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Raw projection CT images from a low-dose screening patient cohort (N=59) were reconstructed at multiple dose levels (100%, 50%, 25%, 10%), two slice thicknesses (1.0mm, 0.6mm), and a medium kernel. Fully-automated nodule detection and segmentation was then applied, from which 12 nodules were selected. Dice similarity coefficient (DSC) was used to assess the similarity of the segmentation ROIs of the same nodule across different reconstruction and dose conditions.
Nodules at 1.0mm slice thickness and dose levels of 25% and 50% resulted in DSC values greater than 0.85 when compared to 100% dose, with lower dose leading to a lower average and wider spread of DSC values. At 0.6mm, the increased bias and wider spread of DSC values from lowering dose were more pronounced. The effects of dose reduction on DSC for CAD-segmented nodules were similar in magnitude to reducing the slice thickness from 1.0mm to 0.6mm. In conclusion, variation of dose and slice thickness can result in very different segmentations because of noise and image quality. However, there exists some stability in segmentation overlap, as even at 1mm, an image with 25% of the lowdose scan still results in segmentations similar to that seen in a full-dose scan.
Radiation dose from CT has continued to be a concern, especially to the medical imaging community. Recent high profile events (CT being identified as the largest single source of medical radiation to the US population, widely reported overexposure incidents, etc.) have sparked action by national and international groups (NIH, FDA, IAEA, and ACR) as well as legislation in California. The purpose of this course is to cover several areas of interest with respect to radiation dose from CT. This course will describe methods being used to measure and report radiation dose in CT, methods to estimate radiation dose to patients as well as scanner technologies that have been used to reduce radiation dose in CT exams.
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