Quantitative optoacoustic signal extraction using sparse signal representation

Experimental verification of our algorithm

source:© 2009 IEEE Transactions on Medical Imaging

We report on a new quantification methodology of optoacoustic tomographic reconstructions under heterogeneous illumination conditions representative of realistic whole-body imaging scenarios. Our method relies on the differences in the spatial characteristics of the absorption coefficient and the optical energy density within the medium. By using sparse-representation based decomposition, we exploit these different characteristics to extract both the absorption coefficient and the photon density within the imaged object from the optoacoustic image. In contrast to previous methods, this algorithm is not based on the solution of theoretical light transport equations and it does not require explicit knowledge of the illumination geometry or the optical properties of the object and other unknown or loosely defined experimental parameters, leading to highly robust performance. The method was successfully examined with numerically and experimentally generated data and was found to be ideally suited for practical implementations in tomographic schemes of varying complexity, including multiprojection illumination systems and multispectral optoacoustic tomography (MSOT) studies of tissue biomarkers. [Read More…]

Fig. 2 Demonstration of the iterative algorithm in [9] for recovering the absorption coefficient out of PAT images. (a) Absorption coefficient, (b) the optoacoustic image, and (c) the reconstruction of the iterative algorithm when the scattering coefficient is known exactly. (d) The reconstruction by the iterative algorithm when the scattering coefficient contains a 3% error. The result demonstrate the vulnerability of forward-model-based inversion schemes to even small modeling inaccuracies.

A. Rosenthal, D. Razansky, and V. Ntziachristos, “Quantitative optoacoustic signal extraction using sparse signal representation”, IEEE Trans. Med. Imag., Vol. 28, pp. 1997-2006 (2009).

Iterative finite-element-based inversion for quantified detection of molecular targets using optoacoustic tomography

source: © 2009 Society of Photo-Optical Instrumentation Engineers (SPIE)

We describe an improved optoacoustic tomography method, that utilizes a diffusion-based photon propagation model in order to obtain quantified reconstruction of targets embedded deep in heterogeneous scattering and absorbing tissue. For the correction we utilize an iterative finite-element solution of the light diffusion equation to build a photon propagation model. We demonstrate image improvements achieved by this method by using tissue-mimicking phantom measurements. The particular strength of the method is its ability to achieve quantified reconstructions in non-uniform illumination configurations resembling whole-body small animal imaging scenarios.  [Read more…]

Fig. 3. OAT images of the 1st (a/b), 4th (c/d), 9th (e/f) and 11th (g/h) iteration of the normalization algorithm, with corresponding light distribution model (logarithmic scale).

Thomas Jetzfellner, Daniel Razansky, Amir Rosenthal, Ralf Schulz, K.-H. Englmeier, and Vasilis Ntziachristos “Iterative finite-element-based inversion for quantified detection of molecular targets using optoacoustic tomography, Proc. SPIE 7258, Medical Imaging 2009: Physics of Medical Imaging, 725812 (13 March 2009)

Optical under-sampling and reconstruction of several bandwidth-limited signals

source: © 2009 IEEE

We demonstrate experimentally an optical system for under-sampling several bandwidth-limited signals with carrier frequencies that are not known apriori and can be located anywhere within a very broad frequency region between 0–18GHz. The system is based on under-sampling asynchronously at three different sampling rates. The optical pulses required for the under-sampling are generated by a combination of an electrical comb generator and an electro-absorption optical modulator. To reduce loss and improve performance the implementation of the optical system is based on a wavelength division multiplexing technique. An accurate reconstruction of both the phase and the amplitude was obtained when two chirped signals each with a bandwidth of about 150 MHz were sampled.  [Read more…]

Alfred Feldster, Yuval P. Shapira, Moshe Horowitz, Amir Rosenthal, Shlomo Zach, and Lea Singer, “Optical Under-Sampling and Reconstruction of Several Bandwidth-Limited Signals,” J. Lightwave Technol. 27, 1027-1033 (2009)

Performance of iterative optoacoustic tomography with experimental data

source: © 2009 Applied Physics Letters

In this letter we experimentally demonstrate the sensitivity and overall performance of iterative correction for light attenuation in optoacoustic tomography as a function of number of iterations and accuracy of the tissue optical properties estimations. Experimental optoacoustic data were obtained by circularly illuminating a tissue-mimicking phantom with a high intensity pulsed near infrared laser and measuring the subsequent acoustic waves using a broadband acoustic hydrophone. We showcase an improvement in image fidelity and quantification due to the iterative inversion but find the method sensitive to the background optical properties and of a diverging behavior when increasing the number of iterations.  [Read more…]

Fig. 2 The reconstruction error of the algorithm as a function of iteration for different assumed reduced scattering coefficient values. In all cases μa=20 cm−1 and σ=0.001. The quality measures showed assumed (a) the standard deviation within the insertion and (b) a root-mean-square error estimate given in Eq. (4).

Thomas Jetzfellnera, Daniel Razansky, Amir Rosenthal, Ralf Schulz, K.-H. Englmeier, and Vasilis Ntziachristos, “Performance of iterative optoacoustic tomography with experimental data,” Appl. Phys. Lett. 95, 013703 (2009)

Design of planar waveguides with prescribed mode-profile using inverse scattering theory

source: © 2009 IEEE Journal of Quantum Electronics

We demonstrate a new method based on inverse scattering theory for designing the refractive index profile of single-mode planar waveguides in order to obtain a desired TE-mode profile. The method enables a direct design of the waveguide profile without the need for iterative optimization algorithms. The design is based on a first order solution to the Gel’fand-Levitan-MarCcaronenko integral equation that gives a simple linear connection between a small change in the scattering data and the corresponding change in the kernel function. This connection reduces the design problem to a simple linear constrained minimization problem which has an explicit solution. Our design method allows adding additional constraints on the refractive index profile such as the waveguide width. The method presented in this paper can be expanded to analyze TM modes and for designing multi-mode planar waveguides.  [Read more…]

Fig. 2 Comparison between the original and the extracted refractive index profiles that were reconstructed from the linearized GLM equation. Both profiles were obtained by changing the refractive index profile of an hyperbolic secant waveguide that corresponds to a reflectionless waveguide. An excellent agreement between the reconstructed (dotted line) and the original (solid line) profiles was obtained for (a) a truncated hyperbolic secant profile and (b) a sinusoidal perturbation.

Itay Hirsh, Moshe Horowitz, Amir Rosenthal, “Design of planar waveguides with prescribed mode-profile using inverse scattering theory,” IEEE Journal of Quantum Electronics ( Volume: 45 , Issue: 9 , Sept. 2009 )