Radiation dose standards and measurements
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The volume CT dose index (CTDIvol) [expressed in units of mGy] should be used for optimizing cardiovascular CT protocols. |
The dose-length-product (DLP) [expressed in units of mGy-cm] should be used for comparing radiation doses and characterizing radiation dose from a cardiovascular CT study. |
Radiation risk
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Estimations of stochastic risk from radiation delivered during medical imaging examinations should be interpreted cautiously, considering the uncertain relationship between dose and risk at low levels of radiation dose. |
Potential risk of future stochastic events must be balanced with the potential benefits of the examination and potential risks of forgoing the examination or obtaining a nondiagnostic examination because of excessive dose reduction. |
General methods for radiation dose reduction
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Appropriate use criteria
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Cardiovascular CT should only be performed if indicated by best available evidence and published guidelines, appropriate use criteria, or certain clinical scenarios or patient-specific clinical factors/comorbidities that support testing for a given patient. |
The cardiovascular CT imaging protocol should be tailored to the clinical question and patient characteristics. |
Scan modes
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Retrospective ECG-gated helical techniques may be used in patients who do not qualify for prospective ECG-triggered scanning because of irregular heart rhythm or high heart rates or both (specific value depends on specific scanner characteristics and cardiovascular indication). |
Prospective ECG-triggered axial techniques should be used in patients who have stable sinus rhythm and low heart rates (typically <60-65 beats/min, but specific values depend on specific scanner characteristics and cardiovascular indication). |
For prospective ECG-triggered axial techniques, the width of the data acquisition window should be kept at a minimum. |
Tube potential
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A tube potential of 100 kV could be considered for patients weighing ≤90 kg or with a BMI ≤ 30 kg/m2; a tube potential of 120 kV is usually indicated for patients weighing >90 kg and with a BMI > 30 kg/m2. Higher tube potential may be indicated for severely obese patients. |
Tube current
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If retrospective ECG-gated helical data acquisition is indicated, ECG-based tube current modulation should be used except in patients with highly irregular heart rhythm. |
The scanner default tube current values should be adjusted, based on each individual patient's size and clinical indication, to the lowest setting that achieves acceptable image noise. |
Scan length
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The scan length should be set at the minimum length clinically necessary. |
Reconstruction slice thickness
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Images should be reconstructed with the greatest possible slice thickness for the given cardiovascular CT indication, and the tube current should be adjusted with the understanding that a lower tube current can be used with the reconstruction of thicker slices. |
Predictors of radiation dose with cardiac CT
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Use of breast shields is not recommended for cardiovascular CT. |
Imaging centers (especially those initiating coronary CT angiography and those with lower case volumes) may participate in collaborative quality improvement programs. |
Applying algorithms for dose optimization in clinical practice
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Individual sites should consider developing site-specific algorithms for radiation dose optimization, which should be reviewed and revised if needed at least annually. |
Considerations for coronary calcium scoring
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Coronary calcium scans should be performed with prospective ECG-triggered axial or prospective ECG-triggered helical techniques, a 120-kV tube potential, a patient size-adjusted tube current, and the widest beam collimation that allows for reconstruction of 3-mm slices. |
Considerations for coronary CT angiography
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If coronary calcium scans can only be performed with retrospective ECG-gated helical scanning, ECG-based tube current modulation should be used along with a 120-kV tube potential, a patient size-adjusted nominal tube current, and the widest beam collimation that allows for reconstruction of 3-mm slices. |
If possible, the patient's heart rate during scanning should be <65 beats/min and ideally <60 beats/min for coronary CT angiography (specific values depend on specific scanner characteristics and cardiovascular indication) to provide the best image quality and allow use of lower-dose acquisition modes. |
Considerations for noncoronary cardiovascular CT
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For some noncoronary cardiovascular CT studies, lower-dose settings can be used and thicker slices reconstructed to achieve acceptable image noise. |
Pulmonary vein anatomic mapping CT studies may be best performed with non-ECG-referenced or single heartbeat techniques for patients with atrial fibrillation. |
Dose monitoring
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CTDIvol [expressed in mGy] and DLP [expressed in mGy-cm] should be recorded for each patient. |
Review of sites’ radiation levels and adherence to institutional algorithms for radiation dose optimization should be performed at least twice per year. |