Sandra S. Halliburton

SCCT guidelines on radiation dose and dose-optimization strategies in cardiovascular CT

Over the last few years, computed tomography (CT) has developed into a standard clinical test for a variety of cardiovascular conditions. The emergence of cardiovascular CT during a period of dramatic increase in radiation exposure to the population from medical procedures and heightened concern about the subsequent potential cancer risk has led to intense scrutiny of the radiation burden of this new technique. This has hastened the development and implementation of dose reduction tools and prompted closer monitoring of patient dose. In an effort to aid the cardiovascular CT community in incorporating patient-centered radiation dose optimization and monitoring strategies into standard practice, the Society of Cardiovascular Computed Tomography has produced a guideline document to review available data and provide recommendations regarding interpretation of radiation dose indices and predictors of risk, appropriate use of scanner acquisition modes and settings, development of algorithms for dose optimization, and establishment of procedures for dose monitoring.

Non-invasive assessment of plaque morphology and remodeling in mildly stenotic coronary segments: comparison of 16-slice computed tomography and intravascular ultrasound

BackgroundNon-invasive identification and characterization of mildly stenotic atherosclerotic lesions is an increasingly important focus of coronary imaging. DesignWe examined the accuracy of multi (16)-slice computed tomography (MSCT) for imaging of these lesions in comparison with intravascular ultrasound (IVUS). MaterialsMildly stenotic segments of the left coronary artery were identified by coronary angiography and analyzed using IVUS and contrast-enhanced MSCT. Independent reviewers evaluated the accuracy of MSCT for presence, composition and distribution of atherosclerotic plaque and remodeling response in comparison to IVUS using receiver operating characteristic (ROC) data analysis. ResultsOf 46 segments in 14 patients, diagnostic characterization by MSCT was possible in 37 (80.4%) segments. In these segments the accuracy of MSCT for identifying plaque presence, calcification, distribution and positive remodeling was consistently greater than 0.90 (reader 1) and 0.87 (reader 2). ConclusionState-of-the-art MSCT can accurately identify mildly stenotic coronary atherosclerosis and provide an assessment of morphology and remodeling response.

Pre-Procedural Imaging of Aortic Root Orientation and Dimensions: Comparison Between X-Ray Angiographic Planar Imaging and 3-Dimensional Multidetector Row Computed Tomography

OBJECTIVES We sought to examine whether contrast-enhanced multidetector row computed tomography (MDCT) allows prediction of X-ray angiographic planes for the root angiogram in the context of transcatheter aortic valve implantation. BACKGROUND Understanding of aortic root orientation relative to the body axis is critical for precise positioning of the stent/valve during transcatheter aortic valve implantation. METHODS Forty patients with severe aortic stenosis underwent conventional X-ray angiography and contrast-enhanced MDCT of the aortic root. Oblique MDCT images of the aortic root, corresponding to X-ray angiographic left anterior oblique (LA)/right anterior oblique (RAO) projections, were created. The cranial/caudal angulation was compared between angiographic and reformatted MDCT images. In addition, root diameter measurements were compared. RESULTS The cranial angulation in the LAO X-ray angiograms (mean LAO: 39+/- 8, n = 38) and matched MDCT images were not significantly different (cranial: 25 +/- 7 vs. 23 +/- 8; p = 0.214). There was a small but significant difference between the caudal angulation in the RAO angiogram (mean RAO: 25 +/- 5, n = 40) and matched CT images (caudal: 21 +/- 9 vs. 29 +/- 10; p = 0.002). The annulus diameter in the LAO projection was not significantly different between X-ray angiography and contrast-enhanced MDCT (2.3 +/- 0.3 vs. 2.4 +/- 0.3; p = 0.052), whereas there was a small but significant difference in the annulus diameter in RAO projections between angiography and MDCT (2.4 +/- 0.3 vs. 2.2 +/- 0.3; p = 0.029). CONCLUSIONS Pre-procedural contrast-enhanced MDCT imaging of the aortic root allows prediction of X-ray angiographic planes and contributes to planning of the transcatheter aortic valve implantation.

Prognostic utility of 64-slice computed tomography in patients with suspected but no documented coronary artery disease

AIMS Although multislice computed tomography (MSCT) detects obstructive coronary artery disease (CAD) with high diagnostic accuracy, there is a paucity of long-term prognostic data. We sought to assess the incremental prognostic value of 64-slice CT in patients with suspected but no documented CAD. METHODS AND RESULTS Coronary MSCT was performed on 227 individuals (61% men, mean age 54 +/- 12 years, 63% with intermediate pre-test probability) without documented CAD, referred for coronary evaluation. Coronary artery disease by MSCT was categorized as follows: none or mild CAD (<50%, n = 172), > or =50% in one vessel (n = 23), two vessels [or in the proximal left anterior descending (LAD), n = 12], and three vessels (or in two vessels including the proximal LAD or left main, n = 20). Baseline risk factors, length of follow-up, and major adverse cardiac events (MACE), including cardiac death, myocardial infarction (MI), and coronary revascularization were recorded. Over a mean follow-up of 2.3 +/- 0.8 years, there were 18 MACE [including four hard events (one cardiac death and three MIs)]. Also, patients with one or more vessel obstructive CAD had increased hard events compared with those with less than one-vessel disease (log-rank statistic P-value 0.01). One or more vessel obstructive CAD was a significant predictor of MACE on univariable and multivariable Cox proportional survival analysis [hazard ratios 29.1 (6.7-126.6) and 9.82 (3.58-27.01), respectively, both P < 0.0001]. In 172 patients, with no or mild CAD, there was 99% freedom from MACE during follow-up. CONCLUSION Multislice computed tomography-classified extent of CAD provides incremental prognostic information in patients with suspected but no documented CAD.

Left atrial epicardial adiposity and atrial fibrillation.

Background—Atrial fibrillation (AF) has been linked to inflammatory factors and obesity. Epicardial fat is a source of several inflammatory mediators related to the development of coronary artery disease. We hypothesized that periatrial fat may have a similar role in the development of AF. Methods and Results—Left atrium (LA) epicardial fat pad thickness was measured in consecutive cardiac CT angiograms performed for coronary artery disease or AF. Patients were grouped by AF burden: no (n=73), paroxysmal (n=60), or persistent (n=36) AF. In a short-axis view at the mid LA, periatrial epicardial fat thickness was measured at the esophagus (LA-ESO), main pulmonary artery, and thoracic aorta; retrosternal fat was measured in axial view (right coronary ostium level). LA area was determined in the 4-chamber view. LA-ESO fat was thicker in patients with persistent AF versus paroxysmal AF (P=0.011) or no AF (P=0.003). LA area was larger in patients with persistent AF than paroxysmal AF (P=0.004) or without AF (P<0.001). LA-ESO was a significant predictor of AF burden even after adjusting for age, body mass index, and LA area (odds ratio, 5.30; 95% confidence interval, 1.39 to 20.24; P=0.015). A propensity score–adjusted multivariable logistic regression that included age, body mass index, LA area, and comorbidities was also performed and the relationship remained statistically significant (P=0.008). Conclusions—Increased posterior LA fat thickness appears to be associated with AF burden independent of age, body mass index, or LA area. Further studies are necessary to examine cause and effect, and if inflammatory, paracrine mediators explain this association.

Prevalence of significant peripheral artery disease in patients evaluated for percutaneous aortic valve insertion: Preprocedural assessment with multidetector computed tomography

OBJECTIVES Percutaneous aortic valve insertion is an emerging treatment option for selected patients with severe aortic stenosis and may be done from a transfemoral or transapical approach. Concomitant atherosclerotic peripheral artery disease limits transfemoral access. We evaluated the potential role of multidetector computed tomography in preoperative assessment of vascular anatomy. METHODS Consecutive patients with severe aortic stenosis were included. Contrast-enhanced computed tomographic angiography of the thoracic and abdominal aorta and iliofemoral arteries was performed. Criteria of unfavorable iliofemoral anatomy were defined as a minimal luminal diameter of the common iliac, external iliac, or common femoral arteries of less than 8 mm, presence of greater than 60% circumferential calcification at the external-internal iliac bifurcation, and severe angulation between the common and external iliac arteries (< 90 degrees ). The prevalence of these criteria was evaluated and infrarenal aortic and iliofemoral arterial anatomy was compared in the groups with and without peripheral artery disease for any of these criteria. RESULTS One hundred patients (79 +/- 9 years, 59% male) were included. A total of 35 (35%) patients had at least one criterion of unsuitable iliofemoral anatomy, including 27 patients with small minimal luminal diameter (<8 mm), 12 patients with severe circumferential calcification at the iliac bifurcation (>60%), and 4 with severe angulation of the iliac arteries (<90 degrees ). CONCLUSIONS Significant atherosclerotic peripheral artery disease is common in the high-risk patient population currently evaluated for percutaneous aortic valve insertion. Computed tomography allows identification of patients with iliofemoral anatomy unfavorable for the transfemoral approach to percutaneous aortic valve insertion.

Aortic root morphology in patients undergoing percutaneous aortic valve replacement: Evidence of aortic root remodeling

OBJECTIVE Percutaneous aortic valve replacement is an emerging therapy for selected patients with severe aortic stenosis. Preoperative imaging of the aortic root facilitates sizing and deployment of the percutaneous aortic valve replacement device. We compared morphologic characteristics of the aortic root in patients with aortic stenosis versus elderly gender-matched controls using multidetector computed tomography. METHODS Twenty-five consecutive subjects with severe calcific aortic stenosis referred for percutaneous aortic valve replacement and 25 elderly gender-matched controls were scanned on a Siemens Definition Dual Source (Siemens Medical, Forchheim, Germany) multidetector computed tomography scanner. Distances from the valve annulus to the coronary artery ostia and sinotubular junction, dimensions of the aortic root, and characteristics of the valve cusps were determined. RESULTS Subjects with aortic stenosis had reduced distance from the aortic valve annulus to the inferior margins of the left and right coronary artery ostium and sinotubular junction compared with controls. There were no significant differences in cross-sectional dimensions of the aortic root. CONCLUSION The distance from the aortic valve annulus to the coronary artery ostia and sinotubular junction is reduced in patients with aortic stenosis compared with controls. This finding suggests that longitudinal remodeling of the aortic root occurs in calcific aortic stenosis and has implications for the design and deployment of percutaneous aortic valve replacement devices.

Coronary artery calcium screening: current status and recommendations from the European Society of Cardiac Radiology and North American Society for Cardiovascular Imaging

Current guidelines and literature on screening for coronary artery calcium for cardiac risk assessment are reviewed for both general and special populations. It is shown that for both general and special populations a zero score excludes most clinically relevant coronary artery disease. The importance of standardization of coronary artery calcium measurements by multi-detector CT is discussed.

Patient-Centered Imaging: Shared Decision Making for Cardiac Imaging Procedures With Exposure to Ionizing Radiation

The current paper details the recommendations arising from an NIH-NHLBI/NCI-sponsored symposium held in November 2012, aiming to identify key components of a radiation accountability framework fostering patient-centered imaging and shared decision-making in cardiac imaging. Symposium participants, working in 3 tracks, identified key components of a framework to target critical radiation safety issues for the patient, the laboratory, and the larger population of patients with known or suspected cardiovascular disease. The use of ionizing radiation during an imaging procedure should be disclosed to all patients by the ordering provider at the time of ordering, and reinforced by the performing provider team. An imaging protocol with effective dose ≤3 mSv is considered very low risk, not warranting extensive discussion or written informed consent. However, a protocol effective dose >20 mSv was proposed as a level requiring particular attention in terms of shared decision-making and either formal discussion or written informed consent. Laboratory reporting of radiation dosimetry is a critical component of creating a quality laboratory fostering a patient-centered environment with transparent procedural methodology. Efforts should be directed to avoiding testing involving radiation, in patients with inappropriate indications. Standardized reporting and diagnostic reference levels for computed tomography and nuclear cardiology are important for the goal of public reporting of laboratory radiation dose levels in conjunction with diagnostic performance. The development of cardiac imaging technologies revolutionized cardiology practice by allowing routine, noninvasive assessment of myocardial perfusion and anatomy. It is now incumbent upon the imaging community to create an accountability framework to safely drive appropriate imaging utilization.

Potential of dual-energy computed tomography to characterize atherosclerotic plaque: ex vivo assessment of human coronary arteries in comparison to histology

BACKGROUND Noninvasive characterization of coronary atherosclerotic plaque is limited with current computed tomography (CT) techniques. Dual-energy CT (DECT) has the potential to provide additional attenuation data for better differentiation of plaque components. OBJECTIVE We attempted to characterize coronary atherosclerotic plaque with DECT. METHODS Seven human coronary arteries acquired at autopsy were scanned consecutively at 80 and 140 kVp with CT. Vessels were perfused with saline, and data were acquired before and after contrast agent injection. Lesions were identified, and attenuation measurements were made from CT image quadrants. CT quadrants were classified as densely calcified, fibrocalcific, fibrous, lipid-rich, or normal vessel wall, corresponding to matched histology images. Attenuation values at each peak tube voltage were compared within plaque types for both noncontrast and contrast scans. Further, dual-energy index (DEI) values computed from attenuation were analyzed for classification of plaque. RESULTS In 14 lesions, a total of 56 quadrants were identified. Histology results classified 8 (14%) as densely calcified, 8 (14%) as fibrocalcific, 9 (16%) as fibrous, 5 (9%) as lipid-rich, and 25 (45%) as normal vessel wall. Calcified lesions attenuated significantly more at 80 kVp in both contrast and noncontrast scans, whereas fibrous plaque attenuated more at 80 kVp only for contrast-enhanced scans. No differences were found for lipid-rich plaques. Using DEI values, only densely calcified plaques could be distinguished from other plaque types except fibrocalcific plaques in contrast images. CONCLUSIONS Only densely calcified and fibrocalcific plaques showed a true change in attenuation at 80 versus 140 kVp. Therefore, calcified plaques could be distinguished from noncalcified plaques with DECT, but further classification of plaque types was not possible.