Rapid T1 estimation using tagged magnetization-prepared gradient-echo MR imaging

T1rho imaging using magnetization-prepared projection encoding (MaPPE)

T1rho contrast weighting using a magnetization-prepared projection encoding (MaPPE) pulse sequence was investigated. Fast radial imaging was implemented by applying magnetization preparation pulses, each followed by multiple RF alpha pulses encoding radial trajectories of k-space. Acquiring multiple views per preparatory pulse imposes view-to-view variation; the resultant distortion of the point-spread function is examined. The issue of maximizing signal while preserving the intended contrast weighting is addressed. Under modification of repetition time and flip angle (alpha), three distinct behavior regimes of the sequence are identified. The utility of the pulse sequence as a quantitative relaxation measurement tool is also examined by comparing imaging and spectroscopy experiments. A mouse was imaged in vitro to demonstrate the viability of application to MR histology. These images exhibit the utility of spinlocking and projection encoding as an aftemative contrast source to both T2-weighted MaPPE images and conventional T2-weighted spin-echo images.

Spin-lattice relaxation time measurement by means of a TurboFLASH technique

Rapid measurements of in vivo proton spin-lattice relaxation times (T1) in human tissues were performed by magnetic resonance imaging in a 1.5 T whole-body super-conducting MR scanner. The measurements employ serial TurboFLASH imaging (Snapshot-FLASH) with scan times for a single experiment below 4 s. Using centric phase encoding order, an appropriate fitting of the T1-parameter from images with minimum motion artifacts is possible. Comparative T1-determination with a multipoint inversion recovery and spin-echo technique was performed on phantoms containing Gd-DTPA solutions with different T1-values. We found a maximum deviation of 3.3% for T1 < 1100 ms and of 12.1% for 1100 ms < T1 < 1700 ms from the results obtained by the IR technique. In vivo measurements of T1-relaxation times were performed in white and grey matter, cerebrospinal fluid, kidney, liver, spleen, muscle, and bone marrow, and yielded values that are in good agreement with reported data.