Direct MRI of Human Teeth using SWIFT Djaudat Idiyatullin, Curt Corum, Adeka McIntosh, Steen Moeller, and Michael Garwood Center for Magnetic Resonance Research (CMRR), Department of Radiology University of Minnesota Medical School, Minneapolis, Minnesota, USA Djaudat Idiyatullin, Curt Corum, Adeka McIntosh, Steen Moeller, Michael Garwood Direct MRI of Human Teeth by SWIFT. At Joint Annual Meeting ISMRM-ESMRMB May 19- May 25, 2007, Berlin, Germany.

1H NMR relaxation properties a tooth Enamel T2 ~70 μs Organic matter and water ~14% by wt. Dentin Organic matter and water ~35% by wt. T2 multi exponential : ~220 μs (28%) ~ 56 μs ( 7%) ~ 12 μs (56%) T1: ~100 ms Cementum T2 ~70 μs ? Organic matter and water ~55% Pulp T2 > 1 ms Connective tissue, vessels and nerves. Only the pulp is visible by conventional MRI. Images of enamel, dentin and cementun have been obtained only by solid-state MRI in vitro.

Reported MRI of Teeth: SPI (Single Point Imaging): Lockhart et al., Proc Finn Dent Soc., (1992) Appel and Baumann, Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology & Endodontics, (2002) STRAFI (Stray-field imaging): Baumann et al., Oral Surgery, Oral Medicine…, (1993) BLAST (Projection MRI): Wu et al., Proc Natl Acad Sci U S A, (1999) FLASH (“Liquid” sequences): Tutton et al., Br J Radiol, (2002) Olt et al., Magn Reson Med, (2004) Gahleitner et al., Rofo, (1998) Lloyd et al., Caries Research, (2000) UTE Gatehouse and Bydder, Clinical Radiology, (2003) SWIFT…

Challenges for direct in vivo MRI of teeth Range of 1H relaxation times (T2): ~ 10 – 100 μs Any echo based sequence unusable! Total acquisition time: for in vivo experiments ~10 minutes SPI and Stray-field imaging impractical! Peak RF power limit (for broadband excitation): Projection MRI (BLAST) impractical?

SWeep Imaging with Fourier Transform (SWIFT) D. Idiyatullin, C. Corum, J.-Y. Park, M. Garwood, Fast and quiet MRI using a swept radiofrequency, Journal of Magnetic Resonance 181, (2006) 342-349.

SWeep Imaging with Fourier Transform (SWIFT) D. Idiyatullin, C. Corum, J.-Y. Park, M. Garwood, Fast and quiet MRI using a swept radiofrequency, Journal of Magnetic Resonance 181, (2006) 342-349.

SWeep Imaging with Fourier Transform (SWIFT) D. Idiyatullin, C. Corum, J.-Y. Park, M. Garwood, Fast and quiet MRI using a swept radiofrequency, Journal of Magnetic Resonance 181, (2006) 342-349.

Direct MRI of a tooth (in vitro) demineralization pulp plaque dentin cementum root sagittal 3D MRI of decayed molar tooth obtained with SWIFT sw = 62.5 kHz, 4.7 T, 10 min.

Direct MRI of a tooth (in vitro) demineralization dentin pulp root coronal 3D MRI of decayed molar tooth obtained with SWIFT sw = 62.5 kHz, 4.7 T, 10 min.

Direct MRI of a tooth (in vitro) Mip and rotation 3D MRI of decayed molar tooth obtained with SWIFT sw = 62.5 kHz, 4.7 T, 10 min.

4 T 1H Quadrature microstrip-loop RF surface coil for dental imaging RF field penetration of the coil in three orthogonal directions 30 cm

Selected slices of 3D images of a normal mandible and surrounding area Selected slices of 3D images of a normal mandible and surrounding area. (4T). LOOK MOM, NO CAVITIES! Gradient-echo 2.5 min sw = 80 kHz, TE = 3ms 256 x 256 x 64 SWIFT 3 min sw = 62 kHz, 256 x 256 x 64

Fillings and crowns in SWIFT images Ceramic crown covering two teeth Dental cement filling (Filling compounds T2 slightly longer than T2 of dentin, or proton density higher?) (In SWIFT images, the ceramic crown does not create a pronounced susceptibility artifact)

Direct MRI of a tooth under “in vivo conditions” Tooth surrounded by sponge in water, 4 T human magnet, total FOV diameter 15cm demineralization 3D FLASH (15 min) TE=3ms sw = 80 kHz 3D SWIFT, orthogonal slices, (10 min) sw = 62.5 kHz

In-vivo conditions, varying bandwidth (sw) sw = 125 kHz sw = 62.5 kHz sw = 31 kHz Tooth surrounded by sponge in water, 4 T human magnet, 3D SWIFT, total FOV diameter 15cm, (10 min)

Conclusions Direct MRI of teeth is feasible with SWIFT Demineralization and associated Decay are easily visible, (First observation of MRI contrast in deminerized tooth?) The SWIFT sequence appears well suited to studying the progress of dental caries and for early stage diagnosis of dental caries.

More SWIFT 1669. Signal Processing and Image Reconstruction for SWIFT 1670. Progress in Rapid and Short Acquisition Delay Imaging with SWIFT 3805. Ultrastructural Organization of Bone and Tendon – Novel Method for Musculoskeletal Imaging of Extremely Fast Relaxing Spins Acknowledgments. We gratefully acknowledge support by NIH grants 5R01CA092004 and 5P41RR008079, the Keck Foundation. Thanks to many others at the CMRR!

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The advantages of SWIFT fast; The method avoids delays for gradient switching, and also time for the excitation pulse (it’s combined with the acquisition period). (b) sensitive to short T2 ; any T2 > 1/sw. (c) reduced motion artifacts; Because the SWIFT method has no “echo time” it is expected to be less sensitive to motion and flow artifacts than conventional MRI methods. (d) reduced signal dynamic range; The different frequencies are excited sequentially the resulting signal is distributed in time, leading to a decreased amplitude of the acquired signal. This allows more effective utilization of the dynamic range of the digitizer. (e) quiet. The SWIFT method uses a small step when changing gradients between projections, and the fast gradient switching that creates loud noise can be avoided.

Direct MRI of the teeth (in vitro) Two hours after extraction sw = 62 kHz, 4.7 T Dried (Three month in room temperature) sw = 125 kHz, 9.4 T

SWeep Imaging with Fourier Transform (SWIFT) D. Idiyatullin, C. Corum, J.-Y. Park, M. Garwood, Fast and quiet MRI using a swept radiofrequency, Journal of Magnetic Resonance 181, (2006) 342-349. Animate this ***

Direct MRI of a tooth (in vitro) demineralization pulp cementum plaque root dentin 3D MRI of decayed molar tooth obtained with SWIFT sw = 62.5 kHz, 4.7 T, 10 min.