Rationale and Objectives
Multidirectional phase-contrast magnetic resonance imaging allows the acquisition of time-resolved velocity fields (vectors) of cardiac and vascular blood flow. Its unique ability to provide vectorial flow information promises to give new insights into hemodynamic physiology. However, up to now appropriate and standardized procedures and software tools are missing to take advantage of all the information contained in the data. The objective of this work is to present a new versatile software tool and to demonstrate its practical value for the examination of multidirectional blood flow.
Materials and Methods
An exemplary selection of data sets from healthy volunteers, patients with cardiovascular pathologies, and healthy domestic pigs has been acquired using a phase-contrast magnetic resonance imaging sequence based on FLASH (fast low angle shot) that encodes velocity as field of three-dimensional vectors. For data processing, we have developed a software tool that integrates the whole workflow, including noise filtering, interactive visualization, and flow quantification.
Results
Using the software tool visualization of complex flow data is easily generated within 5 minutes; interactive exploration of the data is possible in real-time. Exemplary physiologic and pathologic flow patterns were visualized in an intuitive manner. The visual results suggest valuable diagnostic information; its significance, however, must be further evaluated together with the development of more specific data processing.
Conclusions
Multidirectional phase-contrast magnetic resonance imaging is a valuable tool for assessment of cardiac and vascular hemodynamics. With the development of tools that offer standardized and thus comparable visualizations it may be integrated into the clinical routine in the near future.
Phase-contrast flow measurements in magnetic resonance imaging (pc-MRI) are widely used to noninvasively assess hemodynamics. Most often the technique is used to quantify blood flow orthogonal to an imaging slice ( ). It has been demonstrated to yield high precision and reproducibility ( ), but the measurement is limited to one axis. To acquire the entire three-directional (3D) flow (ie, velocity vectors), this technique can be enhanced by additional velocity encoding gradients. Then, acquiring a time-resolved stack of slices or a 3D volume, respectively, velocity maps and particle paths can be calculated inside major vessels being covered.
Although one-directional flow measurements can be postprocessed with commercially available software, no software exists for multidirectional pc-MRI. This lack impedes the use of the data in clinical routine, because it is difficult to interpret visually. There is no commonly accepted application in the radiologic practice. Besides, relatively long acquisition times are considered to be a major limitation. With the development of appropriate software tools appreciation of the data might increase, and new applications for the examination of all vascular pathologies, in pretreatment screening as well as for postoperative follow-up, might be defined.
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Material and methods
Data
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Software Tool
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Preprocessing
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Visualization Techniques
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Probing tool
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Virtual echocardiography
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Vector flow visualization
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Quantification
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Results
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Discussion
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Acknowledgment
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