On-resonance low B1 pulses for imaging of the effects of PARACEST agents.
Application of the exchange-sensitive, low-power RF pulses positioned on the bulk water resonance for imaging of the effects of PARACEST agents is proposed as an alternative to the standard CW off-resonance irradiation. Specifically, we applied a low-power WALTZ-16 RF train, with the 90 degrees pulse unit replaced by a pulse of the fixed length (WALTZ-16*). Using this sequence, the bulk water signal was found to be sensitive to exchange lifetimes with PARACEST complex bound protons, the transverse relaxation time of bulk water, and longitudinal relaxation time of bound protons. In this report, the concept of using WALTZ-16* to "activate" a PARACEST effect is introduced and some of the salient features of this technique with respect to experimental conditions and performance levels are discussed. Computational predictions are verified and explored by comparison with experimental spectroscopic and imaging data. It is shown that WALTZ-16* can be used to detect PARACEST agents with an RF intensity as low as 200 Hz for concentrations as low as a few tens of microM for lanthanide chelates having appropriate water-exchange rates (Tm,Dy).
Department of Radiology, Beth Israel Deaconess Medical Center, Harvard Medical School, 330 Brookline Avenue, Boston, MA 02215, USA. evinogra@bidmc.harvard.edu
Elena
E
Vinogradov
Shanrong
S
Zhang
Angelo
A
Lubag
James A
JA
Balschi
A Dean
AD
Sherry
Robert E
RE
Lenkinski
D003287:Contrast Media / Q000737:chemistry*; D028581:Lanthanoid Series Elements / Q000737:chemistry*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009942:Organometallic Compounds / Q000737:chemistry*
D003287:Contrast Media; D028581:Lanthanoid Series Elements; D009942:Organometallic Compounds; C463281:thulium-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate