Criteria and Test Methods for CT Systems
July 1, 2012 | Evaluations & Guidance
This is a list of the criteria we apply to computed tomography scanners when testing them in our Evaluations, along with the specific tests we perform. Hospitals can use these criteria for their prepurchase and acceptance testing.
Except as noted, this list applies to all types of helical and axial CT scanners.
Noise is measured in a 250 mm diameter water phantom at 120 kVp for both spiral and axial acquisitions. Parameters (mode, mAs, slice thickness, reconstruction filter, and pitch) are selected as required. The noise is defined as the standard deviation of a specified region of interest. The corresponding x-ray dose is measured free in air at the isocenter for all mAs conditions measured. At least three reconstruction filters (e.g., soft tissue, lung, and high resolution) are used to match the spatial resolution characteristics between evaluated systems. (See below for a description of how spatial resolution is measured.) Low-contrast phantom images are obtained at the manufacturer’s specified conditions, at 25 mGy (measured in a 16 cm CTDI CT dose index phantom), and at higher and lower x-ray tube settings. Low-contrast phantom images are assessed both visually...