title: MSE-MRI sequence optimisation for measurement of bi- and tri-exponential T2 relaxation in a phantom and fruit.
abstract: The transverse relaxation signal from vegetal cells can be described by multi-exponential behaviour, reflecting different water compartments. This multi-exponential relaxation is rarely measured by conventional MRI imaging protocols; mono-exponential relaxation times are measured instead, thus limiting information about of the microstructure and water status in vegetal cells. In this study, an optimised multiple spin echo (MSE) MRI sequence was evaluated for assessment of multi-exponential transverse relaxation in fruit tissues. The sequence was designed for the acquisition of a maximum of 512 echoes. Non-selective refocusing RF pulses were used in combination with balanced crusher gradients for elimination of spurious echoes. The study was performed on a bi-compartmental phantom with known T2 values and on apple and tomato fruit. T2 decays measured in the phantom and fruit were analysed using bi- and tri-exponential fits, respectively. The MRI results were compared with low field non-spatially resolved NMR measurements performed on the same samples. The results demonstrated that the MSE-MRI sequence can be used for up to tri-exponential T2 quantification allowing for estimation of relaxation times from a few tens of milliseconds to over a second. The effects of the crusher moment and the TE value on T2 measurements were studied both on the bi-compartmental phantom and on the fruit tissues. It was demonstrated that the sequence should be optimised with regard to the characteristics of the tissue to be examined by considering the effects of water molecular diffusion in the presence of both imaging gradients and gradients produced by susceptibility inhomogeneities.
authors.affiliation: Irstea, UR TERE, 17 Avenue de Cucillé, CS 64427, F-35044 Rennes, France; Université européenne de Bretagne, France.
authors.forename: Hans
authors.initials: H
authors.lastname: Adriaensen
authors.forename: Maja
authors.initials: M
authors.lastname: Musse
authors.forename: Stéphane
authors.initials: S
authors.lastname: Quellec
authors.forename: Alexandre
authors.initials: A
authors.lastname: Vignaud
authors.forename: Mireille
authors.initials: M
authors.lastname: Cambert
authors.forename: François
authors.initials: F
authors.lastname: Mariette
mesh_terms: D000465:Algorithms; D005638:Fruit / Q000033:anatomy & histology*; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D018551:Solanum lycopersicum / Q000033:anatomy & histology*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
keywords: Fruit; Magnetic resonance imaging (MRI); Multi-exponential transverse (T(2)) relaxation; Plant; Relaxometry; Tissue characterisation