XML Template (2014) [8.3.2014–7:22am] //blrnas3/cenpro/ApplicationFiles/Journals/SAGE/3B2/ACRJ/Vol00000/140041/APPFile/SG-ACRJ140041.3d
(ACR)
[1–6] [PREPRINTER stage]
Acta Radiol OnlineFirst, published on March 10, 2014 as doi:10.1177/0284185114527867
Original Article
Monoenergetic extrapolation of cardiac dual energy CT for artifact reduction
Acta Radiologica 0(0) 1–6 ! The Foundation Acta Radiologica 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0284185114527867 acr.sagepub.com
Francesco Secchi1,2, Carlo Nicola De Cecco1,3, James Vance Spearman1, Justin Robert Silverman1, Ullrich Ebersberger1,4, Francesco Sardanelli2,5 and U Joseph Schoepf1
Abstract 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.
Keywords Dual energy CT (DECT), artifact, monoenergetic extrapolation Date received: 21 June 2013; accepted: 23 February 2014
Introduction A dual-energy computed tomography (DECT) postprocessing method was developed in the 1980s to reduce beam-hardening artifacts in CT image 1
Department of Radiology and Radiological Science, Medical University of South Carolina, Charleston, SC, USA 2 IRCCS Policlinico San Donato, Radiology Unit, San Donato Milanese, Italy 3 Department of Radiological Sciences, Oncology and Pathology, University of Rome ‘‘Sapienza’’ – Polo Pontino, Latina, Italy
reconstructions (1,2). However, this DECT technique has not been widely implemented in the clinical setting 4
Department of Cardiology and Intensive Care Medicine, Heart Center Munich-Bogenhausen, Munich, Germany 5 Universita` degli Studi di Milano, Dipartimento di Scienze Biomediche per la Salute, Milano, Italy Corresponding author: Francesco Secchi, Radiology Unit, IRCCS Policlinico San Donato, Piazza Malan 2, San Donato Milanese, Italy. Email: [email protected]
Downloaded from acr.sagepub.com at MCMASTER UNIV LIBRARY on January 5, 2015
XML Template (2014) [8.3.2014–7:22am] //blrnas3/cenpro/ApplicationFiles/Journals/SAGE/3B2/ACRJ/Vol00000/140041/APPFile/SG-ACRJ140041.3d
(ACR)
[1–6] [PREPRINTER stage]
2
Acta Radiologica 0(0)
because it can confer reduced spatial resolution, unstable CT attenuation, and insufficient tube current at low tube voltages (3). DECT is a long-recognized technology with clinical applications arising from its ability to provide materialspecific and energy-specific information (3,4). These applications include but are not limited to analysis of renal stone composition, detection and quantification of tissue lipid and iron content, and optimization of enhancement with iodine-based contrast materials (5– 9). In dual-energy techniques, X-ray sources are operated at two different tube potentials, generating photons at two different energy levels. Characteristic changes in attenuation over the range of photon energies allow differentiation of materials with different atomic numbers. Few experiences in cardiac DECT have been published (10–14) and, to our knowledge, none has investigated the reduction of artifacts from metallic hardware or high iodine contrast concentration in cardiac CT. The purpose of our investigation was to evaluate the potential of monoenergetic extrapolation of cardiac DECT data for reducing artifacts from metal and high iodine contrast concentration.
Material and Methods Patients Our Institutional Review Board approved the study. The study was conducted in HIPAA compliance. Image data of 35 symptomatic, consecutive patients with suspected CAD who had been referred for dualsource CT-based cardiac DECT were analyzed. Patients with a contraindication to iodinated and/or beta-blocking drugs and with a compromised renal function defined as creatinine of 1.2 mg/dL were excluded. Among the 35 patients, 13 were women and 22 were men. The mean age was 61 12 years and the mean body mass index (BMI) was 31 9 kg/m2. All demographic data of our population are shown in Table 1.
CT protocol All examinations were performed on a second generation dual-source CT system (Somatom Definition Flash; Siemens Medical Solutions, Forchheim, Germany). DECT scan was performed after scout with the following parameters: tube voltages, 100 kVp and 140 kVp; gantry rotation time, 280 ms; collimation, 0.6 mm; reconstructed section width, 0.75 mm; and reconstruction increment, 0.3 mm. All 35 patients were scanned using commercially available automated anatomical tube current modulation software (CAREDose4D, Siemens Medical Solutions).
Table 1. Demographic data of study population. Age (years) Height (cm) Weight (kg) BMI (kg/m2) Diabetes (n) Dyslipidemia (n) Smoke (n) Family history of CAD (n)
61 12 166 18 84 17 31 9 12 30 20 23
Age, height, weight, and BMI values are expressed as mean standard deviation. BMI, body mass index; CAD, coronary artery disease.
Electrocardiography (ECG)-synchronization was used. Scan protocols used retrospective ECG gating in cases of irregular heart rate, heart rates >80 bpm, or when functional assessment was desired. Otherwise, prospective ECG triggering was used with scan acquisition during diastole (70% RR) for slower heart rates (10 mm2 around the artifact and/or not allowing the distinction of artifact from blood pool; a score of 1 was defined as submassive artifacts, producing an image alteration in an area of 5 mm2 around the artifact and/or partially inhibiting the distinction of artifact from blood pool; a
Downloaded from acr.sagepub.com at MCMASTER UNIV LIBRARY on January 5, 2015
XML Template (2014) [8.3.2014–7:22am] //blrnas3/cenpro/ApplicationFiles/Journals/SAGE/3B2/ACRJ/Vol00000/140041/APPFile/SG-ACRJ140041.3d
(ACR)
[1–6] [PREPRINTER stage]
Secchi et al.
3
Fig. 1. Artifact arising from densely concentrated contrast material in the superior vena cava at different keV: (a) 40, (b) 60, (c) 80, (d) 100, and (e) 120. For all images, window level was 200 and width 600.
Fig. 2. Artifact arising from sternal wires and bypass clips at different keV: (a) 40, (b) 60, (c) 80, (d) 100, and (e) 120. For all images, window level was 200 and width 600.
score of 2 as moderate artifacts producing an image alteration in an area
(ACR)
[1–6] [PREPRINTER stage]
Acta Radiol OnlineFirst, published on March 10, 2014 as doi:10.1177/0284185114527867
Original Article
Monoenergetic extrapolation of cardiac dual energy CT for artifact reduction
Acta Radiologica 0(0) 1–6 ! The Foundation Acta Radiologica 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0284185114527867 acr.sagepub.com
Francesco Secchi1,2, Carlo Nicola De Cecco1,3, James Vance Spearman1, Justin Robert Silverman1, Ullrich Ebersberger1,4, Francesco Sardanelli2,5 and U Joseph Schoepf1
Abstract 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.
Keywords Dual energy CT (DECT), artifact, monoenergetic extrapolation Date received: 21 June 2013; accepted: 23 February 2014
Introduction A dual-energy computed tomography (DECT) postprocessing method was developed in the 1980s to reduce beam-hardening artifacts in CT image 1
Department of Radiology and Radiological Science, Medical University of South Carolina, Charleston, SC, USA 2 IRCCS Policlinico San Donato, Radiology Unit, San Donato Milanese, Italy 3 Department of Radiological Sciences, Oncology and Pathology, University of Rome ‘‘Sapienza’’ – Polo Pontino, Latina, Italy
reconstructions (1,2). However, this DECT technique has not been widely implemented in the clinical setting 4
Department of Cardiology and Intensive Care Medicine, Heart Center Munich-Bogenhausen, Munich, Germany 5 Universita` degli Studi di Milano, Dipartimento di Scienze Biomediche per la Salute, Milano, Italy Corresponding author: Francesco Secchi, Radiology Unit, IRCCS Policlinico San Donato, Piazza Malan 2, San Donato Milanese, Italy. Email: [email protected]
Downloaded from acr.sagepub.com at MCMASTER UNIV LIBRARY on January 5, 2015
XML Template (2014) [8.3.2014–7:22am] //blrnas3/cenpro/ApplicationFiles/Journals/SAGE/3B2/ACRJ/Vol00000/140041/APPFile/SG-ACRJ140041.3d
(ACR)
[1–6] [PREPRINTER stage]
2
Acta Radiologica 0(0)
because it can confer reduced spatial resolution, unstable CT attenuation, and insufficient tube current at low tube voltages (3). DECT is a long-recognized technology with clinical applications arising from its ability to provide materialspecific and energy-specific information (3,4). These applications include but are not limited to analysis of renal stone composition, detection and quantification of tissue lipid and iron content, and optimization of enhancement with iodine-based contrast materials (5– 9). In dual-energy techniques, X-ray sources are operated at two different tube potentials, generating photons at two different energy levels. Characteristic changes in attenuation over the range of photon energies allow differentiation of materials with different atomic numbers. Few experiences in cardiac DECT have been published (10–14) and, to our knowledge, none has investigated the reduction of artifacts from metallic hardware or high iodine contrast concentration in cardiac CT. The purpose of our investigation was to evaluate the potential of monoenergetic extrapolation of cardiac DECT data for reducing artifacts from metal and high iodine contrast concentration.
Material and Methods Patients Our Institutional Review Board approved the study. The study was conducted in HIPAA compliance. Image data of 35 symptomatic, consecutive patients with suspected CAD who had been referred for dualsource CT-based cardiac DECT were analyzed. Patients with a contraindication to iodinated and/or beta-blocking drugs and with a compromised renal function defined as creatinine of 1.2 mg/dL were excluded. Among the 35 patients, 13 were women and 22 were men. The mean age was 61 12 years and the mean body mass index (BMI) was 31 9 kg/m2. All demographic data of our population are shown in Table 1.
CT protocol All examinations were performed on a second generation dual-source CT system (Somatom Definition Flash; Siemens Medical Solutions, Forchheim, Germany). DECT scan was performed after scout with the following parameters: tube voltages, 100 kVp and 140 kVp; gantry rotation time, 280 ms; collimation, 0.6 mm; reconstructed section width, 0.75 mm; and reconstruction increment, 0.3 mm. All 35 patients were scanned using commercially available automated anatomical tube current modulation software (CAREDose4D, Siemens Medical Solutions).
Table 1. Demographic data of study population. Age (years) Height (cm) Weight (kg) BMI (kg/m2) Diabetes (n) Dyslipidemia (n) Smoke (n) Family history of CAD (n)
61 12 166 18 84 17 31 9 12 30 20 23
Age, height, weight, and BMI values are expressed as mean standard deviation. BMI, body mass index; CAD, coronary artery disease.
Electrocardiography (ECG)-synchronization was used. Scan protocols used retrospective ECG gating in cases of irregular heart rate, heart rates >80 bpm, or when functional assessment was desired. Otherwise, prospective ECG triggering was used with scan acquisition during diastole (70% RR) for slower heart rates (10 mm2 around the artifact and/or not allowing the distinction of artifact from blood pool; a score of 1 was defined as submassive artifacts, producing an image alteration in an area of 5 mm2 around the artifact and/or partially inhibiting the distinction of artifact from blood pool; a
Downloaded from acr.sagepub.com at MCMASTER UNIV LIBRARY on January 5, 2015
XML Template (2014) [8.3.2014–7:22am] //blrnas3/cenpro/ApplicationFiles/Journals/SAGE/3B2/ACRJ/Vol00000/140041/APPFile/SG-ACRJ140041.3d
(ACR)
[1–6] [PREPRINTER stage]
Secchi et al.
3
Fig. 1. Artifact arising from densely concentrated contrast material in the superior vena cava at different keV: (a) 40, (b) 60, (c) 80, (d) 100, and (e) 120. For all images, window level was 200 and width 600.
Fig. 2. Artifact arising from sternal wires and bypass clips at different keV: (a) 40, (b) 60, (c) 80, (d) 100, and (e) 120. For all images, window level was 200 and width 600.
score of 2 as moderate artifacts producing an image alteration in an area
