Taking biopsies can often be a traumatic experience for breast cancer patients. Clinicians must often extract tissue samples from an affected area with a fine needle for detailed examination generally undertaken with the help of ultrasound guidance. However, around 30 percent of all tumors are invisible to ultrasound, so in some cases MRI guidance is used. This is carried out in a two step process: the MRI imaging itself and the insertion of the biopsy needle, for which the patient must be removed from the MRI scanner. The process is often repeated several times before the sample is finally taken. This exhausts patients and is also costly, because the procedure occupies the MRI scanner for a significant period
To meet this challenge scientists at the Fraunhofer institute are working on a project whose aim is the development of a more cost-effective biopsy method that is easier on patients
In the MARIUS project (Magnetic Resonance Imaging Using Ultrasound – systems and processes for multimodal MR imaging), experts from both the Fraunhofer Institute for Biomedical Engineering IBMT in St. Ingbert and the Fraunhofer Institute for Medical Image Computing MEVIS in Bremen are working together towards a quicker and gentler alternative. 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; with the system transforming the initial MRI scan and accurately rendering it on screen. 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 tumor significantly. To track these changes accurately, researchers have applied a method which involves attaching the ultrasound probes while the patient is in the MRI chamber. This produces two comparable sets of data from two separate 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 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 tumor.
To realize this vision, the Fraunhofer researchers are developing a range of new components. “We’re currently working on an ultrasound device that can be used within an MRI scanner,” says IBMT project manager Steffen Tretbar 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 project.
The software developed for the technique is also completely new. “We’re developing a way to track movements in real time by means of ultrasound tracking,” explains MEVIS project manager Matthias Günther. “This recognizes distended structures in the ultrasound images and tracks their movement. We also need to collate a wide range of sensor data in real time.” Some of the sensors gather data about the position and orientation of the attached ultrasound probes while others track the position of the patient.
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 jointly developed technology could also be applied to treatments that use particle or X-ray beams. For tumors 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 tumor with more precision than currently possible and reduce damage to healthy surrounding tissue.