title: Improved fluorescence of indocyanine green in vitro and in vivo after simple cooling procedures.
abstract: Indocyanine green (ICG) is a contrast agent used for detecting angiogenesis with optical imaging (OI). The purpose of this study was to investigate whether cooling procedures increase the signal yield of ICG with OI. Test samples of 0.05 and 0.02 mM ICG in 40% DMSO and 60% DMEM underwent OI at four different temperatures (5, 37, 55 and 75 degrees C). In addition, six athymic rats with an antigen-induced arthritis of the knee and ankle joints underwent OI before and after injection of ICG (10 mg/ml, dose 15 mg/kg) on two separate days with and without cooling of the joints. The fluorescent signals of the test samples and arthritic joints were measured and evaluated for significant differences before and after cooling with a t-test. In vitro studies showed a strong negative correlation between ICG temperature and fluorescent signal. The mean fluorescent signal of arthritic joints (measured in efficiency) was 0.345 before ICG-injection, 4.55 after ICG-injection and before cooling and 9.71 after ICG-injection and after cooling. The fluorescent signal enhancement of arthritic joints with ICG-enhanced OI images increased significantly after cooling (p = 0.02). The signal yield of ICG can be significantly increased by cooling the target pathology. The primary underlying cause of the temperature dependence of ICG is enhanced collisional quenching with increasing temperature. This simple cooling method may be immediately helpful to increase the fluorescence signal yield in current ICG-enhanced OI-studies in patients.
authors.affiliation: Department of Radiology, University of California San Francisco, San Francisco, CA 94107, USA. sophie.boddington@radiology.ucsf.edu
authors.forename: Sophie
authors.initials: S
authors.lastname: Boddington
authors.forename: Elizabeth J
authors.initials: EJ
authors.lastname: Sutton
authors.forename: Ella
authors.initials: E
authors.lastname: Jones
authors.forename: Derk D
authors.initials: DD
authors.lastname: Purcell
authors.forename: Tobias D
authors.initials: TD
authors.lastname: Henning
authors.forename: Sidhartha
authors.initials: S
authors.lastname: Tavri
authors.forename: Reinhard
authors.initials: R
authors.lastname: Meier
authors.forename: Akhilesh
authors.initials: A
authors.lastname: Sista
authors.forename: Yanjun
authors.initials: Y
authors.lastname: Fu
authors.forename: Heike
authors.initials: H
authors.lastname: Daldrup-Link
mesh_terms: D000818:Animals; D000843:Ankle Joint / Q000473:pathology; D001169:Arthritis, Experimental / Q000175:diagnosis*; D003080:Cold Temperature; D004396:Coloring Agents / Q000737:chemistry; D003287:Contrast Media / Q000737:chemistry; D003952:Diagnostic Imaging / Q000379:methods; D005260:Female; D005453:Fluorescence; D007208:Indocyanine Green / Q000737:chemistry*; D007719:Knee Joint / Q000473:pathology; D051381:Rats; D011923:Rats, Nude
chemical_list: D004396:Coloring Agents; D003287:Contrast Media; D007208:Indocyanine Green