Scan-rescan reproducibility of parallel transmission based amide proton transfer imaging of brain tumors

Purpose To evaluate the reproducibility of amide proton transfer (APT) imaging of brain tumors using a parallel transmission-based technique. Materials and Methods Thirteen patients with brain tumors (four low-grade gliomas, three glioblastoma multiforme, five meningiomas, and one malignant lymphoma) were included in the study. APT imaging was conducted at 3T using a 2-channel parallel transmission scheme with a saturation time of 2 seconds and B₁ amplitude of 2 μT. A 2D fast spin-echo sequence with driven-equilibrium refocusing was used for imaging. Z-spectra were obtained at 25 frequency offsets from -6 to +6 ppm (step 0.5 ppm). A point-by-point B₀ correction was performed with a B₀ map. A scan-rescan reproducibility test was performed in two sessions on separate days for each patient. The interval between the two sessions was 4.8±3.5 days. Regions-of-interest (ROIs) were placed to include the whole tumor for each case. A mean and 90-percentile value of APT signal for the whole tumor histogram was calculated for each session. The between-session and within-session reproducibility was evaluated using linear regression analysis, intraclass correlation coefficient (ICC), and a Bland-Altman plot. Results The mean and 90-percentile values of the APT signal for whole tumor ROI showed excellent agreements between the two sessions, with R² of 0.91 and 0.96 in the linear regression analysis and ICC of 0.95 and 0.97, respectively. Conclusion Parallel transmission-based APT imaging of brain tumors showed good reproducibility.