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Implementation of Dixon Methods for Preclinical MR Imaging at High Fields
Kořínek, Radim ; Latta,, Peter (oponent) ; Puková,, Andrea Šprláková - (oponent) ; Bartušek, Karel (vedoucí práce)
Preclinical magnetic resonance (MR) imaging in small animals is a very popular procedure that requires a higher sensitivity, given the small size of the subjects. A higher sensitivity can be reached when an MR imaging system with a high magnetic field is used (e.g., 4.7 T or higher). The benefits of such sensitivity include, for example, a higher resolution, an improved signal-to-noise ratio (SNR), an increased chemical shift, and a longer T1 longitudinal relaxation time. On the other hand, a high field causes stronger static magnetic field deformation along the borders between tissues with different susceptibilities, and it also results in the shortening of the T2 transversal relaxation. Adipose tissue is significantly contained in the human (or mammal) body and is primarily used to store energy in the form of fat. This tissue can be classified into white and brown subsets. Brown adipose tissue is found mainly in new-born children, and a certain (yet very small) amount of such tissue can be traced also in adults. White adipose tissue then ensures the storage of fat as a source of energy. Furthermore, white adipose tissue produces adipokines, hormones, and many other substances important for metabolism. Generally, fat can be regarded as a biomarker in the case of specific diseases (obesity, steatosis – fatty liver disease, and others). Thus, the quantification of fat is a precondition for correct diagnosis. MR imaging comprises a special group of methods for water-fat separation; these methods are referred to as Dixon methods and utilize the principle of chemical shift. In this thesis, a new T2 – weighted sequence for Dixon acquisition is introduced (Chapter 5.3). The proposed sequence is a very time-effective three-point (3PD) method. The newly proposed sequence of fast triple spin echo Dixon (FTSED) is derived from the original fast spin echo sequence (FSE). Such modification of the original FSE sequence leads to a novel FTSED sequence, where three images are acquired simultaneously without any increase of the total acquisition time. The discussed sequence was successfully implemented on a 9.4 T MR imaging system at the Institute of Scientific Instruments, ASCR Brno. The acquired data were calculated through the use of the IDEAL (iterative decomposition of water and fat with echo asymmetry and least-squares estimation) algorithm. The results of the computation are water and fat images, and the fat fraction (FF) can be calculated from these. The sequence was successfully tested in a rat. The successful FTSED implementation on a 9.4 T MR imaging system enables this method to be used in low-field MR imaging systems.
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Implementation of Dixon Methods for Preclinical MR Imaging at High Fields
Kořínek, Radim ; Latta,, Peter (oponent) ; Puková,, Andrea Šprláková - (oponent) ; Bartušek, Karel (vedoucí práce)
Preclinical magnetic resonance (MR) imaging in small animals is a very popular procedure that requires a higher sensitivity, given the small size of the subjects. A higher sensitivity can be reached when an MR imaging system with a high magnetic field is used (e.g., 4.7 T or higher). The benefits of such sensitivity include, for example, a higher resolution, an improved signal-to-noise ratio (SNR), an increased chemical shift, and a longer T1 longitudinal relaxation time. On the other hand, a high field causes stronger static magnetic field deformation along the borders between tissues with different susceptibilities, and it also results in the shortening of the T2 transversal relaxation. Adipose tissue is significantly contained in the human (or mammal) body and is primarily used to store energy in the form of fat. This tissue can be classified into white and brown subsets. Brown adipose tissue is found mainly in new-born children, and a certain (yet very small) amount of such tissue can be traced also in adults. White adipose tissue then ensures the storage of fat as a source of energy. Furthermore, white adipose tissue produces adipokines, hormones, and many other substances important for metabolism. Generally, fat can be regarded as a biomarker in the case of specific diseases (obesity, steatosis – fatty liver disease, and others). Thus, the quantification of fat is a precondition for correct diagnosis. MR imaging comprises a special group of methods for water-fat separation; these methods are referred to as Dixon methods and utilize the principle of chemical shift. In this thesis, a new T2 – weighted sequence for Dixon acquisition is introduced (Chapter 5.3). The proposed sequence is a very time-effective three-point (3PD) method. The newly proposed sequence of fast triple spin echo Dixon (FTSED) is derived from the original fast spin echo sequence (FSE). Such modification of the original FSE sequence leads to a novel FTSED sequence, where three images are acquired simultaneously without any increase of the total acquisition time. The discussed sequence was successfully implemented on a 9.4 T MR imaging system at the Institute of Scientific Instruments, ASCR Brno. The acquired data were calculated through the use of the IDEAL (iterative decomposition of water and fat with echo asymmetry and least-squares estimation) algorithm. The results of the computation are water and fat images, and the fat fraction (FF) can be calculated from these. The sequence was successfully tested in a rat. The successful FTSED implementation on a 9.4 T MR imaging system enables this method to be used in low-field MR imaging systems.
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