Flow dynamics in a 3D printed brain aneurysm model assessed by magnetic particle imaging, magnetic resonance imaging and dynamic subtraction angiography
Jan Sedlacik1, Andreas M. Frölich1, Johanna Spallek2, Nils D. Forkert3, Tobias D. Faizy1, Franziska Werner4,5, Tobias Knopp4,5, Dieter Krause2, Jens Fiehler1, and Jan-Hendrik Buhk1

1Neuroradiology, UKE, Hamburg, Germany, 2Product Development and Mechanical Engineering Design, TUHH, Hamburg, Germany, 3University of Calgary, Calgary, AB, Canada, 4Biomedical Imaging, UKE, Hamburg, Germany, 5Biomedical Imaging, TUHH, Hamburg, Germany

Synopsis

Magnetic particle imaging (MPI) was compared with dynamic magnetic resonance imaging (MRI) and dynamic subtraction angiography (DSA) in a realistic 3D printed aneurysm model. All three methods clearly depicted a distinct pulsatile flow pattern and a delayed contrast agent outflow from the aneurysm. Despite the disadvantages of a much lower temporal resolution of the dynamic MRI and the 2D projection of the DSA, all three methods are valid tools for characterizing the hemodynamics of aneurysms. Especially the radiation free, 3D, high temporal resolution MPI method seems to be a very promising tool for imaging and characterization of hemodynamics.

Introduction

Magnetic particle imaging (MPI) is capable of acquiring 3D datasets with high temporal resolution1, which may be especially beneficial for in vivo hemodynamic imaging. The characterization of the hemodynamics of aneurysms is of particular interest2, since treatment planning and follow-up diagnosis may benefit from this new imaging technique. The purpose of this work was to compare MPI with dynamic magnetic resonance imaging (MRI), and dynamic subtraction angiography (DSA) in a realistic 3D printed aneurysm model3 and to evaluate the capabilities of the different methods.

Materials and Methods

The 3D printed aneurysm model was derived from a static 3D subtraction angiography of a patient with an incidental Internal Carotid Artery (ICA) aneurysm of saccular morphology (ca.5mm diameter). The model was printed with 254µm thick layers of acrylonitrile butadiene styrene at fused deposition modeling using the HP Designjet 3D printer and impregnated with Nano-Seal (Jeln Imprägnierung, Schwalmstedt, Germany)4. The aneurysm model was connected to a peristaltic pump, which was set to deliver a physiological flow and pulsation rate of about 250mL/min and 70/s, respectively. However, due to the peristaltic nature of the pump, the pulsation profile is not comparable with physiology. 4D phase contrast flow quantification (4D pc-fq) and dynamic MRI, i.e. time-resolved contrast enhanced angiography with stochastic trajectories, was performed using a 7T Bruker Clinscan small animal MRI. The 4D pc-fq was triggered with the pump pulsation and measured over 4 hours to obtain sufficient spatial resolution (500µm isotropic) and signal to noise ratio. The dynamic MRI measurement was optimized for fast dynamic MRI acquisition (270ms) while administering a bolus of 3mL 0.05mol(Gd-DOTA)/L with a rate of 1mL/s using a syringe pump and an angiographic catheter with 1mm inner diameter. The tip of the catheter was placed close to the aneurysm model (ca.5cm upstream) to reduce bolus dispersion. The first commercially available preclinical MPI scanner (Bruker/Philips) was used to acquire 1mm isotropic 3D data with 21.5ms temporal resolution while administering a bolus with 50mmol(Fe)/L (MM4, TOPASS GmbH, Berlin, Germany) similarly as for the dynamic MRI measurement. DSA was acquired using a Philips Allura FD20 with a temporal resolution of 33.3ms during bolus injection of 150mg(iodine)/mL (Imeron) similar as for the dynamic MRI and MPI measurements. Image post processing and visualization was done with in house written software using Matlab.

Results

Distinct pulsatile flow as well as lower flow velocities and a vortex inside the aneurysm were clearly detected using 4D pc-fq (Fig.1-3). Dynamic MRI, MPI and DSA also showed a clear pulsation with higher signal or attenuation, i.e. contrast agent concentration, during the low flow pulsation phases as well as a delayed contrast agent outflow from the aneurysm (Fig.1). Single frames around maximum contrast agent concentration allow depicting the contrast agent passage through the model for MPI and DSA but not for dynamic MRI (Fig.4).

Discussion and Conclusion

4D pc-fq enables a nearly perfect depiction and characterization of flow patterns, which is very helpful for better understanding the contrast agent dynamics of our aneurysm model. However, extreme long scan times and averaging over thousands of pulsation cycles renders clinical application impossible, where short dynamic real time measurements are required. All three dynamic methods (MRI, MPI, and DSA) showed the same distinct pulsation as detected with 4D pc-fq and a delayed contrast agent outflow from the aneurysm caused by the vortex inside the aneurysm. The higher contrast agent concentration during the low flow pulsation phase is caused by the constant bolus injection rate resulting in less diluted contrast agent during the low flow and more diluted contrast agent during high flow pulsation phases. The MPI even depicts the secondary low flow pulsation phase by a low broad signal maximum in between two consecutive high sharp signal peaks. This additional fact demonstrates the superior dynamic capabilities of the MPI method with respect to dynamic MRI and DSA. However, all three methods were able to detect the delayed contrast agent outflow from the aneurysm and are, therefore, valid tools to characterize the hemodynamics of aneurysms.

Acknowledgements

We wish to thank the German Research Foundation (DFG), grant no. AD 125 / 5-4, and the Forschungszentrum Medizintechnik Hamburg (fmthh) for financial support and Philips Healthcare for the support and realization of the “Hermann-Zeumer Research Laboratory” including a Philips AlluraClarity Angiography system.

References

1 Weizenecker J, Gleich B, Rahmer J, Dahnke H, Borgert J. (2009)Three-dimensional real-time in vivo magnetic particle imaging. Phys Med Biol; 54: L1-L10.

2 Jeong W, Rhee K. Hemodynamics of cerebral aneurysms: computational analyses of aneurysm progress and treatment. Comput Math Methods Med. 2012;2012:782801.

3 Anderson JR, Thompson WL, Alkattan AK, Diaz O, Klucznik R, Zhang YJ, Britz GW, Grossman RG, Karmonik C. Three-dimensional printing of anatomically accurate, patient specific intracranial aneurysm models. J Neurointerv Surg. 2015 Apr 10

4 Frölich AM, Spallek J, Brehmer L, Buhk JH, Krause D, Fiehler J, Kemmling A. 3D Printing of Intracranial Aneurysms Using Fused Deposition Modeling Offers Highly Accurate Replications. AJNR Am J Neuroradiol. 2015 Aug 20.

Figures

Figure 1: Cyclic repetition of the 4D pc-fq (top) shows distinct pulsation and generally lowered flow inside the aneurysm. Dynamic MRI (second top), MPI (second bottom) and DSA (bottom) also show distinct pulsation and delayed contrast agent outflow from the aneurysm. Pulsations are not perfectly matched between the different methods.

Figure 2: Exemplary false color visualization of the 4D pc-fq at the time point of maximal flow velocity during one pulsation cycle, i.e. ca.0.7s. Lower flow velocity and different flow directions are clearly visible inside the aneurysm.

Figure 3: Exemplary vector field visualization of the 4D pc-fq at the time point of maximal flow velocity during one pulsation cycle, i.e. ca.0.7s. A vortex is clearly visible inside the aneurysm.

Figure 4: Matched frames of dynamic MRI, MPI and DSA during passage of maximal contrast agent concentration (ca. 3-3.5s in Fig.1). While the contrast agent passage can be appreciated in MPI and DSA, it is not visible in MRI.



Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)
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