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Objective: To investigate the influence of bowtie filtration on dedicated cone beam CT (CBCT) of the head and neck. Methods: A validated hybrid simulation technique was used to model a commercial CBCT system with offset scanning geometry, 90kV tube potential and 145x75mm imaging field of view. Three bowtie filters were formulated to produce uniform flux intensity in the projection image of cylindrical objects of diameter 14, 16 and 18 cm. The influence of these simulated filters was compared with the original flat filtration in terms of the output radiation field, the dose delivered to the object, the scatter distribution in projections and the quality of the reconstructed image. Results: Compared against flat filtration, dose reduction for the bowtie case, examined as a function of radial distance within a 16-cm-diameter water cylinder, varied from 8.7% at the centre to 53.8% at the periphery. Scatter reduction, quantified using scatter-to-primary ratio in projection images, was up to 37.6% for a 14-cm-diameter cylindrical contrast phantom. Using the supplied routine image reconstruction, bowtie filtration resulted in comparable noise appearance, contrast resolution and artefact pattern for computational anatomical phantoms, with <5% difference in contrast-to-noise ratio. Conclusion: Bowtie filtration can effectively reduce the dose and scatter in CBCT of the head and neck. For better image quality, corresponding modification to the image pre-processing and reconstruction is needed. Advances in knowledge: The hybrid simulation approach can usefully explore the impact of proposed system component and design changes. [ABSTRACT FROM AUTHOR]

The objective of this study was to assess the radiation exposure levels in victims of a 60Co radiation accident using chromosome aberration analysis and the micronucleus assay. Peripheral blood samples were collected from three victims exposed to 60Co 10 days after the accident and were used for the chromosome aberration and micronucleus assays. After in vitro culture of the lymphocytes, the frequencies of dicentric chromosomes and rings (dic+r) and the numbers of cytokinesis blocking micronuclei (CBMN) in the first mitotic division were determined and used to estimate radiation dosimetry. The Poisson distribution of the frequency of dic+r in lymphocytes was used to assess the uniformity of the exposure to 60Co radiation. Based on the frequency of dic+r in lymphocytes, estimates of radiation exposure of the three victims were 5.61 Gy (A), 2.48 Gy (B) and 2.68 Gy (C). The values were estimated based on the frequencies of CBMN, which were 5.45 Gy (A), 2.78 Gy (B) and 2.84 Gy (C). The estimated radiation dosimetry demonstrated a critical role in estimating the radiation dose and facilitating an accurate clinical diagnosis. Furthermore, the frequencies of dir+r in victims A and B deviated significantly froma normal Poisson distribution. Chromosome aberration analysis offers a reliable means for estimating biological exposure to radiation. In the present study, the micronucleus assay demonstrated a high correlation with the chromosome aberration analysis in determining the radiation dosimetry 10 days after radiation exposure. [ABSTRACT FROM AUTHOR]

This stroke experiment was designed to define the mismatch between perfusion-weighted imaging (PWI) and diffusion-weighted imaging (DWI) in MRI by applying early or instantly acquired PWI. Eight rats were induced with stroke through photothrombotic occlusion of the middle cerebral artery and scanned serially between 1 h and day 3 after induction using DWI and PWI with a 1.5 T MR scanner. The relative lesion volumes (rLV) on MRI and triphenyl tetrazolium chloride-stained specimens were defined as the proportion of lesion volume over brain volume. Discrepancies in the rLV between PWI- and DWI-derived apparent diffusion coefficient (ADC) maps were expressed by subtraction of the ADC from PWI, resulting in three possible patterns: (i) (PWI-ADC > 10% of PWI) denoting a mismatch; (ii) (-(10% of PWI) ⩽ PWI-ADC ⩽ 10% of PWI) denoting a match; and (iii) (PWI-ADC < -(10% of PWI)) denoting a reverse mismatch. The differences were compared with the minuend being either early PWI (ePWI) or instant PWI (iPWI) and the subtrahend being instant ADC (iADC). The occurrence and evolution of PWI-ADC patterns were analysed. Over time, PWI-ADC discrepancies evolved from mismatch, through to match, to reversed mismatch. The PWI-ADC mismatch still existed 3 days after MCA occlusion in one to three of the eight cases. The rLVs and mismatch incidences between the ePWI-iADC and iPWI-iADC models were linear correlated. A higher mismatch rate occurred in iPWI-iADC within day 1 and in ePWI-iADC at day 3. Both ePWI and iPWI proved useful to define PWI-ADC patterns within day 1. At day 3, iPWI appeared more adequate. [ABSTRACT FROM AUTHOR]