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BACKGROUND AND PURPOSE:Neuroinflammation has been implicated in the pathophysiology of Parkinson's disease (PD), which might be influenced by successful neuroprotective drugs. The uptake of [11 C](R)-PK11195 (PK) is often considered to be a proxy for neuroinflammation, and can be quantified using the Logan graphical method with an image-derived blood input function, or the Logan reference tissue model using automated reference region extraction. The purposes of this study were (1) to assess whether these noninvasive image analysis methods can discriminate between patients with PD and healthy volunteers (HVs), and (2) to establish the effect size that would be required to distinguish true drug-induced changes from system variance in longitudinal trials. METHODS:The sample consisted of 20 participants with PD and 19 HVs. Two independent teams analyzed the data to compare the volume of distribution calculated using image-derived input functions (IDIFs), and binding potentials calculated using the Logan reference region model. RESULTS:With all methods, the higher signal-to-background in patients resulted in lower variability and better repeatability than in controls. We were able to use noninvasive techniques showing significantly increased uptake of PK in multiple brain regions of participants with PD compared to HVs. CONCLUSION:Although not necessarily reflecting absolute values, these noninvasive image analysis methods can discriminate between PD patients and HVs. We see a difference of 24% in the substantia nigra between PD and HV with a repeatability coefficient of 13%, showing that it will be possible to estimate responses in longitudinal, within subject trials of novel neuroprotective drugs.

Proton therapy is a treatment modality of increasing utility in clinical radiation oncology mostly because its dose distribution conforms more tightly to the target volume than X-ray radiation therapy. One important feature of proton therapy is that it produces a small amount of positron-emitting isotopes along the beam-path through the non-elastic nuclear interaction of protons with target nuclei such as 12C, 14N, and 16O. These radio isotopes, mainly 11C, 13N, and 15O, al low imaging the therapy dose distribution using positron emission tomography. The resulting positron emission tomography images provide a powerful tool for quality assurance of the treatment, especially when treating inhomogeneous organs such as the lungs or the head-and-neck, where the calculation of the dose distribution for treatment planning is more difficult. This pa per uses Monte Carlo simulations to predict the yield of positron emitters produced by a 250 MeV proton beam, and to simulate the productions of the image in a clinical PET scanner.

We report on the design and characterization of a new ASIC for the RatCAP, a head-mounted miniature PET scanner intended for neurological and behavioral studies of an awake rat. The ASIC is composed of 32 channels, each consisting of a charge sensitive preamplifier, a 5-bit programmable gain in the pole-zero network, a 3rd order bipolar semi-Gaussian shaper (peaking time of 80 ns), and a timing and energy discriminator. The energy discriminator in each channel is used to arm the zero-crossing discriminator and can be programmed to use either a low energy threshold or an energy gating window. A 32-to-1 serial encoder is embedded to multiplex into a single output the timing information and channel address of every event. Finally, LVDS I/O were integrated on chip to minimize the digital noise on the read-out PCB. The ASIC was realized in the TSMC 0.18 [micro]m technology, has a size of 3.3 mm x 4.5 nun and a power consumption of 117 mW. The gate length of the N-channel MOSFET input device of the charge sensitive preamplifier was increased to minimize 1/f noise. This led to a factor ~ 1.5 improvement of the ENC with respect to the first version of the ASIC [1]. An ENC of 650 e-rms was measured with the APD biased at the input. In order to predict the achievable timing resolution, a model was derived to estimate the photon noise contribution to the timing resolution. Measurements were performed to validate the model, which agreed within 12%. The coincidence timing resolution between two typical LSO-APD-ASIC modules was measured using a [sup.68]Ge source. Applying a threshold at 420 keV, a timing resolution of 6.7 ns FWHM was measured. An energy resolution of 18.7% FWHM at 511 keV was measured for a [sup.68]Ge source. Index Terms--ASIC, CMOS, PET, PET/MR, photon noise, RatCAP, timing resolution.

The capability to create high quality images from data acquired by the Rat Conscious Animal PET tomograph (RatCAP) has been evaluated using modified versions of the PET Monte Carlo code Simulation System for Emission Tomography (SimSET). The proposed tomograph consists of lutetium oxyorthosilicate (LSO) crystals arranged in 12 4 x 8 blocks. The effects of the RatCAPs small ring diameter (~ 40 mm) and its block detector geometry on image quality for small animal studies have been investigated. Since the field of view will be almost as large as the ring diameter, radial elongation artifacts due to parallax error are expected to degrade the spatial resolution and thus the image quality at the edge of the field of view. In addition to Monte Carlo simulations, some preliminary results of experimentally acquired images in both two-dimensional (2-D) and 3-D modes are presented. Index Terms--SimSET, small animal imaging.

A study has been carried out to investigate the possibility of using a pair of LSO + APD detector arrays to obtain a noninvasive measurement of the arterial input function for use in PET. The main focus of this study was to determine the spatial resolution and sensitivity required to obtain a high quality image that would permit a precise determination of the region of interest around the wrist artery. From these data a quantitative arterial input function that has minimal interference from the tissue and vein background can be obtained. The detector arrays were operated in coincidence counting mode to obtain planar images of various phantoms to demonstrate the feasibility of the concept. Index Terms--Blood monitor, input function, modeling, radiation detector.

One of the most promising high resolution positron emission tomography detector designs comprises an array of small, optically isolated scintillator crystals each coupled to an independent photosensor, such as an avalanche photodiode (APD). However, crosstalk between crystals (due to Compton scatter, photoelectron escape, or incomplete optical isolation) can significantly degrade performance and is expected to increase as crystals become narrower to improve spatial resolution. Various measures of crosstalk have been determined for different configurations of 4 x 8 blocks of 2 mm x 2 mm lutetium oxyorthosilicate (LSO) crystals coupled to matched Hamamatsu APD arrays. Results indicate that ignoring crosstalk signals could lead to a ~ 30% loss in coincidence sensitivity for a tomograph using these detectors and a decrease in energy resolution of ~ 2 percentage points. Spatial and time resolution would not be significantly affected with most practical front-end architectures. Index Terms--Biomedical nuclear imaging, gamma-ray detectors, optical crosstalk, positron emission tomography (PET), scintillation detectors.