Direct reconstruction of T1from k-space using a radial saturation-recovery sequence

Contrast agent concentration ([CA]) must be known accurately to quantify dynamic contrast-enhanced (DCE) MR imaging. Accurate concentrations can be obtained if the longitudinal relaxation rate constant T1is known both pre- and post-contrast injection. Post-contrast signal intensity in the images is often saturated and an approximation to T1can be difficult to obtain. One method that has been proposed for accurate T1estimation effectively acquires multiple images with different effective saturation recovery times (eSRTs) and fits the images to the equation for T1recovery to obtain T1values. This was done with a radial saturation-recovery sequence for 2D imaging of myocardial perfusion with DCE MRI. This multi-SRT method assumes that the signal intensity is constant for different readouts in each image. Here this assumption is not necessary as a model-based reconstruction method is proposed that directly reconstructs an image of T1values from k-space. The magnetization for each ray at each readout pulse is modeled in the reconstruction with Bloch equations. Computer simulations based on a 72 ray cardiac DCE MRI acquisition were used to test the method. The direct model-based reconstruction gave accurate T1values and was slightly more accurate than the multi-SRT method that used three sub-images.