Chemical exchange saturation transfer MRI using intermolecular double-quantum coherences with multiple refocusing pulses

Abstract

Chemical exchange saturation transfer (CEST) provides a new type of image contrast in MRI. Due to the intrinsically low CEST effect, new and improved experimental techniques are required to achieve reliable and quantitative CEST images. In the present work, we proposed a novel and more sensitive CEST acquisition approach, based on the intermolecular double-quantum coherence with a module of multiple refocusing pulses (iDQC-MRP). Experiments were performed on creatine and egg white phantoms using a Varian 7 T animal MRI scanner. The iDQC-MRP CEST technique showed a substantial enhancement in CEST and nuclear Overhauser enhancement (NOE) signal intensities, compared to the standard single-quantum coherence approach. In addition, the iDQC-MRP approach increased the signal-to-noise ratio of acquired saturation images, compared to the conventional iDQC approach. The new iDQC-MRP CEST sequence provides a promising way for exploiting in vivo CEST and NOE imaging applications.

Nuclear Overhauser Enhancement-Mediated Magnetization Transfer Imaging in Glioma with Different Progression at 7 T

“…Magnetization transfer (MT) imaging is a popular technique used in magnetic resonance imaging (MRI). Chemical exchange saturation transfer (CEST), a specific type of MT imaging, has recently emerged as an important contrast mechanism for MRI in the field of cellular and molecular imaging. − It indirectly detects pools of exchangeable protons through the water signal from low-concentration exogenous or endogenous pools of exchangeable protons (such as amide or imino protons, amine protons, and hydroxyl protons) to the bulk water proton pool. , Irradiation offsets (ppm) around the water resonance frequency are set to acquire water signals. Therefore, MT spectra, also known as Z-spectra, are regarded as symmetric spectra around the water proton resonance.…”

“…1−6 It indirectly detects pools of exchangeable protons through the water signal from low-concentration exogenous or endogenous pools of exchangeable protons (such as amide or imino protons, amine protons, and hydroxyl protons) to the bulk water proton pool. 7,8 Irradiation offsets (ppm) around the water resonance frequency are set to acquire water signals. Therefore, MT spectra, also known as Z-spectra, are regarded as symmetric spectra around the water proton resonance.…”

Pulse sequences for measuring exchange rates between proton species: From unlocalised NMR spectroscopy to chemical exchange saturation transfer imaging

“…The measured signal is generated from spins with distance equal to half of the length of the helix. Therefore, by changing the helix length, which is inversely proportional to the duration and strength of the gradient pulse, the interaction distance between spins is altered making this technique of interest for biological and clinical imaging ( 69),( 70), (71). Recently it was shown that the MT effect of immobilised molecules could be enhanced due to its large homogeneous broadening when saturation transfer experiments are combined with the iMQC method, in which the contrast is described by the m-th power where m is the quantum coherence order.…”

“…The iMQC effect has also been exploited in a preclinical system operating at 4.7T for imaging cartilage using solutions of glycosaminoglycans and cartilage tissue (71). In that case, the signal was shown to be equal to under a weak pulse approximation.…”

“…Another application of the iDQC technique combines the iDQC CEST detection with multiple refocusing pulses for improving image SNR (71). Similarly to a CPMG type of experiment, this approach replaces the single refocusing pulse in the detection period with multiple refocusing pulses (MRP), which gives higher refocusing signal intensity.…”