A microcomputed tomography guided fluorescence tomography system for small animal molecular imaging

Abstract

A prototype small animal imaging system was created for coupling fluorescence tomography ͑FT͒ with x-ray microcomputed tomography ͑microCT͒. The FT system has the potential to provide synergistic information content resultant from using microCT images as prior spatial information and then allows overlay of the FT image onto the original microCT image. The FT system was designed to use single photon counting to provide maximal sensitivity measurements in a noncontact geometry. Five parallel detector locations are used, each allowing simultaneous sampling of the fluorescence and transmitted excitation signals through the tissue. The calibration and linearity range performance of the system are outlined in a series of basic performance tests and phantom studies. The ability to image protoporphyrin IX in mouse phantoms was assessed and the system is ready for in vivo use to study biological production of this endogenous marker of tumors. This multimodality imaging system will have a wide range of applications in preclinical cancer research ranging from studies of the tumor microenvironment and treatment efficacy for emerging cancer therapeutics.

Dynamic dual-tracer MRI-guided fluorescence tomography to quantify receptor density in vivo

“…Applying these principles, imaging fluorescence activity in relatively large tissue volumes (over 5 cm) is feasible. Substantial evidence exists suggesting that volumetric images of fluorescence activity are more accurate if additional information, such as the anatomical features of the tissue, is incorporated in the optical image reconstruction algorithm (29)(30)(31)(32)(33)(34).…”

Computed Tomography-guided Time-domain Diffuse Fluorescence Tomography in Small Animals for Localization of Cancer Biomarkers

“…However, CCD cameras have a limited dynamic range and read-out noise limits their ultimate sensitivity. The second design avoids the potential limitations of CCD camera detection by employing highly sensitive single-photon counting technology based on the use of such detectors as photomultiplier tubes or avalanche photodiodes [10][11][12][13] . The drawback of these more sensitive detection methods is that each detector can only collect light at a single point; therefore, to achieve dense tissue sampling, either many detectors have to be used (which is very expensive), or many projections have to be imaged with the same detector (which can be time consuming).…”

“…In the presented methodology, the respective sensitivities of each detection channel are accounted for by collecting a baseline measurement of excitation light transmitted through a line-diffusor designed to direct equal fractions of light to each detector 15 . Furthermore, the detected light during an experiment is continuously calibrated to the laser reference, in terms of both intensity and mean-time, which could fluctuate over time, by the operation of a laser reference channel 11,15 . The second critical step is the accurate collection and co-registration of anatomical imaging for guided fluorescence reconstructions.…”

“…The majority of research groups have invested in charge-coupled device (CCD)-based systems that provide abundant tissue-sampling but suboptimal sensitivity [4][5][6][7][8][9] , while our group and a few others [10][11][12][13] have pursued systems based on very high sensitivity detectors, that at this time allow dense tissue sampling to be achieved only at the cost of low imaging throughput. Here we demonstrate the methodology for applying single-photon detection technology in a fluorescence tomography system to localize a cancerous brain lesion in a mouse model.…”

“…The fluorescence tomography (FT) system employed single photon counting using photomultiplier tubes (PMT) and information-rich time-domain light detection in a non-contact conformation 11 . This provides a simultaneous collection of transmitted excitation and emission light, and includes automatic fluorescence excitation exposure control 14 , laser referencing, and co-registration with a small animal computed tomography (microCT) system 15 .…”