Apparent diffusion coefficient derived from diffusion-weighted imaging to differentiate between tumor, tumor-adjacent and tumor-distant tissues in resectable rectal adenocarcinoma

Abstract

Purpose: To evaluate feasibility of apparent diffusion coefficient (ADC) at different b-values to differentiate between tumor, tumor-adjacent and tumor-distant tissues in rectal adenocarcinoma (RA).

Materials and methods: Seventy consecutive patients with RA undergoing preoperative diffusion-weighted imaging were retrospectively enrolled. ADCs of tumor, proximal tumor-adjacent tissue (PTA) and tumor-distant tissue (PTD), and distal tumor-adjacent tissue (DTA) and tumor-distant tissue (DTD) were calculated with b-values of 0 and 800 sec/mm², 0 and 1000 sec/mm², 0 and 1500 sec/mm², and multiple b-values of 0, 50, 100, 800, 1000 and 1500 sec/mm². Statistical analysis was performed to determine feasibility of ADC to differentiate between pairwise tissues.

Results: Mean ADC of tumor was lower than those of PTA, PTD, DTA and DTD; and mean ADCs of PTA and DTA were lower than those of PTD and DTD at all b-values, respectively (all P-values < 0.001). ADC cut-offs of 1.089 × 10^-3 mm²/sec (b = 0, 1000 sec/mm²) or 1.215 × 10^-3 mm²/sec (b = 0, 800 sec/mm²), and 1.142 × 10^-3 mm²/sec (b = 0, 1000 sec/mm²) or 0.995 × 10^-3 mm²/sec (b = 0, 1500 sec/mm²) achieved excellent performance in differentiating tumor from PTA or PTD, and tumor from DTA or DTD (area under receiver operating characteristic curves [AUCs]: 0.813 or 0.952, and 0.970 or 0.996), respectively. ADC cut-offs of 1.625 × 10^-3 mm²/sec (b = 0, 800 sec/mm²), and 1.165 × 10^-3 mm²/sec (b = 0, 1500 sec/mm²) could differentiate PTA from PTD, and DTA from DTD (AUCs: 0.709 and 0.673), respectively.

Conclusion: ADC can help differentiate between tumor, tumor-adjacent and tumor-distant tissues in RA.

Keywords: Apparent diffusion coefficient; Diffusion magnetic resonance imaging; Rectal cancer; Tumor-adjacent tissue; Tumor-distant tissue.