Evaluation of stray radiation to the operator for five hand-held dental X-ray devices.

OBJECTIVES: Evaluate stray radiation to the operator, as represented by a plane within the significant zone of occupancy (SZO), produced by five models of hand-held intraoral dental X-ray devices (HIDXDs). METHODS: The stray radiation for five models of HIDXDs was measured, using an anthropomorphic tissue-equivalent head phantom as a scattering object. An ionization chamber was used to measure the air kerma (µGy) at 63 positions in a 160 cm high by 60 cm wide plane that was 10 cm behind the X-ray device, identified as being within the SZO. RESULTS: Based on the measured air kerma from stray radiation of five different HIDXDs, the estimated annual air kerma at all measured spatial positions was calculated. When calculated using a median air kerma of 0.8 mGy at the distal end of the cone, as typically required for digital image receptors, 1 the ranges for estimated annual air kerma in the SZO across the devices were 0.14-0.77 mGy for the median, 0.41-1.01 mGy for the mean, and 1.32-2.55 mGy for the maximum. Similarly, when calculated using a median air kerma of 1.6 mGy as typically required for D-speed film, 2 the ranges for estimated annual air kerma across the devices were 0.28-1.54 mGy for the median, 0.83-2.03 mGy for the mean, and 2.64-5.10 mGy for the maximum. CONCLUSIONS: From measured air kerma values of stray radiation in the SZO, estimated annual exposures to the operator for HIDXDs are expected to be greater than from conventional wall-mounted or portable devices activated from a protected area (at a distance or behind shielding). HIDXDs should therefore only be used when patient accessibility makes their use necessary and the use of a portable device on a stand or a wall-mounted device is not reasonably feasible. This approach would keep occupational radiation exposures of dental workers as low as reasonably achievable.

Investigation of a logistic model for T2* dynamic susceptibility contrast magnetic resonance imaging (dscMRI) perfusion studies.

There are a number of T1- and T2-based dynamic contrast-enhanced magnetic resonance imaging pharmacokinetic modeling approaches to study cancer microvasculature. Alternatively, model-free approaches offer an easy, quantitative assessment of microcirculation. In this work, we investigate a 6-parameter model-free approach applied to a T2*-weighted echo-planar imaging bolus response curve. We tested this new approach on a small cohort of patients with clinically diagnosed primary rectal carcinoma before adjuvant chemoradiotherapy and surgical excision. Comparison with healthy muscle tissue shows that logistic parameters P1/P2, P4, and P5 offer good discrimination between tumor and healthy tissue. Bolus response logistic parameters P4 and P5 have been implicated in previous T1-based works as being important in the assessment of cancer malignancy. Further comparison of T2* parameters with signal attenuation amplitude (maximum signal drop) and percentage baseline signal loss also corroborates the models' ability to quantify the microenvironment.