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Integrating Imaging Modalities for Faster, Gentler Biopsies for Breast Cancer

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Extracting tissue samples can often be a traumatic experience for breast cancer patients. There are also large costs linked with the procedure when magnetic resonance imaging (MRI) is used.

Knowing whether a breast tumor is malignant or not cannot be solely answered by the use of ultrasound and X-rays, or even MRIs, alone. Physicians must often take tissue samples from an affected area with a fine needle for detailed examination. This sort of biopsy is often performed with the assistance of ultrasound, with physicians using and observing a screen for needle guidance. However, as the unfortunate case may be, about 30 percent of all tumors are invisible on ultrasound.

In some instances, MRI is used to guarantee correct needle insertion. This process involves two steps: the imaging itself, which occurs 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. Such a process is usually repeated several times before the sample is finally obtained. Consequently, this exhausts patients and is also costly, because the procedure occupies the MRI scanner for a significant period of time.

Therefore scientists and researchers 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 on the Magnetic Resonance Imaging Using Ultrasound (MARIUS), systems and processes for multimodal MR imaging, project are looking to develop a more cost-effective biopsy technique that is more accessible and easier on patients.

This new method would entail just one scan of the patient’s whole chest at the beginning of the procedure, meaning that the patient has to undergo the scanner just once. The following biopsy is then guided by ultrasound; the technique would alter the original MRI scan and precisely display it on screen. Physicians would have both the live ultrasound scan and a matching MR image available to guide the biopsy needle and display exactly where the tumor is located.

Perhaps the greatest challenge is that the MRI is conducted with the patient lying on their stomach, while during the biopsy they lie on their back. This change of position transforms the shape of the patient’s breast and shifts the position of the tumor considerably. To track these changes correctly, researchers have applied a clever alternative: While the patient is in the MRI chamber during the scan, ultrasound probes, which resemble ECG electrodes, are attached to the patient’s skin to provide a series of ultrasound images. This then produces two comparable sets of data from two separate imaging techniques.

When the patient is subjected to a biopsy in another examination room, the ultrasound probes remain attached and constantly record volume data and track the changes to the shape of the breast. Specific 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 physician can see the conjoined MRI scan along with the ultrasound image on the screen, significantly improving the accuracy of needle guidance towards the tumor.

In order for this method to be effectively sustained, Fraunhofer researchers are developing a variety of new components.

“We’re currently working on an ultrasound device that can be used within an MRI scanner. 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,” said IBMT project manager Steffen Tretbar.

The software developed for the system is also totally new.

“We’re developing a way to track movements in real time by means of ultrasound tracking. 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,” notes MEVIS project manager Matthias Günther.

The main objective of MARIUS is to develop ultrasound tracking to aid breast biopsies. Nonetheless, the developed components could also be utilized in other applications. For example, the MARIUS system and its movement-tracking software could enable 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.

And due to a method applied to reconstruct the image, the heart would appear well defined on MRI scans as opposed to blurred. The jointly developed technology could also be incorporated into 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 accuracy than presently possible and lessen damage to healthy surrounding tissue.

The team is set to present their new alternative technologies and techniques combining MR and ultrasound imaging at MEDICA 2013 in Düsseldorf, Germany, from November 20 to 23.


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