Calculation of the time resolution of the J-PET tomograph using kernel density estimation.

In this paper we estimate the time resolution of the J-PET scanner built from plastic scintillators. We incorporate the method of signal processing using the Tikhonov regularization framework and the kernel density estimation method. We obtain simple, closed-form analytical formulae for time resolution. The proposed method is validated using signals registered by means of the single detection unit of the J-PET tomograph built from a 30 cm long plastic scintillator strip. It is shown that the experimental and theoretical results obtained for the J-PET scanner equipped with vacuum tube photomultipliers are consistent.

Time resolution of the plastic scintillator strips with matrix photomultiplier readout for J-PET tomograph.

Recent tests of a single module of the Jagiellonian Positron Emission Tomography system (J-PET) consisting of 30 cm long plastic scintillator strips have proven its applicability for the detection of annihilation quanta (0.511 MeV) with a coincidence resolving time (CRT) of 0.266 ns. The achieved resolution is almost by a factor of two better with respect to the current TOF-PET detectors and it can still be improved since, as it is shown in this article, the intrinsic limit of time resolution for the determination of time of the interaction of 0.511 MeV gamma quanta in plastic scintillators is much lower. As the major point of the article, a method allowing to record timestamps of several photons, at two ends of the scintillator strip, by means of matrix of silicon photomultipliers (SiPM) is introduced. As a result of simulations, conducted with the number of SiPM varying from 4 to 42, it is shown that the improvement of timing resolution saturates with the growing number of photomultipliers, and that the [Formula: see text] configuration at two ends allowing to read twenty timestamps, constitutes an optimal solution. The conducted simulations accounted for the emission time distribution, photon transport and absorption inside the scintillator, as well as quantum efficiency and transit time spread of photosensors, and were checked based on the experimental results. Application of the [Formula: see text] matrix of SiPM allows for achieving the coincidence resolving time in positron emission tomography of [Formula: see text]0.170 ns for 15 cm axial field-of-view (AFOV) and [Formula: see text]0.365 ns for 100 cm AFOV. The results open perspectives for construction of a cost-effective TOF-PET scanner with significantly better TOF resolution and larger AFOV with respect to the current TOF-PET modalities.

A feasibility study of ortho-positronium decays measurement with the J-PET scanner based on plastic scintillators.

We present a study of the application of the Jagiellonian positron emission tomograph (J-PET) for the registration of gamma quanta from decays of ortho-positronium (o-Ps). The J-PET is the first positron emission tomography scanner based on organic scintillators in contrast to all current PET scanners based on inorganic crystals. Monte Carlo simulations show that the J-PET as an axially symmetric and high acceptance scanner can be used as a multi-purpose detector well suited to pursue research including e.g. tests of discrete symmetries in decays of ortho-positronium in addition to the medical imaging. The gamma quanta originating from o-Ps decay interact in the plastic scintillators predominantly via the Compton effect, making the direct measurement of their energy impossible. Nevertheless, it is shown in this paper that the J-PET scanner will enable studies of the [Formula: see text] decays with angular and energy resolution equal to [Formula: see text] and [Formula: see text], respectively. An order of magnitude shorter decay time of signals from plastic scintillators with respect to the inorganic crystals results not only in better timing properties crucial for the reduction of physical and instrumental background, but also suppresses significantly the pile-ups, thus enabling compensation of the lower efficiency of the plastic scintillators by performing measurements with higher positron source activities.

Data collection: are social workers reliable?

Social workers are required to collect a considerable amount of personal information about clients and their families which may be unrelated to direct clinical work. Administrators often use this for the purpose of payment, service documentation, agency planning, and accountability. The worker's concern about the appropriateness of collecting this data may result in poor compliance or even falsification of information. In a survey of Minnesota social workers, noncompliance with data collection requirements was substantial. The authors also found a significant degree of conflict about privacy and confidentiality issues. These findings suggest a basis of concern for those who must rely on accurate data for administrative planning.

A day hospital program for dual diagnosis patients in a VA Medical Center.

A day hospital program for patients with mental illness and substance abuse problems at a Veterans Affairs medical center uses nonconfrontational group therapy as the primary treatment modality. The goals of the six-to-eight-week program are to reduce substance abuse, improve medication compliance, and reduce the number of hospitalizations. Aftercare is available for patients who complete the program. The authors suggest that patients' ability to relate well to others in group therapy is the primary factor influencing successful outcome. During a 30-month period, 66 percent of the patients admitted to the day hospital program completed it. Three cases illustrating the variable outcomes of patients treated in the program are presented.

Social work practitioners as researchers: is it possible?

Social workers are encouraged and often expected to conduct research in addition to their clinical duties. Unfortunately, few practitioners seem interested and there is usually a lack of tangible supports in most practice settings. To counter this, a support group of non-supervisory clinical social workers in a Department of Veterans Affairs Medical Center met regularly with a social work educator-consultant in order to strengthen research skills, maintain motivation, and promote publication. This group successfully published seven articles with an additional five in process. In contrast, a second research group at the same facility foundered after eight months. Similarities and differences between the two groups are discussed. Recommendations are made about how agencies might encourage and sustain practitioners in the development and publication of clinical research.