Imaging breast adipose and fibroglandular tissue molecular signatures by using hybrid MRI-guided near-infrared spectral tomography

Abstract

Magnetic resonance (MR)-guided near-infrared spectral tomography was developed and used to image adipose and fibroglandular breast tissue of 11 normal female subjects, recruited under an institutional review board-approved protocol. Images of hemoglobin, oxygen saturation, water fraction, and subcellular scattering were reconstructed and show that fibroglandular fractions of both blood and water are higher than in adipose tissue. Variation in adipose and fibroglandular tissue composition between individuals was not significantly different across the scattered and dense breast categories. Combined MR and near-infrared tomography provides fundamental molecular information about these tissue types with resolution governed by MR T1 images.

Fig. 1.

The hardware systems used for integration of NIR measurements through breast tissue are shown. (a) Photograph of the portable NIR instrumentation and control console. (b) Optical fibers extend from the system into the MRI. (c) Open architecture breast array coil houses the optical fiber positioning system and allows for ≈8 cm of vertical motion. (d and e) The first (d) and second (e) generation MR-compatible fiber-positioning mechanisms.

Fig. 2.

Breast images are displayed from MRI and NIR. Anatomically axial (column 1 from left) and coronal (column 2) T1-weighted MR scans through three normal breasts. The coronal slices correspond to the plane of NIR measurement. Fiducial markers attached to each optical fiber are visible at the tissue perimeter and are projected onto the model surface (as dots in column 3). Coronal slices are used to create 2D meshes (column 3), which accurately represent the breast structure in the plane of interest, as well as to locate the measurement positions with millimeter accuracy. Each mesh location (node) is classified to define either adipose or fibroglandular tissue based on segmentation of the MRI grayscale intensities, and the dimensions are shown in millimeters, in the middle column of breast meshes. These meshes are used in the NIR image reconstruction from simultaneously acquired optical data. Images of the corresponding total hemoglobin concentration ([Hb_T], μM) are shown in column 4.

Fig. 3.

Breast images are displayed for MRI and NIR. Anatomically axial (column 1 from left) and coronal (column 2) T1-weighted MRI slices through three normal breasts. Subjects were 69, 43, and 43 years old with scattered (Top), heterogeneously dense (Middle), and heterogeneously dense (Bottom) radiodensities, respectively. (Columns 3–7) Reconstructed images of chromophores and scatter parameters from simultaneously acquired NIR measurements (left to right) are as follows: total hemoglobin concentration ([Hb_T], μM), hemoglobin oxygen saturation (S_tO₂, %), water fraction (H₂O, %), scattering amplitude (A), and SP. The spatial dimensions are similar to Fig. 2, with all breasts being ≈8–10 cm in diameter.

Fig. 4.

Box plots of average properties for adipose and fibroglandular tissues, including scattering parameters of amplitude and power (a), and hemoglobin concentration [Hb_T], oxygen saturation (S_tO₂), and water fraction (b). Bars represent the total range in the values within each tissue type.