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Direction-dependent localization errors in SPECT images.

Publication ,  Journal Article
Roper, J; Bowsher, J; Yin, F-F
Published in: Med Phys
September 2010

PURPOSE: Single photon emission computed tomography (SPECT) is being investigated for imaging inside radiation therapy treatment rooms to localize biological targets. Here, computer simulations were used to analyze locational and directional dependencies in localization errors and to assess the effects of spatial resolution modeling and observer normalization on localization performance. METHODS: SPECT images of the XCAT phantom, containing 12 hot tumors, were reconstructed with detector response function compensation (DRC) and without DRC (nDRC). Numerical observers were forced to select the most suspicious tumor location, using normalized cross correlation (NXC) or un-normalized cross correlation (XC), from 3 cm diameter search volumes that each contained only one tumor. For each tumor site, localization was optimized as a function of the iteration number and postreconstruction smoothing. Localization error, the distance between true and estimated tumor positions, was calculated across the ensembles of 80 images. Direction-dependent localization bias and precision were estimated from the image ensemble. RESULTS: For the six superficial tumors in close proximity to the detector trajectory, mean localization errors were < 2 mm and were lowest or comparable using DRC-NXC, though differences from DRC-XC and nDRC-NXC were not statistically significant. DRC-NXC did provide statistically significantly better localization than nDRC-XC for five of these six tumors. At the other six sites where attenuation was more severe and the distance was generally greater between the tumor and detector, DRC typically did not show better localization than nDRC. Observer normalization improved the localization substantially for a tumor near the hotter heart. Localization errors were anisotropic and dependent on tumor location relative to the detector trajectory. CONCLUSIONS: This computer-simulation study compared localization performance for normalized and un-normalized numerical observers, which were used to estimate tumor positions in SPECT images, reconstructed with and without DRC. For tumors localized to < 2 mm on average, which are good candidates for SPECT-guided radiation therapy, localization performance typically improved by compensating for the detector response function and by using a normalized observer. The observed direction-dependent localization errors have important implications for radiation therapy and are relevant to SPECT imaging in general.

Duke Scholars

Published In

Med Phys

DOI

ISSN

0094-2405

Publication Date

September 2010

Volume

37

Issue

9

Start / End Page

4886 / 4896

Location

United States

Related Subject Headings

  • Tomography, Emission-Computed, Single-Photon
  • Phantoms, Imaging
  • Nuclear Medicine & Medical Imaging
  • Models, Theoretical
  • Image Processing, Computer-Assisted
  • Humans
  • Female
  • Anisotropy
  • 5105 Medical and biological physics
  • 4003 Biomedical engineering
 

Citation

APA
Chicago
ICMJE
MLA
NLM
Roper, J., Bowsher, J., & Yin, F.-F. (2010). Direction-dependent localization errors in SPECT images. Med Phys, 37(9), 4886–4896. https://doi.org/10.1118/1.3481515
Roper, Justin, James Bowsher, and Fang-Fang Yin. “Direction-dependent localization errors in SPECT images.Med Phys 37, no. 9 (September 2010): 4886–96. https://doi.org/10.1118/1.3481515.
Roper J, Bowsher J, Yin F-F. Direction-dependent localization errors in SPECT images. Med Phys. 2010 Sep;37(9):4886–96.
Roper, Justin, et al. “Direction-dependent localization errors in SPECT images.Med Phys, vol. 37, no. 9, Sept. 2010, pp. 4886–96. Pubmed, doi:10.1118/1.3481515.
Roper J, Bowsher J, Yin F-F. Direction-dependent localization errors in SPECT images. Med Phys. 2010 Sep;37(9):4886–4896.

Published In

Med Phys

DOI

ISSN

0094-2405

Publication Date

September 2010

Volume

37

Issue

9

Start / End Page

4886 / 4896

Location

United States

Related Subject Headings

  • Tomography, Emission-Computed, Single-Photon
  • Phantoms, Imaging
  • Nuclear Medicine & Medical Imaging
  • Models, Theoretical
  • Image Processing, Computer-Assisted
  • Humans
  • Female
  • Anisotropy
  • 5105 Medical and biological physics
  • 4003 Biomedical engineering