Fusing MR with Ultrasound for Quicker, Less Invasive Breast Cancer Biopsies

A new medical research project has been initiated to develop a more cost-effective biopsy technique that is both kinder and gentler on patients.

Taking tissue samples can frequently be distressing for breast cancer patients. There are also significant costs associated with the procedure when magnetic resonance imaging is used. The researchers will present new alternative technologies and techniques combining magnetic resonance imaging (MRI) and ultrasound imaging at MEDICA 2013, to be held in Düsseldorf (Germany), November 20–23, 2013.

Determining if a breast tumor is malignant is not a question that ultrasound and X-rays, in addition to MRI scans, can answer by themselves. Frequently, physicians must remove tissue samples from an affected area with a fine needle for detailed examination. This type of biopsy is regularly performed with the aid of ultrasound, with clinicians viewing a screen for needle guidance. Regrettably, approximately 30% of all tumors are invisible to ultrasound. In some instances, magnetic resonance imaging (MRI) is used to ensure an accurate needle insertion. This process involves two steps: the imaging itself, which takes place inside the MRI scanner, and the insertion of the biopsy needle, for which the patient must be removed from the machine to insert the needle accurately. This process is often repeated several times before the sample is finally taken. This tires patients and it is expensive, because the procedure occupies the MRI scanner for a significant period.

In the joint MARIUS project (Magnetic Resonance Imaging Using Ultrasound—systems and processes for multimodal MR imaging), specialists from both the Fraunhofer Institute for Biomedical Engineering IBMT (St. Ingbert, Germany) and the Fraunhofer Institute for Medical Image Computing MEVIS (Bremen, Germany) are working together towards a quicker and gentler alternative.

The new technique would require just one MRI scan of the patient’s entire chest at the start of the procedure, meaning that the patient only has to enter the scanner once. The subsequent biopsy is guided by ultrasound; the system would convert the first MRI scan and accurately render it on screen. Clinicians would have both the live ultrasound scan and a corresponding MR image available to guide the biopsy needle and display precisely where the tumor is situated.

The biggest hurdle of the procedure 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 changes the position of the tumor significantly. To monitor these alterations accurately, researchers have applied an ingenious trick: While the patient is in the MRI chamber during the scan, ultrasound probes, which look like ECG electrodes, are attached to the patient’s skin to provide a succession of ultrasound images. This produces two comparable sets of data from two separate imaging techniques.

When the patient undergoes a biopsy in another exam room, the ultrasound probes remain attached and continually record volume data and monitor 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 enhance the accuracy of needle guidance towards the tumor.

To accomplish this task, 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. “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 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,” explained 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.

Whereas the IBMT team is developing the hardware and new ultrasound techniques, the MEVIS working group is focusing on the software. The key 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.

Related Links:
Fraunhofer Institute for Biomedical Engineering IBMT