Planimetric and continuity equation assessment of aortic valve area (AVA): comparison between cardiac magnetic resonance (cmr) and echocardiography

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1 Planimetric and continuity equation assessment of aortic valve area (AVA): comparison between cardiac magnetic resonance (cmr) and echocardiography Poster No.: C-2058 Congress: ECR 2011 Type: Scientific Paper Authors: C. Mantini, B. Feragalli, J. Pizzicannella, G. Di Giammarco, R. De Caterina, A. Tartaro; Chieti/IT Keywords: Cardiac, MR, Echocardiography, Echocardiography (transoesophageal), Comparative studies, Arteriosclerosis, Calcifications / Calculi DOI: /ecr2011/C-2058 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 22

2 Purpose To prospectively assess the accuracy of cardiac magnetic resonance (cmr) for planimetric and continuity equation measurements of aortic valve area (AVA) in comparison with transthoracic (TTE) and transesophageal (TEE) echocardiography To discuss the role and potential advantages of cmr in the selection of patients for aortic valve replacement Methods and Materials STUDY PROTOCOL A total of 21 patients (15 men, mean age = 65 ± 11 years) with moderate-severe aortic valve stenosis (AVS) revealed by TTE, and scheduled for cardiac surgery, underwent cmr with AVA measurement by planimetric (cine steady-state free precession (SSFP) pulse sequences) and continuity equation (breath-hold phase contrast (PC) fast field echo sequence) methods. In the operating room, after anesthesia induction, a TEE evaluation was performed. TTE AVA is indirectly obtained by Doppler TTE, using the continuity equation (1) on page 14 based on Newton's second law of thermodynamics, involving the conservation of mass. This principle states that the volumetric flow rate through the cardiovascular system is constant, assuming that the blood is incompressible and the conduit is inelastic. Page 2 of 22

3 Based on this principle, definition of AVA by TTE requires three mesurements (2) on page 15: ALVOT: calculated from the measured LVOT diameter (by assuming a circular shape) obtained from a parasternal long axis view. VTILVOT: LVOT velocity measured with pulsed wave Doppler from an apical view (for parallel intercept angle) with the sample volume positioned immediately adjacent to the aortic valve closure plane (to ensure that diameter and flow are measured at the same place). VTIAO: Aortic jet velocity, taking care to obtain the highest velocity signal, indicating a parallel intercept angle [3]. Page 3 of 22

4 Direct planimetry of AVA by cmr and TEE represent an accurate and flow-independent technique for assessment of the severity of aortic stenosis, especially in patients with poor acoustic windows. The planimetry of AVA was defined as the smallest orifice area between the aortic valve cusps at the time of maximal opening in systole. TEE TEE is an invasive technique, usually performed in the operating room, which has limitations in patients with heavily calcified aortic valve leaflets. TEE planimetry of the aortic orifice is performed at the time of maximal opening of the valve during systole (3) on page 15 [4]. Page 4 of 22

5 cmr The high spatial resolution of MRI, along with its inherent ability to distinguish between cardiac structures and the adjacent blood pool without the need for intravenous contrast agent, makes it an excellent means for assessing cardiac valvular anatomy. Additionally, flow-sensitive techniques allow detection of turbulent jets typically seen with valvular stenosis and regurgitation. By combining cine images used for determination of ventricular volumes and phase-contrast images for the quantitation of flow, cardiac MRI can be used as a comprehensive noninvasive, method for assessment of valvular disease [5]. In our institution cmr imaging is performed on a 1.5-T MRI magnet (Achieva; Philips Medical System, Best, Olanda) with a five-element, phased-array cardiac synergy coil for signal reception. For the aortic valve assessment, we use two principal techniques: steady-state free precision (SSFP) and phase-contrast imaging (PC) After localization of the heart using three-plane and oblique survey images, a threechamber view and an oblique coronal view cine image of the aortic outflow tract of the left ventricle are prescribed. These images are used as localizers to prescribe four contiguous cross-sectional cine images of the aortic valve between the outflow tract and the level of the valve tips (4) on page 15. Page 5 of 22

6 The cine images are acquired using a multislice cine steady-state free precession (SSFP) pulse sequence (Gradient-echo) with retrospective vectorcardiographic (VCG) gating during multiple breath holds. A total of 25 cine phases were acquired with a temporal resolution varying between 25 and 50 msec (Tab.1) on page 16. Page 6 of 22

7 The view was considered adequate for planimetry if the aorta had a circular shape and all cusps were visualized simultaneously. TEE and MRI Planimetry of the aortic orifice were performed at the time of maximal opening of the valve during systole (5) on page 16. AVA is also computed from phase-contrast MR images using continuity equation. The technique is based on the principle that spins moving along a magnetic field gradient acquire a phase shift in comparison to stationary spins. The phase shift is proportional to the velocity of the moving spin. Subsequently, two breath hold phase contrast images are acquired in a short-axis plane positioned just beyond the aortic leaflet tips and in the LV outflow tract approximately 1 cm below the aortic annulus. Images are acquired using a cine gradient-echo segmented pulse sequence with retrospective VCG gating and velocity encoding. The velocity encoding is set in the through-plane direction with a maximal encoding velocity of 7 m/ second for the transvalvular phase-contrast image and of 2.5 m/second for the LV outflow tract. For a typical heart rate of 60 bpm, breathhold duration was approximately 20 seconds. If the blood velocities exceed the prescribed encoding velocity aliasing artifact occurs (6) on page 17. As a result, the measurement is not valid even if only a few voxels in the cross section of the vessel are affected [6]. Page 7 of 22

8 A phase (velocity mapping) and a magnitude (anatomy) image are generated simultaneously. Therefore, by tracing the regions of interest instantaneous flow values can be calculated (7) on page 17. REPRESENTATIVE EXAMPLES CASE 1 Page 8 of 22

9 Page 9 of 22

10 CASE 2 on page Page 10 of 22

11 Page 11 of 22

12 CASE 3 on page Page 12 of 22

13 Page 13 of 22

14 STATISTICAL ANALYSIS Agreements between different methods were explored using Lin's concordance correlation coefficient (CCC) and with Bland and Altman analysis. Images for this section: Page 14 of 22

15 1 2 3 Page 15 of 22

16 4 5 Page 16 of 22

17 6 7 8 Page 17 of 22

18 Results 2 2 cmr planimetry (0.75 ± 0.22 cm ) correlated highly to TEE planimetry (0.79 ± 0.18 cm ) with a CCC of 0.76 (CI 95% ). Excluding patients with extensive thickening and heavy calcification of all cusps, the CCC increased to 0.88 (CI 95% ). Page 18 of 22

19 2 AVA measured by continuity equation-cmr (0.71 ± 0.20 cm ) correlated highly with TTE2 derived AVA (0.73 ± 0.23 cm ) with a CCC of 0.82 (CI 95% ) Images for this section: 1 Page 19 of 22

20 2 3 Page 20 of 22

21 Conclusion CMR have recently emerged as a promising method for evaluation of AS in term of: valvular morphology (as the causes of AS) (11) on page quantification of the "true" dimensions of the anatomical orifice area (planimetric techniques) and the "effective" orifice area (continuity equation measure) and the evaluation of cardiac function. The hemodynamic consequence of all forms of aortic stenosis is concentric left ventricle hypertrophy, characterized by thickening of the left ventricle wall, which can be focal or diffuse and symmetric. cmr assessment of AVA showed a high correlation with echocardiography measurents and has the potential to replace current standard techniques for evaluation of aortic valve stenosis A potential limitation for cmr is represented by the presence of heavy and diffuse valvular calcifications that may impaire a correct planimetric assessment References 1. Chun EJ, et al. Aortic stenosis: evaluation with multidetector CT angiography and MR imaging. Korean J Radiol 2008; 9: Pouleur AC, et al. Aortic valve area assessment: multidetector CT compared with MR imaging and transthoracic and transesophageal echocardiography. Radiology 2007; 244: Bax JJ and European Society of Cardiology. Cardiovascular imaging : a handbook for clinical practice. The ESC educational series. 2005, Malden, Mass.: Blackwell Pub. xiii, 296 p. 4. Libby P and Braunwald E. Braunwald's heart disease : a textbook of cardiovascular medicine. 8th ed. 2008, Philadelphia: Saunders/Elsevier. 1 v. Page 21 of 22

22 5. Debl K, et al. Planimetry of aortic valve area in aortic stenosis by magnetic resonance imaging. Invest Radiol 2005; 40: Pouleur AC, et al. Planimetric and continuity equation assessment of aortic valve area: Head to head comparison between cardiac magnetic resonance and echocardiography. J Magn Reson Imaging 2007; 26: Reant P. et al. Absolute assessment of aortic valve stenosis by planimetry using cardiovascular magnetic resonance imaging: comparison with transesophageal echocardiography, transthoracic echocardiography, and cardiac catheterisation. Eur J Radiol 2006; 59: Personal Information Cesare Mantini, Beatrice Feragalli, Jacopo Pizzicannella, Gabriele Di Giammarco, Raffaele De Caterina, Armando Tartaro. Department of Radiology, "G. D'Annunzio" University, Chieti, ITALY cesare. mantini@gmail.com Page 22 of 22