M.Sc Thesis

M.Sc StudentKochavi Eyal
SubjectReal Time MRI Needle Tracking
DepartmentDepartment of Biomedical Engineering
Supervisor PROF. Haim Azhari


Invasive MRI has become clinically available, particularly in neurosurgery and in minimal invasive operations. Most commonly, these procedures involve the insertion of a needle into the treated organ. Thus, monitoring the needle in real time is essential in such cases and rapid imaging techniques are implemented. However, in most rapid imaging techniques image quality is compromised. Thus, the use of special devices or equipment, in order to increase contrast or enable direct needle localization, has been suggested. The objective of this study was to achieve real time needle tracking without the use of any special tracking equipment.

A new technique for MRI needle tracking is presented. The technique is based on k-space (Fourier) investigation of the difference image between the current dynamic frame and a reference one. Using only a few central k-lines of the difference image and a nonlinear optimization procedure the parameters that characterize the spectral signature (Sinc) generated by the needle are resolved, and the needle location is obtained. The procedure was tested in computer simulations and in actual MRI scans. Acceleration factors of five and higher were obtained using only six sampled k-lines. A typical RMS error of 1-2 pixels in needle tip location was achieved.

The suggested method does not require any supplementary equipment as other methods do. The method can be easily implemented in any MR system. The limitation of the method is that it relies on a reference image, which is assumed to be unchanged for the duration of at least several frames.