Example apparatus and methods concern determining whether a target material appears in a region experiencing nuclear magnetic resonance (NMR). One method acquires a baseline value for a magnetic resonance parameter (MRP) while the region is not exposed to a molecular imaging agent that affects the MRP and acquires a series of quantitative values for the MRP while the sample is influenced by a molecular imaging agent. Quantitative values may be acquired during a clinically relevant time period (e.g., 60 minutes) during which the change in the MRP (e.g., T1) caused by the molecular imaging agent is at least 90% of the peak change caused by the molecular imaging agent. The molecular imaging agent may be SBK2 and may produce a desired change in T1 for at least thirty minutes in glioblastoma.