4d flow mri: principles and emmerging applications in ...4d flow mri: principles and emmerging...
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4D Flow MRI: Principles and Emmerging Applications in Aortic disease
SFICV 2019 – JUNE 20TH, VICHY, FRANCE
Arshid AZARINECardio-Vascular ImagingHôpital Paris Saint-Joseph
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Disclosure
Medical Adviser for Arterys ®
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Introduced in late 80’s
2D-PC is a cine sequence ECG gated to cover a cardiac cycle
Principle: 2D-PC evaluates the loss of phase of mobile protons along a bipolar linear magnetic gradient
Thus we can assess velocity and direction ofMobile protons
Background: Fluxometry in MRI using 2DPhase Contrast
Stankovic & al. CD &T, 2014
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Magnitude image:Signal intensity relates to the velocity but with no directional information.
2D Phase Contrast: One-directional through-plane (Z) velocity encoding sequence
Phase image: the blood flow is demonstrated with directional information
1 slice orthogonal to the vessel of interest axis Giving 2 images : • 1 Magnitude image• 1 Phase difference Image
Velocity Map:
Static TissueIntensity = 0
Moving blood:Positive / Negative value
Region of interestContouring XsectionOf the vessel
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Magnitude image:Signal intensity relates to the velocity but with no directional information.
2D Phase Contrast: One-directional through-plane (Z) velocity encoding sequence
Phase image: the blood flow is demonstrated with directional information
In complex aortic diseaseMultiples slices needed orthogonal to each vessel aortic segment = Many breathholds + many fights and time to find the right plane… 6-10 minutes…
Results not always optimal
RA + Coarctation
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4D Flow Imaging
Bogren & Buonocore JMRI 199915 slabs – 6mm Thickness/slabTAC: 60 minutes Temporal Resolution (TR) 112ms Hours/days of post processing
November 2018 TAC: 8:00 minutes – 1.5mm Thk – TR 30msOnline realtime post-processing
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Antero-posterior Superior-Inferior
Magnitude Image
Y Z
X
Right - Left
4D Flow Raw Data
= 1Magnitude & 3 Phase Difference Volumes
4D Flow MR: how does it work?
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Antero-posterior Superior-Inferior
Magnitude Image
Y Z
X
Right - Left
4D Flow Raw Data
•Eddy currents•Noise masking•Filtering of static tissue
= 1Magnitude & 3 Phase difference Volumes
Cloud processing (Protected Health Information)
Preprocessing:Phase Offsets &
Background correction
Helped by AI
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After filtering
Accurate Filtering of eddi currents & offsets errors for reliable Flow Measurement, now helped by DL
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Antero-posterior Superior-Inferior
Magnitude Image
Y Z
X
Right - Left
4D Flow Raw Data
•Eddy currents•Noise masking•Filtering of static tissue
= 1Magnitude & 3 Phase difference Volumes
Preprocessing:Phase Offsets &
Background correction
Helped by AI
Post-Processing:
Visual Flow Analysis
Cloud processing (Protected Health Information)
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Antero-posterior Superior-Inferior
Magnitude Image
Y Z
X
Right - Left
4D Flow Raw Data
•Eddy currents•Noise masking•Filtering of static tissue
= 1Magnitude & 3 Phase difference Volumes
Preprocessing:Phase Offsets &
Background correction
Helped by AI
Post-Processing:
Visual Flow Analysis
Cloud processing (Protected Health Information)
Current trends•Forward Flow•Reverse Flow•Regurgitation Fraction•Peak Velocity
Advanced tools•Wall Shear Stress
Quantitative Flow Analysis
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4D Flow - Checklist just before we start! Optimal ECG Gating (4D = 3D + Time!), retrospective
Explain the patient that the sequence will last 6–10 minutes
Free regular breathing +/- respiratory gating
To Inject or Not To Inject Gadolinium ?
4D Flow is possible without injection
Contrast media increases SNR: larger coverage & shorter acquisition time!
Temporal Resolution / number of Cardiac Frames
Acceleration factor (Compress sensing/ k-t undersampling)
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Recommandation Reason Comment
ECG-gating Retrospective preferred Avoid sequence interruptionCover entire R-R cycle
Crucial for all anatomic areas
VENC Maximum velocity expected(10% higher when possible)
Avoid velocity aliasing Highest is the venc lower is the VNRUse Multiple Venc if available
Temporal Resolution Maximum,
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Analysis step 1: Visual Analysis, 4D Flow offers new tools
Color coding:Red= high velocityBlue= low velocityAdjustable ScaleConsidering the vessel of interest
Velocity VectorsStreamlinesColor velocity 3D MIP
Streamlines: the path that a particle would take if released into the velocity field with the field held constant
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3D Comprehensive visual analysis Of different blood flows:
Laminar, Helical, Eccentric…
Normal Laminar Systolic Flow
Eccentric Turbulent FlowDuring systole in an aortic regurgitation
(Helix: particles revolve around an axisand also have a net forward velocity parallel to the direction of the axis)
HelicalTurbulent Systolic FlowAfter a stenoticComplex Coarctation
Normal central flowWith high velocity
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Analysis Step 2: Flow measurementMulti planar Reformat
• Retrospective 3D multi planar navigation and optimal positioning of any plane within the volume
• Cross sectional ROI placement orthogonal to the vessel axis
• Cloud computing: from anywhere with any device (laptop, tablette…)
Conventional parameters include as in 2D flow:• Forward Flow• Reverse Flow• Regurgitation Fraction• Peak VelocityQuality control apply:- Mass conservationPrinciple!- Comparaison toLV/RV Stroke Volumes
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4D Flow allows Combined Visual and Quantitave Flow AnalysisThe more Complexe is the case the more 4D flow is usefull
2 - optimal measurement
1- risk of error in estimation of the pulmonary RF
Dilated Pulmonary Artery
Vortical turbulent flow
Pulmonary regurgitation
Site 1: 51% of Regugitation FractionSevere PR
Site 2: 42% of Regurgitation Fraction= Moderate pulmonary regurgitation
Combined visual and quantitative analysis is mandatory for a more accurate assessment
2D-PC“Blinded” to the FlowAssessment
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4D Flow MR in Aortic Regurgitation
Vena Contracta = 8mm
PISA= 7mm
4D Flow
TTE
Classical doppler ultrasound parameters can be measured by 4D Flow. Here we find good correlation between TTE & 4D Flow
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Reverse Vortical Flow in Aortic Regurgitation
Vortex: the flow rotates along an axis (just like in a whirlpool) During diastole, ReverseVortical flow is seen in blue « pushing » systolic flow to hit the anterior wall
Visual Analysis tools: Streamlines A Comprehensive visualisation of the blood flow
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4D Flow MR in Valvular diseaseAortic Regurgitation
• Forward Flow• Reverse Flow
Volume• Regurgition
Fraction (FR)• Peak Velocity
Can be Retrospectively & optimaly
Assessed in any plane and location
Ascending Aorta
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Vortical reverse flow in diastolein Aortic RegurgitationComprehensive visualization velocity vectors
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Vortical reverse flowin Aortic Regurgitation: a whirlpool!Comprehensive visualization of different flowsparticles revolving around a point
SystoleAzarine A et Al. Radiographics 2019
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Mesures après Visualisation des Flux Flux laminaires/Flux hélical / Flux vortical
Mesures optimales en évitant les zones de turbulences
Flux antérograde = Volume d’éjection Systolique calculé selon Simpson (en l’absence d’I. Mitrale)
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Kaplan-Meier survival curve showing survival without surgery for conventional indicationsRF of 37% seems to be threshold for severity in CMR (35-40%)
To Further evaluate with 4D flow MRI
S G Myerson et al. Heart 2011;97:A93-A94
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Aortic StenosisEmerging 2D Flow hemodynamic markers
Effective Orifice Area
Bernouilli continuity equation
Stroke Volume (SV) measured at LVOT
Velocity-Time Integral VTIAOis measured at the aortic root 12mm above
CMR derived EOA=SV(LVOT)/VTIAo
Garcia et al. Journal of Cardiovascular Magnetic Resonance 2012
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Assessment of Aortic StenosisCurrent flow-derived parameters
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75 year-old-male with increasing dyspnea moderate aortic stenosis at TTE
75 yo M4D Flow demonstratedModerate Aortic stenosis &Mild aortic regurgitation (12% of FR)
4D FLOW also revealed Sinus venosus ASD with highly significant QP/QS=5!Protosystolic Inverted Right to Left Shunt (vector graph) - PHTRight Ventricle was dilated >150ml/m² with turbulent PA flow
& Partial Anomalous (right) pulmonary veinous return in SVC
PAPVR
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4D Flow and pst procedure follow upPost TAVI Aortic Regurgitation• TAVI: frequency of percutaneous
replacement of the aortic valve is increasing worldwide
• Post TAVI Aortic Regurgitation (AR) is sometimes difficult to assess by TTE
• In this patient AR was diagnosed By TTE after TAVI Implantition, but it’s nature and severity where difficult to assess
• 4D Flow imaging demonstrated minim and mild para prosthetic leak at 2 points in this patient with very calcified annulus
Follow up can be pursued with 4D FLOW MR
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Aortic valve stenosis +/- Aortic dilation4D Flow advanced tools
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Garcia et al. J A C C : C A R D I O V A S C U L A R I M A G I N G , V O L . 1 2 , N O . 2 , 2 0 1 9
Viscous Energy Loss
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Garcia et al. J A C C : C A R D I O V A S C U L A R I M A G I N G , V O L . 1 2 , N O . 2 , 2 0 1 9
Viscous Energy Loss
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Viscous Energy Loss and helical flowPronostic Factor to come?
Garcia et al. J A C C : C A R D I O V A S C U L A R I M A G I N G , V O L . 1 2 , N O . 2 , 2 0 1 9
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4D Flow advanced features:Flow derived Wall Shear Stress (WSS)
Shear Stress
BloodVelovity Profile
Vessel Wall
WSS= v/x v
x
= Blood Viscosity
WSS is expressed in Pa or N/m²
v/x denotes radial velocity gradient at the vessel wall
Indicator for impact of Flow changes onEndothelial cell and extra cellular matrix function
WSS is defined as the tangential viscous shear forces per unit area that is exerted by blood flow to the surface of the vessel
• Assuming blood flow along the vessel, the magnitude of WSS is proportional to the radial velocity gradient at the vessel wall
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Elevated WSS correlated to Elastin degeneration in aortic wall
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Flow Eccentricity BAV patients
• Flow eccentricity was the most sensitive to differences in BAV phenotype• WSS or jet impingement angle and jet flow eccentricity may help better risk-
stratification in patients with ascending aorta aneurysms
Mahadevia R et al. Circulation. 2014 Feb 11; 129(6): 673–682
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4D Flow MR in resistant hypertension in a young adult
Imaging of renal arteries demonstrating large collaterals suggesting coarctation in a Young 38 year old adult with resistant hypertension:Complexe severe coarctation was demonstrated by CMR with 4D Flow
Charpentier, Azarine Vasc Med 2017
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4D Flow MR in Aortic DiseaseAortic Coarctation without bicuspid valve
Systole Diastole
Viscous Energy Loss in Descending Aorta
Systolo-diastolicTurbulent flox through the coarctation
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4D Flow MR in Aortic DiseaseFollow up aortic dissection
True lumen
No regression of the size of the false lumen was noted after endograft. TYPE I or II?4D Flow MRI demonstrates systolic type 1 proximal endoleak (arrow).
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Endovascular Abdominal Aortic Repair (EVAR) Follow up
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Inflow leak from lombar arteries to the aneurysmal sac
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L= AORTIC LUMEN, LA= LOMBAR ARTERIES, E= ENDOLEAK, IMA= INFERIOR MESENTERIC ARTERY
L
IMA
E
LALA
EVAR: Type II b Endoleak
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Right LAInflowLA together 0,04L/min
Left LA
Inflow leak from lombar arteries to the aneurysmal sac
IMA: outflow0,04L/min
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4D Flow MR in Aortic DiseaseTakayasu disease
18 yo FemalewithTakayasu disease under TNF Arterial HypertensionDespite multi drug T.No Renal A. stenosis
Higher velocity in areas w/Aortic wall thickenningElevated aortic Stiffness??
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95
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4D Flow MR in Aortic DiseaseTakayasu disease
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Velocity derived Wall shear stress measurement:Increased Abdominal Aorta WSS in a 18 yo F w/ Takayashu diseaseHypertension without RA Stenosis
WSS MAPduring Diastole
Increased WSSduring Systole
Flow acceleration in the areas of aortic wall thickening
Persistent Inflamatory parietal thickening
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4D Flow MR in Takayasu disease: exploring different vascular beds
With high & low velocity blood flows
Aliasing!!Flow = AUC
CorrectionAlgorythmsNot accurate
If VENC not high enoughPhase wrap artifacts (Aliasing) : measurement errors
Set VENC 10% higher than the Maximum velocity expected
But higher is the VENC, higher is noise!
SCOUT Venc (some constructors)2D-PC Test sequence
Assessing multiple vascular bedsDual or Multiple VENC sequences!
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Brand new! We can avoid phase wrap artifact withDual Venc sequences (x1,5 longer but 2 Vencs)
High Venc (aortic and pulmonaryHemodynamics)
Low Venc (Vena cava connections IVC & SVC flows)
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Low-Venc dataset: Assessment of low flowIVC and SVC connections patency after Senning surgery
High-Venc dataset: assessment of pulmonary and aortic hemodynamics (Aliased on the low-venc dataset)
Exemple of Dual Venc sequence in a patient followed-upAfter Senning repair for Transposition of Great Arteries
Simultaneous Assessment ofLow velocities(IVC/SVC connections)With goodVNR
AndHigh velocitiesWithout aliasing
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4D Flow is a revolutionary new tool in CMR enabling
Optimal flow measurements
A new comprehensive approach by visualizing blood flows
4D Flow enters the field of clinical applications now!
Congenital heart disease, aortic and Valvular heart disease are next
Widespread of new applications are appearing
The more complex the disease the more useful is 4D Flow
Reliability: compare to stroke volume, mass conservation law
Aortic Regurgitation: next Gold Standard??
Dual Venc sequences, when needed, enables good assessment of low and high blood velocities Within the same sequence
4D Flow is ready to go!
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merciThank you for your attention…
You can findThese Pictures Movies, tables & moreIn RadiographicsMay-June 2019ByAzarine A et al.
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