Achievement Of Dura Imaging Based On Non-contrast-enhanced Fast Field Echo Sequence

Part Ⅰ: Achievement of dura imaging based on dual-echo FFE sequence and parameters optimization Objective: Based on dual-echo Fast Field Echo（dFFE）sequence,the weighted subtraction of the front and back two echoes was performed to explore the influence of different MR scanning parameters on the display of dura,in order to achieve non-contrast dura imaging and obtain the optimal scan parameters.Methods: Forty-four healthy volunteers are recruited,including 15 males and 29 females,aged 21-28,with a median age of 24.All subjects are randomly divided into two groups: A（22 subjects）and B（22 subjects）,and receive axial dFFE sequence wholebrain imaging under different scanning parameters.Each subject in group A undergoes 7dFFE sequence scans: three different number of signal averaged（NSA）are performed first,the NSA is set to 4,3 and 2 times respectively;then the NSA is fixed to 3,and four dFFE sequences with different second echo times（SecTE）are performed,which are set to 5 ms,10 ms,12 ms,and 15 ms.While each subject in group B undergoes four dFFE scans: different flip angles（FA）are performed in turn,which are set to 5 °,10 °,20 °and30 ° respectively.The remaining parameters of dFFE sequence in the same group are consistent except for the above parameters.The dFFE sequence contains two echo times（TEs）,through different image subtraction weighting factors（ISWFs）,the front and back two echo images are subtracted to obtain the final target image.The signal intensity values of dura and adjacent skull inner table in all dFFE images from 44 subjects are recorded,and the Signal Intensity Ratio（SIR）and Contrast-to-Noise Ratio（CNR）are calculated;Use one-way ANOVA for those who conform to the normal distribution in the obtained quantitative data,and use Friedman rank test for those who do not.Two imaging physicians used the blind method,and the junior physician first evaluated,the senior physician rechecked mode to subjectively score the dura display degree,artifacts,and overall image quality of the dFFE image,using the Likert five-point score scale,and the scoring results are evaluated by Friedman’s rank test.Results: The dura morphology can be visible almost continuously on dFFE images.Compared with other ISWFs,the SIR and CNR values of the images obtained with the ISWF of 1.55 are the highest（P < 0.05）;There is no statistical difference in CNR values between different NSA,FA and SecTE（P > 0.05）;The SIR values increase with the SecTE（P < 0.01）,when FA is 10°～20°,SIR is higher（P < 0.01）.The subjective score shows that different NSAs have no significant effect on dura visualization,artifacts and overall image quality（P > 0.1）,while the scores of different FA in three aspects are statistically different,and the image score is gradually improving with the increase of FA.The average subjective score of dFFE image under different parameter is about 3points.Comprehensively,with the ISWF of 1.55,NSA of three,SecTE of 10 ms and above,FA of 10°～20°,the display effect of dura is best.Conclusion: The dura in FFE sequence with dual-echo subtraction is continuous,which achieves the dura imaging in FFE sequence.However,the average score of the overall image is medium,the noise particles are slightly large.Part Ⅱ: Achievement of dura imaging with FFE sequence combined with radial K-space encoding technology and clinical validationObjective: To further improve the image quality and signal-to-noise ratio,and reduce the image graininess,based on the scan parameters obtained in the first part,FFE sequence was combined with Radial K-space encoding（rFFE）in order to achieve dura imaging,while improving the contrast between tissues and the display degree of normal dura morphology/signal.And preliminarily verify the visualization of abnormal dural changes（thickened or increased signal intensity）.Methods: 5 volunteers undergo parameter-adjusted rFFE sequence brain local scan,then 31 patients are recruited prospectively（head enhanced-examination is performed with Philips 3.0T MRI,at Shengjing Hospital affiliated to China Medical University from December 2021 to December 2022）,including 11 males,20 females,aged 4-81 with a median age of 48.All 31 patients undergo routine head MR examinations（including axial T₁WI,T₂WI,FLAIR and T₁WI sequence with contrast-agent enhanced）and rFFE sequence,in which 26 patients undergo rFFE scanning before enhancement and 5 patients undergo rFFE scanning after enhancement.An experienced radiologist observes the dural morphology and signal performance in rFFE images（including before and after enhancement）of 31 subjects,and compares rFFE with conventional MR scan sequences.The dural display in the lesion layer from the pre-enhanced rFFE images and the enhanced T₁WI images,is divided into two categories: visible and invisible,the results are expressed by the number of cases [n（%）],and tested by Fisher’s exact probability method.Results: The dura morphology of all patients is clear and continuous on rFFE images,better than the plain MR images（100% and 23.08%,respectively）.The observation of abnormal changes of dura in rFFE sequence is comparable to that of enhanced T₁WI sequence（P = 0.103）.The involved dura was in a larger range and the signal is higher in post-contrast rFFE images than that in enhanced T₁WI sequence.Conclusion: FFE sequence has achieved non-enhanced dura imaging and improvement of image quality at the same time,after combining with radial K-space encoding technology,the visualization of abnormal changes of dura is consistent with that of enhanced T₁WI sequence,which has certain clinical application value.