Neurosurgeons sometimes find it difficult to locate tumors precisely during microsurgery, particularly tumors located in the brain parenchyma because of the absence of boundaries in this region. Image-guided neurosurgical techniques conducted with the help of neuronavigation systems have been developed and have gained importance recently. Accuracy is vital during image-guided neurosurgery. We used a phantom to evaluate the errors introduced during navigation. The three errors evaluated were skin-shift, marker-gap, and table-rotation errors. The skin-shift error occurs if the fiducial markers positioned on the scalp move when the head is fixed to a head holder with head pins. The marker-gap error occurs when the marker ball is positioned incorrectly in the marker socket. The table-rotation error occurs when the operating table is rotated for obtaining an intraoperative MR image and then returned to its original position. Our results indicated that skin shift decreased the navigation accuracy by an error of more than 4 mm, and the gap between the marker ball and the socket resulted in a decrease in navigation accuracy by an error of more than 5 mm. The table-rotation error was found to be negligible. The errors can be avoided by ensuring that the fiducial markers are positioned appropriately on the scalp and the marker ball is fitted well in the marker socket. A phantom is useful for evaluating accuracy, particularly for evaluating errors intrinsic to different operating rooms. Periodic quality assurance by use of a phantom in each operating room might aid in maintaining the accuracy of neuronavigation.
We examine generation dynamics of coherent phonons (CPs) in both of polar and non-polar semiconductors -such as GaAs and Si -based on a polaronic-quasiparticle (PQ) model. In the model concerned, the PQ operator is composed of two kinds of operators. One is a quasiboson operator -defined as a linear combination of a set of pairs of electron operators -and the other is a longitudinal optical (LO) phonon operator. The problem of transient and non-linear Fano resonance (FR) is tackled in particular; the vestige of this quantum interference effect was observed exclusively in lightly n-doped Si immediately after carriers were excited by an ultrashort pulse-laser [M. Hase, et. al., Nature 426, 51 (2003)], though not observed yet in GaAs. It is shown that the phonon energy state is embedded in a continuum state formed by a set of adiabatic eigenstates of the quasiboson. This result implies the possibility of manifestation of the transient FR in the present optically-non-linear system. Moreover, both of a retarded longitudinal susceptibility and an LO-phonon displacement as a function of time are derived in an analytic manner. These physical quantities are mainly affected by an effective interaction between quasiboson and LO-phonon (Mq), and a diagonal part of non-adiabatic interaction integral over time (Iq). Two important results are as follows. (i) The longitudinal susceptibility allows one to calculate photoemission spectra from transient photoexcited-states, which is linear in a weak probe pulse-laser turned on at time tp. An asymmetric spectral profile characteristic of FR comes into existence in undoped Si just in the region of T ′ q12 < tp ≪ T ′ 12 , while this becomes almost symmetric in the region of tp T ′ 12 ; where T ′ 12 and T ′ q12 represent phenomenological damping time-constants of induced carrier-density with isotropic and anisotropic momentum-distribution, respectively, with T ′ q12 ≪ T ′ 12 . The asymmetry in spectra is attributed to both phase factors of arg Mq and ImIq. These factors contribute to spectra in GaAs in a different manner. (ii) The Fourier-transform of LO-phonon displacement into frequency domain is examined. The associated power spectra show an asymmetric spectral-profile due to FR exclusively in undoped Si, however, a symmetric one in GaAs irrespective of ImIq. Such obtained results seem consistent with the reported experimental results. An initial offset phase is also examined, which is extracted from an asymptotic sinusoidal form of LO-phonon displacement. It is found that this phase is affected by arg Mq and ImIq in addition to a pulse area due to pump pulse-laser. According to the results of (i) and (ii), some fundamental features pertinent to CP generation are nicely understood by virtue of the PQ picture of concern.
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