Abstract
ObjectivesTo define normal signal intensity values of amide proton transfer-weighted (APTw) magnetic resonance (MR) imaging in different brain regions.Materials and MethodsTwenty healthy subjects (9 females, mean age 29 years, range 19 – 37 years) underwent MR imaging at 3 Tesla. 3D APTw (RF saturation B1,rms = 2 μT, duration 2 s, 100% duty cycle) and 2D T2-weighted turbo spin echo (TSE) images were acquired. Postprocessing (image fusion, ROI measurements of APTw intensity values in 22 different brain regions) was performed and controlled by two independent neuroradiologists. Values were measured separately for each brain hemisphere. A subject was scanned both in prone and supine position to investigate differences between hemispheres. A mixed model on a 5% significance level was used to assess the effect of gender, brain region and side on APTw intensity values.ResultsMean APTw intensity values in the hippocampus and amygdala varied between 1.13 and 1.57%, in the deep subcortical nuclei (putamen, globus pallidus, head of caudate nucleus, thalamus, red nucleus, substantia nigra) between 0.73 and 1.84%, in the frontal, occipital and parietal cortex between 0.56 and 1.03%; in the insular cortex between 1.11 and 1.15%, in the temporal cortex between 1.22 and 1.37%, in the frontal, occipital and parietal white matter between 0.32 and 0.54% and in the temporal white matter between 0.83 and 0.89%. APTw intensity values were significantly impacted both by brain region (p < 0.001) and by side (p < 0.001), whereby overall values on the left side were higher than on the right side (1.13 vs. 0.9%). Gender did not significantly impact APTw intensity values (p = 0.24). APTw intensity values between the left and the right side were partially reversed after changing the position of one subject from supine to prone.ConclusionWe determined normal baseline APTw intensity values in different anatomical localizations in healthy subjects. APTw intensity values differed both between anatomical regions and between left and right brain hemisphere.
Highlights
Amide proton transfer weighted (APTw) magnetic resonance (MR) imaging is a recently introduced contrast-agent free molecular imaging technique belonging to the chemical exchange saturation transfer (CEST) imaging (Van Zijl and Yadav, 2011; Wu et al, 2016; Van de Ven and Keupp, 2018)
APTw intensity values of female and male subjects were pooled as gender was no significant predictor (p = 0.240) within the mixed model
The Wald statistics of the model suggested that mean APTw values were significantly impacted by side (p < 0.001), brain region (p < 0.001), and the interaction between side and brain region (p < 0.001)
Summary
Amide proton transfer weighted (APTw) magnetic resonance (MR) imaging is a recently introduced contrast-agent free molecular imaging technique belonging to the chemical exchange saturation transfer (CEST) imaging (Van Zijl and Yadav, 2011; Wu et al, 2016; Van de Ven and Keupp, 2018). The signal in APTw imaging originates from amide protons in endogenous proteins and peptides in the brain parenchyma. Protons in amide groups exchange with water protons in their close vicinity. First amide protons are selectively saturated by a radiofrequency pulse tuned at a frequency of + 3.5 ppm from the water resonance. The resulting water saturation level, that is imaged by conventional MR technique, is strongly correlated with the concentration and exchange rate of proteins and peptides in the tissue (Van de Ven and Keupp, 2018)
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