The role of diffusion MR Imaging in diagnosis and follow up of pharyngeal carcinoma

Abstract

Conventional MRI and CT are the chosen imaging modalities when evaluating head and neck cancers; however, sometimes both diagnostic tools yield low sensitivity and accuracy in making the diagnosis, staging, and assessing the post-treatment response. DWI is a technique which analyzes the structures of biolog¬ic tissues at a microscopic level. Apparent diffusion coefficient value, determined from DWI, can help detect the differences in the microstructures of tumor tissues and non-tumor tissues. Therefore, DWI is a useful technique in a clinical practice, which pro¬vides information of histopathological characterization, differential diagnosis, and stage pharyngeal cancer and assessment of treatment response. Furthermore, DWI has the advantages of being non-invasive, thus, requiring no exogenous contrast agents or ionizing radiation, it owns a short imaging time and can be easi¬ly incorporated into routine evaluations During diffusion-weighted MRI, translational motion causes phase dispersion of excited water protons, which leads to a DWI signal loss that can be quantified by calculating the ap¬parent diffusion coefficients (ADC). ADCs are calculated dur¬ing post-processing using at least two different b-values. Varia¬tions in ADC values reflect redistributions of water molecules between intracellular and extracellular tissue compartments, and thus, ADC values depend on microstructure and patho¬physiologic state. Our study concluded that: • MRI has a high sensitivity for detection pharyngeal lesions. • DWI has a higher specificity than conventional MRI and contrast enhanced MRI for characterization of pharyngeal carcinoma. • DWI is able to detect small lesions independent their size as DWI tests the metabolic and histologic status of the lesion. This is more beneficial in detecting small malignant lymph nodes as CT and conventional MRI depends only on the size of the node and not its nature.