Cardiac CT Studies Research Articles

Impact of right ventricular contrast attenuation on the accuracy of right ventricular function analysis at cardiac multi-detector-row CT

Purpose To investigate the impact of right ventricle (RV) contrast attenuation on the accuracy of RV function analysis at cardiac CT performed for coronary imaging. Materials and methods We analyzed multi-phase cardiac dual-source CT studies of 40 consecutive patients (mean age 60.9 ± 12.3 years; 13 women) with normal valve function. Function analyses of both the right and left ventricle (RV and LV) were performed using dedicated post processing software and stroke volumes (SV) were computed for each ventricle. The accuracy of the RV-SV measurements was determined based upon comparison to LV-SV measurement. The level of contrast attenuation of the RV was recorded at three separate regions of interest—below the pulmonary valve, mid-ventricular, and inferior RV. The accuracy of RV function assessment was correlated with the level of attenuation using regression analyses. Results There was a statistically significant correlation between the accuracy of RV function assessment and the level of RV attenuation in the inferior RV (adjusted R 2 = 73.1%, p < 0.0001). When compared to LV-SV measurements, in studies with low RV attenuation (<175 HUs, n = 19) the mean deviation of RV-SV from LV-SV was 29.0 ± 10.8 ml (42.1 ± 13.9%). In studies with high RV attenuation (≥175 HUs, n = 21) the mean deviation of RV-SV from LV-SV was significantly lower 6.9 ± 10.5 ml (9.9 ± 16.0%). Conclusion The accuracy of RV function analysis is dependent on the level of contrast medium attenuation achieved in the inferior RV. There should be at least intermediate attenuation (>175 HUs) to enable accurate functional analysis. At low attenuation levels RV function parameters are prone to underestimation.

Radiation exposure and dose reduction measures in cardiac CT

Noninvasive visualization of the heart by CT is highly accurate and useful, but its association with ionizing radiation and the potential risk of cancer induction has raised concerns. Dose-saving algorithms, new CT scanners, and scanning techniques have been developed to effectively reduce the amount of radiation exposure without deterioration of image quality. Furthermore, additional strategies for dose reduction can be pursued in daily practice following the ALARA (as low as reasonably achievable) principle. However, there still is a high additional dose-saving potential in a consequent application of dose reduction measures, and we recommend individually adapted scan protocols to obtain cardiac CT studies with optimal diagnostic image quality and lowest possible radiation dose.

How to use a prospective gated technique for cardiac CT

A prospective, electrocardiographically gated technique was recently adapted for use with coronary and cardiac multidetector row CT studies. The most widely available form of prospective gating uses "step-and-shoot" axial data acquisition, an incrementally moving table, adaptive electrocardiographic triggering, an improved image reconstruction algorithm, and multiphase reconstruction capability. Studies have shown a 77%-87% effective radiation dose reduction compared with retrospective gating and equal to significantly improved image quality. Comparison with conventional angiography has proven it to be as accurate as retrospective gating for coronary stenosis detection. The technique is not applicable to all patients because there are some restrictions for clinical use, including a limited number of reconstructed phases and a maximum scan heart rate of 68-75 beats/min. However, with careful patient selection and effective heart rate control, prospective gating can be used in a high percentage of cardiac CT examinations. This article reviews the scanning and patient selection protocols for prospective gating and discusses how it may be used in clinical practice.

Abstract 6102: Integration of Non-Contrast Cardiac Computed Tomography and Stress Myocardial Perfusion Imaging in the Emergency Department: Identifying Which Patients with Chest Pain Can be Safely Discharged Home

Over 5 million emergency department (ED) visits occur annually for evaluation of chest pain. A rapid simple imaging algorithm is needed to identify patients with noncardiac chest pain so as to avoid unnecessary hospital admission. We conducted a prospective trial in 1031 low risk patients (60% women; mean age 54±13 years) admitted through the ED to our chest pain unit who had no prior cardiac history, a nondiagnostic ECG for ischemia, and a normal initial troponin. All patients had stress myocardial perfusion imaging (SPECT) with a coronary artery calcium score (CACS) by noncontrast cardiac computed tomography (CT) within 24 hours. Mean patient follow-up was 7.4±3.3 months. SPECT and CT studies were interpreted independently and the CACS quantified as an Agatston score. The mean TIMI risk score was 1.5±0.7. Cardiac events occurred in 29 patients (2.8%): acute myocardial infarction (N=4) or an acute coronary syndrome (ACS, N=21) during admission; or ACS following hospital discharge (N=4). Abnormal SPECT and cardiac events significantly increased with CACS (p&lt;.001), with over a 40-fold increase in event rates for patients with a CACS&gt;400 vs 0(Table ). Only 5 (0.8%) patients with CACS=0 had an abnormal SPECT and none had significant coronary artery disease by angiography. The 2 patients who had a CACS=0 and a cardiac event during their hospitalization both had a normal gated SPECT and no subsequent event in follow-up. The sensitivity of an abnormal CT was significantly higher than an abnormal SPECT for identifying patients with events (93% vs 65%, p&lt;.01, respectively). A sizeable percentage (61%) of our low risk patient cohort had CACS=0 by CT which predicted both a normal SPECT and an excellent short-term outcome. Our data support that low risk patients with chest pain and a CACS=0 can be safely discharged home from the ED, with SPECT reserved for those with an abnormal CT result.

Extra-cardiac findings at cardiac CT: experience with 1,764 patients

To investigate incidental extra-cardiac findings (ECF) at cardiac CT based on indication and impact on patient management. We retrospectively reviewed the reports of 1,764 patients who underwent a cardiac CT study between January 1, 2004 and December 31, 2006, including 463 calcium scorings (CS), 737 coronary CT angiograms (CTA), 341 pulmonary vein stenoses (PVS), and 223 bypass grafts (CABG). ECFs were categorized by type of examination, anatomical location and clinical significance. Comparisons were made between examination types to determine if incidental findings varied by indication. There were 507 ECFs with at least one ECF in 441 patients (25.0%). By examination, there was at least 1 ECF in 79/463 CS studies (17.1%), 196/737 CTAs (26.6%), 80/341 PVSs (23.4%) and 86/223 CABGs (38.6%). In 325 patients (18.4%), the findings were considered clinically important and occurred in 60/463 (12.9%) CSs, 149/737 (20.2%) CTAs, 56/341 (16.4%) PVSs and 60/223 (26.9%) CABGs. Differences between CABG and other indications and CTA vs. CS for incidental and clinically important findings were statistically significant (p < 0.05). Extra-cardiac findings requiring follow-up occur in 18% of patients and are significantly more frequent in coronary artery CTA and coronary artery bypass studies than in calcium scoring studies.

Prospective versus Retrospective ECG Gating for 64-Detector CT of the Coronary Arteries: Comparison of Image Quality and Patient Radiation Dose

To compare image quality and patient radiation dose in a group of patients who underwent 64-detector computed tomography (CT) coronary angiography performed with prospective electrocardiographic (ECG) gating with image quality and radiation dose in a group of patients matched for clinical features who underwent 64-detector CT coronary angiography performed with retrospective ECG gating. Institutional review board approval was obtained for this HIPAA-compliant study, and the informed consent requirement was waived due to the retrospective study design. Two independent reviewers separately scored coronary artery segment image quality and overall image quality for 100 cardiac CT studies (50 in each group). Interobserver variability was calculated. Patient radiation dose for the actual examination z-axis length was recorded, and a normalized dose was calculated for a 12-cm z-axis length of a typical heart. The two groups matched well for clinical characteristics and CT parameters. There was good agreement for coronary artery segment image quality scores between the independent reviewers (kappa = 0.72). Of the 1253 coronary artery segments scored, the number of coronary artery segments that could not be evaluated in each group was similar (1.1% [seven of 614] in the prospective group vs 1.5% [10 of 647] in the retrospective group, P = .53). Image quality scores were not significantly different when matched for chest cross-sectional area (P > .05). Mean patient radiation dose was 77% lower for prospective gating (4.2 mSv) than for retrospective gating (18.1 mSv) (P < .01). Use of 64-detector CT coronary angiography performed with prospective ECG gating has similar subjective image quality scores but 77% lower patient radiation dose when compared with use of retrospective ECG gating.

Assessment of left ventricular function with 16- and 64-slice multi-detector computed tomography

Background Important to the risk stratification and management of cardiac patients is the assessment of left ventricular function (LVEF), thus imaging modalities which can provide both anatomical and functional data is desirable. Electrocardiographic (ECG) gated multi-detector computed tomographic (MDCT) images may provide accurate assessment of LV ejection fraction, volume and dimensions but have shown systemic errors in the past due to slow gantry rotation speed. Methods Between May 2004 and January 2005, 306 patients underwent ECG-gated cardiac CT studies at the Massachusetts General Hospital. Patients with available CT data sets and a recent (within 3 months) ECHO and/or SPECT perfusion imaging were included in the study. ECG-gated data sets were acquired either with a 16-slice or with a 64-slice MDCT. Functional MDCT data sets were reconstructed in 10 cardiac phases (5–95%) with 1.5 mm slices. Images were processed and interpreted by two observers blinded to ECHO and SPECT results. Results A total of 69 patients had MDCT and ECHO or SPECT within 3 months (33 had 16-slice and 36 had 64-slice MDCT). There was fair correlation between LVEF measured by 16-slice MDCT and ‘ECHO or SPECT’ (62 ± 10% vs. 62 ± 10%; r = 0.56). There was poor correlation between LVEF measured by 16-slice MDCT and ECHO (64 ± 10% vs. 59 ± 11%; r = 0.26) and there was good correlation between LVEF measured by 16-slice MDCT and SPECT (62 ± 11% and 64 ± 9%, respectively; r = 0.76). There was very good correlation between LVEF measured by 64-slice MDCT and ‘ECHO or SPECT’ (57 ± 15% vs. 58 ± 13%; r = 0.86). There was very good correlation between LVEF measured by MDCT and ECHO (56 ± 14% vs. 54 ± 15%; r = 0.89) and between LVEF measured by 64-slice MDCT and SPECT (60 ± 13% and 60 ± 14%, respectively; r = 0.90). Conclusion The assessment of LVEF and LV dimensions with 64-slice MDCT provide values which are similar to those obtained by echocardiography and Tc-99m gated SPECT. The accuracy of the 64-slice MDCT with a gantry rotation speed of 330 ms (when compared to ECHO and SPECT) may be superior to that of the 16-slice MDCT at 420 ms gantry rotation.

Comprehensive cardiac CT study: Evaluation of coronary arteries, left ventricular function, and myocardial perfusion—Is it possible?

With advances in multidetector computed tomography (MDCT) technology, the new generation of 64-slice MDCT scanners with submillimeter collimation and a faster gantry rotation allows imaging of the entire heart in a single breath-hold with excellent temporal and spatial resolution. This potentially permits a comprehensive assessment of coronary anatomy, left ventricular function, and myocardial perfusion. As will be seen in this review of the current literature regarding 16- and 64-slice MDCT, there is great promise for a comprehensive cardiac computed tomography (CT) study. The available data support the notion that CT coronary angiography may be an alternative to invasive coronary angiography in symptomatic patients with a low to intermediate likelihood of having coronary artery disease. By use of the same data acquired for CT coronary angiography, evaluation of global and regional left ventricular function and myocardial perfusion can be added to the MDCT evaluation without additional exposure to contrast medium or radiation and may provide a more conclusive cardiac workup in these patients. The potential applications and limitations of coronary stenosis detection, global and regional left ventricular function, and myocardial perfusion assessment by MDCT will be reviewed. The full potential of cardiac MDCT is just beginning to be realized.

Assessment of Coronary Artery Disease by Cardiac Computed Tomography

This scientific statement reviews the scientific data for cardiac computed tomography (CT) related to imaging of coronary artery disease (CAD) and atherosclerosis. Cardiac CT is a CT imaging technique that accounts for cardiac motion, typically through the use of ECG gating. The utility and limitations of generations of cardiac CT systems are reviewed in this statement with emphasis on CT measurement of CAD and coronary artery calcified plaque (CACP) and noncalcified plaque. Successive generations of CT technology have been applied to cardiac imaging beginning in the early 1980s with conventional CT, electron beam CT (EBCT) in 1987, and multidetector CT (MDCT) in 1999. Compared with other imaging modalities, cardiac CT has undergone an accelerated …

Four-Dimensional Imaging of the Heart Based on Near-Isotropic MDCT Data Sets

Lawler LP, Ney D, Pannu HK, Fishman EK our-dimensional cardiac CT is a concept in evolution [1, 2]. In this paper, we define 4D cardiac CT as a processed study that assimilates a series of sequential, static, phase-specific, 3D volume helical data sets into a cine image that reflects the in vivo model of the 3D spatial information mapped to the sequential time and motion relationship of the cardiac cycle. It can be applied to derive morphologic and functional information, but it is distinct from existing tools, which deduce such information from static planar slices of end systole and end diastole alone. This technique will form an important facet of the comprehensive cardiac CT study. The initial relatively high-speed acquisition of electron beam CT (EBCT) [3] provided some of the earliest quantitative CT information on ventricular size and shape and on systolic function. However, this complex technology was never widely available, was limited to prospective gating, and is fast being replaced by the the more versatile mechanical CT where its acquisition parameters in terms of temporal resolution are rapidly approaching those of EBCT. Earlier work with single-detector helical scanning was able to produce animated 2D images of the heart with ventricular values that closely correlated with conventional ventriculography [4]. Materials and Methods Data Acquisition and Processing To generate a 4D data set, one must first acquire a density profile and positional information that characterize each voxel of the heart structure for a series of time points throughout the cardiac systolic and diastolic phases. The patient is scanned in a single breath-hold with simultaneous recording of the ECG signal. Current helical MDCT systems provide near-isotropic voxels from 0.75-mm detector systems (Sensation, Siemens Medical Solutions) giving 0.75to 1-mm slice collimation reconstructed at 50% overlap. Large detector arrays, fast gantry rotation, and segmental reconstruction contribute to a TR of 120–130 msec. Vascular lumen, endocardial surface, and chamber contrast resolution is achieved through a peripheral-venous upper-extremity power injection of 120 mL of nonionic iodinated contrast (Visipaque 320, Amersham Health) delivered at a rate of 3 mL/sec followed by a saline flush from a dual-head injector. Scanning acquisition begins 17 sec after the contrast administration. Unlike coronary CT angiography, which uses only diastolic data, 4D CT utilizes all data derived from irradiating the patient. Effective dose depends on heart rate but is approximately 7.0 mSv for a man and 10.2 mSv for a woman, with a CT dose index of 42.0 mGy. Axial planar data for 3D and 4D postprocessing are reconstructed from the raw data using retrospective gating, which defines a portion of the cardiac cycle as a percentage of the R-R interval. For 4D imaging, a contiguous sequence of nine or more separate “whole-heart” volumes, of equal duration intervals, is generated. These volumes represent the distinct phases (i.e., “time windows”) of cardiac motion (e.g., 10%, 20%, 30%, and so forth up to 90% of the R-R interval). This is a semiautomatic standard process of all cardiac software and is performed at the scanner. The user simply defines the percentage reconstruction desired, and the result is a series of separate stacks of axial images with each stack representing a particular period of the cardiac cycle. Within each time window, all voxels of the heart are represented. The total number of images may be more than 2,000 images, depending on the slice reconstruction used (0.75–1 mm). The data are sent to a 3D workstation that incorporates commercially available volume-rendering software and supports a work-in-progress version of 4D software.

Radiation dose in multidetector row computed tomography cardiac imaging.

Multidetector row computed tomography (MDCT) with its markedly improved temporal and spatial resolution has opened up a new opportunity in cardiac CT imaging. MDCT scanners are increasingly available and have become the preferred CT scanners for the entire spectrum of clinical CT examinations. As a consequence, the number of cardiac CT studies is continuously growing. Because cardiac CT studies involve considerable radiation doses, it is compelling for us to understand the radiation dose estimates associated with cardiac CT imaging. In this article, we review the concepts of radiation dose measurement in CT, discuss MDCT scan parameters affecting radiation exposure, and provide a reference summary of radiation dose estimates associated with MDCT cardiac imaging.

A knowledge-based cone-beam x-ray CT algorithm for dynamic volumetric cardiac imaging.

With the introduction of spiral/helical multislice CT, medical x-ray CT began a transition into cone-beam geometry. The higher speed, thinner slice, and wider coverage with multislice/cone-beam CT indicate a great potential for dynamic volumetric imaging, with cardiac CT studies being the primary example. Existing ECG-gated cardiac CT algorithms have achieved encouraging results, but they do not utilize any time-varying anatomical information of the heart, and need major improvements to meet critical clinical needs. In this paper, we develop a knowledge-based spiral/helical multislice/cone-beam CT approach for dynamic volumetric cardiac imaging. This approach assumes the relationship between the cardiac status and the ECG signal, such as the volume of the left ventricle as a function of the cardiac phase. Our knowledge-based cardiac CT algorithm is evaluated in numerical simulation and patient studies. In the patient studies, the cardiac status is estimated initially from ECG data and subsequently refined with reconstructed images. Our results demonstrate significant image quality improvements in cardiac CT studies, giving clearly better clarity of the chamber boundaries and vascular structures. In conclusion, this approach seems promising for practical cardiac CT screening and diagnosis.