Similarities between simulated spatial spectra of scalp EEG, MEG and structural MRI.

Electrical dipoles oriented perpendicular to the cortical surface are the primary source of the scalp EEGs and MEGs. Thus, in particular, gyri and sulci structures on the cortical surface have a definite possibility to influence the EEGs and MEGs. This was examined by comparing the spatial power spectral density (PSD) of the upper portion of the human cortex in MRI slices to that of simulated scalp EEGs and MEGs. The electrical activity was modeled with 2,650 dipolar sources oriented normal to the local cortical surface. The resulting scalp potentials were calculated with a finite element model of the head constructed from 51 segmented sagittal MR images. The PSD was computed after taking the fast Fourier transform of scalp potentials. The PSD of the cortical contour in each slice was also computed. The PSD was then averaged over all the slices. This was done for sagittal and coronal view both. The PSD of EEG and MEG showed two broad peaks, one from 0.05 to 0.22 cycles/cm (wavelength 20-4.545 cm) and the other from 0.22 to 1.2 cycles/cm (wavelength 4.545-0.834 cm). The PSD of the cortex showed a broad peak from 0.08 to 0.32 cycles/cm (wavelength 12.5-3.125 cm) and other two peaks within the range of 0.32 to 0.9 cycles/cm (wavelength 3.125-1.11 cm). These peaks are definitely due to the gyri structures and associated larger patterns on the cortical surface. Smaller peaks in the range of 1-3 cycles/cm were also observed which are possibly due to sulci structures. These results suggest that the spatial information was present in the EEG and MEG at the spatial frequencies of gyri. This also implies that the practical Nyquist frequency for sampling scalp EEGs should be 3.0 cycles/cm and an optimal interelectrode spacing of about 3 mm is needed for extraction of cortical patterns from scalp EEGs in humans.

Isolation and sequencing of pig Blm and Ubl-1/SUMO-1 genes that relate to the recombination machinery.

BACKGROUND: The gene knockout technique is important in xenotransplantation research. Herein we have described the molecular cloning of two genes that are candidates to overcome the poor rate of homologous recombination. METHODS: Candidate cDNA fragments were amplified by polymerase chain reaction (PCR) with the corresponding primer sets deduced from a multiple alignment analysis of other mammalian genes from a cDNA library prepared from pig spleen tissue. To obtain the full-length cDNA, a 5'- and 3'-RACE PCR experiments was performed. RESULTS: We successfully isolated the cDNA sequences of two pig genes--BLM, a Bloom's syndrome-related gene, and UBL-1/SUMO-1--which are closely related to homologous recombination events. As a result, we verified the sequences of pig BLM and pig UBL-1/SUMO-1. The nucleic acid and amino acid coding sequence homologies of pig BLM gene with the corresponding human gene were 87.3% and 82.9%, respectively. The nucleic acid and amino acid coding sequence homologies of the pig UBL-1/SUMO-1 gene with the human gene were 96.4% and 100%, respectively. CONCLUSION: Current research into homologous recombination provides the possibility for improvement of gene knockout efficiency by regulating the gene expression profiles of recombination-related genes. Transient interference with the expression of pig UBL-1/SUMO-1 and BLM is expected to improve gene targeting. The results of the present study provided important information to design siRNA knockdown vectors. They were also useful for ex ante evaluation of expression profiles of these genes in primary cultures of somatic cells, which may enhance the production of gene knockout pigs.

Molecular cloning of pig Rad51, Rad52, and Rad54 genes, which are involved in homologous recombination machinery.

BACKGROUND: The low rate of homologous recombination in somatic cells is considered to be an urgent issue. Therefore, we molecularly cloned three genes that relate to efficient homologous recombination. METHODS: Polymerase chain reaction (PCR) was performed to isolate candidate cDNA fragments from a pig spleen cDNA library with the corresponding primer sets deduced from multiple alignment analysis of other mammalian genes. A 5'- and 3'-RACE PCR experiment was performed to determine the complete cDNA sequences. RESULTS: The complete cDNA sequences of the pig RAD51, RAD52, and RAD54 genes, which are closely related to homologous recombination events, were identified using molecular cloning technique. The cDNA sequences of three genes were successfully isolated by PCR-based methods. As a result, we determined the sequences of pig RAD51 (1663 bp, 339 aa), RAD52 (1884 bp, 406 aa), and RAD54 (2884 bp, 747 aa). The nucleic acid sequence homologies of the pig RAD51, RAD52, and RAD54 genes compared with the corresponding human genes were 92.9%, 77.3%, and 90.0%; the corresponding amino acid sequence homologies were 98.8%, 71.1%, and 95.0%, respectively. CONCLUSION: The knockout of alpha-1,3-galactosyltransferase in pigs resulted in a drastic reduction in xenoantigenicity. However, other xenoantigens, in particular, the non-Gal antigens, also need to be down-regulated. Gene transfer to alter expression levels of these recombination-related molecules and/or ex ante evaluation of expression profiles of these genes in primary cultures of somatic cells constitute a new approach to enhancing homologous recombination events during the production of gene knockout pigs.

Cloning and in vitro antiapoptotic effects of pig FLIPs.

INTRODUCTION: Cellular FLICE-like protein (cFLIP) inhibits death receptor-mediated apoptosis signal transduction, such as that induced by Fas and TNFR. The present study examined the role of antiapoptotic molecules to protect pig cells from human natural killer (NK) cells in vitro, as a model of delayed-type xenograft rejection. METHODS: Pig FLIPs were cloned using the TBLASTIN program to search for cDNA fragments of pig FLIPs. The sequence was identified using the dideoxy chain termination method and an ABI PRISM3100 genetic analyzer. The cDNA of pig FLIPs was inserted into the cloning site of the chicken beta-actin promoter (pCXN2). The cDNA was then transfected into pig endothelial cells (PEC), to establish several stable PEC clones containing the cDNA. Expression of the pig FLIP gene was evaluated by reverse-transcriptase polymerase chain reaction, and NK cell-mediated cytolysis assessed, using YT cells (an NK-like cell line). RESULTS: The full-length pig FLIP encoding sequence, total 5'-region to 3'-region, was defined for the first time. PEC transfectants with the FLIP showed moderate expression of FLIPs. Transfection of PEC with plasmids encoding FLIPs inhibited NK cell-mediated PEC lysis. While approximately half of parental PEC were injured by the human NK-like YT cells, the injury rate was relatively lower in the transfectants. CONCLUSION: Overexpression of the antiapoptotic molecules, pig FLIPs, has the potential for use in protecting graft cells from human NK cells.

Investigation of cynomolgus monkey complement.

BACKGROUND: The cynomolgus monkey is one of the most popular recipient animals in xenotransplantation experiments. However, studies of the cynomolgus monkey complement are rare. In the present study, based on the study that compared the hemolytic complement titer in cynomolgus monkeys with that in humans, the complement regulatory function of human decay accelerating factor (CD55) in both human and cynomolgus monkey sera was studied. METHODS: Hemolytic complement titers in cynomolgus monkeys were calculated using the same methods as are used in humans. Next, the complement regulatory function of human DAF (CD55) in cynomolgus monkey serum was studied using porcine endothelial cells (PECs) and human DAF. RESULTS: Of the complement titers tested, such as CH50, ACH50, C4, C2, and C3, the values were relatively high, except for the C4 titer. Human DAF on the surface of PEC resulted in nearly identical complement regulatory function in the human and cynomolgus monkey sera. CONCLUSIONS: Human DAF showed nearly the same complement regulatory function in both human and cynomolgus monkey sera.

Role of soft bone, CSF and gray matter in EEG simulations.

Effects of soft skull bone, cerebrospinal fluid (CSF) and gray matter on scalp potentials were examined with highly heterogeneous finite element models of an adult male subject. These models were constructed from segmented T1 weighted magnetic resonance images. Models had voxel resolutions of 1x1x3.2 mm with a total of about 1.5 million voxels. The scalp potentials, due to a dipolar source in the motor cortex area, were computed with an adaptive finite element solver. It was found that the scalp potentials were significantly affected by the soft bone, CSF and gray matter tissue boundaries in the models.

Polarized pulse waves in random discrete scatterers.

In recent years there has been increasing interest in the use of polarization for imaging objects in a cluttered environment. Examples are optical imaging through clouds, optical detection of objects in a biological medium, and microwave detection of objects in clutter. We extend previous studies of continuous-wave scattering to pulse-polarization scattering in discrete scatterers. We solve the time-dependent vector radiative transfer equation for a plane-parallel medium by using Mie scattering and the discrete ordinates method. The time-dependent degree of polarization and cross-polarization discrimination are calculated and verify the advantages of circular over linear polarization in maintaining greater copolarized components rather than cross-polarized components.

Effect of myocardial anisotropy on the torso current flow patterns, potentials and magnetic fields.

The effects of myocardial anisotropy on the torso current flow patterns, voltage and the magnetic field were examined using an anatomically realistic torso model of an adult male subject. A finite element model of the torso was built with 19 major tissue types identified. The myocardial fibre orientation in the heart wall was included with a voxel resolution of 0.078 x 0.078 x 0.3 cm. The fibre orientations from the canine heart which are available in the literature were mapped to our adult male subject's human heart using deformable mapping techniques. The current and potential distribution in the whole torso were computed using an idealized dipolar source of +/-1.0 V in the middle of the septum of the heart wall as a boundary condition. An adaptive finite element solver was used. Two cases were studied. In one case the myocardium was isotropic and in the other it was anisotropic. It was found that the current density distribution shows a very noticeable difference between the isotropic and anisotropic myocardium. The resultant magnetic field in front of the torso was computed using the Biot-Savart law. It was found that the magnetic field profile was slightly affected by the myocardial anisotropy. The potential on the torso surface also shows noticeable changes due to the myocardial anisotropy.

Optical diffusion of continuous-wave, pulsed, and density waves in scattering media and comparisons with radiative transfer.

We discuss several outstanding theoretical problems in optical diffusion in random media. Specifically, we discuss which of several diffusion theories most closely approximates exact solutions of the equation of transfer. We consider a plane wave impinging upon a plane-parallel slab of a random medium as a model problem to compare the diffusion theories with a numerical solution of the equation of transfer for continuous-wave, pulsed, and photon density waves. In addition, we discuss the validity of the diffusion approximation for a variety of parameter settings to ascertain the diffusion approximation's applicability to imaging biological media.

Time-of-Arrival Fluctuations of a Space-Time Gaussian Pulse in Weak Optical Turbulence: an Analytic Solution.

An analytic expression is derived for the long-term temporal broadening (fluctuations of arrival time) of a collimated space-time Gaussian pulse propagating along a horizontal path through weak optical turbulence. General results are presented for nominal parameter values characterizing laser communication through the atmosphere. Specific examples are calculated for both upper-atmosphere and ground-level cross links. It is shown that, for upper-atmosphere cross links, pulses shorter than 100 fs have considerable broadening, whereas at ground level, broadening is predicted in pulses as long as 1 ps.

Sizing emboli in blood using pulse Doppler ultrasound--II: Effects of beam refraction.

A theoretical and numerical study of the acoustic field intensity within a curved flow conduit having 1) diameter similar to the wavelength of the interrogating frequency and 2) speed of sound mismatch with the surrounding medium is presented. The field intensity is shown to vary significantly and in a monotonic fashion across the flow conduit. The resulting insonation of emboli transiting through the Doppler sample volume is explored with a Monte Carlo study of the behavior of the embolus to blood power ratio (EBR). The numerical simulation findings are shown to be in good agreement with previously reported experimental results. A method is explored for estimating embolus diameter when this refraction artifact is present, and shown to yield excellent results when applied to experimental data. Further work toward clinical application of these results is discussed.

Two-frequency mutual coherence function of a Gaussian beam pulse in weak optical turbulence: an analytic solution.

Pulse propagation in a random medium is studied through the calculation of the two-frequency mutual coherence function. An exact integral representation is formulated for the two-frequency mutual coherence function of a Gaussian beam pulse propagating in a weakly fluctuating random medium. Based on the modified von Karman spectrum for refractive-index fluctuations, an analytic approximation to the integral representation is presented and compared with exact numerical results.

Particle-size distribution determination using optical sensing and neural networks.

We present an inverse technique to determine particle-size distributions by training a layered perception neural network with optical backscattering measurements at three wavelengths. An advantage of this approach is that, even though the training may take a long time, once the neural network is trained the inverse problem of obtaining size distributions can be solved speedily and efficiently.

Differential Fourier transform technique for the inverse scattering problem.

An inversion technique was developed for determining the size distribution of randomly distributed tenuous scatterers from the forward scattering pattern. This technique is applicable for 1-D, 2-D, and 3-D scatterers. It does not require matrix inversion or a priori knowledge of functional forms of the size distribution, and it takes advantage of the fast Fourier transform and digital filtering techniques in spectral analysis. A typical error for 10% noise was within a few percent in the estimation of Gaussian size distribution using 1024-point FFT. The usefulness of this technique in practice was shown in experiments with latex spheres and bacteria.

Backscattering enhancement by randomly distributed very large particles.

Recently, the backscattering enhancement by densely distributed particles of a size comparable to the wavelength was reported. It has been explained as the constructive interference of two waves traveling in opposite directions. This enhancement was observed only in densely distributed particles, and its existence in sparsely distributed media has not been verified yet. In this paper we present the experimental evidence of backscattering enhancement by sparsely distributed very large particles. Experiments are conducted using 45-microm latex particles which are approximately 100 times the wavelength. Both copolarized and crosspolarized components are measured for different particle concentrations. Unlike for small particles, backscattering enhancement is most noticeable when the particle concentration is low. The angular width of the peak is comparable to the ratio (wavelength)/(particle size) and is independent of the optical distance.

Diffusion of light in turbid material.

This paper discusses some of the present knowledge of the mathematical techniques used to describe light diffusion in turbid material such as tissues. Attention will be paid to the usefulness and limitations of various techniques. First, we review the transport theory, radiance, radiant energy fluence rate, phase functions, boundary conditions, and measurement techniques. We then discuss the first-order solution, multiple scattering, diffusion approximation, and their limitations. The plane wave, spherical wave, beam wave, and pulse wave excitations are discussed followed by a brief review of the surface scattering effects due to rough interfaces.