A Magnetic Resonance Imaging Study Of Hemodynamics Of Pulmonary Artery And Right Ventricle Diastolic Function In Patients With Repaired Tetralogy Of Fallot At 3.0 Tesla

Objective:1,To validate the accuracy and stability of 3T PC-MRI to measure flow velocity and optimize the value and direction of velocity encoding in a flow phantom in order to supply experiment support for clinical application.2,To compare pulmonary reguigitation(PR) measured by 3T PC-MRI with data provided by echocardiography and evaluate the relationship between PR and RV volume and RV systolic function.3,To identify E-and A-wave flow patterns across the tricusid valve in TOF following repair using 3T PC-MRI and compared the results with data provided by echocardiography and correlate them with measurements of RV volume.Materials and methods1,A flow phantow was positioned inside the sanner with the direction of flow parallel to the long axis of the bore.experiments were performed using a 3.0 Tesla whole-body MR scanner and a heart coil with 8 channel.Routine transvers FSE T2WI and transvers Fastcine PC squenses were performed.The acquisition parameters for FastCine PC sequense were frequently used in clinical practice(TR/TE=auto selected minimun/min full;flip angle:20°,FOV:200×200 mm,matrix:256×256,ETL:1,nex:1,bandwidth:31.25khzo Slice thickness: 5.0 mm,number of cardiac phases of reconstruct:30).The heart rate of a healthy volunteer were accepted for simulation(mean:73 beat/min).First group:The flow rate was 2 ml/s and the velocity encoding(Venc) was 100 cm/s.The direction of Venc was choiced for ALL,Slice,AP,RL and SI respectively.Second group:flow rate was 2 ml/s;the direction of Venc was Slice.Venc increased gradually from 20 cm/s to 200cm/s by 20 cm/s.10 groups of data were acqired.Third group:Venc 150 cm/s,the direction of Venc was Slice.The flow rate was increased gradually from 1 ml/s to 5 ml/s by 0.5 cm/s and o ml/s was also choiced for the flow rate sequentialy.10 group of data were acqired.2,we studied 42 patients(16 female,26 male;mean age 18.7 years,range 10-51 years) after surgical correction of TOF who performed cardiac magnetic resonance imaging and echocardiography within a month.The main sequences and scan parameters inclued:cine Fiesta(TR/TE Minimum/Minimum,flip angle 45°, bandwidth 125 khz,FOV 35×35 cm,matrix size 160×224,Slice thickness 8.0 mm, Slice gap 0 mm,nex 1,phase pFOV 0.75-1,number of cardiac phases of reconstruct 20) in LV two-chamber long-axis view,four-chamber long-axia view,RV two-chamber long-axis view,short-axis view,three-chamber long-axis view and RV outflow tract view;FastCine PC(TR/TE auto selected minimun/min full;flip angle 20°,FOV 400×400 mm,matrix size 256×128,ETL 1,nex 1,bandwidth:31.25 khz.Slice thickness 5.0 mm,number of cardiac phases of reconstruct 30,Venc 150 cm/s)in pulomary artery,aotic artery,mitral valve and tricuspid valve. 3,The study inclued 27 patients following TOF repair who had PC-MRI examinations that included fastcine PC sequence to evaluate ventricle in-flow patterns across the mitral valve and tricuspid valve and cine Fiesta sequence to quantify RV volume simultaneously.Results1,First group:the Slice direction of Venc exhibited the correct direction of flow,included hypointensity in forward flow and hyperintensity in backward flow.the ALL,AP and RL direction of Venc did not reflect the corret flow information.Second group:Different phase aliasing were found in forward and backward flow when Venc was setted at 20,40,60,80 cm/s.Accurate signal intensity were exhibited when Venc was setted at 100,120,140,160,180,200 cm/s,inclued hypointensity in forward flow and hyperintensity in backward flow.The velocity measured with PC-MRI had no significant difference with the actual velocity and retained stability within a cardiac cycle when Venc was setted at 100,120,140,160,180,200 cm/s.Third group:Different phase aliasing were seen when injection flow rate was setted at 3.5 ml/s-5 ml/s.The velocity measured by the PC-MRI technique had a excellent positive liner correlation with injection flow rate(r=0.999,P＜0.001).There was no significant difference between the velocity measured by PC-MRI and the actual velocity(t=0.100,P=0.922).2,The different categories(mild,moderate and severe) of PR measured by PC-MRI had a positive liner correlation with the results measured by echocardiography(r_s=0.606,P＜0.001).By echocardiography criteria,mild PR was present in 10 cases,moderate PR in 32 cases.while PC-MRI showed mild PR in 10 cases(23.8%),moderete PR in 8 cases(19.0%) and severe PR in 24 cases(57.1%) respectively.When PR was divided into mild group and moderate/severe group,the differences in PC-MRI were concordant with the Doppler-derived semiquantitative categories(k=0.606 P＜0.001).PC-MRI was able to differentiate between the categories moderate and severe.The PRF measured by PC-MRI had mild positive correlation with pulmonary regurgitant area measured by echocardiography(r_s =0.438,P=0.004).The pulmonary ANF measured by PC-MRI had significant positive correlation with pulmonary regurgitant area measured by echocardiography(r_s=0.559,P＜0.001).Patients with a transannular patch had a significantly higher PRF and ANF than patients with RVOT patch(u=52.000,P=0.001;u=55.000,P=0.002).Heart function grading(NYHA functional class )was classⅠin 32 cases,classⅡin 9 cases and classⅢin 1 cases.Patients with classⅠhad no significantly different PRF and ANF than patients with classⅡ(u=86.000,P=0.068;u=100.000, P=0.166).Higher PRF was associated with increasing RV-EDVI and RV-ESVI,PRF had significant positive correlation with RV-EDVI and RV-ESVI(r_s=0.500,P=0.001;r_s =0.518,P＜0.001 respectively).However,PRF was not associated with RV-EF and RV-SV(r_s=0.055,P=0.730;r_s=0.248,P=0.113,respectively).When PRF were divided into 3 groups(mild group,moderate group and severe group),there was a significant difference among different groups(x~2=12.530, P=0.002;x~2=13.173,P=0.001) about RV-EDVI and RV-ESVI but no significant difference about RV-EF and RV-SV(x~2=0.032,P=0.984;x~2=4.292,P=0.117).3,The E and A-waves across the tricuspid and mitral valves were identified clearly by PC-MRI.The E velocity(Evelocity)measured by PC-MRI had no significant correlation with that(E) measured by echocardiography(r=0.212,P=0.289),but the A velocity (Avelocity) had mild correlation with that(A) measured by echocardiography (r=0.427,P=0.026).Compared to echocardiography,The Peak velocity measurements of E and A-waves across the tricuspid valves were clearly underestimated by PC-MRI(P＜0.05).The Evelocity/Avelocity and Eflow/Aflow measured by PC-MRI correlated well with E/A measured by echocardiography(r=0.560,P=0.002;r=0.542, P=0.003,respectively).and there were no significant difference among Evelocity/Avelocity,Eflow/Aflow and E/A((?)=1.29,(?)=1.39,(?)=1.41;t=1.624, P=0.116;t=0.182,P=0.857,respectively).According to E/A,patients were categorized into E/A＞1(normal diastolic function) and E/A≤1(diastolic dysfunction) groups.Evelocity/Avelocity and Eflow/Aflow correlated well with E/A measured by echocardiography(k=0.697, P＜0.001 and k=0.571,P=0.003 respectively).Compared to diastolic dysfunction group,normal diastolic function group exhibited more larger RV-EDVI and RV-ESVI(u=34.000,P=0.046;u=29.000, P=0.023,respectively.) but had no significant diffence in RV-EF and RV-SV (u=69.000,P=0.956;u=58.000,P=0.507).Conclusion:1,correct direction of Venc can exhibit the direction of flow;correct Venc is the promise for accurate flow measurement,we can choice a larger Venc to avoid phase aliasing in some extent;3T PC-MRI can measure flow velocity stably and accurately.2,The PRF measured by 3T PC-MRI had well correlation with that measured by echocardiography,and PC-MRI can provide adequate quantitative information to estimate PRF.3T PC-MRI can accurately reflect the difference of pulmonary blood flow causing by RVOT patch and transannular patch.There are well correlation between PRF and RV-EDVI as well as RV-ESVI.3,In flow patterns across the tricuspid valve can be resolved by 3T PC-MRI.but Compared to echocardiography,The Peak velocity measurements of E and A-waves across the tricuspid valves were underestimated by PC-MRI.The Evelocity/Avelocity and Eflow/Aflow measured by 3T PC-MRI can evaluate RV diastolic function.