3.0T MRI Characterization Of Brain Metastases And Its Distinction With High-Grade Gliomas

Objective:To investigate the characterization of brain metastases in different MRI sequences including susceptibility-weighted imaging(SWI),difffusion-weighted imaging(DWI), perfusion weighted imaging(PWI) and two-dimension proton MR spectroscopy(2D ~1H-MRS).To distinguish between brain metastases and high-grade gliomas(gradeⅢand gradeⅣ) on the basis of differences in vascularity,water self-diffusion, microarchitecture and metabolite levels in the tumor and peritumoral regions.Methods:MRI examinations were performed using a 3.0T MR scanner(Signa EXCITEⅡ; GE Medical Systems).In 95 cases with brain metastases,T2~*WI,SWI and contrast-enhanced(CE) T1WI were performed.In 55 cases with brain metastases and 33 cases with high-grade gliomas,DWI,DTI,PWI,CE T1WI and 2D ~1H-MRS were performed.1.The conventional MRI examinationThe protocol consisted of axial T1-weighted(TR/TE=500/8 ms) spin-echo(SE), T2-weighted(4500/102 ms) fast SE,and fluid-attenuated inversion-recovery(FLAIR) (TR/TE=9000/120 ms) with 6 mm slice thickness,240 mm field of view(FOV) and 320×224 matrix.2.T2~*WI and SWI2.1 T2~*WI was obtained using the following parameters:TR/TE=520/20ms;flip angle,20 degrees;matrix,512×512;FOV,256×256 mm;20 slices;slice thickness/gap,6 mm/1mm.Acquisition time was 2 minutes and 14 seconds.2.2 SWI was obtained as a fully velocity-compensated three-dimensional gradient echo sequence using the following parameters:TR/TE=23/13ms;flip angle,20 degrees;matrix,512×448;field of view(FOV),240×240 mm.Acquisition time was 6 minutes and 28 seconds.3.DWI and DTI3.1 DWI was obtained using an axial echo-planar SE sequence:TR/TE= 5000/65 ms;one average;6 mm slice thickness;diffusion gradient encoding in 3 orthogonal directions;b=0,1000 s/mm~2;240 mm FOV;160×192 matrix.Acquisition time was 1 minute.Postprocessing of apparent diffusion coefficient(ADC) maps was performed using standard software on a workstation(Functool 3.1 software;GE Healthcare).In brief,regions of interest(ROIs) were drawn manually in the enhancing tumor, necrosis,peritumoral region and edema outside of peritumoral regionin CE T1WI based ADC images.The ADC value was calculated automatically by the Functool 3.1 software.For normalizing ADC levels,an ADC ratio was calculated as the quotient of the ADC values of the enhancing region and those of an ROI of the same size in the contralateral normal white matter.3.2 DTI was obtained using an axial echo-planar(EPI) spin echo(SE) sequence: TR/TE=6000/minimum ms;5 mm slice thickness;no gap;diffusion gradient encoding in 3 orthogonal directions;b=0,1000 s/mm~2;240 mm FOV;128×128 matrix;NEX=2.Acquisition time was 2 minutes and 48 seconds.Postprocessing was perforned using standard DTI software on a workstation (Functool 3.1 software;GE Healthcare).ROIs were carried over the DWI postprocessing.The ADC/ FA values were calculated automatically.ADC values, relative ADC(rADC),fractional anisotropy(FA) value and relative FA(rFA) were calculated and recorded.4.PWI and CE T1WIFollowing institutional protocol,SE-EPI PWI(TR/TE=1900/ 80ms;slice thickness 6mm;matrix 128×128) was performed using a 5ml/s bolus injection of gadopentetate dimeglumine(Magnevist;Bayer HealthCare Pharmaceuticals) (0.2mmol/kg) and was coregistered with delayed postgadolinium T1-weighted imaging.Postprocessing was perforned using a perfusion processing software package, which generates color cerebral blood volume(CBV) and mean transit-time(MTT) maps.ROIs were selected within the region of maximal CBV for three times and recorded the average CBV,relative CBV(rCBV),MTT and relative MTT(rMTT) values.CE T1WI was then performed in axial,coronal and sagital planes.5.2D ~1H-MRS2D ~1H-MRS was always performed based on CE T1WI to insure accurate voxel placement since the enhanced umor,low intensity necrosis and edema can be distinguished easily.The following parameters were used:a point-resolved spectroscopy sequence (PRESS);TR/TE=1500/144 ms;16 cm FOV;160×160 matrix;10-mm slice thickness;acquisition,1 average;scanning time,4 minutes and 20 seconds.A volume of interest(VOI) was placed on axial T1-weighted images corresponding to the contrast-enhancing area.Automatic prescanning was performed before the spectroscopic scan to ensure adequate water suppression.The full-width half-maximum was kept under 15 Hz and water saturation between 95%and 99%.The details of the postprocessing used for MR spectroscopy was as follows.Within the obtained VOI,separate 1cm×1cm×1cm voxels were individually placed in the enhancing tumor and peritumoral region.The following metabolite peaks were indentified:N-acetylaspartate(NAA) at 2.02-ppm,choline-containing compounds (Cho) at 3.22-ppm,(phospho-) creatine(Cr) at 3.01-ppm,lipid-containing compounds (Lip) in the range of 0.9-1.3 ppm,and lactate(Lac) at 1.35-ppm(an invertedβ-methyl doublet).Metabolite values were calculated automatically from the area under each metabolite peak by the Functool 3.1 software.Metabolite ratios(NAA/Cr,Cho/Cr, Lip/Cr,Lac/Cr,and Cho/NAA) were calculated manually.6.Statistical analysisStatistical analysis was performed using SPSS for Windows release 13.0(SPSS Inc, Chicago,IL,USA).The number of hemorrhage BMs and the grading score between SWI and T2~*WI and different parameters between the brain metastases group and high-grade gliomas group were compared using an unpaired two-tailed Student t test. The level of significance was set at p＜0.05.Results:1.Results from T2~*WI and SWI1.1 SWI could detect 79.2%of all brain metastases,and 100%of brain metastases with intratumoral hemorrhage and/or peritumoral edema.1.2 To detect intratumoral hemorrhage the sensitivity of SWI was significantly higher than T2~*WI,which just detected 69.6%of hemorrhage detected on SWI.2.Results from DWI and DTI2.1 The ADC value of the peritumoral region of high-grade gliomas was significantly higher than that of brain metastases;while the ADC values of enhanced tumor,necrosis and edema outside of the peritumoral region were not significantly different between brain metastases and high-grade gliomas.2.2 The FA value of the enhancing high-grade gliomas was significantly higher than that of brain metastases.3.Results from PWIThe maximal rCBV of enhancing tumors and the peritumoral region of high-grade gliomas were significantly higher than that of brain metastases;while the rMTT was not statistically different between brain metastases and high-grade gliomas.4.Results from 2D ~1H-MRS4.1 The intratumoral Cho/Cr,Cho/NAA,NAA/Cr ratios in brain metastases did not differ statistically from that of high-grade gliomas.4.2 The peritumoral Cho/Cr and Cho/NAA ratios in brain metastases were statistically different from that of high-grade gliomas.The ratios for the high-grade gliomas were significantly higher.The NAA/Cr and Lac/Cr ratios between brain metastases and high-grade gliomas were not statistically different.Conclusion:1.SWI can detect most brain metastases without injection of contrast,and it is even more sensitive in dectecting metastases with intratumoral hemorrhage and peritumoral edema.2.The parameters of DWI,DTI,PWI and 2D ~1H-MRS of the peritumoral region are significantly different between brain metastases and high-grade gliomas,and can be used to demonstrate differences in solitary metastases and high-grade gliomas.3.We strongly suggest the use of a combination of the investigated diagnostic procedures for the peritumoral region to distinguish brain metastases and high-grade gliomas.