Exact and stable interior ROI reconstruction for radial MRI

MRI applications often require high spatial and/or temporal resolution within a region of interest (ROI) such as for perfusion studies. In theory, both spatial resolution and temporal resolution can be significantly improved using a ROI-focused MRI data acquisition scheme. However, in radial MRI, there is no such acquisition-based solution available. Traditional reconstruction methods to image the ROI by reducing the field of view produce aliasing artifacts when the dataset becomes truncated. Here we propose an interior MRI methodology to perform ROI reconstruction without artifacts. Methods: In contrast to the conventional wisdom that the interior problem does not have a unique solution, interior tomography has been recently proposed as an exact and stable solution to this longstanding problem. In this project, a ROI-focused radial MRI data acquisition scheme was developed, aided by a dedicated digital filter. We implemented this method in a 4T 90 cm bore Oxford magnet with a GE phantom and a transceiver TEM head coil. The parameters were 4 gauss/cm sonata gradients, 5 mm slice thickness, TE=30 ms, TR=200 ms, FOVs of 40 cm and 12 cm respectively. Results: Both numerical simulation and phantom experiments have demonstrated that the proposed interior MRI method can exactly reconstruct a ROI with increased spatial resolution (∼4 fold) while keeping the same temporal resolution. The image artifacts from truncated projections are effectively eliminated. No crosstalk with the outside ROI region is involved using the proposed method. Conclusions: Our interior radial MRI method can be used for zoomed-in and fast views of a particular ROI, which can be translated into significant advantages in clinical and pre-clinical applications of many types.