Читать книгу Leksell Radiosurgery - Группа авторов - Страница 56

For patients who require high-quality reduced artifact CT imaging of the brain during Gamma Knife SRS (clips, shunts, MRI-incompatible stents, prior OR, etc.) a good alternative to frame-based CT images is to get the brain CT done without frame early in the morning of the procedure (treatment day) with and without contrast. A brain-contrast CT with 1.25-mm axial plane slices (no frame) provides a rapid way to get the images both with (5-min delay) and without contrast in about 10 min. CT imaging should cover from C2 to 2 cm above the vertex to enhance co-registration accuracy. After return to the Gamma Knife suite, head frame can be placed under conscious sedation and local anesthesia in a standard manner (short bars in the back in patients with anterior frontal lesions, especially eye region targets and shifting the frame forward so that the eye or frontal sinuses are at Y level <165 whenever possible). Patients can then undergo an ICON cone beam CT which can be used as a stereotactic reference. High-quality CT images acquired without frame can be co-registered to a CBCT scan for treatment planning.

Artifact-free high-definition MRI scans (e.g., 3 T without frame or pins) obtained in advance or on the day of the procedure may also fit this paradigm as well. As before, SPGR whole-head 1.5-mm T1 axial postcontrast (C2 to vertex), 3 mm T2 axial no skip whole-head, and specific T2 axial volume studies centered on the target may be performed in this way and co-registered to a cone beam ICON CT.