Techniques to Lower CT Dose
Nepalese Journal of Radiology
Techniques to lower CT dose in fact, due to recent events concerning patient overexposure to CT dose in 2010, the FdA launched The initiative to reduce Unnecessary radiation Exposure from Medical imaging. Through this initiative, the "FdA is advocating the universal adoption of two principles of radiation protection: appropriate justification for ordering each procedure, and careful optimization of the radiation dose used during each procedure. Each patient should get the right imaging exam, at
... the right time, with the right radiation dose." 1 To ensure the right radiation dose, there are several actions that radiological technologists can employ to offer dose-reduction strategies in the imaging suite. These include the following: Dose reduction strategies 1. Proper patient positioning on a CT scanner table is the first step to assure use of dose saving options. Higher noise images can occur when patients are not well centered in the scan field of view (FoV). by positioning the body at isocenter, the need to increase mA to compensate for the noise is eliminated. Utilization of BMI charts. Technologists can reduce dose without image degradation by observing the patient's weight and size. This can be based on the patients' body habitus, or body Mass index (bMi). some radiologists are suggesting that if a patient's bMi is less than 30, a lower kVp and mA can be used. Reducing mA and kVp. With mA, the relationship is directly proportional, meaning if mA is reduced by half, the corresponding dose is reduced by half. if kVp is reduced, the relationship is non-linear (exponentially lower). For example, if you reduce kVp from 120 kVp to 100k Vp (16.5% reduction of kVp) the result is a dose reduction of almost 40%. Limiting the Scan Length/coverage to the ROI. limiting the coverage of the scan will also help reduce dose. More accurately selecting the coverage area limits the start and end location and, therefore, reduces dose. 3D Dose Modulation (AEC). AEC is an option with the ability to optimize dose to achieve the user inputted image quality (iQ) desired. When set up properly this may provide a dose reduction compared to a fixed mA scan set up to deliver the same iQ at the highest attenuation locations. before the scan, the technologist selects the desired noise/iQ. The scanner then automatically tailors the exposure based on the scout and body habitus of the patient.