[Usefulness of the Nasion-fourth Ventricle Line and the Tuberculum Sellae-internal Occipital Protuberance Line as Alternatives to the AC-PC Line in 123I-ioflupane SPECT].

Abstract

Purpose: In ¹²³I-ioflupane single-photon emission computerized tomography, anatomical landmarks are often indistinct, making identification of the anterior commissure-posterior commissure (AC-PC) line difficult in clinical practice. This study evaluated the usefulness of the tuberculum sellae-occipital protuberance (TS-OP) line and the nasion-fourth ventricle (nasion-4V) line, which is routinely used at our institution, as alternative reference lines.

Methods: Angular differences from the AC-PC line were calculated, and inter-observer reproducibility and agreement of each line were assessed using the ICC and Bland-Altman analysis. In addition, ΔSBR (specific binding ratio) was calculated using our institutional reference axis to investigate the effect of angular differences on quantitative values.

Results: The largest angular difference from the AC-PC line was observed for the nasion-4V line (-2.5°), although no significant differences were found among the lines. All lines demonstrated good reproducibility; however, the TS-EOP line showed slightly lower agreement, likely due to differences in recognition of bony morphology. Bland-Altman analysis revealed that the nasion-4V line had the smallest bias, and the TS-IOP line also showed a small bias of less than 1°. Although the nasion-4V line exhibited a relatively larger angular difference, it maintained high reproducibility and agreement. An angular difference of approximately 2.5° resulted in a maximum SBR change of 0.15.

Conclusion: The nasion-4V line demonstrated high reproducibility and agreement, while the TS-IOP line showed minimal deviation and can be defined using bony landmarks. Both may be considered alternative reference lines when the AC-PC line is difficult to identify, with the TS-IOP line potentially representing a more stable option.