Advances in cardiac imaging with 16-section CT systems

Computed Tomography Angiography: Principles and Advances

This review describes current state-of-the-art computed tomography technology required to address human-physiology-based challenges unique to angiographic imaging. Challenges are based on the need to image a bolus of contrast agent traversing inside rapidly moving structures. This article reviews the latest methods to optimize contrast timing and minimize motion.

Challenges in Utilizing CT Coronary Angiography and CT Calcium Scoring to Determine Aeromedical Fitness for Aicrew: A Tale of 3 CTs

The management of coronary artery disease (CAD) in aviators remains as one of the dominant preoccupation in determining vocational fitness. With the emerging awareness and accessibility of non-invasive modalities for assessing CAD, there is an increasing likelihood that aircrew may have undergone some form of functional or anatomic assessment of the coronary circulation, prior to their presentation to the aviation medical examination office. In particular, computer tomographic coronary angiography (CTCA) and CT coronary artery calcium scoring (CACS) had gained significant traction in recent years, as novel scanning algorithms had enabled faster, safer and more affordable imaging. However, the utilization of CTCA and CACS are not without challenges. Against this backdrop, this paper presents three clinical vignettes of aviators who presented to our cardiac department for specialist evaluation and the eventual aeromedical dispositions. The paper also discusses the evolving opportunities and issues in the application of CTCA and CACS findings to aeromedical risk assessment in aviators.

The challenge of asymptomatic coronary artery disease in aircrew; detecting plaque before the accident

Coronary events remain a major cause of sudden incapacitation, including death, in both the general population and among aviation personnel, and are an ongoing threat to flight safety and operations. The presentation is often unheralded, especially in younger adults, and is often due to rupture of a previously non-obstructive coronary atheromatous plaque. The challenge for aeromedical practitioners is to identify individuals at increased risk for such events. This paper presents the NATO Cardiology Working Group (HFM 251) consensus approach for screening and investigation of aircrew for asymptomatic coronary disease.A three-phased approach to coronary artery disease (CAD) risk assessment is recommended, beginning with initial risk-stratification using a population-appropriate risk calculator and resting ECG. For aircrew identified as being at increased risk, enhanced screening is recommended by means of Coronary Artery Calcium Score alone or combined with a CT coronary angiography investigation. Additional screening may include exercise testing, and vascular ultrasound imaging. Aircrew identified as being at high risk based on enhanced screening require secondary investigations, which may include functional ischaemia, and potentially invasive coronary angiography. Functional stress testing as a stand-alone investigation for significant CAD is not recommended in aircrew. Aircrew identified with coronary disease require further clinical and aeromedical evaluation before being reconsidered for flying status.

Image Quality and Radiation Exposure Comparison of a Double High-Pitch Acquisition for Coronary Computed Tomography Angiography Versus Standard Retrospective Spiral Acquisition in Patients With Atrial Fibrillation

OBJECTIVE

The aim of this study was to compare image quality and radiation dose of coronary computed tomography (CT) angiography performed with dual-source CT scanner using 2 different protocols in patients with atrial fibrillation.

METHODS

Forty-seven patients with AF underwent 2 different acquisition protocols: double high-pitch (DHP) spiral acquisition and retrospective spiral acquisition. The image quality was ranked according to a qualitative score by 2 experts: 1, no evident motion; 2, minimal motion not influencing coronary artery luminal evaluation; and 3, motion with impaired luminal evaluation. A third expert solved any disagreement.

RESULTS

A total of 732 segments were evaluated. The DHP group (24 patients, 374 segments) showed more segments classified as score 1 than the retrospective spiral acquisition group (71.3% vs 37.4%). Image quality evaluation agreement was high between observers (κ = 0.8). There was significantly lower radiation exposure for the DHP group (3.65 [1.29] vs 23.57 [10.32] mSv).

CONCLUSIONS

In this original direct comparison, a DHP spiral protocol for coronary CT angiography acquisition in patients with atrial fibrillation resulted in lower radiation exposure and superior image quality compared with conventional spiral retrospective acquisition.

Selecting a CT scanner for cardiac imaging: the heart of the matter

Coronary angiography to assess the presence and degree of arterial stenosis is an examination now routinely performed on CT scanners. Although developments in CT technology over recent years have made great strides in improving the diagnostic accuracy of this technique, patients with certain characteristics can still be "difficult to image". The various groups will benefit from different technological enhancements depending on the type of challenge they present. Good temporal and spatial resolution, wide longitudinal (z-axis) detector coverage and high X-ray output are the key requirements of a successful CT coronary angiography (CTCA) scan. The requirement for optimal patient dose is a given. The different scanner models recommended for CTCA all excel in different aspects. The specification data presented here for these scanners and the explanation of the impact of the different features should help in making a more informed decision when selecting a scanner for CTCA.

Stenosis map for volume visualization of constricted tubular structures: Application to coronary artery stenosis

Although direct volume rendering (DVR) has become a commodity, effective rendering of interesting features is still a challenge. In one of active DVR application fields, the medicine, radiologists have used DVR for the diagnosis of lesions or diseases that should be visualized distinguishably from other surrounding anatomical structures. One of most frequent and important radiologic tasks is the detection of lesions, usually constrictions, in complex tubular structures. In this paper, we propose a 3D spatial field for the effective visualization of constricted tubular structures, called as a stenosis map which stores the degree of constriction at each voxel. Constrictions within tubular structures are quantified by using newly proposed measures (i.e. line similarity measure and constriction measure) based on the localized structure analysis, and classified with a proposed transfer function mapping the degree of constriction to color and opacity. We show the application results of our method to the visualization of coronary artery stenoses. We present performance evaluations using twenty eight clinical datasets, demonstrating high accuracy and efficacy of our proposed method. The ability of our method to saliently visualize the constrictions within tubular structures and interactively adjust the visual appearance of the constrictions proves to deliver a substantial aid in radiologic practice.

Multidetector-row CT: cardiosurgery indications

This article critically evaluates the role of multidetector-row CT before and after cardiosurgical procedures. In addition, technical aspects, such as scan protocols, optimal image reconstruction intervals, image reformation techniques, and data evaluation, are presented and briefly discussed.

Radiation dose and physical image quality in 128-section dual-source computed tomographic coronary angiography: a phantom study

One‐hundred‐and‐twenty‐eight–section dual X‐ray source computed tomography (CT) systems have been introduced into clinical practice and have been shown to increase temporal resolution. Higher temporal resolution allows low‐dose spiral mode at a high pitch factor during CT coronary angiography. We evaluated radiation dose and physical image qualities in CT coronary angiography by applying high‐pitch spiral, step‐and‐shoot, and low‐pitch spiral modes to determine the optimal acquisition mode for clinical situations. An anthropomorphic phantom, small dosimeters, a calibration phantom, and a microdisc phantom were used to evaluate the radiation doses absorbed by thoracic organs, noise power spectrums, in‐plane and z‐axis modulation transfer functions, slice sensitivity profiles, and number of artifacts for the three acquisition modes. The high‐pitch spiral mode had the advantage of a small absorbed radiation dose, but provided low image quality. The low‐pitch spiral mode resulted in a high absorbed radiation dose of approximately 200 mGy for the heart. Although the absorbed radiation dose was lower in the step‐and‐shoot mode than in the low‐pitch spiral mode, the noise power spectrum was inferior. The quality of the in‐plane modulation transfer function differed, depending on spatial frequency. Therefore, the step‐and‐shoot mode should be applied initially because of its low absorbed radiation dose and superior image quality.

PACS numbers: 87.57.‐s; 87.57.C‐; 87.57.cf; 87.57.cm; 87.57.cp; 87.57.Q‐; 87.57.qp; 87.57.uq

Low-dose coronary-CT angiography using step and shoot at any heart rate: comparison of image quality at systole for high heart rate and diastole for low heart rate with a 128-slice dual-source machine

To compare image quality of coronary CT angiography in step-and-shoot mode at the diastolic phase at low heart rates (<70 bpm) and systolic phase at high heart rates (≥70 bpm). We prospectively included 96 consecutive patients then excluded 5 patients with arrhythmia. Coronary CT-angiography was performed using a dual-source 128-slice CT machine, at the diastolic phase in the 55 patients with heart rates <70 bpm (group D) and at the systolic phase in the 36 patients with heart rates ≥70 (group S). Image quality was scored on a 5 point-scale (1, not interpretable; 2, insufficient for diagnosis; 3, fair, sufficient for diagnosis; 4, good; 5, excellent). In addition, we compared the number of stair-step artifacts in the two groups. Mean image quality score was 4 (0.78) in group D and 4.1 (0.34) in group S (NS), with an unequal distribution (p = 0.01). Step artifacts were seen in 44 % of group D and 18 % of group S patients (p = 0.02). In 3 group D patients and no group S patients, the image score was <3 due to artifacts, requiring repeat CT-angiography. When performing dual-source 128-slice CT-angiography, step-and-shoot acquisition provides comparable mean image quality in systole, with less variability and fewer stair-step artifacts, compared to diastole. This method may be feasible at any heart rate in most patients in sinus rhythm, allowing low-dose prospective acquisition without beta-blocker premedication.

The Role of Multidetector CT in the Diagnosis of Retroperitoneal Fibrosis: Report of a Case

Herein, we report a 40-year old man who presented with flank and abdominal pain with dilatation of the bilateral pyelocalyceal system detected in ultrasonography. Computed Tomography (CT) scan showed a soft tissue mass at the level of the fourth and fifth lumbar vertebrae in the retroperitoneal region. There were no blood flow signals in 64-slice multidetector CT (MDCT) which confirms the Retroperitoneal Fibrosis (RPF). Pathological examination showed infiltration of plasma cells, macrophages, lymphocytes and eosinophils accompanied by fibrosis, which is consistent with idiopathic RPF. In conclusion, 64-slice MDCT imaging is useful in the diagnosis of RPF.

Coronary CT angiography: current status and continuing challenges

Coronary CT angiography has been increasingly used in the diagnosis of coronary artery disease owing to rapid technological developments, which are reflected in the improved spatial and temporal resolution of the images. High diagnostic accuracy has been achieved with multislice CT scanners (64 slice and higher), and in selected patients coronary CT angiography is regarded as a reliable alternative to invasive coronary angiography. With high-quality coronary CT imaging increasingly being performed, patients can benefit from an imaging modality that provides a rapid and accurate diagnosis while avoiding an invasive procedure. Despite the tremendous contributions of coronary CT angiography to cardiac imaging, study results reported in the literature should be interpreted with caution as there are some limitations existing within the study design or related to patient risk factors. In addition, some attention must be given to the potential health risks associated with the ionising radiation received during cardiac CT examinations. Radiation dose associated with coronary CT angiography has raised serious concerns in the literature, as the risk of developing malignancy is not negligible. Various dose-saving strategies have been implemented, with some of the strategies resulting in significant dose reduction. The aim of this review is to present an overview of the role of coronary CT angiography on cardiac imaging, with focus on coronary artery disease in terms of the diagnostic and prognostic value of coronary CT angiography. Various approaches for dose reduction commonly recommended in the literature are discussed. Limitations of coronary CT angiography are identified. Finally, future directions and challenges with the use of coronary CT angiography are highlighted.

Interscan reproducibility of computer-aided epicardial and thoracic fat measurement from noncontrast cardiac CT

BACKGROUND

Epicardial fat volume (EFV) measured from noncontrast CT is associated with coronary atherosclerosis and increased risk of major adverse cardiovascular events. Interscan reproducibility of EFV quantification from noncontrast CT has not been reported.

OBJECTIVE

We evaluated the interscan (intrascanner and interscanner) reproducibility of EFV and thoracic fat volume (TFV) measurements from noncontrast CT.

METHODS

We studied 25 consecutive patients who were scanned twice with 4-slice multidetector CT (MDCT), with 120 kVp, 2.5-mm slice thickness (intrascanner) and 23 consecutive patients who were scanned with MDCT and electron beam CT (EBCT) with 3-mm slice thickness (interscanner). For each scan, EFV and TFV were measured from user-defined range of CT slices covering the heart by experienced imaging cardiologists. Voxels within -30 to -190 HU within the epicardial contours was quantified as EFV. TFV was quantified within the heart range automatically. Repeatability coefficient (RC), defined as 1.96 × SD of the differences between pairs of repeated measures, was determined.

RESULTS

Correlations for interscan measurements of EFV and TFV were high for both intrascanner (MDCT-MDCT) and interscanner (EBCT-MDCT) data (correlation coefficient ≥0.98). RC values were lowest (4.3% for EFV and 5.4% for TFV) for intrascanner same-observer measurement. For intrascanner cross-observer measurement, RC values were 10.7% for EFV and 9.0% for TFV. For interscanner data, RC values ranged from 6.8% to 8.2%.

CONCLUSION

Epicardial and thoracic fat measurements with the use of either MDCT or EBCT are highly reproducible.

Coronary imaging of anomalous origins and aneurysms of the left coronary artery by multislice computed tomography

In this paper, we describe two cases of anomalous origin of the left coronary artery and two cases of aneurysm on the left coronary artery. Detailed three-dimensional images were acquired by the multislice computed tomography (MSCT) SOMATOM Sensation Cardiac 64 during clinical studies of cardiac diseases.

X-ray computed tomography of the heart

INTRODUCTION

Cardiac imaging is an emerging application of multidetector computed tomography (MDCT). This review summarizes the current capabilities, possible applications, limitations and developments of cardiac CT.

SOURCES OF DATA

Relevant publications in peer reviewed literature and national and international guidelines are used to discuss important issues in cardiac CT imaging.

AREAS OF AGREEMENT AND CONTROVERSY

There is broad consensus that coronary CT angiography is indicated in patients with an intermediate pre-test probability of coronary artery disease (CAD) when other non-invasive tests have been equivocal. In this context, CT can reliably exclude significant CAD. Cardiac CT also has an established role in the evaluation of bypass grafts and suspected coronary anomalies. Radiation exposure from CT procedures remains a concern, although techniques are now available to reduce the X-ray dosage without significantly compromising the image quality. However, with the current level of knowledge, the cardiac CT examinations are not justified to screen for CAD in asymptomatic individuals. Neither is it considered appropriate in patients with a high pre-test probability of CAD, for whom invasive catheter coronary angiography is usually of more benefit.

GROWING POINTS AND AREAS TIMELY FOR DEVELOPING RESEARCH

The ability to reconstruct the volumetric cardiac CT data set opens up avenues for advanced physiological analyses of the heart. For example, if CT myocardial perfusion assessment becomes a reality, there is potential to revolutionize the practice of MDCT imaging. Research is also ongoing to investigate whether cardiac CT has a role in the appropriate triage of patients with chest pain in the emergency department.

Coronary artery calcification screening: estimated radiation dose and cancer risk

BACKGROUND

Multidetector computed tomography has been proposed as a tool for routine screening for coronary artery calcification in asymptomatic individuals. As proposed, such screening could involve tens of millions of individuals, but detailed estimates of radiation doses and potential risk of radiation-induced cancer are not currently available. We estimated organ-specific radiation doses and associated cancer risks from coronary artery calcification screening with multidetector computed tomography according to patient age, frequency of screening, and scan protocol.

METHODS

Radiation doses delivered to adult patients were calculated from a range of available protocols using Monte Carlo radiation transport. Radiation risk models, derived using data from Japanese atomic bomb survivors and medically exposed cohorts, were used to estimate the excess lifetime risk of radiation-induced cancer.

RESULTS

The radiation dose from a single coronary artery calcification computed tomographic scan varied more than 10-fold (effective dose range, 0.8-10.5 mSv) depending on the protocol. In general, higher radiation doses were associated with higher x-ray tube current, higher tube potential, spiral scanning with low pitch, and retrospective gating. The wide dose variation also resulted in wide variation in estimated radiation-induced cancer risk. Assuming screening every 5 years from the age of 45 to 75 years for men and 55 to 75 years for women, the estimated excess lifetime cancer risk using the median dose of 2.3 mSv was 42 cases per 100 000 men (range, 14-200 cases) and 62 cases per 100 000 women (range, 21-300 cases).

CONCLUSIONS

These radiation risk estimates can be compared with potential benefits from screening, when such estimates are available. Doses and therefore risks can be minimized by the use of optimized protocols.

Assessment of radiation exposure on a dual-source computed tomography-scanner performing coronary computed tomography-angiography

OBJECTIVE

The radiation exposure of a dual-source-64-channel multi-detector-computed-tomography-scanner (Somatom-Defintion, Siemens, Germany) was assessed in a phantom-study performing coronary-CT-angiography (CTCA) in comparison to patients' data randomly selected from routine scanning.

METHODS

240 CT-acquisitions of a computed tomography dose index (CTDI)-phantom (PTW, Freiburg, Germany) were performed using a synthetically generated Electrocardiography (ECG)-signal with variable heart rates (30-180 beats per minute (bpm)). 120 measurements were acquired using continuous tube-output; 120 measurements were performed using ECG-synchronized tube-modulation. The pulsing window was set at minimum duration at 65% of the cardiac cycle between 30 and 75 bpm. From 90-180 bpm the pulsing window was set at 30-70% of the cardiac cycle. Automated pitch adaptation was always used. A comparison between phantom CTDI and two patient groups' CTDI corresponding to the two pulsing groups was performed.

RESULTS

Without ECG-tube-modulation CDTI-values were affected by heart-rate-changes resulting in 85.7 mGray (mGy) at 30 and 45 bpm, 65.5 mGy/60 bpm, 54.7 mGy/75 bpm, 46.5 mGy/90 bpm, 34.2 mGy/120 bpm, 27.0 mGy/150 bpm and 22.1 mGy/180 bpm equal to effective doses between 14.5 mSievert (mSv) at 30/45 bpm and 3.6 mSv at 180 bpm. Using ECG-tube-modulation these CTDI-values resulted: 32.6 mGy/30 bpm, 36.6 mGy/45 bpm, 31.4 mGy/60 bpm, 26.8 mGy/75 bpm, 23.7 mGy/90 bpm, 19.4 mGy/120 bpm, 17.2 mGy/150 bpm and 15.6 mGy/180 bpm equal to effective doses between 5.5 mSv at 30 bpm and 2.6 mSv at 180 bpm. Significant CTDI-differences were found between patients with lower/moderate and higher heart rates in comparison to the phantom CTDI-results.

CONCLUSIONS

Dual source CTCA is particularly dose efficient at high heart rates when automated pitch adaptation, especially in combination with ECG-based tube-modulation is used. However in clinical routine scanning for patients with higher heart rates and corresponding enlarged pulsing window a significant different dose resulted.

Knowledge-based dynamic volumetric cardiac computed tomography with saddle curve trajectory

Motion artifact is still a major issue in cardiac computed tomography because the current motion correction and electrocardiogram gating techniques have not fully addressed this problem. The image quality can be significantly improved by using information about the actual state of the heart and an exact reconstruction algorithm. We propose to extend a cardiac computed tomographic technique, using the knowledge of the volume and the relation between the state and the phase of the heart, to a saddle curve trajectory. This will optimize the image quality by reducing the artifacts resulting from approximate reconstruction and solve the long-object problem. Necessary background is provided, and the effectiveness of the algorithms is demonstrated in numerical simulations with the dynamic thorax phantom.

Radiation exposure in cardiac multislice spiral computed tomography (MSCT)

Computed tomographic (CT) imaging involves exposure to ionizing radiation, with a consequent potential risk to the patient. Here we review the technical factors that affect the radiation dose in cardiac CT diagnostic procedures, the parameters that are used to measure and compare radiation doses, the magnitude of radiation exposure, and how to efficiently reduce it.

Imaging of the heart with computed tomography

Imaging of the heart with computed tomography (CT) was already introduced in the 1980Is and has meanwhile entered clinical routine as a consequence of the rapid evolution of CT technology during the last decade. In this review article, we give an overview on the technology and clinical performance of different CT-scanner generations used for cardiac imaging, such as Electron Beam CT (EBCT), single-slice CT und multi-detector row CT (MDCT) with 4, 16 and 64 simultaneously acquired slices. We identify the limitations of current CT-scanners, indicate potential of improvement and discuss alternative system concepts such as CT with area detectors and dual source CT (DSCT).

Maximizing dose reductions with cardiac CT

Multidetector computed tomography has come a long way in a short time, quickly becoming a standard tool in the cardiac imaging armamentarium. The promise of plaque imaging, combined with both anatomical visualization and stenosis detection, has made this a preferred first line test of many cardiologists and radiologists. This test is well suited to rule out coronary artery disease (obstruction) and still diagnosing subclinical plaque, with may be a good target for anti-atherosclerotic therapies. There has been recent criticism against CT imaging, and cardiac CT specifically, due to the high radiation doses that being employed. New advances have allowed for dramatic dose reductions. These include more routinely performed methods such as dose modulation, and newer methods such as prospective gating or minimizing the field of view. This paper will review the different applications to reduce cardiac CT radiation doses to nominal levels, potentially expanding the applications of cardiac CT by removing one of the biggest barriers.

Accuracy and reproducibility of assessing right ventricular function with 64-section multi-detector row CT: comparison with magnetic resonance imaging

BACKGROUND

Right ventricular (RV) function is very important for those patients with respiratory and cardiovascular disorders that can result in RV impairments. Because of complex geometry of the chamber, it is difficult to accurately measure the RV volumetric parameters with conventional imaging modalities. The purpose of this study was to evaluate whether the 64-MDCT can assess RV function with high accuracy and reproducibility when compared to the results with those of MRI.

METHODS

Forty-seven consecutive subjects underwent retrospectively ECG-gated 64-MDCT and MRI for assessing the ventricular function. Right ventricular end diastolic and end-systolic volume, stroke volume, and ejection fraction were measured with dedicated cardiac analysis software on 64-MDCT and compared with values measured on MRI which served as the reference standard. Agreement between two modalities was assessed with Bland and Altman analysis and linear regression analysis. Repeated measurements were performed to determine intraobserver and interobserver variability.

RESULTS

No significant differences were revealed in calculated RV volumes and EF between the two modalities. Agreement and correlation were similar for RV-EDV (0.4 ± 8.2 ml; r=0.95), RV-ESV (-0.6 ± 4.8; r=0.95), RV-SV (1.1 ± 6.7 ml; r=0.93), and RV-EF (0.9 ± 4.4; r=0.88). The difference of SV of right and left ventricle with 64-MDCT was not statistically significant (p=0.40) and good correlation was obtained (r=0.96). The variability in 64-MDCT measurements was lower than those in MRI.

CONCLUSIONS

ECG-gated 64-MDCT can assess the RV function with high accuracy and reproducibility without geometric assumptions about right ventricle.

Dose reduction and image quality assessment in 64-detector row computed tomography of the coronary arteries using an automatic exposure control system

OBJECTIVE

To evaluate dose reduction and image quality in coronary 64-slice multidetector computed tomography using an automatic exposure control system (AECs).

METHODS

A total of 101 patients were divided into 4 groups. Tube current was 600 and 800 mAs in groups A and B and adapted at 600 and 800 quality-reference mAs using an AECs in groups C and D. Effective dose and organ-equivalent dose were evaluated. Image noise was quantified as standard deviation of air-space attenuation. Two observers assessed technical adequacy and image quality using a 4-point scale.

RESULTS

Effective dose ranged from 8.6 mSv (group C) to 15 mSv (group B) with significant dose reduction for examinations performed at 600 mAs (21.7%) and 800 mAs (29.4%). Contribution of organ-equivalent doses showed higher exposure for lungs (42%) and breast (22%). Noise was significantly higher in groups studied with AECs. Larger coronary segments resulted in higher image quality scores without differences between groups.

CONCLUSION

Automatic exposure control systems provides images of diagnostic quality with substantial dose reduction.

Feature-based characterization of motion-contaminated calcified plaques in cardiac multidetector CT

In coronary calcium scoring, motion artifacts affecting calcified plaques are commonly characterized using descriptive terms, which incorporate an element of subjectivity in their interpretations. Quantitative indices may improve the objective characterization of these motion artifacts. In this paper, an automated method for generating 12 quantitative indices, i.e., features that characterize the motion artifacts affecting calcified plaques, is presented. This method consists of using the rapid phase-correlated region-of-interest (ROI) tracking algorithm for reconstructing ROI images of calcified plaques automatically from the projection data obtained during a cardiac scan, and applying methods for extracting features from these images. The 12 features include two dynamic, six morphological, and four intensity-based features. The two dynamic features are three-dimensional (3D) velocity and 3D acceleration. The six morphological features include edge-based volume, threshold-based volume, sphericity, irregularity, average margin gradient, and variance of margin gradient. The four intensity-based features are maximum intensity, mean intensity, minimum intensity, and standard deviation of intensity. The 12 features were extracted from 54 reconstructed sets of simulated four-dimensional images from the dynamic NCAT phantom involving six calcified plaques under nine heart rate/multi-sector gating combinations. In order to determine how well the 12 features correlated with a plaque motion index, which was derived from the trajectory of the plaque, partial correlation coefficients adjusted for heart rate, number of gated sectors, and mean feature values of the six plaques were calculated for all 12 features. Features exhibiting stronger correlations ([r] epsilon [0.60,1.00]) with the motion index were 3D velocity, maximum intensity, and standard deviation of intensity. Features demonstrating stronger correlations ([r] epsilon [0.60, 1.00]) with other features mostly involved intensity-based features. Edge-based volume/irregularity and average margin gradient/variance of margin gradient were the only two feature pairs out of 12 with stronger correlations that did not involve intensity-based features. Automatically extracted features of the motion artifacts affecting calcified plaques in cardiac computed tomography images potentially can be used to develop models for predicting image assessability with respect to motion artifacts.

Erectile dysfunction and silent coronary artery disease: abnormal computed tomography coronary angiogram in the presence of normal exercise ECGs

BACKGROUND

Erectile dysfunction (ED) and coronary artery disease (CAD) frequently coexist. ED may be present in the absence of cardiac symptoms 3-5 years before a coronary event. Exercise electrocardiography may identify flow-limiting CAD but cardiac computed tomography (CT) may identify early non-calcified plaque disease potentially vulnerable to rupture precipitating an acute event.

METHODS

Twenty men aged 39-69 years with ED and no cardiac symptoms underwent screening for cardiovascular risk including maximal treadmill exercise testing and CT coronary angiography. ED was confirmed using the Sexual Health Inventory for Men questionnaire.

FINDINGS

Eighteen had a low-density lipoprotein cholesterol > 3 mmol/l, none were diabetic and seven were hypertensive controlled on medical therapy. Coronary calcium scores were > 50 in 11 men (range: 54-1234) all of whom had angiographic CAD on CT. Nine of these had normal exercise ECGs. Four men had calcium scores of 6-17 and single plaque disease on CT. Five had normal cardiac CT studies.

INTERPRETATION

Erectile dysfunction may be a predictor of subclinical non-flow limiting CAD not detectable on exercise electrocardiography. Men with organic ED and no cardiac symptoms should be considered as 'cardiac equivalents' and aggressive risk reduction therapy initiated.

Radiation dose exposure in multislice computed tomography of the coronaries in comparison with conventional coronary angiography

BACKGROUND

Radiation dose exposure is increased in multislice spiral computed tomography (MSCT) compared to conventional coronary angiography (CXA).

METHODS

Retrospective data analysis of 56 patients (66+/-8 years, 49 males, body surface area 1.98+/-0.18 m(2), heart rate 64+/-11 bpm) who underwent MSCT and CXA was performed (MSCT: 16-slice scanner, rotation time 0.375 s, 120 kV, ECG-pulsing; CXA: current technique system build in 2003). Ten patients with bypass grafts underwent bypass angiography in CXA and MSCT. To compare the radiation doses of both investigations, the effective dose (ED) was chosen as the analysis variable.

RESULTS

The mean ED for MSCT was 9.76+/-1.84 mSv (n=46) for patients without bypass grafts; with calcium scoring the mean ED was 12.46+/-2.23 mSv (n=46). In comparison, the mean ED of CXA was 2.60+/-1.27 mSv (n=46) for patients without bypass grafts; with bypass grafts (n=10) the mean ED for MSCT was 12.95+/-1.75 mSv, for CXA of 6.27+/-4.04 mSv, respectively. In MSCT heart rates of <or=60 bpm resulted in lower mean ED than heart rates of >60 bpm (8.86+/-1.24 mSv versus 10.53+/-1.86 mSv).

CONCLUSIONS

MSCT is still associated with a higher radiation dose exposure than CXA. The radiation dose relation is more favorable for MSCT than for CXA in patients with bypass grafts in comparison to patients without bypass grafts. This study emphasizes the importance of dose reduction techniques.

Image quality and artifacts in coronary CT angiography with dual-source CT: initial clinical experience

INTRODUCTION

We aimed to characterize artifacts observed in a routine clinical coronary CT angiography (CCTA) performed by a dual-source CT (DSCT) scanner (Definition; Siemens Medical Solutions).

METHODS

Studies of 167 consecutive patients referred for CCTA, performed after beta-blockade (if not contraindicated), were prospectively analyzed for artifacts with a predefined visual approach. American Heart Association coronary segments (n = 2589) were assessed in 40%-80% R-R interval phases by 2 experts for stenosis, plaque presence or composition, and presence or type of artifacts. Each segment was considered evaluable when image quality was diagnostic in at least one cardiac phase. Artifacts included motion (cardiac, respiratory, patient), phase misregistration because of varying heart beats, calcified plaque blooming or beam hardening, metal beam hardening, large patient size, and contrast timing error.

RESULTS

Maximum HR (HR) during CCTA ranged from 45 to 120 beats/min (66.4 +/- 14.8 beats/min). Artifacts of some type were observed in 69 (41.3%) of 167 studies. Calcified plaque was the most common source of artifacts (14.4%), followed by misregistration (13.8%). Only 25 (1%) of 2589 coronary segments, in 6 (4%) of 167 patients were unevaluable, primarily because of calcified plaque blooming (coronary calcium score [CCS], 1112 +/- 1255]. Artifacts were associated with CCS (P = 0.002), change in HR (P = 0.01), age (P = 0.03), and body mass index (P = 0.048). The optimal phase for evaluation of all coronary arteries was 70% (mid-diastole), with a shift toward the systolic phases for HR > 70 beats/min.

CONCLUSION

CCTA artifacts with DSCT were related primarily to calcified plaque and cardiac phase misregistration. When correctly recognized, the artifacts did not have a serious effect on the final interpretation.

Prospectively gated transverse coronary CT angiography versus retrospectively gated helical technique: improved image quality and reduced radiation dose

PURPOSE

To retrospectively compare image quality, radiation dose, and blood vessel assessability for coronary artery computed tomographic (CT) angiograms obtained with a prospectively gated transverse (PGT) CT technique and a retrospectively gated helical (RGH) CT technique.

MATERIALS AND METHODS

This HIPAA-compliant study received a waiver for approval from the institutional review board, including one for informed consent. Coronary CT angiograms obtained with 64-detector row CT were retrospectively evaluated in 203 clinical patients. A routine RGH technique was evaluated in 82 consecutive patients (44 males, 38 females; mean age, 55.6 years). The PGT technique was then evaluated in 121 additional patients (71 males, 50 females; mean age, 56.7 years). All images were evaluated for image quality, estimated radiation dose, and coronary artery segment assessability. Differences in image quality score were evaluated by using a proportional odds logistic regression model, with main effects for three readers, two techniques, and four arteries.

RESULTS

The mean effective dose for the group with the PGT technique was 2.8 mSv; this represents an 83% reduction as compared with that for the group with the RGH technique (mean, 18.4 mSv; P < .001). The image quality score for each of the arteries, as well as the overall combined score, was significantly greater for images obtained with PGT technique than for images obtained with RGH technique. The combined mean image quality score was 4.791 for images obtained with PGT technique versus 4.514 for images obtained with RGH technique (proportional odds model odds ratio, 2.8; 95% confidence interval: 1.7, 4.8). The percentage of assessable coronary artery segments was 98.6% (1196 of 1213) for images obtained with PGT technique versus 97.9% (1741 of 1778) for images obtained with RGH technique (P = .83).

CONCLUSION

PGT coronary CT angiography offers improved image quality and substantially reduced effective radiation dose compared with traditional RGH coronary CT angiography.

Coronary calcium scanning in geriatric cardiology

Coronary artery disease (CAD) is prevalent in the elderly, often leads to disability, and is the number one cause of death in this population. Older adults represent an increasingly important and challenging subset of the population with CAD. They are more likely to have comorbid conditions, atypical presentations, and unfavorable outcomes than their younger counterparts. The available data suggest that standard pharmacologic, thrombolytic, and definitive revascularization techniques have important roles in the treatment of geriatric patients but have been underutilized. Consequently, strategies for optimizing the prevention and treatment of CAD in the elderly are important from both the individual and societal perspectives. Coronary artery calcium has been shown to be highly specific for atherosclerosis, occurring only in the intima of the coronary arteries. There is evidence to show that elevated coronary calcium scores are predictive of future cardiovascular events, both independently of and incrementally to conventional cardiovascular risk factors. This article will review such a screening method, namely coronary calcium scanning, in the field of geriatric cardiology.

Coronary CT Angiography

Owing to ongoing technical refinements and intense scientific and clinical evaluations, computed tomography (CT) of the heart has left the research realm and matured into a clinical application that is about to fulfill its promise to replace invasive cardiac catheterization in selected patient populations. CT coronary angiography is technically more challenging than other CT applications owing to the nature of its target, the continuously moving heart. Rapid technical developments in this field require constant adaptation of acquisition protocols. These challenges, however, are in no way insurmountable for users with knowledge of the general CT technique. The intent of this communication is to provide those interested in and involved with coronary CT angiography with a step-by-step "manual" describing the authors' approach to performing coronary CT angiography. Included are considerations regarding appropriate patient selection, patient medication, radiation protection, contrast enhancement, acquisition and reconstruction parameters, image display and analysis techniques, and the radiology report. The recommendations are based on the authors' experience, which spans the evolution of multi-detector row CT for cardiac applications, from its beginning to the advent of the most current generations of 64-section and dual-source CT technologies, which they believe herald the entrance of this examination into routine clinical practice.

Pediatric Cardiac-Gated CT Angiography: Assessment of Radiation Dose

OBJECTIVE

The purpose of our study was to determine a dose range for cardiac-gated CT angiography (CTA) in children.

MATERIALS AND METHODS

ECG-gated cardiac CTA simulating scanning of the heart was performed on an anthropomorphic phantom of a 5-year-old child on a 16-MDCT scanner using variable parameters (small field of view; 16 x 0.625 mm configuration; 0.5-second gantry cycle time; 0.275 pitch; 120 kVp at 110, 220, and 330 mA; and 80 kVp at 385 mA). Metal oxide semiconductor field effect transistor (MOSFET) technology measured 20 organ doses. Effective dose calculated using the dose-length product (DLP) was compared with effective dose determined from measured absorbed organ doses.

RESULTS

Highest organ doses included breast (3.5-12.6 cGy), lung (3.3-12.1 cGy), and bone marrow (1.7-7.6 cGy). The 80 kVp/385 mA examination produced lower radiation doses to all organs than the 120 kVp/220 mA examination. MOSFET effective doses (+/- SD) were as follows: 110 mA: 7.4 mSv (+/- 0.6 mSv), 220 mA: 17.2 mSv (+/- 0.3 mSv), 330 mA: 25.7 mSv (+/- 0.3 mSv), 80 kVp/385 mA: 10.6 mSv (+/- 0.2 mSv). DLP effective doses for diagnostic runs were as follows: 110 mA: 8.7 mSv, 220 mA: 19 mSv, 330 mA: 28 mSv, 80 kVp/385 mA: 12 mSv. DLP effective doses exceeded MOSFET effective doses by 9.7-17.2%.

CONCLUSION

Radiation doses for a 5-year-old during cardiac-gated CTA vary greatly depending on parameters. Organ doses can be high; the effective dose may reach 28.4 mSv. Further work, including determination of size-appropriate mA and image quality, is important before routine use of this technique in children.

Dose Performance of a 64-Channel Dual-Source CT Scanner1

PURPOSE

To prospectively compare the dose performance of a 64-channel multi-detector row computed tomographic (CT) scanner and a 64-channel dual-source CT scanner from the same manufacturer.

MATERIALS AND METHODS

To minimize dose in the cardiac (dual-source) mode, the evaluated dual-source CT system uses a cardiac beam-shaping filter, three-dimensional adaptive noise reduction, heart rate-dependent pitch, and electrocardiographically based modulation of the tube current. Weighted CT dose index per 100 mAs was measured for the head, body, and cardiac beam-shaping filters. Kerma-length product was measured in the spiral cardiac mode at four pitch values and three electrocardiographic modulation temporal windows. Noise was measured in an anthropomorphic phantom. Data were compared with data from a 64-channel multi-detector row CT scanner.

RESULTS

For the multi-detector row and dual-source CT systems, respectively, weighted CT dose index per 100 mAs was 14.2 and 12.2 mGy (head CT), 6.8 and 6.4 mGy (body CT), and 6.8 and 5.3 mGy (cardiac CT). In the spiral cardiac mode (no electrocardiographically based tube current modulation, 0.2 pitch), equivalent noise occurred at volume CT dose index values of 23.7 and 35.0 mGy (coronary artery calcium CT) and 58.9 and 61.2 mGy (coronary CT angiography) for multi-detector row CT and dual-source CT, respectively. The use of heart rate-dependent pitch values reduced volume CT dose index to 46.2 mGy (0.265 pitch), 34.0 mGy (0.36 pitch), and 26.6 mGy (0.46 pitch) compared with 61.2 mGy for 0.2 pitch. The use of electrocardiographically based tube current-modulation and temporal windows of 110, 210, and 310 msec further reduced volume CT dose index to 9.1-25.1 mGy, dependent on the heart rate.

CONCLUSION

For electrocardiographically gated coronary CT angiography, image noise equivalent to that of multi-detector row CT can be achieved with dual-source CT at doses comparable to or up to a factor of two lower than the doses at multi-detector row CT, depending on heart rate of the patient.

Does two-segment image reconstruction at 64-section CT coronary angiography improve image quality and diagnostic accuracy?

PURPOSE

To prospectively evaluate the effect of single- versus two-segment image reconstruction on image quality and diagnostic accuracy at 64-section multidetector computed tomographic (CT) coronary angiography by using conventional coronary angiography as the reference standard.

MATERIALS AND METHODS

The study design was approved by a human research committee; patients gave informed consent. The study was HIPAA compliant. Forty consecutive patients (22 men, 18 women; mean age, 61 years +/- 8 [standard deviation]) underwent both 64-section multidetector CT coronary angiography and conventional angiography. All data sets were reconstructed by using single- and two-segment image reconstruction algorithms, with resulting temporal resolution of 82.5-165 msec. Two experienced observers independently evaluated image quality and signs of coronary artery disease. A five-level grading scheme was used to grade stenosis (0%, <50%, <70%, <99%, 100%) and image quality (1[unacceptable] to 5[excellent]). Interobserver correlation, Spearman correlation coefficients, and diagnostic accuracy were calculated.

RESULTS

Six hundred coronary artery segments were visible on conventional angiograms, of which 560 (93.3%) were seen by using single-segment and 561 (93.5%) were seen by using two-segment image reconstruction (P=.35). Mean quality scores were not significantly different (P=.22) for single- (3.1 +/- 0.9) and two-segment (3.2 +/- 0.8) reconstruction. Significantly (P=.03) better image quality was observed for two-segment reconstruction only at heart rates of 80-82 beats per minute, at which temporal resolution was approximately 83 msec. For grading coronary artery stenosis, correlation was 0.64 for single- and 0.66 for two-segment reconstruction (P=.43). Significant stenosis (>50%) was detected on a per-segment basis with 77.1% sensitivity and 98.6% specificity by using single-segment and with 79.2% sensitivity and 99.1% specificity by using two-segment image reconstruction.

CONCLUSION

At heart rates of more than 65 beats per minute, use of two-segment reconstruction improves image quality at multidetector CT coronary angiography but does not significantly affect overall diagnostic accuracy compared with single-segment reconstruction.