Contrast agent protocols should consider breast tissue blood flow

Imaging protocols for injected contrast agents should consider variation in tissue blood flow due to mammographic compression, according to a study published in the February 2014 issue of Academic Radiology.

Exogenous contrast agents have become a vital component of breast cancer screening and diagnosis due to their improvement of image signal-to-noise ratio and ability to act as tissue biomarkers.

“Deformation of breast tissue during compression, however, can lead to modifications of regional blood flow that alter tissue oxygenation and metabolism as well as contrast agent delivery,” wrote lead author David R. Busch, PhD, of the University of Pennsylvania in Philadelphia, and colleagues. “Furthermore, the mechanical properties of tumors are generally different from those of the surrounding tissues, and these differences can lead to uncontrolled and heterogeneous vascular responses of the breast to compression. Thus, compression can significantly reduce cancer contrast.”

New technologies such as diffuse optical spectroscopy (DOS) and diffuse optical tomography (DOT) use photons in the near-infrared tissue transmission window to better breast cancer specificity and sensitivity. Hemodynamic parameters in breast cancer provide significant tumor contrast yet clinical DOS/DOT measurements rely on mild compression of the breast tissue. Importantly, the effects of the compression on the vasculature of the breast tissue are usually not taken into account in the analysis of DOT results.

Busch and colleagues measured hemodynamic properties like blood flow and hemoglobin concentration oxygenation in the breasts of 15 healthy volunteers under a variety of compressive loads. The researchers used diffuse optical and diffuse correlation spectroscopies to measure the concentrations of oxygenated and deoxygenated hemoglobin, lipid, water, and microvascular blood flow during axial breast compression in the parallel-plate transmission geometry.

The study’s results indicated that total hemoglobin content decreased up to 30 percent compared to baseline during high-load periods. Relative blood flow measurements had significantly more variation, particularly in the baseline and relaxed periods. Blood flow was significantly reduced by up to 87 percent. Blood oxygenation showed small changes, which were consistently smaller under applied load. It was reduced by about 20 percent under applied pressures of 30 kPa. Tissue scattering slightly changed; it increased during plate separation reduction and then decreased slowly in the full compression period. Water and lipid concentrations varied little.

Such a large change in blood flow during compression can markedly reduce contrast agent delivery to breast tissue or force blood-pooling agents out of the breast, wrote the authors.

“In future studies, it would be interesting to use DCS in transmission to probe the tumor-bearing breast and thereby study the differential vasculature-related responses to compressional stresses. Such differential responses might be useful for tumor detection and characterization,” concluded Busch and colleagues.