7T comprehensive CEST: a clinically feasible multi-exchange-regime CEST protocol

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. 7T comprehensive CEST ! a clinically feasible multi-exchange-regime CEST protocol Moritz Simon Fabian1, Lukas Kamm1, Angelika Barbara Mennecke1, and Moritz Zaiß1,2 1Institute of Neuroradiology, University Hospital Erlangen, Erlangen, Germany, 2High-field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany ! Either Oral or Poster Presentation | Contact Email: Moritz.fabian@uk-erlangen.de KEYWORD: ! CEST agents ! Standardization 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 Table 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 were able to shorten this comprehensive CEST protocol down to 15 minutes [6]. Conclusion The proposed 7T snapshot CEST protocol is able to generate CEST contrasts of three different exchange and B1 saturation regimes simultaneously