new field, and so even if high performance DOI capable modules were available, the appropriate means to characterize and calibrate the modules are not. This work presents an investigation of DOI capable arrays and techniques for characterizing and calibrating those modules. The methods introduced here accurately and reliably characterize and calibrate energy, timing, and event interaction positioning. Additionally presented is a characterization of the spatial resolution of DOI capable modules and a measurement of DOI effects for different angles between detector modules. These arrays have been built into a prototype PET system that delivers better than 2.0 mm resolution with a single-sided-stopping-power in excess of 95% for 511 keV g's. The noise properties of SSPMs scale with the active area of the detector face, and so the best signal-to-noise ratio is possible with parallel readout of each SSPM photodetector pixel rather than multiplexing signals together. This work additionally investigates several algorithms for improving timing performance using timing information from multiple SSPM pixels when light is distributed among several photodetectors.

An evaluation of the centers for Medicare & Medicaid Services' Hospital Acquired Conditions and Present on Admission Indicator Reporting program

Objective: This dissertation evaluated three aspects of the Centers for Medicare and Medicaid Services' Hospital Acquired Conditions and Present on Admission Indicator Reporting program (HACPOA program) to produce three journal articles for publication. ^ Methods: All payer admission records from state inpatient databases from Arizona, New Jersey and Washington states were analyzed for the year 2008. However some analyses required a sample of adult only Medicare patients in the first two studies. California's inpatient data (2004 – 2010) was also analyzed in the third study to examine the reporting and non-payment program elements' impact on the incidence of hospital acquired conditions. ^ Results: Majority diagnoses reported in inpatient prospective payment systems hospitals were present on admission. However, some diagnoses are still coded as "not present on admission" and "insufficient documentation to determine whether or not conditions are present on admission or not". This is important because it reveals that hospital complications still occur in hospitals. Hospital fall and trauma injuries were the most common hospital acquired conditions observed in this study. Predictors of hospital fall injuries include age, gender, number of diagnoses, number of procedures, number of chronic conditions while predictors of hospital trauma injuries include number of e-codes, number of diagnoses and the presence of chronic conditions on a patient's admission records. Finally, the implementation of the present on admission reporting requirement increased reports of certain hospital acquired conditions while the non-payment policy element in the Hospital Acquired Conditions program reduced the incidence of hospital fall and trauma injuries in particular. ^ Conclusion: The implementation of the Hospital Acquired Conditions and Present on Admission Indicator Reporting program has made the state inpatient database a more useful source of data capable of now identifying hospital complications. The reporting and nonpayment program elements in the HACPOA program have also impacted the incidence of hospital acquired conditions. ^