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Comparison of Image Quality and Arterial Enhancement with a Dedicated Coronary CTA Protocol versus a Triple Rule-Out Coronary CTA Protocol

Posted Aug 31, 2009 Updated Apr 7, 2023
By Ethan J. Halpern MD , David C. Levin MD , Shaoxiong Zhang MD , Kevin M. Takakuwa MD
10 min read

Rationale and Objectives

To compare the image quality of dedicated coronary computed tomography angiography (cCTA) to that of triple rule-out (TRO) CTA designed to evaluate the coronary arteries, thoracic aorta, and pulmonary arteries.

Materials and Methods

Consecutive cCTA examinations performed by a single radiologist over 1 year were reviewed. Biphasic injection protocols were employed: 70 mL of optiray-350 followed by 40 mL of saline injected at 5.5 mL/second for dedicated cCTA; 70 mL of optiray-350 followed by 25 mL of the contrast diluted with 25 mL of saline injected at 5.0 mL/second for TRO-CTA. Two independent cardiovascular radiologists reviewed the coronary vessels in each case and rated diagnostic image quality on a 5 point scale (1, suboptimal; 3, adequate; 5, excellent). Vascular enhancement was measured in the coronary arteries, aorta, and pulmonary arteries.

Results

There was excellent interobserver agreement between the cardiovascular radiologists (kappa = 0.91). Coronary image quality score were similar among 260 dedicated cCTA studies and 168 TRO-CTA studies (mean: 3.8–3.9. P > .18). At least one coronary segment demonstrated suboptimal image quality in 8% of examinations, including 18 dedicated cCTA studies and 16 TRO studies ( P = .94). Enhancement was greater in the distal thoracic aorta of TRO patients (336 vs. 311 Hounsfield units; P = .01); no other significant differences in enhancement were identified in the aorta and coronary arteries of dedicated cCTA and TRO studies. Vascular enhancement was adequate for diagnostic evaluation of the pulmonary arteries in all TRO studies.

Conclusions

A TRO-CTA protocol using 95 mL of contrast can provide comparable coronary image quality and coronary vascular enhancement as compared to dedicated cCTA with 70 mL of contrast.

Although much has been written about the application of dedicated coronary computed tomography angiography (cCTA) to the evaluation of coronary disease, fewer studies have examined the use of computed tomography (CT) to simultaneously evaluate the thoracic aorta, and pulmonary arteries . The “triple rule-out” (TRO) CTA study is a tailored examination that is designed to specifically evaluate these three major vascular beds in the thorax. A recent survey of radiology practices found that 33% were involved with CT in the emergency department workup of chest pain, and that 18% were using the TRO study . Physicians may be reluctant to perform TRO studies because of an impression that the TRO is too technically challenging or that the quality of the coronary artery study is compromised in the TRO examination.

Imaging results and clinical outcomes for the emergency department patients in this study have been previously reported . TRO studies demonstrated the presence of moderate to severe coronary disease (>50% luminal diameter stenosis) in 11% of patients, demonstrated a process other than coronary atherosclerosis that explained the clinical presentation in another 11% of patients, and allowed for disposition of the patient without further diagnostic testing in 76% of patients. The current study is designed to compare the image quality of TRO CTA to that of dedicated cCTA to determine whether there is a difference in coronary artery image quality between dedicated cCTA and TRO studies.

Methods

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Coronary CTA Scan Protocol

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Vascular Enhancement and Image Quality Analysis

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Statistical Analysis

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Results

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Table 1

Demographics for Patients in Dedicated cCTA and TRO Groups

Dedicated cCTA TRO_P_ Value Age 58 ± 12 years 50 ± 12 y <.001 Sex (male:female ratio) 57 : 43 45 : 55 .05 Height 1.7 ± 0.09 m 1.7 ± 0.10 m .17 Weight 89 ± 25 kg 85 ± 21 kg .24 Body mass index 30.3 ± 7.6 29.6 ± 6.7 .55

cCTA: coronary computed tomography angiography; TRO: triple rule-out.

Table 2

Study Parameters for Patients in Dedicated cCTA and TRO Groups

Dedicated cCTA TRO_P_ Value Beta-blocker dose 12.2 ± 0.8 mg 11.7 ± 1.0 mg .84 Heart rate 61.5 ± 0.8 beats/min 63.0 ± 1.0 bpm .24 Tube current modulation 43% 48% .52 Scan length 18.4 ± 2.9 cm 21.0 ± 2.0 <.001

cCTA: coronary computed tomography angiography; TRO: triple rule-out.

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Table 3

Subjective Coronary Artery Image Quality in Dedicated cCTA and TRO Patients

Subjective Image Quality Score 1 2 3 4 5 cCTA 3 15 51 111 80 TRO 5 11 37 71 44

cCTA: coronary computed tomography angiography; TRO: triple rule-out.

Figure 1, A 50-year-old female with no risk factors for coronary disease presents to the emergency room with several days of chest pain. Triple rule-out (TRO) evaluation demonstrates atherosclerotic coronary disease. Maximum intensity projection (MIP) images from the TRO study are presented. (a) Curved MIP of the left anterior descending (LAD) artery demonstrates irregular plaque in the proximal LAD (arrow) with 50% diameter stenosis and a focal calcification underlying the area of irregularity. (b) Curved MIP demonstrates a normal circumflex artery (LCX) terminating as a large obtuse marginal branch to the left ventricle (arrow) . (c) Curved MIP demonstrates a normal right coronary artery (RCA) terminating as the posterior descending artery (arrow) . (d) Slab MIP in a left anterior oblique projection demonstrates homogeneous contrast enhancement of the aorta (Ao) and left pulmonary artery (LPA). (e) Slab MIP in a right anterior oblique projection demonstrates homogeneous contrast enhancement of the right pulmonary artery (RPA) as well as segmental and subsegmental branches of the RPA. Contrast material in the superior vena cava (SVC) actually represents dilute contrast from the second phase of the biphasic contrast injection. There is minimal streak from the SVC that does not result in loss of diagnostic quality.

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Table 4

Post-hoc Power Analysis

Difference in Image Quality Scores Power to Detect this Difference 0.4 0.99 0.3 0.88 0.27 0.81 0.26 0.78 0.25 0.75

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Table 5

Enhancement of the Aorta and Left Ventricle in Dedicated cCTA and TRO Patients (Expressed in Hounsfield Units)

Dedicated cCTA TRO_P_ Value Aortic root 341 ± 83 329 ± 84 .25 Upper aorta 322 ± 79 327 ± 85 .60 Mid aorta 316 ± 83 304 ± 85 .24 Lower aorta 337 ± 95 311 ± 88 .03 Upper LV 324 ± 85 310 ± 78 .16 Lower LV 326 ± 93 320 ± 80 .59 Left main CA 308 ± 74 313 ± 78 .59 Right CA 315 ± 77 316 ± 85 .93

cCTA: coronary computed tomography angiography; TRO: triple rule-out; LV: left ventricle; CA: coronary artery.

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Table 6

Pulmonary Artery Opacification in Triple Rule-out Studies

Hounsfield Units Main pulmonary artery 341 ± 101 Right pulmonary artery 325 ± 95 Left pulmonary artery 334 ± 97 Right upper lobe pulmonary artery 331 ± 108 Right lower lobe pulmonary artery 318 ± 99 Left upper lobe pulmonary artery 327 ± 96 Left lower lobe pulmonary artery 331 ± 101

Figure 2, A 59-year-old male with no risk factors for coronary disease presents to the emergency room with acute onset of chest pain and palpitations after taking out the trash in the morning. Triple rule-out (TRO) evaluation demonstrates bilateral pulmonary embolism. (a) Curved maximum intensity projection (MIP) demonstrates a normal left anterior descending (LAD) (arrow) wrapping around the apex of the heart with no focal narrowing. (b) Curved MIP demonstrates a normal circumflex artery (LCX) (arrow) wrapping around the left atrioventricular groove to the crux of the heart with no focal narrowing. The small posterior descending artery (not shown) was a branch of the LCX. (c) Curved MIP demonstrates a normal nondominant right coronary artery (arrow) terminating as an acute marginal branch to the right ventricle. (d) Coronal slab MIP demonstrates homogeneous enhancement of the aorta (Ao) and pulmonary arteries (right pulmonary artery and left pulmonary artery) with multiple bilateral segmental pulmonary emboli. (e) Slab MIP in a right anterior oblique projection demonstrates dilute contrast material in the superior vena cava (SVC) with mild streak artifact into the adjacent ascending aorta, but this does not result in loss of diagnostic quality. The pulmonary emboli within the adjacent right pulmonary artery (arrow) are not obscured by any streaking from the SVC.

Figure 3, A 52-year-old male with no risk factors for coronary disease presents to the emergency room with several episodes of atypical chest pain. There is sharp definition of the aorta, pulmonary arteries, and coronary arteries. A small pulmonary embolus is present. Vascular opacification in the aorta and left ventricle is at approximately 350 Hounsfield units (HU), whereas that in the pulmonary arteries is at approximately 250–300 HU. (a) Globe maximum intensity projection (MIP) demonstrates sharp definition of the left anterior descending (LAD) and left circumflex (LCX) arteries as well as several diagonal and obtuse marginal branches. (b) Slab MIP in a left anterior oblique projection demonstrates the right coronary artery (RCA) (arrow) as well as the left pulmonary artery (arrowhead) . (c) Slab MIP in a different left anterior oblique projection demonstrates the aortic arch as it passes around the right pulmonary artery (arrowhead) . The right coronary artery (arrow) is again visualized. Note homogeneous enhancement of the aorta and pulmonary arteries. Vascular opacification in the aorta and left ventricle is at approximately 350 Hounsfield units (HU), whereas that in the pulmonary arteries is at approximately 250–300 HU. (d) Transaxial image demonstrates all four cardiac chambers with typical levels of opacification in the right heart and left heart. The RCA (arrow) is clearly defined, as is the clot in a right lower lobe pulmonary artery (arrowhead) . Unopacified flow enters the right atrium, adjacent to the interatrial septum, from the inferior vena cava. This image demonstrates a grainy texture because it represents a single 0.7-mm computed tomography slice rather than a slab MIP. (e) Coronal slab MIP demonstrates the right pulmonary artery (large arrowhead) along with segmental and subsegmental branches. Pulmonary venous branches are demonstrated joining the right inferior pulmonary vein. The branch containing the right lower lobe pulmonary embolism (small arrowhead) overlaps with adjacent pulmonary venous branches.

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Discussion

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Radiation Dose

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Study Limitations

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Conclusion

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Academic Radiology, Volume 16, Issue 9
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