DOI:10.2214/AJR.04.1463
AJR 2006; 186:350-360
© American Roentgen Ray Society
MDCT Evaluation of Aortic Valvular Disease
Robert C. Gilkeson1,
Alan H. Markowitz2,
Amit Balgude1 and
Peter B. Sachs1
1 Department of Radiology, University Hospitals of Cleveland and Case Medical
School, 11100 Euclid Ave., Cleveland, OH 44106-5000.
2 Department of Cardiothoracic Surgery, University Hospitals of Cleveland and
Case Medical School, Cleveland, OH 44106-5000.
Received October 7, 2004;
accepted after revision January 31, 2005.
Address correspondence to R. C. Gilkeson
(gilkeson{at}uhrad.com).
Abstract
OBJECTIVE. This essay depicts recent advances of MDCT in the
evaluation of aortic valvular disease.
CONCLUSION. Aortic valvular disease can be assessed with current
MDCT technology. The improved imaging characteristics of MDCT have
significantly decreased artifacts traditionally seen with prosthetic aortic
valves and enabled excellent visualization of valve function. Advances in
ECG-gated MDCT technology offer the opportunity to evaluate a variety of
aortic valvular abnormalities.
Keywords: aorta • cardiac imaging • cardiovascular imaging • MDCT
Introduction
As our population ages, the incidence and complexity of aortic valvular
disease increase. Although advances in drug therapies and increasingly
sophisticated stenting procedures have decreased the rates for coronary artery
bypass surgery, aortic valve surgical procedures have increased. This growing
population of patients offers a significant opportunity for a more
sophisticated approach to imaging of the aortic valve. The development of MDCT
has revolutionized cardiac imaging. Advances in ECG-gated MDCT technology
offer the opportunity to evaluate a variety of aortic valvular abnormalities
[1]. This essay depicts recent
advances of MDCT in the evaluation of aortic valvular disease.
Imaging Protocol
When there is a question of aortic valvular disease at our institution,
studies are performed on a 16-MDCT scanner (MX IDT, Philips Medical Systems).
To optimize CT evaluation of the aortic valve, close attention to both image
acquisition and postprocessing techniques is essential. When there is a
question of aortic valvular disease at our institution, retrospective
ECG-gating is used. Visualization of the aortic valve can be limited in
patients with high heart rates (> 80 beats per minute [bpm]) and
significant arrhythmias, and the often urgent nature of aortic disease can
preclude the routine use of ß-blockers. In the nonemergent patient, beta
blockade is helpful when heart rates are over 70 bpm.
Scanning protocols are dependent on the clinical information. If the entire
thoracic aorta is to be imaged, a slice collimation of 2.0 mm with a 1.0-mm
overlap is used. When a more detailed evaluation of the aortic valve and
coronary arteries is needed, a slice thickness of 1.0 mm is used. With
ECG-gated scans, pitch values of 0.3-0.375 are generally used, with CT
technique parameters between 120 and 140 kV and 350-400 mAs. Optimization of
aortic valve and coronary artery anatomy is achieved with a bolus-tracking
device and the region of interest placed within the aortic root; 100-125 mL of
nonionic contrast material is injected followed by a saline flush at a rate of
4 mL/sec. The patient is scanned in the cephalocaudad direction. Retrospective
ECG-gated images are reconstructed sequentially at every 12.5% of the R-R
interval.
Targeted evaluation of the aortic valve is performed on a dedicated
workstation. Computer software enables review in anatomically appropriate
multiplanar reconstruction planes, and aortic valve motion is reviewed in the
cine mode (Figs. 1A,
1B,
1C, and
1D). Virtual endoscopy of the
aortic valve is performed and reviewed in both volume and surface-shaded
settings. Virtual endoscopic views of the closed valve are obtained on images
obtained at 75% of the R-R interval, the optimal diastolic phase when the
valve is closed and free of motion artifacts.
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Fig. 1A —Optimal imaging planes for evaluation of aortic valve shown in
34-year-old man. Coronal multiplanar reconstruction view shows aortic valve
with imaging plane localizer (lines) in axial oblique plane.
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Fig. 1B —Optimal imaging planes for evaluation of aortic valve shown in
34-year-old man. Oblique axial image depicts aortic valve. R = right coronary
sinus, L = left coronary sinus, N = noncoronary cusp.
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Fig. 1C —Optimal imaging planes for evaluation of aortic valve shown in
34-year-old man. Cine CT image of aortic valve in axial oblique plane,
beginning in end-diastole. Single frame shows appearance of valve leaflets in
end-systole (arrows). On dynamic images, which are available online
(www.ajronline.org),
note opening of valve leaflets with symmetric effacement of aortic valve
during systole and complete closure with diastole.
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Fig. 1D —Optimal imaging planes for evaluation of aortic valve shown in
34-year-old man. Cine CT image of aortic valve in coronal plane. Single frame
shows complete coaptation of aortic valve (arrow) in diastole. On
dynamic images available online
(www.ajronline.org),
note symmetric opening of valve leaflets during cardiac cycle.
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The Normal Aortic Valve
The aortic valve apparatus consists of the aortic valve cusps, aortic
sinuses, commissures, and coronary artery ostia. Multiplanar reconstructions
of the aorta are performed to obtain these views. From a coronal multiplanar
reconstruction (Fig. 1A), an
oblique axial view of the aortic valve is generated. In this optimal oblique
axial imaging plane, the three aortic valve sinuses are well defined
(Fig. 1B). In the cine mode,
the aortic valve leaflets open and close symmetrically. During systole, the
aortic valve opens and there is symmetric effacement of the aortic sinuses
(Fig. 1C). In the coronal
plane, coaptation of the valve leaflets is evaluated
(Fig. 1D). Virtual endoscopic
views can enable a more accurate presurgical evaluation of the aortic valve
(Fig. 2). The improved imaging
characteristics of MDCT have significantly decreased artifacts traditionally
seen with prosthetic aortic valves and have enabled excellent visualization of
valve function (Figs. 3A,
3B,
3C, and
3D).
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Fig. 2 —42-year-old man who presented for evaluation of arrhythmias. Virtual
endoscopic image shows volume-rendered views of aortic valve during
end-diastole. Arrows denote valve leaflets and asterisks, aortic sinuses.
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Fig. 3A —28-year-old woman with Marfan syndrome who presented for evaluation
of status after undergoing St. Jude aortic valve replacement. Coronal
multiplanar reconstruction cine image of normal prosthetic valve motion.
Single frame shows symmetric opening of prosthetic components
(arrow). Prosthetic valve is intact. Dynamic images available online
(www.ajronline.org)
show complete coaptation of valvular components in diastole.
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Fig. 3B —28-year-old woman with Marfan syndrome who presented for evaluation
of status after undergoing St. Jude aortic valve replacement. Oblique sagittal
multiplanar reconstruction cine image of normal St. Jude's prosthetic valve.
Single frame shows symmetric opening of prosthetic components
(arrow). Dynamic images available online
(www.ajronline.org)
show symmetric opening of prosthetic valve leaflets in systole in view of left
ventricle outflow tract.
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Fig. 3C —28-year-old woman with Marfan syndrome who presented for evaluation
of status after undergoing St. Jude aortic valve replacement. Virtual
endoscopic images show prosthetic valve in diastole (C) and in systole
(D). Note origins of reimplanted coronary arteries
(arrows).
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Fig. 3D —28-year-old woman with Marfan syndrome who presented for evaluation
of status after undergoing St. Jude aortic valve replacement. Virtual
endoscopic images show prosthetic valve in diastole (C) and in systole
(D). Note origins of reimplanted coronary arteries
(arrows).
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Fig. 4A —38-year-old man who presented with chest pain and widened
mediastinum. Oblique axial cine image shows aortic valve. Single frame shows
appearance of classic bicuspid valve (arrow). Note symmetric opening
of right and left aortic cusps during cardiac cycle.
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Fig. 4B —38-year-old man who presented with chest pain and widened
mediastinum. Virtual endoscopic view of aorta in systole shows symmetric
appearance of bicuspid valve with ellipsoid configuration of open valve
(arrow).
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Congenital Anomalies of the Aortic Valve
The most important congenital anomaly of the aortic valve is the bicuspid
valve, which affects 0.5-1% of the population
[2]. The classical bicuspid
valve shows two symmetric aortic cusps. During diastole, the open bicuspid
aortic valve assumes an ellipsoid shape (Figs.
4A and
4B). In the aging patient with
a bicuspid aortic valve, the effective valve area gradually decreases (Figs.
5A and
5B). On cine CT, the precise
architecture of the valves and their patterns of commissural fusion can be
identified (Fig. 6). In the
evaluation of patients with suspected bicuspid valves that require valve
repair, several anatomic issues must be addressed for presurgical planning.
The degree of calcification of the valve is important in determining the need
for coronary artery implantation. If the calcification is significant
(Fig. 7), coronary
reimplantation and aortic root replacement may be indicated
[3].
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Fig. 5B —78-year-old woman with aortic stenosis. Corresponding virtual
endoscopic view of aortic valve in systole. Arrow denotes thickened valve
leaflets, and arrowhead shows associated valvular calcification.
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Fig. 6 —58-year-old man with aortic valve stenosis. Cine image shows
moderately stenotic bicuspid aortic valve. Single frame shows thickened valve
leaflets (arrow) and partial fusion of left and right coronary cusps
(asterisk). Dynamic images available online
(www.ajronline.org)
confirm limited excursion of bicuspid valve leaflets.
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Fig. 7 —78-year-old woman with history of calcific aortic stenosis. Virtual
endoscopic view shows heavily calcified valve. While left coronary artery
orifice (arrow) is visualized, right coronary artery orifice is
obscured by heavy calcification.
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Fig. 9 —72-year-old woman with echocardiographic evidence of severe aortic
stenosis. Oblique axial image shows extensive aortic valve calcification
(arrow), consistent with degenerative aortic stenosis.
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Small but significant sinus of Valsalva aneurysms have been reported in the
literature. Although sinus of Valsalva aneurysms have been associated with
trauma and infective endocarditis, a congenital cause is commonly identified
in the literature [4]. Included
as a rare cause of a mediastinal or paracardiac mass, sinus of Valsalva
aneurysms can present with chest pain, conduction abnormalities, and aortic
insufficiency [5]. Involvement
of the noncoronary cusp with extension to the interatrial septum is most
common. These aneurysms and their postoperative appearance are well
characterized with CT, and CT allows precise delineation and depiction of
aortic valve function after surgical repair (Figs.
8A and
8B).
Acquired Abnormalities
A significant patient population is living into their late 70s, 80s, and
90s with degenerative calcific aortic stenosis. Accurate assessment of aortic
valve gradients based on aortic calcification can be performed in the absence
of ECG gating (Fig. 9), and
these studies show excellent correlation of the aortic calcium score with the
degree of valvular stenosis
[6]. Using retrospective ECG
gating, these studies also show accurate architectural delineation of the
aortic valve. Advanced imaging applications enable 3D depiction of the
stenotic aortic valve. Although aortic stenosis can be assessed with ECG-gated
CT (Figs. 10A and
10B), the insufficient aortic
valve can be assessed with CT when a lack of valve closure is documented in
the diastolic phase (Fig.
11).
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Fig. 10A —70-year-old man with aortic stenosis by echocardiography. Coronal
cine CT image shows thickened, calcified degenerative aortic valve.
Single-frame image shows updoming of valve leaflets and stenosis of aortic
valve orifice (arrow). Dynamic images available online
(www.ajronline.org)
confirm valve stenosis and illustrate associated left ventricular
hypertrophy.
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Fig. 10B —70-year-old man with aortic stenosis by echocardiography. Oblique
axial cine CT image of aortic valve. Single frame shows thickened and stenotic
aortic valve (arrow). Comparison of dynamic images available online
(www.ajronline.org)
with Figure 10C, also available online, illustrates markedly compromised valve
opening.
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Fig. 11 —52-year-old man with history of Marfan syndrome. Coronal multiplanar
reconstruction cine image shows aortic insufficiency. Single frame shows lack
of coaptation of aortic valves during diastole (arrow). Findings
depicted on dynamic images of aortic insufficiency, which are available online
(www.ajronline.org),
correlated with findings at echocardiography.
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The superior imaging capabilities of MDCT in the evaluation of aortic
dissection have been described in the literature
[7]. With the use of ECG gating
and cine evaluation, the relationship of the dissection flap to the aortic
valve is well depicted (Figs.
12A,
12B, and
12C). This cine CT capability
is especially important in assessing involvement of the coronary arteries,
because involvement of the coronary arteries necessitates reimplantation of
the coronary arteries in addition to dissection repair (Figs.
13A and
13B).
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Fig. 12A —72-year-old woman with suspected type A dissection. Coronal
multiplanar reconstruction image shows complex type A dissection. Although
flap (arrow) is discontinuous in mid ascending aorta, there is
extension of dissection into aortic root (arrowhead).
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Fig. 12B —72-year-old woman with suspected type A dissection. Cine evaluation
at aortic valve plane. Single frame reveals that dissection (arrow)
extends into noncoronary cusp. Dynamic images available online
(www.ajronline.org)
show involvement of noncoronary cusp with preservation of valve function.
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Fig. 13A —57-year-old man with chest pain and pulmonary edema. Sagittal
oblique cine imaging of aortic valve. Single frame shows dissection flap
(arrows) within proximal ascending aorta. Dynamic views available
online
(www.ajronline.org)
show dissection flap prolapsing through aortic valve in diastole.
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Fig. 13B —57-year-old man with chest pain and pulmonary edema. Coronal cine
image. Single-frame image defines relationship of dissection flap to left
coronary artery (arrow). Dynamic images available online
(www.ajronline.org)
confirm intermittent obstruction of left coronary artery and prolapse through
aortic valve.
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Aortic valve endocarditis is a problematic clinical diagnosis. The classic
presentation is fever, congestive heart failure, renal failure, and systemic
embolic events [8]. Although
the early literature described a sensitivity of only 50%
[9], echocardiography improved
sensitivity to 80%. MRI evaluation of aortic valve infection is less well
characterized; usually abnormalities of perivalvular abscesses and fluid
collections have been described
[10]. This has been true of
the CT literature, in which scattered case reports have described depiction of
perivalvular fluid collections as a manifestation of valve infection
[11]. With the superior
resolution of 16-MDCT and ECG gating, visualization of aortic valve
vegetations is possible and, in some cases, has been superior to
echocardiographic visualization (Figs.
14A and
14B). Advanced tissue
segmentation techniques allow sophisticated presentation of these cases (Figs.
15A,
15B, and
15C).
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Fig. 14A —35-year-old man with fever and bacteremia 2 years after stentless
aortic valve replacement. Axial oblique cine image of aortic valve. Single
frame shows vegetation (arrow) in region of right coronary cusp.
Dynamic images available online
(www.ajronline.org)
confirm mobile vegetation is occupying right aortic sinus.
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Fig. 14B —35-year-old man with fever and bacteremia 2 years after stentless
aortic valve replacement. Virtual endoscopic view of aortic valve shows
vegetation (arrow) within right coronary sinus. Cardiac surgery
reconfirmed periaortic valve abscess and valvular vegetations.
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Fig. 15A —45-year-old woman with history of systemic lupus erythematosus and
clinical evidence of peripheral arterial emboli. Axial oblique ECG-gated view
of aortic valve in diastole shows well-defined soft-tissue mass
(arrow) on aortic valve.
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Fig. 15B —45-year-old woman with history of systemic lupus erythematosus and
clinical evidence of peripheral arterial emboli. Coronal multiplanar
reconstruction view confirms well-defined soft-tissue vegetation
(arrow) on aortic valve.
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Fig. 15C —45-year-old woman with history of systemic lupus erythematosus and
clinical evidence of peripheral arterial emboli. Surface-shaded virtual
endoscopy with tissue segmentation shows endoscopic view of this vegetation
(arrow) in relation to right and left coronary cusp, which at surgery
was consistent with Libman-Sacks endocarditis.
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Inflammatory aortitis usually presents with aortic and great vessel wall
thickening and is often complicated by aneurysms or pseudoaneurysms.
Takayasu's arteritis is a large-vessel vasculitis that classically affects
young Asian women. While often characterized by obstruction and stenosis of
the great vessels, the inflammation can result in weakening of the aortic
annulus and subsequent valve insufficiency
[12]. Though an uncommon
entity, inflammatory aortitis should be considered in patients presenting with
aortic insufficiency (Fig.
16).
Conclusion
This article has described the imaging advances of ECG-gated MDCT in the
evaluation of aortic valvular disease. Once thought to be the domain of
echocardiography and MRI, aortic valvular disease can often be assessed with
current MDCT technology. Further research in dynamic imaging and advances in
contrast agents may provide the physiologic measurements of flow and
transvalvular gradients not possible with our existing technology. These
innovations will strengthen the already growing role CT has defined in the
evaluation of aortic valvular disease.
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Top
Abstract
Introduction
