Unmixing Molecular Agents From Absorbing Tissue in Multispectral Optoacoustic Tomography

Abstract

Detection of intrinsic or extrinsically administered chromophores and photo-absorbing nanoparticles has been achieved by multi-spectral optoacoustic tomography (MSOT). The detection sensitivity of MSOT depends not only on the signal to noise ratio considerations, as in conventional optoacoustic (photoacoustic) tomography implementations, but also on the ability to resolve the molecular targets of interest from the absorbing tissue background by means of spectral unmixing or sub-pixel detection methods. However, it is not known which unmixing methods are optimally suited for the characteristics of multispectral optoacoustic images. In this work we investigated the performance of different sub-pixel detection methods, typically used in remote sensing hyperspectral imaging, within the context of MSOT. A quantitative comparison of the different algorithmic approaches was carried out in an effort to identify methods that operate optimally under the particulars of molecular imaging applications. We find that statistical sub-pixel detection methods can demonstrate a unique detection performance with up to five times enhanced sensitivity as compared to linear unmixing approximations, under the condition that the optical agent of interest is sparsely present within the tissue volume, as common when using targeted agents and reporter genes.

Active Lymphatic Drainage From the Eye Measured by Noninvasive Photoacoustic Imaging of Near-Infrared Nanoparticles

“…39 To quantify the signal, the mean pixel intensities (MPIs) of the signal were extracted from each region (eyes and neck lymph nodes of both sides) using the linear regressionprocessed images. 40 Photoacoustic images were spectrally unmixed with the linear regression algorithm of the native software, with the same 25 lM QC-1 spectrum as well as oxyhemoglobin and deoxyhemoglobin selected as input spectra. Details of the photoacoustic image analysis are provided in Supplementary Material B.…”

Optoacoustic Imaging of Naphthalocyanine: Potential for Contrast Enhancement and Therapy Monitoring

“…The in vitro and in vivo optoacoustic spectra derived from the phantom measurements and in vivo appear similar to each other but not identical. The differences might be attributed to the sparse spatial sampling applied in vivo and possibly spectral alterations due to the wavelength-dependent light fluence distribution (24). Similarly to the observations in Figure 2, Figure 4A also shows a discrepancy between the absorption spectrum measured by a spectrophotometer and the optoacoustic measurements.…”

Mesoscopic and Macroscopic Optoacoustic Imaging of Cancer

“…Imaging of lung cancer and noninvasive imaging of brain tumors in humans appears unlikely to work without at least severe degradation of image quality. Quantification of absorber concentrations in optoacoustic images is considered an unsolved problem, because the wavelength-dependence of light attenuation in tissue distorts the measured optoacoustic spectrum for deep-lying sources (18,91). With time, optoacoustic imaging systems are likely to become more robust and user-friendly as the technology becomes more established.…”

“…We have recently demonstrated that excitation at multiple optical wavelengths, combined with a statistical subpixel detection method (adaptive matched filter-AMF) for spectral unmixing (18), can effectively enhance the sensitivity over single wavelength optoacoustic imaging on the order of 14 to 40 times in molecular imaging applications (19). This performance is summarized in Fig.…”

“…The MSOT sensitivity depends on a number of parameters, such as the depth and volume of the lesion (20), the absorption coefficient of the molecular agent, or the spectral unmixing approach used (18). Although a thorough analysis of the sensitivity capabilities of the technology is yet to be performed, experimental evidence shows detection of approximately 5 pmol of a NIR fluorescent dye in deep tissue in mice (19).…”