Spectral CT and Hounsfield Units: basis for correct interpretation

Abstract

Dual energy CT is a recent upgrade to this diagnostic imaging technique. The purpose of this critical narrative review is to lay out the clinical applications of Hounsfield Units and their variation across the x-ray energy spectrum using DECT. We explore new reconstruction methods and parametric maps helpful for the diagnosis of prevalent pathologies such as fatty liver disease, urolithiasis, and to identify complications after interventions or determine the aggressiveness of tumoral lesions. The energy-resolving capabilities of DECT make it a reliable method for the characterisation of tissue and lesion composition. Lower energy monoenergetic images allow us to increase soft tissue contrast and easily identify tissues with higher contrast uptake. Higher energy monoenergetic images are useful to distinguish between contrast uptake and high attenuation calcium deposits and for metal artifact reduction. Parametric images showing uric acid, iodine, calcium, and other material decompositions can be obtained from spectral data for the diagnosis of tumoral or metabolic diseases, vascular lesions and characterisation of deposition arthritis and urolithiasis.