Numerical simulations of contribution of chemical shift in novel magnetic resonance imaging

Huijun Sun, Tao Lin, Shuhui Cai and Zhong Chen
Lecture Notes in Computer ScienceVolume 4222/2006
Advances in Natural Computation

Abstract
Contribution of chemical shift to intermolecular multiple-quantum coherence (iMQC) imaging signals in two-component systems was simulated and discussed using an efficient numerical algorithm based on the Bloch equations with an additional nonlinear term describing distant dipolar field. Numerical simulation switches back and forth between real and Fourier spaces to handle dipolar field effects in three-dimensional sample. The iMQC signals of each component of two-component systems can be obtained respectively when the second pulse of the CRAZED pulse sequence is selective. Simulation results show that chemical shift provides an edge detection method to regions containing spins with chemical shift offset and selected by the second RF pulse, and different gray value is related to different chemical shift in detected regions. These results indicate that chemical shift may provide new imaging information helpful for iMQC magnetic resonance imaging.

Multiple quantum correlated spectroscopy revamped by asymmetric z-gradient echo detection signal intensity as a function of the read pulse flip angle

Bin Jiang, Huili Liu, China Maili Liu, Chaohui Ye, and China Xi-an Mao
J. Chem. Phys. 126, 054502 (2007)

(Received 28 August 2006; accepted 5 December 2006; published online 1 February 2007)

Heteronuclear multiple quantum (n=±0 and n=±2) correlated spectroscopy revamped by asymmetric z-gradient echo detection (CRAZED) experiments were performed on the spins ³¹P and ¹H in a H₃PO₄ solution in order to determine the optimum flip angle for the read pulse. It has been shown that for the negative quantum signals, the maximum signals appear at =0, and for the positive quantum signals, the maximum signals appear at =. The CRAZED signals were compared to the single quantum signals in two-pulse two-gradient experiments. It is found that the CRAZED signals can also be distinguished into gradient echoes and spin echoes. The gradient-echo-type CRAZED signal requires =0 and the spin-echo-type CRAZED signal requires = for maximum echo intensities, in the same way as in single quantum experiments. ©2007 American Institute of Physics

Simultaneous acquisition and effective separation of intermolecular multiple-quantum signals of different orders

Xiaoqin Zhu, Song Chen, Zhong Chen, Shuhui Cai and Jianhui Zhong
Chemical Physics Letters
Volume 438, Issues 4-6, 20 April 2007, Pages 308-314

Abstract
A three-pulse sequence was designed to simultaneously acquire intermolecular multiple-quantum coherence (iMQC) signals of coherence order n = 2, 1, 0, −1, −2. Analytical expressions were derived from modified Bloch equations. Signal of a specific order was obtained by optimal combinations of data from different acquisition steps. This allows a time saving of 5/7 compared to the phase cycling designs targeted for individual coherence orders. The method also results in pure iMQC signal of all the above five orders which are insensitive to radio-frequency flip angle errors, in contrast to some previous methods. Theoretical predictions are supported by the experimental observations and numerically simulated results.

Magnetic resonance microscopic imaging based on high-order intermolecular multiple-quantum coherences

Jee-Hyun Cho, Sangdoo Ahn, Chulhyun Lee, Kwan Soo Hong, Kee-Choo Chung, Suk-Kyu Chang, Chaejoon Cheong and Warren S. Warren
Magnetic Resonance Imaging
Article in Press, Corrected Proof

Abstract

Most imaging studies using intermolecular multiple-quantum coherences (iMQCs) have focused on the two-spin dipolar interactions — zero and double quantum coherences. Here, we report the results of various experimental studies to assess the feasibility of magnetic resonance microscopy with high-order iMQCs in model systems at 7 and 14 T. Experimental results demonstrated that the iMQC microscopic images with high coherence orders are readily observable at high field and have unique contrast depending on the sample microstructure and coherence order.

Keywords: Intermolecular multiple-quantum coherence; iTQC; iQQC; MR microscopy

Signal enhancement in CRAZED experiments

Signal enhancement in CRAZED experiments
Rosa T. Branca, Gigi Galiana and Warren S. Warren
Journal of Magnetic Resonance
Article in Press, Corrected Proof

Many of the promising applications of the CRAZED (COSY Revamped with Asymmetric Z-gradient Echo Detection) experiments are in biomedical and clinical technologies. In tissue, however, signal from the typical CRAZED experiment is largely limited by transverse relaxation. When relaxation is included, the maximum achievable signal from a prototypical CRAZED sequence, in the linear regime, is proportional to T2/τd. This means that for samples with a short T2, as encountered in vivo, signals from intermolecular multiple-quantum coherences (iMQCs) reach very diminished signal intensities. While relaxation is generally regarded as a fundamental constraint, we show here that when T2 is short but T1 is long, as in tissue, there are simple sequence modifications that can increase signal beyond the T2 limit. To better utilize the available signal intensity from iMQCs we propose a method to substitute part of the transverse magnetization with the longitudinally modulated magnetization. In this paper we show, with both simulations and experimental results, that in the presence of strong transverse relaxation the standard CRAZED scheme is not the optimal method for observing iMQCs, and can be improved upon with simple modifications.

Keywords: CRAZED; iZQC; iDQC; Dipolar demagnetization time