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Chapter 12
Vascular and Cardiac CT in Small Animals
Giovanna Bertolini and Luca Angeloni
Additional information is available at the end of the chapter
http://dx.doi.org/10.5772/intechopen.69848
Abstract
Computed tomography (CT) is increasingly available in veterinary practice. As for humans,
CT has a tremendous potential in various clinical scenario. Oncology and traumatized dogs
and cats are probably the veterinary patients that get more benet from new CT appli‐
cations. However, the most amazing progresses are in vascular and cardiac applications.
The advent and rapid diusion of advanced scanner technology (multidetector row) oer
unparalleled diagnostic opportunity in daily practice for comprehensive evaluation of com‐
plex cardiovascular diseases. New skills and knowledge are necessary for radiologists and
nonradiologists for understanding this revolutionary eld of radiology.
Keywords: CT angiography, cardiac CT, vascular anomalies, portosystemic shunt,
vascular ring anomalies, cardiac diseases
1. Introduction
Computed tomography (CT) is a cross‐sectional imaging modality based on the absorption of
X‐rays in the patient. The overall performance of a CT system depends on several key compo‐
nents, comprising the X‐ray source, a high‐powered current generator, number of detectors,
detector electronics, data transmission systems, and the computer system for image pre and
post processing [1]. CT angiography (CTA) rst became possible with the advent of spiral CT
in the early 1980s, which combined simultaneous continuous gantry rotation and table move‐
ment, succeeding the axial or step‐and‐shoot acquisition mode of conventional CT scanners
[2, 3]. In this manner, the tube‐detector system takes a helical or spiral path around the patient
moving through the gantry while the detectors collect the data. The x‐y plane is the plane of
the slice, whereas the z direction is along the axis of the patient (Figure 1).
© 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons
Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,
distribution, and reproduction in any medium, provided the original work is properly cited.
The scan volume is composed of thousands of volume elements (voxels). Ideally, for high‐quality
images, voxels should be of equal dimensions in all three spatial axes (x‐y‐z), so that the spatial
resolution is isotropic, which means equal in all directions.
The isotropic resolution is a fundamental prerequisite for high‐quality vascular studies and post‐
processing reconstruction. The temporal resolution is the second essential requirement for vascular
and cardiac CT studies. Larger volume coverage with isotropic resolution and high temporal
resolution (fast scanning) was not possible using single‐detector spiral CT. For this, at the end of
the 1990s, all major manufacturers introduced the rst generation of (MDCT) systems, having 4
rows of detectors and systems with 8, 10, and 16 detector arrays became available after few years.
The 4‐ and 8‐slice systems still showed inherent limitations regarding scan times and had limited
z‐axis resolution (with fully isotropic acquisition being possible for limited body volume). The
advent of 16‐MDCT scanners in 2001 represented a breakthrough in medical imaging, allow‐
ing routine scanning of larger volumes with true isotropic, submillimeter spatial resolution. 16‐
MDCT transformed CT from a transaxial cross‐sectional technique into a truly three‐dimensional
(3D) imaging modality. This technology, still largely available in veterinary practice, has been
overwhelmed in human eld and in most advanced veterinary centers by newer CT scanners
with 64, 128, 256, and 320 detector rows. Compared with 4‐MDCT scanners, the performance of
64‐MDCT scanners has increased more than 20 times, due to the increase in the number of detec‐
tor rows and rotation [4]. The most recent dual‐source CT scanner (DSCT), which features two
tube‐detector arrays, can achieve a rotation time of up to 0.25 s and a volume coverage speed of
up to 737 mm/s [5]. Voluntary breath holding is not possible in veterinary patients as it is in con‐
scious adult human patients. Thus, veterinary patients are usually anesthetized and intubated
Figure 1. Schematization of in plane, longitudinal resolution, and isotropic voxel.
Computed Tomography - Advanced Applications252
during the scans. The reduced data acquisition time of faster MDCT scanners and DSCT results
in shorter anesthesia or, in selected cases, in decreased need of anesthesia.
2. Principles of MDCT angiography
The simultaneous acquisition of several sections not only results in an extremely increased
scan speed but also in an extension of the CT scan range with isotropic resolution, which allow
for reconstructing images in any arbitrary plane without loss of image quality. When properly
used, MDCT scanners can provide high‐quality three‐dimensional (3D) mapping of the vascu‐
lature, allowing simultaneous evaluation of the vascular lumen, as well as the vessel wall and
surrounding structures. Contrast medium (CM) is essential for CT angiography (CTA). In our
patients, CM is usually injected through an intravenous catheter placed in a peripheral vein.
When injected, CM reaches the heart and then travels throughout the body in the cardiovas‐
cular circulation. The goal of CTA is to achieve adequate opacication (magnitude of contrast
enhancement) in the vascular territory of interest, within a certain time (timing of CM), and to
maintain a consistent level of enhancement throughout scanning (shaping of CM) [6, 7]. CM
concentration and injection protocol need to be adapted to the patient characteristics, the vas‐
cular territory of interest, and to take advantage of the capabilities of the MDCT scanner used.
Intravascular aenuation of at least 300–400 HU along the full longitudinal extent of the target
vasculature and throughout the duration of acquisition is considered to be a prerequisite for
high‐quality CTA. Vascular contrast enhancement is inuenced by various interacting factors:
(1) patient‐related factors, (2) CM‐related factors, and (3) MDCT scanner‐related factors.
Principal patient factors that aect vascular enhancement are cardiac output and body weight.
Veterinary patients have wide ranges of body weight and heartbeat. Thus, when designing
a CTA protocol, it is essential to consider these characteristics to achieve high‐quality results
consistently [8, 9]. In particular, the body weight is the most important patient‐related fac‐
tor aecting the magnitude of contrast enhancement in vascular studies (they are inversely
related). Interindividual variability in vascular contrast enhancement may be reduced by
adjusting the overall iodine dose (by increasing CM volume and/or iodine concentration) and
by increasing the injection rate proportional to body weight. The timing of CM is inuenced
by the cardiac output (inversely related). In patients with normal cardiac output, peak arte‐
rial contrast enhancement is achieved shortly after CM injection. In patients with decreased
cardiac output, CM is distributed and clears slowly, leading to delayed and persistent peak
arterial enhancement. In patients with higher cardiac output (small/toy breeds and cats or
larger patients with diseases such as anemia or sepsis), CM distribution is unpredictable. A
xed scan delay is not recommended for CTA in veterinary patients.
Two methods are possible to predict how CM will behave in a given patient (injection indi‐
vidualization): (1) test bolus and (2) automated bolus triggering or bolus tracking. For the
test bolus method, a small amount of CM is injected and multiple low‐dose nonincremental
scans are taken over the region of interest (ROI) until the contrast is visualized in the selected
vessel. For rst generations of MDCT scanners (4–8 MDCT), this time can be used directly
as the scanning delay for subsequent CTA. When using faster MDCT scanners, however, an
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additional time must be calculated to obtain a diagnostic delay, considering the scan speed, to
not “outrun” the CM bolus. Using bolus‐triggering technique, test bolus injection is not neces‐
sary. All state‐of‐art MDCT systems feature this option. Multiple images are obtained over the
ROI in a nonincremental manner during CM injection and the scan is initiated automatically
when the density within the vessel exceeds a predetermined Hounseld unit (HU) value.
A mechanical power injector is essential for MDCT angiography. This device allows pre‐
programming of the CM volume and ow rate and the seing of an injection pressure limit.
Injection protocol parameters that may inuence the opacication of target vessels are (1)
injection duration (volume:rate), (2) rate of injection, and (3) volume of CM injected (duration
× rate). In particular, arterial enhancement depends on the ow rate (mL/s). When the whole
CM bolus is delivered at a constant injection rate (uniphasic injection), there is an upslope and
downslope of the CM distribution curve and the vascular enhancement may be not uniform
during volume acquisition [10, 11]. This characteristic is less important for short scan ranges
(e.g., CTA of the liver, pancreas, etc.) or with newer fast scanners, but may be problematic when
scanning larger vascular territories (e.g., aortoiliac CTA) or using slower CT scanners. Biphasic
injection (a rapid phase, followed by a second slower phase) and multiphasic, exponentially
decelerating techniques (multiphasic‐rate injection bolus with exponentially decreasing rate)
provide more uniform enhancement with a longer plateau phase and may be indicated for
larger volume coverage using slow scanners. In our experience, saline ushing following uni‐
phasic CM bolus using same rate and of half‐to‐same volume (using a dual‐barrel injector
system) eectively improves contrast distribution in the vascular system during acquisition.
3. MDCTA of vascular diseases
MDCT has brought about dramatic changes in veterinary vascular imaging during the past
decade, leading to once unconceivable noninvasive diagnostic possibilities. Nowadays,
CT‐angiography is reported to be the method of choice for in vivo vascular anatomy depiction
and for the diagnosis of various vascular pathological conditions [12–15]. A wide spectrum of
vascular thoracic and abdominal disorder may be studied with MDCT angiography. MDCT
angiographic studies are frequently used for detailed assessment and interventional planning
in case of congenital and acquired vascular thoracic or abdominal anomalies. Other indica‐
tions for MDCTA include vascular thrombosis and trauma.
3.1. Thoracic CTA applications
The thoracic vascularization includes systemic vasculature and pulmonary vessels. Systemic arte‐
rial thoracic vasculature is provided by branches of the thoracic aorta. The pulmonary arteries
supply 99% of the blood ow to the lungs and participate in gas exchange at the alveolar capillary
membrane, while the bronchial branches of the bronchoesophageal artery supply the supporting
structures of the lungs, including the pulmonary arteries. The pulmonary and bronchial arteries
have rich and complex anastomoses at the capillary level. The venous drainage of the thorax is
provided by cranial vena cava and azygos vein system. CM distribution after peripheral intra‐
venous injection diers among the heart and the systemic and pulmonary arteries and veins,
Computed Tomography - Advanced Applications254
and this should be considered when designing a CT protocol. The delay between the start of CM
injection and the initiation of scanning should be tailored based on scanner performance and
the patient’s characteristics (using the bolus test or the bolus tracking technique, as said before).
The ROI will be placed on dierent vascular structures, the aorta, or the main pulmonary artery,
depending on the clinical purpose. Clinical indications for MDCTA of the thorax include anoma‐
lies of the aortic arch and its branches, bronchial and bronchoesophageal arterial anomalies, and
systemic thoracic veins diseases [16–18]. Pulsatile artifacts are critical for the accurate diagnosis of
aortic arch anomalies, especially in small veterinary patients. With slower 8–16‐MDCT scanners,
acquisition of near‐isotropic dataset with spiral acquisition mode and a half‐scan interpolation
reconstruction (50% overlap) algorithm aid the distinction between motion artifacts and intrinsic
disease. Scanners with 40 or more rows can routinely imaging of the thoracic aorta using electro‐
cardiogram (ECG) gating. At our center, which is equipped currently with a second‐generation
DSCT scanner, all CT examinations of patients with suspected or known aortic arch pathologies
or other cardiovascular anomalies are now ECG‐gated or acquired in sub‐second ash spiral
mode, resulting in the freezing of cardiovascular and respiratory motions.
Most vascular ring anomalies found in dogs are persistent right aortic arch (PRAA) with left‐sided
ligamentum arteriosum, with the heart base making up the ventral portion of the ring. PRAA
has been described associated with patent ductus arteriosus (PDA). One‐third of dogs with
PRAA also have an aberrant left subclavian artery that may take a retroesophageal position,
contributing to esophageal compression. The right aberrant subclavian artery arises from the
normally left‐sided aortic arch, distal to the left subclavian artery, or from a bisubclavian
trunk is generally reported incidentally (Figure 2).
Enlarged bronchial branches of bronchoesophageal artery (bronchoesophageal artery hypertro‐
phy (BEAH)) and other nonbronchial thoracic arteries (e.g., intercostal, internal mammary,
and inferior phrenic arteries) are frequently observed in patients with chronic pulmonary
embolism. These vessels respond to chronic pulmonary ischemia and decreased pulmonary
blood ow with hypertrophy or enlargement, trying to maintain blood ow to the aected
lung and participate in gas exchange through the peripheral systemic‐pulmonary arterial
anastomoses. Thoracic CTA show prominent bronchial branches at the bronchial bifurcation,
continuing their course along the bronchi, describing a tortuous path, and ultimately anasto‐
mose with the subsegmental pulmonary arteries (Figure 3).
Figure 2. Right aberrant subclavian artery. E, esophagus.
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Congenital paern of BEAH is described in dogs in association with systemic‐to‐pulmonary
stula (with left or right main pulmonary artery) [17, 18]. This paern might result from per‐
sistent embryonic pulmonary‐systemic connection, as hypothesized for PDA. In these cases,
a large vessel (5–8 mm diameter) is seen in middle mediastinum, emptying into the proximal
part of the left or right pulmonary artery through a small orice. A dense periesophageal
vascular network accompanies the congenital form of BEAH (Figure 4).
A persistence of the left cranial vena cava (CrVC) is probably the most common thoracic venous
anomalies in our patients [19]. Persistent left CrVC alone is often an incidental CT nding,
but may cause esophageal stenosis and may be associated with severe cardiovascular defects.
Figure 3. Acquired paern of BEAH in a dog with chronic bronchopulmonary disease. A. Thin volume‐rendered image
of the thorax (the head is on the right). The arrow indicates the enlarged bronchoesophageal artery. B. Arrows indicate
hypertrophied subsegmental bronchial arteries coursing along the corresponding bronchus.
Computed Tomography - Advanced Applications256
The left persistent CrVC results from incomplete atrophy of the embryonic left cranial cardi‐
nal vein. Two types are described in dogs and cats: (1) a complete type, with nonatrophied
left cranial cardinal vein retaining its embryological connection with the coronary sinus; (2)
an incomplete type, in which the distal portion of the persistent vein atrophies, whereas the
proximal portion persists and receives the hemiazygos vein.
In oncology patients, MDCTA is indicated for the assessment and interventional planning in
case of mediastinal masses or tumors of the thoracic wall involving the thoracic vasculature.
3.2. Abdominal vascular diseases
Most common abdominal vascular diseases involve the caudal vena cava and the portal sys‐
tem. Caudal vena cava anomalies often have no or lile clinical signicance in themselves, but
they are often associated with other vascular anomalies, such as portosystemic shunts that are
clinically relevant [20–22]. In veterinary literature, MDCT angiographic studies are frequently
reported for congenital portosystemic shunt assessment in dogs and cats [23–26]. Moreover,
it is widely used also for the assessment of other pathological conditions of the portal system,
such as acquired portal collaterals (APSS), portal vein aneurysm, and portal vein thrombosis
[27–29]. Congenital anomalies of the abdominal segment of the descending aorta are rarely
reported in small animals, and include variable paern of renal arteries, aortic aneurism, and
common celiacomesenteric trunk. Among acquired conditions, local thrombosis in the distal
aorta with embolization to the iliac and/or femoral artery is the most common indication for
MDCTA in dogs and cats (Figure 5A).
Figure 4. Congenital paern of bronchoesophageal artery hypertrophy with artery‐to‐pulmonary stula (not visible
here). Note the enlarged bronchoesophageal artery arising from the thoracic aorta and the dense mediastinal vascular
network (dorsal view).
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The selection of an MDCTA scan protocol varies in consideration of the type of anomaly
suspected and the vascular district (arterial, portal, or venous) potentially involved. For a
comprehensive evaluation of the abdominal vascular structures, a multiphasic approach is
necessary, including at least two vascular phases: arterial and portal venous phase that is
also useful for the hepatic parenchyma evaluation. When CM is injected, opacication of the
hepatic artery and its branches is encountered rst, followed by the portal system, hepatic,
and systemic veins. In veterinary literature, the peak aortic enhancement of normal dogs
varies between 2 and 9.8 s, and peak enhancement of the portal vein varies between 14.6
and 46 s after contrast medium injection. Given the great diversity of patients’ character‐
istics (body weight and cardiac output), the use of bolus test or automatic bolus‐triggering
techniques for the individualization of scan delays in multiphasic MDCT examinations is
needed.
A dual‐ or three‐phase MDCT exam can provide excellent visualization of complex vascu‐
lar anomalies and oer a comprehensive overview of the entire portal system and related
parenchymal organs. Various new congenital and acquired phenotypes of portosystemic col‐
laterals have been described using MDCT technology [24–26, 30] (Figures 6 and 7). Good
opacication of the portal venous system allows detection of endoluminal lling defects in
case of portal vein thrombosis and simultaneous assessment of secondary portal collaterals
(portosystemic and/or portoportal collateral vessels) (Figure 8).
A third vascular phase, corresponding to the interstitial hepatic phase, allows optimal visu‐
alization of systemic veins, which is essential for the evaluation of venous thrombosis and
vascular invasion (Figure 5B). Most caudal segments of the caudal vena cava are prone to
congenital variation, which is generally clinically silent themselves (Figure 9), but are often
associated with CPSS or other vascular and nonvascular anomalies that can be of great clinical
relevance.
The arterial phase is useful for detection of high‐ow vascular connections (arteriovenous
stula) at any level of the body. MCDTA images show enlarged, tortuous arteries, and premature
Figure 5. A. Aortoiliac thromboembolism in a dog with nephrotic syndrome. B. Caudal vena cava thrombosis in an
oncologic patient (hepatic carcinoma).
Computed Tomography - Advanced Applications258
lling of the veins (Figure 10). In the liver, an early arterial phase can reveal complex hepatic
arteriovenous malformations (HAVM) that are congenital anomalous connections between
branches of the hepatic artery and hepatic portal vessels.
In traumatized patients, active bleeding due to arterial or venous vascular injuries can be
revealed by CM extravasation in the arterial and portal venous phases. In oncology patients,
a three‐phase MDCT abdominal examination provides useful information of vascular blood
supply of tumors and local vascular invasion, allowing detailed interventional and surgical
planning.
Figure 6. Extrahepatic congenital portosystemic shunt, in which the left gastric vein (LtGV) and the splenic vein had no
communication with the portal vein (PV). Both veins join the anomalous vessel (PSS) that empty in the caudal vena cava
(CVC). A. Dorsal thin‐MIP (maximum intensity projection) showing the end of PSS into the CVC. B. Volume‐rendered,
frontal view showing the course of the PSS.
Figure 7. Congenital extrahepatic PSS between the left gastric vein and the right azygos vein. A. Volume‐rendered
image, frontal view. Ao, aorta, Az, azygos vein. B. Volume rendered ventral view. PV, portal vein; GDV, gastroduodenal
vein; SV, splenic vein; cdMV, caudal mesenteric vein. PSS, portosystemic shunt.
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Figure 10. Peripheral arteriovenous communications in a dog. A. Volume rendering of arterial phase. Note the early
enhancement of the left femoral vein. B. MIP of same volume, showing several small tortuous vessels in both legs and
the muscular swelling.
Figure 8. Portal venous phase in dogs with thrombosis of the portal system. A. The arrow indicates a lling defect in the
splenic vein. B. Large arrow indicates a large lling defect in intrahepatic portal branches. The thin arrow shows some
retroperitoneal varices, due to portal hypertension.
Figure 9. A. Dorsal MPR in a cat. The prerenal segment of the CVC is left sided (persistent left supracardinal vein and
anomalous regression of the right one). B. Duplication of the prerenal segment of the CVC (partial duplication for
persistent left supracardinal vein).
Computed Tomography - Advanced Applications260
4. Cardiac CT
In humans, since the advent of advanced scanner technology having 64 or more detectors,
the heart and coronary arteries are routinely imaged as a motion‐free volume of data. Most
recent MDCT and DSCT scanners can obtain a true volumetric data set of the entire heart and
adjacent structures that can be reconstructed at any point in the cardiac cycle, making CT an
important imaging modality for the comprehensive assessment of cardiac morphology and
function. While echocardiography remains the rst‐line imaging modality, CT has become an
increasingly utilized complementary imaging modality for assessment of coronary and non‐
coronary cardiac structures, including the cardiac chamber and valves, the pulmonary arteries
and veins, the thoracic aorta and its proximal branches, the cardiac veins, and the pericardium.
Cardiac CT was rst described in veterinary literature in 2011 for canine coronary artery
assessment using a 64‐MDCT scanner [31]. Later, other studies have been published describing
morphological characteristics of various cardiac structures and comparing echocardiography,
magnetic resonance (MR) and CT measurements [32, 33]. As for humans, cardiac CT in veteri‐
nary patients has now become an increasingly utilized modality for the assessment of cardiac
congenital conditions, cardiac and paracardiac masses, and pericardial diseases [34–36]. In
clinical practice, morphological evaluation of these conditions is generally performed with
non‐ECG‐gated CT protocols, as a part of a thoracic CT examination. Most recent MDCT is not
only fast but also has high spatial and temporal resolutions, multiplanar reconstruction (MPR)
capabilities, and a wide eld of view, which provides information of the heart, mediastinum,
and adjacent structures, including the lungs. A non‐ECG‐gated CT examination, however, is
not a reliable way for comprehensive evaluation of small cardiac structures (e.g., coronary
arteries and valves), congenital heart diseases, cardiac sizes and in many other clinical situa‐
tions using rst generation of MDCT scanners (≤64 rows) [32, 33]. With most advanced MDCT
scanners (e.g., 128–320 detector rows) and DSCT technology, it is possible to obtain high‐reso‐
lution, submillimetric data in a few seconds, providing excellent morphological detail of the
heart and paracardiac structures, having minimal or no motion artifacts. For instance, at our
center, now equipped with a second generation of dual‐source 128‐slice CT systems, cardio‐
thoracic CT examination can be performed at a high‐pitch, up to 3.4 with gantry rotation time
of 0.28 s and a temporal resolution of 75 ms (Figure 11).
4.1. Cardiac CT basic principles
For motion‐free and of diagnostic value imaging of the heart, high temporal and spatial resolu‐
tion are both essential, especially in veterinary patients who have variable heart rates. CT data
should be assessed during certain phases of the cardiac cycle with lile cardiac motion. Ideally, a
complete data set of the whole heart would be acquired within a single phase of the cardiac cycle
without movement. Two methods are possible for virtually freezing the heart: prospective gating
with sequential or step‐and‐shoot scanning mode and retrospective ECG gating (spiral) [37, 38].
In prospective ECG‐triggered sequential CT‐scanning using partial‐scan technique, the scan is syn‐
chronized to the motion of the heart in order to acquire data preferably in the diastolic phase,
when cardiac motion is minimal. After every scan, the table moves by the width of the acquired
scan range in the z‐direction toward the next scan position in order to provide gap‐less volume
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coverage (step‐and‐shot). The delay time for scan acquisition after an R‐wave is individually
based on a prospective estimation of the R‐R intervals, aempting to acquire the data during
the diastolic phase of the heart. Using this technique, small changes in heart rate during the
sequential scan can cause acquisition in inconsistent heart phases and thus inconsistent volume
coverage, resulting in artifacts at the intersections of adjacent image stacks and subsequent
misregistration of lesions along z‐axis. This may represent a limitation especially for veterinary
patients, where many cardiac structures are small and complex 3D structures that require the
highest possible image quality. Moreover, with prospective ECG triggering, estimation of the
next R‐R interval may be incorrect when heart‐rate changes are present, such as in patients
with arrhythmia or with a single premature ventricular contraction, which makes sections of
the heart entirely uninterpretable.
In retrospectively ECG‐gated spiral scanning, reconstructions of a continuous spiral scan are
synchronized to the movement of the heart by using an ECG trace that is recorded simulta‐
neously. The great advantage of retrospectively ECG‐gated MDCT‐spiral scanning is that it
provides an isotropic, 3D image data set of the complete cardiac volume without gaps and
misregistration of data. Retrospective ECG gating data are available during all phases of the
cardiac cycle and this oers the possibility of retrospectively modifying the synchronization
of the ECG trace and data reconstruction, choosing the best R‐R interval for image analysis.
Individual adjustment of the image‐interval‐position is extremely useful for imaging those
patients with fast and irregular heart rate.
The scanner technology available greatly inuences the scan protocol for cardiac CT evalu‐
ation. The maximum pitch in single source MDCT is usually about 1.5. Last generation of
DSCT scanners allow pitch value up to 3.4. This results in maximum scan speed of 737 mm/s,
which allows continuous volume coverage of a whole body in one second or less with iso‐
tropic resolution [38]. Since this impressive temporal resolution, pharmacological pretreat‐
ment for heart rate modulation is not necessary in our patients. High‐detailed images of the
heart can be obtained also in awake patients, independently on the heart rate. However, using
Figure 11. Non‐ECG‐gated, high‐pitch 128‐DSCT (Flash mode) of the thorax in a dog with pulmonary embolism.
A transverse view. Arrows show the lling defects in pulmonary vessels, due to thrombosis. Cardiac structures are
“freezed” (lv, left ventricle).
Computed Tomography - Advanced Applications262
this approach, cardiac function evaluation is not possible. In our experience, low‐pitch retro‐
spective ECG‐gated 128‐DSCT cardiac examination performed without any pharmacological
pretreatment to reduce patient’s heart rate provides excellent images, useful either for mor‐
phological or functional assessments.
Factors inuencing the CM hemodynamic distribution are similar to those described before
for CTA. CM injection protocol should take into account the body weight and cardiac out‐
put of the patient. Both the bolus test and the bolus‐triggering techniques can be used for
CM injection individualization for cardiac evaluation. In standard cardiac CT for coronary
artery evaluation, the ROI is placed in the ascending aorta. In this approach, the left ventricu‐
lar and left atrial walls and cavities, as well as left‐sided valves, will be uniformly opacied
(Figures 12 and 13). However, depending on the contrast agent infusion protocol, the right‐sided
Figure 12. Retrospective ECG‐gated cardiac examination with 128‐DSCT (low pitch). Note the absence of motion
artifacts (the patient was under general anesthesia, mechanically ventilated). The ROI has been placed on the ascending
aorta (standard cardiac CT). Note the great enhancement of the aorta, left atrium, and ventricle.
Figure 13. Retrospective ECG‐gated cardiac CT in a dog (128‐DSCT).
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chambers, walls, and valves may or may not be suitable for interpretation. Optimal timing for
right heart good opacication can be achieved placing the ROI for test bolus or bolus track‐
ing in the main pulmonary artery. Achievement of diagnostically adequate homogeneous
enhancement of the right atrium can be dicult because of mixing of unopacied blood from
the caudal vena cava with high‐aenuating contrast agent‐opacied blood from the cranial
vena cava. Streak artifacts due to high concentration of CM in the cranial vena cava or right
atrium may obscure some structures or simulate the presence of masses or thrombotic lesions.
Dual or triple CM bolus injection technique may lead to a more uniform opacication of right‐
sided cardiac structures. This may be necessary for the evaluation of patients with certain
congenital heart diseases or cardiac masses.
4.2. Cardiac CT clinical applications
With ECG‐gated cardiac CT examination, the anatomy of the heart is clearly depicted. MDCT
is the preferred imaging modality when anomalous origin and course of coronary arteries
is suspected [32, 39] (Figure 14). Compared to human literature, reports of congenital artery
anomalies in animals are sparse, presumably because coronary artery disease is less common
in veterinary patients and rarely of clinical signicance, unless in the seing of pulmonary
valve stenosis (PS). Further, advanced diagnostic imaging of the heart is not routinely per‐
formed, thus underestimating the frequency of coronary anomalies in our patients. ECG‐
gated cardiac CT allows the simultaneous evaluation of other noncoronary structures of the
heart. Left and right chambers are well dened from the cardiac muscular wall and from
interventricular and interatrial septum. Small structures, such as atrioventricular valves, aor‐
tic and pulmonary valves, papillary muscles of both ventricles, and trabeculae carneae are
easily distinguishable [31].
Figure 14. Retrospective ECG‐gated cardiac CT in a dog with anomalous right origin of septal coronary artery branch
(128‐DSCT).
Computed Tomography - Advanced Applications264
Using retrospective ECG‐gated mode with full cardiac cycle available, functional evaluations
of the heart are also possible. In postprocessing, multiplanar analysis (MPR) of volume data‐
set allows standard planar and volumetric measurements, using same image planes normally
used in echocardiography [32–35]. ECG‐gated cardiac CT is also useful in patients with con‐
genital cardiac defects such as PDA, PS, or more complex congenital heart diseases. Moreover,
it is helpful for planning surgical and interventional procedures [16, 40] (Figures 15, 16).
Figure 15. 128‐DSCT, ECG‐gated cardio CT in PDA in a dog (pre‐interventional assessment) and corrected PDA with
Amplaer duct occluder (VR on the right).
Figure 16. Retrospective ECG‐gated cardiac 128‐DSCT in dogs with pulmonic stenosis. A. Images on the left have been
automatically reconstructed by the software in best‐systolic phase and those on the right in best diastole (less motion
artifacts). B. VR of another dog with pulmonic stenosis and post stenotic bulge of right ventricular outow tract.
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In clinical practice, primary or metastatic cardiac tumors can be easily identied during routine
non‐ECG‐gated examination of the thorax. However, ECG‐gated cardiac imaging in patients
with suspected or known cardiac‐paracardiac or pericardial tumors minimizes motion‐related
artifacts and allows a more precise delineation of the lesion margins (Figure 17).
Author details
Giovanna Bertolini* and Luca Angeloni
*Address all correspondence to: bertolini@sanmarcovet.it
Diagnostic and Interventional Radiology Division, San Marco Veterinary Clinic, Padova, Italy
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