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Method for Automatic Tube Current Selection for Obtaining a Consistent Image Quality and Dose Optimization in a Cardiac Multidetector CT

2009; Korean Society of Radiology; Volume: 10; Issue: 6 Linguagem: Inglês

10.3348/kjr.2009.10.6.568

2005-8330

Weiwei Qi, Jianying Li, Xiangke Du,

Cardiac Imaging and Diagnostics

Method for Automatic Tube Current Selection for Obtaining a Consistent Image Quality and Dose Optimization in a Cardiac Multidetector CTObjective: To evaluate a quantitative method for individually adjusting the tube current to obtain images with consistent noise in electrocardiogram (ECG)-gated CT cardiac scans. Materials and Methods:The image noise from timing bolus and cardiac CT scans of 80 patients (Group A) who underwent a 64-row multidetector (MD) CT cardiac examination with patient-independent scan parameters were analyzed.A formula was established using the noise correlation between the timing bolus and cardiac scans.This formula was used to predict the required tube current to obtain the desired cardiac CT image noise based on the timing bolus noise measurement.Subsequently, 80 additional cardiac patients (Group B) were scanned with individually adjusted tube currents using an established formula to evaluate its ability to obtain accurate and consistent image noise across the patient population.Image quality was evaluated using score scale of 1 to 5 with a score of 3 or higher being clinically acceptable. Results:Using the formula, we obtained an average CT image noise of 28.55 Hounsfield unit (HU), with a standard deviation of only 1.7 HU, as opposed to a target value of 28 HU.Image quality scores were 4.03 and 4.27 for images in Groups A and B, respectively, and there was no statistical difference between the image quality scores between the two groups.However, the average CT dose index (CTDIvol) was 30% lower for Group B. Conclusion:Adjusting the tube current based on timing bolus scans may provide a consistent image quality and dose optimization for cardiac patients of various body mass index values.oronary CT angiography (CCTA) imaging is gradually becoming mainstream clinical application with the introduction of the 64-row detector CT with fast gantry rotation speed and wide coverage that can cover the whole heart in less than 10 seconds (1-5).The need to reduce X-ray dose to cardiac patients has also grown considerably (6)(7)(8).This is because cardiac helical CT scans use sub-millimeter slice thicknesses and slow helical pitches to satisfy the requirements of complete coverage for all cardiac phases for high resolution coronary artery imaging and functional measurement.Special attention has been paid to younger patients, and also to female patients due to the exposure of breasts during cardiac scans (9).Many hardware and software techniques have been developed in CT applications to effectively reduce the X-ray dose required to obtain a desired image quality (10-13).Recently, the step-and-shot cardiac imaging mode has also been introduced to avoid overlap scans, which are inherent to the helical mode, and dramatically reduces the