CT chapter 1 quiz

An x-ray beam consists of bundles of energy known as photons. During imaging, photons may pass through, be redirected by, or absorbed by a structure.

An x-ray beam consists of bundles of energy known as ________.

true

Artifacts always degrade the quality of an image. True False

Metals are dense and have the greatest capacity for beam attenuation. Consequently metals are represented as white on a CT image.

How are metals represented on a CT image? As white areas As grey areas As black areas

In the creation of the CT image, the processed data are converted into shades of gray for viewing during the image phase.

In which part of the CT process are the data converted into shades of gray for viewing? Image display Data acquisition Image reconstruction

False

The larger the object being scanned, the thinner the CT slice required. True False

True

The sagittal plane divides the body into right and left sections. True False

The bits of data acquired by the system with each scan are called raw data. The terms scan data and raw data are used interchangeably.

The terms scan data and ___________ data are used interchangeably to refer to the computer data waiting to be processed to create an image.

True

True or False? The degree to which an x-ray beam is reduced by an object is known as attenuation. True False

Artifacts are objects seen on the image but not present in the object scanned. They always degrade the quality of the image.

What are image artifacts? Substances used to create a temporary artificial density between objects The photons in an x-ray beam The data that form the CT slice Objects seen on a CT image that are not present in the object scanned

Measurements of the beam attenuation capability of an object are expressed in Hounsfield units (HU), named after Godfrey Hounsfield, one of the pioneers in the development of CT. Hounsfield units are also referred to as CT numbers, or density values.

What are used to quantify the degree that a structure attenuates an x-ray beam? Contrasting agents Attenuation coefficients Hounsfield units Pixels

Contrast agents fill a structure with a material that has a different density the structure itself.

What can be used to create a temporary artificial density difference between two objects on a CT image?

In CT, the x-ray beam passes through the patient's body and is recorded by detectors. Then the computer creates the CT image. The number of x-ray photons that pass through the body determine the shades of gray on the image.

What determines the shades of gray on a CT image? The thickness of the CT slice The quantity of x-ray photons Air-filled structures The scanning protocol

The step-and-shoot scan mode is commonly referred to as axial scanning, conventional scanning, or serial scanning.

What is another name for step-and-shoot scan mode? Axial Volumetric Spiral Helical

Density is the mass of a substance per unit volume. Put more simply, it is the degree to which matter is concentrated.

What is density? The degree to which matter is concentrated The degree to which an x-ray beam is reduced by an object The number of photons that pass through a structure The amount of x-ray beam that is absorbed per unit of thickness

The most common matrix size is 512. This means there are 512 rows of pixels down and 512 columns of pixels across.

What is the most common matrix size in CT? 1024 512 128 256

The word pixel is used for the term picture element. A composite of thou-sands of pixels creates the CT image that displays on the CT monitor.

What is the name for each two-dimensional square in a CT slice? matrix pixel cross-section cube

High voltage propels the electrons from the x-ray tube filament to the anode. The area of the anode the electrons hit and where the x-ray beam is produced is called the focal spot.

What is the name for the area of the anode where the electrons strike and the x-ray beam is produced? reconstruction processor focal spot gantry space cloud

The process in CT by which different tissue attenuation values are averaged to produce one less accurate pixel reading is called volume averaging. The slice thickness has a significant effect on the degree of volume averaging that is present on an image. The X and Y dimensions of the pixel also affect the likelihood of volume averaging.

What is the name of the process in CT by which different attenuation values are averaged to produce one less accurate pixel reading? Image averaging Pixel averaging Z axis averaging Volume averaging

Changing the image plane from axial to coronal is indicated for two reasons. The primary reason is when the anatomy of interest lies vertically rather than horizontally. The secondary reason is to reduce artifacts created by surrounding structures.

What is the primary reason for changing the image plane from axial to coronal? The anatomy of interest lies vertically rather than horizontally To attenuate the x-ray beam To reduce artifacts created by surrounding structures To eliminate volume averaging

The ability of the x-ray tube to withstand the resultant heat is called its heat capacity.

What is the term for the ability of an x-ray tube to withstand resultant heat? Thermal energy Kinetic energy Heat dissipation Heat capacity

A CT slice represents a specific plane in the patient's body. The thickness of the plane is referred to as the Z axis.

What is the thickness of a cross-sectional CT slice called? Q axis Y axis Z axis X axis

The term inferior refers to movement toward the feet (down) and is synonymous with the term caudal.

Which directional term refers to movement towards the feet? Anterior Inferior Posterior Superior

The term superior defines movement toward the head (up) and is used interchangeably with the term cranial or cephalic.

Which directional term refers to movement towards the head? Inferior Superior Posterior Anterior

In general, the smaller the object being scanned, the thinner the CT slice required. Thicker slices increase the likelihood a very small object will not show up on the scan.

Which is a drawback of using thicker CT slices when imaging? They increase the number of slices that are produced. They increase radiation dosage. They decrease the pixel size. They increase the likelihood of missing very small objects.

The main advantages of CT over conventional radiography are the elimination of superimposed structures, the ability to differentiate small differences in density of anatomic structures and abnormalities, and the superior quality of the images.

Which is not an advantage of CT over conventional radiography? The elimination of superimposed structures The ability to differentiate small differences in density of anatomic structures and abnormalities The depiction of a three-dimensional object as a two-dimensional image The superior quality of the images

The X and Y dimensions of the pixel affect the likelihood of volume averaging. The larger the X and Y dimensions the larger the pixel and therefore the more likely that the pixel will contain tissues of different densities causing volume averaging.

Why does using a small pixel size reduce the likelihood of volume averaging? It limits the amount of data to be volume averaged. It decreases the thickness of the plane. It changes the temporal resolution. It increase beam attenuation.

Artifacts that result from preferential absorption of the low-energy photons, which leaves higher-intensity photons to strike the detector array, are called beam-hardening artifacts.

__________ artifacts appear as dark streaks or vague areas of decreased density on a CT image.

Spatial resolution is one of the criteria for evaluating CT image quality.

__________ resolution describes the ability of a system to define small objects distinctly.

All directional terms are based on the body being viewed in the anatomic position. The term lateral refers to movement toward the sides of the body.

___________ refers to movement towards the sides of the body.

False

o differentiate adjacent objects on a CT image, there cannot be a density difference between the two objects. True False