Multi-modal Medical Imaging Methods In Assessment And Prediction Of Lower Limb Ischemic Disease

Part Ⅰ: Discussing of Cuff-Induced Skeletal Muscle Microvascular Perfusion of Lower Extremity by MR multiple sequencesObjective The purpose of this study was to evaluate the skeletal muscle microvascular perfusion changes in the lower extremities under cuff compression paradigm with BOLD、IVIM and ASL MRI techniques.Materials and Methods Fifteen healthy young volunteers（seven men and eight women;mean age 21 years）underwent ASL,BOLD and IVIM MR imaging,and transcutaneous oxygen pressure（TcPO₂）measurement of the lower extremity at baseline,under cuff compression with pressures of 20 mmHg and 40 mmHg above systolic pressure,and at recovery.All the MRI measurements were carried out on a 3.0 T MRI unit（HDxt,GE Healthcare）with a cardiac coil.Results Blood flow,T2^* and f in the experimental side showed significant differences among the 4 statuses in all muscle groups（all P < 0.05）except f in the anterior muscle group（P = 0.236）.Whether there existed significant differences or not,blood flow and T2^* values in the experimental side gradually decreased under 20-mmHg and 40-mmHg cuff compression statuses,while f showed an increase tendency.Most muscle groups exhibited significant differences in parameter values between experimental and control sides when the cuff compression pressure was lifted to 40 mmHg above systolic pressure.Blood flow and T2^* showed significant positive correlation with TcPO₂ measurements（ρ = 0.465 [P = 0.001] and ρ = 0.522 [P < 0.001],respectively）,while f showed significant negative correlation with TcPO₂ measurement（ρ =-0.351[P = 0.018]）.Conclusions Multi-parametric MR techniques including ASL,BOLD and IVIM provide useful and complementary information about tissue perfusion in the lower extremity of healthy humans.Perfusion-related metrics derived from these techniques correlates with TcPO₂ measurements.Part Ⅱ: T2 and T2^* mapping of skeletal muscles in lower extremities in healthy volunteers and patients with peripheral arterial occlusive diseaseObjective The purpose of this study was to investigate the feasibility of magnetic resonance imaging T2 and T2^*mapping in calf muscles of healthy volunteers and patients with lower extremity atherosclerotic occlusive disease（LEAOD）.Materials and Methods The prospective study was approved by the local ethics committee.Sixteen healthy young subjects,ten age-matched healthy elderly subjects and sixteen patients with LEAOD were enrolled in this study.Axial T2-mapping and T2^*-mapping sequences were performed for bilateral calves in the mid-calf level,which were conducted on a 3.0 T MRI with a cardiac coil.Regions of interest（ROIs）were drawn manually in the anterior（ant）,lateral（lat）,gastrocnemius（gas）and soleus（sol）muscles on GE ADW4.4 workstation.Results The T2 value of the tibialis anterior muscle of healthy volunteers was significantly lower than that of other muscles（P<0.0001）.T2 values showed significant differences between healthy young and elder group in all muscle groups except the gastrocnemius muscle（all P<0.0125）.The T2 value of gastrocnemius muscle was significantly positively correlated with BMI in healthy volunteers（r = 0.497,P = 0.010）.The T2 values of soleus and gastrocnemius muscles in LEAOD patients were significantly higher than those in elderly volunteers（both P=0.006）,and the T2^* values of each muscle group were significantly lower than those in elderly subjects（both P<0.0125）.Conclusions T2 and T2^* mapping can evaluate the microscopic characteristics of the lower extremity muscles in a noninvasive and objective way,and may add value in the diagnosis and prognosis of LEAOD when combined with conventional imaging and clinical examinations.Part Ⅲ: Using different stimulation patterns to explore changes in skeletal muscle oxygenation levels dependent on MRI signalsObjective To compare the three commonly used paradigms in skeletal BOLD MRI: gas inhalation,cuff compression induced ischemia and postocclusive reactive hyperemia,and exercise.Materials and Methods In this prospective study,12 young（mean age,22 years ± 0.9）and 10 elderly（mean age,58 years ± 5.0）healthy subjects underwent 3.0-T BOLD MRI under the three paradigms.Signal intensity time curves were generated and quantitative parameters were calculated from the curves.Meanwhile,stress transcutaneous oxygen pressure（Tc PO₂）measurements were obtained and utilized as comparison to BOLD MRI.Measurement reproducibility was assessed with intraclass correlation coefficients（ICCs）.Differences in the maximal BOLD signal variation,the correlation with Tc PO₂,and the age-related change between paradigms were statistically analyzed.Results Ischemia and reactive hyperemia paradigm derived Min_Ischemiaand Max_Hyperemiashowed the highest interobserver reproducibility（ICC,0.993 and 0.985）and interscan reproducibility（ICC,0.920 and 0.903）.The Friedman test indicated significant differences in BOLD variation amplitudes of different paradigms in the anterior muscle group（P < 0.0001）.The plantar dorsiflexion exercise paradigm elicited the largest BOLD T2^* variation（15.48% ± 10.56%）,followed by ischemia（8.30% ± 6.33%）.Negligible to weak changes were observed during gas inhalation.Correlations with Tc PO₂ measurements were found in the ischemic phase（r = 0.966,P < 0.001）and in the postexercise phase（r =-0.936;P < 0.001）.Min_Ischemia,Max_Hyperemia,Max_Postexercise,and Slope_Postexerciseshowed significant differences between young and elderly subject groups（all P < 0.01）.Conclusions Ischemia and reactive hyperemia have superior reproducibility,and exercise could induce the largest BOLD signal variation.Key parameters from the two paradigms show age-related differences.These two paradigms may be preferred in further applications.