PULSE SEQUENCES AND VISUALIZATION OF INST RUMENTS

While initially advocated primarily for intrasurgical Visualization (e . g., craniotomy), interventional MRI rapidly evolved into roles in im age-guided localization for needle-based procedures, minimally invasiv e neurosurgical procedures, and thermal ablation of cancer. In this co ntest, MRI pulse sequences and scanning methods serve one of four prim ary roles: (1) speed improvement, (2) device localization, (3) anatomy /lesion differentiation and (4) temperature sensitivity. The first par t of this manuscript deals with passive visualization of MR-compatible needles and the effects of field strength, sequence design, and orien tation of the needle relative to the static magnetic field of the scan ner. Issues and recommendations are given for low-field as well as hig h-field scanners. The second part contains methods reported to achieve improved acquisition efficiency over conventional phase encoding (wav elets, locally focused imaging, singular Value decomposition and keyho le imaging). Finally, the last part of the manuscript reports the curr ent status of thermosensitive sequences and their dependence on spin-l attice relaxation time (T1), water diffusion coefficient (D) and proto n chemical shift (delta).