Radiography Exam Computed Tomography (CT) Basics

Question 1

In computed tomography, the Hounsfield unit (HU) value for water is:

Accepted Answer

0 HU

Answer

By definition in the Hounsfield scale, water is assigned a value of 0 HU, serving as the reference point for the CT density scale.

Question 2

The CT scan parameter that most directly controls the radiation dose to the patient is:

Accepted Answer

mAs (tube current × time)

Answer

The mAs (product of tube current in mA and scan time in seconds) is the primary determinant of radiation dose in CT, as it controls the number of x-ray photons produced.

Question 3

Which CT reconstruction algorithm produces images with the sharpest edges and highest spatial resolution, typically used for lung and bone imaging?

Accepted Answer

High-frequency (edge-enhancing) kernel

Answer

High-frequency or edge-enhancing reconstruction kernels amplify high spatial frequencies, producing sharper edges at the cost of increased image noise — ideal for bone and lung detail.

Question 4

In helical (spiral) CT, pitch is defined as:

Accepted Answer

Table travel per rotation divided by the total collimation width

Answer

Pitch = table distance traveled per 360° rotation ÷ total x-ray beam collimation width. A pitch of 1 means table travel equals beam width per rotation.

Question 5

The CTDI (CT Dose Index) metric most commonly used to represent dose for a specific scanner and protocol is:

Accepted Answer

CTDIvol (volumetric CTDI)

Answer

CTDIvol is the most widely used single-number representation of CT dose for a given protocol, accounting for pitch and providing a volume-averaged dose estimate.

Radiography Exam Practice Test

Radiography Exam Practice Test

Radiography Exam Computed Tomography (CT) Basics