FIG 2. Patient 2 (astrocytoma, WHO grade II).

Top left and top right, The Flashpoint Position Encoder is used to localize the borders of the tumor in projection onto the skull before craniotomy. The dotted lines (arrows) mark the calculated actual position of the hand-held device. Additionally, an MR Track Pointer (arrowheads) mounted on the hand-held device is used. On T2-weighted single-shot fast spin-echo sequences, the instrument, filled with a sodium chloride solution, is displayed with high signal intensity. The sagittal view (top right) shows a slight deviation between the calculated and imaged positions caused by a short delay between image update (every 3 seconds) and optical tracking update (four per second).

Bottom left and bottom right, After craniotomy, this approach is used again to define the borders of the tumor in projection to the dura.