Thus, instead of using pH buffered solution with or without bovine serum albumin to mimic the extracellular fluid used for extracellularly-distributed probes8, 21, 22 or using cancer cells to mimic intra-tumor conditions used for tumor imaging with BTPDM114, we used a strategy to generate a calibration curve in cultured proximal tubular cells, which mimics intracellular conditions in murine kidneys in vivo. The gene discussed is ALB; the disease is neoplasm.