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J Thorac Cardiovasc Surg 2007;133:260-262
© 2007 The American Association for Thoracic Surgery
Brief Communication |
a Departments of Diagnostic Radiology and Medical Physics, University Hospital Freiburg, Freiburg, Germany
b Department of Cardiovascular Surgery, University Hospital Freiburg, Freiburg, Germany.
Received for publication August 9, 2006; accepted for publication August 25, 2006. * Address for reprints: Alex P. Frydrychowicz, MD, University Hospital Freiburg, Department of Diagnostic Radiology, Hugstetter Str. 55, 79106 Freiburg, Germany. (Email: alex.frydrychowicz{at}uniklinik-freiburg.de).
In light of the current discussion about the effect of blood flow on arterial wall remodeling,1-3
the investigation of vascular hemodynamics within the aorta is of great interest. It has the potential to greatly enhance the understanding of the pathogenesis and progression of vascular diseases and to aid in the decision of whether treatment is warranted. Noninvasive magnetic resonance imaging (MRI), with its intrinsic sensitivity to blood flow, offers the unique possibility to simultaneously acquire morphology and spatially coregistered hemodynamic information noninvasively.4
Electrocardiography-synchronized and respiration-controlled 3-dimensional magnetic resonance (MR) velocity mapping (flow-sensitive 4-dimensional MRI), a state-of-the-art MRI technique, was used to acquire time-resolved, 3-dimensional, morphologic, and 3-directional blood flow data. Visualization was performed with a commercially available software tool initially developed for engineering applications, which allowed for several 3-dimensional visualization modes for a detailed visual inspection of local hemodynamic features associated with complex vascular geometries (Appendix E1).5 A homemade software tool was used to quantify blood flow information at multiple locations along the vascular tree.
Based on an exemplary patient measurement, the possibilities of time-resolved 3-dimensional flow visualization and MR-based quantitative flow analysis are demonstrated, which might influence therapeutic strategies in individual patients in addition to standard clinical diagnostic testing.
Anatomic Findings and Clinical Summary
In this symptomatic patient MR angiography depicted a moderate coarctation of the aortic arch (Figure 1). However, in addition to the stenosis, unusual origins of the supra-aortic branches were diagnosed. A large right common carotid artery was directly followed by the left internal carotid artery. At the height of the coarctation, both the left and right subclavian arteries originated. The right subclavian artery crossed behind the esophagus to the right side as a lusoric artery (Figure 1, white asterisk). Directly distal to the stenosis, the left external carotid artery (Figure 2) branched from the aorta.
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Four-dimensional MR velocity mapping was performed for an additional overview over the flow alterations and hemodynamic status after the surgical procedure. Figure 1, B, resembles particle traces at late systole. The highly accelerated flow within the bypass graft can be clearly appreciated. Additionally, overt vertical and considerable helical blood flow in the descending aorta distal to the bypass anastomosis were observed. Severe blood flow alterations, even further downstream to the site of the bypass, points toward the effect of the performed surgical procedure and the long-term alteration of vessel wall parameters because the helical flow is associated with altered wall shear rates. Also, the efficiency of vascular filling expressed by the energy loss caused by enhanced transverse kinetic energy is jeopardized and might lead to a changed distribution of blood flow further downstream. (These findings can be appreciated in more detail by viewing the time-resolved particle traces shown in Figure E1.)
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1-mimetics. Using this medication, the patient had a relief of neurological symptoms in her daily life. Despite the limitations, such that MRI is not as widely available as ultrasonography and not ubiquitously available, the technique offers a unique possibility for comprehensive assessment of 3-dimensional vascular hemodynamics, especially in complex vascular geometries. More notably, the added information content not assessable with other imaging modalities has the potential to influence therapeutic decision making, as in the case presented here. However, further serial assessments and patient studies are necessary to evaluate the potential to influence therapeutic decision making and planning of operative procedures in vascular disease.
Additional Information on methodology
The investigation was performed on a 3T-MR-scanner (TRIO; Siemens Medical Solutions, Erlangen, Germany) using a previously described and modified radiofrequency-pulse spoiled gradient echocardiographic sequence with interleaved 3-directional velocity encoding. Imaging parameters were as follows: velocity encoding, 150 cm/s; spatial resolution, 2.1 x 3.2 x 3.5 mm3; sagittal oblique field of view, 400 x 300 mm2; flip angle, 15°; echo time, 3.5 ms; repetition time, 6.1 ms; bandwidth, 480 Hz per pixel. Respiratory-controlled imaging was performed based on adaptive navigator gating, allowing for free breathing. After the MR scan, the acquired flow-sensitive 4-dimensional MR data underwent fully automated noise filtering and eddy current correction.
For visualization, a commercially available software package (EnSight; CEI, Apex, NC) was used. Visualization options included 3-dimensional streamlines, time-resolved 3-dimensional particle traces, and 2-dimensional time-resolved vector fields. With these visualization options, a temporal and spatial description of flow characteristics in 3 dimensions was performed.
References
This article has been cited by other articles:
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  E. Weigang, F. A. Kari, F. Beyersdorf, M. Luehr, C. D. Etz, A. Frydrychowicz, A. Harloff, and M. Markl Flow-sensitive four-dimensional magnetic resonance imaging: flow patterns in ascending aortic aneurysms. Eur. J. Cardiothorac. Surg., July 1, 2008; 34(1): 11 - 16. [Abstract] [Full Text] [PDF]
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