Relaxation anisotropy of quantitative MRI parameters in biological tissues

Thesis event information

Date and time of the thesis defence

Place of the thesis defence

Leena Palotie Audiotrium 101A (Aapistie 5A)

Topic of the dissertation

Relaxation anisotropy of quantitative MRI parameters in biological tissues

Doctoral candidate

Master of Science Nina Hänninen

Faculty and unit

University of Oulu Graduate School, Faculty of Medicine, Research Unit of Medical Imaging, Physics and Technology

Subject of study

Medical physics and technology

Opponent

Professor Dimitrios Karampinos, Technical University of Munich

Custos

Professor Miika Nieminen, University of Oulu

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Orientation anisotropy of MRI has potential to detect ostheoarthritis in cartilage

Magnetic resonance imaging (MRI) is a widely used clinical imaging method. It is well suited for studying a wide range of different tissue types. In addition to anatomical images, MRI can be used to obtain quantitative values describing the state of the tissue. However, some tissue types exhibit properties that make MRI parameters dependent on their orientation. In this case also the obtained MR image is different if the target is imaged in different orientations. This possibly reduces the reliability of diagnosis based on such images.

In the thesis, orientation dependence of different MRI parameters was studied in different biological tissues. In addition, the possibility of using orientation dependence to observe structural changes in tissue was studied in cartilage. Orientation dependence is typically observed in structurally highly organized tissues such as cartilage and tendon. Thus, orientation dependence could have the potential to indirectly analyze the structure of this kind of tissue.

Orientation dependence of the MRI parameters was studied by imaging different tissue samples in a preclinical MRI device. The studied tissue samples included bovine cartilage and tendon samples, and brain, heart, spinal cord and kidney samples from mice. The samples were measured in different orientations and a quantitative value for the orientation dependence was calculated. This made it possible to compare the orientation dependence between different parameters, as well as tissue types. The potential use of orientation dependence as a method to analyze tissue structure was studied by imaging human cartilage samples with different stages of degeneration.

The results showed that MRI parameters varied greatly in their orientation dependence. Furthermore, ordered collagenous tissues, cartilage and tendon, showed clear orientation dependence. The other investigated soft tissues did not exhibit notable orientation dependence. Orientation dependence of T2 parameter in cartilage was observed to be significantly lower for cartilage samples of advanced degeneration compared to less degenerated samples. These findings indicate that orientation dependence is a significant phenomenon in MRI of cartilage and tendon, and it has potential to be used as a biomarker for observing osteoarthritic degeneration in cartilage.
Last updated: 27.9.2022