Anomalous T2 relaxation in normal and degraded cartilage.
To compare the ordinary monoexponential model with three anomalous relaxation models-the stretched Mittag-Leffler, stretched exponential, and biexponential functions-using both simulated and experimental cartilage relaxation data.



Monte Carlo simulations were used to examine both the ability of identifying a given model under high signal-to-noise ratio (SNR) conditions and the accuracy and precision of parameter estimates under more modest SNR as would be encountered clinically. Experimental transverse relaxation data were analyzed from normal and enzymatically degraded cartilage samples under high SNR and rapid echo sampling to compare each model.



Both simulation and experimental results showed improvement in signal representation with the anomalous relaxation models. The stretched exponential model consistently showed the lowest mean squared error in experimental data and closely represents the signal decay over multiple decades of the decay time (e.g., 1-10 ms, 10-100 ms, and >100 ms). The stretched exponential parameter αse showed an inverse correlation with biochemically derived cartilage proteoglycan content.



Experimental results obtained at high field suggest potential application of αse as a measure of matrix integrity. Simulation reflecting more clinical imaging conditions, indicate the ability to robustly estimate αse and distinguish between normal and degraded tissue, highlighting its potential as a biomarker for human studies. Magn Reson Med 76:953-962, 2016. © 2015 Wiley Periodicals, Inc.
Laboratory of Clinical Investigation, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, USA.
David A
DA
Reiter
Department of Bioengineering, University of Illinois at Chicago, Chicago, Illinois, USA.
Richard L
RL
Magin
Department of Bioengineering, University of Illinois at Chicago, Chicago, Illinois, USA.
Weiguo
W
Li
Departamento de Análisis Matemático, Universidad de La Laguna, La Laguna, Tenerife, Spain.
Juan J
JJ
Trujillo
Departamento de Matemática, Estadística e Investigación Operativa, Centro Universitario de la Defensa Universidad de Zaragoza, Zaragoza, Spain.
M
M
Pilar Velasco
Laboratory of Clinical Investigation, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, USA.
Richard G
RG
Spencer
D000818:Animals; D016477:Artifacts; D002356:Cartilage / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D002357:Cartilage Diseases / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D002417:Cattle; D003198:Computer Simulation; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008954:Models, Biological; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
cartilage; fractional calculus; magnetic resonance; multiexponential T2; proteoglycan; spin-spin relaxation