Whole‐brain amide proton transfer (APT) and nuclear overhauser enhancement (NOE) imaging in glioma patients using low‐power steady‐state pulsed chemical exchange saturation transfer (CEST) imaging at 7T

Abstract

Purpose To explore the relationship of APT and NOE signal intensities with respect to different World Health Organization (WHO) brain tumor grades (II to IV) at 7T. Materials and Methods APT-based and NOE-based signals at 7T using low-power steady-state CEST were compared among de novo primary gliomas of different WHO grades (II to IV). The quantitative APT and NOE signals, calculated by fitting approach using extrapolated semi-solid MT reference (EMR) signals, were compared with the magnetization transfer ratio asymmetry (MTRasym) analysis, commonly used in APT-weighted MRI. Results The observed NOE signals of all glioma grades were significantly lower than normal brain tissue (p < 0.01). NOE signals significantly differed between low-grade (II) gliomas and high-grade (III & IV) gliomas (p < 0.05). APT signals showed no difference between the tumor regions for any glioma grades (M = 3.08 %, 2.64 %, and 3.10 %, 95% CI = 2.81 % ~ 3.33 %, 2.36 % ~ 2.91 %, and 2.85 % ~ 3.36 % for grade II, III, and IV, respectively), and between normal brain tissue and all glioma grades (p = 0.08, M = 4.29 % and 2.94 %, 95% CI = 3.57 % ~ 4.99 % and 2.47 % ~ 3.41 % for normal and average grade II, III, and IV), while MTRasym differed significantly between normal tissue and all glioma grades (p < 0.05). Conclusion NOE contributes substantially to APT weighted MRI at 7T at low RF saturation power and provides a promising biomarker for glioma grading.

Improving the detection sensitivity of pH‐weighted amide proton transfer MRI in acute stroke patients using extrapolated semisolid magnetization transfer reference signals

“…Next, two-pool MTC spectra (free bulk water and semisolid) were generated by the EMR technique (36, 37, 42–44). The semi-solid MTC model fitting under a non-steady-state (NS) condition can be described from the modified Bloch equations (45, 46).…”

Optimization and repeatability of multipool chemical exchange saturation transfer MRI of the prostate at 3.0 T

“…The direct saturation (DS), CEST, and nuclear Overhauser effect (NOE) pools were modeled using Lorentzian lineshapes, described as a function of the saturation frequency, ω by: …”

Chemical exchange saturation transfer (CEST) signal intensity at 7T MRI of WHO IV° gliomas is dependent on the anatomic location

“…The region of interest (ROI) of each patient was defined as the whole tumor region, made up of peritumoral edema (as displayed in T 2 ‐weighted images) and contrast enhancement, as displayed in gadolinium contrast‐enhanced T 1 images but excluding necrotic tumor regions. Following CEST, metrics were calculated and analyzed for location dependence: APT, dns‐APT, and NOE CEST signals based on the AREX approach (mean and maximum [max] APT AREX , dns‐APT AREX , and mean NOE AREX ), and APT and NOE CEST signals based on the linear difference method (APT LD , NOE LD ) . To assess possible influences of B 1 field inhomogeneity on CEST parameters, the signal intensities of the investigated ROIs were also evaluated at B 1 maps.…”