Introduction Blood velocity and quantitative parameters such as wall shear stress (WSS) can be investigated non-invasively with 4D Flow MRI, and a comparison of these parameters between patients with ruptured and un-ruptured intracranial aneurysms (IAs) has been suggested to be useful in the differentiation between aneurysms at risk for rupture and stable aneurysms. In this context, although ruptured IAs cannot be easily scanned with 4 D flow MRI in-vivo, these, like un-ruptured IAs, can be modeled and 3D printed. The upscaled 3 D printed flow phantoms can then be scanned with 4D Flow MR at unsurpassed conspicuity. Herein, we investigate the feasibility of measuring detailed blood flow information in small IAs in-vivo (less than 7 mm in size) and comparing the data with data obtained from scanning in-vitro scaled-up and 3D printed models of the same IAs.
Methods Four patients presenting with one, and one patient presenting two incidentally discovered small aneurysm(s) were scanned with 4D flow sequences at 7Twith a resolution of 0.76 × 0.76 × 0.8 mm3. Based on non-invasive imaging studies, the same aneurysms were numerically modelled, upscaled, 3D printed and assembled in an MR-compatible, dynamic flow circuit filled with a fluid chosen for its Reynolds and Womersley numbers. 4D Flow MR data were then acquired at 3T with this setting.
Results In the patient with two IAs, one was missed (positioning error) while the other proved to be too small (<2 mm) to be captured at 0.76 × 0.76 × 0.8 mm3 resolution, suggesting that 2 mm may be the lower limit of our current protocol. When successful, however, 4D Flow at 7 Tesla revealed sharply defined velocity vectors and derived parameters. 3T measures of 4D Flow in the upscaled 3D printed replica of the same aneurysms (figure 1) demonstrated fairly similar velocity patterns when compared to in-vivo data.
Conclusion We successfully obtained sub-millimetric in-vivo 4D Flow scans in small IAs at 7T. 4D Flow at 3T of aneurysm-specific 3D printed replicas yielded flow patterns comparable to those obtained in-vivo. These findings suggest that a larger comparative study of upscaled 3D printed of ruptured and unruptured small IAs could provide useful insight into the role of hemodynamics in rupture of small IAs.
Disclosures B. Jagadeesan: 1; C; Microvention, Medtronic. 2; C; Microvention, CvRx. M. Toloui: None. O. Amili: None. S. Schmitter: None. S. Moen: None. K. Ugurbil: None. A. Grande: None. F. Coletti: None. P. Van de Moortele: None.
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