Ultrasound mediated bioluminescence tomography for high sensitivity, high spatial resolution 3D imaging
Lead Research Organisation:
University of Nottingham
Department Name: Faculty of Engineering
Abstract
Optical imaging is a unique and powerful technique for implementation of 'refinement' and 'reduction' within the Principles of Humane Experimental Techniques. Using traditional disease models, infected animals (ranging between 3-10) are sacrificed at defined time points and tissues are excised for determination of pathogen numbers and localization. For example, a six time point experiment would result in the use of 18-60 animals. In contrast, the non-invasive nature of optical imaging allows the course of an infection to be monitored simply by imaging the visible or near infrared signal detected from within the same group of animals, typically six to eight in total. Importantly, multiple imaging of the same animal throughout an experiment allows disease progression to be followed with extreme accuracy and consistency, while allowing each animal to act as its own control.
There is a major drawback in using optical imaging as light is heavily scattered by tissue which results in poor quality images. For example in tracking stem cells in tissue, optical scattering means that we cannot tell where precisely where the cells go in the body, how many are at a particular and what their action is. This severely hampers research into understanding the use of stem cells in aiding the body's immune response.
We propose to develop an imaging system that combines ultrasound and optical techniques to significantly improve the spatial resolution and sensitivity of bioluminescence imaging. Information from the ultrasound will be used in two ways to address this problem. Firstly, as ultrasound makes a small change to the mechanical properties of the tissue, this can be used to modulate the bioluminescent light produced within the tissue. This provides a modulated light 'beacon' which can be used to precisely probe different regions of the tissue, thus overcoming the effects of light scattering and improving spatial resolution. Secondly we will use the ultrasound image to provide 3D maps of tissue structure.
Both modulated light beacons and structural information will be used to inform an image reconstruction algorithm based on our widely used NIRFAST software (www.nirfast.org). The system will be demonstrated in studies of nude mice during the course of the project. Based on our proof of concept data, we anticipate that the spatial resolution will be a maximum of 0.5mm, compared to the current state of the art of 2.5mm. This will contribute to a significant impact on the 3Rs. Replacement: better imaging will inform more accurate computational models; Reduction: imaging enables the same animals to used over time and more accurate quantitative imaging allows fewer animals to be used in a single study; Refinement: through the improved quality of research findings.
There is a major drawback in using optical imaging as light is heavily scattered by tissue which results in poor quality images. For example in tracking stem cells in tissue, optical scattering means that we cannot tell where precisely where the cells go in the body, how many are at a particular and what their action is. This severely hampers research into understanding the use of stem cells in aiding the body's immune response.
We propose to develop an imaging system that combines ultrasound and optical techniques to significantly improve the spatial resolution and sensitivity of bioluminescence imaging. Information from the ultrasound will be used in two ways to address this problem. Firstly, as ultrasound makes a small change to the mechanical properties of the tissue, this can be used to modulate the bioluminescent light produced within the tissue. This provides a modulated light 'beacon' which can be used to precisely probe different regions of the tissue, thus overcoming the effects of light scattering and improving spatial resolution. Secondly we will use the ultrasound image to provide 3D maps of tissue structure.
Both modulated light beacons and structural information will be used to inform an image reconstruction algorithm based on our widely used NIRFAST software (www.nirfast.org). The system will be demonstrated in studies of nude mice during the course of the project. Based on our proof of concept data, we anticipate that the spatial resolution will be a maximum of 0.5mm, compared to the current state of the art of 2.5mm. This will contribute to a significant impact on the 3Rs. Replacement: better imaging will inform more accurate computational models; Reduction: imaging enables the same animals to used over time and more accurate quantitative imaging allows fewer animals to be used in a single study; Refinement: through the improved quality of research findings.
Technical Summary
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 um 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.
Planned Impact
In addition to the academic community, researchers in industry utilising pre-clinical optical imaging will similarly benefit from the availability of a technique that can provide high spatial resolution, quantitative 3D maps of cellular function.
The impact on the 3Rs will be;
Replacement: Through its use of novel non-invasive technique, the system will provide a better understanding of the processes (functional, normal, diseased and structural) involved in each individual study. This information can then be used in sophisticated multi-physical simulation studies to provide a better understanding of the involved processes without the need of additional animal models. Through computational models, imaging protocols, system design and animal studies can be refined to provide the highest accuracy in imaging, without the need for real models.
Reduction: The developed technique will have a dramatic effect on the reduction of the number of animal models used due to the non-invasive nature of the imaging modality to provide absolute spatial maps of cellular function and structure. This in turn allows the same animal to be used in a continuous study without the need for its sacrifice, thereby reducing future use of animals.
Refinement: The use of the same individual models for the non-invasive imaging not only benefits animals, but also improves the quality of research findings. The improved spatial resolution will allow more accurate measurements and require fewer animals to achieve statistical significance.
The NIRFAST software is publicly available with user support provided to academia and industry. The algorithms and software developed so far have been supplied free of charge to several companies for use in their own research and development, including Philips Research Hamburg (Germany), ART Inc. (Montreal, PQ, Canada), Kodak Inc., (Rochester NY) and Xenogen Inc., (Now Perkin Elmer, Oakland CA). If successfully demonstrated, the instrumentation would also be in high demand and we will look for a commercial partner (either one of our current partners or via our technology transfer offices) as the project progresses.
The wider public will benefit from the proposed technique as optical molecular imaging is now utilised in many applications such as cancer research, cell based therapy and the development of pharmaceutical drugs.
The impact on the 3Rs will be;
Replacement: Through its use of novel non-invasive technique, the system will provide a better understanding of the processes (functional, normal, diseased and structural) involved in each individual study. This information can then be used in sophisticated multi-physical simulation studies to provide a better understanding of the involved processes without the need of additional animal models. Through computational models, imaging protocols, system design and animal studies can be refined to provide the highest accuracy in imaging, without the need for real models.
Reduction: The developed technique will have a dramatic effect on the reduction of the number of animal models used due to the non-invasive nature of the imaging modality to provide absolute spatial maps of cellular function and structure. This in turn allows the same animal to be used in a continuous study without the need for its sacrifice, thereby reducing future use of animals.
Refinement: The use of the same individual models for the non-invasive imaging not only benefits animals, but also improves the quality of research findings. The improved spatial resolution will allow more accurate measurements and require fewer animals to achieve statistical significance.
The NIRFAST software is publicly available with user support provided to academia and industry. The algorithms and software developed so far have been supplied free of charge to several companies for use in their own research and development, including Philips Research Hamburg (Germany), ART Inc. (Montreal, PQ, Canada), Kodak Inc., (Rochester NY) and Xenogen Inc., (Now Perkin Elmer, Oakland CA). If successfully demonstrated, the instrumentation would also be in high demand and we will look for a commercial partner (either one of our current partners or via our technology transfer offices) as the project progresses.
The wider public will benefit from the proposed technique as optical molecular imaging is now utilised in many applications such as cancer research, cell based therapy and the development of pharmaceutical drugs.