DIXON MRI APPLICATIONS
Transcript of DIXON MRI APPLICATIONS
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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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ob
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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
chairish.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
½
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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