Z-axis modulation

Figure 6. Block diagram of z-axis modulation system...

Figure 8. Photograph of z-axis modulated oscilloscope display obtained during...

John SD (1999) Trends in pediatric emergency imaging. Radiol Clin North Am 37 995-1034 Kalra MK, Maher MM, Kamath RS et al (2004a) Sixteen-detector row CT of abdomen and pelvis study for optimization of Z-axis modulation technique performed in 153 patients. Radiology 233 241-249 Kalra MK, Maher MM, Toth TL et al (2004b) Comparison of Z-axis automatic tube current modulation technique with fixed tube current CT scanning of abdomen and pelvis. Radiology 232 347-353... 

Figure 3. Dependence of the Young s module on the multiplicity of linear deformation Az at stretching and squeezing of natural rubber along z axis. Calculation has been done in accordance with the eq. (78) (see the explanations in text). 

Fig. 8.19. Vector representation of a H-13C HMQC experiment. The first 90° pulse along y rotates the equilibrium magnetization of the proton spin, /H, from the z axis to the x axis. After a time /d = 1/2/Hx, the antiphase coherence 2/J1/ t (see Appendix IX) is at its maximum. A 90° pulse on carbon along y then transforms the antiphase coherence into a MQ (multiple quantum) coherence (the 2/J1/ component is shown). During t the MQ evolves (with a 180 refocusing pulse on proton in the middle), until a further 90 pulse on carbon along x transforms the —2/ / component (shown at its maximum for clarity) into a 2/ /f antiphase coherence. After the time fd, in-phase coherence of the proton spin develops. The latter is detected during h. Its initial intensity is modulated by the carbon Larmor frequency during t (if proton refocusing has been used), thus originating a proton-carbon cross peak.

To overcome these difficulties, the z-filter experiment was adapted to MQMAS by Amoureux et al. [24]. In this three-pulse scheme the two hard pulses (excitation of the MQ coherences and conversion into OQ coherence) are followed by a short delay during which the magnetisation is stored along the z-axis as zero-quantum coherences and then transferred into observable IQ coherences using a selective n/2 pulse (Fig. 5a). The symmetrisation of the echo and antiecho pathways during the two hard pulses (p=0—> 3—>0) forces an equal intensity of the echo and antiecho signals, leading to amplitude-modulated FIDs and, thus, to pure absorption spectra. This is a robust method, easy to optimise. 

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