AbstractID: 9713 Title: Effect of multislice versus single slice X-ray CT on noise power spectrums
In X-ray CT screening for the early detection of lung cancer, low dose techniques and thin slices are being prevalently used.
However, noise, particularly low frequency noise, may reduce nodule detectability in situations where contrast is low, e.g. ground
glass nodules. The purpose of this work is to investigate the noise power spectrum (NPS) using typical low dose lung cancer
screening techniques on multislice and single slice CT images. Modulation transfer functions (MTFs) were obtained from a multislice
(Sensation 16, Siemens Medical Systems) and single slice (CT/I, GE Medical Systems) CT scanner using the Droege and Morin
method. A water phantom was scanned on the multislice scanner at 120kVp, 37.5 mAs, 1.5 pitch, 1mm reconstructed slice thickness
and a medium (B30f) frequency reconstruction kernel. The same phantom was also scanned on the single slice scanner at 120kVp,
40mAs, 1.5 pitch, 1mm slice width and with a similar (Standard) kernel. A centered, circular region of interest within each image
was used to establish the standard deviation in Hounsfield Units (HU). The NPS was calculated from the water images for each
scanner/kernel combination at the above described techniques. The standard deviation of the water phantom on the multislice scanner
was approximately 34.2HU compared to 30.0 HU on the single slice (which used slightly higher mAs). The NPS spectrums reveal
greater noise power in the lower and middle frequencies of the multislice scanner. The influence of these lower frequency noise
characteristics, and their effect on nodule detectability, should be considered in protocol design.