title: Optimal HMPAO α value for Lassen's correction algorithm obscured by statistical noise.
abstract: OBJECTIVE
  [(99m)Tc] D,L-hexamethyl-propyeneamine oxime ((99m)Tc-HMPAO), a brain perfusion tracer, suffers significant underestimation of regional cerebral blood flow (rCBF). Lassen et al. developed their linearization algorithm to correct the influence of back-diffusion of the tracer, and proposed their parameter α as 1.5. Based on mathematical modeling and literature review, recently, a new α value of 0.5 has been proposed for Lassen's correction algorithm for (99m)Tc-HMPAO, although correction using the old α value of 1.5 was confirmed to be sufficient. Inugami et al. reported that linearization correction gives a stable correlation coefficient over a wide range of α. Our hypotheses are that statistical noise is the source of the stable correlation coefficient presented by them and that the robustness of the correlation coefficient is the reason why many studies confirmed the value of α as 1.5.
  
  
  METHODS
  Statistical noise was added in silico to the count, whose relationship with flow was α = 0.5. Then, the count was corrected by Lassen's linearization algorithm with a variety of α.
  
  
  RESULTS
  This study confirmed the hypothesis that smaller α values (strong correction) increase the noise at high flow values, leading to nominal increases in correlation coefficient as α decreases.
  
  
  CONCLUSIONS
  Despite this, adoption of the new, smaller α value of 0.5 would be more useful clinically in regaining the contrast between low-flow and high-flow areas of the brain.
authors.affiliation: Division of Nuclear Medicine, Department of Radiology, National Center for Global Health and Medicine, 1-21-1 Toyama, Shinjuku-ku, Tokyo, 162-8655, Japan. kame-tky@umin.ac.jp.|Division of Nuclear Medicine, Department of Radiology, School of Medicine, Keio University, 35 Shinanomachi, Shinjuku-ku, Tokyo, 160-8582, Japan. kame-tky@umin.ac.jp.
authors.forename: Masashi
authors.initials: M
authors.lastname: Kameyama
authors.affiliation: Division of Nuclear Medicine, Department of Radiology, School of Medicine, Keio University, 35 Shinanomachi, Shinjuku-ku, Tokyo, 160-8582, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Murakami
authors.affiliation: Department of Radiology, School of Medicine, Keio University, 35 Shinanomachi, Shinjuku-ku, Tokyo, 160-8582, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Jinzaki
mesh_terms: D000465:Algorithms; D001921:Brain / Q000098:blood supply / Q000000981:diagnostic imaging; D002560:Cerebrovascular Circulation; D007091:Image Processing, Computer-Assisted; D008962:Models, Theoretical; D059629:Signal-To-Noise Ratio; D019690:Technetium Tc 99m Exametazime; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods*
chemical_list: D019690:Technetium Tc 99m Exametazime
keywords: 99mTc-HMPAO; Image contrast; Lassen’s linearization correction algorithm; Renkin–Crone’s equation; Single photon emission computed tomography