INVITED REVIEW-COMPUTED TOMOGRAPHIC ANGIOGRAPHY (CTA) OF THE THORACIC CARDIOVASCULAR SYSTEM IN COMPANION ANIMALS

Clinical utility of a new protocol of cardiac computed tomography in dogs

OBJECTIVES

The characteristics of non-electrocardiography- and electrocardiography-gated multidetector computed tomography have not been extensively studied in veterinary clinics but it can be useful for cardiac imaging. This study aimed to ascertain the differences between non-electrocardiography and electrocardiography gating methods and to establish their clinical utility based on patient history.

METHODS

Six client-owned dogs (two with patent ductus arteriosus, two with heart base tumour, one with pericardial mesothelioma, and one with normal health) were included in this study. All the dogs were examined using a non-electrocardiography-gated scan, followed by a retrospective electrocardiography-gated scan. Images were reviewed to determine the optimal scan timing and R-R interval in non-electrocardiography- and electrocardiography-gated images, respectively, for detailed coronary artery imaging, diagnostic quality of the best coronary artery visualisation in non-electrocardiography- and electrocardiography-gated images through visual assessment of the main coronary artery branches, and branching patterns of the left coronary artery. Further, we compared the size and margin demarcation of the heart or pericardial lesions in non-electrocardiography- and electrocardiography-gated images obtained from patients with heart or pericardial tumours.

RESULTS

The optimal scan timing and R-R interval were the second-scan timing and end-diastole (70%-90%), respectively. Second-scan non-electrocardiography-gated images allowed coronary artery evaluation, indicating high-grade quality in visual assessment, except for the septal branch. Electrocardiography-gated images, but not non-ECG-gated images, clearly revealed pericardial nodules in two dogs.

CLINICAL SIGNIFICANCE

Our findings suggest the respective clinical utilities of non-electrocardiography- or electrocardiography-gated imaging using high-slice cardiac computed tomography based on patient history.

Evaluation of Pulmonary Hypertension in Dogs with Heartworm Disease Using the Computed Tomographic Pulmonary Trunk to Aorta Diameter Ratio

Dirofilaria immitis causes proliferative pulmonary endoarteritis that leads to the appearance of chronic precapillary pulmonary hypertension (PH) in dogs. Pulmonary trunk to aorta ratio (PT:Ao ratio) obtained by computed tomography (CT) was studied and the quantitative measure of the diameters of the pulmonary trunk (PT), the descending thoracic aorta (DAo) and ascending thoracic aorta (AAo) were evaluated for the determination of the presence of moderate to severe PH in 59 dogs. The diagnosis of PH was echocardiographically determined, based on the determination of the right pulmonary artery distensibility (RPAD) index (<29.5%), and compared with other parameters for estimating PH. The results showed a very high concordance: 0.976 (p-value 0.000) between the two CT methods (PT:DAo and PT:AAo) with an excellent intraclass correlation coefficient > 0.95. Moreover, cut-off values of ≥1.111 for PT:DAo, and ≥1.057 for PT:AAo were determined for dogs with an RPAD index < 29.5%, which suggests a cut-off value between healthy dogs and the presence of PH. As has been previously published, The PT:Ao ratios did not determine the presence of mild PH, so the measurements cannot be considered useful for the early diagnosis of PH in dogs with heartworm.

Non-electrocardiography- and electrocardiography-gated computed tomography angiography for the evaluation of feline coronary arteries

Objectives

Few studies have directly compared the clinical feasibility of electrocardiography-gated and non-electrocardiography-gated multidetector computed tomography for evaluating coronary arteries in veterinary medicine. We aimed to characterize and visualize feline coronary arteries using these two imaging modalities. We hypothesed that ECG-gated MDCT is superior to or advantageous to the non-ECG gated.

Methods

This prospective, controlled, comparative pilot study examined six client-owned cats (five clinically normal and one with hypertrophic cardiomyopathy) using non-electrocardiography-gated and retrospective electrocardiography-gated scans. Optimal non-electrocardiography scan timing or electrocardiography-gated R-R reconstruction interval for coronary artery visualization was determined. The degree of opacification and sharpness of proximal coronary branches was subjectively graded; coronary dominance, left coronary artery branching types, and the diameter and length of coronary artery branches were also assessed.

Results

Non-electrocardiography-gated images provided the least information on the bilateral coronary artery ostium and proximal segments, while electrocardiography-gated images clarified the detailed course of the main coronary branches at diastole in all cats. The degree of opacification and sharpness of the coronary arteries was subjectively evaluated as good/excellent in all cats. Coronary dominance (left: four; right: two) and left coronary artery branching types (three different patterns, two additional tortuous branches) varied. Body weight and sex were not significantly associated with coronary artery length or diameter. Vertebral heart score positively correlated with the right coronary artery and negatively correlated with the left main coronary artery.

Clinical significance

Electrocardiography-gated multidetector computed tomography provides images with adequate resolution to identify the anatomy of feline coronary arteries. Detailed morphological knowledge of feline coronary vessels will enable novel diagnostic and therapeutic methods in veterinary medicine.

Voxel model of a rabbit: assessment of absorbed doses in organs after CT examination performed by two different protocols

The objective of this work was to assess absorbed doses in organs and tissues of a rabbit, following computed tomography (CT) examinations, using a dedicated 3D voxel model. Absorbed doses in relevant organs were calculated using the MCNP5 Monte Carlo software. Calculations were perfomed for two standard CT protocols, using tube voltages of 110 kVp and 130 kVp. Absorbed doses were calculated in 11 organs and tissues, i.e., skin, bones, brain, muscles, heart, lungs, liver, spleen, kidney, testicles, and fat tissue. The doses ranged from 15.3 to 28.3 mGy, and from 40.2 to 74.3 mGy, in the two investigated protocols. The organs that received the highest dose were bones and kidneys. In contrast, brain and spleen were organs that received the smallest doses. Doses in organs which are stretched along the body did not change significantly with distance. On the other hand, doses in organs which are localized in the body showed maximums and minimums. Using the voxel model, it is possible to calculate the dose distribution in the rabbit's body after CT scans, and study the potential biological effects of CT doses in certain organs. The voxel model presented in this work can be used to calculated doses in all radiation experiments in which rabbits are used as experimental animals.

Effects of airway pressure on contrast enhancement and diameter of the pulmonary artery in healthy dogs as determined by use of computed tomography angiography

OBJECTIVE

To evaluate effects of airway pressure on contrast enhancement and diameter of the pulmonary artery and determine the optimal airway pressure for pulmonary CT angiography in dogs.

ANIMALS

8 healthy Beagles.

PROCEDURES

Thoracic CT was performed at end-expiration (0 cm H₂O) and 2 positive-pressure end-inspirations (10 and 20 cm H₂O). Attenuation curves of enhancement for the sinus of the pulmonary trunk artery were obtained by use of a bolus technique. Contrast medium (300 mg of I/kg) was administered IV, and CT imaging began at the time of peak enhancement. At each pressure, time to peak enhancement, ratio of blood flow from the caudal vena cava to the right side of the heart (K_CdVC), and enhancement characteristics and diameter changes of the pulmonary artery were evaluated.

RESULTS

All dogs had a significant delay for time to peak enhancement in the sinus of the pulmonary trunk artery as airway pressure increased. The K_CdVC progressively increased as airway pressure increased, and there was low contrast enhancement and increased pulmonary artery filling defects at 20 cm H₂O. All pulmonary arteries had marked increases in diameter as pressure increased. Arterial distensibility in the gravity-dependent cranial lung region was greater than that in the gravity-independent caudal lung region at the 2 positive-pressure end-inspirations.

CONCLUSIONS AND CLINICAL RELEVANCE

Airway pressure affected time to peak enhancement, K_CdVC, contrast enhancement, and pulmonary artery diameter. Results suggested that 10 cm H₂O could be an optimal pressure for evaluation of the pulmonary artery of dogs by use of CT angiography. (Am J Vet Res 2019;80;756-763).

Electrocardiography-gated cardiac CT angiography can differentiate brachycephalic dogs with and without pulmonary valve stenosis and findings differ from transthoracic echocardiography

Pulmonary valve stenosis (PS) is one of the most commonly diagnosed congenital heart defects in dogs. Currently, transthoracic echocardiography (TTE) is the standard modality used to evaluate PS. Image acquisition by TTE can be challenging in some brachycephalic breeds of dogs. The use of echocardiographic-gated CT angiography (ECG-gated CTA) in veterinary medicine is limited. This retrospective method comparison study investigated right and left ventricular outflow diameters by sedated ECG-gated CTA and unsedated TTE in 14 brachycephalic dogs with PS and 12 brachycephalic dogs without PS. Measurements of ventricular outflow structures were made in early systole and end diastole for both modalities and then compared for significance between systolic and diastolic phases, as well as between the two modalities. Ratios of the pulmonary trunk diameter to the aorta at different locations (aortic valve, aortic annulus, and ascending aorta) and in different planes (transverse, sagittal) were compared between dogs with PS and without PS, as well as within dogs, by both TTE and ECG-gated CTA. Transthoracic echocardiography and ECG-gated CTA both detected significantly greater pulmonary trunk to aorta ratios in dogs with PS at all aortic locations (P < 0.05). Pulmonary valve to aortic valve ratios were significantly smaller in dogs with PS (P < 0.05). Pulmonary trunk to aorta and pulmonary valve to aorta ratios were achieved with good anatomic detail using ECG-gated CTA. Ratios of the pulmonary trunk and pulmonary valve relative to the aorta may be useful to evaluate for PS using a modality that is underutilized for cardiac assessment.

Detection of intra-cardiac thrombi and congestive heart failure in cats using computed tomographic angiography

Arterial thromboembolism is a life-threatening condition in cats most commonly secondary to cardiac disease. Echocardiography is the reference standard to evaluate for presence of a thrombus. In humans, computed tomographic (CT) angiography is becoming widely used to detect left atrial thrombi precluding the use of sedation. The purpose of this prospective, controlled, methods comparison pilot study was threefold: (1) describe new CT angiography protocol used in awake cats with cardiac disease and congestive heart failure; (2) determine accuracy of continuous and dynamic acquisition CT angiography to identify and characterize cardiac thrombi from spontaneous echocardiographic contrast using transthoracic echocardiography as our reference standard; (3) identify known negative prognostic factors and comorbidities of the thorax that CT angiography may provide that complement or supersede echocardiographic examination. Fourteen cats with heart disease were recruited; 7 with thrombi and 7 with spontaneous echocardiographic contrast. Echocardiography and awake CT angiography were performed using a microdose of contrast. Six of 7 thrombi were identified on CT angiography as filling defects by at least one reviewer within the left auricle (n = 6) and right heart (n = 1). Highest sensitivity (71.4%) was in continuous phase and highest specificity (85.7%) was in dynamic studies with fair to moderate interobserver agreement (0.38 and 0.44). CT angiography identified prognostic cardiac information (left atrial enlargement, congestive heart failure, arterial thromboembolism) and comorbidities (suspected idiopathic pulmonary fibrosis, asthma). This study indicates CT angiography can readily identify cardiac thrombi, important prognostic information and comorbidities, and can be safely performed in cats with cardiac disease and congestive heart failure.

Use of ECG-gated computed tomography, echocardiography and selective angiography in five dogs with pulmonic stenosis and one dog with pulmonic stenosis and aberrant coronary arteries

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.

Use of dual-phase contrast computed tomography for evaluation of the normal canine male genital tract

OBJECTIVES

To evaluate the use of dual-phase contrast-enhanced computed tomography for the depiction of the features of the male genital tract, highlighting differences between entire and neutered dogs.

METHODS

Computed tomography exams of 23 entire and 23 neutered male dogs with no history of urogenital disease were included in this retrospective study, with exams acquired pre-, 30 and 98·9 ±27·4 seconds after intravenous contrast administration. The genital structures were subjectively evaluated for visibility, contrast enhancement and enhancement pattern and differences between entire and neutered dogs were described. Objective measurements of attenuation and size of the prostatic tissue were acquired.

RESULTS

The root, body and glans of the penis could be evaluated in all dogs and appeared larger in entire dogs, though objective measurements could not be reliably made because these structures are small and curved. There was contrast enhancement of the cavernous structures, most reliably in the bulb and corpus spongiosum and most frequently in entire dogs in the delayed post-contrast phase. In entire dogs, the small testicular vessels most commonly had a vermiform shape in the early post-contrast phase, and a homogeneous appearance in the delayed phase. Sternal recumbency with the coxofemoral joints extended improved visibility of the genital structures.

CLINICAL SIGNIFICANCE

Dual-phase contrast-enhanced computed tomography is useful for depiction of the structures of the male genital tract, with the early phase especially highlighting the vascular and the delayed phase the cavernous structures.

Cardiac-gated computed tomography angiography in three alpacas with complex congenital heart disease

BACKGROUND

The prevalence of congenital heart disease is higher in camelids than in other domestic species and complex defects, often involving the great vessels, are more frequently encountered in llamas and alpacas than in other species. Some of these complex defects can be difficult to accurately characterize via echocardiography, the most commonly used diagnostic imaging technique to evaluate the heart in veterinary patients. Contrast-enhanced, electrocardiogram (ECG)-gated computed tomography (CT) has proven utility for the evaluation of human patients with certain congenital heart defects, including those with conotruncal septation defects and other abnormalities involving the formation of the great vessels.

METHODS

Three alpaca crias, 4 days, 5 weeks and 14 months of age were clinically evaluated and subjected to a complete color-flow Doppler echocardiogram and a contrast-enhanced ECG-gated CT.

RESULTS

These alpacas exhibited a variety of clinical findings including lethargy, failure to thrive, exercise intolerance, heart murmur, and/or respiratory difficulty. All three crias were subsequently diagnosed with complex cardiac defects including pulmonary atresia with a ventricular septal defect (VSD), a truncus arteriosus with a large VSD, and a double outlet right ventricle with a large VSD and aortic hypoplasia. In each case, the diagnosis was confirmed by postmortem examination.

CONCLUSION

Color flow echocardiographic evaluation identified all of the intra-cardiac lesions and associated flow anomalies but contrast-enhanced ECG-gated CT permitted more accurate assessment of the morphology of the extracardiac structures and permitted a more precise determination of the exact nature and anatomy of the great vessels.