CT and MRI of Aortic Valve Disease: Clinical Update

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Current Radiology Reports e-ISSN 2167-4825Volume 4Number 9 Curr Radiol Rep (2016) 4:1-14DOI 10.1007/s40134-016-0176-6

CT and MRI of Aortic Valve Disease:Clinical Update

Richard Hallett, Sina Moainie, JamesHermiller & Dominik Fleischmann

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CARDIOVASCULAR IMAGING (A BIERHALS, SECTION EDITOR)

CT and MRI of Aortic Valve Disease: Clinical Update

Richard Hallett1,2• Sina Moainie3

• James Hermiller4• Dominik Fleischmann5

Published online: 25 July 2016

� Springer Science+Business Media New York 2016

Abstract

Purpose of Review Imaging of the aortic valve and asso-

ciated aortic root pathology has historically been primarily

imaged by echocardiography. Recent advances in com-

puted tomography (CT) and magnetic resonance (MR)

imaging hardware and software have made routine, high-

resolution CT/MR assessment of morphology of the aortic

root and aortic valve practical and robust.

Recent Findings Improvements in ECG-synchronized CT

imaging have led to motion-free imaging of the aortic root

in most patients. MR techniques, including 4D flow MR

imaging, add additional information for assessment of the

aortic valve. These newer techniques are valuable for

classification and prognosis of the cardiovascular mani-

festations of bicuspid aortic valve (BAV) disease. CT

imaging has become integral to pre- and post-procedural

assessment of patients considered for transcatheter aortic

valve repair (TAVR). Post-processing techniques that

afford maximal information for surgical and interventional

management have developed in parallel to these

techniques.

Summary CT and MR imagings have developed into

robust techniques that yield diagnostic and prognostic

information in patients with a variety of aortic valve and

root pathology. This review includes review of recent

advances in available hardware and software. We also

discuss methods to maximize imaging value in assessment

of BAV, and in patients before and after TAVR.

Keywords Computed tomography � Magnetic resonance

imaging � Aortic valve � 4D Flow � Phase-contrast MRI �Transcatheter aortic valve replacement

Introduction

Imaging assessment of the aortic valve was long a domain

of echocardiography. In recent years, advances in imaging

and post-processing technology have allowed confident

imaging of aortic valve pathology by CT and MRI.

This article is part of the Topical Collection on Cardiovascular

Imaging.

Electronic supplementary material The online version of thisarticle (doi:10.1007/s40134-016-0176-6) contains supplementarymaterial, which is available to authorized users.

& Richard Hallett

[email protected]

Sina Moainie

[email protected]

James Hermiller

[email protected]

Dominik Fleischmann

[email protected]

1 Chief, Cardiovascular Imaging, Northwest Radiology

Network, Cardiovascular Imaging, St. Vincent Heart Center

of Indiana, Indianapolis, IN, USA

2 Adjunct Assistant Professor of Radiology, Department of

Radiology, Stanford University School of Medicine,

Stanford, CA, USA

3 Director of Aortic Surgery, St. Vincent Medical Group, St.

Vincent Heart Center of Indiana, Indianapolis, IN, USA

4 Director of Interventional Cardiology, St. Vincent Medical

Group, St. Vincent Heart Center of Indiana, Indianapolis, IN,

USA

5 Professor of Radiology, Chief of Cardiovascular Imaging,

Director, Computed Tomography, Department of Radiology,

Stanford University School of Medicine, Stanford, USA

123

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Likewise, native aortic valve and aortic root disease,

including protean manifestations of bicuspid aortic valve

(BAV) disease, are well visualized and classified by CT/

MR imaging. Both CT and MRI are valuable, and often

complementary, for assessment of patients with BAV.

Novel techniques including 4D flow MRI have shown

promise for improving consistency and diagnostic yield for

aortic valve assessment. Evolving in tandem with refine-

ments in transcatheter aortic valve replacement (TAVR)

techniques, CT has become a critical tool for TAVR device

sizing, access route selection, detection of anatomic con-

traindications, and important extravascular findings. These

imaging techniques require thorough knowledge of aortic

root anatomy, and an understanding of the imaging tech-

nology utilized for data acquisition.

Anatomy of the Aortic Valve and Root

The aortic valve is an integral part of the aortic root, a

larger complex of structures that serves to separate the left

ventricle from the systemic circulation. As traversed by

blood from proximal to distal, these structures include the

aortic annulus (also called the ‘‘virtual basal ring’’), aortic

valve leaflets, commissures, and interleaflet triangles

[1, 2••, 3]. The leaflets are termed right (R), left (L), and

noncoronary (N). The junction of the sinuses of Valsalva

(SOV) and the ascending (tubular) aorta, representing the

highest point of leaflet attachment, is termed the sino-

tubular junction (STJ) (Fig. 1). The normal aortic valve has

three semilunar leaflets that create a triangular opening in

systole, and show complete central coaptation in diastole.

Variations in development can result in valves that are

unicuspid (single, deformed leaflet), bicuspid (two leaflets

in varying arrangements), or quadricuspid (four leaflets).

Owing to superior spatial resolution, ECG-synchronized

CT provides excellent depiction of aortic root anatomy. A

detailed discussion of aortic root anatomy is beyond the

scope of this article. Recent works are available that pro-

vide a thorough discussion of relevant aortic root anatomy,

structure, and function as well as radiologic-pathologic

correlation [2••, 3].

Technical Developments—CT

Synchronization of the electrocardiogram (ECG) to the

acquired CT dataset is essential to obtain motion-free

imaging of the aortic valve apparatus [4–6]. While ECG

synchronization techniques were conceived in the 1970s

[7] and have been available for clinical use since electron-

beam CT [8], the past decade has seen considerable

refinement in technical scanner specifications and syn-

chronization techniques [9, 10]. Current scanners deliver

rotation times as short as 250 ms and heart rate indepen-

dent temporal resolution of 66 ms. As a result, motion-free

imaging of the aortic root can be reliably obtained in most

patients.

The choice of ECG synchronization technique will

depend on the clinical question. If cine assessment of valve

motion is needed, or if measurements are needed in both

systole and diastole, retrospective ECG synchronization

(gating) is utilized. Retrospective ECG synchronization

results in greater radiation dose than prospective (‘‘step-

Fig. 1 Anatomy of the aortic root. a Blood-pool inversion volume-

rendered (BPI-VR) oblique coronal image. The aortic root consists of

structures from the annulus (virtual basal ring, black arrow) to the

sinotubular junction (pink arrows). The right and left sinuses of

Valsalva are depicted (dashed ovals). The left main coronary artery is

also visualized (arrowhead). b BPI-VR thick slab image looking into

the left sinus of Valsalva. Note the interleaflet triangles (I) the left

leaflet attachment near the sinotubular junction (arrowheads). The

central coaptation point of the commissures is seen in the middle of

the slab (arrow), with the left main coronary ostium visualized

cephalad to this point (Color figure online)

49 Page 2 of 14 Curr Radiol Rep (2016) 4:49

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and-shoot’’) and prospectively triggered, high-speed helical

(Flash mode) acquisitions [11–13]. However, use of ECG-

modulated mA (‘‘ECG pulsing’’) with retrospective tech-

nique allows full diagnostic dose to be administered only in

the segments of the R–R interval that are most important

for diagnosis [14]. This technique can result in dose sav-

ings of 40 % or more compared to standard retrospective

scanning [15••].

The use of automated tube potential selection [15••] and

iterative reconstruction (IR) techniques has also allowed

further reduction in patient radiation dose [16, 17]. IR

techniques utilize complex mathematical modeling (‘‘iter-

ations’’) and more precise modeling of scanner geometry

and noise statistics to more efficiently reconstruct image

data. The end result of IR technique is high-resolution

image quality with less noise, fewer blooming artifacts, and

improved contrast- and signal-to-noise ratios (CNR, SNR)

[18, 19]. IR techniques allow routine image acquisition at

100 kVp, which reduces estimated radiation dose 31 %

versus standard 120 kVp [20]. Recent refinement in IR

techniques, such as model-based IR (MBIR), further

improves image reconstruction quality and allows addi-

tional dose savings [21, 22].

Technical Developments—MRI

Imaging of the aortic valve by MRI is robust, and in many

ways offers complementary information to CT imaging.

Valvular anatomy can be classified; planimetry can be

performed; and the thoracic aorta can be well assessed by

current contrast-enhanced and noncontrast techniques

(Fig. 2). The ability to directly measure flow and calculate

transvalvular gradients by phase-contrast imaging is a clear

advantage for MR imaging. A recent best evidence sum-

mary concluded that MRI and echocardiography were

‘‘equally reliable’’ in assessment of the aortic valve,

although MRI was found to have better inter- and

intraobserver reliability and was better for assessment of

severe aortic stenosis [23].

4D Flow MRI

An emerging technique that directly impacts aortic valve

imaging has been the development of volumetric, time-

resolved three-dimensional phase-contrast (‘‘4D Flow’’)

MR imaging [24, 25••]. Originally described in 1991 by

Pelc et al. [26••], 4D flow has become increasingly clini-

cally useful.

Utilizing data acquisition over many heartbeats, with

respiratory-triggered or respiratory-compensated tech-

niques, PC data for an entire volume can be generated with

seven degrees of information (anatomy in x, y, z planes;

magnitude in x, y, and z planes; and time). Use of a blood-

pool MR contrast agent improves 4D flow data [27, 28]. A

recent consensus statement provides an excellent descrip-

tion of 4D flow technique, corrections, and results as well

as topics of ongoing research [25••]. 4D flow techniques are

valuable for numerous disease states including valvular

disease, aortopathies and aortic dissection, and congenital

heart disease [25••, 29–33].

Briefly, advantages of 4D Flow MRI over 2D-PC tech-

niques include free-breathing acquisition, lack of need for

precise plane placement to capture maximal flow/velocity

data, and the ability to interact with the data offline

(without the patient remaining on the table) on dedicated

processing software. Prescription of a single volume slab

acquires data that can be interrogated to yield flow data

across any plane within that volume (Fig. 3). This is par-

ticularly helpful when multiple 2D-PC acquisitions would

need to be acquired (e.g., congenital heart disease, aortic

Fig. 2 Standard aortic valve assessment by MRI. a 3-chamber

balanced SSFP cine frame shows dephasing jet at and above the aortic

valve (arrows) related to valvular aortic stenosis. LA left atrium, LV

left ventricle. b 3-chamber balanced SSFP cine frame from diastole

shows dephasing jet extending across the aortic valve into the LVOT,

consistent with aortic regurgitation (arrowheads). c Short-axis image

of the aortic valve in systole shows very poor excursion of the three

leaflets (arrows). Valve area tracing (planimetry) showed valve

orifice area of 0.8 cm2, consistent with severe AS

Curr Radiol Rep (2016) 4:49 Page 3 of 14 49

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coarctation), and can decrease time required to complete

the exam. Since 4D flow MRI acquisition is volumetric,

demonstration and quantification of eccentric valvular jets

and flow patterns are enhanced [34].

In patients with severe AS, stratification and manage-

ment decisions are currently based on three parameters:

transvalvular gradient, aortic valve area (AVA), and peak

velocity. While useful, these standard measurements fail to

account for pressure recovery, and do not perform well in

low-pressure/gradient states. These patient populations

include those with normal ejection fraction (EF) with low-

stroke volume and severe AS and low gradients, low EF/

low flow severe AS, and paradoxical AS (severe LVH with

low-stroke volume) [35, 36]. 4D flow MR can more fully

assess these physiologic states by estimating viscous and

turbulent kinetic energy (TKE) losses [29, 37].

Some drawbacks are inherent to 4D Flow techniques.

Acquisition time, initially quite lengthy ([60 min), was

associated with increased motion-related artifacts and

limited the technique to generally healthy (research)

patients [29]. Advances in acquisition techniques and other

technical improvements have decreased scan times to

\20 min, with some centers reporting acquisition times of

5 min or less [38, 39]. Additionally, the large amount of

data generated can produce long reconstruction and post-

processing times. Recent cloud-based service utilizing

massively parallel graphical processing unit (GPU) archi-

tecture has allowed client-based interaction with the 4D

flow data with less time penalty (Video1). 4D flow data are

also susceptible to motion-related artifacts and other arti-

facts inherent to 2D-PC techniques [25, 40]. Recent work

comparing 2D-PC MR with 4D Flow has suggested that

peak flow measurements determined by 4D flow are lower

in magnitude than 2D flow [41, 42]. More study is needed

to more fully understand the precise degree of compara-

bility between the two techniques.

Bicuspid Aortic Valve: Current Imaging with CT/MRI

Bicuspid Aortic Valve: Background

Bicuspid aortic valve (BAV) is a common (1–2 % of

general population) congenital disorder that manifests as a

variable fusion of the aortic cusps and commissures. BAV

is associated with aneurysms of the aortic root and several

patterns of aortopathy involving the thoracic aorta includ-

ing the transverse thoracic aorta [2, 43, 44]. The relative

contributions of the congenital connective tissue disorder

versus effects of altered hemodynamics in BAV aortopathy

remain controversial [45, 46]. Indeed, many now consider

management considerations in BAV patients to be similar

to those with Marfan syndrome; thus imaging considera-

tions may have utility for Marfan and related connective

tissue disease disorders. A recent thorough review provides

further information on diagnosis and surgical management

of these and other aortic root disorders [2].

Fig. 3 4D Flow MRI in a 25-year-old patient with complex

congenital heart disease (double outlet right ventricle, pulmonic

atresia, VSD; status post-Rastelli procedure, RV-PA conduit). Screen

capture from 4D Flow review and measurement software shows

volumetric slab dataset in three orthogonal planes. Measurement of

flow across the aortic valve is performed at the level of the dilated

aortic root, (circular gate, arrowheads), with cardiac output data noted

at right of the image (arrow), approximately 5 L/m. High velocity

flow, indicated by red color, is seen at the RV-PA conduit (**).

Gradient was calculated at 18 mmHg. Focal high velocity jet also

seen within the aortic valve, gradient calculated at 25 mmHg. Note

the eccentric stenotic jet across the aortic valve (red arrow, lower

right panel), which strikes the right lateral wall of the ascending aorta.

Similar types of abnormal flow patterns are implicated in differing

patterns of aortic aneurysm development in BAV patients (Color

figure online)


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Histopathologically, the aortopathy of BAV manifests as

decreased levels of fibrillin-1, increased levels of matrix

metalloproteinases, and cystic medial necrosis within

affected segments of the aortic wall [47–50]. BAV is also

associated with aortic coarctation and up to tenfold

increased risk of aortic dissection (AD) [51–53]. Inheri-

tance is likely autosomal dominant with incomplete pene-

trance; mutations in the NOTCH1 and ACTA2 genes have

been implicated [49, 54]. Interestingly, dilatation of the

aortic root and ascending aorta occurs in BAV patients

without significant valvular dysfunction [55, 56], as well as

family members of BAV patients who themselves are

without BAV [43, 50, 57], suggesting that long-term

familial screening is necessary.

Surgical management guidelines for aortic aneurysm in

BAV patients recommend surgery earlier than tricuspid

aortic valve patients. The Society of Thoracic Surgeons

Clinical Practice guidelines recommend surgery in BAV

patient when the root or ascending aorta exceeds 5.0 cm,

growth rate of[5 mm/yr occurs, or at 4.5 cm if there is a

family history of AD [58••]. Surgical decision-making also

supports an indexed measurement system for aortic

aneurysm measurement, where aneurysm size is indexed to

a patient-specific internal control such as body surface area

(aortic size index [2.75/m2) [59] or the diameter of the

descending aorta. Therefore, imaging specialists can play a

crucial role in BAV patient management by defining both

the presence and morphology of BAV as well as the tem-

poral evolution of thoracic aortic size.

Imaging of BAV

Transthoracic echocardiography (TTE) is generally the

first modality to assess BAV. However, secondary to

limited acoustic windows and adult body habitus, TTE

does not consistently evaluate the mid-distal ascending

and transverse thoracic aorta. Additionally, technical

issues related to heavy calcification and body habitus

may limit assessment; the number and arrangement of

cusps may be unclear in up to 25 % of patients [60]. 3D

TTE may provide significantly better visualization and

classification of BAV [61]. CT and MR imaging allows

determination of BAV morphology in nearly all patients

[62]. BAV morphology can be classified using the sys-

tem described by Sievers and Schmidtke, based on

analysis of 304 surgical BAV specimens [63]. The

number and arrangement of raphes (defined as the con-

joint or ‘‘fused’’ portions of two adjacent leaflets that

become a malformed commissure), the spatial positions

of cusps, and presence of valvular stenosis and/or

insufficiency are important for classification [63, 64]

(Fig. 4).

Fig. 4 Sievers classification of bicuspid aortic valve. Short-axis

diagrams of the aortic valve viewed from the left ventricle (as in CT).

Coronary ostia are noted by the double lines. R right, L left,

N noncoronary. Types are defined by the number of raphes: type 0 is a

‘‘true’’ bicuspid valve with no raphes (Lateral or AP subcategories).

Type 1 represents 1 raphe (red line), and represents three subcate-

gories, L-R, R-N, and N-L. Type 2 consists of valves with two raphes,

with only one subcategory, between L-R and R-N. Type 1, L-R is the

most common (71 %). Additional subcategory designations are

assigned for valvular stenosis (S), insufficiency (I), balanced stenosis

and insufficiency (B), and normal function (No). Adapted from

references ___ and ___. (Sievers and Blaye-Felice articles) (Color

figure online)


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CT is an accurate technique for assessment and classi-

fication of BAV. Classification is most reliable by review-

ing both diastolic and systolic datasets, with the latter aiding

in assessment of BAV raphes [65] (Fig. 5). Calcification is

easily depicted and can be scored in a similar manner to

coronary calcium; high scores correlate with significant

Fig. 5 CT Assessment of

bicuspid aortic valve. a Sievers

type 1, L-R BAV. Diastolic

phase image shows bicuspid

aortic valve. A raphe is

suggested but difficult to

visualize (arrow). The

remainder of the BAV is

vertically oriented and

symmetric (arrowheads).

b Systolic phase image shows

the raphe (arrow) between the

left and right cusps

(arrowheads) to better

advantage, indicating that the

valve is type 1, L-R rather than

type 0, vertical.

NC = noncoronary cusp.

c Sievers type 0 (lateral) BAV.

Diastolic phase short-axis CT

image. Note the symmetric

leaflets and vertical orientation

(arrows). d Systolic phase

short-axis CT image showing

classic ‘‘fishmouth’’ appearance

of symmetric BAV leaflets

(arrows)

Fig. 6 MR Planimetry of bicuspid aortic valve. a Short-axis systolic

image from cine SSFP series. There is a raphe between the right and

noncoronary sinus (arrowheads), consistent with type 1, R-N BAV. A

focus of valvular calcium is depicted as a focal signal void (arrow).

b Planimetry of the valve in systole (blue shaded area) shows an area

of 0.9 cm2, consistent with severe stenosis. c Curve (peak velocity on

y-axis, time on x-axis) from 2D-PC imaging shows peak velocity of

5.5 m/s (green line), consistent with severe stenosis and peak pressure

gradient estimation (modified Bernoulli equation) of [100 mmHg

(Color figure online)


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valvular gradients by echocardiography. Recent work sug-

gests an Agatston score of 1651 as an appropriate cut-off to

identify valves with significant gradient compared to

echocardiographic data [66]. Planimetry can be performed

to assess stenosis and insufficiency; aortic valve area

(AVA) results correlate well with echocardiographic pres-

sure gradients [3, 67, 68].

Routine MRI assessment of aortic valve morphology and

standard velocity/pressure information obtained by 2D-PC

MRI is now standard technology. BAV morphology can be

classified, planimetry performed (Fig. 6), and peak veloci-

ties/transvalvular gradients calculated by standard tech-

niques including balanced steady-state-free precession

(SSFP) cine imaging and 2D-PC assessment of flow.

However, BAV patients have higher incidences of aortic

dissection (AD) and mortality (even with normal-sized

aortas), and considerable variation exists in operative

decision-making in BAV patients with aneurysm [69].

Therefore, additional information may be valuable to tailor

management of BAV patients. 4D flow MRI can acquire

standard measurements, and can provide both qualitative

assessment of abnormal flow patterns and quantitative

information regarding the effect of the pathological flow

patterns [29], potentially becoming a more complete

assessment tool for BAV patients [70].

Aortic dilatation in BAV patients is likely related to a

combination of hemodynamic and tissue factors

[46, 71, 72]. Specific BAV morphology does correlate with

specific phenotypic manifestations in the thoracic aorta.

For example, L-R fusion is associated with larger SOV

Fig. 7 Patterns of aneurysmal disease in bicuspid aortic valve.

a Isolated root aneurysm (arrows), in a patient with Type 1, L-R

BAV. Isolated root dilatation is more commonly seen with this BAV

type. b Ascending thoracic aortic aneurysm without root dilatation, in

a patient with type 1, R-N BAV. MIP image from thoracic MRA

shows an aneurysm of the ascending thoracic aorta (ASC), with

normal-sized aortic root (arrows). Type 1, R-N BAV typically

presents at a younger age, have more valvular stenosis, and show

preferential dilatation of the ascending aorta. c Dilatation of the entire

root and ascending thoracic aorta. Patient with type 1, R-N BAV

exhibits 44 mm aneurysm of the aortic root (arrows), as well as

55 mm aneurysm of the ascending thoracic aorta (ASC). d Preferential

marked dilatation of the ascending aorta. Patient with a Type 0, lateral

BAV. Calcifications of the BAV can be seen (arrows). Note the

preferential dilatation of the ascending thoracic aorta (ASC), reaching

8 cm. There is no dilatation of the transverse thoracic aorta (Tr)


123


dimensions, whereas R-N fusion is more commonly asso-

ciated with ascending aortic and arch dilatation [73–75].

Additionally, BAV patients with predominant valvular

stenosis (often L-R fusion phenotype) tend to have larger

SOV measurements, whereas dominant valvular insuffi-

ciency is associated with greater dilatation of the ascending

aorta [75] (Fig. 7). Pathologic flow states at the BAV, as

well as resultant abnormal flow-related changes in the aorta

can be well assessed by 4D flow MRI (Fig. 8).

MRI provides flow velocity information on BAV by

cine and 2D-PC imaging, and MRA provides characteri-

zation of areas of aortic dilatation. 4D flow MRI suggests

that various aneurysmal phenotypes are at least in part

related to the angle of the eccentric jet across the abnormal

valve and resultant regional wall shear stress (WSS) dif-

ferences [70, 74]. 4D Flow MRI also allows estimation of

viscous energy and turbulent kinetic energy (TKE) losses,

and other markers that may prove valuable for clinical

decision-making [37] (Fig. 8).

TAVR: Maximizing Preprocedural Information

Since the first report of placement in a human in 2002 [76],

TAVR has evolved from an experimental procedure into an

accepted tool in treatment of severe, symptomatic AS.

Recently, indications have expanded including valve-in-

valve placement, and clinical trials are now underway with

less severe operative risk populations. Additional access

routes and devices continue to be explored and refined.

Long-term follow-up and comparison to surgical aortic

valve replacement (SAVR) from the initial studies is now

available.

Data from the Placement of Aortic Transcatheter Valves

(PARTNER-1) have shown favorable results in high-risk

aortic stenosis patients undergoing TAVR with the Edwards

SAPIEN Valve, showing similar 5-year mortality rates ver-

sus SAVR [77]. Improved survival vs. SAVR at 2 years in

high-risk patients treated with Medtronic CoreValve was

recently reported [78]. Inoperable patients undergoing

TAVR also showed improved survival and functional status

versus standard treatment [79]. More recently, results of

TAVR in comparison to SAVR were reported for interme-

diate-risk patients in the PARTNER-IIA trial, utilizing the

second-generation Edwards XT valve. TAVR and SAVR

results were similar [80]. Furthermore, patients treated with

the third-generation SAPIEN-3 TAVRvalvewere compared

in a propensity-matched analysis to the SAVR patients from

PARTNER IIA, and TAVR was superior with half the

mortality and disabling stroke at one year [81]. Patient age

has also been shown to be less important, with little differ-

ence in major adverse events and one-year survival reported

in nonagenarians versus other patients [82]. A thorough

assessment of current results, complications, subgroup

analysis, and newer device designs can be found in recent

reviews [83, 84••].

Pre-TAVR imaging is critical—at our institutions CT is

an essential tool. Generation of submillimeter, isotropic

voxels with high spatial resolution, coverage of both the

heart and access vessels in one contrast injection, and

available offline review and interpretation position CT well

as a ‘‘one-stop shop’’ for pre-TAVR assessment. For dis-

cussion of other imaging modalities, the reader is directed

to an excellent review of available imaging modalities and

techniques by Caruso et al. [85].

Fig. 8 4D Flow of BAV. Panel

of images from assessment of

BAV. Note high velocity flow

across the symmetric BAV

(upper left panel, arrowheads).

Eccentric flow extending to

contact the right lateral aspect

of the ascending aorta is noted

(arrow, upper right panel).

Color-coded phase (flow) data

are displayed on the magnitude

data in orthogonal planes on the

lower panels


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The aortic annulus is an oval-shaped, 3D structure [86],

and is especially well suited for CT imaging assessment

(Fig. 9). Unlike standard echocardiography, CT allows full

3D assessment of annular morphology and dimensions,

valvular planimetry [68], and assessment of root geometry.

In the same scanning setting, CT can assess obstructive

coronary artery disease (such that invasive coronary

angiography may not be required) [87], determine access

routes [88], and identify significant extracardiac incidental

findings, some of which could represent contraindications

to TAVR. Up to 19 % of patients have iliofemoral access

vessel caliber unsuitable for access; necessitating

transapical or other access routes [89]. Up to two-thirds of

patients have incidental findings at TAVR CT, and up to

half of these require additional workup [89, 90].

Unsuspected malignancy has been detected in 4 % of

patients [89]. These findings reinforce the need for metic-

ulous review of extracardiac CT data.

CT imaging for TAVR planning can be performed with

a number of different protocols, including single or double

injections. Acquisition of the ECG-synchronized imaging

of the heart as well as nonsynchronized CTA of available

access vessels is necessary to determine the safest route for

accurate device delivery. The protocol for single injection

CT acquisition one institution is available in Table 1. Since

many TAVR candidates have underlying chronic kidney

disease, CT acquisition protocols are also adapted to

acquire diagnostic datasets at lower CM doses [91]. The

risk of exacerbating pre-existing renal dysfunction appears

to be low when the amount of CM given is no more than

Fig. 9 CT assessment of aortic root for TAVR planning. a Short-axis

volume-rendered CT image shows heavily calcified (arrows),

trileaflet aortic valve. The origin of the left main coronary artery is

noted (arrow). b Short-axis measurement of the annulus with

measurements of major and minor axis, area, and perimeter for

device sizing. Note the absence of annular calcification; annular

calcification can predispose to paravalvular aortic regurgitation after

device placement. c Long-axis image of aortic root (perpendicular to

image 9B) shows measurement of distance from annulus to left main

coronary artery (arrow). Distances of\10 mm may preclude current

TAVR device placement, secondary to potential for coronary

compromise. d Volume-rendered oblique coronal image through the

aortic root shows measurements for TAVR. The left main coronary

artery is shown (arrow). Distances from the annulus to LM origin

(15.9 mm) and from the annulus to the sinotubular junction (dotted

line, 20.1 mm) are listed. Calcifications at the aortic valve are

displayed in green (Color figure online)


123


twice the estimated glomerular filtration rate (eGFR) [92].

Therefore, we limit CM volumes in patients with renal

disease that are no more than twice the eGFR, adjusted for

body weight: [CM (mL) = 2 9 eGFR9pt. weight (kg)/

75 kg].

Accurate measurement of the aortic annulus is impera-

tive, as undersizing of the annulus (and device) leads to

higher incidences of paravalvular aortic regurgitation

(PVR) [86, 93, 94]. Moderate to severe PVR, in turn, has

been shown to be an independent predictor of mortality.

Fig. 10 Paravalvular aortic regurgitation (PVR) after TAVR.

a Short-axis image at the aortic annulus in diastole shows a gap

between the TAVR device and the left lateral margin of the annulus

(arrow). L = device flow lumen. b Short-axis image through the

sinuses of Valsalva show eccentric positioning of the device,

restricted by heavily calcified leaflets (arrowheads). c Longitudinal

image (perpendicular to figure B) shows communication along the

margin of the device (arrowheads), allowing severe PVR

Fig. 11 Annular/subannular

calcification, planning for

TAVR. a Oblique sagittal MIP

image through the aortic root

shows a large, angulated

calcification (arrow) extending

from the annulus (arrowheads)

into the LVOT, eventually

becoming embedded in the

interventricular septum.

b Short-axis image of the LVOT

below the annulus shows the

calcification beneath the L/R

leaflets (arrows). c Volume-

rendered hollow image shows

extent of valvular, annular,

subannular, and LVOT

calcification. Note the heavy

calcification at the leaflet and

annular level (arrow)


123


Mild–to-moderate oversizing (10–15 % annular area) [95]

has been recommended to decrease PVR without increas-

ing risks of annular rupture. CT-sizing protocols have been

shown to lead to a larger implanted valve (vs. TEE) in up to

one-third of TAVR patients [95]. Not all authors have

found this hypothesis to hold true; Freeman et al. reported

no consistent relationship between annular sizing by CT

and risk of patient-prosthesis mismatch (PPM), and pos-

tulate that PPM may be related to a native annulus that is

undersized relative to patient body size. [96].

The aortic annulus is a dynamic structure, and dimen-

sions are larger during systole, therefore systolic mea-

surements (25-35 % R–R interval, or absolute time of

200–250 ms after R-wave) are recommended to avoid

device undersizing [95, 97••]. The exact choice of systolic

reconstruction phase is controversial; in our practice, we

choose the systolic phase with maximal valve opening and

least motion-related artifact. Perimeter measurement is also

greatest in systole although may be less influenced by

changes in cardiac phase; this may be due to annular

reshaping. Depiction of the amount and location of

valvular, annular, and subannular LVOT calcium is a

predictor for post-TAVR PVR [98, 99], potentially inter-

fering with complete apposition of the device to the aortic

wall [98] (Fig. 10). Extensive calcification extending into

the LVOT may require higher positioning of the device to

decrease PVR risk (Fig. 11). CT can also determine the

line of perpendicularity and optimal C-arm angles for flu-

oroscopic monitoring during TAVR, eliminating the need

for contrast aortography while allowing optimal device

deployment visualization [100, 101].

Vascular access route determination is a critically

important part of the TAVR planning process. CT robustly

depicts vascular calcifications and centerline methods

provide accurate minimum luminal measurements, leading

to change in access direction in up to 43 % of patients

[102, 103].

CT can provide adequate access information for stan-

dard transfemoral (TF), transapical (TAp), and potential

direct/transaortic (Tao) and transsubclavian (TS) routes.

We utilize transsubclavian (TS) as an alternative access

when other access routes are unavailable, but avoid it in

patients with prior CABG or extensive vessel tortuosity.

Recently described TAo access [104] allows accurate

device delivery in patients with challenging access anat-

omy with potentially fewer complications. TAo access

requires only an upper ministernotomy or minithoracotomy

(right parasternal), which causes less respiratory compro-

mise than a complete ministernotomy for TA access. TAo

access also provides an easier path for sheath placement,

and may result in less direct myocardial injury. Access

must be obtained at least 5–7 cm (depending on device)

above the level of the valve; a ‘‘porcelain aorta’’ is a

contraindication to TAo access. We find preprocedural 3D

mapping images and/or video improves operator confi-

dence and understanding of nontraditional access routes

(video 3).

Conclusion

Recent advances in CT and MRI technology have allowed

introduction of techniques that provide robust functional

and anatomic information on aortic valve disease. 4D Flow

MR imaging is an emerging technique that allows volume

acquisition of phase-contrast MR data that can be interro-

gated offline (including cloud-based platforms) in any

plane. Current assessment of the spectrum of BAV disease

brings together complementary information from CT and

4D flow MR applications. Advances in CT imaging hard-

ware, protocols, and post-processing techniques have pro-

ven beneficial to the growing number of patients

considered for TAVR procedures. Continual refinement of

aortic valve imaging techniques and emerging new tech-

nologies can be expected to add additional benefits in the

future.

Funding James Hermiller reports personal fees from Edwards and

Medtronic.

Compliance with Ethical Guidelines

Conflict of Interest Richard Hallett, Sina Moainie, and Dominik

Fleischmann each declare no potential conflicts of interest.

Human and Animal Rights and Informed Consent This article

does not contain any studies with human or animal subjects per-

formed by any of the authors.

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