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Poster communications

Effects of sequence parameters on reliability of multi-exponential T2 measurements

Abstract : Most biological tissues exhibit multi-exponential relaxation behaviour which characterisation is useful for assessment of human diseases and for non-clinical fields as plant sciences. Besides relaxation curve sampling problems, the reliability of T2 quantification depends on multiple factors. Crusher gradients, used for spurious echoes suppression produce signal loss f and the apparent T2 decreases. Diffusion of water molecules throughout the gradients generated by susceptibility inhomogeneities T2’ and diffusion acting imaging gradients T2’’ [2] also affects T2 quantification: 1/T2apparent=1/T2intrinsic+1/T2’+1/T2’’ (Eq-1), with 1/T2’~TE²D (Eq-2) (-mean square distribution of the local field gradients, TE-Echo Time, D-self-diffusion constant) and 1/T2’’~G²δ²D(Δ-δ/3)/TE (Eq-3) (G-gradient strength, δ-gradient duration, Δ-distance from the gradient lobe centres). The impact of the technical parameters on the signal depends on T2 values and can thus lead to erroneous interpretation for multi-exponential relaxation. Therefore, TE and crusher momentum effects on bi-exponential T2 measurements were investigated. Experiments were performed on a 1.5T scanner (Avanto, Siemens) with a 512-echo CPMG-MRI sequence. Four solutions of T2=26, 125, 502 and 1248ms (reference MRI values for: TE=7.1ms; crusher-momentum=5x10-6T.s/m) in 50%-50% volume ratio was combined generating six different elements with bi-exponential relaxation. The effects of (1) crusher-momentum and (2) TE were investigated from images acquired with: (1) crusher-momentum=5, 25 and 50x10-6T.s/m; TE=12ms and (2) TE=7.1, 9.1 and 12ms; crusher momentum=5x10-6T.s/m. In the second case, a tri-exponential transverse relaxation in porous system (apple) was also explored. Diffusion effects led to T2 decrease when the crusher momentum increased (Fig-1), especially for long-T2 components. The experimental results matched well with the predicted trend (Eq-3). The relative intensity (IR) ratio close to 50%-50% was not affected. T2 changes due to the diffusion throughout readout gradients (Eq-3) and to the signal loss f were not significant in the range of TE investigated. Consequently, T2 in the phantom was not affected by TE changes (Fig-2). However, in the porous apple tissues, susceptibility effects (Eq-2), induce the decrease of T2 (and changes in IR) with TE increase, the phenomenon being marked for long-T2 components (Fig-3). T2 and associated signal intensity quantification depend on technical factors in the imaging sequence. The sequence parameters have to be optimised for reliable measurements with regards to the various effects and tissues under investigation, especially when susceptibility effects are expected.
Keywords : T2
Document type :
Poster communications
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https://hal.inrae.fr/hal-02597419
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Submitted on : Friday, May 15, 2020 - 10:33:53 PM
Last modification on : Friday, April 9, 2021 - 9:10:03 AM

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  • HAL Id : hal-02597419, version 1
  • IRSTEA : PUB00036189

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Hans Adriaensen, Maja Musse, S. Quellec, Audrey Vignaud, François Mariette. Effects of sequence parameters on reliability of multi-exponential T2 measurements. ESMRMB, European Society for Magnetic Resonance in Medicine and Biology, Oct 2012, Lisbonne, Portugal. 2012. ⟨hal-02597419⟩

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