Characterization of a commercial bioluminescence tomography‐guided system for pre‐clinical radiation research

Xiangkun Xu*, Zijian Deng, Daniel Sforza, Zhishen Tong, Yu‐Pei Tseng, Ciara Newman, Merle Reinhart, Paul Tsouchlos, Tim Devling, Hamid Dehghani, Iulian Iordachita, John W. Wong, Ken Kang‐Hsin Wang*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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Abstract

Background: Widely used Cone‐beam computed tomography (CBCT)‐guided irradiators have limitations in localizing soft tissue targets growing in a low‐contrast environment. This hinders small animal irradiators achieving precise focal irradiation.

Purpose: To advance image‐guidance for soft tissue targeting, we developed a commercial‐grade bioluminescence tomography‐guided system (BLT, MuriGlo) for pre‐clinical radiation research. We characterized the system performance and demonstrated its capability in target localization. We expect this study can provide a comprehensive guideline for the community in utilizing the BLT system for radiation studies.

Methods: MuriGlo consists of four mirrors, filters, lens, and charge‐coupled device (CCD) camera, enabling a compact imaging platform and multi‐projection and multi‐spectral BLT. A newly developed mouse bed allows animals imaged in MuriGlo and transferred to a small animal radiation research platform (SARRP) for CBCT imaging and BLT‐guided irradiation. Methods and tools were developed to evaluate the CCD response linearity, minimal detectable signal, focusing, spatial resolution, distortion, and uniformity. A transparent polycarbonate plate covering the middle of the mouse bed was used to support and image animals from underneath the bed. We investigated its effect on 2D Bioluminescence images and 3D BLT reconstruction accuracy, and studied its dosimetric impact along with the rest of mouse bed. A method based on pinhole camera model was developed to map multi‐projection bioluminescence images to the object surface generated from CBCT image. The mapped bioluminescence images were used as the input data for the optical reconstruction. To account for free space light propagation from object surface to optical detector, a spectral derivative (SD) method was implemented for BLT reconstruction. We assessed the use of the SD data (ratio imaging of adjacent wavelength) in mitigating out of focusing and non‐uniformity seen in the images. A mouse phantom was used to validate the data mapping. The phantom and an in vivo glioblastoma model were utilized to demonstrate the accuracy of the BLT target localization.

Results: The CCD response shows good linearity with < 0.6% residual from a linear fit. The minimal detectable level is 972 counts for 10 × 10 binning. The focal plane position is within the range of 13–18 mm above the mouse bed. The spatial resolution of 2D optical imaging is < 0.3 mm at Rayleigh criterion. Within the region of interest, the image uniformity is within 5% variation, and image shift due to distortion is within 0.3 mm. The transparent plate caused < 6% light attenuation. The use of the SD imaging data can effectively mitigate out of focusing, image non‐uniformity, and the plate attenuation, to support accurate multi‐spectral BLT reconstruction. There is < 0.5% attenuation on dose delivery caused by the bed. The accuracy of data mapping from the 2D bioluminescence images to CBCT image is within 0.7 mm. Our phantom test shows the BLT system can localize a bioluminescent target within 1 mm with an optimal threshold and only 0.2 mm deviation was observed for the case with and without a transparent plate. The same localization accuracy can be maintained for the in vivo GBM model.

Conclusions: This work is the first systematic study in characterizing the commercial BLT‐guided system. The information and methods developed will be useful for the community to utilize the imaging system for image‐guided radiation research.
Original languageEnglish
Pages (from-to)6433-6453
Number of pages21
JournalMedical Physics
Volume50
Issue number10
Early online date26 Aug 2023
DOIs
Publication statusPublished - Oct 2023

Bibliographical note

Acknowledgments:
This work was supported by the grants from National Cancer Institute, National Institutes of Health of USA (R21CA223403, R37CA230341, and R01CA240811) and Cancer Prevention and Research Institute of Texas RR200042, and RP180770.

Keywords

  • radiation therapy
  • image‐guidance
  • bioluminescence tomography
  • small animal irradiator
  • pre‐clinical research

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