Ultra low dose CT for attenuation correction in PET/CT

In this paper, we present an ultra low-dose CT acquisition and reconstruction technique that provides sufficient image quality for PET attenuation correction while keeping the CT dose to a minimum. With PET/CT, CT is used instead of radioactive transmission sources to acquire data for attenuation correction. While this results in higher radiation dose to the patient, the CT images are also viewed with the PET images and provide an anatomical reference to aid the physician in localizing tumors. We found that using low tube voltage and current results in severe shading and CT number shifts and causes artifacts and quantitative errors in PET images. By adding a simple low pass filter to CT reconstruction prior to the logarithmic step, shading and CT number shifts are reduced substantially. The resulting CT number accuracy and uniformity of the images with the proposed approach makes them acceptable for PET attenuation correction.