title: Accuracy of177Lu activity quantification in SPECT imaging: a phantom study.
abstract: BACKGROUND
  The aim of the study is to assess accuracy of activity quantification of177Lu studies performed according to recommendations provided by the committee on Medical Internal Radiation Dose (MIRD) pamphlets 23 and 26. The performances of two scatter correction and three segmentation methods were compared. Additionally, the accuracy of tomographic and planar methods for determination of the camera normalization factor (CNF) was evaluated. Eight phantoms containing inserts of different sizes and shapes placed in air, water, and radioactive background were scanned using a Siemens SymbiaT SPECT/CT camera. Planar and tomographic scans with177Lu sources were used to measure CNF. Images were reconstructed with our SPEQToR software using resolution recovery, attenuation, and two scatter correction methods (analytical photon distribution interpolated (APDI) and triple energy window (TEW)). Segmentation was performed using a fixed threshold method for both air and cold water scans. For hot water experiments three segmentation methods were compared as folows: a 40% fixed threshold, segmentation based on CT images, and our iterative adaptive dual thresholding (IADT). Quantification error, defined as the percent difference between experimental and true activities, was evaluated.
  
  
  RESULTS
  Quantification error for scans in air was better for TEW scatter correction (<6%) than for APDI (<11%). This trend was reversed for scans in water (<10% for APDI and <14% for TEW). For hot water, the best results (<18% for small objects and <5% for objects >100 ml) were obtained when APDI and IADT were used for scatter correction and segmentation, respectively. Additionally, we showed that planar acquisitions with scatter correction and tomographic scans provide similar CNF values. This is an important finding because planar acquisitions are easier to perform than tomographic scans. TEW and APDI resulted in similar quantification errors with APDI showing a small advantage for objects placed in medium with non-uniform density.
  
  
  CONCLUSIONS
  Following the MIRD recommendations for data acquisition and reconstruction resulted in accurate activity quantification (errors <5% for large objects). However, techniques for better organ/tumor segmentation must still be developed.
authors.affiliation: Medical Imaging Research Group, Department of Radiology, University of British Columbia, Vancouver, British Colombia, Canada. curibe@bccrc.ca.|Department of Physics and Astronomy, University of British Columbia, Vancouver, British Colombia, Canada. curibe@bccrc.ca.|Department of Molecular Oncology, BC Cancer Research Centre, Vancouver, British Colombia, Canada. curibe@bccrc.ca.
authors.forename: Carlos F
authors.initials: CF
authors.lastname: Uribe
authors.affiliation: Medical Imaging Research Group, Department of Radiology, University of British Columbia, Vancouver, British Colombia, Canada.|Department of Physics and Astronomy, University of British Columbia, Vancouver, British Colombia, Canada.
authors.forename: Pedro L
authors.initials: PL
authors.lastname: Esquinas
authors.affiliation: Medical Imaging Research Group, Department of Radiology, University of British Columbia, Vancouver, British Colombia, Canada.
authors.forename: Jesse
authors.initials: J
authors.lastname: Tanguay
authors.affiliation: Vancouver Coastal Health Authority, Vancouver, British Colombia, Canada.
authors.forename: Marjorie
authors.initials: M
authors.lastname: Gonzalez
authors.affiliation: Department of Physics, Engineering Physics and Optics, Université Laval, Quebec City, Quebec, Canada.
authors.forename: Emilie
authors.initials: E
authors.lastname: Gaudin
authors.affiliation: Department of Medical Imaging, CHU de Quebec-Université Laval, Quebec City, Quebec, Canada.|Department of Radiology and Nuclear Medicine, Université Laval, Quebec City, Quebec, Canada.
authors.forename: Jean-Mathieu
authors.initials: JM
authors.lastname: Beauregard
authors.affiliation: Medical Imaging Research Group, Department of Radiology, University of British Columbia, Vancouver, British Colombia, Canada.
authors.forename: Anna
authors.initials: A
authors.lastname: Celler
keywords: 177Lu; APDI; Dosimetry; Quantification; Scatter correction; TEW