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Abstract

Introduction
Chemical exchange saturation transfer (CEST) MR imaging detects the signal of low concentrated molecules utilizing proton
exchange and selective RF saturation. The CEST effect is dependent on the RF saturation scheme, more specifically on RF
pulse type, shape, duration and B1 level. So far, 7T CEST measurements in vivo [1-3] focus only on saturation parameters
selecting one specific exchange regime, e.g. either low B1, intermediate B1 or high B1 CEST sequences are used in different
patient studies. Therefore, we establish a 7T snapshot CEST protocol, which labels all of these CEST effects simultaneously.
Applying this comprehensive protocol to patients suffering from multiple sclerosis, brain tumor or stroke is expected to
provide deeper insight into the CEST properties of these pathologies.
Methods
Measurements are conducted at a MAGNETOM Terra 7T scanner (Siemens Healthineers AG, Erlangen, Germany) with a
32Rx/8Tx-channel head coil (Nova Medical, Wilmington, MA), and are approved by the local ethics committee.
The CEST image readout was the 3D snapshot GRE MIMOSA CEST [4,5]. Low B1 CEST measurements for detection of Amide,
NOE, Amine and MT pool were done according to [1]. Intermediate B1 CEST (GluCEST) is measured according to [2]. High B1
CEST is realized by adiabatic spin-lock pulses for hydroxyl CEST [3]. An overview regarding the saturation scheme of the
measurements is shown in Figure 1.
Results & Discussion
Figure 2 shows that we could generate all desired CEST contrast of all different exchange and B1 regimes with similar
homogeneity within one protocol. All contrast show few imperfection (Figure 2), which can still be improved using better
B0/B1 mitigation/correction and less sensitive evaluation metrics. From the original sampling with a total scan time of about
40 minutes, we are able to shorten this comprehensive CEST protocol down to 15 minutes (data not shown). [6]
Conclusion
The proposed 7T snapshot CEST protocol is able to generate CEST contrasts of three different exchange and B1 saturation
regimes simultaneously.