Displaying the results from NMR pulse sequence simulations as stereo diagrams

Abstract

In some situations, it is so easy to simulate a pulse sequence that the simulation is done even before one has developed an experimental “feel” for the imperfections of a given pulse sequence. Recalling the pedagogical nature of Bloch diagrams, it is beneficial to display calculated spin magnetizations in a similar manner. However, for spin systems with the potential for dipolar or quadrupolar order, the length and the, orientation of the spin magnetization vectors are variable. To indicate both the length and the orientation of a vector on a 2D display, be it on paper or a computer screen, requires some three-dimensional visual cuing. Herein, the possibilities of stereo diagrams are explored. Stereo diagrams are most commonly seen by chemists as ORTEP diagrams of crystal structures ( 1). As is known to many chemists, stereo diagrams may be viewed with the aid of a low-cost stereo viewer (2) or without any aid whatsoever, using the technique of naked-eye stereopsis (3). Naked-eye stereopsis is an easily learned technique for many people. As an introduction to stereo diagrams, the evolution of the deuterium spin magnetization for a solution-state spin-echo pulse sequence, 90,” -~~-180,0T~-ACQ, with e2qz,Q/ h = 0 kHz, is shown in Fig. 1. As the off-resonance condition increases, finite pulse length effects reduce the refocusing efficiency of the spin-echo pulse sequence. Since the quadrupole coupling constant is zero, there can be no quadrupolar order; thus the length of the spin magnetization vector will be constant, in the absence of relaxation effects, and equal to the equilibrium magnetization, MO. The radius of the sphere is set equal to MO. “X” marks the spot on the trace where signal acquisition is to begin. In viewing the stereo diagram with naked-eye stereopsis, the instructions of J. C. Speakman are helpful (3): “look at the diagram from your normal reading distance, with spectacles if these be worn ordinarily; be careful to keep the horizontal line relating the pair parallel to a line connecting your eyes. To foster the illusion, at first, it may help to hold a piece of card (say, 20 cm X 8 cm) as an extension of the nose, so that the right eye sees only the right-hand picture, and ‘vice versa’. Be sure the diagram is well illuminated and free from unilateral shadows cast by the card. When