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Vascular and Cardiac CT in Small Animals

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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
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 benet from new CT appli
cations. However, the most amazing progresses are in vascular and cardiac applications.
The advent and rapid diusion of advanced scanner technology (multidetector row) oer
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 xy 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 (, 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 (xyz), 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 opacication (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 aenuation 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 inuenced by various interacting factors:
(1) patient‐related factors, (2) CM‐related factors, and (3) MDCT scanner‐related factors.
Principal patient factors that aect 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 aecting 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 inuenced
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
Vascular and Cardiac CT in Small Animals
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 Hounseld 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 seing of an injection pressure limit.
Injection protocol parameters that may inuence the opacication 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) eectively 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 diers among the heart and the systemic and pulmonary arteries and veins,
Computed Tomography - Advanced Applications254
Vascular and Cardiac CT in Small Animals
Congenital paern of BEAH is described in dogs in association with systemic‐to‐pulmonary
stula (with left or right main pulmonary artery) [17, 18]. This paern 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 orice. 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 paern 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 lile clinical signicance in themselves, but
they are often associated with other vascular anomalies, such as portosystemic shunts that are
clinically relevant [2022]. 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
[2729]. Congenital anomalies of the abdominal segment of the descending aorta are rarely
reported in small animals, and include variable paern 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 paern 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).
Vascular and Cardiac CT in Small Animals
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, opacication 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
A dual‐ or three‐phase MDCT exam can provide excellent visualization of complex vascu‐
lar anomalies and oer 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
opacication 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
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
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.
Vascular and Cardiac CT in Small Animals
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 [3436]. 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 lile 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
Vascular and Cardiac CT in Small Animals
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, aempting 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 oers 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 inuences 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 inuencing 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 opacied
(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).
Vascular and Cardiac CT in Small Animals
chambers, walls, and valves may or may not be suitable for interpretation. Optimal timing for
right heart good opacication 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 dicult because of mixing of unopacied blood from
the caudal vena cava with high‐aenuating contrast agent‐opacied 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 opacication 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 signicance, unless in the seing 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 dened 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
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
Amplaer 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 outow tract.
Vascular and Cardiac CT in Small Animals
In clinical practice, primary or metastatic cardiac tumors can be easily identied 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:
Diagnostic and Interventional Radiology Division, San Marco Veterinary Clinic, Padova, Italy
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Computed Tomography - Advanced Applications266
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Vascular and Cardiac CT in Small Animals
... Over the last several decades, non-invasive imaging of small animal models provides in vivo insights into the structural and functional phenotypes with physiological and clinical relevance. The current non-invasive imaging modalities allow from a wide range of vertebrate animal models, including light-sheet fluorescent microscopy 4 , echocardiography 5 , magnetic resonance imaging (MRI) 6 , x-ray computed tomography (CT) 7 , positron emission tomography (PET) 8 , and/or single-photon emission computed tomography (SPECT) 9 , and a combination of these imaging techniques [10][11][12] . Each imaging technique provides the unique degree of tissue penetration, resolution, and contrast to image the specific animal models from zebrafish to mouse to swine models, and the combination of these complementary techniques allows for addressing the spatial and temporal resolution, field of view (FOV), and relative phenotypes in response to the particular imaging needs. ...
... For example, echocardiography is a portable tool to assess cardiac function by interrogating the contracting/relaxing heart chambers and open/closure of the valves in real-time. In contrast, CT and MRI are bulky but offer larger FOV and/or finer spatial resolution needed for cardiac anatomy and vascular system 7,13 . ...
Full-text available
Complementary to mainstream cardiac imaging modalities for preclinical research, photoacoustic computed tomography (PACT) can provide functional optical contrast with high imaging speed and resolution. However, PACT has not been demonstrated to reveal the dynamics of whole cardiac anatomy or vascular system without surgical procedure (thoracotomy) for tissue penetration. Here, we achieved non-invasive imaging of rat hearts using the recently developed three-dimensional PACT (3D-PACT) platform, demonstrating the regulated illumination and detection schemes to reduce the effects of optical attenuation and acoustic distortion through the chest wall; thereby, enabling unimpeded visualization of the cardiac anatomy and intracardiac hemodynamics following rapidly scanning the heart within 10 s. We further applied 3D-PACT to reveal distinct cardiac structural and functional changes among the healthy, hypertensive, and obese rats, with optical contrast to uncover differences in cardiac chamber size, wall thickness, and hemodynamics. Accordingly, 3D-PACT provides high imaging speed and nonionizing penetration to capture the whole heart for diagnosing the animal models, holding promises for clinical translation to cardiac imaging of human neonates. High-speed non-invasive photoacoustic tomography reveals cardiac anatomy and cardiovascular hemodynamics in rats.
The determination of arterial vascular distribution patterns can contribute to more detailed knowledge on arterial systems. In this context, the aim of the present study was to describe the collateral aortic branches in the collared peccary, aiming to define a standard model for this species, providing information through comparative anatomy for analysis of some evolutionary aspects of the order Artiodactyla. Ten young male animals were employed. The vascular system was washed with a saline solution and then perfused with Neoprene 450 latex coloured with red or yellow pigment, followed by collateral aorta branch dissections and analyses. The contrasted digital radiography technique was applied to two animals, which were initially perfused with a barium sulphate solution (1 g/ml) and Neoprene 450 latex at a 1:3 ratio, and subsequently, the digital radiographic examination was performed. The aortic arch of the collared peccary emitted the brachiocephalic trunk and the left subclavian artery, while eight symmetric pairs of dorsal intercostal arteries originated from the thoracic aorta. The abdominal aorta, in turn, exhibited the celiac, cranial mesenteric, renal, caudal mesenteric, testicular, external iliac, internal iliac and sacral arteries as the collateral branches in all studied animals. Therefore, no relevant variations were observed regarding the arrangement of the arterial distribution of the aorta, thus suggesting a static standard model in the collared peccary.
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Coronary artery anomalies represent a disease spectrum from incidental to life-threatening. Anomalies of coronary artery origin and course are well-recognized in human medicine, but have received limited attention in veterinary medicine. Coronary artery anomalies are best described in the dog, hamster, and cow though reports also exist in the horse and pig. The most well-known anomaly in veterinary medicine is anomalous coronary artery origin with a prepulmonary course in dogs, which limits treatment of pulmonary valve stenosis. A categorization scheme for coronary artery anomalies in animals is suggested, dividing these anomalies into those of major or minor clinical significance. A review of coronary artery development, anatomy, and reported anomalies in domesticated species is provided and four novel canine examples of anomalous coronary artery origin are described: an English bulldog with single left coronary ostium and a retroaortic right coronary artery; an English bulldog with single right coronary ostium and transseptal left coronary artery; an English bulldog with single right coronary ostium and absent left coronary artery with a prepulmonary paraconal interventricular branch and an interarterial circumflex branch; and a mixed-breed dog with tetralogy of Fallot and anomalous origin of all coronary branches from the brachiocephalic trunk. Coronary arterial fistulae are also described including a coronary cameral fistula in a llama cria and an English bulldog with coronary artery aneurysm and anomalous shunting vessels from the right coronary artery to the pulmonary trunk. These examples are provided with the intent to raise awareness and improve understanding of such defects.
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Persistent left cranial vena cava (PLCVC) is an uncommon congenital thoracic venous anomaly in dogs. This study examines the clinical and CT findings of dogs diagnosed with PLCVC incidentally. In this study, complete type of PLCVC was diagnosed in 26 dogs with CT angiography. Shih tzu (17 cases) and Pekingese dogs (3 cases) were overrepresented. There was no gender predisposition, and the average age at presentation was 10.3 years. Of 26 dogs, one dog had a bridging vein connecting right and left cranial vena cavae, and another dog showed azygos vein terminating PLCVC. On the thoracic CT images in the third dog, the right cranial vena cava was absent so that right brachiocephalic vein ended to PLCVC. However, the right costocervical vein drained another vein coursing caudally to the right atrium with azygos vein. In conclusion, CT angiography is a very useful method to diagnose PLCVC and variations of related thoracic vein anomalies in dogs.
Full-text available
Objectives: To investigate the feasibility of high-pitch CT pulmonary angiography (CTPA) in 3rd generation dual-source CT (DSCT) in unselected patients. Methods: Forty-seven patients with suspected pulmonary embolism underwent high-pitch CTPA on a 3rd generation dual-source CT scanner. CT dose index (CTDIvol) and dose length product (DLP) were obtained. Objective image quality was analyzed by calculating signal-to-noise-ratio (SNR) and contrast-to-noise ratio (CNR). Subjective image quality on the central, lobar, segmental and subsegmental level was rated by two experienced radiologists. Results: Median CTDI was 8.1 mGy and median DLP was 274 mGy*cm. Median SNR was 32.9 in the central and 31.9 in the segmental pulmonary arteries. CNR was 29.2 in the central and 28.2 in the segmental pulmonary arteries. Median image quality was "excellent" in central and lobar arteries and "good" in subsegmental arteries according to both readers. Segmental arteries varied between "excellent" and "good". Image quality was non-diagnostic in one case (2%), beginning in the lobar arteries. Thirteen patients (28%) showed minor motion artifacts. Conclusions: In third-generation dual-source CT, high-pitch CTPA is feasible for unselected patients. It yields excellent image quality with minimal motion artifacts. However, compared to standard-pitch cohorts, no distinct decrease in radiation dose was observed.
Pulmonic stenosis (PS) is the most common congenital cardiac disease in dogs. Boxers and English bulldogs are among the most commonly affected breeds and also commonly associated with an aberrant coronary artery (CA). If an aberrant CA is suspected and balloon valvuloplasty indicated, an intra-operative angiography is recommended prior to the procedure. ECG-gated computed tomography (CT) can be used to screen for CA anomalies in a quick and minimally-invasive way (preventing side effects associated with selective catheter angiography) and allowing early planning of the procedure. The aim of this case series was to report CT findings associated with PS diagnosed by echocardiography. Our database was retrospectively searched for cases of dogs with PS diagnosed by echocardiography, where an ECG-gated CT was performed. A total of six cases were retrieved: all were diagnosed with severe PS. Four dogs had concurrent congenital defects: two dogs had a patent ductus arteriosus, one dog had a ventricular septal defect and an overriding aorta, one dog had an aberrant CA. Detailed CT findings of all cases were reported, including one case of a patent ductus arteriosus and an overriding aorta not identified by transthoracic echocardiography. In addition, an abnormal single left coronary ostium, with a pre-pulmonic right CA was described. In conclusion, despite echocardiography remaining the gold standard for diagnosis and assessment of PS, ECG-gated-CT angiography is a complementary diagnostic method that may provide additional relevant information, shorten surgery/anaesthesia time and reduce the amount of radiation to which the clinician is subjected.
Background: Biphasic injection protocols are frequently used because they yield homogenous contrast enhancement. We hypothesize that with faster scanners and shorter scan times, biphasic injection protocols are no longer necessary. Purpose: To evaluate whether a monophasic injection protocol is equivalent to a biphasic protocol in terms of contrast enhancement and homogeneity. Material and methods: Repeated high-pitch CTA (pitch 3) and conventional standard-pitch computed tomography angiography (CTA) (pitch 1.2) from the cervical region to the symphysis was performed in seven beagles (11.2 ± 2.5 kg) in a cross-over study design. Arterial contrast enhancement was measured along the z-axis in the ascending, descending, and abdominal aorta and the iliac arteries. The z-axis is the longitudinal axis of the human body and at the same time the direction in which the CT table is moving. The data were analyzed using repeated measures ANOVA with a post-hoc t-test and visual assessment of the scans. Results: In high-pitch CTA, monophasic injection protocols were superior to biphasic injection protocols in enhancement levels (P < 0.05) and enhancement homogeneity along the z-axis (P < 0.05). In conventional CTA, enhancement levels did not differ. Contrast homogeneity was better for biphasic protocols. Conclusion: High-pitch CTA monophasic injection protocols are superior to biphasic injection protocols, due to a higher and more homogeneous contrast enhancement with the same amount of contrast medium used.
To compare and contrast the findings of intra-operative mesenteric portovenography (IOMP) and computed tomography angiography (CTA) for the visualisation and identification of the extrahepatic and intrahepatic portal venous system in the normal dog. Retrospective study of dogs with raised post-prandial bile acids concentrations, normal portal venous pressures and grossly normal portal vasculature that had undergone both CTA and IOMP was performed. Images and video were compared with the published anatomic literature. Ten dogs met the inclusion criteria. CTA documented the portal vein and its tributaries in all 10 dogs. IOMP documented the portal vein and the cranial mesenteric vein in all 10 dogs and the splenic vein in 1 dog but failed to show the caudal mesenteric and gastroduodenal veins in any dog. CTA documented more extrahepatic portal venous tributaries than IOMP. Both techniques documented the intrahepatic portal vasculature completely with equal clarity. There was a large difference between the ability of the two techniques to delineate the normal portal vasculature; CTA consistently visualised the extrahepatic portal vasculature more completely than the IOMP and, as such, might be considered the modality of choice for imaging the normal portal vasculature in the dog. © 2015 British Small Animal Veterinary Association.
Cross-sectional imaging of the heart utilizing computed tomography and magnetic resonance imaging (MRI) has been shown to be superior for the evaluation of cardiac morphology and systolic function in humans compared to echocardiography. The purpose of this prospective study was to test the effects of two different anesthetic protocols on cardiac measurements in 10 healthy beagle dogs using 64-multidetector row computed tomographic angiography (64-MDCTA), 3T magnetic resonance (MRI) and standard awake echocardiography. Both anesthetic protocols used propofol for induction and isoflourane for anesthetic maintenance. In addition, protocol A used midazolam/fentanyl and protocol B used dexmedetomedine as premedication and constant rate infusion during the procedure. Significant elevations in systolic and mean blood pressure were present when using protocol B. There was overall good agreement between the variables of cardiac size and systolic function generated from the MDCTA and MRI exams and no significant difference was found when comparing the variables acquired using either anesthetic protocol within each modality. Systolic function variables generated using 64-MDCTA and 3T MRI were only able to predict the left ventricular end diastolic volume as measured during awake echocardiogram when using protocol B and 64-MDCTA. For all other systolic function variables, prediction of awake echocardiographic results was not possible (P = 1). Planar variables acquired using MDCTA or MRI did not allow prediction of the corresponding measurements generated using echocardiography in the awake patients (P = 1). Future studies are needed to validate this approach in a more varied population and clinically affected dogs. © 2015 American College of Veterinary Radiology.
In humans, the process of development of collateral vessels with hepatopetal flow around the portal vein in order to bypass an obstruction is called "cavernous transformation of the portal vein." The purpose of this retrospective, cross-sectional, multicentric study was to describe presumed cavernous transformation of the portal vein in small animals with portal vein obstruction using ultrasound and multidetector-row computed tomography (MDCT). Databases from three different institutions were searched for patients with an imaging diagnosis of cavernous transformation of the portal vein secondary to portal vein obstruction of any cause. Images were retrieved and reanalyzed. With MDCT-angiography, two main portoportal collateral pathways were identified: short tortuous portoportal veins around/inside the thrombus and long portoportal collaterals bypassing the site of portal obstruction. Three subtypes of the long collaterals, often coexisting, were identified. Branches of the hepatic artery where involved in collateral circulation in nine cases. Concomitant acquired portosystemic shunts were identified in six patients. With ultrasound, cavernous transformation of the portal vein was suspected in three dogs and one cat based on visualization of multiple and tortuous vascular structures corresponding to periportal collaterals. In conclusion, the current study provided descriptive MDCT and ultrasonographic characteristics of presumed cavernous transformation of the portal vein in a sample of small animals. Cavernous transformation of the portal vein could occur as a single condition or could be concurrent with acquired portosystemic shunts. © 2015 American College of Veterinary Radiology.
To describe the anatomy of congenital portosystemic shunts involving the right gastric vein in dogs. Retrospective review of a consecutive series of dogs managed for congenital portosystemic shunt. Twenty-two dogs met the inclusion criteria of a congenital portosystemic shunt involving the right gastric vein with recorded intraoperative mesenteric portovenography or computed tomography angiography and gross observations at the time of surgery. Of these, 20 (91%) had a shunt that entered the pre-hepatic caudal vena cava at the level of the epiploic foramen and two (9%) had a shunt that entered the post-hepatic caudal vena cava at the level of the diaphragm. Shunts entering the pre-hepatic caudal vena cava could be further classified into three consistent subdivisions. The morphology of each shunt type described appeared to be a result of an abnormal communication between the left gastric vein and the caudal vena cava, the presence or absence of an abnormal communication between the splenic, left gastric and portal veins and the subsequent development of preferential blood flow through essentially normal portal vessels within the portal venous system. The abnormal communication (shunt) was through the left gastric vein and not the right gastric vein, as might have been expected. This information may help with surgical planning in cases undergoing shunt closure surgery. © 2015 British Small Animal Veterinary Association.
Preureteral vena cava (circumcaval ureter, retrocaval ureter) occurs in a third of the feline population and has been associated with ureteral strictures in humans. The aim of this retrospective cross-sectional study was to describe the contrast-enhanced multidetector row computed tomographic (MDCT) characteristics of presumed preureteral vena cava in a group of cats. Medical records from two institutions located in different continents were searched from 2010-2013 for cases with complete contrast-enhanced MDCT examinations of the abdomen (i.e. included the entire course of the ureters and prerenal and renal segments of the caudal vena cava) and a diagnosis of preureteral caudal vena cava. For cases meeting inclusion criteria, CT scan data were retrieved and characteristics of the preureteral caudal vena cava were recorded. Presence of concomitant renal or ureteral diseases was also recorded. A total of 272 cats had contrast-enhanced abdominal CT scans during the study period and of these, 68 cats (22.43 ± 4.96%) had a diagnosis of presumed preureteral vena cava. In all affected cats, a "reverse-J ureter" was observed, i.e. a ureter running medially at the level of L4-5, passing dorsally to the caudal vena cava and then exiting ventrally between the caudal vena cava and aorta returning to its normal position. Having a preureteral vena cava resulted in an increased risk for concurrent urinary signs (OR = 3.00; CI: 95%; 1.28-6.99; P = 0.01). Findings supported the use of contrast-enhanced MDCT for characterizing morphology of preureteral vena cava and its relation with ureters in cats. © 2015 American College of Veterinary Radiology.