title: Negative contrast Cerenkov luminescence imaging of blood vessels in a tumor mouse model using [68Ga]gallium chloride.
abstract: BACKGROUND
  Cerenkov luminescence imaging (CLI) is an emerging imaging technique where visible light emitted from injected beta-emitting radionuclides is detected with an optical imaging device. CLI research has mostly been focused on positive contrast imaging for ascertaining the distribution of the radiotracer in a way similar to other nuclear medicine techniques. Rather than using the conventional technique of measuring radiotracer distribution, we present a new approach of negative contrast imaging, where blood vessel attenuation of Cerenkov light emitted by [68Ga]GaCl3 is used to image vasculature.
  
  
  METHODS
  BALB/c nude mice were injected subcutaneously in the right flank with HT-1080 fibrosarcoma cells 14 to 21 days prior to imaging. On the imaging day, [68Ga]GaCl3 was injected and the mice were imaged from 45 to 90 min after injection using an IVIS Spectrum in vivo imaging system. The mice were imaged one at a time, and manual focus was used to bring the skin into focus. The smallest view with pixel size around 83 μm was used to achieve a sufficiently high image resolution for blood vessel imaging.
  
  
  RESULTS
  The blood vessels in the tumor were clearly visible, attenuating 7% to 18% of the light. Non-tumor side blood vessels had significantly reduced attenuation of 2% to 4%. The difference between the attenuation of light of tumor vessels (10% ± 4%) and the non-tumor vessels (3% ± 1%) was significant. Moreover, a necrotic core confirmed by histology was clearly visible in one of the tumors with a 21% reduction in radiance.
  
  
  CONCLUSIONS
  The negative contrast CLI technique is capable of imaging vasculature using [68Ga]GaCl3. Since blood vessels smaller than 50 μm in diameter could be imaged, CLI is able to image structures that conventional nuclear medicine techniques cannot. Thus, the negative contrast imaging technique shows the feasibility of using CLI to perform angiography on superficial blood vessels, demonstrating an advantage over conventional nuclear medicine techniques.
authors.affiliation: Singapore Bioimaging Consortium, Agency for Science, Technology and Research, Singapore, Singapore. steinberg137@gmail.com.
authors.forename: Jeffrey D
authors.initials: JD
authors.lastname: Steinberg
authors.forename: Anandhkumar
authors.initials: A
authors.lastname: Raju
authors.forename: Prashant
authors.initials: P
authors.lastname: Chandrasekharan
authors.forename: Chang-Tong
authors.initials: CT
authors.lastname: Yang
authors.forename: Karen
authors.initials: K
authors.lastname: Khoo
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Abastado
authors.forename: Edward G
authors.initials: EG
authors.lastname: Robins
authors.forename: David W
authors.initials: DW
authors.lastname: Townsend