5 Quantitative Techniques of Comprehensive Assessment of Aortic Valve Disease Using MRI

224



S.M. Ko



• Measurement of velocity in the blood is assessed at the

“through-plane” imaging plane that is positioned perpendicular to the vessel.

• “In-plane” phase-contrast pulse sequences, allowing

assessment of velocity along the course of a flow jet, and

can assist in planning the “through-plane” slice.



• PC cardiac MRI generates a magnitude image reflecting the anatomy of the chosen imaging plane, and

phase velocity maps encoding the velocities within

each voxel.

• The pressure gradient across the aortic valve is estimated

by the modified Bernoulli equation, ΔP = 4V2, where P is

the pressure (mmHg) drop across the stenosis and V is

velocity (m/s).

• An important tendency to underestimate the true value in

severe AS in flow-based assessment using phase-contrast

cardiac MRI because of the lower temporal resolution of

cardiac MRI than Doppler echocardiography and intravoxel dephasing of spins related in part to acceleration,

turbulence, and partial volume averaging within the vena

contracta (Fig. 17.7) [2].



17.5.2 Measurement of LV Volume, Systolic

Function, and Mass

• Cardiac MRI with balanced SSFP pulse sequence is considered to be the standard of reference for the assessment

of LV volume and myocardial mass. Increased LV mass

(pressure overload LV hypertrophy) is a predictor of LV

dysfunction.



Fig. 17.5 Example of measurement of ascending aorta dimensions.

Oblique coronal image of CT shows the measurement of aortic root and

tubular portion of the ascending thoracic aorta during mid-diastole in

patient with severe BAV stenosis. BAV stenosis is related to aneurysmal

dilatation of the tubular portion of the ascending aorta as like this case



a



17.5.3 Measurement of AVA

• AVA either using direct planimetry with balanced SSFP

or continuity equation with PC cardiac MRI.



b



Fig. 17.6 Example of measurement of LVOT area and diameters. (a, b) Double oblique axial images of CT show the measurement of area (a) and

diameters (b) of the most narrowed LVOT portion during mid-systole



17



Aortic Valvular Heart Disease



225



a



b



Peak velocities vs Time



c



Legend:

Data

Spline (+/– 1)



cm/sec



277



d



246

215

184

153

122

91

60

Time

(ms)



29

–2



0



82



164



246



328



410



492



574



656



738



820



–33



Fig. 17.7 Example of velocity mapping in AS. (a, b) Quantitative

through-plane flow assessment above aortic valve using the PC cardiac

MRI. Magnitude image (a), phase image (b), corresponding PC velocity

map (c), and 4D flow image (d). The peak velocity is 2.7 m/s with an



estimated pressure gradient of 29 mmHg according to the modified

Bernoulli equation. Abnormal systolic helical flow is seen in the aneurysmal ascending thoracic aorta of patient with severe BAV stenosis on 4D

flow image (d) (http://extras.springer.com/2015/978-3-642-36396-2)



• Direct planimetry is less optimal in patients with calcific

AS because of cusp calcification and turbulent jet flow

hampering accurate visualization of the true orifice [2, 8].



regurgitant volume are measured directly as the antegrade

and retrograde transaortic volume flow rates.

• The direct quantification of the regurgitant flow and

fraction correlates well with the semiquantitative

assessments provided by Doppler echocardiography

and angiography.

• The regurgitation fraction limits of cardiac MRI for AR

have been estimated by using cardiac MRI as follows:

mild <20 %, moderate 20–40 %, and severe >40 %

(Fig. 17.8) [2].



17.5.4 Flow Quantification for the Grade of AR

• PC cardiac MRI is performed just proximal to the aortic

valve annulus or at the proximal ascending aorta above

the sinotubular junction, and total stroke volume and



226



S.M. Ko



a



c



b



400

Positive flow



350

300



Flow (ml/s)



250

200

150

Negative flow



100

50

0



0



250



500



750



Time (ms)



Fig. 17.8 Example of flow mapping in AR. (a–c) Three-chamber (a)

and ascending aorta (b) b-SSFP cardiac MR images obtained during

diastole demonstrate a central regurgitant jet below the aortic valve. (c)

Graph of aortic flow obtained by PC cardiac MRI shows predominant



17.6



antegrade flow in systole and retrograde flow in diastole. Quantitative

analysis by PC cardiac MRI yield a regurgitant volume of 31.8 ml and

fraction of 41 % (a) above the aortic valve and a regurgitant volume of

18.4 ml and fraction of 23 % below the aortic valve (b)



Bicuspid Aortic Valve Disease



• The most common congenital cardiovascular malformation with a prevalence of 1–2 % of the population.

• Association with an increased incidence of valvular complications (aortic stenosis, aortic regurgitation, and infective endocarditis) and aortic complications (dilatation of

the ascending aorta, aneurysm formation, and dissection).

• The morphological characteristics of the BAV include

unequal cusp size (due to fusion of two cusps leading to

one larger conjoined cusp), the presence of central raphe

or ridge, and smooth cusp margins. Right and left coronary cusp fusion (A-P phenotype) is the most common



•



•



•

•



pattern of BAV and associated with AS and coarctation of

the aorta.

BAV with right coronary and noncoronary cusp fusion

(R-N phenotype) is associated with a more significant

cuspal pathology, with a particularly more rapid progression of AS and AR in the young patients.

The typical imaging features of the BAV include a single

commissural line in diastole and an elliptical-shaped orifice in systole.

In patients with a prominent raphe or extensively calcified

valve cusps, the BAV may appear as the TAV in diastole.

AS is the most common complication of BAV with

development of superimposed calcific change earlier in life.



17



Aortic Valvular Heart Disease



a



227



b



c



Fig. 17.9 BAV with eccentric AR. (a–c) Oblique axial images obtained

during mid-systole (a) and mid-diastole (b) (http://extras.springer.

com/2015/978-3-642-36396-2) show bicuspid aortic valve with prolapse of valvular leaflet (arrow). (c) (http://extras.springer.com/2015/



978-3-642-36396-2) b-SSFP cardiac MR image obtained during diastole demonstrates an eccentric regurgitant jet (arrowhead) below the

aortic valve toward mitral valve anterior leaflet



• AR is caused by prolapse of a larger conjoined cusp,

fibrotic retraction of the cusps, aneurysmal dilatation of

the aortic root, and valve annulus or valvular destruction

secondary to infective endocarditis (Fig. 17.9) [9, 10].



tions such as AR and cardiac MRI provide functional information of QAV as well as its morphology (Fig. 17.10) [11].



17.8

17.7



Quadricuspid Aortic Valve

Disease (QAV)



• A very rare congenital cardiac anomaly and a well-recognized

cause of a significant AR requiring surgical treatment.

• Cardiac CT provides an accurate assessment of morphology

of QAV, and associated congenital anomaly and its complica-



Sinus of Valsalva Aneurysm with AR



• Rare and either congenital or acquired (infective endocarditis, degenerative, and injury).

• Associated cardiac anomalies: VSD, AR, BAV, and coronary anomalies.

• The right coronary sinus (72 %), noncoronary sinus

(22 %), and left coronary sinus (6 %).