Abstract:In this paper, the finite-element method (FEM) simulation of ultrasound brain surgery is presented. The overheating problem of the post-target bone, which is one of the limiting factors for a successful ultrasound brain surgery, is considered. In order to decrease bone heating, precise choices of frequency, focal pressure, and scanning path are needed. The effect of variations in the mentioned scanning parameters is studied by means of the FEM. The resulting pressure and temperature distributions of a transdural ultrasound brain surgery are simulated by employing the FEM for solving the Helmholtz and bioheat equations in the context of a two-dimensional MRI-based brain model. Our results show that for a suitable value of the frequency, an increase in focal pressure leads to a decrease in the required duration of the treatment and is associated with less heating of the surrounding normal tissue. In addition, it is shown that at a threshold focal pressure, the target temperature reaches toxic levels whereas the temperature rise in the bone is minimal. Wave reflections from sinus cavities, which result in constructive interference with the incoming waves, are one of the reasons for overheating of the bone and can be avoided by choosing a suitable scanning path. PACS

The absorbed ultrasound energy is changed into heat in a dissipative medium. This could be of great advantage in treating tumors in a noninvasive manner, by raising their temperature to cytotoxic levels. In this study we investigated whether using a fixed-focus transducer can destroy breast tumor cells, especially in early stages, in a cost-effective manner and reduce treatment time significantly. An appropriate fixed-focus transducer was designed, and the resultant acoustic pressure was calculated by solving the Rayleigh integral. A two-dimensional breast model was constructed from the magnetic resonance image (MRI) of a cancerous breast. Then, the induced temperature elevation was calculated using the bioheat equation and applying the finite element method (FEM) to the model. Results demonstrate that this transducer can generate a temperature of up to 61 C in 3 s, which is sufficient to destroy cancer cells, particularly in early stages.

SHRIMP U-Pb dating of zircon from two representative samples of the Bardkish syenitic pluton, Urumieh plutonic complex, northwestern Iran, yielded a Late Cretaceous weighted mean 206 Pb/ 238 U age of 91.1 ±0.8 Ma (Turonian). The pluton is characterized by high K 2 O content, Ti-Nb-Ta depletion, enrichment in light rare earth elements and large ion lithophile elements compared to high field strength element, Mg-rich biotite and calcic amphibole, suggesting a shoshonitic affinity. Geochemical features of the Bardkish syenite are consistent with derivation by fractional crystallization of initial mafic parent magmas. It is most likely that primary magma of the syenite originated from a metasomatized subcontinental lithospheric mantle source with minor crustal component, and underwent a fractional crystallization process during its emplacement. The estimates of trapping pressures and temperatures suggest that crystallization began at the middle crustal level (less than 11 km) near 700-730 C. The generation of the Bardkish syenite could be related to the subduction of Neo-Tethyan oceanic crust beneath the Central Iranian microcontinent and it possibly marks a major magmatic episode prior to the final closure of the Neo-Tethyan ocean in northwest Iran.

Zircon U-Pb age, mineral compositional, elemental and Sr-Nd isotopic data are documented for intermediate to felsic rocks in the Takht batholith, a Late Oligocene igneous complex in the southeastern segment of the Urumieh-Dokhtar belt, Iran, to investigate magma genesis in the context of regional tectonics. A large part of the magmatic belt formed by northward subduction of the Neotethys before the Arabia-Eurasia continental collision. Zircon U-Pb age data indicate the batholith crystallized at ∼25 Ma, an age consistent with previous results. Geochemical data indicate that the rocks share features typical of calc-alkaline magmas and I-type granitoids. The least evolved magma inferred from the data has basaltic andesite composition, consistent with either of the following origins: (i) a partial melt of the mantle followed by differentiation, or (ii) a partial melt of the lower crust. With increasing SiO 2 , ( 87 Sr/ 86 Sr) 25Ma increases from 0.7053 to 0.7073, and εNd 25Ma decreases from −0.3 to −2.9, consistent with increasing effects of assimilation-fractional crystallization, although processes such as magma mixing and melting of heterogeneous source rocks cannot be entirely ruled out. Aluminum-in-hornblende thermometry indicates that the batholith might have emplaced at ∼6.5 km or shallower paleo-depths. Moho depth proxies Sr/Y and (La/Yb) N yield crustal thickness of ∼20-30 km, showing no evidence for magma processing within thick crust. Overall, our results indicate that the Takht batholith is a Cordilleran-type batholith formed beneath a continental or transitional arc of normal crustal thickness. This is consistent with the notion that Arabia and Eurasia have collided in a diachronous manner, propagating from the northwest to the southeast since the Late Eocene-Early Oligocene.

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