Dosimetric characterization and image quality evaluation of the AIRO mobile CT scanner

Radiation dose and image quality from a recently introduced mobile CT imaging system are presented. Radiation dose was measured using a conventional 100 mm pencil ionization chamber and CT polymethylmetacrylate (PMMA) body and head phantoms. Image quality was evaluated with a CATPHAN 500 phantom. Spatial resolution, low contrast resolution, Modulation Transfer Function (MTF), and Normalized Noise Power Spectrum (NNPS) were analyzed. Radiation dose and image quality were compared to those from a multi-detector CT scanner (Siemens Sensation 64). Under identical technique factors radiation dose (mGy/mAs) from the AIRO mobile CT system (AIRO) is higher than that from a 64 slice CT scanner. Based on MTF analysis, both Soft and Standard filters of the AIRO system lost resolution quickly compared to the Sensation 64 slice CT. The Siemens scanner had up to 7 lp/cm for the head FOV and H40 kernel and up to 5 lp/cm at body FOV for the B40f kernel. The Standard kernel in the AIRO system was evaluated to have 3 lp/cm and 4 lp/cm for the body and head FOVs respectively. NNPS of the AIRO shows low frequency noise due to ring-like artifacts which may be caused by detector calibration or lack of artifact reducing image post-processing. Due to a higher dose in terms of mGy/mAs at both head and body FOV, the contrast to noise ratio is higher in the AIRO system than in the Siemens scanner. However detectability of the low contrast objects is poorer in the AIRO due to the presence of ring artifacts in the location of the targets.