3 1.2.2 MR Angiography

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Contents

1.1 Introduction . . . . 3

1.2 Imaging Modalities . . . . 3

1.2.1 Multidetector Row CTA . . . . 3

1.2.2 MR Angiography . . . . 4

1.2.3 3D Rotational Angiography . . . . 5

1.3 G ross Anatomy . . . . 5

1.3.1 Coronary arteries . . . . 6

1.3.2 Supra-aortic Vessels . . . . 7

1.3.3 Intercostal Arteries . . . . 8

1.3.4 Anterior Spinal Artery . . . . 8

1.3.5 Bronchial Arteries . . . . 8

1.4 Congenital Variants and Abnormalities . . . . 10

1.4.1 Coronary Arteries . . . . 10

1.4.2 Supra-aortic Vessels and Aortic Arch . . . . . 10

1.4.3 aortic Coarctation . . . . 13

1.5 Acquired Aortic Disease . . . . 15

1.5.1 Dissection . . . . 15

1.5.2 Aneurysms . . . . 15

1.6 Conclusions . . . . 17

1.1 Introduction

Traditionally radiological imaging of the human body has been limited to a two-dimensional depiction of a three-dimensional reality. The thoracic aorta modalities most commonly used were plain (chest) radiography, (digital subtraction) angiography and single-slice computerized tomography (CT). Over the last decade tre- mendous technical advancements have been made in various imaging modalities. The speed of data acquisition with CT scanning and MRI has increased, thus en- abling fast, high-resolution axial imaging. The concur- rent development of advanced 3D volume-rendering techniques, which require high computational speed, al- lowed for the development of CT angiography (CTA), magnetic resonance angiography (MRA) and 3D rotational angiography (3D-RA). In this chapter a brief

overview on the technical aspects of the currently available modalities will be given and advantages and disadvantages of each technique will be discussed. The radiological anatomy of the thoracic aorta and its branches as depicted with these new imaging techniques will be described in detail.

1.2 Imaging Modalities

For successful evaluation of vascular pathology in general, an imaging study must enable accurate measurements, demonstrate intraluminal abnormalities and mural disease, and depict (patency of) side branches [1]. Evaluation of vascular disease is facilitated by 3D techniques, and improves appreciation of the geometry of vascular structures and lesions. The currently available imaging modalities that allow for 3D evaluation of the thoracic aorta are multidetector row CTA, contrast- enhanced MRA and 3D-RA.

1.2.1 Multidetector Row CTA

Compared with single-slice CT the scanning speed of multidetector row CT has increased 40-fold, which makes it possible to scan the entire thorax in a short breath-hold. The present generation of multidetector row or multislice CT scanners allows for a simultaneous acquisition of up to 16 slices, while in the near future systems with over 64 detectors will become available.

With multidetector row CT a single acquisition yields a volume of data, instead of a number of slices (as when using helical CT). Thusfar resolution in the z-axis (ªslice thicknessº) was a limiting factor in image quality for multiplanar reconstruction (MPR). With an increase of the number of detectors, the resolution increases as well, and thus (near) isotropic imaging becomes possible (i.e., imaging with a resolution that is equally high in all directions).

Radio-Anatomy

of the Thoracic Aorta.

3D Imaging of the Aorta (CT, MRI and 3D Rotational Angiography)

Jos C. van den Berg

1

Chapter

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It has been demonstrated that in order to get optimal enhancement of the thoracic aorta preferably high- concentration contrast medium should be used (more than 300 mg I/ml), followed by flushing with a saline bolus [2±4]. The scan delay can be optimized, and the contrast medium dose can be reduced by using a test- bolus technique, or by using an automatic bolus recog- nition system(bolus triggering) [3]. Scanning protocols vary with different systems and manufacturers. With a four-row detector most examinations are performed with 2.5-mm collimation and a table speed of 15±

20 mm per rotation, while using a 16-row detector collimation is reduced to 1.5 mm, and the table speed can be increased to 36 mm per rotation. Contrast medium is injected at a flow-rate of 3±5 ml/s, for a total volume of 120 ml.

The radiation dose for CTA is at least 2±3 times lower than the dose for angiography [5].

Anatomic coverage should include the thoracic inlet (in order to evaluate congenital anomalies of the supra- aortic arches) and the diaphragm(which can help to determine the side of the descending aorta) [5].

3D volume-rendering techniques permit real-time, interactive evaluation in any plane and projection. This enhances understanding of vessel dilatation, mural thrombus and branch vessel anatomy, and further allows visualization of both vascular structures and adja- cent viscera and airways [1, 5]. After obtaining the vo- lumetric data set, a number of postprocessing image reconstruction options are available [5]:

l MPR: 2D sections with a thickness of 1 voxel (fast, easily performed at the CT scanner).

l Variable-thickness displays consisting of an assimila- tion of various sections.

l Maximum-intensity projection (MIP) in which images are derived by projecting the highest attenua- tion voxel in a ray through the scan volume onto an image plane; vessels running in close proximity of osseous structures or calcifications can be easily ob- scured.

l Shaded surface display: this method uses a single threshold to choose relevant (high-density) voxels;

because of the threshold this method is susceptible to artifacts, and may fail to demonstrate vascular calcifications.

l 3D volume-rendering techniques (require a separate workstation): each voxel is adjusted for opacity, color and brightness according to each CT value, according to preset color and opacity maps; the advantage of this technique is that no threshold levels are being selected, thus avoiding the possibility of altering ap- parent diameters of vessels [6].

Reversing the window-level transfer function, we can produce virtual angioscopic images [7, 8].

In summary the advantages of multidetector row CT include shorter imaging time, greater axial coverage,

motion artifact suppression, improved z-axis resolution, higher axial spatial resolution, decreased total dose of iodinated contrast medium and real-time interactive 3D display facilities on workstations.

1.2.2 MR Angiography

Traditionally, MRI, using T1-weighted spin-echo (black blood) imaging and cine-MRI is well suited for evaluation of the gross anatomy of the thoracic aorta, as well as for evaluation of pericardial, pleural and mediastinal effusions [9]. Flow-based methods of imaging (using time-of-flight or phase-contrast properties) yield bright blood images using gradient-echo techniques [10]. The limitation of the latter techniques, however, is that they rely on the physical properties of flowing blood (velo- city, direction, etc.), making the technique susceptible for artifacts, which may result in overestimation of ste- noses or even a false diagnosis of occlusion of a vessel.

Furthermore the spatial resolution and signal-to-noise ratio provided by these 2D techniques do not allow evaluation of small vessel lesions or small side branches [11].

The most-suited technique currently used in the evaluation of thoracic aortic anatomy and disease is dynamic subtraction MRA, using gadolinium (0.2 mmol/

kg, flow rate of antecubital injection 2 ml/s) as the in- travenous contrast agent [10, 12±16]. Gadoliniumshort- ens the T1 of blood, and therefore allows shorter imaging times. Thus, fewer flow-related and motion-related artifacts occur, and therefore the technique can demonstrate subtle aortic lesions, such as penetrating ulcers, and small intercostal arteries. After a plain MRI, intra- venous contrast agent is administered. Using bolus tim- ing (either by using a test bolus or real-time fluoroscopic triggering) the arrival of the contrast agent can be timed, and the contrast-enhanced sequence is performed [10, 17]. This is followed by subtraction of the two series. The limitation of this test-bolus technique is the potential for diminished artery-to-vein contrast, associated additional cost of test-bolus contrast and the potential difficulty to observe the test bolus in distal vessels or in cases with slow flow [17]. To further re- duce respiratory motion artifacts and artifacts related to cardiac motion and pulsatile flow, electrocardio- graphic triggering techniques can be used [9, 18]. The images thus obtained can either be viewed on a slice- to-slice basis, or can be reconstructed on a computer workstation into a MIP image. The appearance of MIP reconstructions resembles that of conventional angiography, and MIP reconstructions are therefore useful in planning of surgical procedures [13]. Using 3D reconstruction techniques it is also possible to obtain an internal view of the vessel and its walls (virtual intra-arterial endoscopy) [13]. It is of importance to evaluate

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both source images and reconstructed images, in order to optimize diagnostic yield (e.g., a dissection can be easily overlooked by evaluating MIP images alone) [18].

Scanning parameters may vary depending on the type and the manufacturer of the MRI system, and will not be listed here.

1.2.3 3D Rotational Angiography

Conventional rotational angiography images are obtained by performing a motorized movement at con- stant speed of the C-armaround the patient during continuous contrast agent injection. To obtain 3D images from a conventional rotational angiographic run two methods exist. One consists of an examination in two phases, where at first the C-armmakes a sweep, ac- quiring images that act as a mask for the subsequent data acquisition. Subsequently a return sweep is performed while contrast agent is injected throughout the entire period of data acquisition [19, 20].

The other technique of obtaining 3D-RA images is directly based on conventional rotational angiographic images without the use of subtraction [21±23].

With both techniques images are transferred to a workstation, where they are converted into pseudo-CT slices (the image intensifier being considered a multi- line detector). Using specific algorithms that correct for image intensifier and contrast distortion, the data set is reconstructed into a volume-rendered image. During this reconstruction process two different types of image correction are performed to limit visual distortion to a minimum: pincushion distortion correction, which is used for reducing the environmental influences caused by the earth`s magnetic field, and isocenter correction, which corrects all the movement imperfections intro- duced by the rotating C-arm[24]. The 3D volume obtained in this way can be rotated and viewed in any direction, and optimal tube positioning (angulation, skew) can be chosen. Determination of vessel geometri- cal properties (length, diameter) can be done manually or using automated vessel analysis software. This software can also provide an endoscopic view (virtual angioscopy), used for evaluation of the vessel interior. Re- cent developments in software, using an unenhanced and a contrast-enhanced run, also allow visualization of calcifications. The same method can provide an improved depiction of stent location and its relation to the calcified plaque and vessel wall. Important information on flow characteristics can be gathered fromthe cinefluoroscopic angiographic images.

A disadvantage of the 3D-RA technique is nonvisua- lization of the thrombus. The same is true for conventional angiography. Calcification, however, can be demonstrated using 3D-RA using either the source images showing some indirect signs of the presence of a

thrombus (discrepancy between angiographic lumen and location of calcification) or the calcified plaque software.

The main use of 3D-RA is in a therapeutic setting in the interventional suite. Use as a diagnostic modality in cases with complex anatomy is another field of applica- tion of 3D-RA. The major advantage of 3D-RA is that owing to the short reconstruction times the physician can optimize projection and make adjustments during the interventional procedure, in order to ensure the optimal outcome, without additional procedure time.

Table 1.1 lists advantages and disadvantages of the various three-dimensional imaging techniques.

1.3 Gross Anatomy

The thoracic aorta starts at the level of the aortic valves in the right anterior mediastinum. The aortic root is formed by the three sinuses of Valsalva (Fig. 1.1).

The ascending thoracic aorta then follows an upward and subsequent left laterodorsal course through the thoracic cavity and is continuous with the aortic arch. The aortic arch has the shape of a semicircle, and slightly ventral to the vertex it gives off its three largest branches (innominate artery, left common carotid artery and left subclavian artery). Finally it makes a downward turn as the descending thoracic aorta. The transition of the aortic arch to the descending thoracic aorta lies at the level of the isthmus (insertion of the li- gamentum arteriosum, the remainder of the ductus Bo- talli). At the level of the diaphragmthe aorta starts its abdominal course. The diameter of the thoracic aorta normally measures 3.3 cm at the aortic root, 3.0 cm at the mid-ascending portion, 2.7 cm at the level of the aortic arch and 2.4 cmat the proximal descending aorta [25]. Along the course of the thoracic aorta several side branches originate, and these are described in the following.

Jos C. van den Berg Chapter 1 Radio-Anatomy of the Thoracic Aorta. 3D Imaging of the Aorta (CT, MRI and 3D Rotational Angiography) 5

Table 1.1 Advantages and disadvantages of the various three- dimensional imaging techniques

Feature of technique CTA CE-MRA 3D-RA

Diameter measurements + + +

Demonstration of thrombus + + ±

Demonstration of calcification + Ô +

Demonstration of vessel wall + + ±

Intraluminal detail + + ±

Branch vessels + + +

Dynamic flow information ± ± +

Monitoring intervention ± ± +

CTA computerized tomography angiography, CE-MRA contrast- enhanced magnetic resonance angiography, 3D-RA 3D rotational angiography

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1.3.1 Coronary arteries

The left main coronary artery arises from the left posterior Valsalva sinus and divides into the left anterior or descending artery (running to the left of the common trunk of the pulmonary artery and the left circumflex artery (following the left atrio-ventricular groove) (Fig. 1.2). The right coronary artery originates fromthe

right anterior coronary sinus, caudally fromthe left coronary artery and prior to giving of its first branch (conus artery) it runs rightward posterior and infe- riorly. With optimization of spatial resolution, decreas- ing scanning time and proper cardiac gating, these four main coronary arteries can be visualized using CT [26, 27] and MRI [28].

Fig. 1.1. aAxial computerized tomography (CT) at the level of the aortic sinus (arrow). The trilobar appearance is clearly appreciated; part of the main stem of the left coronary artery is clearly seen (arrowhead).bAxial CT at a slightly lower level than inademonstrating the origin of the right coronary artery (arrow).c Axial CT at a level below that inbdepicting cusps of aortic valves (arrow).dAxial CT at the level of the common

trunk of the pulmonary artery (asterisk) demonstrating the site of anastomosis (arrow) of the aorto-coronary bypass graft (arrowhead). e Curved reformatted multiplanar reconstruction (MPR) demonstrating the full course of the bypass graft (arrow). fVolume-rendering technique (VRT) image depicting a aorto-coronary bypass graft to advantage (arrow)

a b

c d

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1.3.2 Supra-aortic Vessels

The first and largest branch is the innominate or bra- chio-cephalic artery, which arises from the commence- ment of the aortic arch. It divides into the right subclavian and common carotid artery (Figs. 1.3, 1.4.). The innominate artery is bordered by the right innominate vein and pleura on the right side, and is crossed in front by the left brachiocephalic vein. Initially the

course of the innominate artery is in front of the trachea, and then to the right of it. The second branch is the left common carotid artery that arises slightly to the left of the innominate artery. It extends upward, at first in front and then to the left of the trachea. Finally the left subclavian artery arises fromthe aortic arch, behind the left common carotid artery, and ascends lat- eral to the trachea.

e f

Fig. 1.1e,f

a b

Fig. 1.2. aAxial CT; aortic root with heavily calcified right (arrowhead) and left (arrow) coronary arteries; the ostiumof the right coronary artery is located in the anterior Valsalva sinus.

bAxial CT; slightly higher plane, demonstrating the ostium of the left coronary artery (arrowhead), originating in the left posterior Valsalva sinus.

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1.3.3 Intercostal Arteries

In most patients there are nine pairs of intercostal arteries that originate fromthe posterior aortic wall along the lower nine intercostals spaces [29]. In general, the orifices of the left and right intercostal arteries are located in close proximity to each other (Fig. 1.5).

1.3.4 Anterior Spinal Artery

The most important arterial feeding vessel of the thora- columbar part of the spinal cord is the most dominant of the anterior radiculomedullary arteries (also known as the great anterior radiculomedullary artery or artery of Adamkiewicz). This artery arises from the radiculomedullary artery, which is a division of the posterior branches of intercostal and lumbar arteries. The distal portion of the great anterior radiculomedullary artery forms a characteristic ªhairpinº turn. The artery originates in 68±73% of cases fromleft intercostal or lumbar arteries, with the level of origin ranging fromthe level of the ninth intercostals to the second lumbar artery (in 62±75% of cases at the ninth to twelfth intercostal artery) [30, 31]. With use of meticulous technique the artery of Adamkiewicz can be visualized in 66.7±69% of cases using MRA, and in 68±90% of cases using CTA [30±33].

1.3.5 Bronchial Arteries

Almost all bronchial arteries originate from the thoracic aorta between the level of Th4 and Th7 [29]. There are usually two bronchial arteries supplying the right side.

The first commonly arises from the descending aorta as a common intercostobronchial trunk with the third right posterior intercostal artery, and has a posterolater- ally lying orifice. The second important artery is the common right and left bronchial artery, which arises fromthe anterior surface and supplies both lungs. On the left side a separate left bronchial artery is usually present, and arises fromthe anterolateral surface of the aorta. Many variations occur, including origins from the internal thoracic artery, left subclavian artery and inferior thyroid artery (Figs. 1.6, 1.7).

Fig. 1.2c Curved reformatted MPR demonstrating the main stemof the left coronary artery, and its bifurcation into the left anterior or descending artery (arrowhead) and the left circumflex artery (arrow)

c

Fig. 1.3. a3D rotational angiography (3D-RA); cinefluoroscopic image of selective injection into the innominate artery.b 3D- RA; reconstructive zoom with measurements (yellow arrows) of the innominate artery distally from stenosis at its origin (white

arrow); green, red, and blue arrows indicate orientations of x-, y-, and z-axes.c3D-RA; cut plane (red) indicating the plane of cross-section used for the measurements

a b c

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Fig. 1.4. aAxial CT of a patient after deceleration trauma demonstrating extravasation of the contrast medium at the level of the aortic arch (arrow).bSagittal oblique MPR demonstrating aortic rupture at the inner curve of the aortic arch, at the level

of the isthmus (arrowhead).cSagittal oblique MPR slightly lat- eral fromslice shown inb showing extension of the rupture (arrowhead).d VRT image demonstrating semicircular extension of the rupture to advantage (arrowhead).

a b

c d

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1.4 Congenital Variants and Abnormalities

1.4.1 Coronary Arteries

The commonest congenital anomalies are a left circumflex artery arising fromthe right coronary artery or right sinus and separate origins of the left circumflex and left anterior or descending artery fromthe left coronary sinus. Right coronary aneurysms (either congenital or acquired) can be clearly depicted using 3D techniques, thus aiding surgeons in preoperative planning [26, 34]. The aortic sinus itself can also demonstrate aneurysmal degeneration, which can be depicted using 3D imaging techniques [18]. Finally 3D techniques can be used to demonstrate aorto-coronary bypass grafts.

1.4.2 Supra-aortic Vessels and Aortic Arch

The normal aortic arch configuration with the innominate artery, the left common carotid artery and the left subclavian artery is seen in about 70% of patients (Fig. 1.8). The most frequent variant is a common origin of the brachiocephalic and the left common carotid arteries (a so-called bovine trunk).The second most frequent variation is a left vertebral artery, directly arising from the aorta; other but less common (less than 1%) variants are a common origin of both common carotid arteries, the presence of two brachiocephalic arteries Fig. 1.4. eVRT image with the cut plane running through the

aortic arch (same level as the MPR in Fig. 1.9b) demonstrating contrast extravasation (arrowhead); the relationship to supraaortic vessels can be clearly seen (asterisk left subclavian

artery).fVRT image with the cut plane perpendicular to the aortic arch; semicircular extension of contrast extravasation (arrowhead)

e f

Fig. 1.5.Magnetic resonance angiography (MRA); maximum-intensity projection (MIP) reconstruction demonstrating lower intercostal arteries (arrowheads)

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Fig. 1.6. aAxial CT; origin of the left hypertrophied left bronchial artery (arrow) in a patient with aortic coarctation.bAxial CT; slice at a level below that inademonstrating the subsequent course of the left bronchial artery.cSagittal MPR; the course of the left bronchial artery (arrow), and the origin of an intercostal artery (arrowhead) can be clearly seen.dSagit- tal oblique MPR demonstrating coarctation (arrowhead) at a typical location at the level of the aortic isthmus.eShaded surface display of the descending thoracic aorta; the arrow indi- cates the level of the origin of the left bronchial artery. (Courtesy of Richard G. McWilliams, Liverpool, UK)

a b

c

d

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and finally a separate origin of all four great vessels [29].

The commonest malformation of the aortic arch is a left aortic arch with an aberrant origin of the right subclavian artery (arteria lusoria) (Fig. 1.9). In this type of malformation the right subclavian artery arises distally fromthe left subclavian artery and the right and left common carotid arteries. Another common anomaly is the presence of a right aortic arch, in which the ascending thoracic aorta arches posteriorly to the right side of trachea and esophagus (Fig. 1.10).

Vascular rings are characterized by encirclement of the trachea and esophagus by the aortic arch and associated structures. Vascular rings are the result of an ab- normal embryologic development of the paired fourth

aortic arches, in which primitive aortic arches fail to fuse or regress normally. Typically, each embryonic arch gives rise to their respective common carotid artery and subclavian artery. Normally the embryonic right arch regresses, while the left aortic arch persists, result- ing in a left-sided aortic arch and great vessels. When the left embryonic arch regresses, the result is a right aortic arch, while failure of either arch to regress results in a double aortic arch. The commonest (symptomatic) vascular rings are associated with a complete double aortic arch, an incomplete double aortic arch with an atretic portion, a left aortic arch with an aberrant right subclavian artery (arteria lusoria, see before) and a right aortic arch with an aberrant left subclavian artery [11] (Fig. 1.11).

Fig. 1.7. aCoronal MPR; aortic arch with main supra-aortic arteries: innominate artery (curved arrow), left common carotid artery (arrow) and left subclavian artery (arrowhead).bSagit- tal MPR; descending thoracic aorta (asterisk) with several intercostal arteries (arrowheads).cCurved reformatted MPR; origin of the common intercostobronchial trunk (arrow) and bifurcation into the right bronchial artery and the intercostal artery (arrowhead)

a b

c

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3D reconstructions of CT and MRI images can obvi- ate the need for diagnostic angiography [13, 35]. Imag- ing studies should be evaluated for aortic position, coarctation, vascular compression of airways, collateral vessel formation and aortopulmonary shunts [6].

1.4.3 Aortic Coarctation

Aortic coarctation is one of the commonest congenital cardiovascular lesions, defined as a congenital narrowing of the aorta characterized by stenosis of the juxta- ductal aorta (i.e., at the ductus arteriosus just distal to the origin of the left subclavian artery) [36]. 3D gadolinium-enhanced imaging is helpful in determining coarctation severity by demonstrating collateral vessels (e.g., intercostal and bronchial arteries), which are indi- Jos C. van den Berg Chapter 1 Radio-Anatomy of the Thoracic Aorta. 3D Imaging of the Aorta (CT, MRI and 3D Rotational Angiography) 13

Fig. 1.8. aAxial CT in a patient with type A dissection; the intimal flap is clearly seen (arrowhead). bAxial CT of the same patient at the level of the origin of the supra-aortic vessels demonstrating the common origin of the innominate artery and the left common carotid artery (bovine trunk; asterisk).

c Coronal MPR demonstrating the extent of the intimal flap (arrow) with calcification; the flap is limited to the ascending thoracic aorta.dCoronal MPR; bovine trunk clearly depicted (asterisk).

a b

c d

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Fig. 1.8. eSagittal oblique MPR demonstrating dilation of the ascending thoracic aorta, the origin of the supra-aortic vessels and aneurysmal changes in the descending thoracic aorta.

fVRT image; depiction of the intimal flap (arrow) in the ascending thoracic aorta

e f

Fig. 1.9. aAxial CT at the level of the aortic arch (arrow); patient with aneurysmof an aberrant right subclavian artery (asterisk).b3D reconstruction; posterior view demonstrating the extent of an aneurysmto advantage (arrowhead); origin of the right subclavian artery on the posterior aspect of the aortic arch (arrow). (Courtesy of Reinhard S. Pamler, Ulm, Germany)

a

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cative of the hemodyamic significance of the lesion [11], while black blood images can demonstrate location and length of the aortic narrowing [10].

1.5 Acquired Aortic Disease

1.5.1 Dissection

MRI and CTA are established techniques in the assessment of aortic dissection, and are able to classify dissection according to the De Bakey or Stanford classifica- tion [9] (Figs. 1.13, 1.14). Detection of the intimal flap is best done using contrast-enhanced MRA or CTA [5].

High signal intensity/density within the false and true lumina is a finding consistent with patency, and allows for visualization of the intimal flap; in general, the

true lumen has a higher density/signal intensity than the false lumen, owing to faster flow [11]. Delayed phase imaging can be used to depict the false lumen better [10]. The precise extent of an intimal flap and its relationship to the arch vessels can be clearly defined with customized reconstructions following the aortic course and angioscopic views [1].

1.5.2 Aneurysms

Thoracic aortic aneurysms occur in up to 10% of el- derly patients, and are most commonly atherosclerotic in etiology (Figs. 1.15, 1.16). In the evaluation of aneurysms accurate depiction of aortic caliber, morphology, relationship to aortic arch vessels and the presence of thrombus or ulceration are of importance in deciding whether and how to intervene.

Fig. 1.10. aAxial CT; right-sided aortic arch (arrow); note the presence of the double superior caval vein (arrowheads).bAxial CT at a lower level demonstrating the course of the descending thoracic aorta to the right side of the vertebral column (arrow)

Fig. 1.11. a3D-RA; default reconstruction in a patient with a double aortic arch; smaller ventral arch (arrowhead) and larger posterior arch (arrow). b 3D-RA; reconstructive zoom, more clearly depicting the separate origin of the left and right sub-

clavian arteries and both common carotid arteries (absence of innominate artery).c 3D-RA; true cranio-caudad view depicting the double arch to advantage

a b

a b c

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Fig. 1.12. aMRA; MIP reconstruction in a patient with a false aneurysm(asterisk) at the level of aortic coarctation (treated with percutaneous balloon angioplasty in the past (arrow)).bMRA; MPR showing the distal extent of a false aeurysm(asterisk)

Fig. 1.13. aAxial CT at the level of the carina (asterisk) in a patient with widening of the descending thoracic aorta and an intimal flap (arrowhead); type B dissection.bCoronal MPR in the same patient depicting a larger-diameter false lumen (asterisk) and a small-diameter true lumen (arrow); note the differ- ence in the enhancement with higher density in the, high-flow, true lumen

a b

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Volume-rendered imaging has become indispensable for the evaluation of endovascular stent placement, by demonstrating the spatial relationship between the aorta and major arch branches [1].

1.6 Conclusions

3D vascular imaging techniques offer a significant advantage over traditional imaging techniques. Using these techniques, we can performanatomical dissection in vivo, thus helping in identifying disease, and helping in preoperative planning of surgical and endovascular procedures. Technical developments are rapidly evol- ving, and in the near future even more sophisticated imaging systems will emerge.

Fig. 1.14. aSagittal oblique MIP fromMRA; dissection flap (arrow) in the distal descending thoracic aorta.bSagittal oblique MIP fromMRA; extension of the intimal flap in the aortic arch

(arrowhead) and the left subclavian artery (arrow); patient with type B dissection with secondary extension into type A

Fig. 1.15.Sagittal MPR of a patient with aneurysmof the descending thoracic aorta (asterisk); the absence of mural thrombus can be appreciated, as well as the relative position of the aneurysm with respect to the supra-aortic vessels: left common carotid artery (arrow) and left subclavian artery (arrowhead)

a b

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