Off-resonance spin locking for MR imaging.
Off-resonance spin locking is investigated as a low power method for achieving low field spin-lattice relaxation contrast using high field clinical MR imaging systems (e.g., 1.5 tesla). Spin-lattice relaxation times and equilibrium magnetizations in the off-resonance rotating frame (T1 rho(off), beta) were measured for tissue-mimicking phantom materials as a function of the ratio of the amplitude to the resonance offset of the spin-locking pulse (f1/delta). The phantom materials consisted of vegetable oil to simulate fat and two different gels containing 2% and 4% agar to simulate nonfatty tissues with different macromolecular compositions. These measurements were used to verify a signal strength equation for a multislice off-resonance spin-locking technique implemented on a clinical MR imaging system operating at 1.5 tesla. Although the oil showed little change in image contrast with increasing f1/delta, the two gels demonstrated a strong variation which provided improved discrimination compared to T1-weighted imaging. Off-resonance spin locking is suggested as a method for improving delineation of breast lesions and a preliminary clinical example from a patient volunteer is presented.
Santyr
G E
GE
Department of Medical Physics, University of Wisconsin, Madison.
Fairbanks
E J
EJ
Kelcz
F
F
Sorenson
J A
JA
D001943:Breast Neoplasms / Q000175:diagnosis*; D005260:Female; D018226:Fibroadenoma / Q000175:diagnosis*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008961:Models, Structural; D010938:Plant Oils
D010938:Plant Oils