Scientific Exhibit Authors: M. Sugiyama, Y. Takehara, T. Saito, N. Ooishi, M. Alley,

Transcription

1 Abnormal flow dynamics within the ascending aorta of the patients with aortic valve stenosis. Assessments with phase resolved three dimensional phase contrast MR image (4DFlow). Poster No.: C-2504 Congress: ECR 2013 Type: Scientific Exhibit Authors: M. Sugiyama, Y. Takehara, T. Saito, N. Ooishi, M. Alley, T. Wakayama, M. Terada, S. Yoshihara, H. Sakahara ; Hamamatsu/JP, Stanford, CA/US, Hino/JP, Iwata/JP Keywords: Dilatation, Imaging sequences, Computer Applications-3D, MRAngiography, MR, Cardiovascular system, Arteries / Aorta, Aneurysms DOI: /ecr2013/C-2504 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. Page 1 of 25

2 Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 2 of 25

3 Purpose Abnormal flow dynamics associated with aortic valve stenosis (AS) is widely believed to be related to post-stenotic dilatation of the ascending aorta, or sometimes hemorrhages from the gastrointestinal angiodysplasia, which is now believed to be due to the breaking down of the coagulation factor VIII by the abnormal flow occurring around the stenosed (1) valve. The purpose of the study is to characterize the flow dynamics of the ascending aorta in AS patients by phase resolved 3D phase contrast MRI (4D-FLOW). Methods and Materials Three AS patients diagnosed with echocardiography and cardiac catheterization were examined on 3T MR scanner. ECG gated, gradient-echo-based coronal 4D-Flow covering the whole heart and the ascending aorta was performed following the contrast enhanced MR Angiography (Gd3DMRA) performed for the determination of the aortic boundary. Age-matched five patients without AS were also examined in a same way. Written informed consent was acquired in all patients. MR imaging All examinations were performed on 3.0T MR scanner (Discovery 750, GE Healthcare, WI, USA). 2D PC cine study Prior to 4D-Flow, 2D PC cine was performed on the transverse section. The maximum flow velocity was calculated within the thoracic aorta, and the velocity encoding value (VENC) was determined. Gd 3D MRA Prior to flow measurements, time resolved contrast enhanced 3 dimensional MR angiography (Gd3DMRA) was performed with a bolus injection of gadolinium chelate (0.1 mmol/kg). A 3D data set of arterial dominant phase was picked out and was used to determine the boundary of the inner wall of the arteries. Then, 4D-Flow was performed 4D-Flow data acquisitions: The 4D-Flow is based on a SPGR sequence encoding flow velocities in three orthogonal directions. Page 3 of 25

4 The parameters used were TR/TE/FA/NEX of / /15/1, FOV of 32 cm, Matrix of 224x224, 2 mm thickness, 60 partitions, phases during one cardiac cycle and imaging time of 10 min (with reduction factor of 2). ECG gating and respiratory compensation were also combined. VENC was optimized based on the values measured with 2D PC cine study performed prior to the 4Dflow. Acquired data were transferred to a workstation and were post-processed with flow analysis software (flova, R-`tech, Japan). The velocity data derived from 4D-Flow and the geometric data of the boundary of the aortic wall determined by Gd3DMRA were interpolated, and we could delineate streamlines or calculate the wall shear stress (WSS) of the arbitrary arteries within the field of view, and can overview the change of WSS related to cardiac cycle as color maps. Results The Flow Dynamics Streamline images delineated the vortex and/or helical flow within the dilated ascending aorta throughout the cardiac cycle in all AS patients. The abnormal flow appears from the base of ascending aorta throughout all cardiac cycle within all AS patients. On the other hand the flow pattern of the control patients is mostly laminar at systole with brief turbulence while diastole. This implies an important roll of the AS in the formation of abnormal flow dynamics at systole and subsequent dilatation. Page 4 of 25

5 Fig. 1: The streamline and the WSS of a 71-year-old male with AS in a cardiac cycle. The streamline delineates helical/vortex flow throughout a whole cardiac cycle in the ascending aorta. The WSS around the abnormal flow dynamics is remarkably reduced. References: Radiology, Hamamatsu Universit School of Medicine, Hamamatsu Universit School of Medicine, University Hospital - Hamamatsu/JP Page 5 of 25

6 Fig. 2: The streamline and the WSS of a 76-year-old female (control case) in a cardiac cycle. The flow pattern of the control patients is mostly laminar at systole with brief turbulence while diastole. References: Radiology, Hamamatsu Universit School of Medicine, Hamamatsu Universit School of Medicine, University Hospital - Hamamatsu/JP The Wall Shear Stress The Wall Shear Stress (WSS) calculated at the ascending aorta showed reduced WSS less than 0.5 Pa of the wall due to the complex abnormal flow dynamics in all three patients. In two AS patients partial high WSS appeared on the aortic wall around the vortex and/or helical flow. The phenomenon might be the consequence of the higher velocity of the vortex and/or helical flow. Another probable cause may be the discrepancy beteween coordinates of the flow vectors and boundary data derived from phaseaveraged enhanced MR angiogram. Page 6 of 25

7 Fig. 3: The WSS of an AS patient (the same case as Fig.1) at systole. The WSS of the dilated ascending aorta is reduced due to the complex abnormal flow dynamics. References: Radiology, Hamamatsu Universit School of Medicine, Hamamatsu Universit School of Medicine, University Hospital - Hamamatsu/JP Page 7 of 25

8 Fig. 4: The WSS at systole of a control case (the same case as Fig.2). WSS is homogeneously high at the ascending aorta compared to the AS patients. References: Radiology, Hamamatsu Universit School of Medicine, Hamamatsu Universit School of Medicine, University Hospital - Hamamatsu/JP Page 8 of 25

9 Fig. 5: Partially high WSS is depicted in the ascending aorta at systole within a 73year-old male (AS patient). References: Radiology, Hamamatsu Universit School of Medicine, Hamamatsu Universit School of Medicine, University Hospital - Hamamatsu/JP Page 9 of 25

10 Fig. 6: The streamline of the AS patient (the case shown in Fig.5) depicts remarkablly high magnitude of vortex and/or helical flow nearby the high WSS portion. References: Radiology, Hamamatsu Universit School of Medicine, Hamamatsu Universit School of Medicine, University Hospital - Hamamatsu/JP The Oscillatory Shear Index The Oscillatory Shear Index (OSI) calculated at the ascending aorta showed higher OSI within the dilated portion of ascending aorta (see Fig.10 for the formula). Partially lower OSI was observed at the dilated ascending aorta in two AS patients. The phenomenon is probably caused by the shape of the dilated ascending aorta which somehow formed fixed and stable vortex and/or helical flow. However, at the bulged portion of the dilatation, lower WSS and higher OSI are still observed. These portion of the aorta might be the key for formation of the dilatation within AS patients. Page 10 of 25

11 Fig. 7: The OSI of an AS patient (the same case as Fig.1). Higher OSI is seen on the wall nearby the complex abnormal flow dynamics. References: Radiology, Hamamatsu Universit School of Medicine, Hamamatsu Universit School of Medicine, University Hospital - Hamamatsu/JP Page 11 of 25

12 Fig. 8: The OSI of a control case (the same case as Fig.2). The calculated OSI of the control group shows stable and low OSI compared to the AS patients. References: Radiology, Hamamatsu Universit School of Medicine, Hamamatsu Universit School of Medicine, University Hospital - Hamamatsu/JP Page 12 of 25

13 Fig. 9: Partially lower OSI was observed at the dilated ascending aorta in a 73year-old AS patient (the same case as Fig.5). Higher OSI is still seen at base of the ascending aorta. References: Radiology, Hamamatsu Universit School of Medicine, Hamamatsu Universit School of Medicine, University Hospital - Hamamatsu/JP Page 13 of 25

14 Fig. 10: The formula for OSI calculation. References: Radiology, Hamamatsu Universit School of Medicine, Hamamatsu Universit School of Medicine, University Hospital - Hamamatsu/JP Images for this section: Page 14 of 25

15 Fig. 3: The WSS of an AS patient (the same case as Fig.1) at systole. The WSS of the dilated ascending aorta is reduced due to the complex abnormal flow dynamics. Page 15 of 25

16 Fig. 7: The OSI of an AS patient (the same case as Fig.1). Higher OSI is seen on the wall nearby the complex abnormal flow dynamics. Page 16 of 25

17 Fig. 1: The streamline and the WSS of a 71-year-old male with AS in a cardiac cycle. The streamline delineates helical/vortex flow throughout a whole cardiac cycle in the ascending aorta. The WSS around the abnormal flow dynamics is remarkably reduced. Page 17 of 25

18 Fig. 4: The WSS at systole of a control case (the same case as Fig.2). WSS is homogeneously high at the ascending aorta compared to the AS patients. Page 18 of 25

19 Fig. 2: The streamline and the WSS of a 76-year-old female (control case) in a cardiac cycle. The flow pattern of the control patients is mostly laminar at systole with brief turbulence while diastole. Page 19 of 25

20 Fig. 8: The OSI of a control case (the same case as Fig.2). The calculated OSI of the control group shows stable and low OSI compared to the AS patients. Page 20 of 25

21 Fig. 9: Partially lower OSI was observed at the dilated ascending aorta in a 73-year-old AS patient (the same case as Fig.5). Higher OSI is still seen at base of the ascending aorta. Page 21 of 25

22 Fig. 5: Partially high WSS is depicted in the ascending aorta at systole within a 73-yearold male (AS patient). Page 22 of 25

23 Fig. 6: The streamline of the AS patient (the case shown in Fig.5) depicts remarkablly high magnitude of vortex and/or helical flow nearby the high WSS portion. Page 23 of 25

24 Fig. 10: The formula for OSI calculation. Page 24 of 25

25 Conclusion Streamline or pathline images delineated the vortex and/or helical flow within the dilated ascending aorta throughout the cardiac cycle in all AS patients, which were not observed in the control patients. The wall shear stress (WSS) calculated at the ascending aorta showed reduced WSS less than 0.5 Pa of the wall due to the complex abnormal flow dynamics in all three patients. The flow patterns of the control group in the ascending aorta was mostly laminar at systole with brief turbulence while diastole. 4D-FLOW method successfully delineated abnormal flow dynamics and lower WSS and higher OSI that may be affecting the integrity of the wall of the ascending aorta in AS patients. References 1. Loscalzo J. From clinical observation to mechanism--heyde's syndrome. N Engl J Med Nov 15;367(20): Personal Information Page 25 of 25