SPECT was performed using a dual-head gamma camera (Infinia
TM; GE Healthcare, Buckinghamshire, UK) and an ELEGP collimator (GE Healthcare, Buckinghamshire, UK). The energy range was centered at 159 keV with a width of 10%, and a 2-min rotation was performed 14 times in a continuous mode. The matrix size was 64 × 64 pixels.
The procedures of DTARG are presented in
Fig 2 [11 (
link)]. A two-time intravenous injection of 123I-IMP (111 MBq product, respectively) was administered by a radiologist at a 30-min interval. The injected dose volume was calculated by the following equation:
Injected dose volume (MBq) = 111 ×
exp (−0.0525 ×
t)
where
t represents the elapsed time from the Japan standard time (UTC +9) of 12:00. SPECT data collection commenced simultaneously with the intravenous injection of 123I-IMP. Dynamic SPECT scanning was performed for 28 min (0–28 and 30–58 min after the start of the first injection of 123I-IMP). Approximately 10 min after the first 123I-IMP intravenous injection, 2 mL of arterial blood was obtained from the radial or femoral artery, and the standard input function was calibrated. The sample arterial blood radioactivity concentration was measured using a well counter (DCM-200
TM; ALOKA, Tokyo, Japan). Approximately 20 min after the first 123I-IMP intravenous injection, 1,000 mg of acetazolamide was intravenously administered. The cross-calibration factor (CCF) between the SPECT images and the well counter system was determined in advance by comparing the average pixel counts derived from the regions of interest (ROIs) on the reconstructed emission images and the well counter radioactivity-counting rate.
The uniformity correction and center-of-rotation calibration were performed using the clinical routine software on the SPECT system. Stereotactic anatomic standardization was also performed on the scan data using three-dimensional stereotactic surface projections (3D-SSP, Nihon Medi-Physics, Tokyo, Japan) [12 (
link)]. The ROIs were placed on the standardized images both at rest and following the acetazolamide challenge, using an automatic ROI definition software (NEURO FLEXER, Nihon Medi-Physics, Tokyo, Japan) [13 (
link)]. This software automatically placed three-dimensional ROIs on 10 arterial territories, including the bilateral anterior cerebral artery, bilateral middle cerebral artery (MCA), bilateral anterior part of MCA, bilateral posterior part of MCA, and bilateral posterior cerebral artery. The ROIs were also placed on 10 segments, including the bilateral hemisphere, bilateral basal ganglia, bilateral thalamus, bilateral cerebellar hemisphere, pons, and vermis of the cerebellum (
Fig 3).
Kaga T., Kato H., Imai T., Ando T., Noda Y., Miura T., Enomoto Y., Hyodo F., Iwama T, & Matsuo M. (2023). Non-invasive regional cerebral blood flow quantification in the 123I-IMP autoradiography using artificial neural network. PLOS ONE, 18(3), e0281958.