DIXON MRI APPLICATIONS

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DIXON MRI APPLICATIONS Andrew T. Trout, MD @AndrewTroutMD

Transcript of DIXON MRI APPLICATIONS

Page 1: DIXON MRI APPLICATIONS

DIXON MRI APPLICATIONSAndrew T. Trout, MD

@AndrewTroutMD

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Disclosures

• Philips Healthcare – Travel support

• Perspectum Diagnostics – In-kind support

for research

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Disclosures

I am a simple guy

–The physics discussed are

simplified and are meant only

to give a general

understanding of what is

happening

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Basics of the Dixon Method

• Capitalizes on chemical shift

difference between water and fat

• Acquire images different TEs to

model phase shift

W. Thomas Dixon, Ph.D.

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In Out In

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Basics of the Dixon Method

Simplistically:

–Decomposes signal into:

• Component contributed by lipid

• Component contributed by

water

–Can be recombined any

number of ways

allfreedownload.com

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Basics of the Dixon Method

• Two point Dixon–Acquire data in and out of phase

• Post process

In

In = water + fat

Out

Out = water - fat

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Basics of the Dixon Method

In = water + fat Out = water - fat

+ =Water image

-In = water + fat Out = water - fat

=Fat image

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Basics of the Dixon Method

• Variable number of echoes acquired (2

point is most simplistic)

–Higher = longer scan time

–Higher = better SNR

–Higher = better fat:water separation

–Quantitative techniques require more echoes

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Basics of the Dixon Method

• Can be applied to basically any sequence– Cartesian (e.g. FSE, SSFP, GRE)

– Non-Cartesian (e.g. radial, spiral, PROPELLER)

• Can generally BH or trigger

• In general, applying Dixon to a sequence requires slight lengthening of the TE and TR to allow encoding of chemical shift

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Applications of the Dixon Method

• Improved fat saturation

• Precise co-registration of images

• Fat and iron quantification

• Fat mapping

• Whole body MRI and PET/MRI

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Improved Fat Saturation

T2W TSE SPAIR Dixon T2W TSE (water)

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Improved Fat Saturation

BH T1 FSPGR FS Dixon T1W GRE (water)

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Benefits of Dixon vs. Spectral Fat Sat

Less susceptibility to B0 inhomogeneity

–Significant inhomogeneity (e.g. near metal) can

still be problematic [fat:water swapping]

Water Fat In Out

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Precise Co-registration

Water FatIn Out

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Precise Co-registration3 minute, RTr

WaterFat In Out

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Tissue Fat and Iron Quantification

Water

Fat In phase Fat Fraction Map

Out of phase T2*/R2* Map

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Tissue Fat and Iron Quantification

CCHMC 4 seq Diffuse Liver Dz MRI (~15 min)

–Elastography

–Dixon fat/iron

–Coronal T2 (anatomy)

–Axial T2 (anatomy &

liver volume)

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Tissue Fat and Iron Quantification

r = 0.98

r = 0.97

r = 0.98 12 – 23%

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Tissue Fat and Iron Quantification

r = 0.98 r = 0.98

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Fat Mapping

subcutaneous

retroperitoneal

peritoneal

peritoneal + retroperitoneal = visceral

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Fat Mapping

• Intra-abdominal (visceral) adiposity

correlates w/ cardiovascular risk factors in

adolescent girls

• High proportion of visceral fat w/ relatively

low subQ fat = metabolically high risk

Caprio S, et al. Am J Clin Nutr. 1996 Jul;64(1):12-7.

Taksali SE, et al. Diabetes. 2008 Feb;57(2):367-71.

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Fat Mapping

Dixon-based techniques may be able to

identify and quantify brown fat by MRI

–In rodents, >water content in brown fat

Rasmussen JM, et al. PLoS One. 2013 Oct 30;8(10):e77907.

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Whole Body Imaging / PET/MRI

Catana C. Magn Reson Imaging Clin N Am. 2017 May;25(2):231-243.

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Conclusions

• Multiple applications of the Dixon Method

–Improved fat saturation

–Fat and iron quantification

–Tissue mapping

• If you aren’t using it – give it a try

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THANK YOU

@AndrewTroutMD