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Rad 0318 Part I

Physics and Instrumentation

The ability of a system to differentiate, on the image, objects with similar densities is known as: low-contrast resolution
Each two-dimensional square of data that make up the CT image is called a: pixel
How many pixels are contained in a 1,024 matrix image? 1,048,576
Beam attenuation can be defined as: the phenomenon by which an x-ray beam passing through a structure is decreased in intensity or amount because of absorption and interaction with matter
Why does the administration of iodinated contrast media result in an enhanced image? Iodinated contrast material increases the ability of enhanced structure to attenuate the x-ray beam
The x-ray beam sources for CT produce x-ray energy that is polychromatic. This means that: the beam comprises photons with varying energies
An object that appears on the image but is not present in the object scanned is called a: artifact
What is an advantage of filtering the x-ray beam? Filtering reduces the radiation dose to the patient
Scan thickness is primarily important for the part it plays in: volume averaging
How many CT numbers are assigned to each pixel in the image matrix? One
What is another name for raw data? scan data
When in anatomic position, the arms are: down by the sides, palms facing forward
The power capacity of the generator is listed in: kilowatts (kW)
The ability of the tube to withstand by-product heat is called: heat capacity
Regarding the detectors in the CT system, geometric efficiency is controlled primarily by: detector spacing and aperture
Which component of the CT system converts the electric signal supplied by the detectors into a digital format? analog-to-digital converter
A precise set of steps to be performed in a specific order to solve a problem describes: an algorithm
What is interpolation? A mathematical method of estimating an unknown value using the known values on either side of the unknown
The central processing unit (CPU) performs what function? Interprets computer program instructions and sequences tasks
All the thousands of bits of data acquired by the CT system with each scan are called: raw data
The DAS reads each arriving ray and measures how much of the beam has been attenuated. This is: a ray sum
In CT image creation using a third-generation design, a complete set of ray sums is known as: view
The process of converting the data from the attenuation profile to a matrix is known as: back projection
The process of applying a filter function to an attenuation profile is known as: convolution
Increasing the scan field of view: increases the number of detector cells collecting data
What is the function of the digital-to-analog converters? Converts the digital signal from the computer into an analog signal for the display monitor
Why is it necessary to convert the digitized data from the reconstruction processor to shades of gray? So that an image can be displayed on the monitor
What Hounsfield values are in the naturally occurring range? -1,000 to 1,000
Decreasing the window width in a CT image decreases: the anatomic diversity displayed
The window width of a specific CT image is set at 300, and the level (or center) is set at 100. How is a structure with a measurement of 280 HU displayed? It is white
On a CT image an ROI is placed within a structure and measured. Its standard deviation is 0. What can be determined about this structure? It is very homogenous
For which application are the raw data necessary? To decrease the display field size
A magnification factor of 1.5 is used to enlarge the image data, resulting in: an image that is larger and may allow a more accurate cursor placement for measurements
Compared with conventional radiographic images, CT localizer images: are of slightly poorer image quality
What are key aspects of the axial method of data acquisition? The table remains stationary while the x-ray tube rotates within the gantry, collecting data
The interscan delay inherent in an axial scan method is caused by which factor? Table movement between data acquisition
The practice of grouping more than one axial scan in a single breath-hold is often referred to as: clustering
Compared with helical scanning, what are the primary disadvantages to the axial method of scanning? Total examination time is longer; data reconstruction is more limited
What is it called when a patient breathes differently with each data acquisition and areas of anatomy seem to be misplaced in the z axis? Misregistration
The goal of helical interpolation methods is to: take the slant and the blur out of the helical image so that they closely resemble images taken from axial methods
What is the pitch in the following scenario: 16-slice scanner, 0.5 mm slice thickness, table movement of 12 mm per rotation? 1.5
How much anatomy (lengthwise) will be covered in a helical scan when the following parameters are selected: 15 seconds total acquisition time, 0.5 seconds gantry rotation time, 2 mm slice thickness, 4 slices per rotation, pitch of 1.5? 360 mm
What is a disadvantage of a bone algorithm? It reduces the visibility of soft tissue structures
What is a partial scan? A scan that collects data from 180 degrees tube arc, plus the degree of arc of the fan angle
What two main features are assessed to measure image quality? Spatial resolution and contrast resolution
What is spatial frequency? The number of line pairs visible per unit length
A graphical representation of the CT systems' capability of passing information through it to the observer is called: modulation transfer function (MTF)
Which term describes an isotropic voxel? A cube
The ability to differentiate a structure that varies only slightly in density from its surrounding is referred to as: low-contrast resolution
An image of a water phantom displays a range of pixel values. What can be said about this image? It is "noisy"
When discussing the quality of a CT image, what is meant by temporal resolution? How rapidly data are acquired; it is controlled by gantry rotation speed, the number of detector channels in the system, and the speed with which the system can record changing signals
How often is the accuracy of a scanner's slice thickness tested? Semiannually
A water phantom is scanned and several ROIs are placed in the resulting image. The ROIs placed at the perimeter of the image measure differently from the ROIs near the center. This indicates a problem with: cross-field uniformity
A water phantom is scanned and several ROIs are placed in the resulting image. The standard deviation measurements from the ROIs range from 15 to 25. What can be said about the image? It is noisy
What can be done to improve the linearity of a CT system? Daily calibrations
What quality control test must be performed by a medical physicist? Radiation dose measurements
Artifacts that result from undersampling are called: aliasing artifacts
Raw data that results from an MDCT scan acquisition is used so that the 1-mm slices are combined to produce thicker slices for viewing. This is called: image reconstruction
Assume the raw data are still available. In what scenario would it be impossible to create an MPR? Source images vary in gantry tilt
A limitation of scanner-created MPRs is: In most cases, only straight sagittal and coronal planes can be automatically generated
What is a disadvantage to workstation-created MPRs? To produce the highest quality MPRs the thinnest slices must be sent to the workstation. This amount of data can slow down the PACS
Another name for surface rendering is: shaded-surface display
In creating a surface-rendered image, what can happen if the threshold set is too narrow? Actual protruding structures can be imperceptible
VR techniques assign each voxel an opacity value based on its ___. This value determines the degree the voxel will contribute to the final image. Hounsfield units
The process of selectively removing or isolating information from the 3D data set is referred to as: segmentation
Which electronic system allows clinicians to input an electronic order for a CT exam and transmits that order to the CT department? CPOE
What two electronic elements form the radiology information infrastructures? RIS and PACS
Computers that act on requests from other networked computers, rather than from a person inputting directly into it, are called: servers
The computers that are integral to the functioning of the PACS are referred to as: core servers
The amount of data that can be transmitted between two points in the network in a set period of time is known as: bandwidth
A scheme that compresses an image without any loss of information when the image is decompressed is called: lossless
DICOM refers to a: universally adopted standard for medical image interchange
A device that is used to automatically load and unload optical discs is called a: optical jukebox
Created by: silsila622