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T1 : - Time constant for recovery of longitudinal magnetisation

90 0. 90 0. 90 0. 90 0. 90 0. 90 0. 90 0. 90 0. Lecture 15: SUMMARY. Longitudinal magnetisation. T1 : - Time constant for recovery of longitudinal magnetisation

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T1 : - Time constant for recovery of longitudinal magnetisation

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  1. 900 900 900 900 900 900 900 900 Lecture 15: SUMMARY Longitudinal magnetisation • T1: • - Time constant for recovery of longitudinal magnetisation • arises from random fluctuating B-fields in sample due to molecular motion of the molecules (and so spin with a magnetic moment). • Measure using saturation or inversion recovery M M = M (1- exp (- t/T )) z Saturation recovery z o 1 M o Time after pulse M M = M (1- exp (- t/T )) z z o 1 M o Time after pulse Use 2nd 900 pulse to knock longitudinal magnetisation into transverse plane to be detected by receive coil along My.

  2. 900x Mxy Random phases Coherence T2 T2* time Lecture 15: SUMMARY Transverse magnetisation • Dephasing arises due to three processes: • (i) T2 relaxation: Arises from random fluctuating B-fields in sample. Described by T2 time constant. • (ii) Chemical shift • (iii) Inhomogeneities in static B-field • Three processes lead to transverse time constant T2* - (ii) and (iii) refocussed by SPIN ECHO.

  3. CPMG sequence 1800y 1800y 1800y 1800y 900x t t t t t t t Mxy 900x Mxy = Mxy0exp(-t/T2) T2 T2* 2t 6t time 4t

  4. Magnetic Resonance: • Lecture 16: • 10) Nuclear Spin Relaxation • B) MICROSCOPIC PROPERTIES • 10.3 Mechanisms and Origin of Nuclear Spin Relaxation • Theory and calculation of T1: • transition probablities

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