The acoustic and thermal properties as well as the temperature change within a tissue volume during high-intensity focused ultrasound ablation are critically important for treatment planning and monitoring. Described in this article is a tomographic reconstruction method used to determine the tissue properties and increase in temperature in a 3-D volume. On the basis of the iterative finite-element solution to the bioheat equation coupled with Tikhonov regularization techniques, our reconstruction algorithm solves the inverse problem of bioheat transfer and uses the time-dependent temperature measured on a tissue surface to obtain the acoustic absorption coefficient, thermal diffusivity and temperature increase within the subsurface volume. Numerical simulations were performed to validate the reconstruction algorithm. The method was initially conducted in ex vivo experiments in which time-dependent temperature on a tissue surface was measured using high-resolution, non-invasive infrared thermography.

We present experimental evidence that the quantitative accuracy of bioluminescence tomography (BLT) can be significantly improved by incorporating prior spatial distribution of optical properties of heterogeneous media obtained from diffuse optical tomography (DOT).

We present for the first time experimental evidence that the quantitative accuracy of bioluminescence tomography (BLT) can be significantly improved by incorporating prior spatial distribution of optical properties of heterogeneous media obtained from diffuse optical tomography (DOT). A series of experiments were conducted using a CCD-based scanning system where millimeter-size bioluminescent targets were embedded in a 3 x 3 x 5 cm optically heterogeneous scattering medium. The results show that the BLT images with the recovered optical property distribution in place are considerably better reconstructed compared to that without such prior information, in terms of the location, size and source strength of the targets.

We present a new method that can provide high resolution images of absolute optical absorption coefficient in heterogeneous turbid media. In this method, acoustic measurements in conventional photoacoustic tomography are combined with diffusing light measurements to separate the product of absorption coefficient and optical fluence or photon density. We validate this method using a series of tissuelike phantom experiments. The experimental results show that targets as small as 0.5 mm in diameter with optical absorption contrasts as low as 1.5 relative to a 50 mm diameter scattering background medium can be clearly detected.

A multi-physics model is developed to predict the transient nonlinear behaviors of electric-stimulus- responsive hydrogels when the hydrogels are immersed into a bathing solution subject to an externally applied electric field. The presently developed model consists of the transient convection-diffusion equations for concentration distribution of diffusive ions, the Poisson equation for electric field and the mechanical equations for deformation. In consideration of the mathematical model involving chemo-electro-mechanics, a true meshfree, implicit numerical scheme is implemented for solution of the transient nonlinear partial differential governing equations. The transient responds including the hydrogel deformation, ionic concentrations and electric potentials interior and exterior the hydrogel are numerically investigated, in which the simulating results in good agreement with the experimental or published results validate the presently developed multi-field model.

We report on experimental demonstration of photoacoustic tomography for reconstructing the optical absorption coefficient images of heterogeneous media. Photoacoustic images are obtained from a series of tissuelike phantom experiments using a finite element-based reconstruction algorithm coupled with a scanning photoacoustic imaging system. The experimental results show that optical absorption images can be quantitatively reconstructed when the photon diffusion model is coupled with the Helmholtz photoacoustic wave equation.

We report on for the first time in vivo 3D bioluminescence tomography of gene expression based on our finite element reconstruction algorithm. The initial results obtained from two mice show that luciferase expressed in the mouse liver can be clearly detected in three dimensions

We show that a 5mm-diameter target containing different concentrations of bioluminescent cancer cells in a 3x3cm cubic tissue-like phantom can be three-dimensional imaged using our finite element-based bioluminescence tomography techniques. Luminescent light emitted from 4 sides of the phantom was measured with a thermoelectric-cooling CCD camera

Introduction. Non-invasive monitoring of gene expression in living animals is an active area of molecular imaging and has proven useful to identify real time gene transfer. Improvements in optical imaging techniques have lead to the mounting luciferase reporter systems. Standard 2D bioluminescence limits the interpretation of gene expression in vivo. Bioluminescence tomography (BLT), the 3D extension of bioluminescence imaging, offers a new tomographic method for molecular imaging. BLT captures the spatial distribution of luciferase light signal in three dimensions, which provides a powerful tool for studies such as cancer imaging, cell trafficking and protein function. Methods. 22-gram, male BALB-C mice were used for in vivo experiments. Mice tail veins were injected with 1 ml and 2 ml of 10ug/ml luciferase DNA expression plasmid in PBS. Twenty-four hours after injections, animals were anesthetized and administered D-luciferin at 140mg/kg i.p.. Bioluminescence images were acquired 5 min after D-luciferin administration. The mice were immersed in an imaging chamber filled with 0.5% intralipid as a coupling medium. The stage was rotated 3X at 90° and the emitted bioluminescence was collected for 3 minutes using a cooled CCD camera. Results. Figs. 1a and 1b (20ug and 10ug dose respectfully) show the imaging chamber containing the mouse under measurement in the absence and presence of intralipid solution. Fig. 1c shows the bioluminescence from a single 90o data point. Figs. 2b and d (20ug and 10ug dose respectfully) were obtained from a single cross section of the mouse at the z-axis=20mm. Figs. 2a and c (20ug and 10ug dose respectfully) are reconstructed 3D images at multiple planes showing the complete bioluminescence distribution. Conclusion. The purpose of these studies were to validate the algorithm for converting bioluminescence into a three dimensional images and the instrumentation used to obtain the images, hence the justification for the two DNA doses. The results provide more detail with regard to real time gene expression in that the lower plasmid DNA dose appears in the lower lobe of the liver whereas the higher DNA dose yields more expression in the upper lobes of the liver. We are investigating the use of this technology for imaging brain tumors using RG2 cells permanently transformed to constituitively express luciferase. The anticipation is that this can be used to assay for in vivo gene transfer to brain tumors. View Large Image Figure ViewerDownload Hi-res image Download (PPT)