Xinhui Duan PhD, Presenter: Nothing to Disclose

Jia Wang PhD, Abstract Co-Author: Nothing to Disclose

Shuai Leng PhD, Abstract Co-Author: Nothing to Disclose

Bernhard Schmidt PhD, Abstract Co-Author: Employee, Siemens AG

Thomas Allmendinger, Abstract Co-Author: Employee, Siemens AG

Cynthia H. McCollough PhD, Abstract Co-Author: Research Grant, Siemens AG

Katharine Grant PhD, Abstract Co-Author: Employee, Siemens AG

To evaluate in phantoms the differences in CT image noise and artifact level between commercial CT detectors with distributed electronics and those with direct coupling of the photodiode and ADC, which is intended to decrease system electronic noise.

Cylindrical water phantoms of 20, 30 and 40-cm diameter were scanned using two CT scanners, one equipped with the integrated detector (Stellar detector on Siemens Definition FLASH) and the other with conventional detector (Siemens Definition AS+). All other scanning parameters were identical. Scans were acquired at four tube potentials (80, 100, 120 and 140 kV), 10 tube currents (60 to 600 mA) and a 0.5 s rotation time. Images were reconstructed with 1 mm thickness and a medium smooth kernel (B30). Two semi-anthropomorphic phantoms were also scanned to mimic the shoulder and abdomen regions, with tube potentials of 80 and 120 kV, and a quality reference mAs of 240. Image noise was quantified as the standard deviation of CT number (STD) in uniform regions of interest (ROI). Artifact level was quantified as the difference in STD between regions containing streak artifacts and adjacent artifact-free ROI. Noise power spectra were also computed.

For cylindrical phantoms, the reduction of image noise depended on phantom size and tube current. Low signal scans, e.g. low tube currents or large phantoms, had larger noise reductions, up to 40% for a 30 cm phantom using 80 kV. This translated to up to 50% in dose reduction for the equivalent image noise. The integrated detector behaved much more closely to an ideal detector, where noise should be inversely proportional to the square root of dose. Streak artifacts through regions of high attenuation (e.g. through the shoulders) were greatly reduced for the integrated detector, especially in lower dose scans, with artifact reductions up to 45%. There was no visible change in the shape of the noise power spectra between the two types of detectors.

The integrated detector resulted in substantially reduced levels of electronic noise, resulting in reductions in image noise and artifacts compared with conventional detectors.

The integrated CT detector will enable dose reduction and improved image quality in situations where low photon counts are measured, such as in low-dose, dual-energy or large patient scans.

Duan, X, Wang, J, Leng, S, Schmidt, B, Allmendinger, T, McCollough, C, Grant, K, Integration of a CT Detector’s Photo-Diode and Analog-to-Digital Converter (ADC) into a Single Application-Specific-Integrated Circuit: Impact on Image Noise and Artifacts in a Clinical CT System.  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12027595.html