Figure 7.

Spectral dependence of signal change after injection. (A) Signal strength as a function of interrogation wavelength before and after contrast agent injection. Data from all conditional experiments were averaged. Thin traces: preinjection conditions. Bold traces: after nigrosin or ICG injections, signals increased in magnitude across all wavelengths except for 900 nm. (B) The difference in preinjection spectra from postinjection spectra (bold-thin traces) reveals the spectral-dependent changes imparted by the contrast agent injection. Notably, nigrosin injections have a different spectral-dependent magnitude shift than do ICG injections. (C) Absorption characteristics of the injected dyes. Spectrophotometer scans of blood extracted from animals 1 hour after initial systemic injection. Blood scans after injection were subtracted from blood scans before injection to reveal the absorption spectra of the injected dye. Absorbance units were normalized to a value of 1 over the wavelengths tested in retinal scans (700–900 nm). The changes in stimulus-evoked signal strength show consistency with the absorption spectra of the injected dye.