Combining MRI with ultrasound gives a quicker technique for breast cancer biopsy
18 November 2013
The Fraunhofer Institute for Biomedical Engineering has developed a technique that combines MRI with ultrasound scans to make biopsy taking quicker and less traumatic for breast cancer patients.
Researchers from the Fraunhofer Institute for Biomedical Engineering IBMT in St Ingbert and the Fraunhofer Institute for Medical Image Computing MEVIS in Bremen are working together on the project, called MARIUS (magnetic resonance imaging using ultrasound — systems and processes for multimodal MR imaging).
To test whether a breast tumour is malignant a tissue sample must be taken with a fine needle guided by ultrasound imaging. However, around 30% of tumours are invisible to ultrasound, which requires MRI imaging to ensure correct needle insertion. This can require several steps of MRI imaging, removal from the scanner, and needle insertion before the needle is inserted accurately in the tumour tissue. This exhausts patients and is also costly, because the procedure occupies the MRI scanner for a significant period.
The new technique would require just one scan of the patient’s entire chest at the beginning of the procedure, meaning that the patient only has to enter the scanner once. The subsequent biopsy is guided by ultrasound; the system would transform the initial MRI scan and accurately render it on screen. Doctors would have both the live ultrasound scan and a corresponding MR image available to guide the biopsy needle and display exactly where the tumour is located.
The biggest challenge is that the MRI is performed with the patient lying prone, while during the biopsy she lies on her back. This change of position alters the shape of the patient’s breast and shifts the position of the tumour significantly. To track these changes accurately, ultrasound probes, which resemble ECG electrodes, are attached to the patient’s skin to provide a succession of ultrasound images during the MRI scan. This produces two comparable sets of data from the two imaging techniques.
When the patient undergoes a biopsy in another examination room, the ultrasound probes remain attached and continually record volume data and track the changes to the shape of the breast. Special algorithms analyze these changes and update the MRI scan accordingly. The MR image changes analogously to the ultrasound scan. When the the biopsy needle is inserted into the breast tissue, the doctor can see the reconciled MRI scan along with the ultrasound image on the screen, greatly improving the accuracy of needle guidance towards the tumour.
“We’re currently working on an ultrasound device that can be used
within an MRI scanner,” says IBMT project manager Steffen Tretbar.
“These scanners generate strong magnetic fields, and the ultrasound
device must work reliably without affecting the MRI scan.”
Ultrasound probes that can be attached to the body to provide 3D
ultrasound imaging are also being developed by the team as part of
The primary objective of MARIUS is to develop ultrasound tracking to aid breast biopsies. Nevertheless, the developed components could also be used in other applications. For instance, the MARIUS system and its movement-tracking software could allow slow imaging techniques such as MRI or positron emission tomography (PET) to accurately track the movements of organs that shift even when a patient is lying still.
Aside from the liver and the kidneys, which change shape and position during breathing, this includes the heart, whose contractions also cause motion. Thanks to a technique applied to reconstruct the image, the heart would appear well defined on MRI scans instead of blurred.
The technology could also be applied to treatments that use particle or X-ray beams. For tumours located in or on a moving organ, the new technology could target the rays so that they follow the movement. These beams could hit the tumour with more precision than currently possible and reduce damage to healthy surrounding tissue.