Sensitive J‐coupled metabolite mapping using Sel‐MQC with selective multi‐spin‐echo readout

Abstract

The selective multiple quantum coherence technique is combined with a read gradient to accelerate the measurement of a specific scalar-coupled metabolite. The sensitivities of the localization using pure phase encoding and localization with the read gradient are compared in experiments at high magnetic field strength (17.6 T). Multiple spin-echoes of the selective multiple quantum coherence edited metabolite are acquired using frequency-selective refocusing of the specified molecule group. The frequency-selective refocusing does not affect the J-modulation of a coupled spin system, and the echo time is not limited to a multiple of 1/J to acquire pure in-phase or antiphase signal. The multiple echoes can be used to accelerate the metabolite imaging experiment or to measure the apparent transverse relaxation T 2 . A simple phase-shifting scheme is presented, which enables the suppression of editing artifacts resulting from the multiple spin-echoes of the water resonance. In 1 H NMR spectroscopy, the spectral overlap of resonances is a common problem when information about a specific metabolite (e.g., lactate [Lac]) is desired in vivo. In the last decades, several types of spectral editing schemes were developed to filter the metabolite of interest from coresonant or overlapping signals (1-4). The class of multiple quantum coherence (MQC) filters using magnetic field gradients for editing provides robust single-shot editing techniques. One of the single-shot editing filters is the frequency selective multiple quantum coherence editing scheme (Sel-MQC) proposed by He et al. (5). This selective MQC filter enables editing of a single scalar-coupled spin system with simultaneous suppression of water and other resonances in one scan.Successful applications of the Sel-MQC editing sequence have been shown in several studies in which the metabolite of interest is overlapped by other spins with a similar chemical shift. For instance, in extracranial tumor tissues, the Lac CH 3 resonance (at 1.33 parts per million [ppm]) has been filtered from overlapping methylene groups of mobile lipids (5,6). A recent preliminary study on healthy and cancerous human breast tissue has shown a robust application of the Sel-MQC editing sequence to detect polyunsaturated fatty acids (PUFA) (7). The olefinic methylene protons of PUFA at 5.3 ppm that are coupled with the allylic methylene protons of unsaturated acyl chains at 2.8 ppm were detected in breast tissue, and the PUFA pattern is sensitive to breast tissue changes, including cancerous alterations. An adiabatic version of the Sel-MQC scheme was used by de Graaf et al. (8) to detect the ␤H1-glucose resonance at 4.63 ppm in rat brain in vivo. Executing the Sel-MQC sequence with adiabatic radiofrequency pulses allows optimal sensitivity when surface coils are used. In recent years, several extensions of the Sel-MQC editing scheme have been developed, such as Hadamard encoding for localization (9,10), multislice selection using spatial-spectral selective pulses (11), T 1 and T 2 relaxation ...

Ex vivo porcine model to measure pH dependence of chemical exchange saturation transfer effect of glycosaminoglycan in the intervertebral disc

“…Lac imaging was performed as a check to ensure that Lac was successfully incorporated into the IVD in order to manipulate the pH. The selective multiple quantum coherence editing sequence (Sel‐MQC) filter combined with 2D chemical shift imaging scheme was used to detect the Lac signal amplitude in the IVD specimens before and after administration of the Na‐Lac solution in the IVDs (). The Sel‐MQC filter enables the suppression of co‐resonant lipid signals and Lac signal detection in a single scan.…”

Coherence pathway analysis of J-coupled lipids and lactate and effective suppression of lipids upon the selective multiple quantum coherence lactate editing sequence

“…We have shown in this study that the antiphase term of the lactate signal at the echo can be removed by using τ 1 =(1/2J Lac ) − t 1 and the gradient ratio 1:β:2. In contrast, He et al's original scheme [16] and all other studies using the Sel-MQC sequence [17][18][19][20][21][22][23][24][25][26] have employed τ 1 =1/(2J Lac ) regardless of the gradient ratio. In such conditions, the existence of the antiphase term at the echo is inevitable, which results in distortion of the doublet shape of lactate.…”

“…The sequence achieves an improved lipid suppression compared to the basic structure of the first type of MQC sequences [9] by employing multiple spectrally selective RF pulses. The sequence has been utilized to successfully suppress lipid signals and detect lactate from local tumors in numerous in vivo studies [17][18][19][20][21][22][23][24][25][26]. However, when tissues with high lipid concentrations, e.g., calf muscles, were studied, significant amounts of lipids passed through the sequence [20,27].…”