High-resolution diffusion-weighted imaging for monitoring breast cancer treatment response

Abstract

Rationale and objectives: The aim of this work was to compare a high-resolution diffusion-weighted imaging (HR-DWI) acquisition (voxel size = 4.8 mm(3)) to a standard diffusion-weighted imaging (STD-DWI) acquisition (voxel size = 29.3 mm(3)) for monitoring neoadjuvant therapy-induced changes in breast tumors.

Materials and methods: Nine women with locally advanced breast cancer were imaged with both HR-DWI and STD-DWI before and after 3 weeks (early treatment) of neoadjuvant taxane-based treatment. Tumor apparent diffusion coefficient (ADC) metrics (mean and histogram percentiles) from both DWI methods were calculated, and their relationship to tumor volume change after 12 weeks of treatment (posttreatment) measured by dynamic contrast enhanced magnetic resonance imaging was evaluated with a Spearman's rank correlation.

Results: The HR-DWI pretreatment 15th percentile tumor ADC (P = .03) and early treatment 15th, 25th, and 50th percentile tumor ADCs (P = .008, .010, .04, respectively) were significantly lower than the corresponding STD-DWI percentile ADCs. The mean tumor HR-ADC was significantly lower than STD-ADC at the early treatment time point (P = .02), but not at the pretreatment time point (P = .07). A significant early treatment increase in tumor ADC was found with both methods (P < .05). Correlations between HR-DWI tumor ADC and posttreatment tumor volume change were higher than the STD-DWI correlations at both time points and the lower percentile ADCs had the strongest correlations.

Conclusion: These initial results suggest that the HR-DWI technique has potential for improving characterization of low tumor ADC values over STD-DWI and that HR-DWI may be of value in evaluating tumor change with treatment.

Figure 1

Representative apparent diffusion coefficient maps of an invasive breast carcinoma acquired with high-resolution diffusion-weighted imaging (DWI; left) and standard DWI (right). The tumor is visible as a hypointense region in the center of the breast.

Figure 2

Pre- (top row) and early treatment (bottom row) high-resolution diffusion-weighted images of an invasive breast carcinoma. Left column: b = 600 images; right column: apparent diffusion coefficient (ADC) maps. The tumor is visible as a hypointense region in the center of the breast on the ADC maps. This region appears less hypointense on the early treatment ADC map.

Figure 3

(a) Pre- and (b) early-treatment tumor ADC values were measured at 15th, 25th, 50th, 75th, and 90th percentile. Statistically significant differences between HR-DWI and STD-DWI measurements were found at 15th percentile in pretreatment and at 15th, 25th, and 50th percentiles after early treatment. ADC, apparent diffusion coefficient; HR-DWI, high-resolution diffusion-weighted imaging; STD-DWI, standard diffusion-weighted imaging.

Figure 4

Example correlations for the pretreatment tumor 15th percentile ADCs and absolute tumor volume change between visit 1 and visit 3 for (a) HR-DWI (r² = 0.83, P = .0007) and (b) STD-DWI (r² = 0.62, P = .01). ADC, apparent diffusion coefficient; HR-DWI, high-resolution diffusion-weighted imaging; STD-DWI, standard diffusion-weighted imaging.

Figure 5

Plots of estimated pretreatment Spearman’s correlations for HR-DWI and STD-DWI tumor ADC metrics. Spearman’s correlations were calculated to assess the relationship between tumor ADC metrics (mean and percentile ADCs) and tumor volume change at the end of treatment. The strongest correlation with tumor volume change was found for HR-DWI 15th percentile ADC. ADC, apparent diffusion coefficient; HR-DWI, high-resolution diffusion-weighted imaging; STD-DWI, standard diffusion-weighted imaging.