Intravoxel incoherent motion MR imaging: comparison of diffusion and perfusion characteristics between nasopharyngeal carcinoma and post-chemoradiation fibrosis.

OBJECTIVES

To compare the intravoxel incoherent motion (IVIM) diffusion and perfusion characteristics of nasopharyngeal carcinoma (NPC) and post-chemoradiation fibrosis to aid in their differentiation.

METHODS

Fifty-three (64 %) patients with newly diagnosed NPC and 30 (36 %) patients with biopsy-proven post-chemoradiation fibrosis were recruited into tumour and fibrosis groups respectively. Diffusion-weighted magnetic resonance (MR) imaging was performed using 13 b values (0-1,000 s/mm(2)). Their respective IVIM parameters (D, pure diffusion; f, perfusion fraction; D, pseudodiffusion coefficient) were obtained.

RESULTS

D and f were significantly lower in NPC (D = 0.752 ± 0.194 × 10(-3) mm(2)/s, P <0.001; f = 0.122 ± 0.095, P <0.001) than in fibrosis (D = 1.423 ± 0.364 × 10(-3) mm(2)/s; f = 0.190 ± 0.120); while D was significantly higher in NPC (111.366 ± 65.528 × 10(-3) mm(2)/s, P <0.001) than in fibrosis (77.468 ± 62.168 × 10(-3) mm(2)/s). Respective cut-off values with sensitivity, specificity and accuracy were: D = 1.062 × 10(-3) mm(2)/s (100 %, 100 %, 100 %); f = 0.132 (66.0 %, 100 %, 78.3 %); D = 85.283 × 10(-3) mm(2)/s (100 %, 90.7 %, 96.4 %).

CONCLUSION

NPC and post-chemoradiation fibrosis have distinctive IVIM parameters. IVIM MR imaging is potentially useful in discrimination between NPC and fibrosis.

KEY POINTS

• New MRI techniques offer greater help in the assessment of nasopharyngeal carcinoma. • Tumour and post-chemoradiation fibrosis have distinctive intravoxel incoherent motion diffusion/perfusion parameters. • Non-invasive IVIM MRI may help differentiate between tumour and fibrosis. • Pure diffusion is a robust independent discriminating factor which improves diagnostic confidence.