Speaker
Description
INTRODUCTION
Here we present “DentMRI – Gen I” (Fig. 1(a)), a home-made special-purpose MRI scanner designed with the goal of demonstrating dental imaging at low field (260 mT). We use two variations of zero echo time (ZTE) pulse sequences (Fig. 1(b)): standard PETRA [1,2], and Double Radial Non Stop Spin Echo (DRaNSSE), which we have devised to address limitations we encounter with PETRA. We perform image reconstruction by Algebraic Reconstruction Techniques (ART, [3]).
METHODS
“DentMRI – Gen I” operates with a “C”-shaped permanent NdFeB magnet that provides 260 mT over a spherical region of 150 mm in diameter. The system is equipped with a gradient system capable of reaching strengths > 0.4 T/m along any spatial direction and a TxRx RF solenoid coil able to induce a flip angle of 90 degrees in a few microseconds.
RESULTS
Figure 2(c) contains selected slices from the full 3D ART reconstruction of a rabbit head employing a PETRA sequence with 0.5 mm isotropic resolution. We acquired two images: one with a short (90 µs) dead time (Fig. 3(c) top) with a scan time of 61 minutes; and one with a long (1 ms) dead time (Fig. 2(c) middle) with a scan time of 31 minutes. The bottom image in Fig. 3(c) shows difference between both images to highlight hard tissues.
Figure 3 shows ART reconstructions slices from DRaNSSE (top) and PETRA (bottom) acquisitions. Images were acquired with 1 mm isotropic resolution with a total scan time of 30 (15) minutes for DRaNSSE (PETRA). Due to the long echo time for the second echo (10 ms), tissue contrast is higher with DRaNSSE.
DISCUSSION/CONCLUSION
In the present work we have demonstrated the capability of our new low-cost “DentMRI – Gen I” scanner to simultaneously image hard and soft biological tissues; we have devised a new pulse sequence (DRaNSSE) that, compared to standard sequences such as PETRA, yields higher SNR images and enhanced tissue contrast.
ACKNOWLEDGMENT
This work was supported by the European Commission under Grants 737180 (FET-OPEN: HISTO-MRI) and 481 (ATTRACT: DentMRI). S. Aja-Fernández acknowledges Ministerio de Ciencia e Innovación of Spain for Research grant RTI2018-094569-B-I00
REFERENCES
[1] M. Weiger, K. P. Pruessmann, A.-K. Bracher, S. Köhler, V. Lehmann, U. Wolfram, F. Hennel, and V. Rasche, “High-resolution ZTE imaging of human teeth,” NMR in Biomedicine, vol. 25, no. 10, pp. 1144–1151, oct 2012. [Online]. Available: http://doi.wiley.com/10.1002/nbm.2783
[2] D. M. Grodzki, P. M. Jakob, and B. Heismann, “Ultrashort echo time imaging using pointwise encoding time reduction with radial acquisition (PETRA),” Magnetic Resonance in Medicine, vol. 67, no. 2, pp. 510–518, feb 2012.
[3] R. M. Gower and P. Richtarik, “Randomized iterative methods for linear systems,” SIAM Journal on Matrix Analysis and Applications, vol. 36, no. 4, pp. 1660–1690, 2015.
