Image Quality in CT Scans

The contrast resolution provided by ______________ is considerably better than that available in radiography.

The ability to image low-contrast objects with CT is limited by the size and uniformity of the object and by the ______________ of the system.

If a ______________ medium such as water is imaged, each pixel should have a value of zero.

This variation in CT numbers above or below the average value is the ______________ of the system.

The magnitude of noise is equal to the ______________ deviation of the CT number values within the region of interest.

Noise is the percentage ______________ deviation of a large number of pixels obtained from a water bath image.

The patient radiation dose, the number of x-rays used by the detector to produce the image, controls the ______________.

In statistics, noise is called a ______________ deviation and is symbolized by σ.

If the CT imaging system is properly adjusted, the value of ______ should be zero.

The characteristic of having constant pixel values in all regions of the reconstructed image is called ______ uniformity.

A histogram or line graph can be plotted using an internal software package to test ______ uniformity.

If all values of the histogram or line graph are within two standard deviations of the mean value, the system is said to exhibit ______ spatial uniformity.

The 'cupping' artifact is caused by ______ beam hardening.

The 'cupping' artifact can be demonstrated by imaging the water bath inside a ______ ring to simulate bone.

Noise appears on the image as ______.

Low-______ images appear very smooth to the eye, and high-______ images appear spotty or blotchy.

Noise should be evaluated daily through imaging of a ______-cm-diameter water bath.

The ROI must encompass at least ______ pixels when the CT technologist measures noise.

Computed tomography imaging systems must be ______ frequently so that water is consistently represented by CT number zero.

Uniformity is defined as the ______ of the CT numbers of an image of a homogeneous material across the scan field.

Uniformity is calculated using the following equation: |______ - ______|, which is the difference in the mean CT number in the centre from that at the periphery of the image.

When a uniform object such as a water bath is imaged, each pixel should have the same ______ because each pixel represents precisely the same object.