Delayed Contrast Enhanced MRI In The Diagnosis Of Brain Metastasis Of Lung Cancer

Objective:The purpose of this study was to compare the imaging with difference delayed phases after gadolinium injection in MRI for brain metastases of lung cancer,and to evaluate an optimal sequence of the MRI.Materials and Methods: This is a prospectie study about patients with brain metastases of lung cancer underwent a brain MRI using 3.0-T scanner by Philips from February 2019 to July 2019 in our hospital.After Gadolinium(0.2 mmol/Kg)injection,they performed a TIWI TSE sequence scan with no delayed phase(0-min delayed phase,D0).The same sequence scan was performed after Gadolinium injection with 5-min delayed phase(D5),8-min delayed phase(D8),12-min delayed phase(D12)and 15-min delayed phase(D15)respectively.The number of lung metastatic lesions of the brain in the scan with various delayed phase has been counted to choose the optimal sequence.The above process was done by 2 radiologists who were blinded to the results of each other.Then the size of lesions scanned by the best sequence MRI has been measured.The parenchymal structure(including the contrast enhancement)score,margin score,and the total score of each lesion was evaluated.At the same time,the signal intensity of all lesions scanned with different delayed phase sequence was measured,and the values of CE(Contrast Enhancement),CNR(Contrast to Noise Ratio),CER(Contrast Enhanced Ratio)and CBR(Contrast to Brain Ratio)of each lesion were calculated.Friedman test and paired t-test was used to analyse above data by SPSS 17.0 software.P<0.05 was consider statistically significant.Results:(1)A total of 182 cases of brain metastases of lung cancer were found.D0 scan detected 144 leisons;D5 scan detected 177 leisons;D8 scan detected 182 leisons;D12 and D15 scan also detected 182 leisons.We found more 33 lesions in D5 scan compared with D0 scan,which were all less than 7 mm in diameter,accounting for 18.1%.There were 5 new detected lesions in D8 scan compared with D5 scan,which were less than 5 mm in diameter,accounting for 2.74%.No new lesions were detected in D12 and D15 scan.(2)To find the best scan sequence of each lesion,the optimal delayed phase scan imaging of each lesion has been evaluated.The number(ratio)of lesion with the best imaging of different delayed phase including D0,D5,D8,D12 and D15 as the optimal phase was 1(0.55%),19(10.44%),30(17.03%),35(19.78%)and 97(53.30%),respectively.(3)It was considered that there were statistical differences in the parenchymal structure(including the contrast enhancement)score,margin score,the total score,CE,CNR,CER and CBR in the brain metastases of lung cancer among different delayed phases scan(all P < 0.001).The t-test results show that there were also statistical differences between D0 scan and the other delayed phases scan in parenchymal structure(including the contrast enhancement)score,margin score,the total score,CNR and CBR(all P < 0.05).It has statistical differences between D5 and D12 scan,D5 and D15 scan(P=0.015,P=0.09,respectively)in the parenchymal structure(including the contrast enhancement)score.The total scores showed statistical difference between D5 and D15 scan(P=0.05).The contrast enhancement(CE)showed statistically significant differences between D5 and D8,D5 and D12,D5 and D15,D8 and D15 scan(all P < 0.001).CER also showed statistical differences among different delayed phases scan(all P < 0.05).CBR showed statistical difference only between D5 and D12 scan(P=0.005).Conclusion:Compared the imaging quality of MRI with various delayed phase sequence for brain metastasis of lung cancer,we found that scan with any delayed phase was better than no delayed phase in terms of parenchymal structure(including contrast enhancement)score,margin score,the total score,CE,CNR,CER and CBR.The delayed time of 8 minutes or more was more conducive to display the micro-lesions(diameter less than 7 mm).Therefore,we recommend that MRI delayed enhancement scan should be routinely performed in the first-diagnosis of lung cancer to identify the stage,and the delayed phase should be at least 8 minutes,so as to improve the detection efficiency of brain metastasis.