title: Acquisition protocols and correction methods for estimation of the heart-to-mediastinum ratio in 123I-metaiodobenzylguanidine cardiac sympathetic imaging.
abstract: Septal penetration of high-energy photons affects quantitative results in imaging of (123)I-labeled tracers. We investigated acquisition protocols (collimator choice and energy window setting) and correction methods for estimating the heart-to-mediastinum (H/M) ratio in cardiac (123)I-metaiodobenzylguanidine (MIBG) imaging.
  
  
  METHODS
  Four hours after (123)I-MIBG injection, 40 patients successively underwent planar anterior chest imaging with the medium-energy (ME) (ME method) and low-energy high-resolution (LEHR) (LEHR method) collimators. A 20% energy window was used for both collimators. Another 40 patients were imaged successively with the ME collimator and a 20% window (ME method), the low-medium-energy (LME) collimator and a 20% window (LME20 method), and the LME collimator and a 15% window (LME15 method). The H/M ratios obtained by the LEHR, LME20, and LME15 methods were corrected using their correlations with the H/M ratio obtained by the ME method (empiric correction). The (123)I-dual-window (IDW) correction was also applied to remove the influence of high-energy photons.
  
  
  RESULTS
  Without correction, severe underestimation of the H/M ratio was shown for the LEHR method using the ME method as a standard, and this underestimation increased with increasing H/M ratios. Underestimation substantially decreased using the LME20 method and further using the LME15 method. Empiric correction reduced the error in the H/M ratio by the LEHR method, but the error was still evident. After empiric correction, the H/M ratios with the LME collimator were comparable to those with the ME collimator. The IDW correction only partially reduced underestimation by the LEHR method and caused a small overestimation for the LME15 method.
  
  
  CONCLUSIONS
  The use of an LME collimator appears to be acceptable for cardiac (123)I-MIBG imaging as an alternative to an ME collimator, and the application of a 15% energy window is recommended when an LME collimator is used. Empiric correction is also expected to improve exchangeability between H/M ratios calculated with ME and LME collimators. Neither the use of an LEHR collimator nor the use of IDW correction is recommended.
authors.affiliation: Department of Diagnostic Radiology, Kitasato University School of Medicine, Sagamihara, Kanagawa, Japan. inoueys34@gmail.com
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Inoue
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Abe
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Itoh
authors.forename: Yuji
authors.initials: Y
authors.lastname: Asano
authors.forename: Kei
authors.initials: K
authors.lastname: Kikuchi
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Sakamoto
authors.forename: Keiji
authors.initials: K
authors.lastname: Matsunaga
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Ogino
authors.forename: Takahiro
authors.initials: T
authors.lastname: Iizuka
authors.forename: Hideki
authors.initials: H
authors.lastname: Mochizuki
mesh_terms: D019797:3-Iodobenzylguanidine; D000368:Aged; D005260:Female; D006321:Heart / Q000000981:diagnostic imaging / Q000294:innervation*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008482:Mediastinum / Q000000981:diagnostic imaging*; D011877:Radionuclide Imaging; D012189:Retrospective Studies; D013564:Sympathetic Nervous System / Q000000981:diagnostic imaging*
chemical_list: D019797:3-Iodobenzylguanidine
keywords: 123I-metaiodobenzylguanidine (MIBG); collimator; energy window; heart-to-mediastinum (H/M) ratio; septal penetration