Velocity-encoded Cine MRI Research Articles

Dilatation of the ascending aorta is associated with presence of aortic regurgitation in patients after repair of tetralogy of Fallot

To evaluate the association between aortic morphology and elasticity with aortic regurgitation in surgically corrected of tetralogy of Fallot (TOF) patients. We retrospectively identified 72 consecutive patients with surgically corrected TOF and 27 healthy controls who underwent cardiac MRI evaluation. Velocity-encoded cine MRI was used to quantify degree of aortic regurgitation (AR) in TOF patients. Ascending aorta diameters were measured at standard levels on MRA images. Aortic pulse-wave velocity (PWV) was quantified with MRI. Morphological and functional MRI variables were compared between groups of TOF patients with and without clinically relevant AR and controls. The association between aortic morphology and elasticity with the presence of AR was evaluated using univariate and multivariate logistic regression. The majority of TOF patients had only trace AR. Nine TOF patients (12 %) had an AR fraction higher than 15 %. Indexed aorta diameter at the sinotubular junction (p = 0.007), at the RPA level (p = 0.006), and low left ventricular ejection fraction (LVEF) (p = 0.015) showed the strongest associations with the presence of at least mild AR, which persisted after controlling for age and gender. Increased ascending aorta dimension is associated with AR in patients after repair of TOF. LVEF was also low in the group of patients with relevant AR compared to those without, suggesting even mild to moderate AR may contribute to LV dysfunction in these patients. Enlarged ascending aorta may be an indication for precise quantification of regurgitant fraction with MRI, since symptomatic patients may need aortic valve repair when moderate regurgitation is present.

Aortic valve planimetry by high-resolution 3-dimensional MR image acquisition with a breath-hold: comparison with conventional cine MR imaging and echocardiography to assess the severity of aortic valve stenosis

Methods In 88 consecutive patients (66.9 ± 9.59 years, 63% men) with varying degrees of aortic valve stenosis, high-resolution 3D SSFP images (3D planimetry; 2.0 mm slice thickness, 20 contiguous slices; image matrix, 256 ‘ 209) were acquired with single breath-hold during mid systole and mid diastole. SSFP cine MR imaging (2D planimetry) and velocity-encoded cine MRI (slice thickness, 4.5 mm) in three levels of aortic valve were also performed. AVA area was measured by two experienced observers using commercial software (iNtuition, TeraRecon). MR imaging measurements and image quality were compared with transthoracic echocardiographic measurements of effective aortic orifices (EAO) using the continuity equation (1 = severe blurring of images, 2 = moderate blurring of valve contours; 3 = mild blurring of valve contours, 4 = excellent and no artifact). Sensitivity for accurate measurement and receiver operating characteristic (ROC) curve were calculated. Intraand interobserver agreements were determined by using intraclass correlation coefficient (ICC). Results Mean AVA derived by 3D planimetry, 2D planimetry, and echocardiography were 0.77 ± 1.04 cm, 0.72 ± 1.16 cm, and 0.75 ± 0.32 cm, respectively. The ICC value of 3D planimetry was higher than 2D planimetry [0.799 (CI, 0.691-0.869) vs. 0.743 (CI, 0.605-0.832)] with echocardiographic EAO as the standard of reference. The grade of image quality of 3D planimetry was superior to 2D planimetry (3.65 ± 0.65 vs. 3.17 ± 0.65). The correlation coefficients of maximum peak velocity on velocity-encoded cine MR imaging with 3D planimetry and that with 2D planimetry were 0.42 (p < 0.05) and 0.35 (p < 0.05). Intraand interobserver agreements for 3D planimetry were excellent [ICC = 0.949 (CI, 881-979) and 0.846 (CI, 0.636-0.935), respectively; both, p = 0.000).

Inferior vena caval blood flow affects the quality of CTPA during pregnancy

Sir, I read with great interest the paper by Drs Schaefer-Prokop and Prokop [1] in the December 2008 issue of European Radiology, highlighting the protocols to optimize the image quality of CT pulmonary angiography (CTPA) in pregnant individuals. I appreciate the authors’ editorial work, which comprehensively overviewed the limitations of CTPA related to physiological changes during pregnancy and summarized the options to overcome them. In an attempt to shed further light on the effect of altered caval blood flow deteriorating the quality of CTPA, I would like to draw attention to a recent paper by Kuzo et al. [2], who quantitatively measured caval blood flow in healthy subjects by velocity-encoded cine MRI. They found that caval blood flow significantly increases during continuous inspiration and decreases during the Valsalva manoeuvre compared with free breathing. When the ratio of inferior vena cava to superior vena cava blood flow was taken into consideration, it increases during continuous inspiration (2.37), and decreases during breath-hold at end inspiration (1.90), breath-hold at end expiration (1.94), and at Valsalva manoeuvre (1.51) compared with free breathing (2.04). They concluded that CTPA should be performed with only a small inspiration or no inspiration before acquiring CT data. It has also been demonstrated by a Doppler study that hepatic venous pulsatility is decreased during pregnancy, being completely flat with increasing gestational age, which is attributed to increased cardiac output and the pressure effects of the enlarged gravid uterus [3]. Similarly, the compliance of the inferior vena cava is likely to be decreased during pregnancy by the same mechanism, leading to continuous forward flow of unopacified blood into the right atrium. Knowledge of physiological changes taking place during pregnancy will enable us to modify our acquisition protocols accordingly.

Velocity Encoded Cine MRI for the Assessment of Left Ventricular Diastolic Function

SI (%) Normals n= 24 Fabry n= 24 p-Value Septal basal 24 ± 5 17 ± 4 <0.001* Lateral basal 25 ± 4 18 ± 4 <0.001* Inferior basal 23 ± 4 18 ± 6 <0.001* Anterior basal 28 ± 4 17 ± 4 <0.001* ∗ p< 0.05 compared to normals. Conclusion: Patients with Fabry disease have reduced left ventricular strain and intraventricular dyssynchrony, although left ventricular ejection fraction remained normal. The impaired regional systolic function may be due to the LVH and subsequent fibrosis associated with the disease process. DTI techniques quantify regional dysfunction despite normal global function using traditional parameters. doi:10.1016/j.hlc.2008.05.131 131 Velocity Encoded Cine MRI for the Assessment of Left Ventricular Diastolic Function Rae F. Duncan, Benjamin K. Dundon ∗, Adam J. Nelson, Matthew I. Worthley, Kerry Williams, Michael C. Leung, Cynthia Piantadosi, Gary Y. Liew, Payman Molaee, Stephen G. Worthley

Disparity between ratios of diameters and blood flows in central pulmonary arteries in postoperative congenital heart disease using MRI

To compare the relative severity of stenoses of right or left pulmonary arteries with differences in flow to each lung after repair of congenital heart disease (CHD). A total of 15 patients with postoperative congenital heart disease underwent MRI to evaluate branch pulmonary artery stenoses. Spin-echo images and MR angiography were used to assess morphology, and velocity-encoded cine (VEC) MRI was used to measure flow in the right and left pulmonary arteries. The ratios of the narrowest diameters of the right to left pulmonary arteries (R/L size) and right to left pulmonary arterial flow (R/L flow) were compared using Spearman's correlation. F test was used to assess the significance of the regression coefficients. R/L size ratio varied from 0.50 to 2.66, while the R/L flow ratio varied from 0.36 to 12.02. There was an exponential relationship between R/L size and R/L flow, with r2=0.78 and P=0.001. However, severity of morphologic stenoses was not clinically useful for predicting flow reduction. Prediction residuals ranged from -136% to 54% of the true R/L flow. Anatomical evaluation of the pulmonary arteries does not predict accurately differential blood flow in patients with pulmonary stenoses. Therefore, blood flow measurements are essential when considering the need for further surgical or interventional procedures.

Ressonância magnética é útil em valvopatia

Reperfusion injury, hemodynamics, blood volume.conformation, it shows low intra- and interobserver variability and allows right ventricle quantification, a chamber usually difficult to access on echocardiograms. These qualities are the CMR’s calling card for inclusion in the follow-up of ventricular function and mass of patients with valvular heart disease (such as aortic stenosis), as well as for functional comparison after surgical intervention. Velocity-encoded cine-MRI allows the assessment of blood flow velocity across a cardiac vessel or valve. It is equivalent to Doppler echocardiography, but offers the advantage of accessing blood flows in any orientation without being limited by an acoustic window. Using the modified Bernoulli equation, it is possible also to derive transvalvular pressure gradient. One of the cardiologist’s biggest concerns is that of CMR safety in patients with a mechanical prosthetic valve. It is well established that it is safe to expose a patient with this type of prosthesis to the magnetic fields generally used on CMR (1.5 Tesla). The magnetic force acting on the material is too weak compared to that imposed by the surgical attachment of the prosthesis. On the other hand, these prostheses produce artifacts of signal void (dark area on the MRI image), because the magnetic field becomes distorted by the metallic content. These artifacts often extend to the surrounding structures, depending on the pulse sequence used (this is usually less marked in spin-echo sequences). Consequently, the evaluation of turbulent jets, especially those of lower magnitude, is compromised. With bioprostheses, this effect is usually restricted to the valve annulus and does not interfere significantly in the MRI interpretation.Described around six years ago, the delayed-enhanced technique consists in acquiring images approximately 10 to 20 minutes after the intravenous injection of a contrast medium (gadolinium) preceded by an inversion-recovery pulse6. In addition to allowing the visualization of minimal areas of myocardial necrosis/fibrosis, this technique shows excellent correlation with the pathological anatomy in several heart diseases

Faster flow quantification using sensitivity encoding for velocity‐encoded cine magnetic resonance imaging: In vitro and in vivo validation

To test the agreement between conventional and sensitivity-encoded (SENSE) velocity encoded cine (VEC) MRI in a flow phantom and in subjects with congenital and acquired heart disease. Flow measurements were performed in a 1.5 T scanner using a segmented k-space VEC MRI sequence and then repeated with a SENSE factor of 2. The flow phantom used a piston pump to generate physiologic arterial waveforms (0.5-4.9 L/min). In the subjects, flow measurements were performed in the ascending aorta (N = 33) and/or the main pulmonary artery (N = 24). Utilization of SENSE reduced the scan time by 50%. In the phantom, measurements without and with SENSE agreed closely with a mean difference of 0.01 +/- 0.08 L/min or 0.12% +/- 3.8% (P = 0.68). In the subjects, measurements without and with SENSE also agreed closely with a mean difference of 0.08 +/- 0.36 L/min or 1.3% +/- 7.2% (P = 0.08). Compared with standard imaging, the use of SENSE reduced the signal-to-noise ratio (SNR) by 28% in the phantom (N = 10) and 27% in vivo (N = 22). VEC MRI flow measurements with a SENSE factor of 2 were twice as fast and agreed closely with the conventional technique in vitro and in vivo. VEC MRI with SENSE can be used for rapid and reliable quantification of blood flow.

Delivery and assessment of endovascular stents to repair aortic coarctation using MR and X‐ray imaging

To investigate the utility of MR and X-ray imaging for characterizing aortic coarctation and flow, and guiding the endovascular catheter to place a stent to repair the coarctation. The descending aorta in eight dogs was looped with elastic band and tightened distal to the subclavian artery. Balanced fast field echo (bFFE) and velocity-encoded cine (VEC) MRI sequences were used for device tracking and measuring aortic flow. A T1-weighted fast-field echo sequence (T1-FFE) was used to visualize the coarctation and roadmap the aorta. Nitinol stents were guided by a nitinol guidewire and placed under MR guidance. Aortic coarctation was visible on MR and X-ray imaging. The procedure success rate was 88%. VEC MRI measured the changes in aortic flow (baseline = 1.3 +/- 0.2, coarctation = 0.2 +/- 0.02, and stent placement = 0.8 +/- 0.1 liters/minute). A significant reduction in iliac blood pressure was measured after coarctation, but it was reversed by stent placement. The stent lumen was visible on X-ray fluoroscopy, but not on MRI. Stent deployment to repair aortic coarctation is feasible under MR guidance. The combined use of MR and X-ray imaging is effective for anatomic and functional evaluation of aortic coarctation dilation, which may be crucial for optimal therapy.

Coarctation of the aorta: pre and postoperative evaluation with MRI and MR angiography; correlation with echocardiography and surgery

To compare MRI and MRA with Doppler-echocardiography (DE) in native and postoperative aortic coarctation, define the best MR protocol for its evaluation, compare MR with surgical findings in native coarctation. 136 MR studies were performed in 121 patients divided in two groups: Group I, 55 preoperative; group II, 81 postoperative. In group I, all had DE and surgery was performed in 35 cases. In group II, DE was available for comparison in 71 cases. MR study comprised: spin-echo, cine, velocity-encoded cine (VEC) sequences and 3D contrast-enhanced MRA. In group I, diagnosis of coarctation was made by DE in 33 cases and suspicion of coarctation and/or aortic arch hypoplasia in 18 cases. Aortic arch was not well demonstrated in 3 cases and DE missed one case. There was a close correlation between VEC MRI and Doppler gradient estimates across the coarctation, between MRI aortic arch diameters and surgery but a poor correlation in isthmic measurements. In group II, DE detected a normal isthmic region in 31 out of 35 cases. Postoperative anomalies (recoarctation, aortic arch hypoplasia, kinking, pseudoaneurysm) were not demonstrated with DE in 50% of cases. MRI is superior to DE for pre and post-treatment evaluation of aortic coarctation. An optimal MR protocol is proposed. Internal measurement of the narrowing does not correspond to the external aspect of the surgical narrowing.

Pulmonary and Aortic Blood Flow Measurements in Normal Subjects and Patients After Single Lung Transplantation at 0.5 T Using Velocity Encoded Cine MRI

It is the purpose of this study to compare pulmonary and aortic blood flow measurements obtained in patients after single lung transplantation (SLTX) with those in volunteers. METHODS/MATERIAL: In nine patients after SLTX (three male, six female) and nine volunteers (seven male, two female), double oblique phase contrast cine-MRI sequences perpendicular to the direction of blood flow were obtained in the ascending aorta, main, right, and left pulmonary artery on a 0.5-T unit (Philips Gyroscan; Best, the Netherlands) (repetition time, 600 to 800 ms; echo time, 8 ms; alpha=30; field of view=280 mm matrix, 128x256, ECG gating, temporal resolution 16 time frames/RR interval). An initial in vitro study using the same sequence on a nonpulsatile flow phantom showed excellent correlation (r=0.99) between MRI measurements of flow velocity and flow volume and true velocity and flow volume. Measurements of blood flow volume (mL/min), peak mean systolic velocity, resistive index, and distensibility index were obtained in each vessel. We found excellent correlations between left and right cardiac output as measured by velocity encoded cine-MRI (VEC-MRI) in the ascending aorta and main pulmonary artery both in normal volunteers (r=0.95) and in patients (r=0.91). Differential pulmonary blood flow measurements in volunteers showed that 55% of the right cardiac output was directed to the right and 45% to the left lung. Differential pulmonary blood flow in patients showed that most of the blood flow (81%) reaches the transplanted lung and only 19% reaches the patient's own lung (SLTX: 4.5+/-1.8 L/min, patient's own lung: 1.2+/-0.8 L/min). There were significant differences (p<0.05) in peak mean systolic velocity and resistive index obtained in the pulmonary arteries, both between normal volunteers and patients and between measurements obtained in the patient's own lung and the transplanted lung. VEC-MRI blood flow measurements are a promising noninvasive tool to monitor the hemodynamic changes of pulmonary blood flow after SLTX.

Assessment of popliteal arterial occlusive disease with 2D time-of-flight MRA.

The purpose of this study was to evaluate both morphology and blood flow in peripheral arteries with occlusive lesions using MR angiography (MRA) and velocity-encoded cine MRI. Two-dimensional time-of-flight MRA and velocity-encoded cine MRI were performed in nine patients with peripheral arterial occlusive disease. Findings on MR angiograms were verified by conventional angiography. All the stenotic lesions in the popliteal arteries were depicted by MRA. The degree of the stenoses in the artery was overestimated by MRA. Major collateral circulations were demonstrated. Velocity-encoded cine MRI provided flow velocity information on the arteries above and below the stenoses. The flow velocity waveform was monophasic above and below the stenosis. The peak systolic velocity in the artery below the stenosis was reduced compared with that above the stenosis (p < 0.05). The combination of MRA and velocity-encoded cine MRI has clinical potential for the evaluation of peripheral arterial occlusive disease.

Evaluation of left atrial contribution to left ventricular filling in aortic stenosis by velocity-encoded cine MRI

Velocity-encoded cine MRI (VEC-MRI) can measure volume flow at specified sites in the heart. This study used VEC-MRI to measure flow across the mitral valve to compare the contribution of atrial systole to left atrial filling in normal subjects and patients with left ventricular hypertrophy. The study population consisted of 12 normal subjects (mean age 34.5 years) and nine patients with various degrees of left ventricular hypertrophy resulting from aortic stenosis (mean age 70 years). VEC-MRI was performed in double-oblique planes through the heart to measure both the mitral inflow velocity pattern (E/A ratio) and the volumetric flow across the mitral valve. The left atrial contribution to left ventricular filling (AC%) was calculated. The results were compared with Doppler echocardiographic parameters. The VEC-MRI-derived mitral EA ratios showed a significant linear correlation with EA ratios calculated from Doppler echocardiography ( r = 0.94), and the VEC-MRI-derived E/A ratios (2.1 ± 0.5 vs 1.0 ± 0.4) and AC% values (24.9 ± 7.2 vs 45.7 ± 16.4) were significantly different between normal subjects and patients with aortic stenosis ( p < 0.01 in both groups). The same differences were seen in the Doppler echocardiographic parameters. The VEC-MRI-derived E/A ratio and AC% showed significant hyperbolic and linear correlations with left ventricular mass indexes ( r = 0.95 and 0.86). In addition, the VEC-MRI-determined E/A ratio and the volumetric AC% displayed a highly significant hyperbolic correlation ( r = 0.95). Thus VEC-MRI can be used to evaluate left ventricular diastolic filling characteristics in normal subjects and patients with abnormalities of diastolic filling.

Velocity-encoded cine MRI in the evaluation of left ventricular diastolic function: Measurement of mitral valve and pulmonary vein flow velocities and flow volume across the mitral valve

Left ventricular diastolic function has been evaluated by means of analysis of the flow pattern through the mitral valve. Velocity-encoded cine magnetic resonance imaging (VEC-MR) is a new method for characterizing flow patterns in the heart. The feasibility of using VEC-MR to measure early diastolic (E) and atrial systolic (A) peak flow velocities and E/A ratios in the mitral inflow, as well as systolic (X), early diastolic (Y), and atrial systolic (Z) peak flow velocities and X/Y ratios in the pulmonary vein, was evaluated in 10 normal volunteers. The VEC-MR-derived velocities and indexes were compared with Doppler-derived results. Volumetric flow across the mitral valve was also used to measure stroke volume, cardiac output, and the left atrial contribution of left ventricular filling. VEC-MR yielded lower peak velocities than Doppler echocardiography. The velocities of the two measurements showed a significant linear correlation (Doppler E velocity = 1.30 × VEC-MR + 1.6 cm/sec, r = 0.68; Doppler A velocity = 1.83 × VEC-MR − 5.2 cm/sec, r = 0.83; and Doppler X velocity = 0.45 × VEC-MR + 0.09 cm/sec, r = 0.74). Consequently the E/A and X/Y ratios measured by these two methods showed statistically significant linear correlations with r values of 0.94 and 0.83. The volume of blood flow across the mitral valve measured by VEC-MR (5610 ± 620 ml/min) was not statistically different from the cardiac output measured from the ascending aorta by VEC-MR (5670 ± 590 ml/min) or by left ventricular cine magnetic resonance imaging (5440 ± 614 ml/min). The left atrial contribution to left ventricular filling was 25.9 ± 7.5%. Our results indicate that VEC-MR can be used not only for evaluation of left ventricular diastolic filling from the mitral valve and pulmonary vein flow velocities but also for quantitative measurement of the volume of blood flow across the mitral valve.