Usefulness of the frontal lobe bottom and cerebellum tuber vermis line as an alternative clue to set the axial angle parallel to the AC-PC line in I-123 IMP SPECT imaging: a retrospective study.

We aimed to investigate whether the frontal lobe bottom and cerebellum tuber vermis (FLB-CTV) line on brain perfusion scintigraphy, using iodine-123 isopropyl iodoamphetamine single photon emission computed tomography (I-123 IMP SPECT) images, is useful to determine an axial angle parallel to the anterior commissure-posterior commissure (AC-PC) line. We measured the angular differences between the AC-PC line and the FLB-CTV line on midsagittal brain magnetic resonance imaging (MRI) scans of 100 patients. We also evaluated the angular differences of the FLB-CTV line between the IMP SPECT images and the computed tomography for attenuation correction (CTAC) images in the same 100 patients, using a reference line on the CTAC images. Furthermore, the inter-reader reproducibility of the FLB-CTV line measurements on IMP SPECT images of 50 patients between two readers was evaluated using the intra-class correlation coefficient (ICC) and 95% confidence interval (CI). The mean and standard deviation of the angular differences between the AC-PC and FLB-CTV lines on midsagittal brain MRI scans were - 1.24° and 1.14°, respectively. The mean and the standard deviation of the angular differences of the FLB-CTV line in the IMP SPECT and CTAC images were 0.87° and 0.48°, respectively. The ICC of the FLB-CTV line measurements on IMP SPECT images was 0.99 (95% CI 0.98-0.99). We demonstrated that the FLB-CTV line was almost parallel to the AC-PC line and could be reconstructed using IMP SPECT images. The FLB-CTV line can be used as additional evidence to set the axial angle parallel to the AC-PC line.