Physics in medicine and biology
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Comparative Study
A novel AIF tracking method and comparison of DCE-MRI parameters using individual and population-based AIFs in human breast cancer.
Quantitative analysis of dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) data requires the accurate determination of the arterial input function (AIF). A novel method for obtaining the AIF is presented here and pharmacokinetic parameters derived from individual and population-based AIFs are then compared. A Philips 3.0 T Achieva MR scanner was used to obtain 20 DCE-MRI data sets from ten breast cancer patients prior to and after one cycle of chemotherapy. ⋯ Regarding the kinetic parameters, the CCC values for K(trans), v(p) and v(e) as estimated by AIF(ind) and AIF(pop) are 0.65, 0.74 and 0.31, respectively, based on the region of interest analysis. The average CCC values for the voxel-by-voxel analysis are 0.76, 0.84 and 0.68 for K(trans), v(p) and v(e), respectively. This work indicates that K(trans) and v(p) show good agreement between AIF(pop) and AIF(ind) while there is a weak agreement on v(e).
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Previous studies have shown that procedure-induced prostate edema during permanent interstitial brachytherapy (PIB) can cause significant variations in the dose delivered to the prostate gland. Because the clinical impact of edema-induced dose variations strongly depends on the magnitude of the edema, the temporal pattern of its resolution and its interplay with the decay of radioactivity and the underlying biological processes of tumor cells (such as tumor potential doubling time), we investigated the impact of edema-induced dose variations on the tumor cell survival and tumor control probability after PIB with the (131)Cs, (125)I and (103)Pd sources used in current clinical practice. The exponential edema resolution model reported by Waterman et al (1998 Int. ⋯ The effect of edema on (103)Pd PIB was slightly greater, even though the decay half-life of (103)Pd (17 days) is longer than that of (131)Cs (9.7 days), because the advantage of the longer (103)Pd decay half-life was negated by the lower effective energy of the photons it emits (∼21 keV compared to ∼30.4 keV for (131)Cs). In addition, the impact of edema could be reduced or enhanced by differences in the tumor characteristics (e.g. potential tumor doubling time or the α/β ratio), and the effect of these factors varied for the different radioactive sources. There is a clear need to consider the effects of prostate edema during the planning and evaluation of permanent interstitial brachytherapy treatments for prostate cancer.
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Measurements of temperature elevations induced by sonications in a single intact cadaver skull filled with soft-tissue mimicking phantom material were performed using magnetic resonance thermometry. The sonications were done using a clinical transcranial ultrasound therapy device operating at 230 kHz and the measurements were compared with simulations done using a model incorporating both the longitudinal and shear wave propagation. Both the measurements and simulations showed that in some situations the temperature increase could be higher in the phantom material adjacent to the skull-base than at the focus, which could lead to undesired soft-tissue damage in treatment situations. ⋯ Mathematical bases for both the methods and simulations utilizing them were presented. It was found that utilizing the anti-focus in solid media and regularized phasing, the fraction of temperature increase of the brain tissue at the focus and the peak temperature increase adjacent to the skull-base can be increased from 1.00 to 1.95. This improves the efficiency of the sonication by reducing the energy transfer to the skull-base.
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Clinical Trial
Cerebral monitoring during carotid endarterectomy using near-infrared diffuse optical spectroscopies and electroencephalogram.
Intraoperative monitoring of cerebral hemodynamics during carotid endarterectomy (CEA) provides essential information for detecting cerebral hypoperfusion induced by temporary internal carotid artery (ICA) clamping and post-CEA hyperperfusion syndrome. This study tests the feasibility and sensitivity of a novel dual-wavelength near-infrared diffuse correlation spectroscopy technique in detecting cerebral blood flow (CBF) and cerebral oxygenation in patients undergoing CEA. Two fiber-optic probes were taped on both sides of the forehead for cerebral hemodynamic measurements, and the instantaneous decreases in CBF and electroencephalogram (EEG) alpha-band power during ICA clamping were compared to test the measurement sensitivities of the two techniques. ⋯ The post-CEA CBF were significantly higher (+43.2 ± 16.9%) than the pre-CEA CBF. The CBF responses to ICA clamping were significantly faster, larger and more sensitive than EEG responses. Simultaneous monitoring of CBF, cerebral oxygenation and EEG power provides a comprehensive evaluation of cerebral physiological status, thus showing potential for the adoption of acute interventions (e.g., shunting, medications) during CEA to reduce the risks of severe cerebral ischemia and cerebral hyperperfusion syndrome.
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In (19)F MRI oximetry, a method used to image tumour hypoxia, perfluorocarbons serve as oxygenation markers. The goal of this study is to evaluate the impact of perfluorocarbon distribution and concentration in (19)F MRI oximetry through a computer simulation. The simulation studies the correspondence between (19)F measured (pO(FNMR)(2)) and actual tissue oxygen tension (pO(2)) for several tissue perfluorocarbon distributions. ⋯ Hence, perfluorocarbon distribution in tissue and blood has a serious impact on the reliability of (19)F MRI-based measures of oxygen tension. In addition, the presence of perfluorocarbons influences the actual oxygen tension. This finding may be of great importance for further development of (19)F MRI oximetry.