Data acquisition electronics for gamma ray emission tomography using width-modulated leading-edge discriminators.

We present a new high-performance and low-cost approach for implementing radiation detection acquisition systems. The basic elements used are charge-integrating ADCs and a set of components encapsulated in an HDL (hardware definition language) library which makes it possible to implement several acquisition tasks such as time pickoff and coincidence detection using a new and simple trigger technique that we name WMLET (width-modulated leading-edge timing). As proof of concept, a 32-channel hybrid PET/SPECT acquisition system based on these elements was developed and tested. This demonstrator consists of a master module responsible for the generation and distribution of trigger signals, 2 x 16-channel ADC cards (12-bit resolution) for data digitization and a 32-bit digital I/O PCI card for handling data transmission to a personal computer. System characteristics such as linearity, maximum transmission rates or timing resolution in coincidence mode were evaluated with test and real detector signals. Imaging capabilities of the prototype were also evaluated using different detector configurations. The performance tests showed that this implementation is able to handle data rates in excess of 600k events s(-1) when acquiring simultaneously 32 channels (96-byte events). ADC channel linearity is >98.5% in energy quantification. Time resolution in PET mode for the tested configurations ranges from 3.64 ns FWHM to 7.88 ns FWHM when signals from LYSO-based detectors are used. The measured energy resolution matched the expected values for the detectors evaluated and single elements of crystal matrices can be neatly separated in the acquired flood histograms.

Design and performance evaluation of a coplanar multimodality scanner for rodent imaging.

This work reports on the development and performance evaluation of the VrPET/CT, a new multimodality scanner with coplanar geometry for in vivo rodent imaging. The scanner design is based on a partial-ring PET system and a small-animal CT assembled on a rotatory gantry without axial displacement between the geometric centers of both fields of view (FOV). We report on the PET system performance based on the NEMA NU-4 protocol; the performance characteristics of the CT component are not included herein. The accuracy of inter-modality alignment and the imaging capability of the whole system are also evaluated on phantom and animal studies. Tangential spatial resolution of PET images ranged between 1.56 mm at the center of the FOV and 2.46 at a radial offset of 3.5 cm. The radial resolution varies from 1.48 mm to 1.88 mm, and the axial resolution from 2.34 mm to 3.38 mm for the same positions. The energy resolution was 16.5% on average for the entire system. The absolute coincidence sensitivity is 2.2% for a 100-700 keV energy window with a 3.8 ns coincident window. The scatter fraction values for the same settings were 11.45% for a mouse-sized phantom and 23.26% for a rat-sized phantom. The peak noise equivalent count rates were also evaluated for those phantoms obtaining 70.8 kcps at 0.66 MBq/cc and 31.5 kcps at 0.11 MBq/cc, respectively. The accuracy of inter-modality alignment is below half the PET resolution, and the image quality of biological specimens agrees with measured performance parameters. The assessment presented in this study shows that the VrPET/CT system is a good performance small-animal imager, while the cost derived from a partial ring detection system is substantially reduced as compared with a full-ring PET tomograph.

A nosocomial outbreak of influenza during a period without influenza epidemic activity.

The objective of this study was to describe a nosocomial outbreak of influenza during a period without influenza epidemic activity in the community. Outbreak investigation was carried out in an infectious diseases ward of a tertiary hospital. Presence of two or more of the following symptoms were used to define influenza: cough, sore throat, myalgia and fever. Epidemiological survey, direct immunofluorescence, viral culture, polymerase chain reaction, haemagglutination-inhibition test in throat swabs and serology for respiratory viruses were performed. Twenty-nine of 57 healthcare workers (HCW) (51%) and eight of 23 hospitalised patients (34%) fulfilled the case definition. Sixteen HCW (55%) and three inpatients (37%) had a definitive diagnosis of influenza A virus infection (subtype H1N1). Among the symptomatic HCW, 93% had not been vaccinated against influenza that season. Affected inpatients were isolated and admissions in the ward were cancelled for 2 weeks. Symptomatic HCW were sent home for 1 week. On the seventeenth day of the outbreak the last case was declared. The incidence of cases in this outbreak of influenza, which occurred during a period without influenza epidemic activity in the community, was notably high. Epidemiological data suggest transmission from healthcare workers to inpatients. Most healthcare workers were not vaccinated against influenza. Vaccination programmes should be reinforced among healthcare workers.

Plantain allergy (Plantago lanceolata): assessment of diagnostic tests.

A study was made of 55 patients with skin prick test results for Plantago lanceolata of 3 mm2 or more. They were evaluated in relation to the response elicited by 10 mg/ml of histamine HCl. Patients with a response to Plantago less intense than the response to histamine were considered as having a "negative" response, whereas those whose response to Plantago was more intense than the response to histamine were considered as having a "positive" response. In 35 cases a radioallergosorbent test (RAST) was performed and in 22, nasal provocative testing (NPT). The frequency of positive response was 0.63 for skin tests, 0.11 for RAST and 0.72 for NPT. Among the patients with positive NPT, the frequencies of positive response to skin tests and RAST were 0.71 and 0.6 (p < 0.05), respectively. Results are discussed and study methods are proposed.

Allergy to Alternaria. II. Diagnostic comparison of skin-tests and RAST.

The diagnosis of Alternaria allergy is difficult and tests in vivo and in vitro usually do not give results as satisfactory as those obtained with other allergens. We studied 33 patients with a cutaneous response of 2 mm2 or more to skin-prick tests for Alternaria (extract containing 104 micrograms/ml of Alt-1). Results were compared with those of RAST. Skin tests were positive in 75.8% of cases (the resulting papule was the same size as or larger than that elicited by 10 mg/ml histamine) and negative in 24.2% of cases. RAST was positive in 75% of cases and negative in 25%. There was no significant difference in the frequencies. RAST was positive four times more often in males than in females; when these figures were corrected for population data, the ratio was 2:1. The coefficient of correlation between the intensity of skin-test and RAST results was r = 0.51 (p < 0.05). These findings are evaluated and results are discussed.

Diagnosis of allergy to cat epithelium in clinical practice. I. Value of skin tests.

Seventy atopic patients were studied. Pin-prick skin tests with cat epithelium extract (Ifidesa-Aríste-gui) were made. The results were compared by dividing the patients into a group with clinical manifestations of contact with cats and a group without clinical manifestations of contact with cats. Our results show that skin tests for cat epithelium, such as those carried out routinely in clinical practice, are not very sensitive or specific, and, therefore, are not suitable for diagnosis or prevalence studies.

Allergy to Alternaria. I. Clinical aspects.

We studied 66 patients allergic to mould Alternaria. 53% males and 47% females, with 60% diagnosed as having asthma versus 40% rhinitis, only 29% had allergy to Alternaria without any other cutaneous reactivity while 71% were polisensitized, more frequently to D. pteronyssinus, grass pollen, Cladosporium and cat epithelium. We compared the patients allergic to Alternaria with those allergic to grass pollen and D. pteronyssinus.