magnetic resonance image (mri)-guided interventions involving percutaneous biopsies of lesions, or trajectory alignment with prospective stereotaxy are conducted in real time using rapid image acquisition. a mechanism of passively localizing a device and calculating its orientation is desired to improve interventional outcomes in these situations. in this work, we propose and evaluate an image-based technique to determine the position and alignment of a linearly shaped interventional device within an ex-vivo tissue specimen. low resolution 3d orientation scan data is processed to produce a virtual line tting using principal component analysis. the line tting algorithm was incorporated into a biopsy needle tracking system implemented with an mrscanner operated using a footswitch. a gui application was written to collect foot pedal input and display automated visualization of device placement inside the scanner room. placement time trials (n=3) conducted with this system using porcine muscle and phantom samples suspended in rigid frames with inserted gadolinium-enhanced targets. the mean targeting error across all directions was 3:6 mm and 5:1 mm for the phantom trials and ex-vivo trials respectively. the average entry-to-target time was 247 sec. device localization during trials was adequate to contain a 11-gauge titanium biopsy needle within a visualization slice volume of 10 mm after 93:8% of alignments over insertion lengths between 30 mm to 110 mm at insertion angles between 1:4 to 20 from the static magnetic eld and frequency encoding axes. practical considerations were identi ed and occupational exposure measurements were collected as part of determining the system's overall feasibility.