Imaging evaluation focused on microstructural tissue changes using tensor-valued diffusion encoding in breast cancers after neoadjuvant chemotherapy: is it a promising way forward?

Background: Single diffusion encoding is a widely used, noninvasive technique for probing the tissue microstructure in breast tumors. However, it does not provide detailed information about the microenvironmental complexity. This study investigated the clinical utility of tensor-valued diffusion encoding for evaluating microstructural changes in breast cancer after neoadjuvant chemotherapy (NAC).

Methods: We retrospectively included patients underwent chemotherapy for histologically proven invasive breast cancer between July 2020 and June 2023 and monitored the tumor response with breast magnetic resonance imaging (MRI), including tensor-valued diffusion encoding. We reviewed pre- and post-NAC MRIs regarding chemotherapy in 23 breast cancers. Q-space trajectory imaging (QTI) parameters were estimated at each time-point, and were compared with histopathological parameters.

Results: The mean total mean kurtosis (MK), anisotropic mean kurtosis (MK), and microscopic fractional anisotropy (µFA) were significantly decreased on post-NAC MRI compared with pre-NAC MRI, with the large effect size (ES) in MK and µFA (0.81±0.41 0.99±0.33, ES: 0.48, P=0.03; 0.48±0.30 0.73±0.27, ES: 0.88, P<0.001; 0.58±0.14 0.68±0.11, ES: 0.79, P=0.003; respectively). Regarding prognostic factors, tumors with high Ki-67 expression showed significantly lower pre-NAC mean diffusivity (MD) and higher pre-NAC µFA compared to tumors with low Ki-67 expression (0.98±0.09 1.25±0.20, P=0.002; and 0.72±0.07 0.57±0.10, P=0.005; respectively). And negative progesterone receptor (PR) group revealed significantly lower MK, MK, and isotropic mean kurtosis than positive PR group on the post-NAC MRI (0.60±0.31 1.03±0.40, P=0.008; 0.36±0.21 0.61±0.33, P=0.04; and 0.23±0.17 0.42±0.25, P=0.046; respectively).

Conclusions: QTI parameters reflected the microstructural changes in breast cancer treated with NAC and can be used as noninvasive imaging biomarkers correlated with prognostic factors.