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52: Dose Reduction Strategies for CT Cardiac Imaging
3rd Annual Scientific Meeting
S19
Introduction: Atrial fibrillation (AF) is the most common arrhythmia encountered in clinical practice and has been independently associated with increased mortality. The relationship between AF and coronary artery disease (CAD) has been inconsistently defined. Coronary artery calcification (CAC) identified on cardiac computed tomography (cardiac CT) has been found to be a sensitive, though not specific, marker for CAD. To our knowledge, there h ave been no studies published that examine the relationship between AF and CAD as assessed by 64-Slice Multi-Detector Computed Tom ography (MDCT). Methods: We retrospectively evaluated the 64-Slice MDCT examinations of 30 patients with a known history of non-valvular AF (AF group) who underwent imaging to define the pulmonary vein anatomy prior to planned pulmonary vein isolation and AF ablation. We then compared them with 30 patients without a known history of AF (SR group) who had a 64-Slice MDCT to assess for the presence of obstructive CAD. Both groups were determined serially based on the date of their 64-Slice MDCT. Patients with a prior history of clinically significant CAD or angina were excluded. All 64-Slice MDCTs were reviewed for the presence or absence of CAC as a marker for CAD. Our criteria for estimating the severity of CAC was the following: mild = very small amount of non-obstructive disease in one or two vessels; moderate = small amount of non-obstructive disease in three vessels, intermediate amount of non-obstructive disease in two vessels, or large amount of non-obstructive disease in one vessel; severe = intermediate amount of non-obstructive disease in three vessels, large amount of disease in two or more vessels, or any obstructive lesions. Results: CAC was detected in 46.7% of patients with AF but only 36.7% of patients without AF (p=0.153), suggesting a trend towards a significant association between AF and CAD (Figure 1). Furthermore, patients with AF and CAC were also more likely to have disease categorized as moderate or severe, 26.7% versus 13.3% (p=0.167). Conclusions: The prevalence of CAD in patients with non-valvular AF appears to be more common than previously thought based on our assessment of CAC identified on 64-Slice MDCT. Addi tional investigation with a larger patient population and more objective measurement of CAC (i.e., volume of calcium) is warranted to further define this relationship. Figure 1: Presence of Coronary Artery Calcification
p = 0.153 50 40
AF group
Percentage of 30 Patients 20
SR group
10 0 Coronary Artery Calcification
51 Meave A, Kimura E, Meléndez G, Castillo F, Es pinola N, Lamothe PA, Alexanderson E. Assessment of Ventricular Non Compaction: A Compara tive Study of Cardiac Computed Tomography, Cardiac Magne tic Resonance and Echocardiography Instituto Nacional de Cardiología Ignacio Chávez, Mexico City, Mexico Introduction: Left ventricular non-compaction (LVNC) is characterized by the presence of an extensive non-compacted myocardial layer of the cavity of the left ventricle (LV). LVNC is thou ght to result from a failure of trabecular regression that occurs during normal embryonic development. Major clinical complications are cardiac failure, thromboembolism, and malignant arrhythmias. On the basis of echocardiographic studies, its prevalence has been estimated at 0.05% in the general population. Although the diagnosis of LVNC is usually made using echocardiography, recently cardiac magnetic resonance (CMR) imaging definition was done. There is not a cardiac computed tomography (CCT) of LVNC at present. Our objective was to establish specific CCT criteria for the diagnosis of pathological noncompaction.
Methods: We studied 8 consecutive patients with LVNC with echocardiogram, CMR and CCT, using the 17-segment m odel. We compared the finding of CMR and CCT with 10 healthy volunteers, 10 subjects with dilated myocardiopathy and 10 with hypertensive heart disease. The ratio of Non-compacted (NC) to compacted (C) myocardium and was calculated for each group in systole and diastole. Results: The ratio of NC/C was significantly higher in the NC group than the healthy, dilated and hypertensive groups. The ratio N/C in de LVNC group was 2.1 ± (0.2) vs 1.40, 1.39 and 1.46 of the healthy, hypertensive and dilated subjects respectively evaluated by de CCT and all had good correlation with CMR and echocardiography. Conclusion: The patients with LVNC have a ratio NC/C significantly higher than the rest of the groups. The CCT is a reliable method for the diagnosis and characterization of this entity due to its excellent visualization of the endocardium. Oral Session X: Radiation Exposure Abstracts 52-57 52 Raupach R1, Bruder H1, Primak AN 2, Liu X2, McCollough CH2, Schmidt B1, Flohr TG1. Dose Reduction Strategies for CT Cardiac Imaging 1 Siemens Healthcare Sector, Germany 2 Mayo Clinic College of Radiology, Rochester, MN Introduction: CT has become an important tool for cardiac diagnostics. Its use in daily routine requires radiation dose reduction in ECG-controlled scans to the lowest achievable level without compromising image quality. Methods: We compare different approaches for cardiac CT examinations with regard to image quality and their potential for dose reduction. Five methods were analyzed: A. helical scan with constant tube current, B. helical scan with real-time ECG-controlled tube current modulation at which 20% of the maximum power were applied outside the desired cardiac phase (CP), C. helical scan as in B but with reduction to 4% outside the CP of interest, D. triggered sequential acquisition and E. adaptively triggered sequential scans with dynamic temporal windows. For each method, the CT scan was simulated on the basis of 60 ECGs recorded during coronary CTA examinations. The hear t rate varied between 40 and 103 bpm with an average of 71 bpm. Image quality in terms of reliability matching the desired CP as well as dose reduction was evaluated. Results: As a reference, method A allows reconstructing at arbitrary CP with maximum image quality, but at highest dose. Methods B, C and E show the same reliability (98%) while method D misses the desired CP in 18%, resulting in reduced image quality (motion artifacts). Compared with approach A radiation dose can be reduced by 45% (B), 54% (C), 75% (D) and 68% (E) on an average. Method B allows functional imaging, however, related with the highest dose of BE. Conclusion: The sequential scan (D) yields the lowest dose, but suffers from inconsistent image quality. Low current helical (C) and adaptively triggered sequential scan (E) provide lowest patient dose at high reliability. 53 Hausleiter J, Hermann F, Meyer T, Gerber TC, Ach enbach S, McCollough C, Martinoff S. International Prospective Multicenter Study on Radiation Dose Estimates Of Coronary CT Angiography In Daily Practice – Results from the PROTECTION I Study Deutsches Herzzentrum Muenchen, Munich, Germany Mayo Clinic Rochester, MN and Jacksonville, FL Friedrich Alexander University Erlangen–Nuremberg, Nuremberg, Germany Introduction: Cardiac CT angiography (CCTA) has evolved as a useful non-invasive imaging modality. The exposure to ionizing radiation associated with cardiac CT angiography (CCTA) has raised serious concerns. The international PRospective Multicenter Study On RadiaTion Dose Estimates Of Cardiac CT AngIOgraphy IN Daily Practice (PROTECTION I) is a prospective, international, industryindependent, multicenter study, which investigates the magnitude of
S19
Introduction: Atrial fibrillation (AF) is the most common arrhythmia encountered in clinical practice and has been independently associated with increased mortality. The relationship between AF and coronary artery disease (CAD) has been inconsistently defined. Coronary artery calcification (CAC) identified on cardiac computed tomography (cardiac CT) has been found to be a sensitive, though not specific, marker for CAD. To our knowledge, there h ave been no studies published that examine the relationship between AF and CAD as assessed by 64-Slice Multi-Detector Computed Tom ography (MDCT). Methods: We retrospectively evaluated the 64-Slice MDCT examinations of 30 patients with a known history of non-valvular AF (AF group) who underwent imaging to define the pulmonary vein anatomy prior to planned pulmonary vein isolation and AF ablation. We then compared them with 30 patients without a known history of AF (SR group) who had a 64-Slice MDCT to assess for the presence of obstructive CAD. Both groups were determined serially based on the date of their 64-Slice MDCT. Patients with a prior history of clinically significant CAD or angina were excluded. All 64-Slice MDCTs were reviewed for the presence or absence of CAC as a marker for CAD. Our criteria for estimating the severity of CAC was the following: mild = very small amount of non-obstructive disease in one or two vessels; moderate = small amount of non-obstructive disease in three vessels, intermediate amount of non-obstructive disease in two vessels, or large amount of non-obstructive disease in one vessel; severe = intermediate amount of non-obstructive disease in three vessels, large amount of disease in two or more vessels, or any obstructive lesions. Results: CAC was detected in 46.7% of patients with AF but only 36.7% of patients without AF (p=0.153), suggesting a trend towards a significant association between AF and CAD (Figure 1). Furthermore, patients with AF and CAC were also more likely to have disease categorized as moderate or severe, 26.7% versus 13.3% (p=0.167). Conclusions: The prevalence of CAD in patients with non-valvular AF appears to be more common than previously thought based on our assessment of CAC identified on 64-Slice MDCT. Addi tional investigation with a larger patient population and more objective measurement of CAC (i.e., volume of calcium) is warranted to further define this relationship. Figure 1: Presence of Coronary Artery Calcification
p = 0.153 50 40
AF group
Percentage of 30 Patients 20
SR group
10 0 Coronary Artery Calcification
51 Meave A, Kimura E, Meléndez G, Castillo F, Es pinola N, Lamothe PA, Alexanderson E. Assessment of Ventricular Non Compaction: A Compara tive Study of Cardiac Computed Tomography, Cardiac Magne tic Resonance and Echocardiography Instituto Nacional de Cardiología Ignacio Chávez, Mexico City, Mexico Introduction: Left ventricular non-compaction (LVNC) is characterized by the presence of an extensive non-compacted myocardial layer of the cavity of the left ventricle (LV). LVNC is thou ght to result from a failure of trabecular regression that occurs during normal embryonic development. Major clinical complications are cardiac failure, thromboembolism, and malignant arrhythmias. On the basis of echocardiographic studies, its prevalence has been estimated at 0.05% in the general population. Although the diagnosis of LVNC is usually made using echocardiography, recently cardiac magnetic resonance (CMR) imaging definition was done. There is not a cardiac computed tomography (CCT) of LVNC at present. Our objective was to establish specific CCT criteria for the diagnosis of pathological noncompaction.
Methods: We studied 8 consecutive patients with LVNC with echocardiogram, CMR and CCT, using the 17-segment m odel. We compared the finding of CMR and CCT with 10 healthy volunteers, 10 subjects with dilated myocardiopathy and 10 with hypertensive heart disease. The ratio of Non-compacted (NC) to compacted (C) myocardium and was calculated for each group in systole and diastole. Results: The ratio of NC/C was significantly higher in the NC group than the healthy, dilated and hypertensive groups. The ratio N/C in de LVNC group was 2.1 ± (0.2) vs 1.40, 1.39 and 1.46 of the healthy, hypertensive and dilated subjects respectively evaluated by de CCT and all had good correlation with CMR and echocardiography. Conclusion: The patients with LVNC have a ratio NC/C significantly higher than the rest of the groups. The CCT is a reliable method for the diagnosis and characterization of this entity due to its excellent visualization of the endocardium. Oral Session X: Radiation Exposure Abstracts 52-57 52 Raupach R1, Bruder H1, Primak AN 2, Liu X2, McCollough CH2, Schmidt B1, Flohr TG1. Dose Reduction Strategies for CT Cardiac Imaging 1 Siemens Healthcare Sector, Germany 2 Mayo Clinic College of Radiology, Rochester, MN Introduction: CT has become an important tool for cardiac diagnostics. Its use in daily routine requires radiation dose reduction in ECG-controlled scans to the lowest achievable level without compromising image quality. Methods: We compare different approaches for cardiac CT examinations with regard to image quality and their potential for dose reduction. Five methods were analyzed: A. helical scan with constant tube current, B. helical scan with real-time ECG-controlled tube current modulation at which 20% of the maximum power were applied outside the desired cardiac phase (CP), C. helical scan as in B but with reduction to 4% outside the CP of interest, D. triggered sequential acquisition and E. adaptively triggered sequential scans with dynamic temporal windows. For each method, the CT scan was simulated on the basis of 60 ECGs recorded during coronary CTA examinations. The hear t rate varied between 40 and 103 bpm with an average of 71 bpm. Image quality in terms of reliability matching the desired CP as well as dose reduction was evaluated. Results: As a reference, method A allows reconstructing at arbitrary CP with maximum image quality, but at highest dose. Methods B, C and E show the same reliability (98%) while method D misses the desired CP in 18%, resulting in reduced image quality (motion artifacts). Compared with approach A radiation dose can be reduced by 45% (B), 54% (C), 75% (D) and 68% (E) on an average. Method B allows functional imaging, however, related with the highest dose of BE. Conclusion: The sequential scan (D) yields the lowest dose, but suffers from inconsistent image quality. Low current helical (C) and adaptively triggered sequential scan (E) provide lowest patient dose at high reliability. 53 Hausleiter J, Hermann F, Meyer T, Gerber TC, Ach enbach S, McCollough C, Martinoff S. International Prospective Multicenter Study on Radiation Dose Estimates Of Coronary CT Angiography In Daily Practice – Results from the PROTECTION I Study Deutsches Herzzentrum Muenchen, Munich, Germany Mayo Clinic Rochester, MN and Jacksonville, FL Friedrich Alexander University Erlangen–Nuremberg, Nuremberg, Germany Introduction: Cardiac CT angiography (CCTA) has evolved as a useful non-invasive imaging modality. The exposure to ionizing radiation associated with cardiac CT angiography (CCTA) has raised serious concerns. The international PRospective Multicenter Study On RadiaTion Dose Estimates Of Cardiac CT AngIOgraphy IN Daily Practice (PROTECTION I) is a prospective, international, industryindependent, multicenter study, which investigates the magnitude of