Field strength and dose dependence of contrast enhancement by gadolinium-based MR contrast agents

The relaxivities r(1) and r(2) of magnetic resonance contrast agents and th e T-1 relaxation time values of tissues are strongly field dependent. We pr esent quantitative data and simulations of different gadolium-based extrace llular fluid contrast agents and the modulation of their contrast enhanceme nt by the magnetic field to be able to answer the following questions: How are the dose and field dependences of their contrast enhancement? Is there an interrelationship between dose and field dependence? Should one increase or decrease doses at specific fields? Nuclear magnetic relaxation dispersi on data were acquired for the following contrast agents: gadopentetate dime glumine, gadoterate meglumine gadodiamide injection and gadoteridol injecti on, as well as for several normal and pathological human tissue samples. Th e magnetic filed range stretched from 0.0002 to 4.7 T, including the entire clinical imaging range. The date acquired were then fitted wit the appropr iate theoretical models. The combination of the diamagnetic relaxation rate s (R-1 = 1/T-1 and R-2 = 1/T-2) of tissues with the respective paramagnetic contributions of the contrast agents allowed the prediction of image contr ast at any magnetic field. The results revealed a nearly identical field an d dose-dependent increase of contrast enhancement induced by these contrast agents within a certain dose range. The target tissue concentration (TTC) was an important though nonlinear factor for enhancement. The currently rec ommended dose of 0.1 mmol/kg bodyweight seems to be a compromise close to t he lower limits of diagnostically sufficient contrast enhancement for clini cal imaging at all field strengths. At low field contrast enhancement might be insufficient. Adjustment of dose or concentration, or a new class of co ntrast agents with optimized relaxivity, would be a valuable contribution t o a better diagnostic yield of contrast enhancement at al fields.