Ultrasound mediated bioluminescence tomography for high sensitivity, high spatial resolution 3D imaging

Aims

This project aims to reduce the number of animals needed in long time course studies by combining ultrasound with bioluminescence imaging to improve 3D spatial resolution and maximise the quantitative data that can be obtained from each animal.

Background

Traditional approaches for long term in vivo studies, for example, to track disease progression require groups of animals (up to ten) to be killed at defined time points and tissues removed for analysis (e.g. cell count, pathogen numbers). Longitudinal imaging offers an opportunity to reduce animal use in these studies, but due to optical scattering, current state of the art optical imaging systems lack quantitative accuracy and spatial resolution. This project will combine ultrasound with bioluminescence imaging (BLI) to create a new imaging platform to enable non-invasive, long term longitudinal imaging within the same group of animals. Combining these technologies will improve spatial resolution of the images, increasing the amount and quality of the data generated using this approach.

A traditional six time point experiment would use 18-60 animals, but the current approach would require up to eight animals. Multiple imaging of the same animal throughout an experiment allows long term studies to be followed accurately with less variability.

Research details and methods

This project will build on initial efforts to combine ultrasound and BLI to develop a small animal ultrasound-mediated BLI platform capable of providing (i) ultrasound images of the tissue structure; (ii) 3D maps of bioluminescence from the ultrasound modulated signals; and (iii) unmodulated bioluminescence images. Professor Morgan will collaborate with Dr Hamid Dehghani at the University of Birmingham to modify the widely used NIRFAST software for reconstructing images to allow quantitative mapping of the signals from the new BLI platform. The development of the imaging system and the accuracy of the reconstruction algorithm will be tested in specially constructed tissue phantoms with known optical and acoustic properties. The validity of the system for in vivo imaging will be assessed in a variety of in vivo experiments already ongoing within the Morgan laboratory. This will include tracking mesenchymal stem cells in vivo and imaging bacterial infection/colonisation of indwelling devices, such as catheters.

An imaging system that combines ultrasound and optical techniques will be developed with the capability to significantly improve the spatial resolution and quantitative accuracy of bioluminescence imaging (BLI). Enhancement of the information obtainable from current BLI systems will be achieved by first modulating the bioluminescent light emitted in the tissue with a focused ultrasound beam. This produces an ultrasound modulated light 'beacon' within the tissue in the region of the ultrasound focus which can be used to reduce the effects of light scattering and improve the image spatial resolution. To provide an added layer of information conventional ultrasound imaging will be carried out enabling images of tissue structure to be co-registered. Both modulated light beacons and structural information will inform a reconstruction algorithm based on our widely used NIRFAST reconstruction code enabling the two datasets to be merged. The potential of the system to outperform current state of the art BLI will be demonstrated through a number of exemplar pre-clinical 3D imaging studies, including tracking of mesenchymal stem cells in nude mice. Based on our proof of concept data the 3D image spatial resolution will be improved by at least a factor of 5 (500 µm compared with 2.5 mm) enabling more accurate and consistent clinical data to be obtained from a smaller set of animals. This will contribute to a significant impact on the 3Rs. Replacement: better imaging will inform more accurate computational models; Reduction: imaging enables longitudinal studies on the same cohort, more accurate quantitative imaging allows fewer animals to be used in a study; Refinement: through the improved quality of research findings.

Ahmad J, Jayet B, Hill PJ, Mather ML, Dehghani H, Morgan SP (2018). Ultrasound-mediation of self-illuminating reporters improves imaging resolution in optically scattering media. Biomed. Opt. Express 9(4):1664-1679. doi: 10.1364/BOE.9.001664.

Jayet B, Morgan SP, Dehghani H (2018). Incorporation of an ultrasound and model guided permissible region improves quantitative source recovery in bioluminescence tomography. Biomed. Opt. Express 9(3): 1360-1374. doi: 10.1364/BOE.9.001360.

Zhang Q, Mather ML, Morgan SP (2015). Numerical investigation of the mechanisms of ultrasound-modulated bioluminescence tomography. IEEE Trans Biomed Eng. 62(9): 2135-43. doi: 10.1109/TBME.2015.2405415. 

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Strategic grant

Grant reference number

NC/L00187X/1

Award date:

Sep 2014 - May 2018

Grant amount

£349,668 (Co-funded by EPSRC)