About us - sinapse

Fat quantification in the
liver using SAGE
Scott Hanvey, John Foster, Stuart
Ballantyne, Nazim Ghouri, Naveed Sattar
Beatson West of Scotland Cancer Centre
& the University of Glasgow, Scotland, UK
Introduction
• Background to 1H MRS in liver fat
quantification
• Project using 1H MRS at the Beatson
• Steps involved in using SAGE
Background
• MRS can measure liver fat by measuring lipid
peaks
• Peaks correspond to different metabolites and
are identified by their frequencies (ppm)
• The dominant peaks in liver are H2O and lipids
Metabolites
• Healthy liver of 36 year old woman
• Area under a peak can quantify the amount
of metabolite in voxel
• No absolute y-axis scale, so ratio needed for
objective quantification
Scan protocol
• Single or multi-voxel? SV SNR↑
• SV generally used in liver because of distance from
coil to organ
• Point RESolved Spectroscopy (PRESS) – 90° then
two 180 ° orthogonal section-selective pulses
• To ↑ SNR, ↑ voxel, ↑ number of scans, ↑ field
strength
MRS challenges
• Respiration, cardiac pulsation or peristalsis can
↑ line widths, ↑ frequency shifts, ↓ peak areas,
↓ quality of water suppression
• Respiration/movement in liver MRS
lead to data contamination
• Voxel should be away from major
vessels/edge of liver
Lipid peaks
•
•
•
•
Grade 0: < 5% fat
Grade 1: 6%-33% fat
Grade 2: 34%-66% fat
Grade 3: > 66% fat
• Lipid consists of multiple peaks
• Dominated by methyl (CH3) and methylene (CH2)
at 0.9-1.1 ppm and 1.3-1.6 ppm
Fat
%
Total _ lipid =
(Fat + H 2O )
Project: Relationship of body
fat to insulin resistance in SAs
• South Asians (SA) are high risk for diabetes & heart
disease
• Investigating whether SA have ↑ liver fat & if this
explains their greater insulin resistance
• Recruiting healthy European & SA volunteers to
assess whole body fat (particularly liver fat), insulin
resistance & fitness
• Using IDEAL quant and MRS
IDEAL quant
• Iterative Decomposition of water and fat with Echo
Asymmetry and Least-squares estimation Quantitative
• Prototype sequence
• Uses resonant freq diffs between H2O and fat,
measured as phase diff in multiple echoes
• Generates H2O, Fat, Field Map, T2* corr: H2O, Fat,
IP, OP, R2*, Fat Fraction in one scan
• Investigating alongside more established MRS
From the scanner
• No water peak
• Need software to analyse
• Need to export
Using SAGE
• It is possible to display SAGE on a linux using the
network protocol Telnet
• Prevents need to use scanner console
Loading raw data
• Raw data is displayed as P files
• Important to back up as these can be lost
Raw data file
• Raw data comes w/o reconstruction or phase correction
Loading raw data
• Select Recons > Spectrum
• Selecting one of the PROBE will remove the H2O frames
Reconstruction
• Processes raw SV to localised spectrum
Phase correction
• Select Processing > Phase
Reconstruction
• Manual or automatic phase correction
Zoom
Unsuppressed H2O peak?
• Click on Display > New Display > Stack
Stack display
• First 2 frames contain unsuppressed H2O ref peaks
Isolating ref peaks
• Select Display > Zoom Panel
Zoom Panel
• Change spatial dimensions to select frames of data
Zoom Panel
• 0 to 1 gives the unsuppressed H2O frames
Spectrum display
• This changes the stack and spectrum displays
Analysis
• Select Analysis > Analyze Spectrum
Integral of H2O peak
• Adjust L & R pos to measure unsuppressed H2O integral
Zoom panel
• 2 to 33 displays the frames with H2O suppression
Spectrum display
• Again this results in a change to the spectrum
Integral of lipid peak
• Adjust L & R pos to calculate integral of lipid peak
Conclusion
• MRS can be used for liver fat quantification
• MRS of the abdomen is limited by spectral
resolution, SNR & motion
• SAGE offers a method for MRS analysis &
unsuppressed H2O frames w/o exporting
Things can get messy!