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Spin‐lock imaging of intrinsic susceptibility gradients in tumors
Author(s) -
Zu Zhongliang,
Janve Vaibhav,
Gore John C.
Publication year - 2020
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.28155
Subject(s) - nuclear magnetic resonance , chemistry , diffusion , relaxation (psychology) , magnetic susceptibility , amplitude , spin–lattice relaxation , dispersion (optics) , analytical chemistry (journal) , physics , optics , crystallography , biology , chromatography , nuclear quadrupole resonance , thermodynamics , neuroscience
Purpose Previous studies have shown that diffusion of water through intrinsic susceptibility gradients produces a dispersion of the spin‐lattice relaxation rate in the rotating frame ( R 1 ρ ) over a low range of spin‐locking amplitudes (0 < ω 1 < 100 Hz), whereas at higher ω 1 and high magnetic fields, a second dispersion arises due to chemical exchange. Here, we separated these different effects and evaluated their contributions in tumors. Methods Maps of R 1 ρ and its changes with locking field were acquired on intracranial 9‐L tumor models. The R 1 ρ changes due to diffusion ( R 1 ρ Diff ) were calculated by subtracting maps of R 1 ρ at 100 Hz ( R 1 ρ [100 Hz]) from those at 0 Hz ( R 1 ρ [0 Hz]). The R 1 ρ changes due to exchange ( R 1 ρ Ex ) were calculated by subtracting maps of R 1 ρ at 5620 Hz ( R 1 ρ [5620 Hz]) from those of R 1 ρ at 100 Hz ( R 1 ρ [100 Hz]). Measurements of vascular dimensions and spacing were performed ex vivo using 3D confocal microscopy. Results The R 1 ρ changes at low ω 1 in tumors (5.24 ± 1.78 s −1 ) are substantially ( p = 3.7 6 ) greater than those in normal tissues (1.36 ± 0.70 s −1 ), which we suggest are due to greater contributions from diffusion through susceptibility gradients. Tumor vessels were larger and spaced less closely compared with normal brain, which may be 1 factor contributing the susceptibility within 9‐L tumors. The contrast between tumor and normal tissues for R 1 ρ Diff is larger than for R 1 ρ Ex and for the apparent R 2w . Conclusion Images that are sensitive to the variations of spin‐lock relaxation rates at low ω 1 provide a novel form of contrast that reflects the heterogeneous nature of intrinsic variations within tumors.