T1rho -dispersioparametrien kartoitus nivelrustossa

Thesis event information

Date and time of the thesis defence

Place of the thesis defence

Auditorium P117 (Aapistie 5B). Remote access: https://oulu.zoom.us/j/64589994772?pwd=eGpqb1VXejN4cW9CaG11YUlLU3A3Zz09

Topic of the dissertation

T1rho -dispersioparametrien kartoitus nivelrustossa

Doctoral candidate

Master of Science Hassaan Elsayed

Faculty and unit

University of Oulu Graduate School, Faculty of Medicine, Medical Imaging, Physics and Technology (MIPT)

Subject of study

Medical physics and technology

Opponent

Professor Raimo Sepponen, Aalto University

Custos

Professor Miika Nieminen, University of Oulu

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A study of articular cartilage using several MRI parameters

Magnetic resonance imaging (MRI) is a widely used diagnostic method in medicine, and it can provide anatomical and diagnostic data from biological tissue. Quantitative MRI parameters, such as T2 and T1rho can give insights into tissue structure and composition. In addition, T1rho dispersion contains information from a range of slow molecular processes.

Relaxation dispersion parameters are metrics computed from two or more T1rho measurements in order to quantify the information embedded in the T1rho dispersion. In this monograph, three different dispersion parameters were evaluated: correlation time, R1rho (=1/T_1rho ) ratio, and R1rho difference. Correlation time is a characteristic property of the tissue that can be fitted from multiple T1rho measurements. Both R1rho ratio and R1rho difference quantify the resemblance between a single T1rho measurement and T2.

The purpose of this monograph was to examine the sensitivity of dispersion parameters to changes in spin-lock frequency as well as to varying collagen fiber network orientations in articular cartilage with respect to B0. In addition, the relation between dispersion parameter and tissue properties was investigated. Finally, the dispersion parameters were assessed as biomarkers of tissue changes in an experimental model of post-traumatic osteoarthritis.

All dispersion parameters studied in this monograph were able to show laminar appearance of cartilage. Correlation time as well as R1rho difference are potentially independent from off-resonance shifts in measurements. Contrast enhancement effects on R1rho ratio were observed by increasing the off-resonance shift. Both correlation time and R1rho ratio showed sensitivity to collagen fiber network orientation. This observation was, however, not confirmed for R1rho difference. The histological and biomechanical properties of cartilage could not be statistically predicted based on dispersion parameters due to the small sample size. Nevertheless, it was found that correlation time could distinguish between intact and degraded cartilage, while R1rho ratio and R1rho difference might be sensitive to within-sample changes in degraded cartilage.
Last updated: 21.10.2021