Abstract
In this study, we evaluated the dependence of saturation pulse length on APT imaging of diffuse gliomas using a parallel transmission-based technique. Twenty-two patients with diffuse gliomas (9 low-grade gliomas, LGGs, and 13 high-grade gliomas, HGGs) were included in the study. APT imaging was conducted at 3T with a 2-channel parallel transmission scheme using three different saturation pulse lengths (0.5 s, 1.0 s, 2.0 s). The 2D fast spin-echo sequence was used for imaging. Z-spectrum was 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. Magnetization transfer ratio (MTRasym) and ΔMTRasym (contrast between tumor and normal white matter) at 3.5 ppm were compared among different saturation lengths. A significant increase in MTRasym (3.5 ppm) of HGG was found when the length of saturation pulse became longer (3.09 ± 0.54% at 0.5 s, 3.83 ± 0.67% at 1 s, 4.12 ± 0.97% at 2 s), but MTRasym (3.5 ppm) was not different among the saturation lengths in LGG. ΔMTRasym (3.5 ppm) increased with the length of saturation pulse in both LGG (0.48 ± 0.56% at 0.5 s, 1.28 ± 0.56% at 1 s, 1.88 ± 0.56% at 2 s and HGG (1.72 ± 0.54% at 0.5 s, 2.90 ± 0.49% at 1 s, 3.83 ± 0.88% at 2 s). In both LGG and HGG, APT-weighted contrast was enhanced with the use of longer saturation pulses.
Highlights
Chemical exchange saturation transfer (CEST) has attracted great attention in the area of molecular imaging as a novel contrast mechanism in MR imaging [1]
In both LGG and HGG, Z-spectrum of tumor was steeper than that of normal appearing white matter (NAWM), indicating less magnetization transfer (MT) effect in tumor compared with NAWM
Increase of saturation pulse length resulted in decreased signal intensity in entire range of Z-spectra in both LGG and HGG as well as in NAWM, which indicated that MT effect and direct saturation became larger in all tissues with longer saturation pulses
Summary
Chemical exchange saturation transfer (CEST) has attracted great attention in the area of molecular imaging as a novel contrast mechanism in MR imaging [1]. CEST contrast is obatined by applying a saturation pulse at the resonance frequency of a slow-intermediate exchanging proton site (-NH, -OH, -H2O) of endogenous or exogenous agents, and the resulting saturated or partially saturated protons are transferred to bulk water via chemical exchange. Saturation Pulse Length in APT Imaging of Gliomas collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the 'author contributions' section
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