Perfusion and diffusion MRI combined with ¹¹C-methionine PET in the preoperative evaluation of suspected adult low-grade gliomas

Abstract

Perfusion and diffusion magnetic resonance imaging (pMRI, dMRI) are valuable diagnostic tools for assessing brain tumors in the clinical setting. The aim of this study was to determine the correlation of pMRI and dMRI with ¹¹C-methionine positron emission tomography (MET PET) in suspected low-grade gliomas (LGG) prior to surgery. Twenty-four adults with suspected LGG were enrolled in an observational study and examined by MET PET, pMRI and dMRI. Histological tumor diagnosis was confirmed in 23/24 patients (18 gliomas grade II, 5 gliomas grade III). The maximum relative cerebral blood volume (rCBV(max)) and the minimum mean diffusivity (MD(min)) were measured in tumor areas with highest MET uptake (hotspot) on PET by using automated co-registration of MRI and PET scans. A clearly defined hotspot on PET was present in all 23 tumors. Regions with rCBV(max) corresponded with hotspot regions in all tumors, regions with MD(min) corresponded with hotspot regions in 20/23 tumors. The correlation between rCBV(max) (r = 0.19, P = 0.38) and MD(min) (r = -0.41, P = 0.053) with MET uptake in the hotspot was not statistically significant. Taken into account the difficulties of measuring perfusion abnormalities in non-enhancing gliomas, this study demonstrates that co-registered MET PET and pMRI facilitates the identification of regions with rCBV(max). Furthermore, the lack of a clear positive correlation between tumor metabolism in terms of MET uptake and tumor vascularity measured as rCBV(max) suggests that combined pMRI/PET provides complementary baseline imaging data in these tumors.

Fig. 1

a Box plots showing the distribution of rCBV_max ratios for the entire sample (n = 24). b Scatter plot showing the correlation between maximum MET uptake (HS/cortex ratio) and rCBV_max values in PET hotspot regions in all tumor samples (n = 23). Straight line, regression line, dotted lined: 95 % CI

Fig. 2

a Box plots showing the distribution of MD_min values for the entire sample (n = 24). b Scatter plot showing the correlation between maximum MET uptake (HS/cortex ratio) and MD_min values (×10⁻³ mm²/s) in PET hotspot regions in all tumor samples (n = 23). Straight line, regression line, dotted lined: 95 % CI

Fig. 3

Patient 8. Preoperative MET PET and MRI of a right-sided frontal oligodendroglioma grade II in a 31-year-old female. a MET PET shows the hotspot region of the tumor. b T2-weighted FLAIR MRI shows a high signal intensity tumor. c T1-weighted contrast-enhanced MRI shows minimal contrast enhancement in the tumor area. d DSC perfusion MRI with rCBV color map shows high perfusion in the tumor area. e DSC perfusion MRI with rCBV grey-scale map shows high perfusion in the region corresponding to the PET hotspot. The ROIs in the tumor and in the contralateral normal appearing white matter are marked. f dMRI where the MD_min value in the region corresponding to the PET hotspot is lower than MD in the medial portion of the tumor (but minimally increased compared to normal appearing contralateral white matter)