Simplified TRS398 dosimetry protocol for dose determination in high-energy electrons beams.

A method is proposed to simplify the IAEA TRS398 dosimetry code of practice in respect to dose determination of high-energy electron beams. The proposed method eliminates the use of the intermediate beam quality Q(int) (and beam quality correction factor k(Q,Q(int))) applicable for cross calibration and subsequent use of the user's chamber for dose determination in water for high-energy electron beams. This method allows calculation of the dose to water calibration factor for the user's instrument at the reference beam quality N(D)(w,Q0) directly from a cross calibration in a high-energy electron beam of quality Q(cross) at the user's institute.

Age related preservation and loss in optimized brain SPECT.

Background: Recent single photon emission computed tomography (SPECT) studies have reported age related increases in regional brain perfusion (called preservation here) as well as losses.

Aim: To apply optimized SPECT processing to better define and understand both age related preservation and loss in brain SPECT.

Methods: Brain SPECT was performed on 85 healthy subjects using Tc hexamethylpropylene amine oxime (HMPAO), processed using findings from recent optimization work, and subjected to voxel based statistical analysis.

First photon detection in time-resolved transillumination imaging: a theoretical evaluation.

First photon detection, as a special case of time-resolved transillumination imaging, is studied through the derivation of the temporal probability density function (pdf) for the first arriving photon. The pdf for different laser intensities, media and second and later arriving photons were generated. The arrival time of the first detected photon reduced as the laser power increased and also when the scattering and absorption coefficients decreased.

Optimisation of brain SPET and portability of normal databases.

Use of a normal database in quantitative regional analysis of brain single-photon emission tomography (SPET) facilitates the detection of functional defects in individual or group studies by accounting for inter-subject variability. Different reconstruction methods and suboptimal attenuation and scatter correction methods can introduce additional variance that will adversely affect such analysis. Similarly, processing differences across different instruments and/or institutions may invalidate the use of external normal databases.

Spatial resolution in fast time-resolved transillumination imaging: an indeterministic Monte Carlo approach.

The spatial resolution achievable in time-resolved optical transillumination imaging through a turbid (scattering and absorbing) medium has been reassessed theoretically. The temporal point spread function was constructed assuming a delta function input pulse, a approximately 50 mm thick medium and a small detector with zero risetime. Temporal profiles were derived from an indeterministic Monte Carlo simulation for different time scales.

An indeterministic Monte Carlo technique for fast time of flight photon transport through optically thick turbid media.

A time-resolved indeterministic Monte Carlo (IMC) simulation technique is proposed for the efficient construction of the early part of the temporal point spread function (TPSF) of visible or near infrared photons transmitted through an optically thick scattering medium. By assuming a detected photon is a superposition of photon components, the photon is repropagated from a point in the original path where a significant delay in forward propagation occurred. A weight is then associated with each subsequently detected photon to compensate for shorter components.