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

Abstract

Parallel transmission-based APT imaging of brain tumors showed good reproducibility.

Grading diffuse gliomas without intense contrast enhancement by amide proton transfer MR imaging: comparisons with diffusion- and perfusion-weighted imaging

“…Since CEST imaging is highly sensitive to B0 inhomogeneity, shimming and correction for B0 inhomogeneity in the postprocessing are crucial. The accuracy and reproducibility of the APT imaging scheme used in the present study was confirmed in patients with various types of brain tumour [16].…”

“…This problem was solved in the present study by using the two amplifiers of a parallel transmission system in alternation [15,16], enabling 2 s of saturation at 100 % duty-cycle. A 2012 study showed that the APT contrast obtained with the 2-s saturation was higher than the corresponding values obtained with 0.5-s or 1-s saturation in various types of human brain tumours including gliomas [26].…”

“…For the APT imaging, the acquisition software was modified to alternate the operation of the two transmission LGG, low-grade glioma; HGG, high-grade glioma; M, male; F, female; O, oligodendroglioma; A, diffuse astrocytoma; OA, oligoastrocytoma; AO, anaplastic oligodendroglioma; AA, anaplastic astrocytoma; AOA; anaplastic oligoastrocytoma; GBM, glioblastoma multiforme; rt., right; lt., left channels during the RF saturation pulse, which enables long quasi-continuous RF saturation at a 100 % RF duty-cycle and a special RF shimming for the saturation homogeneity of the alternated pulse [15,16]. On a single axial slice corresponding to a maximum crosssection area of a tumour, two-dimensional (2-D) APT imaging was performed using a saturation pulse with a duration of 2 s (40 × 50 msec, sinc-gauss-shaped elements) and a saturation power level of B 1,rms = 2.0 μT [15,16]. For acquiring a Zspectrum, the imaging was repeated at 25 saturation frequency offsets from ω = −6 to +6 ppm with a step of 0.5 ppm as well as one far-off-resonant frequency (ω = −1560 ppm) for signal normalization.…”

“…A ΔB0 map for off-resonance correction was acquired separately using a 2D gradient-echo with identical spatial resolution for a point-by-point ΔB0 correction [15,16].…”

Simultaneous pH‐sensitive and oxygen‐sensitive MRI of human gliomas at 3 T using multi‐echo amine proton chemical exchange saturation transfer spin‐and‐gradient echo echo‐planar imaging (CEST‐SAGE‐EPI)

“…However, this sequence only measured R 2 characteristics and could not correct for B 0 using phase information available via multiple gradient echoes. The fast EPI readout available using CEST‐SAGE‐EPI vastly improves acquisition times over slower, single‐slice, or volumetric approaches . Song et al and others have described single‐echo EPI approaches to speed up acquisition time; however, these studies lacked concurrent measurement of subsequent echoes that would allow for estimation of R 2 , , and B 0 .…”