Todd C. Soesbe1, Federico A. Rojas-Quijano1, A. Dean Sherry1, 2
1Advanced Imaging Research Center, UT Southwestern Medical Center, Dallas, TX, United States; 2Department of Chemistry, The University of Texas at Dallas, Dallas, TX, United States
We have recently shown for Eu3+-based PARECEST agents that the same water molecule exchange that enables the CEST effect can also facilitate severe bulk water line broadening via the T2-exchange (T2ex) mechanism. T2ex can significantly reduce the bulk water T2 (i.e. negative contrast) even without spin saturation, causing the PARACEST agent to behave like a susceptibility or T2 agent. This makes Off minus On imaging of PARACEST agents difficult since the regions of uptake appear dark in both images. We have also recently shown that the ultra-short TE times (<10 μs) used in the Sweep Imaging with Fourier Transform (SWIFT) pulse sequence can reclaim the loss in signal due to T2ex to enable fast and sensitive in vivo PARACEST imaging using simple Off minus On image subtraction. Here, we use the same SWIFT-CEST method to image a Tb3+-based PARACEST agent in vivo.