| Popis: |
Magnetic resonance imaging (MRI) provides excellent soft tissue .contrast and penetration, however standard MRI techniques are unable to image structures such as tendons, bones, macromolecular deposition and organs such as stomach. These structures contain ultra-short spinspin (T2*) relaxation times which decay too rapidly to be detected. In order to obtain a signal from ultra-short T2* tissue in a high field scanner, a nov~ ultra-short echo time .. (UTE) technique was developed on a software and hardware basis. The technique is a Single Point Imaging (SPI) variant which I have named diagonal-SPRITE. While the original SPI techniques are not appropriate for biological tissues due to hardware limitations such as duty cycle and excessively long scan times, diagonal-SPRITE optimizes gradient use within hardware limitations such that spatial and temporal resolution are appropriate for in vivo studies. The diagonal-SPRITE pulse program was written and further modified in order to optimize the sequence from a hardware point of view. SPI theory was expanded. Blurring, susceptibility and other types of artefacts were identified, studied and minimized. A long T2* suppression pulse was developed specifically for UTE at high field acquisitions. Diagonal-SPRITE was tested on phantoms and then used to scan organs of healthy murine models in vivo, in order to highlight T2* tissue components, to generate T2* maps of tissue and to study the T2* shortening of iron based particles. Diagonal-SPRITE is tailored for use in preclinical studies where high magnetic fields and strong gradients are involved. In the future, diagonal-SPRITE may be used for studies of fibrotic tissues, oxygen enhancement and macromolecular deposition. Such experiments were not successfully achieved due to a lack of mouse disease models and hardware limitations. |
