Cherenkov Light Emission in Pure Cherenkov Emitters for Prompt Gamma Imaging.

Proton range verification (PRV) in proton therapy by means of prompt-gamma detection is a promising but challenging approach. High count rates, energies ranging between 1 MeV and 7 MeV, and a strong background complicate the detection of such particles. In this work, the Cherenkov light generated by prompt-gammas in the pure Cherenkov emitters TlBr, TlCl and PbF2 was studied. Cherenkov light in these crystals can provide a very fast timing signal with the potential to achieve very high count rates and to discern between prompt-gammas and background signals. Crystals of 1×1 cm2 and thicknesses of 1 cm, 2 cm, 3 cm and 4 cm were simulated. Different photodetector configurations were studied for 2.3 MeV, 4.4 MeV, and 6.1 MeV prompt-gammas. TlCl achieved the greatest number of detected Cherenkov photons for all energies, detector dimensions, and photodetector efficiency modeling. For the highest prompt-gamma energy simulated, TlCl yielded approximately 250 Cherenkov detected photons, using a hypothetical high-performance photodetector. Results show the crystal blocks of 1 cm × 1 cm × 1 cm have greater prompt-gamma detection efficiency per volume and a comparable average number of detected Cherenkov photons per event.

18 F-sodium fluoride positron emission tomography of the racing Thoroughbred fetlock: Validation and comparison with other imaging modalities in nine horses.

BACKGROUND: Early and accurate detection of stress remodelling in racehorses is of utmost importance to prevent catastrophic injuries. Current imaging techniques have limitations in assessing early changes predisposing to catastrophic breakdowns. Positron emission tomography (PET) using 18 F-sodium fluoride (18 F-NaF) is a sensitive method for the detection of early bone turnover and may improve early recognition of subtle injuries. OBJECTIVES: To validate the clinical use of 18 F-NaF PET in Thoroughbred racehorses, to assess the value of PET in the detection of bone lesions and to compare PET results with findings of other advanced imaging modalities, clinical examination and pathology. STUDY DESIGN: Experimental exploratory study. METHODS: Twenty fetlocks from nine Thoroughbred racehorses were imaged using 18 F-NaF PET, computed tomography (CT) and scintigraphy. Five fetlocks were also imaged with magnetic resonance imaging and four fetlocks were also examined histologically. Imaging findings were independently reviewed by three board certified radiologists. Imaging, clinical and histopathological findings were correlated. RESULTS: PET imaging was well-tolerated by all horses. PET detected focal areas of 18 F-NaF uptake in instances where other imaging modalities did not identify abnormalities, in particular in the proximal sesamoid bones. Maximal standardised uptake values could be measured to quantify the activity of lesions. Areas of 18 F-NaF uptake corresponded to regions of increased vascularity and increased osteoblastic activity. MAIN LIMITATIONS: Limited number of cases. CONCLUSIONS: 18 F-NaF PET imaging of the Thoroughbred fetlock is feasible and compares favourably with other imaging modalities in detecting stress remodelling in Thoroughbred racehorses. PET appears to be a beneficial imaging modality when used for early detection of stress remodelling in an effort to prevent catastrophic musculoskeletal injuries in this population of horses.

Measurement of mobility and lifetime of electrons and holes in a Schottky CdTe diode.

We report on the measurement of drift properties of electrons and holes in a CdTe diode grown by the travelling heating method (THM). Mobility and lifetime of both charge carriers has been measured independently at room temperature and fixed bias voltage using charge integration readout electronics. Both electrode sides of the detector have been exposed to a 241Am source in order to obtain events with full contributions of either electrons or holes. The drift time has been measured to obtain the mobility for each charge carrier. The Hecht equation has been employed to evaluate the lifetime. The measured values for µτe/h (mobility-lifetime product) are in agreement with earlier published data.