Preliminary low-dose hybrid imaging protocol scan optimization in single photon emission computed tomography
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Abstract
Background and aim
The CT component of SPECT/CT is required for attenuation correction (AC) and anatomical localization (AL) in SPECT/CT imaging.
The aim of this preliminary study is to evaluate quantitatively the image quality of different low-dose CT protocols for AL-AC, in order to reduce the patient’s radiation exposure while keeping the interpretation unchanged.
Material and methods
Using the 16-section CT component of a commercially available SPECT/CT scanner, we compared the standard protocol indicated by application specialists (main parameters: 120kV, 80mA, 0.8s, pitch 1.37) with different CT scans acquisitions with manually adjusted x-ray tube voltage (kV range 100-140), anode current (mA range 40-100), rotation time (s range 0.5-1), and pitch (p range 0.938- 1.75).
The imaging performance of the CT system was evaluated using Cathpan 600 phantom (Phantom Laboratory, Salem, NY, USA). We evaluated uniformity (U), contrast-to-noise ratio for objects with nominal contrast of 1% (CNR1%), spatial resolution (SR) and CT linearity (L). The Volume Computed Tomography Dose Index (CTDIvol) was registered by the scanner software and compared with the different scanner acquisitions.
Results
The results of standard protocol results were U=0.46 HU, CNR1%=1.37, CNR0.5%=0.98, SR= 7 line pairs/cm, L=0.998 and CTDIvol=4.12mGy.
The results of experimental protocols (24 acquisitions), expressed as mean, standard deviation and minimum-maximum, were U= 0.48±1.11 (0.02-2.51) HU, CNR1%=1.28±0.4 (0.39-2.08), SR= 7 line pairs/cm, L=0.998±0.001 (0.993-0.998) and CTDIvol=3.81±1.73 (1.29-7.44) mGy.
An analysis of the data identified the combinations of scan parameters that have image quality comparable to the standard acquisition protocol for correcting the attenuation and anatomical localization, obtaining a significant reduction in the CTDIvol.
Conclusion
The different settings of tube voltage, anode current, scan time, and pitch allow to reduce the CTDIvol up to -37.9% for AL and AC purposes, maintaining an image quality comparable to the factory protocol. Further studies should be performed to verify the effect on attenuation map of the reduced kV, using an anthropomorphic phantom.
Keywords: Hybrid imaging, nuclear medicine, CT, phantom, attenuation correction.
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