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Implications of CT noise and artifacts for quantitative 99m Tc SPECT/CT imaging
Author(s) -
Hulme K. W.,
Kappadath S. C.
Publication year - 2014
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4868511
Subject(s) - nuclear medicine , imaging phantom , correction for attenuation , image quality , single photon emission computed tomography , iterative reconstruction , noise (video) , image noise , attenuation , physics , tomography , emission computed tomography , spect imaging , medicine , positron emission tomography , computer science , radiology , optics , artificial intelligence , image (mathematics)
Purpose: This paper evaluates the effects of computed tomography (CT) image noise and artifacts on quantitative single‐photon emission computed‐tomography (SPECT) imaging, with the aim of establishing an appropriate range of CT acquisition parameters for low‐dose protocols with respect to accurate SPECT attenuation correction (AC).Methods: SPECT images of two geometric and one anthropomorphic phantom were reconstructed iteratively using CT scans acquired at a range of dose levels (CTDI vol = 0.4 to 46 mGy). Resultant SPECT image quality was evaluated by comparing mean signal, background noise, and artifacts to SPECT images reconstructed using the highest dose CT for AC. Noise injection was performed on linear‐attenuation ( μ ) maps to determine the CT noise threshold for accurate AC.Results: High levels of CT noise ( σ ∼ 200–400 HU) resulted in low μ ‐maps noise ( σ ∼ 1%–3%). Noise levels greater than ∼10% in 140 keV μ ‐maps were required to produce visibly perceptible increases of ∼15% in 99m Tc SPECT images. These noise levels would be achieved at low CT dose levels (CTDI vol = 4 μ Gy) that are over 2 orders of magnitude lower than the minimum dose for diagnostic CT scanners. CT noise could also lower (bias) the expected μ values. The relative error in reconstructed SPECT signal trended linearly with the relative shift in μ . SPECT signal was, on average, underestimated in regions corresponding with beam‐hardening artifacts in CT images. Any process that has the potential to change the CT number of a region by ∼100 HU (e.g., misregistration between CT images and SPECT images due to motion, the presence of contrast in CT images) could introduce errors in μ 140 keV on the order of 10%, that in turn, could introduce errors on the order of ∼10% into the reconstructed 99m Tc SPECT image.Conclusions: The impact of CT noise on SPECT noise was demonstrated to be negligible for clinically achievable CT parameters. Because CT dose levels that affect SPECT quantification is low (CTDI vol ∼ 4 μ Gy), the low dose limit for the CT exam as part of SPECT/CT will be guided by CT image quality requirements for anatomical localization and artifact reduction. A CT technique with higher kVp in combination with lower mAs is recommended when low‐dose CT images are used for AC to minimize beam‐hardening artifacts.