Post on 23-Mar-2018
Handout 1
Answers for life.© Siemens GmbH 2016 All rights reserved.
Body Diffusion MRI:Basics and BeyondXiaodong Zhong, PhDSenior R&D Expert, MR R&D Collaborations, Siemens HealthcareAdjunct Assistant Professor, Radiology and Imaging Science, Emory UniversityAtlanta, GA
© Siemens GmbH 2016. All rights reserved.
Body Diffusion MRI: Basics and BeyondOutline
█ Basics of diffusion MRI and body diffusion Physics Pulse sequence Apparent diffusion coefficient (ADC) Common artifacts and parameter
optimization
█ Advanced topics New diffusion sequence techniques Motion correction / registration Advanced acceleration technique
© Siemens GmbH 2016. All rights reserved.
Body Diffusion MRI: Basics and BeyondOutline
█ Basics of diffusion MRI and body diffusion Physics Pulse sequence Apparent diffusion coefficient (ADC) Common artifacts and parameter
optimization
█ Advanced topics New diffusion sequence techniques Motion correction / registration Advanced acceleration technique
© Siemens GmbH 2016. All rights reserved.
Background PhysicsWhat is Diffusion?
The process of Brownian motion
Source: http://en.wikipedia.org/wiki/Brownian_motion
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Background PhysicsWhat is Diffusion?
Diffusion in Isotropic
Medium e.g. water
Diffusion in
Oriented Tissue
E1E2 E3
E1
E2
E3
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Background PhysicsWhat is Diffusion Imaging?
`
time
No differentiation between bound and free proton
Signal difference
more mobility
restricted mobility
90o
180o
Phase dispersion
Handout 2
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Body DiffusionDiffusion Sequence Card Parameters
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Bipolar diffusion encoding scheme.
Benefits:
• better eddy current compensation
=> less spatial distortions
• better for WB-DWI
Monopolar (Stejskal-Tanner)diffusion encoding scheme.
Benefits:
• shorter TE’s possible
• higher SNR => less averages needed
• better for DWI in breast, abdomen, pelvis
RFADC
Gdiff
Gr
Gp
RFADC
Gdiff
Gr
Gp
Background PhysicsDiffusion Encoding Schemes and Sequence Designs
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Diffusion weighting factor, b-value Sets the measurement sensitivity to diffusion Determined by strength of diffusion gradient (G), duration of gradient ()
and duration between the two gradients () Direction of sensitivity can be altered by changing diffusion gradient
direction
Background PhysicsBasic Ideas (1)
time
diffusion gradient diffusion gradient
G G
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DW images (b-value images) Reflect the estimate of the water diffusion rate at that pixel The greater the b-value, the stronger the diffusion weighting, and the higher
the contrast (hyperintense) in pathogenic regions (reduced diffusion) Primary application for early detection of cerebral ischemic stroke, more
sensitive to early changes after a stroke than T1 or T2 weighted images*
* S. Warach et al., J. Cereb. Blood Flow Metab. 16 (1996)
b = 0, not DW (T2 weighted image)
b = 500 s/mm2 b = 1000 s/mm2
Background PhysicsBasic Ideas (2)
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Apparent diffusion coefficient (ADC) A measure of the strength (velocity) of diffusion in tissue Free of the influence of T1 and T2 effects The stronger the diffusion, the greater the diffusion coefficient Exhibits darker contrast (hypointense) in pathogenic regions (reduced
diffusion)
B = 1000 s/mm2ADC map
Background PhysicsBasic Ideas (3)
Compare
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Diffusion Weighted Imaging (DWI)Fundamental Equation
S(0)
b
S(b)
∙
Handout 3
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Diffusion Weighted Imaging (DWI)Fitting the ADC
Generally, more b-values give better fitting
2-pt: / -> partly due to the perfusion effect3-pt: /
6-pt: 0.7 /
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ADCb-value filter for ADC maps calculation
Selectable b-value range for ADC calculation
• eliminate perfusion effects by excluding lower b-values
(organ specific e.g. < 150 s/mm2… ) from ADC calculation
ADC calc. from b 0,100,600
ADC calc. from b 100, 600
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Diffusion Weighted Imaging (DWI)What is the optimal b-value?
Siemens recommended b-values
Anatomy b-value1 b-value 2 b-value 3
Liver 50 400 800
Prostate 50 400 800
Cervix 50 400 800
Kidney 50 400 800
Pancreas 50 400 800
Whole Body 50 800
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Anisotropy: In tissue water diffusion is limited by tissue boundaries
Diffusion encoding can be applied to any directions, but typically three main orthogonal axes
If the same b-value is used
: Isotropic DW image (geometric averaging), or trace-weighted image (TraceW) Averaged ADC map Reflect diffusion weight independent of diffusion orientation.
Background PhysicsBasic Ideas (3)
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Background PhysicsDiffusion Mode Options
Used in most applications and is the standard for all diffusion sequences
Can be used to replace 3-Scan Trace. Will add SNR to images but will also increase time
Used in Whole body diffusion. Reduces TE and overall scan time. Allows for larger amounts of averaging. Note: No Trace weighted Images
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b=50 s/mm2 b=400 s/mm2 b=800 s/mm2
Averaged ADC
DWI ExamplesFree breathing EP2D-DIFF 3-Scan Trace
Handout 4
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Multiple measurements/repetitions can be used to improve SNR
Multiple b-value images can be acquired to improve the ADC calculation
Different averages can be set to different b-values to efficiently use the scan time
The DW images can be inverted to mimic a PET-like appearance
Background PhysicsBasic Ideas (4)
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Background Physicsb-value Averaging
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DWI Examples3-Scan Trace vs 4-Scan Trace vs Increased Averages
3 scan trace
B 50(1avg), 400(2avg), 800
(4avg)
TA: 3:15
4 scan trace
B 50(1avg), 400(2avg), 800
(4avg)
TA 4:34
3 scan trace
B 50(1avg), 400(2avg), 800
(7avg)
4:15
• Increase in SNR from 3 scan trace to 4 scan trace
• Time penalty isn’t that severe in order to improve overall SNR
• Adding averages to the later b-value improves SNR to an already signal deficient image
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DWIb-value Image Extrapolation
Calculated b-value
S(b) = image signal at b-value b
b = b - b0
∆ ∙
© Siemens GmbH 2016. All rights reserved.
Courtesy University of Homburg/Saar, Germany
DWI Examplesb-value Image Extrapolation
b = 0 s/mm2 b = 750 s/mm2 b = 2000 s/mm2
• Extrapolating images to b = 2000 s/mm2 reveals the presence of water restriction
within a peri-tumoral margin in liver metastases (red arrow).
• Furthermore, it is observed that the contrast between metastases and background tissue
is improved (green arrows).
Courtesy Royal Marsden Hospital / UK
Example liver DWI
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Background Physicsb-value Image Extrapolation & Inverted Grayscale
Handout 5
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DWI Examplesb-value Image Extrapolation & Inverted Grayscale
acquired b = 900 s/mm2 computed b = 1500 s/mm2
patient with multiple metastases along thespine from a primary prostate tumour
The contrast in the computed image isimproved compared to the acquired imageas signal from tissues such as the kidneys,testes and salivary glands (red, green and
blue arrows respectively) has been reduced.
Example WB-DWI
Courtesy Royal Marsden Hospital / UK
© Siemens GmbH 2016. All rights reserved.
Courtesy University of Homburg/Saar, Germany
4-years-old female patient with suspicion of Wilms tumorMIP images based on high b-value (800 s/mm2)5 steps composed
Whole Body DWIPediatric tumor staging
© Siemens GmbH 2016. All rights reserved.
Courtesy: Anwar Padhani, Mount Vernon Cancer Centre, UK
pre …. and … post 8 days after chemo cycle
Courtesy: Mount Vernon Cancer Centre, UK
Whole Body DWITherapy Control of a patient with Hodgkin’s Disease
© Siemens GmbH 2016. All rights reserved.
Courtesy: Mount Vernon Cancer Centre, UK
Typical Artifacts in Diffusion (1)Chemical Shift Artifacts in EPI
• Single shot: chemical shift differences have more time to evolve
• Low bandwidth along phase encode chemical shift of > 30 pixels
kphase
kread
© Siemens GmbH 2016. All rights reserved.
Courtesy: Mount Vernon Cancer Centre, UK
Typical Artifacts in Diffusion (1)Chemical Shift Artifacts in EPI
Solution: Fat suppression.
© Siemens GmbH 2016. All rights reserved.
Courtesy: Mount Vernon Cancer Centre, UK
Typical Artifacts in Diffusion (2)N/2 ghosting in EPI
Eddy currents and other imperfections cause phase differences between even and odd lines
Shifted by N/2 from main image
Phase correction not always perfect
N/2
After phase correctionBefore phase correction
Handout 6
© Siemens GmbH 2016. All rights reserved.
Courtesy: Mount Vernon Cancer Centre, UK
Typical Artifacts in Diffusion (2)N/2 ghosting in EPI
Possible reasons and solutions for N/2 EPI ghosts
Mechanical resonance of scanner components – Use appropriate echo spacing (Tesp), for example, avoid 0.6-0.79 ms for Tim Trio
iPAT reconstruction artifacts – Increase the number of reference lines (36-42), at the cost of recon time but not acquisition time
Tesp
b=50
© Siemens GmbH 2016. All rights reserved.
Courtesy: Mount Vernon Cancer Centre, UK
Typical Artifacts in Diffusion (3)Long Echo Spacing and TE
• Leads to longer TE
• More distortion
• More ghosting
• Decreased SNR
TE 115Echo Spacing 1.3
TE 60Echo Spacing 0.5
Possible solutions: • Shorten echo spacing and TE as possible.
© Siemens GmbH 2016. All rights reserved.
Typical Artifacts in Diffusion (4)Off-Center Patient Positioning
• Critical to position the patient in the center of the magnet to ensure consistent image quality!!
© Siemens GmbH 2016. All rights reserved.
Courtesy: Mount Vernon Cancer Centre, UK
Typical Artifacts in Diffusion (5)Free Breathing vs. Navigator
Navigator Triggered
Free Breathing
TA: 5:00
TA: 3:43
• Note the improved sharpness in the sequence Navigator
• Navigator is longer but uses less averages to reduce scan time
• Navigator will produce more consistent image quality
• Free breathing is a great option for most routine exams
© Siemens GmbH 2016. All rights reserved.
Typical Artifacts in Diffusion (6)ADC Thresholding
Thresholding the ADC can lead to removal of anatomy
Noise Level = 10
Noise Level = 60
© Siemens GmbH 2016. All rights reserved.
Typical Artifacts in Diffusion (7)Image Resolution
Stair-step artifact, likely from low spatial resolution
Interpolation ON
May need to switch ON interpolation when 128 matrix is used
Handout 7
© Siemens GmbH 2016. All rights reserved.
Basics of diffusion MRI and body diffusionKey Take Aways
Basic diffusion concepts and principles b-value Diffusion weighted images (b-value images) ADC
Very wide applications Liver, prostate, rectum, breast, etc Whole-body Therapy monitoring, tumor staging, etc
Common artifacts in diffusion and important parameters for optimization Ghosting, failed fat suppression, etc Echo Spacing, TE, iPAT, etc
© Siemens GmbH 2016. All rights reserved.
Body Diffusion MRI: Basics and BeyondOutline
█ Basics of diffusion MRI and body diffusion Physics Pulse sequence Apparent diffusion coefficient (ADC) Common artifacts and parameter
optimization
█ Advanced topics New diffusion sequence techniques Motion correction / registration Advanced acceleration technique
Body DiffusionNew Sequences in Diffusion Imaging
syngo RESOLVE syngo ZOOMit
Three Body Diffusion SequencesPros and Cons
Sequence Applications Advantages Disadvantages
Single-shot EPI
Liver, Prostate, Whole Body, Prostate, Pelvis, Lung, Breast, Rectal CA, Pancreas, Kidney
• Most Commonly used diffusion in the field
• Can be used in all body applications
• More distortion than some techniques
RESOLVE Prostate, Pelvis, Breast • Reduced distortion • Longer scan times
• Unable to use for free breathing applications
ZOOMit Prostate, Rectal CA, Pancreas, Kidney, Breast
• Reduced distortion• Zoomed Field of
Views
• Only availableon pTX systems (Parallel Transmit)
• Not useful for whole body diffusion
RESOLVEPrinciple
Porter DA & Heidermann RM (2009). High resolution diffusion weighted imaging using readout-segmented echo-planar imaging, parallel imaging and a two-dimensional navigator-based reacquisition. Magn Reson Med, 62(2), 468-475.
• Readout-segmented, multi-shot diffusion-weighted EPI
• High-quality, high-resolution DWI and DTI
• Reduced susceptibility and blurring artefacts due to reduced TE and echo spacing
• Insensitivity to motion-induced phase errors
• Reduced SAR in comparison to TSE-based methods
Conventional single shot epi
k-space trajectory
Single shot
Long TE
Long Echo Spacing
RESOLVE
k-space trajectory
Readout direction (kx)
Ph
as
e-e
nc
od
e d
ire
cti
on
(k
y)
1st shot 2nd shot 3rd shot 4th shot 5th shot
RESOLVEBetter delineation of tumor boundaries for prostate carcinoma
T2 TSE
T2 TSE
RS-EPI DW images showed improved image quality compared to SS-EPI technique at 3T and is a feasible technique in the pelvis for producing high-resolution DWI.
National University Hospital, Singapore
Conventional
b0
Conventional
b800
Conventional
ADC
RESOLVE
b0
RESOLVE
b800
RESOLVE
ADC
Thian YL. (2014). Readout-segmented echo-planar imaging for diffusion-weighted imaging in the pelvis at 3T – A feasibility study. Acad Radiol, 21, 531-537.
•*The statements by Siemens' customers described herein are based on results that were achieved in the customer's unique setting. Since there is no "typical“
•hospital and many variables exist (e.g., hospital size, case mix, level of IT adoption) there can be no guarantee that other customers will achieve the same results.
Handout 8
RESOLVEExcellent correspondence to anatomy for rectal carcinoma
T1 3D VIBE FatSat, post contrast
T2 TSE fused with RESOLVE b1000
RESOLVE
b1000 ADC mapb0
Conventional DWI
National University Hospital, Singapore
b1000b0 ADC map
RESOLVESuperior delineation of breast tumor boundaries
Conventional DWI, b750 and ADC map, matrix 192, SL 4 mm, TA 2:47 min
Seoul St. Mary s Hospital, Seoul, South Korea
RESOLVE, b750 and ADC map, matrix 192, SL 4 mm, TA 4:10 min
Rs-EPI was superior to ss-EPI […] for anatomical structure distinction, ghosting artifact and overall image quality […]. Rs-EPI was superior to ss-EPI in SNR and CNR.
•*The statements by Siemens' customers described herein are based on results that were achieved in the customer's unique setting. Since there is no "typical“
•hospital and many variables exist (e.g., hospital size, case mix, level of IT adoption) there can be no guarantee that other customers will achieve the same results.
Kim, HJ, Kim SH et al. (2014) . Readout-segmented echo-planar imagingin diffusion-weighted MR imaging in breastcancer: Comparison w ith single-shot echo-planarimaging in image quality. Korean J Radiol, 15(4), 403-410.
Syngo ZoomItNew Sequence
syngo ZOOMit
Shapeyour
image
ZoomItPrinciple
• Utilizes 2 orthogonal pulses for slice selection
• No need for oversampling
• Reduced distortion
• Utilized in Prostate, Pelvis, Kidney, Pancreas
• Only available currently on pTX systems (Skyra, Prisma)
https://www.healthcare.si emens.com/magnetic-resonance-imaging/options-and-upgrades/clinical-applicati ons /syngo-zoomit/features
ZoomIt in ProstateLess distortions, better tumor delineation
ZOOMit DWI, matrix 58 x 98, FoV 71 x 120, SL 3 mm, TA 4:21
b100 b400 b800 b1200 ADC
Conventional DWI, matrix 96 x 128, FoV 190 x 190, SL 3 mm, TA 4:28Kantonsspital Aarau, Aarau, Switzerland
ZoomIt in KidneyHigher resolution, better differentiation of cortex & medulla
Conventional DWI2.1 mm x 2.1 mm
ZOOMit DWI1.4 mm x 1.4 mm
Handout 9
ZoomIt in RectumBetter delineation of rectal carcinoma with less distortions
University Hospital IKRN, Mannheim, Germany
Conventional DWI b=50, ADC
ZOOMit
3D T2 SPACE - morphology
Emerging New Improvements in Body Diffusion (1)Motion-compensation*
A series of correction/refinement algorithms can be applied on b-value images Inplane-registration of images Filtering of images Denoising of images Rescaling of images to
compensate signal loss due tomotion
Improvements Correction for the left
lobe signal loss Correction for the
misregistration of diffusion weighted images for ADC calculation
* Siemens research w ork-in-progress development.
Original Moco
Emerging New Improvements in Body Diffusion (1)Motion-compensation*
* Siemens research w ork-in-progress development.
b=50, 6 acqs b=400, 9 acqs b=800, 15 acqs
Original
Moco
Emerging New Improvements in Body Diffusion (1)Motion-compensation*
* Siemens research w ork-in-progress development.
b=50, 6 acqs b=400, 9 acqs b=800, 15 acqs
Original
Moco
Emerging New Improvements in Body Diffusion (1)Motion-compensation*
* Siemens research w ork-in-progress development.
Original
Moco
ADC~ 610
ADC~ 90
Emerging New Improvements in Body Diffusion (2)Simultaneous Multi-Slice*
Simultaneous excitation of multiple slices with blipped CAIPIRINHA1
* Siemens research w ork-in-progress development. 1 Setsompop, K. (2012). Blipped-controlled aliasing in parallel imaging for simultaneous multislice echo planar imaging
w ith reduced f-factorpenalty. Magn Reson Med, 67, 1210-1224.
Handout 10
Emerging New Improvements in Body Diffusion (2)About 40% time reduction without compromise2
* Siemens research w ork-in-progress development.
NYU School of Medicine, MAGNETOM Skyra, Head/Neck 20
Conventional
TA 2:20
SMS 2TA 1:211
(42% reduction in scan time)
1 Note that scan time reduction may not be an exact factor of slice acceleration as scan times depends on the TR value specif ied and also because of a fast reference scan required for slice separation. 2 Young, MG, Shepherd TM et al. Multiband sequence reduces scan time for diffusion MRI and tractography in
clinical patients. RSNA, 2014.
b0 b1000 ADC
© Siemens GmbH 2016. All rights reserved.
Advanced topicsKey Take Aways
Understand three diffusion sequences and when to utilize each pulse sequence Single-shot EPI RESOLVE ZoomIt
Emerging new improvements Motion correction / registration Advanced acceleration techniques: Simultaneous multi-slice
acquisition (Multiband)
© Siemens GmbH 2016. All rights reserved.
Body Diffusion MRI: Basics and BeyondAcknowledgement
• Peter Kollasch, PhD• Marcel Dominik Nickel, PhD• Elisabeth Weiland, PhD• Vibhas Deshpande, PhD• Brian Dale, PhD
© Siemens GmbH 2016 All rights reserved.
Page 58 Magnetic Resonance
Answers for life.© Siemens GmbH 2016 All rights reserved.
Thank youfor your attention!