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Spin-lock imaging of intrinsic susceptibility gradients in tumors.

ABSTRACT: 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 (R1 ? ) over a low range of spin-locking amplitudes (0 < ?1 < 100 Hz), whereas at higher ?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 R1 ? and its changes with locking field were acquired on intracranial 9-L tumor models. The R1 ? changes due to diffusion ( R1?Diff ) were calculated by subtracting maps of R1 ? at 100 Hz (R1 ? [100 Hz]) from those at 0 Hz (R1 ? [0 Hz]). The R1 ? changes due to exchange ( R1?Ex ) were calculated by subtracting maps of R1 ? at 5620 Hz (R1 ? [5620 Hz]) from those of R1 ? at 100 Hz (R1 ? [100 Hz]). Measurements of vascular dimensions and spacing were performed ex vivo using 3D confocal microscopy. RESULTS:The R1 ? changes at low ?1 in tumors (5.24 ± 1.78 s-1 ) are substantially (p = 3.76 ) 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 R1?Diff is larger than for R1?Ex and for the apparent R2w . CONCLUSION:Images that are sensitive to the variations of spin-lock relaxation rates at low ?1 provide a novel form of contrast that reflects the heterogeneous nature of intrinsic variations within tumors.

SUBMITTER: Zu Z

PROVIDER: S-EPMC7558740 | biostudies-literature | 2020 May

REPOSITORIES: biostudies-literature

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