MRI-guided diffuse optical spectroscopy of malignant and benign breast lesions

Abstract

We present the clinical implementation of a novel hybrid system that combines magnetic resonance imaging (MRI) and near-infrared (NIR) optical measurements for the noninvasive study of breast cancer in vivo. Fourteen patients were studied with a MR-NIR prototype imager and spectrometer. A diffuse optical tomographic scheme employed the MR images as a priori information to implement an image-guided NIR localized spectroscopic scheme. All patients who entered the study also underwent gadolinium-enhanced MRI and biopsy so that the optical findings were cross-validated with MR readings and histopathology. The technique quantified the oxy- and deoxyhemoglobin of five malignant and nine benign breast lesions in vivo. Breast cancers were found with decreased oxygen saturation and higher blood concentration than most benign lesions. The average hemoglobin concentration ([H]) of cancers was 0.130+/-0.100 mM, and the average hemoglobin saturation (Y) was 60+/-9% compared to [H]=0.018+/-0.005 mM and Y=69+/-6% of background tissue. Fibroadenomas exhibited high hemoglobin concentration [H]=0.060+/-0.010 mM and mild decrease in oxygen saturation Y=67+/-2%. Cysts and other normal lesions were easily differentiated based on intrinsic contrast information. This novel optical technology can be a significant add-on in MR examinations and can be used to characterize functional parameters of cancers with diagnostic and treatment prognosis potential. It is foreseen that the technique can play a major role in functional activation studies of brain and muscle as well.

Figure 1

Patient placement into the MR bore. Source fibers were attached on the inner side of the pedant breast, and detector fiber bundles were placed on the outer side of the breast, using appropriate plates that compress the breast softly. Light was shined sequentially through the 24 source fibers and acquired in parallel on the other side by the detector fiber bundles so that multiple projections were collected for each source fiber.

Figure 2

Two-dimensional representation of the three-dimensional problem of overlaying the optical mesh onto the MR image. Different voxels of the optical mesh correspond to different tissue types or combinations of them. By setting appropriate thresholds, each of the optical mesh voxels can be assigned to one tissue type that has an average absorption coefficient and an average reduced scattering coefficient that is common to all voxels of the same tissue type.

Figure 3

The experimental simultaneous MR-optical examination protocol. Only the segments relevant to the measurement of intrinsic contrast are shown.

Figure 4

Two-dimensional plot of the hemoglobin saturation and concentration measured from selected malignant and benign breast lesions using MR-guided DOS. The baseline measurements represent average values calculated from each breast examined. The normal lesions correspond to areas enhancing on MR after gadolinium administration, but were not identified as suspicious on the X-ray mammogram or diagnosed as malignant by MR.

Figure 5

Plots of (a) hemoglobin concentration and (b) saturation as a function of lesion size.