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 RadiologyUniversity of Minnesota Medical School,

Minneapolis, Minnesota, USADjaudat 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.

DentinOrganic 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 msConnective tissue, vessels and nerves.

Only the pulp is visible by conventional MRI.Images of enamel, dentin and cementun havebeen 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.

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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.

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Direct MRI of a tooth (in vitro)

sagittal3D MRI of decayed molar tooth obtained with SWIFTsw = 62.5 kHz, 4.7 T, 10 min.

demineralization

pulp

cementum

plaque

rootdentin

Direct MRI of a tooth (in vitro)

coronal3D MRI of decayed molar tooth obtained with SWIFTsw = 62.5 kHz, 4.7 T, 10 min.

demineralization

pulp

root

dentin

Direct MRI of a tooth (in vitro)

Mip and rotation3D MRI of decayed molar tooth obtained with SWIFTsw = 62.5 kHz, 4.7 T, 10 min.

4 T 1H Quadrature microstrip-loopRF surface coil for dental imaging

RF field penetration of the coil in three

orthogonal directions 30 cm

SWIFT3 minsw = 62 kHz,256 x 256 x 64

Gradient-echo2.5 minsw = 80 kHz, TE = 3ms256 x 256 x 64

LOOK MOM, NO CAVITIES!

Selected slices of 3D images of a normal mandible and surrounding area. (4T).

(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)

Fillings and crowns in SWIFT images

Dental cement filling Ceramic crown covering two teeth

Direct MRI of a toothunder “in vivo conditions”

Tooth surrounded by sponge in water,4 T human magnet, total FOV diameter 15cm

3D SWIFT, orthogonal slices, (10 min)sw = 62.5 kHz

3D FLASH (15 min)TE=3mssw = 80 kHz

demineralization

In-vivo conditions, varying bandwidth (sw)

sw = 62.5 kHzsw = 125 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!

End

The advantages of SWIFT

(a) 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 extractionsw = 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 ***

x

p

x

. . .

(c)

(b)

(a)

Gx

Gy

Gz

1

RF

-c

acq

dw

a

Tp

TR

Direct MRI of a tooth (in vitro)

3D MRI of decayed molar tooth obtained with SWIFTsw = 62.5 kHz, 4.7 T, 10 min.

demineralization

pulp

cementum

plaque

rootdentin