placed on the patient table. SPECT data are collected for 360° in a circu-
lar orbit of 20 cm, when the detector heads are in 180° configurations. In
the case of 90° configurations, the default radius is applied as given by the
manufacturer. In a proper COR-corrected system, the point sources
should be visible in all projection images.
This method is also used to check the head alignment and noncircular
orbit configuration in multihead camera systems with the computer
software.
Quality Control Tests for CT Scanners
Most of the CT quality control tests are performed by menu-driven soft-
ware protocols provided by the manufacturer. First, a checkup automati-
cally executes a set of CT warm-up acquisitions, automatic function checks,
and air calibration. This checkup is performed daily and guarantees
optimum image quality.
The next daily test is the quality control test that is performed by using
a quality phantom provided by the manufacturer. After the phantom is
installed in the CT field, data are acquired by a menu-driven protocol pro-
vided by the manufacturer to calculate the CT value of water (HU), pixel
noise, and tube voltage. This test must be performed prior to the first patient
examination.
Quality Control Tests for CT Scanners 179Fig. 12.18. An illustration of the effect of a misaligned center of rotation. A
“donut”-shaped image appears from inaccurately aligned center of rotation. (From
Todd-Pokropek A. The mathematics and physics of emission computerized tomo-
graphy (ECT). In: Esser PD, Westerman BR, eds.Emission Computed Tomography.
New York: Society of Nuclear Medicine 1983; 3.)