Breast specialists emphasize functional, physical, and chemical aspects of imaging

March 12, 2007

The dominance of x-ray mammography in breast screening seems unlikely to change before ECR 2008, or even ECR 2018. But when it comes to clarifying a positive read or assessing the cause of symptomatic breast pain, a whole host of alternative diagnostic approaches are waiting in the wings.

The dominance of x-ray mammography in breast screening seems unlikely to change before ECR 2008, or even ECR 2018. But when it comes to clarifying a positive read or assessing the cause of symptomatic breast pain, a whole host of alternative diagnostic approaches are waiting in the wings.

Lesion's elastic component is interpreted via the classical Maxwell model. Tumor exhibits strongly elevated values of elasticity. (Provided by R. Sinkus)

"It is the future in reach," said Dr. Ralph Sinkus, a researcher at the Ecole Supérieure di Physique et de Chimie Industrielles (EPSCI) in Paris. "These are the techniques that are very near to clinical reality."

Elastography is one such approach on the brink of clinical application. The technique is based on palpating tissue to detect abnormalities as lumps. As healthy tissue becomes malignant, its viscoelastic properties change. But deep-seated tumors, or small growths, may still be missed by even the most experienced practitioner.

Elastography provides an objective way of highlighting differences in tissue elasticity, according to Sinkus. Because elasticity itself cannot be imaged, a two-step approach is required.

The tissue is first vibrated to set up a series of acoustic waves. These waves travel slowly through soft, elastic tissue and more quickly through stiffer tissue. A modality sensitive to motion, such as MRI or ultrasound, is then used to image the waves, gaining information on the tissue's elastic properties.

Invasive ductal carcinoma is clearly visible as an area of increased wavelength, indicating the lesion's altered viscoelastic properties. (Provided by R. Sinkus)

"The basic concept is very simple," he said. "The MRI unit or the ultrasound machine is nothing but a digital camera to us. Making an image out of these waves is where the physics comes in. Clinicians will never need to see those equations. To them, it is just software."

EPSCI researchers, working with the Institute Curie in Paris, plan to study the clinical potential of ultrasound elastography. The data derived from ultrasound are not as precise as those acquired with MRI, but the modality is considerably cheaper and more widely available, and the accuracy of its results may improve over time. This means that MR elastography can be ruled out as a first-line breast screening tool, but the same is not necessarily true for ultrasound elastography.

Sinkus envisages MR elastography becoming a valuable adjunct to contrast-enhanced MR mammography for the workup of suspicious breast lesions. This could improve the specificity of breast MRI by up to 20%.

The addition of perfusion imaging and/or MR proton and phosphorus spectroscopy could also help differentiate benign masses from malignancies, according to Dr. Christiane Kuhl, a professor of radiology at the University of Bonn in Germany. Switching to blood-pool contrast agents could have diagnostic advantages for breast MRI, but these agents have not yet received regulatory approval for clinical breast imaging work.

Contrast-enhanced T1-weighted gradient-echo MRI of right breast in transverse orientation. Note invasive ductal carcinoma and corresponding maximum signal enhancement after bolus injection. (Provided by R. Sinkus)

Kuhl hopes that the emergence of functional techniques in breast MR examinations will prevent overtreatment. Some ductal carcinoma in situ findings flagged on x-ray mammography may never become invasive. But without knowing which these are, physicians could still refer patients for inappropriately aggressive therapy.

"We desperately need more information regarding the biological prognostic behaviour of cancers. I would hope that with the more functional techniques that breast MR is able to provide, we will be able to get some surrogate markers for biological aggressiveness, too," she said.

Optical imaging is another promising technology hovering on the horizon, according to Dr. Christoph Bremer of the Institute of Clinical Radiology at the University of Münster in Germany. Techniques are sufficiently accurate that optical imaging can reveal just a few receptors on a tumor cell.

Most fluorochromes under investigation for breast imaging fluoresce in the near-infrared region of the electromagnetic spectrum. This type of light can travel significant distances through tissue, unlike visible light, which is absorbed strongly.

The advent of whole-body tomographic optical imaging systems, equivalent to CT or MR scanners, is unlikely, Bremer said. Surface imaging techniques that allow practitioners to essentially take a photograph at a wavelength specific to an injected fluorochrome appear more promising. The combination of this approach with laparoscopic devices could still enable imaging within the breast. This may be a real help to breast surgeons when it comes to excising suspicious masses.

"You could potentially inject a fluorochrome that attaches to the breast tumor to see where the margins are and then apply simple intraoperative technology," he said. "It is cheap, rapid, and basically online. That's a scenario that is really not far away from clinical application."