Fig 2. Time course of bioluminescence imaging (BLI) signal intensity after lentiviral (LV) transduction of mouse brain. A, Long-term evolution of the BLI signal intensity in a group of mice (n = 10) injected with 17-ng p24 of LV-Fluc and in a group injected with 8.4-ng p24 control vector (LV-enhanced green fluorescent protein [EGFP], n = 4). After a peak at days 8 to 14, the signal intensity declines during the first month to 16% of the maximum value at day 37 and then remains constant at 17.5 ± 2.3% of the maximum value from days 42 to 365. A linear regression line is drawn from days 37 to 365 (R² = 0.027) for LV-Fluc and for all time points for LV-EGFP (R² = 0.041). B, BLI of a representative animal shows an initial rise in signal intensity at week (W) 1 followed by a decrease and thereafter a stabilization of the signal intensity. The control animal shown represents the highest signal intensity seen in a control animal. GFP indicates green fluorescent protein; D, day; p, photons. (Reprinted by permission from Macmillan Publishers: Deroose et al. Mol. Therapy 2006;14:423–31, copyright 2006)