Amide proton transfer imaging for differentiation of tuberculomas from high-grade gliomas: Preliminary experience

Tuberculomas can occasionally masquerade as high-grade gliomas (HGG). Evidence from magnetisation transfer (MT) imaging suggests that there is lower protein content in the tuberculoma microenvironment. Building on the principles of chemical exchange saturation transfer and MT, amide proton transfer (APT) imaging generates tissue contrast as a function of the mobile amide protons in tissue's native peptides and intracellular proteins. This study aimed to further the understanding of tuberculomas using APT and to compare it with HGG.

Twenty-two patients (n = 8 tuberculoma; n = 14 HGG) were included in the study. APT was a 3D turbo spin-echo Dixon sequence with inbuilt B₀ correction. A two-second, 2 μT saturation pulse alternating over transmit channels was applied at ±3.5 ppm around water resonance. The APT-weighted image (APTw) was computed as the MT ratio asymmetry (MTR_asym) at 3.5 ppm. Mean MTR_asym values in regions of interest (areas = 9 mm²; positioned in component with homogeneous enhancement/least apparent diffusion coefficient) were used for the analysis.

MTR_asym values of tuberculomas (n = 14; 8 cases) ranged from 1.34% to 3.11% (M = 2.32 ± 0.50). HGG (n = 17;14 cases) showed MTR_asym ranging from 2.40% to 5.70% (M = 4.32 ± 0.84). The inter-group difference in MTR_asym was statistically significant (p < 0.001). APTw images in tuberculomas were notable for high MTR_asym values in the perilesional oedematous-appearing parenchyma (compared to contralateral white matter; p < 0.001).

Tuberculomas demonstrate lower MTR_asym ratios compared to HGG, reflective of a relative paucity of mobile amide protons in the ambient microenvironment. Elevated MTR_asym values in perilesional parenchyma in tuberculomas are a unique observation that may be a clue to the inflammatory milieu.