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Background Cardiac CT, with or without contrast, is a chest CT performed primarily for the morphologic evaluation of the cardiac chambers, valves, ventricular myocardium, coronary arteries and veins, aortic root, central pulmonary arteries and veins and pericardium. Contrast-enhanced CT is performed after intravenous (IV) administration of iodinated contrast to optimize evaluation of the cardiac chambers, myocardium, valves and pericardium. In addition to coronary calcium scoring, unenhanced cardiac CT is also used to evaluate cardiac valves, pericardium, and cardiac masses. (ACR, 2006b) Research Structure and morphology The assessment of aortic valve stenosis using MDCT is feasible with good diagnostic accuracy. The sensitivity of MDCT for the identification of patients with aortic stenosis was 100%, specificity was 93.7%, positive and negative predictive values were 97 and 100%. CT imaging may develop into an alternative imaging tool in patients who require exact assessment of the opening or regurgitant orifice of the aortic or mitral valve and in whom other more commonly used methods, such as echocardiography and magnetic resonance imaging, fail to provide all relevant information. Currently, available clinical data are too limited to allow identification of specific patient subsets in which CT imaging would be the first-choice diagnostic test. (Schroeder, 2008) Anatomy of the coronary venous system can be accurately assessed with MDCT.
(Schroeder, 2008) Cardiac function Ventricular function is adjunct information that can be obtained from standard coronary CT angiography investigations without altering the image acquisition protocol, and the ability of CT to provide accurate right ventricular assessment might be useful in several clinical conditions including congenital heart disease, carcinoid heart disease, or prior to lung transplantation. Various studies have shown that for these left ventricular functional parameters, MDCT correlated well with magnetic resonance imaging, echocardiography, or gated SPECT. Although CT imaging allows accurate assessment of left and right ventricular function, CT examinations will in most cases not be performed specifically for that purpose.
Other diagnostic tests without radiation exposure or the need for contrast injection (i.e. echocardiography) are the methods of choice. (Schroeder, 2008) While several pre-clinical and clinical studies have documented that MDCT allows assessment of myocardial viability, clinical data are currently too limited to allow recommendations on the use of CT for the assessment of perfusion and viability. (Schroeder, 2008) Coronary artery disease (CAD) is believed to be the underlying cause in approximately two-thirds of patients with heart failure and low ejection fraction. Ghostine, et al. evaluated the diagnostic accuracy of 64-slice CT in identifying ischaemic heart failure (IHF) in patients with left ventricular systolic dysfunction but without clinical suspicion of CAD compared with conventional coronary angiography. Overall, accuracy, sensitivity, specificity, positive predictive value, and negative predictive value of CT for identifying CAD by segment was 96, 73, 99, 92, and 97%, respectively; by patient was 95, 98, 92, 91, and 98%, respectively; and for identifying IHF was 95, 90, 97, 93, and 95%, respectively.
Non-invasive 64-slice CT assessment of the extent of CAD may offer a valid alternative to angiography for the diagnosis of IHF. (Ghostine, 2008) Andreini, et al. assessed the safety, feasibility, and diagnostic accuracy of 16-slice MDCT in patients with dilated
cardiomyopathy (DCM) of unknown etiology. The study included 61 unknown origin DCM patients (ejection fraction:
33.9 +/- 8.6%, group 1) and 139 patients with normal cardiac function with indications for coronary angiography (group 2, control population). In group 1, all cases with normal (44 cases) or pathological (17 cases) coronary arteries by conventional coronary angiography were correctly detected by MDCT, with, in 1 case, disparity of stenosis severity. In group 1, sensitivity, specificity, and positive and negative predictive values of MDCT for the identification of 50% stenosis were 99%, 96.2%, 81.2%, and 99.8%, respectively. In group 2, sensitivity and negative predictive values were lower than in group 1 (86.1% vs. 99% and 96.4% vs. 99.8%, respectively); specificity (96.4%) and positive predictive value (86.1%) were not significantly different versus group 1. The investigators concluded that MDCT is feasible, safe, and accurate for identification of idiopathic versus ischemic DCM, and may represent an alternative to coronary angiography. (Andreini, 2007) Advances in CT technology have significantly improved temporal and spatial resolutions. In a meta analysis and review of the literature, van de Vleuten et al. compared MDCT and MRI for evaluating left ventricular function. The analysis indicated that the global left ventricular functional parameters measured by contemporary multi-detector row systems Cardiac Computed Tomography (CT), Coronary Artery Calcium Scoring and Cardiac CT Angiography - Commercial Medical Management Guideline combined with adequate reconstruction algorithms and post-processing tools show a narrow diagnostic window and are interchangeable with those obtained by MRI. (van der Vleuten, 2006) Professional Societies Indications for contrast-enhanced cardiac CT include cardiac functional evaluation, especially in patients in whom cardiac function may not be assessed by magnetic resonance imaging (automatic implantable defibrillator, pacemaker, general MRI contraindications, etc.) or echocardiography (e.g., poor acoustic window). (ACR, 2006b) The role of CT scanning in patients is increasing due to the development of multidetector CT with better spatial and temporal resolution and ECG gating. These advances permit assessment of left ventricular function, including stroke volume and ejection fraction. Despite much early enthusiasm, there are as yet few studies documenting the value of cardiac CTA in assessing congestive heart failure. Thus, the role of cardiac CT as compared to nuclear cardiology is in evolution. (ACR, 2006c) Number of slices It is a common misconception that 64-slice CT scanners are better than 16-slice CT scanners in diagnostic quality and for a variety of exams. However, in applications in which patient movement is less of a critical issue, 16-slice scanners provide the same diagnostic quality as 64-slice systems. According to ECRI Institute's Health Devices clinical engineering staff, 16-slice scanners are appropriate for coronary artery calcium scoring, while 64-slice scanners are recommended for cardiac imaging. (ECRI, 2008) There is evidence that a 40-slice computed tomography scanner can detect the presence of and/or the progression of coronary artery disease within patients who are symptomatic or who have undergone previous cardiac interventions.
There were no studies that specifically evaluated the diagnostic performance of 32-slice scanners and therefore insufficient evidence that the use of a 32-slice scanner can accurately detect the presence or progression of coronary artery disease. (Hayes, 2008) In a 2007 meta-analysis, Vanhoenacker, et al. demonstrated a significant improvement in the accuracy for the detection of coronary artery stenosis for 64-slice CT when compared with previous scanner generations. Fifty-four studies were included in the meta-analysis: 22 studies with four-detector CT angiography, 26 with 16-detector CT angiography, and six with 64-detector CT angiography. The pooled sensitivity and specificity for detecting a greater than 50% stenosis per segment were 0.93 (95% confidence interval [CI]: 0.88, 0.97) and 0.96 (95% CI: 0.96, 0.97) for 64-detector CT angiography, 0.83 (95% CI: 0.76, 0.90) and 0.96 (95% CI: 0.95, 0.97) for 16-detector CT angiography, and 0.84 (95% CI: 0.81, 0.88) and 0.93 (95% CI: 0.91, 0.95) for four-detector CT angiography, respectively. Results indicated that with newer generations of scanners, the diagnostic performance for assessing coronary artery disease has significantly improved, and the proportion of nonassessable segments has decreased. (Vanhoenacker, 2007) Grosse, et al conducted a prospective study of 40 patients (28 men, 12 women) to measure both the quality and the accuracy of images taken with a 40-slice MSCT. The researchers compared the images from all 40 patients taken during the MSCT to those obtained during a conventional intracoronary angiography (ICA) in the detection of clinically significant CAD. Patients currently taking oral beta-blockers were not excluded from the study. No additional administration of beta-blockers was used during the MSCT. One cardiologist and 2 radiologists who were blinded to each patient's IAC results analyzed the MSCT images. Images from the ICA revealed significant CAD in 30/40 patients (75%). MSCT correctly diagnosed 39/40 patients, with 29 patients having significant stenosis and 10 patients having no significant CAD. Of the 545 vessel segments studied during the MSCT, 43 segments (7.9%) could not be evaluated due to motion artifacts (n=15), small vessel size and poor contrast enhancement (n=14), severe calcifications (n=10), and opacity of adjacent structures (n=4). MSCT detected significant stenosis ( 50%) in all vessels yielding a sensitivity, specificity, positive predictive value (PPV), and NPV of 87%, 99%, 98%, and 95%, respectively. When the researchers measured MSCT findings for stenosis of the proximal coronary segments, sensitivity, specificity, and NPV increased to Cardiac Computed Tomography (CT), Coronary Artery Calcium Scoring and Cardiac CT Angiography - Commercial Medical Management Guideline 96%, 99%, and 99% respectively. Patient analysis also produced a high NPV (91%) for the exclusion of significant CAD.
Forty-slice CT demonstrated a high diagnostic accuracy in the detection of clinically significant CAD per patient and per vessel segment. (Grosse, 2007) Watkins et al. performed a prospective, blinded study (n=85) at 2 institutions to determine the feasibility and diagnostic accuracy of coronary angiography using 40-channel multidetector computer tomography with multi-segment reconstruction for the detection of obstructive coronary artery disease (CAD). Of 1,145 segments that were suitable for analysis, 1,045 (91.3%) were evaluable on multidetector computer tomography. In a patient-based analysis, the sensitivity, specificity, and positive and negative predictive values for detecting subjects with or =1 segment with or =50% stenosis were 98%, 93%, 94% and 93%, respectively. Coronary angiography using 40-channel multidetector computer tomography with multi-segment reconstruction accurately detects coronary segments and patients with obstructive CAD, with a small number of non-evaluable cases. (Watkins, 2007) In a prospective study, Lim, et al. compared the accuracy of 40-slice CT angiography with invasive selective coronary angiography in the detection of significant coronary stenosis ( or =50% lumen diameter narrowing). Thirty consecutive patients with suspected coronary artery disease underwent both invasive coronary angiography and MSCT. Average sensitivity, specificity, positive predictive value, and negative predictive value of MSCT were 99, 98, 94, and 99%, respectively. (Lim, 2006)
Additional product information:
eSpeed, LightSpeed, BrightSpeed and HiSpeed series (GE Imatron, Inc.); Brilliance CT (Phillips Medical); SOMATOM series (Siemens); Aquilon series (Toshiba)
Additional search terms:
calcified plaque, calcium scan, CAT scan, computerized axial tomography, coronary artery scan, CT scan, helical, spiral, ultrafast CT References and Resources Resources American College of Radiology (ACR). ACR practice guideline for the performance and interpretation of computed tomography angiography (CTA). October 2006a. Available at: http://www.acr.org/SecondaryMainMenuCategories/ quality_safety/guidelines/dx/cardio/ct_angiography.aspx. Accessed April 7, 2009.