Figure 1.
Peritumoral hyperintensity on NOE mediated CEST compared to standard MRI.
Left frontal glioblastoma in a 59 year old man at 3 Tesla, CE-T1 (A) and T2-weighted images (B). On the selected slice the CEST contrast at 7 Tesla, based on MTRasym (C), displays peritumoral hyperintensities at equal extent compared to the edema on T2-weighted images. In contrast to T2-weighted images, the CEST peritumoral hyperintensity displays an irregular border and subareas of different signal intensity.
Figure 2.
Tumor satellite lesion displays hyperintense on NOE mediated CEST.
Tumor satellite of a glioblastoma subcortical temporal right in a 67 year old woman. The satellite presents a clear enhancement on CE-T1 (arrow in A) and barely displays on the T2-weighted image (arrow in B). In contrast, the satellite displays clearly hyperintense on CEST based on MTRasym (C) and matches with the area of contrast enhancement on the CE-T1 image (A). Furthermore also CSF in lateral ventricles and cerebral sulci displays hyperintense on MTRasym.
Table 1.
Qualitative analyses of NOE-mediated CEST contrast on 3D co-registered data.
Figure 3.
Regions of interest (ROI) selection for spectral analysis and MTRasym quantification.
Left occipital glioblastoma of a 79 year old patient, CE-T1 (A) and T2-weighted images (B) with color coded ROIs: CE-T1 tumor, isolated CEST HIR within CE-T1 margins, tumor necrosis, PTCH within T2 edema margins, CSF and CLNAWM. CEST contrast based on MTRasym (C): Same ROIs illustrated in green for improved visualization. Z-spectrum (D) and asymmetry analysis (E) shown. Analyses of Z-spectra reveals that a decrease of NOE upfield effects at −3.3 ppm causes the hyperintense MTRasym contrast in the tumor regions, while no clear APT peak around +3.3 ppm could be identified in any of the analyzed tissues. Even though MTRasym shows high intensities both in CSF and isolated CEST HIR within CE-T1 tumor, Z-spectrum analysis reveals that the underlying asymmetry has a different origin: no saturation transfer is apparent in CSF at ±3.3 ppm (D black line) while in tumor regions (D dark green, dark blue and light blue lines) MTRasym = 0 reflects that NOE signals (−3.3 ppm) and saturation transfer effects at the opposite side of the Z-spectrum (+3.3 ppm) are of equal size. Furthermore the width of the Z-spectrum of CSF is decreased due to the longer T2 relaxation time.
Figure 4.
Boxplots of MTRAsym quantification from regions of interest (ROI) analysis over all glioblastoma patients.
Boxplots of mean MTRAsym values on CEST contrast over all patients (N = 12). Overall mean MTRasym (red stars) and outliers (red crosses) are additionally illustrated. MTRasym values in all tumor areas (CE-T1 tumor, isolated CEST HIR in CE-T1 tumor, tumor necrosis) and CSF are significantly higher than in CLNAWM (p<0.001). Average signal intensity in PTCH within T2 edema margins is significantly higher (p<0.001) than in CLNAWM and significantly lower (p = 0.015) than in CE-T1 tumor and tumor necrosis (p<0.001). The whiskers of the boxplot for isolated CEST HIR indicate a high variance within this group, which is due to smaller ROI size and the fact that the isolated CEST HIR were visually selected relative to surrounding signal intensity in CE-T1 tumor.