FIGURE 1.

Nuclear scans after intravenous administration of the P‐gp substrate ^99mTc‐MIBI to an MDR1 wildtype dog (a) and a dog homozygous for ABCB1‐1Δ (b). The images demonstrate diminished radioactivity in the brain of the wildtype dog due to P‐gp efflux of ^99mTc‐MIBI, while the radioactivity of the brain P‐gp deficient dog cannot be distinguished from surrounding tissues.