Gene Cho, Presenter: Nothing to Disclose

Melanie Moccaldi RT, Abstract Co-Author: Nothing to Disclose

Linda Moy MD, Abstract Co-Author: Nothing to Disclose

Sungheon Kim, Abstract Co-Author: Nothing to Disclose

Eric Sigmund PhD, Abstract Co-Author: Stockholder, Abbott laboratories

Diffusion-weighted imaging (DWI) senses tissue structure by restricted water diffusion, and its advanced variant, diffusion tensor imaging (DTI), provides sensitivity to directional anisotropy. Since the average diameter of breast ducts are much larger than that of brain white matter axons (~60 µm vs. ~1-2 µm), a longer diffusion time is required to accentuate the directional anisotropy of breast ducts than for brain white matter. To that end, we measured DTI parameters in normal fibroglandular tissue (FGT) at two different diffusion times to determine if apparent anisotropy increases with diffusion time.

This prospective, IRB-approved, HIPAA compliant study enrolled 19 consecutive subjects (ages 26 to 69 years) from 11/04/11 to 2/22/12, who underwent routine breast MRI and a DTI protocol at a 3T scanner using a 7-channel breast coil. We used a stimulated echo DTI sequence with axial echo-planar imaging readout (TR/TE - 7700/40 ms, 192 x 132 matrix, 10 slices, 1.8 x 1.8 x 4 mm resolution, b = 0, 500 s/mm2, 6 directions, 3 averages). Scans at two diffusion times (tD = 30 and 520 ms) were acquired by varying the stimulated echo mixing time. Maps of mean diffusivity (MD), fractional anisotropy (FA), and diffusion eigenvalues (λ1, λ2, λ3) were generated. Regions of interest (ROI) were manually drawn in contiguous regions of FGT on all slices to estimate mean values of all DTI parameters, individually, in both left and right breasts. Group statistical comparisons with a paired Student’s t-test were performed to compare values from the two diffusion times.

Group DTI (avg. ROI size = 3.2±1.7 cm2/slice) results at tD = 30 ms were FA = 0.24±0.083, MD = 1.79±0.42 µm2/ms, λ  1  /λ 2 /λ3 =  2 .19±0.47/1.74±0.44/1.34±0.43 µm2/ms. At tD = 520 ms, FA = 0.33±0.10, MD = 1.68±0.25 µm2/ms, λ1/λ2/λ3 = 2.24±0.21/1.68±0.24/1.16±0.30 µm2/ms. Significant differences (p<0.05) between the two diffusion times were observed for both FA and λ3.

Changes in FGT DTI parameters at longer diffusion times are consistent with increased restriction to transverse diffusion, possibly from confinement in oriented ductal tubules. Future work will test whether this improves discrimination of healthy FGT from cancerous lesions.

DTI at long diffusion times increases sensitivity to fibroglandular anisotropy and may improve normal / lesion discrimination as well as architectural mapping of the ductal tree (“ductography”).

Cho, G, Moccaldi, M, Moy, L, Kim, S, Sigmund, E, Observation of Time-Dependent DTI Anisotropy in Breast Fibroglandular Tissue.  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12031044.html