Filtration to reduce paediatric dose for a linear slot-scanning digital X-ray machine.

This paper describes modelling, application and validation of a filtration technique for a linear slot-scanning digital X-ray system to reduce radiation dose to paediatric patients while preserving diagnostic image quality. A dose prediction model was implemented, which calculates patient entrance doses using variable input parameters. Effective dose is calculated using a Monte Carlo simulation. An added filter of 1.8-mm aluminium was predicted to lower the radiation dose significantly. An objective image quality study was conducted using detective quantum efficiency (DQE). The PTW Normi 4FLU test phantom was used for quantitative assessment, showing that image contrast and spatial resolution were maintained with the proposed filter. A paediatric cadaver full-body imaging trial assessed the diagnostic quality of the images and measured the dose reduction using a 1.8-mm aluminium filter. Assessment by radiologists indicated that diagnostic quality was maintained with the added filtration, despite a reduction in DQE. A new filtration technique for full-body paediatric scanning on the Lodox Statscan has been validated, reducing entrance dose for paediatric patients by 36 % on average and effective dose by 27 % on average, while maintaining image quality.

Caffeine and stress: implications for risk, assessment, and management of hypertension.

Caffeine use is widespread, and its consumption increases during periods of stress. Caffeine raises blood pressure by elevating vascular resistance, and this effect is larger and more prolonged in hypertensive patients than in normotensive. The pressor response to caffeine occurs equally in persons at rest and under stress. The elevated baseline pressures of the hypertensive patient are therefore increased by both caffeine and stress, potentially leading to undesirably high pressures. Such combined effects on blood pressure may potentially confound the evaluation of hypertension, and possibly reduce the effectiveness of antihypertensive therapy. These effects are not abolished by pharmacologic tolerance to caffeine, as tolerance may not be complete with daily intake. The contribution of caffeine's effects to the development of hypertension warrants continued study, and caffeine use by patients merits consideration in terms of assessment and management of this disorder.

Epidemiologic assessment of screening tests for antibody to human T lymphotropic virus type I (HTLV-I).

We tested 196 sera from a human T lymphotropic virus type I (HTLV-I) risk group (prostitute women) with two commercial "research" enzyme-linked immunoabsorbent assays (EIA) for HTLV-I antibodies. All tested sera were characterized by HTLV-I Western immunoblots and by HTLV-I radioimmunoprecipitation assays. The estimated sensitivities of the EIA tests were 93.8 percent and 100 percent, and the specificities were 98.8 percent and 95.8 percent, respectively, using recommended criteria for seropositivity (requiring reactivity to both gag p24 and env gp46 or gp61/68). Calculated negative predictive values remained excellent (greater than 99.9 percent and 100 percent, respectively) at lower seroprevalence rates but the positive predictive values were only 7.3 percent and 2.3 percent when calculated for a seroprevalence rate of 0.1 percent. These results emphasize the importance and need for additional HTLV-I supplementary serologic testing when screening populations with low HTLV-I seroprevalence rates.