1. 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.

2. 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.

3. 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…

4. 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?

5. 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)

6. 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)

7. 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)

8. 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.

9. 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.

10. 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.

11. 4 T 1H Quadrature microstrip-loop RF surface coil for dental imaging
RF field penetration of the coil in three orthogonal directions
30 cm

12. 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

13. 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)

14. 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

15. 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)

16. 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.

17. 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 5R01CA and 5P41RR008079, the Keck Foundation.
Thanks to many others at the CMRR!

18. End

19. 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.

20. 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

21. 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)
Animate this ***

23. 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.