Study On The Optimization Of BOLD Magnetic Resonance Ischemia-reactive Hyperemia Model Of Skeletal Muscle Of Calf

Purpose:prospective study to find out the reasons why the BOLD time signal intensity curve of calf muscle presented a variety of trends in ischemic period of Ischemia-reactive hyperemia model of the calf,by using ultrasonic spectrum doppler monitoring popliteal blood flow to ensure the accuracy and effectiveness of the ischemic model,and to optimize the ischemic hyperemia model.Method: This study was approved by the ethics committee and all subjects gave informed consent.18 healthy male volunteers(13 males,5 females;age:26.4±1.8 years[mean±standard deviation])uderwent BOLD-MRI of the calf muscles.the ischemia-reactive hyperemia model of the lower leg was established by applying an automatic pneumatic tourniquet to the middle of the thigh to pressurize and occlude the femoral artery.The study included two different models:P1 model(The tourniquet pressure was 50 mmHg higher than that of the upper brachial artery)and P2 model(The tourniquet pressure was set to the pressure of popliteal artery blood flow completely interrupted).In the P2 model,the pressure of the tourniquet was determined by ultrasonic doppler examination of the popliteal artery blood flow.Each volunteer had a half-hour interval between BOLD scans of the two models.The 3.0T superconducting magnetic resonance scanner(Verio,Siemens,Erlangen,Germany)was used in the experiment.The 3d-t1 wi anatomic image used fast small-angle excitation sequence,and the BOLD functional image used single-shot single-echo gradient echo plane echo imaging(SS-GRE-EPI)sequence.BOLD signal strength of tibial anterior,tibial posterior,soleus,gastrocnemius,and peroneus was measured and BOLD time signal curve was obtained.Five parameters(MIV:minimum value in Ischemia period;PHV:MEV:medium value in ischemia period;EV;end value in hyperaemia period which is the average BOLD signal of the last five time points;TTP:time to peak,from tourniquet deflation to BOLD peak signal)were measured.The cox-stuart trend test was used to analyze the trend of ischemic curve.Paired t-test and non-parametric test were used to analyze the parameter differences of BOLD time signal curve under the same P1 and P2 model of muscle,and one-way anova or non-parametric test were used to analyze the parameter differences between muscles.Result:1.In P1 model,popliteal artery ultrasound monitoring showed that the blood supply to skeletal muscles of the lower legs decreased but did not interrupt at this time.BOLD time signal curve of ischemia showed a significant downward trend,which was tested by cox-stuart trend,P < 0.05,which was statistically significant.In the P2 model,ultrasound monitoring showed that the popliteal arterial blood flow was zero and the blood supply to the skeletal muscles of calf was completely interrupted.In this model,the BOLD time signal curve of ischemic phase presented a variety of trends,with an upward trend,a downward trend and no trend of fluctuation near the baseline.All the trends were tested by cox-stuart trend test,and P < 0.05 was considered statistically significant.Among the various ischemic trends in P2 model,the rising trend accounts for the highest proportion(55.6%),the declining trend(24.4%)and the non-trend(20%).Soleus muscle showed an upward trend of 77.8%,accounting for the highest proportion.2.In P1 model,MEV and MIV of 5 muscles measured in calf skeletal muscle were significantly lower than in P2 model.The TTP of the tibial anterior muscle in P1 model(24.39±13.33 s)was lower than that in P2 model(33.67±10.12 s),and the EV in P1 model(0.0442±0.0214)was higher than that in P2 model(0.0107±0.0184).There was no significant difference in PHV;The PHV of tibial posterior muscle was lower in P1 model(0.0979±0.0471)than in P2 model(0.1382±0.0482),and EV was higher in P1 model(0.0279±0.0293)than in P2 model(0.0096±0.0179),with no significant difference in TTP;The PHV of gastrocnemius muscle in P1 model(0.0729±0.0424)was lower than that in P2 model(0.1084±0.0438),and there was no significant difference in EV and TTP;The EV of soleus muscle in P1 model(0.0645±0.0764)was higher than that in P2 model(0.0206±0.0336),and there was no significant difference in TTP and PHV;There was no significant difference in PHV,EV and TTP of peroneal muscle.The above differences were statistically significant,P < 0.05.3.In P1 model,BOLD time signal intensity curve parameters showed no significant difference between the five calf muscle groups.In the P2 model,there was a difference in PHV between the five muscles,and no significant difference in the residual parameters.4.Popliteal artery FV,PS,TAMx,TAMn and PI in P1 model were significantly lower than the values of each parameter when the tourniquet was not pressurized,P < 0.05,which was statistically significant..Popliteal artery blood flow parameters and BOLD time signal curve parameters of some muscles have a linear correlation,but there is no significant regularity.Conclusion: The P1 model was superior to the P2 model after comparing the two models of ischemia-reactive congestion in the calf.In P1 model,where the tourniquet pressure was 50 mmHg higher than that of the ipsilateral brachial artery,the arterial blood supply to the lower legs decreased but was not interrupted.In this model,the BOLD time signal intensity curve showed a downward trend in the ischemic phase and was below the baseline;During the hyperemia phase,the BOLD signal rose to a peak and then fell back to near the baseline.The trend of BOLD time signal curve in this model conforms to the perfusion state of skeletal muscle in the lower leg at this time,with good repeatability.When BOLD magnetic resonance is used to study PAOD vascular reserve capacity,it can more accurately reflect the vascular reserve capacity of the lower leg,which is better than the P2 model.In the P2 model,where the tourniquet pressure was high enough to completely interrupt the arterial blood supply to the calf tissue,the BOLD time signal intensity curve of ischemic phase showed multiple trends,which did not conform to the perfusion state of the calf tissue and did not reflect the vascular reserve capacity at this time.Currently,the P2 model is not suitable for BOLD magnetic resonance to evaluate PAOD's vascular reserve capacity in the calf.In P2 model,BOLD signal in ischemic phase presented multiple trends,which might be caused by the interruption of blood supply to the calf and the change of the calf tissue from aerobic metabolism to anaerobic metabolism.The specific reasons and mechanism were still unclear.