### Quantitative Photoacoustic Tomography

Photoacoustic tomography is an emerging imaging modality developed over the past decade which combines the benefits of optical contrast and ultrasound propagation. The optical methods provide information about the distribution of chromophores which are light absorbing molecules within the tissue. The chromophores of interest are, for example, haemoglobin and melanin. In addition, chromophores are utilised in tomographic contrast agent based imaging in which case they are dyes, nanoparticles or genetically expressed markers that are used as contrast agents. The ultrasonic waves carry this optical information directly to the surface with minimal scattering, thus retaining accurate spatial information as well.

Quantitative photoacoustic tomography is a technique in which also the absolute concentration of chromophores is estimated. This is a hybrid imaging problem in which the solution of one inverse problem acts as a data for another ill-posed inverse problem. We develop computational methods for quantitative photoacoustic tomography. The implementation is based on Bayesian framework.

*Simulated (top row) and reconstructed (bottom row) absorption and scattering distributions*.

**Inverse Problems Insights**

An insights story on quantitative photoacoustic tomography was published in *Inverse Problems* 2013. For full story, see Quantitative photoacoustic tomography using the radiative transfer equation.

**Seniors working on quantitative photoacoustic tomography**

**Past and present collaborators**

Doctor Ben Cox, University College London, Department of Medical Physics and Bioengineering

Professor Simon Arridge, University College London, Department of Computer Science, Centre for Medical Image Computing

**Recent publications**

A. Pulkkinen, V. Kolehmainen, J.P. Kaipio, B.T. Cox, S.R. Arridge, and T. Tarvainen Approximate marginalization of unknown scattering in quantitative photoacoustic tomography,

*Inverse Problems and Imaging*, Accepted for Publication, 2014.A. Pulkkinen, B.T. Cox, S.R. Arridge, J.P. Kaipio, and T. Tarvainen A Bayesian approach to spectral quantitative photoacoustic tomography,

*Inverse Problems*, 30:065012, 2014.T. Tarvainen, A. Pulkkinen, B.T. Cox, J.P. Kaipio, and S.R. Arridge, Bayesian image reconstruction in quantitative photoacoustic tomography,

*IEEE Trans Med Imag*, 32(12):2287-2298, 2013.T. Saratoon, T. Tarvainen, B.T. Cox, and S.R. Arridge, A gradient-based method for quantitative photoacoustic tomography using the radiative transfer equation,

*Inverse Problems*, 29:075006, 2013.T. Tarvainen, A. Pulkkinen, B.T. Cox, J.P. Kaipio and S.R. Arridge, Image reconstruction in quantitative photoacoustic tomography using the radiative transfer equation and the diffusion approximation, in

*Proc. SPIE 8800, Opto-Acoustic Methods and Applications*, V. Ntziachristos and C.P. Lin Eds., 880006, 2013.T. Saratoon, T. Tarvainen, S.R. Arridge and B.T. Cox, 3D quantitative photoacoustic tomography using the δ-Eddington approximation, in

*Proc. SPIE 8581, Photons Plus Ultrasound: Imaging and Sensing 2013*, A.A. Oraevsky and L.V. Wang Eds., 85810V, 2013.T. Tarvainen, , B.T. Cox, J.P. Kaipio, and S.R. Arridge, Reconstructing absorption and scattering distributions in quantitative photoacoustic tomography,

*Inverse Problems*, 28:084009, 2012.B. Cox, T. Tarvainen, and S. Arridge, Multiple illumination quantitative photoacoustic tomography using transport and diffusion models, in Tomography and Inverse Transport Theory, Contemporary Mathematics, 559:1-12, Amer. Math. Soc., 2011.