Free‐breathing 3D CEST MRI of human liver at 3.0 T

Abstract

Purpose To develop a novel 3D abdominal CEST MRI technique at 3 T using MR multitasking, which enables entire‐liver coverage with free‐breathing acquisition. Methods k‐Space data were continuously acquired with repetitive steady‐state CEST (ss‐CEST) modules. The stack‐of‐stars acquisition pattern was used for k‐space sampling. MR multitasking was used to reconstruct motion‐resolved 3D CEST images of 53 frequency offsets with entire‐liver coverage and 2.0 × 2.0 × 6.0 mm3 spatial resolution. The total scan time was 9 min. The sensitivity of amide proton transfer (APT)‐CEST (magnetization transfer asymmetry [MTRasym] at 3.5 ppm) and glycogen CEST (glycoCEST) (mean MTRasym around 1.0 ppm) signals generated with the proposed method were tested with fasting experiments. Results Both APT‐CEST and glycoCEST signals showed high sensitivity between post‐fasting and post‐meal acquisitions. APT‐CEST and glycoCEST MTRasym signals from post‐mean scans were significantly increased (APT‐CEST: −0.019 ± 0.017 in post‐fasting scans, 0.014 ± 0.021 in post‐meal scans, p < 0.01; glycoCEST: 0.003 ± 0.009 in post‐fasting scans, 0.027 ± 0.021 in post‐meal scans, p < 0.01). Conclusion The proposed 3D abdominal steady‐state CEST method using MR multitasking can generate CEST images of the entire liver during free breathing.

Free‐breathing abdominal chemical exchange saturation transfer imaging using water presaturation and respiratory gating at 3.0 T

“…A limitation of this study is that, unlike previous publications, 6,12 we did not ask the participants to fast or have a meal before the MR scans. Therefore, the CEST signal at 3.5 ppm (i.e., amide) and À3.5 ppm (i.e., nuclear Overhauser enhancement), as well as the MTR asymmetry, for the liver tissue may be low, making our results subject to the influence of noise and leading to decreased statistical power.…”

“…Nevertheless, a preliminary experiment of fasting and meal was performed on a healthy subject using three different B1 powers for CEST saturation, and the results (Figure 9) show that the postmeal MTR asymmetry values of APT and glycogen yielded by the proposed sequence are higher than the corresponding postfasting values, which is consistent with the previous studies. 6,12 The second limitation of the study is that the 2D readout used by the proposed sequence may hinder the potential retrospective image realignment when large through-plane motion occurs. The 3D readout is compatible with the proposed sequence, but its acquisition efficiency needs to be greatly improved to avoid too long an echo train and total scan time.…”

“…A more recent work by Han et al employed the MR multitasking technique to implement 3D free-breathing abdominal CEST imaging. 12 The technique still needs further optimizations (e.g., in B1 power, scan time) and validation on patient cohorts for clinical application. 12 In this study, we developed a free-breathing abdominal CEST sequence by using a water presaturation module and respiratory gating.…”

“…12 The technique still needs further optimizations (e.g., in B1 power, scan time) and validation on patient cohorts for clinical application. 12 In this study, we developed a free-breathing abdominal CEST sequence by using a water presaturation module and respiratory gating. In brief, a module that saturates free water was performed before the CEST saturation to remove the dependency of signal on the variation of TR.…”

“…In case a long CEST saturation and thus the steady state cannot be reached, 11 the strategy does not abolish signal variability induced by variation of TR in respiratory‐triggered data acquisition. A more recent work by Han et al employed the MR multitasking technique to implement 3D free‐breathing abdominal CEST imaging 12 . The technique still needs further optimizations (e.g., in B1 power, scan time) and validation on patient cohorts for clinical application 12 …”