Computed Tomography and Advanced Imaging Questions and Answers Flashcards

In CT imaging, what does the term 'Hounsfield unit (HU)' measure?

Answer: The attenuation value of tissue relative to water

Hounsfield units quantify the x-ray attenuation of a tissue relative to water (0 HU), with air at −1000 HU and dense bone at +1000 HU.

Which CT windowing setting would best display pulmonary parenchyma?

Answer: Window width 1500, level −600 (lung window)

A wide window width (~1500 HU) centered at a low level (~−600 HU) is used for lung windows to display the air-filled parenchyma with adequate contrast.

What is the primary advantage of helical (spiral) CT over conventional axial CT?

Answer: Continuous data acquisition allowing volume imaging and multiplanar reconstruction

Helical CT acquires a continuous volume of data during one breath-hold, enabling multiplanar reconstructions and reducing motion artifacts.

In CT, pitch is defined as:

Answer: Table distance traveled per gantry rotation divided by beam collimation

Pitch = table feed per rotation ÷ total beam collimation; a pitch >1 means faster coverage but can reduce dose and slice overlap.

Which artifact in CT is caused by very dense structures (such as metal implants) and appears as dark and light streaks radiating from the object?

Answer: Beam-hardening/metal artifact

Metal implants absorb x-rays so strongly that insufficient photons reach the detector, causing beam-hardening and photon starvation, producing characteristic streak artifacts.

What does CTDI (CT Dose Index) measure?

Answer: Radiation dose profile along the z-axis for a single CT scan rotation

CTDI measures the absorbed dose along the z-axis (scan direction) for a single axial rotation and is a standardized CT dose descriptor.