Quantification of right ventricular volume measured by use of real-time three-dimensional echocardiography and electrocardiography-gated 64-slice multidetector computed tomography in healthy dogs

Nicole L. LeBlanc Department of Clinical Sciences, College of Veterinary Medicine, Oregon State University, Corvallis, OR 97331.

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Katherine F. Scollan Department of Clinical Sciences, College of Veterinary Medicine, Oregon State University, Corvallis, OR 97331.

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Abstract

OBJECTIVE To evaluate accuracy of quantification of right ventricle volume (RVV) by use of 3-D echocardiography (3DE) and ECG-gated multidetector CT (MDCT).

ANIMALS 6 healthy hound-cross dogs.

PROCEDURES ECG-gated MDCT and complete 3DE examinations were performed on each dog. Right ventricular end-diastolic volumes (EDVs), end-systolic volumes (ESVs), stroke volume (SV), and ejection fraction (EF) were measured for 3DE and MDCT data sets by use of software specific for RVV quantification. Correlation and level of agreement between methods were determined. Intraobserver and interobserver variability were assessed for 3DE.

RESULTS No significant differences were detected between SV and EF obtained with MDCT and 3DE. Significant differences were detected between right ventricular EDV and ESV obtained with MDCT and 3DE. No significant difference in heart rate was detected between methods. The correlation between MDCT and 3DE was very good (r = 0.87) for EDV and ESV, moderate (r = 0.60) for EF, and poor (r = 0.31) for SV. Bland-Altman analysis revealed a systematic underestimation of RVV derived by use of 3DE, compared with the RVV derived by use of MDCT (mean bias, 15 and 10.3 mL for EDV and ESV, respectively). Intraobserver (EDV, 12%; ESV, 18%) and interobserver (EDV, 14%; ESV, 11%) variability were acceptable for 3DE.

CONCLUSIONS AND CLINICAL RELEVANCE There was substantial variance for RVV measured by use of 3DE in healthy dogs and a significant underestimation of volumes, compared with results for MDCT, despite the fact there were no significant differences in SV and EF.

Abstract

OBJECTIVE To evaluate accuracy of quantification of right ventricle volume (RVV) by use of 3-D echocardiography (3DE) and ECG-gated multidetector CT (MDCT).

ANIMALS 6 healthy hound-cross dogs.

PROCEDURES ECG-gated MDCT and complete 3DE examinations were performed on each dog. Right ventricular end-diastolic volumes (EDVs), end-systolic volumes (ESVs), stroke volume (SV), and ejection fraction (EF) were measured for 3DE and MDCT data sets by use of software specific for RVV quantification. Correlation and level of agreement between methods were determined. Intraobserver and interobserver variability were assessed for 3DE.

RESULTS No significant differences were detected between SV and EF obtained with MDCT and 3DE. Significant differences were detected between right ventricular EDV and ESV obtained with MDCT and 3DE. No significant difference in heart rate was detected between methods. The correlation between MDCT and 3DE was very good (r = 0.87) for EDV and ESV, moderate (r = 0.60) for EF, and poor (r = 0.31) for SV. Bland-Altman analysis revealed a systematic underestimation of RVV derived by use of 3DE, compared with the RVV derived by use of MDCT (mean bias, 15 and 10.3 mL for EDV and ESV, respectively). Intraobserver (EDV, 12%; ESV, 18%) and interobserver (EDV, 14%; ESV, 11%) variability were acceptable for 3DE.

CONCLUSIONS AND CLINICAL RELEVANCE There was substantial variance for RVV measured by use of 3DE in healthy dogs and a significant underestimation of volumes, compared with results for MDCT, despite the fact there were no significant differences in SV and EF.

Accurate assessment of structure and function of the RV is an integral component of a complete cardiological evaluation of veterinary patients. Assessment of RV performance is particularly important in patients with pulmonary hypertension, congenital heart disease, and acquired myocardial disease that affects the RV. There is evidence in human medicine to suggest that RV function is strongly associated with outcomes for many conditions.1

In clinical settings, echocardiography offers a noninvasive, readily accessible method for quantitative assessment of RV structure and function. Unfortunately, it has historically been difficult to measure RV size by use of echocardiography with conventional imaging planes, largely because of the complex anatomic shape of the RV. The RV is crescent-shaped in cross section and triangular in a long-axis view with pronounced myocardial trabeculation, compared with the anatomic configuration of the LV.1,2 Traditionally, the RV is divided into 3 distinct components, which consist of an inflow region with the TV, chordae tendinae, and papillary muscles; a trabeculated apical portion; and a smooth myocardial outflow region.3 One-dimensional echocardiographic and 2DE methods are suboptimal for accurate assessment of RV size and function because the various regions of the RV cannot be imaged simultaneously. Additional factors that add to the challenge of assessing the RV by use of echocardiography include distinguishing the endocardial surface with heavy trabeculation and structural changes to RV preload associated with respiration.2,4

The development of matrix-array transducers and real-time 3DE allows imaging of the entire RV simultaneously, and accurate quantification of RVV is aided by use of software specific for RVV quantification. In humans, quantification of RVV and EF by use of 2DE methods is not recommended in the American Society of Echocardiography guidelines for assessment of the right side of the heart.1 Furthermore, cross-sectional imaging modalities such as cardiac MRI and MDCT are valid noninvasive means of assessing the RV without having to make geometric shape assumptions. Currently, cardiac MRI is considered the criterion-referenced standard for measurement of RVV, LV volume, and EF in humans.5–7 For humans, there is a strong correlation of RVV between 3DE and a volumetric criterion-referenced standard, although both 2DE and 3DE typically underestimate RVV obtained by use of cardiac MRI.1 However, evidence indicates there is less underestimation for RVV quantification by use of 3DE than by use of 2DE.8,9 Comparison of RVV obtained by use of cardiac-gated MDCT and cardiac MRI suggests that the volumes obtained are comparable and strongly correlated.6

There have been substantial recent advances in veterinary medicine regarding assessment of the right side of the heart. Characterizations of structure and function of the right side of the heart in clinically normal dogs have been published.10–13 However, those studies did not address RV size determined by use of 3DE. To the authors’ knowledge, there is only a single veterinary study14 in which investigators used advanced technology to assess RVV. Furthermore, 3DE software specific for RVV assessment has recently become commercially available for veterinary medicine. Before this technology can be used to assess clinical veterinary patients, validation is required to determine feasibility and accuracy.

The purpose of the study reported here was to evaluate the accuracy and repeatability of RVV estimation by use of 3DE and MDCT. We hypothesized that RVV measured by use of 3DE would systematically underestimate RVV, compared with results obtained by use of MDCT. We also hypothesized that there would be acceptable intraobserver and interobserver variability.

Materials and Methods

Animals

Six sexually intact (3 females and 3 males) young adult (13 months old) purpose-bred hound-cross dogs were enrolled in the study. Median body weight was 22.4 kg (range, 19.5 to 23.8 kg). The dogs were assessed as healthy on the basis of results of a physical examination, CBC, biochemical analysis, ECG, and complete echocardiographic examination. The study was approved by the Institutional Animal Care and Use Committee at Oregon State University.

Anesthesia

All dogs were anesthetized for ECG-gated contrast-enhanced MDCT and echocardiography. Dogs were sedated with butorphanol tartrate (0.1 to 0.2 mg/kg, IM), and a catheter was inserted into a cephalic vein. Anesthesia was induced with propofol (3 to 5 mg/kg, IV, titrated to effect). An endotracheal tube was placed, and anesthesia was maintained with isoflurane delivered in oxygen. Lactated Ringer solution was administered (10 mL/kg/h, IV) for the duration of anesthesia. To minimize possible effects of differences in duration of anesthesia on ventricular function, 3 dogs were arbitrarily assigned to first undergo ECG-gated MDCT and then echocardiography, and the other 3 dogs underwent echocardiography first followed by ECG-gated MDCT. There was an interval of 5 to 15 minutes between MDCT and echocardiography for each dog.

ECG-gated MDCT

Contrast-enhanced MDCT images were acquired by use of a 64-row detector CT scanner. Dogs were placed in sternal recumbency, and ECG electrodes were attached to the forelimbs and left hind limb. The MDCT scans were performed with the following scanning settings: 0.5-mm collimation, 0.5-mm reconstruction interval, 512 × 512 matrix, 163- to 213-mm display field of view, pitch factor of 0.829, gantry rotation speed of 350 milliseconds, 120 kV, 200 to 500 mA, and 0° tilt. Contrast images were obtained with contrast mediumb injected by use of a dual-barrel power injector.c The 3-phase injection included an initial fast flow rate of contrast medium (5 mL/s), a second slower flow rate of contrast medium (2 mL/s), and a final fast flow rate of sterile saline (0.9% NaCl) solution (5 mL/s); total volume of contrast agent was 1 mL/kg, and total volume of saline solution was 0.5 mL/kg. The main pulmonary artery was used as the region of interest for automated bolus tracking to obtain images with contrast opacification of the right side of the heart. Scanning was triggered when the main pulmonary artery had a value of 130 to 160 Hounsfield units.

The MDCT images were transferred to a server for offline analysis and a workstation with RV analysis software.d Images were reconstructed in 10% increments of the R-R interval. Multiplanar reconstruction images were created to display long- and short-axis views of the RV. The functional analysis software displayed the 4-chamber, 2-chamber, and short-axis views of the RV with automated regions of interest for contrast detection (Figure 1). The region of interest was manually adjusted on the long-axis images to include the entire RV from the TV annulus to the pulmonic valve. The region of interest for the short-axis view was manually adjusted to ensure inclusion of the entire RV lumen. After adjustments were completed, the software computed RVV at each 10% increment of the R-R interval. The EDV was defined as the frame with the maximum volume, and ESV was defined as the frame with the lowest volume.

Figure 1—
Figure 1—

Representative MDCT images of the RV in a healthy dog in a short-axis view (A), RV outflow tract (B), and RV inflow region (C) obtained by use of postprocessing software and a 3-D cast of the RV lumen (D). In all panels, the RV lumen is blue. In panel D, the outflow tract is on the left side of the image, and the RV inflow region is on the right side of the image.

Citation: American Journal of Veterinary Research 79, 4; 10.2460/ajvr.79.4.404

Papillary muscles and trabeculae were included in the RVV. The SV was calculated as EDV - ESV, and EF was calculated as the percentage change of those volumes ([EDV - ESV]/EDV × 100). The software for quantification of MDCT RVV generated 1 cardiac cycle from the CT scan; therefore, the MDCT volumes were measured once by 1 observer (NLL). Additional scans that would have yielded multiple measurements for each dog were not obtained to avoid the potential deleterious consequences of repeated injection of iodinated contrast medium (eg, contrast-induced nephropathy).

Echocardiography

A comprehensive echocardiographic examination was performed on each dog by use of a study protocol that consisted of M-mode, 2-D, pulsed-wave Doppler, and 3-D imaging with continuous ECG monitoring with an ultrasound unit.e All examinations were performed by the same board-certified veterinary cardiologist (NLL). All 3DE data were collected by use of a 1- to 5-MHz matrix transducer.

For the 3DE data, echocardiographic images were acquired in wide-angled full-volume acquisition mode from a modified LAP imaging window over 4 consecutive cardiac cycles to yield a complete data set in accordance with American Society of Echocardiography guidelines.1 The traditional LAP 4-chamber view was modified by use of a more cranial probe position to optimize the images of the right side of the heart (Figure 2). Acquisition was triggered by appropriate recognition of the R wave on an ECG. Care was taken to ensure the entire RV was included in the 3-D pyramidal data set, and 4 wedge-shaped subvolumes were obtained for each complete cardiac cycle.

Figure 2—
Figure 2—

A 2DE image showing the modified LAP window in a healthy dog with the RV optimized for 3DE. Notice the ECG tracing at the bottom of the image. Tick marks on the right side of the image are at intervals of 1 cm.

Citation: American Journal of Veterinary Research 79, 4; 10.2460/ajvr.79.4.404

Images were stored digitally and analyzed offline by use of a workstation with commercial software designed for quantification of 3-D RVV.f By use of a 3-D cine loop, the software automatically displayed six 2-D slices from the modified LAP window to provide orientation. Those six 2-D slices included 3 images of the LV in the 4-chamber, 2-chamber, and 5-chamber views and 3 images of the RV in the 4-chamber, 2-chamber, and short-axis views (Figure 3). Reference points were manually placed to denote the mitral valve, LV apex, and aortic valve annulus on the LV images and the TV, RV apex, and endocardial border of the mid-RV in the short-axis view on the RV images. The inflow region, outflow region, and RV trabeculations were included in quantification of RVV (Figure 4). The software automatically defined end-diastole and end-systole and subsequently calculated values for EDV, ESV, SV, and EF. Each echocardiographic measurement was obtained in quintuplicate, and mean values were calculated for statistical analysis.

Figure 3—
Figure 3—

Representative 2DE images of the mitral valve (MV; A), apex of the LV (B), aortic valve (distance between AVI and AV2; C), RV (D), apex of the RV (E), and cranial (AJL) and caudal (PJL) limits of the RV (F) in a healthy dog obtained by use of postprocessing RVV software. Panels A and D represent a 4-chamber view, panels B and E represent a 2-chamber view, panel C represents a 3-chamber view, and panel F represents a short-axis view. The dashed lines in panels C through F represent an axis for image manipulation. Notice the ECG tracing at the bottom of panel F.

Citation: American Journal of Veterinary Research 79, 4; 10.2460/ajvr.79.4.404

Figure 4—
Figure 4—

Software-generated depictions of 3-D end-diastolic (A) and end-systolic (B) images of the RV in a healthy dog. The RV outflow tract is on the left side of each image, and the RV inflow region is on the right side of each image.

Citation: American Journal of Veterinary Research 79, 4; 10.2460/ajvr.79.4.404

Approximately 6 months after MDCT volumes were measured, echocardiographic measurements were determined by 2 observers (NLL and KFS). The observers were not aware of the MDCT results while determining 3DE measurements.

Statistical analysis

Statistical analysis was performed with commercially available software.g Data were considered to not have a normal distribution because of the small sample size. Heart rate, EDV, ESV, SV, and EF data were reported as median and range. The Wilcoxon signed rank test was performed to determine absolute differences of RVV and heart rate between methods. Agreement between RVV obtained by use of 3DE and MDCT was assessed by use of the methods of Bland and Altman. Bias (ie, the mean difference of MDCT against 3DE RVV) was determined, and the SD of these differences was used to determine the 95% limits of agreement (± 2 SD). The correlation between values for 3DE and MDCT was assessed with the nonparametric Spearman correlation. Correlations were considered excellent at r ≥ 0.9, very good at r ≥ 0.7 and < 0.9, moderate at r ≥ 0.5 and < 0.7, and weak at r < 0.5.

Intraobserver variability was assessed with data for 1 observer (NLL), who performed the initial measurement of RVV for the 3DE data for all dogs and then repeated the measurements 2 weeks later. Interobserver variability was tested by use of measurements performed by 2 observers (NLL and KFS), who were not aware of the results of the other observer. The mean coefficient of variation was used to evaluate intraobserver and interobserver variability; it was calculated as coefficient of variation percentage = (SD of the measurements/mean of the measurements) × 100. For all analyses, significance was set at P < 0.05.

Results

Results of complete echocardiographic examinations were obtained for all dogs. For 5 of 6 dogs, MDCT conducted in accordance with the described protocol yielded images with excellent opacification of the RV without streaking or motion artifact. Heart rate did not differ significantly (P = 0.84) during acquisition of MDCT (median, 68 beat/min; range, 50 to 100 beats/min) and 3DE (median, 73 beats/min; range, 44 to 94 beats/min) data.

Median and range values for RV EDV, ESV, SV, and EF obtained by use of MDCT and 3DE were calculated (Table 1). There was no significant difference in SV or EF between MDCT- and 3DE-derived values, but there was a significant difference in EDV and ESV between the 2 methods. Correlation between MDCT and 3DE was very good (r = 0.87) for EDV and ESV, moderate (r = 0.60) for EF, and poor (r = 0.31) for SV.

Table 1—

Median (range) values obtained for RV variables of 6 healthy dogs by use of MDCT and 3DE.

VariableMethodRaw valuesIndexed values*
EDV (mL)MDCT59.44 (51.01–77.47)2.79 (2.33–3.26)
 3DE45.85 (37.74–57.96)2.16 (1.68–2.46)
ESV (mL)MDCT35.60 (27.09–42.56)1.70 (1.24–1.86)
 3DE23.77 (18.70–35.72)1.16 (0.82–1.51)+
SV (mL)MDCT24.84 (17.92–34.91)1.12 (0.92–1.47)
 3DE20.98 (14.54–25.18)0.96 (0.73–1.15)
 MDCT41.80 (33.09–46.89)
 3DE46.06 (38.48–51.02)

The MDCT values represent results of a single examination, whereas 3DE values represent the mean for 5 cine loops.

Values were indexed by use of RVV divided by body weight.

Within a variable, value differs significantly (P = 0.03) from the MDCT value.

Within a variable, value differs significantly (P = 0.01) from the MDCT value.

— = Not applicable.

Bland-Altman analysis revealed a systematic underestimation of EDV, ESV, and SV derived from 3DE measurements, compared with values obtained with MDCT measurements (Figure 5). There was a slight overestimation of EF on the basis of the 3DE measurements, compared with EF determined by use of MDCT measurements. There was smaller bias for SV (4.79; 95% agreement limits, −5.61 to 15.19) and EF (−3.57; 95% agreement limits, −15.53 to 8.39) than for EDV (15.06; 95% agreement limits, −3.49 to 33.61) and ESV (10.26; 95% agreement limits, −1.15 to 21.66). Interobserver variability was 14% for EDV and 11% for ESV with 3DE measurements. Intraobserver variability was 12% for EDV and 18% for ESV with 3DE measurements.

Figure 5—
Figure 5—

Bland-Altman plots of the comparison between MDCT and 3DE for measurement of EDV (A), ESV (B), SV (C), and EF (D) in 6 healthy dogs. Each circle represents results for 1 dog. In each plot, bias is indicated by the horizontal dotted line, and 95% limits of agreement are indicated by the solid lines.

Citation: American Journal of Veterinary Research 79, 4; 10.2460/ajvr.79.4.404

Discussion

The importance of RV size and function has been increasingly recognized in veterinary medicine in recent years. Clinical relevance of RV size and function has been documented in human medicine, although accurate noninvasive assessment has developed slowly because of the complex geometry of the RV. Investigators have evaluated the use of M-mode and 2DE indices to evaluate RV size and function in dogs10,11 and cats,15 although the limitations of 2DE for RV assessment are numerous. In humans, it is not recommended that 2DE be used to evaluate RV EF1; instead, it is recommended that 3DE be used to evaluate EF.1 The authors are aware of only 1 veterinary study14 conducted to evaluate use of 3DE for assessing RVV and EF. Results of that study14 and the study reported here indicate that measuring RVV with 3DE is feasible and repeatable in dogs. Similar to results obtained for humans,1 results for the dogs of the present study revealed an underestimation of RVV obtained by use of 3DE, compared with RVV obtained by use of MDCT. However, correlation for data of the present study and the lack of significant differences in SV or EF between methods suggested that either method may be used to evaluate global RV function and monitor patterns for disease states.

Differences in RVV measured by use of cross-sectional imaging modalities (eg, cardiac MRI and MDCT), compared with values measured by use of 3DE, represent a consistent, systematic underestimation of chamber volume for 3DE in both humans9,16 and dogs.14 There are several reasons for this systematic difference, including limited spatial resolution of 3DE because of current technological aspects. Spatial and temporal resolution are excellent for cardiac MRI and MDCT, whereas the technological aspects of 3DE continue to develop. This limitation of 3DE has been reported,8,14,16 but improvements are expected with advances in 3DE probe, machine, and software technology.

In addition to differences in technological aspects, MDCT and 3DE differ in the method used for volume calculation. Many MDCT volume software programs, including the one used in the study reported here, involve use of the Simpson method to sum-mate a stack of discs to calculate EDV and ESV. Conversely, 3DE software involves the use of manually marked reference points to allow for detection of the endocardial border and subsequent quantification of volume. These differences in methods may introduce substantial variances in volume that may (or may not) have clinical importance.

Other contributory factors to the difference between 3DE and MDCT may include effects of ventilation, injection of contrast medium, change in recumbency position between modalities, and detection of the endocardial border. The MDCT scans were acquired during a postinspiratory breath-holding period to minimize artifacts attributable to respiratory motion during acquisition of images. Thus, MDCT RVVs were measured during full inspiration, whereas 3DE RVVs were not measured at a specific time in the respiratory cycle. The RV preload increases during inspiration; therefore, this may have resulted in larger MDCT volumes.2 In addition, the rapid injection of iodinated contrast medium (total volume, 1.5 mL/kg) during MDCT scanning may also have increased RV preload, which would result in larger EDV and ESV MDCT measurements. Finally, the excellent myocardial border distinction that is provided by iodinated contrast medium with MDCT yields superior detection of the endomyocardial border over that for 3DE and, thus, potentially higher values for MDCT.

There are interesting concordant and discordant results between the study reported here and the previously published study14 of dogs in which RVV was investigated by use of advanced imaging techniques. Both studies found that RVVs measured with 3DE were significantly lower than those measured with MDCT. In the previous study,14 EDV, ESV, SV, and EF all differed significantly between the methods, whereas in the present study, SV and EF did not differ significantly between 3DE and MDCT. Both studies found strong correlations between MDCT and 3DE RVV, despite significant differences for actual EDVs and ESVs. Also, both studies found a similar moderate correlation for EF and poor correlation for SV between the 2 methods. It is difficult to make a direct comparison between results of the study reported here and the previous study14 because several factors were not equivalent (the echocardiographic and MDCT machines, postprocessing software for the MDCT images, method of injection of contrast medium, and median body weight of the dogs all differed). This may have been attributable to differences in equipment or to a slightly larger population of dogs in the previous study (n = 10) than in the present study (6).

Finally, results of the present study suggested that there was acceptable intraobserver and interobserver variability. Although repeatability standards for assessment of the right side of the heart have not been established for veterinary cardiology, echocardiographic variables with variation in excess of 20% are undesirable.11 Results of the repeatability analysis for the present study were consistent with similar human16 and canine14 studies that were conducted to assess 3DE-derived RVV.

The present study had several limitations. There was a small number of dogs, with minimal variability in age and body weight. Although all relevant RV structures were identified on MDCT images, the RV outflow tract was particularly difficult to identify on all 3DE datasets. The canine RV is a wide structure, and increases in width of the 3DE volume result in a commensurate reduction in temporal resolution, which may have impacted the correlation between results for MDCT and 3DE. In addition, the 3DE RV software did not allow users to define end-diastole and end-systole; therefore, this software limitation combined with low temporal resolution may have resulted in comparison of volumes determined at different times within the cardiac cycle. Gain settings for 3DE may have contributed to the underestimation of RVV because high gain settings increase thickness of the endocardial wall and reduce cavity size, whereas low gain settings result in decreased echogenicity of the endocardial border.17 Given these limitations, it is possible that 3DE with contrast enhancement may be used to better delineate the RV chamber in dogs. Further studies to identify optimal techniques are needed.

Results of the study reported here indicated that 3DE could feasibly be used to measure RVV in healthy dogs, with acceptable reproducibility. Measures of RVV obtained by use of 3DE underestimated those made by use of MDCT; therefore, results of these imaging techniques are not interchangeable. A larger prospective study of dogs with and without cardiac disease is needed to delineate the benefits and constraints of both methods.

Acknowledgments

Supported by research funds from the Department of Clinical Sciences, College of Veterinary Medicine, Oregon State University.

The authors thank Darcy Palmer, Amy Berry, Robyn Panico, Cynthia Viramontes, and Jason Wiest for technical assistance.

ABBREVIATIONS

2DE

2-D echocardiography

3DE

3-D echocardiography

EDV

End-diastolic volume

EF

Ejection fraction

ESV

End-systolic volume

LAP

Left apical

LV

Left ventricle

MDCT

Multidetector CT

RV

Right ventricle

RVV

Right ventricle volume

SV

Stroke volume

TV

Tricuspid valve

Footnotes

a.

Toshiba Aquilion 64 CT, Toshiba America Medical Systems Inc, Tustin, Calif.

b.

Isovue 370, Empower CTA, Bracco Diagnostics Inc, Princeton, NJ.

c.

Empower CTA, Bracco Diagnostics Inc, Princeton, NJ.

d.

Vitrea workstation software, version 6.7.4, Vital Images Inc, Minnetonka, Minn.

e.

Philips iE33, Philips Medical Systems, Andover, Mass.

f.

TomTec Imaging Systems GmbH, Munich, Germany.

g.

GraphPad Prism, version 6.0h, GraphPad Software Inc, La Jolla, Calif.

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  • Figure 1—

    Representative MDCT images of the RV in a healthy dog in a short-axis view (A), RV outflow tract (B), and RV inflow region (C) obtained by use of postprocessing software and a 3-D cast of the RV lumen (D). In all panels, the RV lumen is blue. In panel D, the outflow tract is on the left side of the image, and the RV inflow region is on the right side of the image.

  • Figure 2—

    A 2DE image showing the modified LAP window in a healthy dog with the RV optimized for 3DE. Notice the ECG tracing at the bottom of the image. Tick marks on the right side of the image are at intervals of 1 cm.

  • Figure 3—

    Representative 2DE images of the mitral valve (MV; A), apex of the LV (B), aortic valve (distance between AVI and AV2; C), RV (D), apex of the RV (E), and cranial (AJL) and caudal (PJL) limits of the RV (F) in a healthy dog obtained by use of postprocessing RVV software. Panels A and D represent a 4-chamber view, panels B and E represent a 2-chamber view, panel C represents a 3-chamber view, and panel F represents a short-axis view. The dashed lines in panels C through F represent an axis for image manipulation. Notice the ECG tracing at the bottom of panel F.

  • Figure 4—

    Software-generated depictions of 3-D end-diastolic (A) and end-systolic (B) images of the RV in a healthy dog. The RV outflow tract is on the left side of each image, and the RV inflow region is on the right side of each image.

  • Figure 5—

    Bland-Altman plots of the comparison between MDCT and 3DE for measurement of EDV (A), ESV (B), SV (C), and EF (D) in 6 healthy dogs. Each circle represents results for 1 dog. In each plot, bias is indicated by the horizontal dotted line, and 95% limits of agreement are indicated by the solid lines.

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