James V. Spearman

Monoenergetic extrapolation of cardiac dual energy CT for artifact reduction

Background Monoenergetic extrapolation of cardiac dual-energy computed tomography (DECT) could be useful in artifact reduction in clinical practice. Purpose To evaluate the potential of monoenergetic extrapolation of cardiac DECT data for reducing artifacts from metal and high iodine contrast concentration. Material and Methods With IRB approval and in HIPAA compliance, 35 patients (22 men, 61 ± 12 years) underwent cardiac DECT with dual-source CT (100 kVp and 140 kVp). Contrast material injection protocols were adapted to the patient’s weight using non-ionic low-osmolar 370 mgI/mL iopromide. Datasets were transferred to a stand-alone workstation and dedicated monoenergetic analysis software was used for postprocessing. Reconstructions with the following five photon energies were generated: 40 keV, 60 keV, 80 keV, 100 keV, and 120 keV. Artifact severity was graded on a 5-point Likert scale (0, massive artifact; 5, absence of artifact). The size of artifact and image noise (expressed as HU) in anatomic structures adjacent to the artifact were measured. Quantitative and subjective image quality was compared using Friedman and Wilcoxon tests. Results We observed artifacts arising from densely concentrated contrast material in the superior vena cava (SVC) in 18 patients, from sternal wires in 14, from bypass clips in eight, and from coronary artery stents in seven. Artifact size in monoenergetic reconstructions from 40 to 120 keV decreased from 21.3 to 19 mm for the SVC (P < 0.001), from 8.4 to 2.6 mm for sternal wires (P < 0.001), from 6.4 to 2.2 mm for bypass clips (P < 0.001), and from 5.9 to 2.7 mm for stents (P < 0.001), respectively. The quality score changed from 0.2 to 3.8 for the SVC (P < 0.001), from 0.1 to 4 for sternal wires (P < 0.001), from 0 to 3.9 for bypass clips (P < 0.001), and from 0 to 3.9 for stents (P < 0.001). Lowest noise in adjacent structures was found at 80 keV for the SVC (39.1 HU), for sternal wires (33.3), for bypass clips (26.9), and for stents (33.9). Conclusion A significant reduction of high-attenuation artifacts can be achieved by use of higher monoenergetic energy levels with cardiac DECT. However, image noise in anatomic structures affected by artifacts is lowest at 80 keV, which suggests an evaluation approach that makes use of multiple energy levels for a complete diagnosis.

High-pitch coronary CT angiography at 70 kVp with low contrast medium volume: comparison of 80 and 100 kVp high-pitch protocols.

AbstractThe purpose of this article is to evaluate image quality and radiation dose of prospectively electrocardiogram (ECG)-triggered high-pitch coronary computed tomography angiography (CCTA) at 70 kVp and 30 mL contrast medium.One hundred fifty patients with a heart rate ⩽70 beats per minute (bpm) underwent CCTA using a second-generation dual-source computed tomography (CT) scanner and were randomized into 3 groups according to tube voltage and contrast medium volume (370 mg/mL iodine concentration) (100 kVp group, 100 kVp/60 mL, n = 55; 80 kVp group, 80 kVp/60 mL, n = 44; 70 kVp group, 70 kVp/30 mL, n = 51). Objective and subjective image quality along with the effect of heart rate (HR) and body mass index (BMI) was evaluated and compared between the groups. Radiation dose was estimated for each patient.CT attenuation and image noise were higher in the 80 and 70 kVp groups than in the 100 kVp group (all P < 0.001). Signal-to-noise ratios (SNRs) and contrast-to-noise ratios (CNRs) were lower in the 70 kVp group than in the 80 and 100 kVp groups (all P < 0.05). There was no difference for subjective image quality between the groups (P > 0.05). HR did not affect subjective image quality (all P > 0.05), while patients with BMI <23 kg/m2 had higher image quality than patients with BMI ≥23 kg/m2 (P < 0.05). Compared with the 100 kVp group, the radiation dose of the 70 kVp group was reduced by 75%.In conclusion, prospectively ECG-triggered high-pitch 70 kVp/30 mL CCTA can obtain diagnostic image quality with lower radiation dose in selected patients with BMI <23 kg/m2 compared with 80/100 kVp/60 mL CCTA.

Is Contrast Medium Osmolality a Causal Factor for Contrast-Induced Nephropathy?

The exact pathophysiology of contrast-induced nephropathy (CIN) is not fully clarified, yet the osmotic characteristics of contrast media (CM) have been a significant focus in many investigations of CIN. Osmotic effects of CM specific to the kidney include transient decreases in blood flow, filtration fraction, and glomerular filtration rate. Potentially significant secondary effects include an osmotically induced diuresis with a concomitant dehydrating effect. Clinical experiences that have compared the occurrence of CIN between the various classes of CM based on osmolality have suggested a much less than anticipated advantage, if any, with a lower osmolality. Recent animal experiments actually suggest that induction of a mild osmotic diuresis in association with iso-osmolar agents tends to offset potentially deleterious renal effects of high viscosity-mediated intratubular CM stagnation.

Effect of Automated Attenuation-based Tube Voltage Selection on Radiation Dose at CT: An Observational Study on a Global Scale

PURPOSE To evaluate the effect of automated tube voltage selection (ATVS) on radiation dose at computed tomography (CT) worldwide encompassing all body regions and types of CT examinations. MATERIALS AND METHODS No patient information was accessed; therefore, institutional review board approval was not sought. Data from 86 centers across the world were analyzed. All CT interactions were automatically collected and transmitted to the CT vendor during two 6-week periods immediately before and 2 weeks after implementation of ATVS. A total of 164 323 unique CT studies were analyzed. Studies were categorized by body region and type of examination. Tube voltage and volume CT dose index (CTDIvol) were compared between examinations performed with ATVS and those performed before ATVS implementation. Descriptive statistical methods and multilevel linear regression models were used for analysis. RESULTS Across all types of CT examinations and body regions, CTDIvol was 14.7% lower in examinations performed with ATVS (n = 30 313) than in those performed before ATVS implementation (n = 79 275). Relative reductions in mean CTDIvol were most notable for temporal bone CT (-56.1%), peripheral runoff CT angiography (-48.6%), CT of the paranasal sinus (-39.6%), cerebral or carotid CT angiography (-36.4%), coronary CT angiography (-25.1%), and head CT (-23.9%). An increase in mean CTDIvol was observed for renal stone protocols (26.2%) and thoracic or lumbar spine examinations (6.6%). In the multilevel model with fixed effects ATVS and examination type, and the interaction of these variables and the random effect country, a significant influence on CTDIvol for all fixed efects was revealed (ATVS, P = .0031; examination type, P < .0001; interaction term, P < .0001). CONCLUSION ATVS significantly reduces radiation dose across most, but not all, body regions and types of CT examinations.

Ultralow-Radiation-Dose Chest CT: Accuracy for Lung Densitometry and Emphysema Detection

OBJECTIVE The purpose of this study was to determine whether ultralow-radiation-dose chest CT can be used for quantification of lung density and for emphysema detection in participants undergoing lung cancer screening. SUBJECTS AND METHODS Fifty-two patients were prospectively enrolled and underwent scanning twice with low-dose CT (reference parameters, 120 kV, 50 effective mAs) and ultralow-dose CT (reference parameters, 80 kV, 4-5 effective mAs). Images were reconstructed by filtered back projection (FBP) for low-dose CT and FBP and iterative reconstruction (IR) for ultralow-dose CT. Radiation dose was recorded. Image noise, mean lung attenuation, 15th percentile of lung attenuation, and emphysema index were measured in each image series and compared. Test characteristics of ultralow-dose CT in detecting more than subtle emphysema (emphysema index≥3%) were calculated. RESULTS The effective dose of low-dose CT was 2.1±0.5 mSv, and that of ultralow-dose CT was 0.13±0.04 mSv. Compared with the findings for low-dose CT, absolute overestimation of emphysema index was 7% on ultralow-dose CT images reconstructed with FBP and 2% on those processed with IR. The 15th percentile of lung attenuation was underestimated by 21.3 HU on ultralow-dose FBP images and by 5.8 HU on IR images. No relevant bias was observed for mean lung attenuation. Four patients (8%) had more than subtle emphysema. The emphysema index measured at ultralow-dose CT with FBP and IR had 100% and 100% sensitivity and 92% and 96% specificity in identifying patients with more than subtle emphysema at a cutoff of greater than 12.1% for FBP and greater than 6.7% for IR. CONCLUSION Ultralow-dose chest CT performed for lung cancer screening can be used for quantification of lung density and for emphysema detection. IR improves the accuracy of ultralow-dose CT in this setting.

Image quality and radiation dose of lower extremity CT angiography at 70 kVp on an integrated circuit detector dual-source computed tomography

Background Despite the well-established requirement for radiation dose reduction there are few studies examining the potential for lower extremity CT angiography (CTA) at 70 kVp. Purpose To compare the image quality and radiation dose of lower extremity CTA at 70 kVp using a dual-source CT system with an integrated circuit detector to similar studies at 120 kVp. Material and Methods A total of 62 patients underwent lower extremity CTA. Thirty-one patients were examined at 70 kVp using a second generation dual-source CT with an integrated circuit detector (70 kVp group) and 31 patients were evaluated at 120 kVp using a first generation dual-source CT (120 kVp group). The attenuation and image noise were measured and signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. Two radiologists assessed image quality. Radiation dose was compared. Results The mean attenuation of the 70 kVp group was higher than the 120 kVp group (575 ± 149 Hounsfield units [HU] vs. 258 ± 38 HU, respectively, P < 0.001) as was SNR (44.0 ± 22.0 vs 32.7 ± 13.3, respectively, P = 0.017), CNR (39.7 ± 20.6 vs 26.6 ± 11.7, respectively, P = 0.003) and the mean image quality score (3.7 ± 0.1 vs. 3.2 ± 0.3, respectively, P < 0.001). The inter-observer agreement was good for the 70 kVp group and moderate for the 120 kVp group. The dose-length product was lower in the 70 kVp group (264.5 ± 63.1 mGy × cm vs. 412.4 ± 81.5 mGy × cm, P < 0.001). Conclusion Lower extremity CTA at 70 kVp allows for lower radiation dose with higher SNR, CNR, and image quality when compared with standard 120 kVp.

Transient Ischemic Dilation of the Left Ventricle on SPECT: Correlation with Findings at Coronary CT Angiography

Transient ischemic dilation (TID) in the setting of abnormal stress–rest cardiac SPECT myocardial perfusion imaging (MPI) has been linked with increased cardiovascular risk. However, the significance of TID in the setting of an otherwise normal SPECT MPI study has not been clearly established. In this study, cardiac CT was used to evaluate the prevalence of atherosclerotic lesions and the severity of coronary artery stenosis in patients with TID of the left ventricle with or without associated myocardial perfusion defects on SPECT MPI. Methods: The study population consisted of 1,553 consecutive patients who had undergone both cardiac CT and SPECT MPI within 1 mo between January 1, 2006, and September 1, 2011. Patients included in the study group had a pathologic TID value defined as ≥1.18 for men and ≥1.22 for women. Coronary CT angiography was used to evaluate each coronary segment for the presence and composition of atherosclerotic plaque and the degree of coronary stenosis. TID-positive patients were compared with a 2:1 risk-factor-matched-pair control cohort without TID. Results: TID was identified in 30 patients who were compared with TID-negative risk-factor-matched controls (n = 60). When compared with the TID-negative control cohort, TID-positive patients had no significant differences in the presence and extent of atherosclerosis, the degree of coronary artery stenosis, or the calcium score at cardiac CT. Similarly, there were no significant differences in these CT measures in TID-positive patients with a normal perfusion study (n = 20) when compared with TID-negative patients with a normal perfusion study (n = 48). In addition, there was no significant difference in the incidence of major adverse cardiac events when comparing both the TID-positive patients and the TID-negative control cohort and when comparing patients who were TID-positive with normal perfusion with patients who were TID-negative with normal perfusion. Conclusion: The presence of TID with an otherwise normal SPECT MPI study does not translate into a greater extent of coronary artery disease as assessed by cardiac CT or increased risk for future major adverse cardiac events.

Cardiac CT for myocardial ischaemia detection and characterization—comparative analysis

The assessment of patients presenting with symptoms of myocardial ischaemia remains one of the most common and challenging clinical scenarios faced by physicians. Current imaging modalities are capable of three-dimensional, functional and anatomical views of the heart and as such offer a unique contribution to understanding and managing the pathology involved. Evidence has accumulated that visual anatomical coronary evaluation does not adequately predict haemodynamic relevance and should be complemented by physiological evaluation, highlighting the importance of functional assessment. Technical advances in CT technology over the past decade have progressively moved cardiac CT imaging into the clinical workflow. In addition to anatomical evaluation, cardiac CT is capable of providing myocardial perfusion parameters. A variety of CT techniques can be used to assess the myocardial perfusion. The single energy first-pass CT and dual energy first-pass CT allow static assessment of myocardial blood pool. Dynamic cardiac CT imaging allows quantification of myocardial perfusion through time-resolved attenuation data. CT-based myocardial perfusion imaging (MPI) is showing promising diagnostic accuracy compared with the current reference modalities. The aim of this review is to present currently available myocardial perfusion techniques with a focus on CT imaging in light of recent clinical investigations. This article provides a comprehensive overview of currently available CT approaches of static and dynamic MPI and presents the results of corresponding clinical trials.

Influence of technical parameters on epicardial fat volume quantification at cardiac CT.

OBJECTIVES To systematically analyze the influence of technical parameters on quantification of epicardial fat volume (EATV) at cardiac CT. METHODS 153 routine cardiac CT data sets were analyzed using three-dimensional pericardial border delineation. Three image series were reconstructed per patient: (a) CTAD: coronary CT angiography (CTA), diastolic phase; (b) CTAS: coronary CTA, systolic phase; (c) CaScD: non-contrast CT, diastolic phase. EATV was calculated using three different upper thresholds (-15HU, -30 HU, -45HU). Repeated measures ANOVA, Spearmans rho, and Bland Altman plots were used. RESULTS Mean EATV differed between all three image series at a -30HU threshold (CTAD 87.2 ± 38.5 ml, CTAS 90.9 ± 37.7 ml, CaScD 130.7 ± 49.5 ml, P<0.001). EATV of diastolic and systolic CTA reconstructions did not differ significantly (P=0.225). Mean EATV for contrast enhanced CTA at a -15HU threshold (CTAD15 102.4 ± 43.6 ml, CTAS15 105.3 ± 42.3 ml) could be approximated most closely by non-contrast CT at -45HU threshold (CaScD45 105.3 ± 40.8 ml). The correlation was excellent: CTAS15-CTAD15, rho=0.943; CTAD15-CaScD45, rho=0.905; CTAS15-CaScD45, rho=0.924; each P<0.001). Bias values from Bland Altman Analysis were: CTAS15-CTAD15, 4.9%; CTAD15-CaScD45, -4.3%; CTAS15-CaScD45, 0.6%. CONCLUSIONS Measured EATV can differ substantially between contrast enhanced and non-contrast CT studies, which can be reconciled by threshold modification. Heart cycle phase does not significantly influence EATV measurements.

Giant Left Ventricular Pseudoaneurysm as a Complication After Mitral Valve Replacement Surgery

57-year-oldwomanpresentedwith seizure, exertional Ashortness of breath (New York Heart Association Class III) and angina-like chest pain. Her cardiac history revealed successful bioprostheticmitral valve replacement for endocarditis 1 year prior. Chest radiography detected a 9-cm mass overlying the left hilum with an incomplete right border (Fig 1A, arrows). On transthoracic echocardiography, there was a communication from the posterior mitral valve annulus with an apparent left ventricular (LV) pseudoaneurysm (PSA) measuring approximately 51 52 mm (Fig 1B). Visualized valves showed thickening of the mitral valve leaflets with adjacent high-density