title: Attenuation-emission alignment in cardiac PET/CT based on consistency conditions.
abstract: OBJECTIVE
  In cardiac PET and PET/CT imaging, misaligned transmission and emission images are a common problem due to respiratory and cardiac motion. This misalignment leads to erroneous attenuation correction and can cause errors in perfusion mapping and quantification. This study develops and tests a method for automated alignment of attenuation and emission data.
  
  
  METHODS
  The CT-based attenuation map is iteratively transformed until the attenuation corrected emission data minimize an objective function based on the Radon consistency conditions. The alignment process is derived from previous work by Welch et al. ["Attenuation correction in PET using consistency information," IEEE Trans. Nucl. Sci. 45, 3134-3141 (1998)] for stand-alone PET imaging. The process was evaluated with the simulated data and measured patient data from multiple cardiac ammonia PET/CT exams. The alignment procedure was applied to simulations of five different noise levels with three different initial attenuation maps. For the measured patient data, the alignment procedure was applied to eight attenuation-emission combinations with initially acceptable alignment and eight combinations with unacceptable alignment. The initially acceptable alignment studies were forced out of alignment a known amount and quantitatively evaluated for alignment and perfusion accuracy. The initially unacceptable studies were compared to the proposed aligned images in a blinded side-by-side review.
  
  
  RESULTS
  The proposed automatic alignment procedure reduced errors in the simulated data and iteratively approaches global minimum solutions with the patient data. In simulations, the alignment procedure reduced the root mean square error to less than 5 mm and reduces the axial translation error to less than 1 mm. In patient studies, the procedure reduced the translation error by > 50% and resolved perfusion artifacts after a known misalignment for the eight initially acceptable patient combinations. The side-by-side review of the proposed aligned attenuation-emission maps and initially misaligned attenuation-emission maps revealed that reviewers preferred the proposed aligned maps in all cases, except one inconclusive case.
  
  
  CONCLUSIONS
  The proposed alignment procedure offers an automatic method to reduce attenuation correction artifacts in cardiac PET/CT and provides a viable supplement to subjective manual realignment tools.
authors.affiliation: Department of Radiology, University of Washington Medical Center, 4000 15th Avenue NE, Box 357987, Seattle, Washington 98195-7987, USA. aalessio@u.washington.edu
authors.forename: Adam M
authors.initials: AM
authors.lastname: Alessio
authors.forename: Paul E
authors.initials: PE
authors.lastname: Kinahan
authors.forename: Kyle M
authors.initials: KM
authors.lastname: Champley
authors.forename: James H
authors.initials: JH
authors.lastname: Caldwell
mesh_terms: D000465:Algorithms; D016477:Artifacts; D006321:Heart / Q000000981:diagnostic imaging*; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D049268:Positron-Emission Tomography / Q000379:methods*; D013382:Subtraction Technique; D014057:Tomography, X-Ray Computed / Q000379:methods*
references.citation: J Nucl Med. 2004 Jun;45(6):1029-39
references.pmid: 15181138
references.citation: J Nucl Cardiol. 2006 Nov;13(6):821-30
references.pmid: 17174813
references.citation: Med Phys. 2006 Nov;33(11):4095-103
references.pmid: 17153389
references.citation: J Nucl Med. 2005 Sep;46(9):1481-7
references.pmid: 16157531
references.citation: IEEE Trans Med Imaging. 2000 Dec;19(12):1211-9
references.pmid: 11212369
references.citation: J Nucl Med. 2007 Feb;48(2):188-93
references.pmid: 17268013
references.citation: J Nucl Med. 2007 May;48(5):794-801
references.pmid: 17475969
references.citation: Radiology. 2003 Mar;226(3):906-10
references.pmid: 12616024
references.citation: Phys Med Biol. 2008 Oct 21;53(20):5705-18
references.pmid: 18812649
references.citation: J Nucl Med. 2007 Nov;48(11):1912-3; author reply 1913-4
references.pmid: 17978359
references.citation: J Nucl Med. 1995 Nov;36(11):2138-47
references.pmid: 7472611
references.citation: J Nucl Med. 2007 Jul;48(7):1112-21
references.pmid: 17574974
references.citation: Semin Nucl Med. 2003 Jul;33(3):166-79
references.pmid: 12931319
references.citation: Circulation. 2002 Jan 29;105(4):539-42
references.pmid: 11815441
references.citation: J Nucl Med. 2002 Sep;43(9):1137-43
references.pmid: 12215550
references.citation: Eur J Nucl Med Mol Imaging. 2008 Feb;35(2):305-10
references.pmid: 17909791