Study Of Lower Extremity Deep Vein Thrombosis MR Imaging Based On LIBRE Fat Suppression Pulse

Background and projective: Deep vein thrombosis(DVT)often occurs in the lower extremities.It is a common disease in clinical practice,characterized by insidiousness and high incidence and can cause fatal pulmonary embolism.Accurate thrombus staging is the key to DVT treatment,and DVT patients at different stages usually adopt different treatment methods.Black-blood thrombus imaging(BTI)technique can accurately identify DVT and provide additional information for thrombus staging.However,non-uniform fat suppression of BTI with conventional fat saturation preparation is obvious due to the field inhomogeneities and large field of view(FOV)imaging,which can affect the accuracy of detecting and staging of thrombus.To address this issue,a field inhomogeneity insensitive BTI technique was developed by incorporating LIBRE pulses for fat free and large FOV thrombus imaging.Methods: The study was carried out in two steps.First,in the study of LIBRE-vf-FSE,numerical simulation was conducted to optimize the parameters of LIBRE pulses,including the flip angle,pulse duration,and frequency offset of the proposed LIBRE-vf-FSE sequence and evaluated the sensitivity of different LIBRE parameters to B0 and B1 field inhomogeneities.The feasibility of fat suppression in LIBRE-vf-FSE was verified by comparing with Fat Sat(Fat Saturation)and WE(Water Excitation)in phantom and healthy volunteer experiments.Second,LIBRE with optimized parameters was incorpoirated into the BTI sequence to achieve uniform fat suppression in DVT imaging.Fat suppression effect of LIBRE-BTI was verified in healthy volunteer experiments and compared with Fat Sat and WE methods.Then the LIBRE parameters with the best fat suppression effect were selected.Finally,LIBRE pulse with optimal parameter was used in the DVT imaging with LIBREBTI.And WE method were also performed in BTI for comparison.Signal-to-noise ratio(SNR)of fat was used to evaluate the level of fat suppression,standard deviation(SD)of fat SNR was used to evaluate the uniformity of fat suppression and contrast-to-noise ratio(CNR)was used to evaluate the contrast between tissues.Results: In the study of LIBRE-vf-FSE,the three groups of LIBRE parameters optimized by numerical simulation showed more uniform fat suppression than conventional Fat Sat and WE in both phantom and volunteer experiments.LIBRE(1.10 ms,360 Hz and 60°)worked best in the three LIBRE parameters.Average oil SNRs obtained by LIBRE(1.10 ms,360 Hz,and 60°),WE,and Fat Sat were(180.1 vs.280.2 vs.811.2)in phantom experiments,and average fat SNRs and SDs in legs obtained by LIBRE(1.10 ms,360 Hz,and 60°),WE,and Fat Sat were(85.1 vs.105.0 vs.105.1)and(22.4 vs.27.4 vs.56.4)in vivo experiments,respectively.In the volunteer experiments of LIBRE-BTI,LIBRE(1.20 ms,380 Hz and 70°)obtained the best fat suppression effect.The fat SNRs and SDs obtained by LIBRE(1.20 ms,380 Hz and 70°),Fat Sat and WE in healthy volunteer experiments were(175.5 vs.271.0vs.405.5),(50.3 vs.101.4 vs.171.1).In the DVT patient experiments of LIBRE-BTI,LIBRE achieved more complete fat suppression(fat SNR: 99.7 vs.140.8),more uniform fat suppression(fat SD: 47.2 vs.68.1)and higher muscle-to-fat CNR(32.1 vs.5.5)than WE.Conclusion: The LIBRE-BTI imaging sequence of lower extremity deep vein thrombosis based on LIBRE fat suppression pulses proposed in this study not only realized the visualization of vein thrombosis,but also achieves a more uniform suppression of lower extremity fat signals,thus has great potential for the accurate staging of DVT.