Relaxivity Measurement of Gd-BnDOTA Conjugates

Stock solutions of 5 mM G5–Gd-BnDOTA conjugates were serially diluted to concentrations of 0.125 to 0.500 mM with PBS, pH 7.4. Relaxivity measurements were performed using a previous protocol [17 (link)] at ∼22°C using a 3-Tesla clinical scanner (Achieva 3.0 T, Philips Medical System, The Netherlands) using a manufacturer-supplied surface receiver coil (SENSE-Flex-M). A series of single slice 2D inversion recovery (IR) turbo spin echo images of the solutions were acquired with an acceleration factor of 8, an effective TE around 34 ms, and inversion recovery times (TI = 50, 100, 350, 750, 1250, 2500 and 5000 ms). The R₁ values for each dilution were determined by fitting ROI intensity values from variable IR images using Igor Pro [18 ]. The longitudinal relaxivity, r_1, was obtained from the slope of 1/T₁ versus (Gd[III]) plots determined from region of interest measurements.