1- I2MR, Inserm, CHU de Rangueil, Toulouse,

2- I3M, Université de Montpellier 2, Montpellier,

3- ALARA

OCFIA (ANR 2007)

‘optimised computational functional imaging for arteries’

Nouveaux marqueurs de la pathologie de l’aorte

thoracique

Detector size numberReconstruction algorithms

Iterative reconstructions

• Wider (Zaxis direction)

• Finer (spatial resolution)

• Faster (scan speed)

Spatial resolutionMinimal slice thickness

Focal spot size

Matrix size

TAVI / TEVAR Planning :

Radiation dose

Aorta CAP CTA: -34%

Iodine load: -44%

SCANNER DE PERFUSION

AF (ml/min/100 ml)

Injection de 40 cc d’iode

Débit ~ 5-7 cc/s

Acquisitions itératives

Recalage élastique

VELOCITY (m/sec)

VORTICITY (m.s-2)

WALL SHEAR STRESS (WSS) (Pa)

AORTIC WALL STRESS – COMPLIANCE

3D CTA

Definition of inlet and outlet boundary condition

At the aortic inlet, boundary conditions were set according to typical physiological conditions with pulsatile pressure of 120/80 mmHg, a heart rate of 75 BPM, and an average cardiac output.Flow distribution conditions of 12% to the IA, 8% to the LCCA and 7% to the LSA were imposed. At the descending aorta outlet, the time-dependent flow rate at the descending aorta was dictated by mass conservation, leaving about 75% of blood to flow towards lower body.

Evaluation 3D de la fonction globale et segmentaire du ventricule gauche

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Applications cliniques

Anévrysmes

Dissections

Suivi post therapeutique

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Conclusions: dimensional differences in thoracic aorta between systolic and diastolic phase are significant.

Annals of Vascular Surgery 2016

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Displacement force vector are helicoidal & force magnitude changes over the cardiac cycle.

Incr

eas

in d

iam

. in

mm

Initial Transversal Diameter

30-39 40-49 > 50 mm

R. Limat et al.

5,29± 0,59

6,88± 0,91

7,45± 1,71

Rates of growth of aortic aneurysms are highly variable among different individuals. The ‘simplified’ Law of Laplace cannot explain why different

patients initially presenting with equivalent maximum diameters, have different rates of diameter progression afterwards.

WSS quantification could be an important biomarker of disease progression

Front. Physiol., 10 July 2017

Tissue histopathology. Aortic wall regions are exposed to elevated WSS (middle, red region), due to eccentric transvalvular BAV flow (left). This manifests in the expression of abnormal tissue metrics of aortopathy (right).

The aortic media regulates tissue biology and biomechanics

Applications cliniques

Anévrysmes : risque evolutifs

Dissections

Suivi post therapeutique

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Applications

1. Sélection des bons candidats pour l'aorte ascendante et les Type B non compliquées

1. Travaux expérimentaux

2. Essais cliniques

2. Stratégie thérapeutique

3. Étude de suivi

• Entry tears• Re entry• True and false lumen • Collaterals

Satoshi Numata et al. Eur J Cardiothorac Surg 2016;49:1578-1585

D Dillon-Murphy Biomech Model Mechanobiol. 2016; 15:

Streamlines

peak systole mid diastole

WSS vectors OSI oscillatory shear index

Medical Engineering & Physics, Volume 36, Issue 3, 2014, 275–284

Entry Tear 1

Entry Tear 2

Recommendations Class Level

In all patients with AD, medical therapy including pain relief and blood pressure control is recommended.

I C

In patients with type A AD, urgent surgery is recommended. I B

In patients with acute type A AD and organ malperfusion, a hybrid approach (i.e. ascending aorta and/or arch replacement associated with any percutaneous aortic or branch artery procedure) should be considered.

IIa B

In uncomplicated type-B AD, medical therapy should always be recommended.

I C

In uncomplicated type-B AD, TEVAR should be considered. IIa B

In complicated type-B AD, TEVAR is recommended. I C

In complicated type-B AD, surgery may be considered. IIa C

IIa

Do you routinely stent uncomplicated type B aortic dissection?

54,8% do not routinely stent uncomplicated TBAD

37,4% routinely stent based on various imaging criteria

7,8% routinely stent 130 centers in US & worlwide

Adverse events :StrokeDeath Paraplegia Retrograde dissectionReinterventionCOSTS

Pros:Long term benefit (mortality)

Remodelling

A patient-specific approach designed to intervene only in patients that are at high risk of developing complications should improve the long-term outcome of these patients.

G Van Bogerijen, J Tolenaar & al. J Vasc Surg 2014;59:1134-43.)

• Aortic geometry Level

• Aortic diameter > 40 mm A

• Rapid enlargement > 10 mm/y A

Radiologic Predictors

• Entry tears characteristics

• Primary entry tear > 10 mm A

• False lumen characteristics A

• FL diameter of >22 mm A

Applications

1. Sélection des bons candidats pour l'aorte ascendante et les Type B non compliquées

1. Travaux expérimentaux

2. Essais cliniques

2. Stratégie thérapeutique

3. Étude de suivi

Ratio of tear maximum width to aortic diameter.

Relationship between tear height and flow rate in false lumen.

Relationship between tear position and flow rate in the false lumen.

Zhuo Cheng, & al. Journal of Vascular Surgery, 2013,

CONCLUSION•Elevated WSS immediately distal to the origin of LSA accompanies the development of a RTAD and may therefore constitute a new risk factor for this condition. •CFD simulations may therefore potentially be of predictive value in risk stratification of RTAD in patients with type B dissection. Those patients should be monitored more frequently by means of clinical examination ;and imaging and more rigid control of hypertension should be applied.

Authors YearNo. of cases

Study focus of CFD modelling and simulations

Alimo hammadi 2015 13D flow domain combined with 3 element Windkessel models of patient-specific FSI

simulations

Chen et al. 2013 1 Flow communication/exchange between TL and FL

Cheng et al. 2010 1 Patient-specific model for detailed analysis of hemodynamics

Cheng et al. 2014 1 In vivo velocity comparison between PC-MRI and CFD simulations

Cheng et al. 2015 8 Effects of morphological features of dissected aorta on hemodynamic changes.

Karmonik et al. 2011 1Simulated 4 scenarios with entrance or exit tear present or occluded, simulating EVAR

and surgical treatment.

Karmonik et al. 2011 1 Quantitative assessment of hemodynamic changes of WSS in the FL after EVAR.

Karmonik et al. 2012 1 Association between aortic geometries changes and hemodynamic changes

Karmonik et al. 2013 1 Comparison of type B dissection with healthy aorta

Shang et al. 2015 14Correlation of CFD simulations with long-term clinical outcomes in medically managed

and surgically treated patients.

Tse et al. 2011 1 Quantitative analysis of hemodynamics in pre-and post aneurysmal dissecting aorta.

Wan Ab Naim 2014 1Impact of number of re-entry tears on hemodynamic changes (with simulation of re-entry

tear of 10 and 16mm diameter, respectively).

Wan Ab Naim et 2015 1Vortical structure and its interaction with WSS to predict FL formation, with simulation

of increased and decreased diameters of the FL.

Zhang et al. 2014 3 Wall pressure changes and effects on longitudinal propagation of aortic dissection.

International Journal of Cardiology2016,

Applications

1. Sélection des bons candidats pour l'aorte ascendante et les Type B non compliquées

1. Travaux expérimentaux

2. Essais cliniques

2. Stratégie thérapeutique

3. Étude de suivi

Can we predict the results of Rx

Stent Graft

Short S.G. to exclude entry tear?

Long thoracic S. G.?

Additional bare stent / distal aorta ?

Fenestration?

Bare stents in aorta or branches?

False lumen occlusions?

Anton…

Applications

1. Sélection des bons candidats pour l'aorte ascendante et les Type B non compliquées

1. Travaux expérimentaux

2. Essais cliniques

2. Stratégie thérapeutique

3. Étude de suivi

The Windkessel effect.

TEVAR stiffened the thoracic aorta by 2-fold diminish the Windkessel function considerably and might be associated with TEVAR-related complications, including stent-graft-induced dissection and aneurysmal dilatation.

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Computational fluid dynamics may assist in the prediction of aortic thrombus formation in hemodynamically complex cases and help guide repairstrategies.

VORTICITE

Functional vascular imaging of virtual dual branches, Chimney or Periscope stent grafts configurations

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4D PC-MRI

Combining Anatomy and Function

Biomech Model Mechanobiol. 2016; 15: 857–876.

Comparison of CFD data and acquired 4D PC-MRI flow data at peak systole and mid-diastole. Also shown are the CT image data at two locations showing suspected secondary tears which were not apparent on the 4D PC-MRI data

Acquisition Time

20s

40s

40s / 40 slices

(8 cm with 2mm thickness = 30 min)

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Fidelity

Accuracy

4D Flow

MRI and CFD integrated method

PIV CFD

4D FlowHigh scanning timeTime of x-, y-, or z-dir sample selectionMotion artifactRespirationLow signalVelocity of ENCoding (VENC)

CFD (MFN)Boundary conditions (pressure)Physical models (static, viscosity..)Wall definition

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Validation

Inlet

YALES2BIO (0,7mm)

4 D Flow MRI (2mm)

Scanners

Rapidité

Résolution spatiale

Dynamique

Perfusion

Accessibilité

Les études fonctionnelles nécessitent une vérification et une validation.

Irradiation

Conditions limites

Post traitement

Importance des conditions limites?Importance de la résolution spatiale?