Development and validation of a real-time reduced field of view imaging driven by automated needle detection for MRI-guided interventions

Automatic tracking and scan plane control in MRI-guided therapy is an active area of research. However, there has been little research on tracking needles without the use of external markers. Current methods also do not account for possible needle bending, because the tip does not get tracked explicitly. In this paper, we present a preliminary method to track a biopsy needle in real-time MR images based on its visible susceptibility artifact and automatically adjust the next scan plane in a closed loop to keep the needle's tip in the field of view. The images were acquired with a Single Shot Fast Spin Echo (SSFSE) sequence combined with a reduced field of view (rFOV) technique using 2D RF pulses, which allows a reduction in scan time without compromising spatial resolution. The needle tracking software was implemented as a plug-in module for open-source medical image visualization software 3D Slicer to display the current scan plane with the highlighted needle. Tests using a gel phantom and an ex vivo tissue sample are reported and evaluated in respect to performance and accuracy. The results proved that the method allows an image update rate of one frame per second with a root mean squared error within 4 mm. The proposed method may therefore be feasible in MRI-guided targeted therapy, such as prostate biopsies.