In breast screening lesions might be discovered which have to be checked for malignancy. To do so, a biopsy can be performed in which a needle is inserted into the breast to recover sample cells from the lesion for further research. This biopsy is usually performed under the guidance of an imaging modality. For MRI-guided biopsies, the patient has to move in between getting the scan and having the biopsy, due to the limited space inside the bore and the limitations induced by the strong magnetic field. Two options are discussed: a robotic system inside the MRI scanner and a robotic system outside the MRI scanner, the latter of which will be used in this assignment. Between making the MRI scan and getting the biopsy, the patient has to move, which might mean that the lesion moves due to for instance breathing or muscle relaxation. Real-time imaging can be used to update the location of the lesion to help the doctor target the lesion more accurately.
The real-time imaging is done by putting markers on the breast, which are tracked using an OptiTrack system. The location of the markers is used in combination with the marker locations in the MRI scan to determine the current breast configuration and lesion location using the Thin Plate Spline algorithm. Algorithms have been implemented to label the markers to their previous frames and thus also to the marker locations in the MRI scan. Simulation results have been used to find an optimal combination of algorithms, which is explained to be the distance, angle, and height algorithms. The algorithms have been implemented and experiments are performed with different marker sizes and numbers of markers to find their influence on the total performance of the system. Using 8 mm markers no biopsies could be performed, which was achievable with marker sizes of 12, 16, and 20 mm. Biopsies could be performed for marker totals up to and including 9 (and 8 for 16 mm markers), where jumping markers were observed for the greatest part when using more markers. From the results, it is concluded that the size of the marker is of lesser importance than the number of markers. A follow-up experiment is suggested in which the validation of the lesion location is examined using the different marker sizes and the number of markers.
All performed biopsies have a sub-millimeter accuracy, which is better than the average accuracy that Marta reached in her research (2.21 mm). When comparing these results to a study performed in 2009, in which 20 biopsies were performed on breast phantom and 32 biopsies on patients' breasts, a clear increase in biopsy accuracy can be seen.
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