title: Optimization of SPECT-CT Hybrid Imaging Using Iterative Image Reconstruction for Low-Dose CT: A Phantom Study.
abstract: BACKGROUND
  Hybrid imaging combines nuclear medicine imaging such as single photon emission computed tomography (SPECT) or positron emission tomography (PET) with computed tomography (CT). Through this hybrid design, scanned patients accumulate radiation exposure from both applications. Imaging modalities have been the subject of long-term optimization efforts, focusing on diagnostic applications. It was the aim of this study to investigate the influence of an iterative CT image reconstruction algorithm (ASIR) on the image quality of the low-dose CT images.
  
  
  RESULTS
  Examinations were performed with a SPECT-CT scanner with standardized CT and SPECT-phantom geometries and CT protocols with systematically reduced X-ray tube currents. Analyses included image quality with respect to photon flux. Results were compared to the standard FBP reconstructed images. The general impact of the CT-based attenuation maps used during SPECT reconstruction was examined for two SPECT phantoms. Using ASIR for image reconstructions, image noise was reduced compared to FBP reconstructions for the same X-ray tube current. The Hounsfield unit (HU) values reconstructed by ASIR were correlated to the FBP HU values(R2 ≥ 0.88) and the contrast-to-noise ratio (CNR) was improved by ASIR. However, for a phantom with increased attenuation, the HU values shifted for low X-ray tube currents I ≤ 60 mA (p ≤ 0.04). In addition, the shift of the HU values was observed within the attenuation corrected SPECT images for very low X-ray tube currents (I ≤ 20 mA, p ≤ 0.001).
  
  
  CONCLUSIONS
  In general, the decrease in X-ray tube current up to 30 mA in combination with ASIR led to a reduction of CT-related radiation exposure without a significant decrease in image quality.
authors.affiliation: Department of Radiology and Nuclear Medicine, University Hospital Magdeburg, Magdeburg, Germany.
authors.forename: Oliver S
authors.initials: OS
authors.lastname: Grosser
authors.affiliation: Department of Radiology and Nuclear Medicine, University Hospital Magdeburg, Magdeburg, Germany.
authors.forename: Dennis
authors.initials: D
authors.lastname: Kupitz
authors.affiliation: Department of Radiology and Nuclear Medicine, University Hospital Magdeburg, Magdeburg, Germany.
authors.forename: Juri
authors.initials: J
authors.lastname: Ruf
authors.affiliation: Department of Radiology and Nuclear Medicine, University Hospital Magdeburg, Magdeburg, Germany.
authors.forename: Damian
authors.initials: D
authors.lastname: Czuczwara
authors.affiliation: Department of Radiology and Nuclear Medicine, University Hospital Magdeburg, Magdeburg, Germany.
authors.forename: Ingo G
authors.initials: IG
authors.lastname: Steffen
authors.affiliation: Department of Radiology and Nuclear Medicine, University Hospital Magdeburg, Magdeburg, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Furth
authors.affiliation: Department of Radiology and Nuclear Medicine, University Hospital Magdeburg, Magdeburg, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Thormann
authors.affiliation: Department of Radiology and Nuclear Medicine, University Hospital Magdeburg, Magdeburg, Germany.
authors.forename: David
authors.initials: D
authors.lastname: Loewenthal
authors.affiliation: Department of Radiology and Nuclear Medicine, University Hospital Magdeburg, Magdeburg, Germany.
authors.forename: Jens
authors.initials: J
authors.lastname: Ricke
authors.affiliation: Department of Radiology and Nuclear Medicine, University Hospital Magdeburg, Magdeburg, Germany.
authors.forename: Holger
authors.initials: H
authors.lastname: Amthauer
mesh_terms: D000328:Adult; D000465:Algorithms; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007091:Image Processing, Computer-Assisted / Q000379:methods; D064847:Multimodal Imaging / Q000295:instrumentation / Q000379:methods*; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D015203:Reproducibility of Results; D015899:Tomography, Emission-Computed, Single-Photon / Q000295:instrumentation / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000295:instrumentation / Q000379:methods*; D014965:X-Rays