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

Abstract

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.

Technical assessment of a mobile CT scanner for image‐guided brachytherapy

“…The effect of reconstruction filter is shown in [Fig. (b)], with the sharp reconstruction filter giving highest MTF, falling to 10% at ~0.55 mm −1 and limiting resolution down to ~(1/2/0.55) = 0.9 mm feature size, consistent with previously published work …”

“…Previous studies reported the performance of the mobile CT scanner within the context of its primary indication in image‐guided spine surgery. Weir et al assessed the Airo in terms of its imaging performance in comparison to MDCT for image‐guided surgery, including dosimetric characterization and image quality analysis. Their work showed spatial resolution up to 4 lp/cm in the head field‐of‐view (FOV) for the mobile scanner, compared to 7 lp/cm resolution from a Siemens Sensation 64‐slice MDCT scanner for the same FOV .…”

“…Weir et al assessed the Airo in terms of its imaging performance in comparison to MDCT for image‐guided surgery, including dosimetric characterization and image quality analysis. Their work showed spatial resolution up to 4 lp/cm in the head field‐of‐view (FOV) for the mobile scanner, compared to 7 lp/cm resolution from a Siemens Sensation 64‐slice MDCT scanner for the same FOV . The Airo was also found to exhibit higher radiation dose than the Sensation 64 for comparable technique factors (50% increase for head, 85% increase for body phantom), and ring‐like artifacts were noted as contributors to increased low‐frequency noise in the image NPS …”

First experiences with the Airo mobile intraoperative CT scanner in acetabular surgery—An analysis of 10 cases

“…Regarding image quality, the compromises made to enable the device to be handy and mobile, and to allow the large gantry opening were at the expense of a reduced image quality . This is reflected in the values of subjective image quality where the best rating was not assigned (see Figure with a typical example).…”

“…The radiation exposure to the patient is difficult to assess, as CT radiation doses are hardly comparable to fluoroscopy doses. Compared with radiation doses of stationary CT scanners, the doses with the Airo seem to be comparable or slightly higher . Usually, after osteosynthesis of the acetabulum, a postoperative CT is the standard imaging to verify the surgical procedure.…”