title: A phantom study: Should124I-mIBG PET/CT replace123I-mIBG SPECT/CT?
abstract: OBJECTIVE
  The isotope123I is commonly labeled with meta-iodobenzylguanidine (mIBG) for imaging of neuroendocrine tumors, such as pheochromocytomas and neuroblastomas.123I-mIBG SPECT/CT imaging is performed for staging, follow-up and selection of patients for treatment with131I mIBG. As an alternative to123I,124I-mIBG PET/CT may be used, potentially taking advantage of the superior PET image quality. The purpose of this study was to investigate whether124I PET/CT improves image quality as compared with123I SPECT/CT for equal patient effective radiation dose (in mSv).
  
  
  METHODS
  Phantom measurements were performed using the NEMA-2007 image quality phantom. SPECT and PET reconstruction settings were used with and without time-of-flight (TOF) and point-spread-function (PSF) modeling. As a measure of image quality, the contrast-to-noise ratio (CNR) was calculated. The ratio of the123I to124I activity concentration was determined at which the contrast-to-noise ratio was equal for both modalities. This metric was defined as the contrast equivalent activity ratio (CEAR).
  
  
  RESULTS
  CEARs of 47.7, 25.6, 23.1, 14.6, 10.0, and 9.1 were obtained for a TOF and PSF modeled124I reconstruction method and an attenuation and scatter-corrected123I reconstruction method for sphere sizes of 10 to 37 mm, respectively. As the effective radiation dose of124I-mIBG is higher than of123I-mIBG (in mSv/MBq), an equal effective dose corresponds to a CEAR of 5 to 10. Therefore, CEARs higher than 5 to 10 indicate that124I PET/CT outperforms123I SPECT/CT in the sense of image quality for equal patient effective radiation dose.
  
  
  CONCLUSIONS
  The CEAR is much larger than a factor of 5 to 10 (needed for equal patient effective radiation dose) for most of the reconstruction methods and sphere sizes. Therefore,124I-mIBG PET/CT is expected to improve image quality and/or may be used to reduce effective patient dose as compared with123I-mIBG SPECT/CT.
authors.affiliation: Department of Radiology and Nuclear Medicine, UMC Utrecht, Utrecht, The Netherlands.|Image Sciences Institute, UMC Utrecht, Utrecht, The Netherlands.
authors.forename: Casper
authors.initials: C
authors.lastname: Beijst
authors.affiliation: Department of Radiology and Nuclear Medicine, UMC Utrecht, Utrecht, The Netherlands.
authors.forename: Bart
authors.initials: B
authors.lastname: de Keizer
authors.affiliation: Department of Radiology and Nuclear Medicine, UMC Utrecht, Utrecht, The Netherlands.
authors.forename: Marnix G E H
authors.initials: MGEH
authors.lastname: Lam
authors.affiliation: Department of Radiation Oncology, UMC Utrecht, Utrecht, The Netherlands.
authors.forename: Geert O
authors.initials: GO
authors.lastname: Janssens
authors.affiliation: Princess Máxima Center for Pediatric Oncology, Utrecht, The Netherlands.
authors.forename: Godelieve A M
authors.initials: GAM
authors.lastname: Tytgat
authors.affiliation: Department of Radiology and Nuclear Medicine, UMC Utrecht, Utrecht, The Netherlands.
authors.forename: Hugo W A M
authors.initials: HWAM
authors.lastname: de Jong
mesh_terms: D019797:3-Iodobenzylguanidine / Q000493:pharmacokinetics*; D006801:Humans; D018358:Neuroendocrine Tumors / Q000000981:diagnostic imaging; D019047:Phantoms, Imaging; D000072078:Positron Emission Tomography Computed Tomography; D049268:Positron-Emission Tomography; D015899:Tomography, Emission-Computed, Single-Photon; D014057:Tomography, X-Ray Computed
chemical_list: D019797:3-Iodobenzylguanidine
keywords: 123I SPECT/CT; 124I PET/CT; CNR; image quality; mIBG; phantom