ABSTRACT
AC can be associated with a small, but additional radiation dose, especially if CT is used for this purpose in SPECT/CT scanners. e typical stress and rest dose from such CT-AC scans is in the order of 0.3-1.3 mSv [5] and therefore it is not negligible when compared to the dose from radioisotopes, especially for new low-dose protocols. To reduce the AC radiation dose, various new designs have been developed for SPECT scanners. One vendor has developed an integrated system with 5 µSv eective dose in which photons from x-ray source are detected by solidstate detectors with a fan beam collimator operating in high-counting-rate mode [6]. e scan time for the acquisition of the AC maps in this mode is 60 s. Another example of low-dose AC technology is the at-panel x-ray detector system, providing low-dose (0.12 mSv) CT images [7]. A transmission image of the entire heart can be obtained from a single 60 s rotation of the gantry while the patient is breathing normally. By acquiring the transmission image during tidal respiration, the attenuation data are averaged over multiple respiratory cycles to match the position of the heart during the SPECT acquisition. Furthermore, since the x-ray detector and the SPECT detectors are located on the same rotatable gantry, the emission and transmission images can be acquired with little or no table translation between scans, which also reduces misalignment between emission and transmission data.
