ASRT Practice Exam 2025 – Complete Study Resource

The Hounsfield unit (HU) plays a critical role in computed tomography (CT) imaging by measuring the radiodensity of various tissues. This unit provides a quantitative scale that allows for the differentiation of tissues based on their composition and density, which is essential for accurate diagnosis and assessment of medical conditions.

In CT scans, the radiodensity of a substance is expressed in Hounsfield units, where air is assigned a value of -1000 HU, water is 0 HU, and dense bone can have values exceeding +1000 HU. Since different tissues and substances in the body have unique atomic compositions and densities, the Hounsfield units help in distinguishing these variations. For instance, fat appears less dense than water and will have a negative value, whereas tumors or calcified tissues will have positive values, aiding clinicians in identifying and characterizing structures.

This measurement is crucial for radiologists and technologists to not only interpret CT images correctly but also to determine the appropriate course of action for patient management. The use of Hounsfield units facilitates a standardized approach to understanding the differences between various types of tissues and pathology in CT imaging.