Boosting (19) F MRI-SNR efficient detection of paramagnetic contrast agents using ultrafast sequences.

(19) F MRI offers high specificity but usually low sensitivity. Here, paramagnetic relaxation enhancement is assessed as a method to improve SNR efficiency in (19) F MRI. Compounds with short relaxation times are used that combine fluorine and a paramagnetic ion within the same molecule. Different molecular designs provide T1 values in the range of 1.4-15 ms and T2*/T1 ratios from 0.3 to 1. Gradient echo, as well as ultrafast radial MR sequences, is optimized to achieve highest SNR efficiency. Compared to nonparamagnetic compounds, ultrafast sequences can yield a gain of up to a factor 27 in sensitivity, whereas the gain with gradient echo is only factor 11. Comparison among the paramagnetic compounds shows that T2*/T1 close to unity is a prerequisite for highest SNR efficiency gain and that best results are obtained for compounds with T1 in the range of 1-5 ms.