DIXON MRI APPLICATIONSAndrew T. Trout, MD

@AndrewTroutMD

Disclosures

• Philips Healthcare – Travel support

• Perspectum Diagnostics – In-kind support

for research

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

Basics of the Dixon Method

Simplistically:

–Decomposes signal into:

• Component contributed by lipid

• Component contributed by

water

–Can be recombined any

number of ways

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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

½

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

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

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

Improved Fat Saturation

T2W TSE SPAIR Dixon T2W TSE (water)

Improved Fat Saturation

BH T1 FSPGR FS Dixon T1W GRE (water)

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

Precise Co-registration

Water FatIn Out

Precise Co-registration3 minute, RTr

WaterFat In Out

Tissue Fat and Iron Quantification

Water

Fat In phase Fat Fraction Map

Out of phase T2*/R2* Map

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)

Tissue Fat and Iron Quantification

r = 0.98

r = 0.97

r = 0.98 12 – 23%

Tissue Fat and Iron Quantification

r = 0.98 r = 0.98

Fat Mapping

subcutaneous

retroperitoneal

peritoneal

peritoneal + retroperitoneal = visceral

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.

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.

Whole Body Imaging / PET/MRI

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

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

THANK YOU

@AndrewTroutMD