SA-CME ARTICLE Computed Tomography Angiographic Assessment of Acute Chest Pain Matthew M. Miller, MD, PhD,* Carole A. Ridge, FFRRCSI,w and Diana E. Litmanovich, MDz Acute chest pain leads to 6 million Emergency Depart- Abstract: Acute chest pain is a leading cause of Emergency Depart- ment visits per year in the United States.1 Evaluation of acute ment visits. Computed tomography angiography plays a vital diag- chest pain often leads to a prolonged inpatient assessment, nostic role in such cases, but there are several common challenges with assessment duration often exceeding 12 hours. The associated with the imaging of acute chest pain, which, if unrecog- estimated cost of a negative inpatient chest pain assessment nized, can lead to an inconclusive or incorrect diagnosis. These 2,3 imaging challenges fall broadly into 3 categories: (1) image acquis- amounts to $8 billion per year in the United States. ition, (2) image interpretation (including physiological and pathologic The main challenge to diagnosis is the broad range of mimics), and (3) result communication. The aims of this review are to pathologies that can cause chest pain. Vascular causes describe and illustrate the most common challenges in the imaging of include pulmonary embolism (PE), traumatic and acute chest pain and to provide solutions that will facilitate accurate spontaneous aortic syndromes including aortic transection, diagnosis of the causes of acute chest pain in the emergency setting. dissection, intramural hematoma, and penetrating athero- sclerotic ulcer, aortitis, and coronary artery disease. The Key Words: acute chest pain, challenges, pulmonary angiography, latter will not be discussed in detail because of the com- aortography, computed tomography plexity and breadth of this topic alone. CT angiography is (J Thorac Imaging 2017;32:137–150) playing an increasing role in the assessment of acute chest pain because of its ability to rapidly identify vascular causes LEARNING OBJECTIVES of chest pain4–8 with the aim of improving patient After completing this SA-CME activity, physicians outcomes. should be better able to: There are, however, several common challenges asso- 1. Recognize the most common challenges of computed ciated with the imaging of acute chest pain, which, if tomography (CT) angiography performed for acute unrecognized, could lead to an incorrect diagnosis. These chest pain and describe steps that can be taken to potential challenges lie in image acquisition, image inter- optimize image quality and interpretation. pretation, and result communication. 2. Identify the most common physiological mimics in acute In this review, we describe the most common radio- chest pain imaging and describe strategies to identify logic challenges encountered in acute chest pain assessment them. and suggest solutions to facilitate accurate diagnosis of 3. Accurately identify and differentiate acute causes of vascular causes of chest pain in the emergency setting. chest pain from their pathologic mimics. 4. Describe the optimal methods of communication related OPTIMIZING IMAGE ACQUISITION to acute thoracic imaging. Suboptimal image acquisition can be avoided by the use of carefully selected imaging parameters, particularly avoiding motion and other artifacts. These parameters are of paramount importance to the acquisition of diagnostic quality images. From the *Department of Radiology, Duke University Hospital, Durham, NC; zDepartment of Radiology, Beth Israel Deaconess CT Pulmonary Angiography Medical Center and Harvard Medical School, Boston, MA; and wDepartment of Radiology, Mater Misericordiae University Hos- CT is a sensitive tool for the evaluation of pulmonary pital, Dublin, Ireland. arteries and for detection of PE.9 However, suboptimal Dr Miller is a Breast Imaging Fellow at Duke University Hospital, studies account for up to 10.8% of all CT pulmonary Durham, NC; Dr Litmanovich is an Associate Professor of 10 Radiology in Cardiothoracic Imaging, Director of Cardiac CT, angiograms performed. Suboptimal image quality can Director of Cardiothoracic Fellowship, and Director of Radiology arise when motion artifact obscures the pulmonary arteries Course for Primary Clinical Experience at Beth Israel Deaconess or nonopacification of the pulmonary arteries mimics or Medical Center and Harvard Medical School, Boston, MA; obscures a PE.11 Dr Ridge is a Consultant Radiologist at Mater Misericordiae University Hospital, Dublin, Ireland. The authors, faculty and all staff in a position to control the content of Motion Artifact this CME activity and their spouses/life partners (if any) have dis- closed that they have no financial relationships with, or financial Respiratory Motion interests in, any commercial organizations pertaining to this edu- Challenge. Respiratory motion can result in artifactual cational activity. duplication of normal physiological structures or over- Correspondence to: Diana E. Litmanovich, MD, Department of lapping of adjacent structures—for example, a pulmonary Radiology, Beth Israel Deaconess Medical Center, 330 Brookline Ave., Boston, MA 02215 (e-mail: [email protected]). artery and an airway. Volume averaging of these 2 adjacent Copyright r 2017 Wolters Kluwer Health, Inc. All rights reserved. structures may then produce the appearance of a filling DOI: 10.1097/RTI.0000000000000267 defect or termination of the vessel mimicking a PE J Thorac Imaging Volume 32, Number 3, May 2017 www.thoracicimaging.com | 137 Copyright r 2017 Wolters Kluwer Health, Inc. All rights reserved. Miller et al J Thorac Imaging Volume 32, Number 3, May 2017 FIGURE 1. Challenges of image acquisition, pulmonary arteries. A and B, Motion artifact creating apparent filling defects in all arteries on 1 slice (white arrows), which can mimic PE. Comparison with lung windows demonstrates blurring of all bronchial structures on the same slice (black arrows), confirming motion artifact. C, Suboptimal opacification in the main pulmonary artery (arrow) due to transient interruption of contrast from deep inspiration during contrast injection, which can lead to missed findings. (Fig. 1A). This may result in overdiagnosis of segmental artifactual filling defects will often be present throughout all and subsegmental PE.12 of the pulmonary arteries on the same image, and if these Solution. Steps to help prevent this challenge include apparent filling defects are cross-referenced with lung win- (1) coaching the patient before CT on the importance of dow images, blurring or duplication of the bronchovascular a sustained breath-hold and (2) using a scan direction from bundle is often evident on the same image (Figs. 1A, B). the lung bases toward the apices. High-pitch dual-source CT pulmonary angiography can lead to good-quality images, where motion artifact is a particular challenge.13 Cardiac Motion These techniques enhance the visualization of the lower- Challenge. Pulsation artifacts arising from cardiac lobe pulmonary arteries where motion artifact and motion can also result in volume averaging and apparent pulmonary emboli are most likely to occur. After these filling defects in the pulmonary arteries adjacent to the steps have been taken, any artifacts arising from respiratory heart, mimicking PE. motion can be recognized by cross-referencing soft tissue Solution. Identification of duplicated physiological and lung window images. On soft tissue windows, structures in the lung adjacent to the heart may raise 138 | www.thoracicimaging.com Copyright r 2017 Wolters Kluwer Health, Inc. All rights reserved. Copyright r 2017 Wolters Kluwer Health, Inc. All rights reserved. J Thorac Imaging Volume 32, Number 3, May 2017 Acute Chest Pain a suspicion of pulsation artifact. If pulsation artifact is and when optimal it ranges from 42% to 62%.19 If a considered a major limiting factor to achieving a diagnosis, questionable filling defect is detected, attention should also prospective electrocardiogram (ECG)-gated CT pulmonary be paid to secondary signs of PE, such as vessel dilation, angiography can be performed; images are typically pulmonary infarction, right heart strain, or pleural effusion. acquired at 70% of the R-R interval.14 If these secondary signs of PE are absent and KIVC is elevated, transient interruption of the contrast bolus may Patient Motion have occurred. Challenge. Motion artifact due to patient motion on the scanning table is a particular challenge in the acutely ill Shunt Physiology or confused patient. Challenge. A right-to-left intracardiac shunt or an Solution. Patient coaching may reduce the impact of intrapulmonary shunt can allow a portion of injected con- patient motion during pulmonary CT angiography. In the trast to bypass the pulmonary arterial tree, thereby leading case of an intubated or confused patient, however, this to decreased opacification of the pulmonary arteries.20 A strategy may not be sufficient. High-pitch imaging can min- rarer left-to-right intracardiac shunting can also contribute imize the impact of patient motion. If, however, CT pulmo- to suboptimal pulmonary arterial opacification by allowing nary angiography is nondiagnostic because of unpreventable nonopacified blood from the left heart to mix with and patient motion, alternative imaging modalities such as lower- dilute the bolus of contrast as it enters the right heart. limb Doppler ultrasound to exclude an associated deep Solution. A right-to-left shunt can be recognized by venous thrombosis can be considered. the presence of pulmonary arterial hypoenhancement coupled with