Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Association of Biomedical Physics (AIFB)
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To study the impact of setup errors on the dose to the target volume and critical structures in the treatment of cancer of nasopharynx with intensity modulated radiation therapy (IMRT). ⋯ The isocenter position should be verified regularly to ensure that the goal of IMRT is achieved.
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Wall shear stress (WSS) appears to contribute significantly in the initiation and progression of atherosclerotic disease. The purpose of this work is to present in vivo systolic and diastolic WSS calculations in the human ascending aorta by the application of three straightforward methodologies based on Poiseuille's theory of flow. ⋯ In vivo calculation of WSS in the ascending aorta is feasible by phase-contrast MRI flow measurements and straightforward methodologies based on Poiseuille's theory of flow. However, measurements based on maximum flow velocity show larger deviations compared to measurements based on mean flow volume or mean flow velocity.
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An increasing number of magnetic resonance whole-body units operating at field strengths of 3T and beyond are currently installed in research institutions as well as clinical facilities. This review wants to describe the changes in physical properties at higher field strength and the resulting implications for clinical and experimental examinations of the whole body. An overview is provided on the resulting advantages and disadvantages for anatomical, functional and biochemical MR examinations in different regions of the body (except the brain). ⋯ Nearly quadratic increase of RF energy deposition with increasing field strengths results in clear limitations for some common sequence types which work without any problems at 1.5 T. New strategies with multi-channel RF excitation have the potential to overcome limitations due to RF inhomogeneities, but a few years of further technological development seem necessary. Many problems have to be solved in the near future regarding the variety of MR techniques and applications in all parts of the human body.
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The purpose of the present work was to estimate the parameter 'a' describing the generalised equivalent uniform dose (gEUD) for tumours and its dependence on radiobiological parameters. The consequences of uncertainties in a on the gEUD were also studied. An estimate of a was found by requiring that, for a given target dose distribution, the mechanistic EUD (based on radiobiological linear quadratic modelling) equals gEUD. ⋯ The estimated values of a ranged from -25.6 to -22.4 for all combinations of dose distributions and parameter sets. Uncertainties in a were found to give only small uncertainties in gEUD. Although the current work shows limitations of the gEUD model for tumours, gEUD may still be preferable for biological treatment plan optimization, evaluation and reporting.
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The aim of the study was a comparison of 2 novel macromolecular contrast agents, Gadomer-17 and Polylysine-Gd-DTPA, with commercially available Gd-DTPA in determining the quality of tumor microvasculature by dynamic contrast enhanced MRI. Three groups of 5 mice with SA-1 tumors were studied. To each group of animals one contrast agent was administered; i.e. the first group got Gd-DTPA, the second group Gadomer-17 and the third group Polylysine-Gd-DTPA. ⋯ PS and BV values were calculated for each contrast agent. Based on the values, contrast agents were classified according to their performance in characterizing tumor microvasculature. Results of our study suggest that Gadomer-17 and Polylysine-Gd-DTPA are significantly superior to Gd-DTPA in characterizing tumor microvasculature.