Fast mapping of the T1-relaxation in magnetic resonance imaging with advanced spiral k-space sampling and interleaving methods at 3 Tesla and 7 Tesla

Magnetic Resonance Imaging (MRI) is a non-invasive form of three-dimensional imaging that delivers good soft-tissue contrast, especially so for brain tissue. The contrast depends, amongst other things, on the underlying physical characteristics of the tissue. With the imaging of (_1^1)H proton signals as done in this work, the relaxation time T1 is of special interest. In qualitative MRI imaging parameters are chosen in a way that the desired tissue contrast is given at the time of image sampling. Quantitative MRI, on the other hand, aims to determine the underlying physical characteristics of the tissue directly, as they allow inferring information about the microstructural composition of the brain. Quantitative MRI also offers the advantage of providing an objective measure of the condition of the tissue of interest, so that large-scale automated evaluation may also become feasible. A disadvantage of quantitative MRI lies with the generally prolonged measurement time over qualitative MRI. In this work, the TAPIR method for determination of the T1 relaxation time is accelerated by using a spiral k-space trajectory instead of the common Cartesian k-space sampling scheme. Additionally, an improved procedure for correcting image artifacts that result from delays in the gradient system of the MRI scanner is developed and evaluated. The accuracy of measuring T1 is improved with a reduction of the median error from -2.8% to -0.2% for phantom measurements at 3 Tesla by reducing the important sequence parameters echo time (TE), and repetition time (TR). Simultaneously, imaging is accelerated by a factor of up to 3.3. To this aim, this work also utilizes the compressed sensing image reconstruction technique. The parameter TE is decoupled from other sequence parameters by using a spiral k-space trajectory, which improves the determination of rapid T1 relaxation decisively. The method for correcting the delay in the gradient of the MRI scanner is accelerated further within the imaging setup at the ultra-high field strength of 7 Tesla. A new method for interleaving of the RF pulses is also introduced, which is coined MIPI (Multi Inversion Pulse Interleaving) TAPIR. It allows for reaching a high time resolution in measuring T1 relaxation with less distortion of the relaxation process of the spin system of interest. In addition to TE, MIPI enables decoupling of TR from the remaining parameters of the imaging sequence and consequently removes another trade-off in the parameterization of the spiral TAPIR sequence. Finally, the influence of the magnetization transfer effect is investigated, especially regarding the TAPIR method of inversion efficiency computation. In summary, the spiral TAPIR method developed in this work enables whole-brain T1 mapping with high accuracy in clinically acceptable imaging times by combining a spiral readout with improved gradient delay correction and compressed sensing image reconstruction. In conjunction with the new MIPI scheme for interleaving inversion pulses, TE and TR may be chosen optimally to also allow for mapping of rapidly relaxing tissue