Study guide CT (IMAGE PRODUCTION)

varying of the mA based on the thickness (or density) of the anatomic section being scanned is known as?

Automated dose modulation

Reconstructs raw data into usable image data

Computer system

Dense materials (like bone) attenuate MORE/LESS radiation and result in a HIGHER/LOWER signal from the detector.

MORE/LOWER

Determines the maximum spatial resolution for a given sampling frequency

Nyquist Frequency

Formula for pitch

Pitch = Table speed/beam width

Converting raw data to image data requires several steps in a process called?

Reconstruction

Smaller/larger pixels produce the best spatial resolution

Smaller

T/F The number of photons in the beam is proportional to the radiation dose to the patient and the exposure of the detectors?

True

If the pitch is > 1, what happens to the spatial resolution? Dose? scan time?

-scan time is quicker -spatial resolution is reduced -dose is reduced **there are missing views at each body section. This results in a faster scan with lower spatial resolution

If the pitch is < 1, what happens to the spatial resolution? Dose? scan time?

-spatial resolution is increased -dose is increased -scan time is slower **there is overlap in the helix and the scanner is getting extra views of each body section. This results in a very slow scan with very high spatial resolution.

Uniform detector arrays can produce very THIN/THICK slices of data for all detector rows, but a LOWER/HIGHER radiation dose is required in order to INCREASE/REDUCE image noise

THIN/HIGHER/REDUCE

extends vertically across the scanner, representing data coordinates in terms of anterior and posterior.

Y-axis

extends longitudinally through the scanner, representing data coordinates in terms of superior and inferior.

Z-axis

PSF(point spread function) is used to quantify the amount of _________ that occurs within an object

blurring

The ____________ of raw data into image data adjusts each pixel to demonstrate the desired level of edge enhancement (sharpness)

convolution

The process through which scan data is mathematically filtered to better visualize specific tissue types

convolution

Filtration has the effect of increasing/decreasing the beam intensity while increasing/decreasing the average beam energy

decreasing/increasing

Captures and converts x-ray photons into analog electrical signals, a.k.a. radiation readings

detectors

Electrical signals from the detector array are useless until the attenuation information they carry is converted to a ________ signal. This process takes place in the _________ _________ _________

digital/data acquisition system (DAS)

If beam intensity doubles, the patient dose HALVES/DOUBLES and the exposure to the detectors also HALVES/DOUBLES

doubles/doubles

kVp has an direct proportional relationship to ________ & ________

energy and intensity

Electrical power is supplied to the x-ray tube by a ________-__________ ______________

high-voltage generator

A high/low pitch results in a faster scanner with lower/higher resolution images.

high/lower

As acquisition thickness ___________, spatial resolution ____________ (in the _____-axis) and partial volume averaging ___________

increases/decreases/z/increases

involves estimating an unknown numeric value within a set of known values

interpolation

The energy and intensity of the x-ray beam are controlled by the technologist setting which three prime exposure factors?

mA, kVp, & rotation time

Information leaving the DAS is digital (binary) attenuation readings known as ________ data

raw

bowtie filter increases/reduces the intensity of the beam on the outer edges of the patient where less radiation is needed

reduces

Formula for total scan time

scan time = [total scan length/beam width x pitch] x rotation time

A low pitch results in a slower/faster scan but with higher/lower resolution images.

slower/higher

Smallest pixels are produced when using the smallest/largest DFOV

smallest

the ability of the scanner to visualize small objects, small spaces between objects, and edges of objects

spatial resolution

Axial mode uses which method where the scan data is acquired one section at a time?

step-and-shoot

The incoming power supply to the x-ray system (220 V, alternating current) is not capable of producing these technical settings, so the electrical current must be changed. For the filament circuit, a ________-__________ transformer is used to create the high-amperage necessary for __________ emission

step-down/thermionic

For the x-ray tube circuit, a _______-_______ transformer is used to create the high-voltage necessary for x-ray production

step-up

A wider/smaller window width results in a wider scale of contrast....more gray and less black or white

wider

controls the midpoint of CT numbers displayed in the digital image, which influences the overall brightness of the displayed image

window level

controls the range of CT numbers (and tissue types) displayed in the digital image, which influences thecontrast (grayscale) in the displayed image

window width

The ________ location represents the specific slice, and the _____and ____ coordinates represent the location with the slice.

z-axis/x & y

How do you increase voxel size?

↑DFOV ↑section width ↓matrix

Ways to decrease noise:

↑mAs ↑kVp ↑DFOV ↑Voxel size ↑section width ↑slice thickness ↑pre-detector opening ↓Pitch/table speed(<1:1) -using smooth/soft tissue or low pass filter

ways to improve spatial resolution

↑matrix ↑sampling rate (VPR) ↑#of detectors ↓DFOV ↓pixel ↓Focal spot size ↓detector (aperture) size ↓beam width ↓slice thickness ↓pitch

Which of these measurements is NOT usually acquired using a simple region-of-interest (ROI) tool? A. Average HU value B. Maximum HU value C. Standard deviation D. Area (cm2)

B. A simple region of Interest tool will show the average hounsfield values, the standard deviation, and usually the total area. The maximum hounsfield value is not displayed.

Which of these quantitative analysis methods in CT can be used to identify the maximum Hounsfield value in an area of concern? A. Region-of-interest ellipse B. Histogram analysis C. Ejection fraction D. Calcium scoring

B. Histogram analysis is useful when specific hounsfield values need to be evaluated. A region of interest only shows the average hounsfield values and standard deviation. If the technologist or radiologist needs to see maximum values, the histogram must be used.

The thickness of a voxel in CT is defined by which of these variables? A. Acquisition thickness B. Reconstruction slice thickness C. Total beam collimation D. Matrix dimensions

B. The thickness of a voxel is determined by the reconstruction slice thickness. If the slice thickness is 3.0 mm, the voxel will be 3.0 mm deep.

Histogram analysis is useful for which of these applications? A. Real-time tracking of contrast enhancement B. Measuring the size of a suspicion lesion C. Evaluating the efficiency of heart contractions D. Defining the range of CT numbers in an ROI

D. Histogram analysis is a special technique which shows the frequency of specific seating numbers in a region of interest.

Measures analog electrical signals and converts to digital raw data

DAS

If rotation time is reduced by half, the mA must be doubled/halved to retain the same total photon intensity

Doubled

Extends horizontally across the scanner, representing data coordinates in terms of right and left.

X-axis

The ___________ filament serves as the source of electrons

cathode

During an axial scan, the total amount of anatomical coverage per tube rotation is dependent on which of these variables? 1 - The number of active detector rows 2 - The thickness of active detector rows 3 - The pitch

1 & 2

Which of the following is used for long-term storage of digital image data? A. Picture Archiving and Communication System (PACS) B. Electronic Health Record (EHR) C. International Classification of Diseases, 10th Edition (ICD-10) D. Digital Imaging and Communication in Medicine (DICOM)

A

Modifying the center of an axial image during retrospective reconstruction requires changes to which data coordinates? Choose multiple. A. X-axis B. Y-axis C. Z-axis

A & B

Changing the center of a coronal image requires changes to which data coordinates? Choose multiple. A. X-axis B. Y-axis C. Z-axis

A & C

Iterative reconstruction is an alternative to traditional reconstruction and helps to: (more than 1 answer) A. Reduce patient dose B. Decrease scan time C. Decrease require contrast volume D. Increase image quality

A & D

Compared to a pitch of 1.5, a pitch of 1.1 will result in: (Choose multiple answers) A. Increased dose B. Increased spatial resolution C. Increased total scan time

A, B & C

Select all parameters that CAN be changed retrospectively. A. Scan start and end locations B. Slice thickness C. Display Field-of-View D. Reconstruction algorithm E. Scan field-of-view F. Acquisition thickness G. Slice interval

A, B, C, D, & G

When imaging a patient's paranasal sinuses, which of the following procedures may help prevent beam-hardening artifact? A. Angle the gantry to avoid dental implants B. Decrease the kVp C. Use straps to prevent patient motion D. Clean the Mylar window prior to scanning

A. Beam hardening artifact is caused by very dense objects in the scan field. If a patient has dental implants, the technologist should angle the gantry to prevent the dental implants from appearing in the scan. In this question, no other answer options will have any effect on beam hardening artifact.

What CT artifact may result from excessive absorption of the x-ray beam? A. Beam hardening artifact B. Motion artifact C. Ring artifact D. Partial volume averaging E. Out-of-field artifact

A. Beam hardening artifact is the result of excessive absorption of the X-ray beam. The detectors do not receive enough information in this results in the streaks that extend from the dense objects.

Adjacent areas with significant density differences can cause an artifact called: A. Edge-gradient artifact B. Cone beam artifact C. Ring artifact D. Partial volume averaging E. Out-of-field artifact

A. Edge gradient artifact is a form of beam hardening artifact. It occurs in areas where the adjacent structures have very different densities. A common area for edge gradient artifact to appear is at the interface between contrast and air. Normally, contrast does not cause edge gradient artifact. But if contrast is directly adjacent to are the large gradient and density may cause streak artifact.

A CT detector configuration is changed from 0.625 mm x 16 rows to 1.25 mm x 8 rows. The change may result in: A. Decreased patient dose B. Increased spatial resolution C. Increased beam coverage D. Increased scan time

A. In this situation, the detector configuration has been changed to use thicker detector rows, but the same total beam coverage. Thicker detector rows require less radiation to produce a quality signal, which allows for a decrease in patient dose. This change will actually decrease the spatial resolution, but the total scan time and beam coverage will stay the same

Which of these variable changes will increase temporal resolution? A. Increased pitch B. Increased rotation time C. Increased reconstruction thickness D. Increased kilovoltage potential

A. Increasing the pitch increases the temporal resolution. This is because increased pitch results in a faster overall scan, which helps to reduce motion artifact. Any variable change that makes the scan faster results in less motion artifact and better temporal resolution.

Estimating an unknown value in a series of known values is a mathematical process called: A. Interpolation B. Filtration C. Convolution D. Back-projection

A. Interpolation is the process of estimating an unknown value when the surrounding values are known. Interpolation is an important part of helical scanning. This is what allows the spiral-shaped raw data to be converted into axial image data.

What combination of variables will result in the least amount of image noise? A. Pitch = 0.9, Reconstruction Thickness = 5.0, Tube voltage = 140, Matrix Size = 512 x 512 B. Pitch = 1.0, Reconstruction Thickness = 3.5, Tube voltage = 130, Matrix Size = 512 x 512 C. Pitch = 1.1, Reconstruction Thickness = 2.0, Tube voltage = 120, Matrix Size = 1024 x 1024 D. Pitch = 1.2, Reconstruction Thickness = 1.0, Tube voltage = 110, Matrix Size = 1024 x 1024

A. Of the options listed here, the tube voltage (kVp) is the primary factor influencing the image noise. Using a large to voltage, such as 140 kVp, will increase the amount of photons getting to the receptors and therefore decrease the image noise.

By definition, the acquisition thickness is the same as the: A. Detector row thickness B. Reconstruction slice thickness C. Reconstruction slice interval D. Acquisition mode

A. The acquisition thickness is the same as the detector row thickness. If the detector rows are 2.5 mm thick, the acquisition thickness would be described as 2.5 mm. This can only be changed by combining detector rows.

Changing the thickness of a voxel may also change: A. The tissue types included in the voxel B. The matrix size of the digital image C. The pixel size in the digital image

A. The size of a voxel is important because it changes how much tissue gets included in the voxel display. As slice thickness increases, the voxel thickness increases, and more tissue is averaged into that voxel. This potentially changes the appearance of the voxel when it is displayed as a pixel on the CT image.

Which of these scenarios will produce cervical spine images with the best spatial resolution? A. 12 cm display field-of-view (DFOV) B. 15 cm display field-of-view (DFOV) C. 17 cm display field-of-view (DFOV) D. 22 cm display-field-of-view (DFOV)

A. The smallest display field of view will produce images with the best spatial resolution. This is because the pixels become smaller and therefore have the ability to produce sharp images of smaller objects. That's the idea of high spatial resolution.

The signal produced by a detector is a(n): A. Analog electrical signal B. Processed image data C. Raw digital data D. Unprocessed binary data

A. When detectors capture reminant x-ray photons they produce an electrical signal that is proportional to the number of photons they received. More photons means a stronger signal. This electrical signal is sent to other components of the scanner where it is converted to a raw (unprocessed) digital signal and later a digital image (processed) signal that is suitable for viewing.

Which of these scans will have the best spatial resolution? A. 600 mA, 1.0 second rotation time, 1.0 mm slices, bone algorithm B. 500 mA, 1.0 second rotation time, 2.0 mm slices, standard algorithm C. 400 mA, 0.5 second rotation time, 3.0 mm slices, bone algorithm D. 300 mA, 0.5 second rotation time, 4.0 mm slices, standard algorithm

A. the largest mA is desirable because this is expected to reduce the amount of image noise and increase the clarity of spatial resolution in the image. The longest rotation time is preferred because longer rotation times result in more projections through the patient and better spatial resolution. Thinner slices improve spatial resolution since small slices can visualize smaller parts. The bone algorithm, like other edge enhancing algorithms, increase spatial resolution by adding more sharpness to the image.

If using a 400 WW and 40 WL, the cerebral spinal fluid in the brain will appear as: A. White B. Gray C. Black

B. Cerebrospinal fluid is slightly more dense than water, giving it a hounsfield value of + 15. This falls within the window width, which means this fluid will be displayed with some shade of gray. Had this number been above the window width, it would be displayed as white. If it was below the window width, it would be displayed as black.

If a radiologist needs to know the ratio of fluid to blood in a cerebral lesion, what quantitative tool can help to estimate this ratio? A. Region-of-interest ellipse B. Histogram analysis C. Ejection fraction D. Calcium scoring

B. Histogram analysis is sometimes used to evaluate the frequency of specific tissue types within an area of concern. A simple region of Interest tool only shows the average of all hounsfield values, but the histogram analysis shows the frequency of all values. Histogram analysis can be used to compare the amount of blood in a lesion compared to fluid in the lesion.

Increasing the average photon energy can reduce beam-hardening, this can be achieved by: a. Increasing mAs b. Increasing filtration c. Increasing collimation d. All of the above

B. Increasing mAs and collimation has nothing to do with the ENERGY...they both deal with the QUANTITY(# OF X-RAYS)

Increasing the reconstruction slice thickness results in: A. Visualization of more anatomy with increased spatial resolution B. Visualization of more anatomy with decreased spatial resolution C. Visualization of less anatomy with increased spatial resolution D. Visualization of less anatomy with decreased spatial resolution

B. Increasing the reconstruction slice thickness adds more anatomic data to each image. As a result, this allows visualization of more anatomy. The major disadvantage of thicker slices is decreased spatial resolution. As slice thickness increases, spatial resolution decreases.

Which of these scenarios will result in gaps in the reconstructed image information? A. When the slice interval is equal to the slice thickness B. When the slice interval is greater than the slice thickness C. When the slice interval is less than the slice thickness

B. Normally, the slice interval should be set equal to the slice thickness. In this scenario, one slice ends and the next begins with no gaps. Gaps are created in the data set when the slice interval is greater than the slice thickness. It would be like adding gaps in between the slices of a loaf of bread.

Which of the following is NOT considered a "post-processing" application of the CT image data? A. Multiplanar Reformation B. Retrospective Reconstruction C. 3D Rendering D. Region-of-Interest measurements

B. Post processing refers to any manipulation of CT image data, not the raw data. Retrospective reconstruction uses the raw data to create a new image data, so this is not technically considered post-processing.

Which of these scenarios will result in images with the best contrast resolution? A. Soft tissue algorithm with 1.0 mm slices B. Soft tissue algorithm with 2.0 mm slices C. Bone algorithm with 1.0 mm slices D. Bone algorithm with 2.0 mm slices

B. The main issue affecting contrast resolution is image noise. Image noise is reduced by using softening algorithms and thicker reconstruction slices. In this question, the soft tissue algorithm in 2.0 mm slices results in the least amount of image noise and therefore the best contrast resolution. The side effect of this option is a decrease in spatial resolution

When using a CT scanner with non-uniform detector rows, which of the following statements is true: A. The outer rows are thinner B. The inner rows require less radiation dose C. The inner rows have the highest spatial resolution D. The inner and outer rows have the same physical thickness

C

Select an algorithm that would be useful for viewing soft tissue changes around the cranium? (more than 1 answer) A. Edge-enhancing algorithms B. Bone algorithms C. Smoothing algorithms D. Standard algorithms

C & D Unlike the bone algorithm, the standard algorithm and smoothing algorithms decrease edge enhancement. These types of algorithms are commonly used to view soft tissues, including soft tissues around the cranium. Soft tissues should not be viewed with any kind of edge-enhancing or bone algorithm. This would create more image noise that makes the soft tissues difficult to see.

Using a larger reconstruction slice thickness results in which of the following? 1. Decreased image noise 2. Decreased spatial resolution 3. More total image slices A. 1 only B. 2 only C. 1 and 2 only D. 1,2, and 3

C. Thicker slices result in less image noise because there is more information in each slice. However, the spatial resolution that decreases. This is because more data is average together, and some of the smaller details will get lost in the slice. Using thicker slices actually results in fewer total slices in the image series. It would be like cutting a loaf of bread with thicker slices. It's the same loaf, but there are fewer total slices.

The specific process that accelerates electron in an x-ray tube is: A. Evacuation of air in the envelope B. Themionic emission C. Application of a voltage D. Bremsstrahlung electron interactions

C. All options listed are valuable in the x-ray production process, but only the voltage actually causes electrons to accelerate through the tube. A "voltage" is the same as the kilovoltage potential (kVp).

A patient in the emergency department is suspected of having a blowout fracture of right maxillary sinus. Structural damage to the eye will be best demonstrated with which of these filters? A. Edge-enhancing algorithms B. Bone algorithms C. Smoothing algorithms D. Sharpening algorithms

C. All soft tissues, including the soft tissues of the eye, should be evaluated using images Reconstructed with a smoothing algorithm. This makes soft tissues look smooth and easier to see. The other algorithms listed create more edge enhancement, which is good for viewing bones but not good for viewing soft tissues.

The mathematical filtration of CT data to enhance the appearance of specific tissue types is called: A. Interpolation B. Filtration C. Convolution D. Back-projection

C. Convolution is part of the reconstruction process. This is what the computer system uses to enhance the appearance of certain tissues. For example, the bone algorithm convolutes the scan data into image data that best demonstrates bone.

Of the following options, what reconstruction slice thickness will display images with the highest level of contrast resolution? A. 0.625 mm B. 1.25 mm C. 5.0 mm D. 3.75 mm

C. For contrast resolution, thicker slices are better. In this particular question, 5.0 mm is the thickest slice, therefore it will result in the bests contrast resolution. The main side effect of using thicker slices is a reduction in spatial resolution. In other words, the image will have less noise and a smoother appearance, but the amount of detail will be reduced.

Consider the following scenario. Several QC tests were performed on four different scanners. Based on the results of these tests, which scanner has the least amount of image noise? A. Water phantom average = - 0.5 HU Water phantom; standard deviation = 1.2; Line pairs = 12 lp/cm B. Water phantom average = 1.0 HU Water phantom; standard deviation = 3.1; Line pairs = 14 lp/cm C. Water phantom average = -11 HU Water phantom; standard deviation = 0.2; Line pairs = 13 lp/cm D. Water phantom average = 2.0 HU Water phantom; standard deviation = 2.0; Line pairs = 10 lp/cm

C. Image noise is based on the standard deviation. The lowest standard deviation represents the least amount of image noise. In this question, the lowest standard deviation is 0.2.

Consider a PACS network in which imaging studies are distributed directly to specific reading stations and to the PACS archive server. What is the main advantage of this distribution system? 1 - Prior studies are immediately accessible 2 - Images are duplicated in the PACS archive server and at the reading workstation 3 - If the archiver server goes down, images can still be sent to specific reading stations A. 1 only B. 2 only C. 2 and 3 only D. 1, 2, and 3

C. There are two different paths by which images are distributed to both the PACS servers and the Radiologist's reading station in this type of network. The advantage to this type of system is that if the PACS server fails, images can still be sent to the Radiologist reading station. Another advantage is having multiple copies of the same study. One copy is sent to the PACS archive server and one copy is sent directly to the Radiologist reading station. This makes it less likely that entire studies could be lost in the PACS servers.

Based on feedback from an ACR site-visit, your imaging department needs to design a new low-dose CT protocol for patient's less than 30 pounds. Which of these detector configurations would be most suited for this protocol? A. 1 mm x 16 rows B. 2 mm x 8 rows C. 4 mm x 4 rows D. 0.5 x 8 rowS

C. Thicker detector rows allow for a decrease in radiation and patient dose. This is because the detector rows have a larger surface area to absorb radiation. Less radiation is required, which results in a decrease in patient dose. In this question, 4 mm detector rows is the largest option and therefore allows for the lowest dose

Increasing mA in CT has the effect of: A. Increasing dose to the patient B. Increasing exposure to the detector elements C. Increasing the intensity of the beam D. All answers listed are true

D

Increasing the window width of a CT image will result in: A. Increased brightness B. Decreased brightness C. Increases contrast D. Decreased contrast

D

What does convolution do to the image quality when it is added to the back-projection reconstruction process? a. Normalize the attenuation coefficients to ensure tissues are displayed with correct CT numbers b. Increases the number of projections thereby reducing streaking artifacts c. Improves contrast resolution by reducing scatter radiation d. Enhances important characteristics of attenuation profiles thus reducing streak and star artifacts

D

Which of the follow is a potential benefit of increasing the CT acquisition thickness from 0.5 to 1 mm? A. Increased scan time B. Increased spatial resolution C. Decreased beam coverage D. Decreased patient dose

D

Which of these matrices will have the best spatial resolution? A. 1024 x 1024 B. 512 x 512 C. 256 x 256 D. 2048 x 2048

D. The largest matrix will always have the best spatial resolution. Compressing more pixels into the same area makes the pixels smaller. Smaller pixels are able to create detailed images of smaller objects. This is the idea of high spatial resolution.

Which of these reconstruction algorithms are likely to produce the best spatial resolution? A. Standard algorithm B. Soft tissue algorithm C. Brain algorithm D. Bone algorithm

D. Different algorithms create different levels of sharpness, or spatial resolution, in the reconstructed images. Edge enhancing algorithms, such as the bone algorithm in this question, create more sharpness and better spatial resolution. The major side effect of using edge enhancing algorithms is an increase in image noise.

Consider an imaging protocol that calls for very high contrast images of the brain. Which of these settings will display an image with the highest contrast? A. window width = 550, window level = 45 B. window width = 1500, window level = 50 C. window width = 300, window level = 80 D. window width = 40, window level = 30

D. Only window width controls the contrast of the image. In this question, the window level can be completely ignored. The highest contrast is achieved by the smallest window width. This is because less gray is allowed in the image, and more black and white.

Which of the following term(s) is/are commonly used to describe a CT scanner's ability to differentiate objects with similar linear attenuation coefficients? 1. Spatial resolution 2. Sensitivity 3. Contrast resolution A. 1 only B. 3 only C. 1 and 2 only D. 2 and 3 only

D. The ability of a CT scanner to accurately image objects with similar densities is termed contrast resolution or sensitivity. A CT scanner with poor contrast resolution or low sensitivity has difficulty separating tissues whose linear attenuation coefficients are nearly equal.

Which of the following technical factors exhibits an effect upon longitudinal spatial resolution? 1. Detector pitch 2. Interpolation algorithm 3. Display field of view (DFOV) 4. Detector collimation A. 1 & 2 only B. 3 & 4 only C. 1 and 3 only D. 2, 3, & 4 only E. All the above

D. The factors that affect longitudinal spatial resolution and the SSP include the type of spiral interpolation algorithm inherent to the system and the selected detector pitch. Thin-section image reconstruction reduces or completely eliminates broadening of the SSP and also improves longitudinal spatial resolution.

A radiologist is requesting changes to the brightness and contrast of images being used for a CT-guided biopsy in the pelvis. Which of these windowing techniques will result in the darkest image with the highest contrast? A. window width = 450, window level = 45 B. window width = 1500, window level = 40 C. window width = 300, window level = 30 D. window width = 40, window level = 100

D. The highest contrast is achieved by the smallest window width, which in this case is 40. The darkest image, or least bright image, is achieved by the largest window level, which in this case is 100.

Which of these scans will have the best contrast resolution? A. 600 mA, 0.3 second rotation time, 1.0 mm slices, bone algorithm B. 500 mA, 0.4 second rotation time, 2.0 mm slices, standard algorithm C. 400 mA, 0.5 second rotation time, 3.0 mm slices, bone algorithm D. 300 mA, 1.0 second rotation time, 4.0 mm slices, standard algorithm

D. The mA and rotation time should be considered together, since mA x rotation time results in the total mAs. The highest total mAs will increase contrast resolution. Contrast resolution is also increased by thicker slices and smoothing algorithms, such as the standard algorithm. This is because all these characteristics will reduce the amount of image noise.

Which of the following would increase the signal-to-noise ratio of a CT image? A. Decreased aperture size B. Decreased mAs C. Increased filtration D. Increased aperture size

D. The signal-to-noise ratio of a CT image is increased when a larger amount of x-ray photons are absorbed by the detectors. From the choices given, only an increase in aperture size (beam width) would accomplish that.

When reviewing 2.5 mm slices of a CTA abdomen, you see what looks like an embolism. However, when reviewing the 1.25 mm slices the embolism is not visible. This is most likely an error called: A. Beam hardening artifact B. Motion artifact C. Ring artifact D. Partial volume averaging E. Out-of-field artifact

D. The thicker slices average certain tissues together and created the appearance of an embolism. The thinner slices do not show the embolism, so this error is called partial volume averaging.

Phantom measurement of the uniformity of a CT system is performed primarily to assess the negative effects of: A. partial volume averaging. B. noise. C. detector drift. D. beam hardening.

D. The uniformity of a CT system describes its ability to maintain relatively consistent CT values across the entire image of an object of equal density, such as a water-filled phantom. Beam hardening occurs as low-energy x-ray photons are absorbed when the beam passes through the patient. The average photon energy of the beam increases along the path and may result in a loss of system uniformity.

When scanning a patient's chest, the axial images demonstrate ring artifact. This might be prevented in the future by: A. Using EKG gating B. Placing the patient's arms above his/her head C. Providing breathing instructions D. Correctly calibrating the detector array

D. There are several causes of ring artifact. One cause is miscalibration of the detector array. Obviously, this can be corrected by recalibrating the scanner.

The principal advantage of thin detector rows is: A. Faster scan time B. Lower patient dose C. Lower x-ray output D. Higher spatial resolution

D. Thinner detector rows can image smaller parts, which is essentially the definition of high spatial resolution. The down is side is that this usually requires a higher tube output and therefore a higher patient dose. The width of the detector rows may or may not affect the scan time.

The use of thick reconstruction slices can result in an error called: A. Beam hardening artifact B. Motion artifact C. Ring artifact D. Partial volume averaging E. Out-of-field artifact

D. This artifact results in tissues or pathologies being lost in the image because the slice is too thick. Thick slices average a significant amount of tissue together, which can cause small pathologies in small portions of tissue to disappear. The result of tissue averaging can also create the appearance of objects or pathologies in the image that are not actually there.

Which of these variable changes can a technologist make to increase the spatial resolution of a CT image? A. Increase the matrix size B. Decrease the matrix size C. Increase the display field-of-view (DFOV) D. Decrease the display field-of-view (DFOV)

D. Two changes would increase the spatial resolution: increase matrix size and decreased DFOV. The technologist CANNOT change the matrix size because this is a fixed characteristic of the scanner. This leaves decreasing the DFOV as the only option.

What effect on resolution does increasing rotation time have?

Decreases resolution

What (is) are the major function(s) of the DAS? 1. measures the transmitted radiation from the detectors 2. converts electrical signal to a digital signal 3. transmits the digital signal to the main computer A. 1 ONLY B. 2 ONLY C. 2 & 3 D. 1 & 3 E. 1, 2, &3

E

The typical WW and WL for imaging of the abdomen is WW 400 and WL 40. If a certain pixel has a CT number of -49 HU, what color will the pixel be on the screen? Black, white, or a shade of gray?

Gray HU values above the WW will display as white, and HU values below the WL will display as black. Everything else gets a specific shade of gray. This is a low HU, but does it fall below the window width? With a WW of 400 and WL of 40, pixels in the range of -160 to +240 will be assigned a shade of gray. This pixel is within that range.

Smaller, dense objects and areas of sharp borders between varying densities are represented by a low/high spatial frequency signal

High

An important part of helical scanning. This is what allows the spiral-shaped raw data to be converted into axial image data.

Interpolation

reconstruction process known to result in lower patient doses and improved image quality

Iterative reconstruction

Decreased pitch requires MORE/LESS interpolation

LESS

Non-uniform detector arrays require MORE/LESS radiation dose, but the slices are THINNER/THICKER and show MORE/LESS detail

LESS/THICKER/LESS

Larger objects of uniform density are presented by a low/high spatial frequency signal

Low

Each pixel has only __#___ CT number and displays only ___#___ shade of gray

ONE/ ONE

The loss of tissue visibility when different tissue types are averaged together within a slice and displayed with the same Hounsfield Units (HU).

Partial volume averaging

A ratio describing the distance the table moves during scanning compared to the beam width

Pitch

________-__________ collimators are positioned before the patient and shape the beam as it exits the tube housing. These collimators are adjusted to ensure the x-ray beam width (geometry) is only as wide as the activated detectors

Pre-patient

Increasing the acquisition thickness of a CT scan means: A. Combining detector rows together to function as one row B. Increasing the displayed slice thickness C. Combining reconstructed slices together to form thicker slices D. Increasing the space between spirals in the helix

A

A CT scanning protocol is set to use a pitch of 0.79. This will result in: A. Overlap in the scan data B. Missing views in the scan data C. Overlap and missing views in the scan data D. Scan data without overlap or missing views

A

Changing the slice position of a sagittal image requires changes to which data coordinates? Choose multiple. A. X-axis B. Y-axis C. Z-axis

A

If the rotation time of a scan is increased, what other exposure parameter should be changed to maintain the same total exposure to the detector array? A. Decrease mA B. Decrease kVp C. Increase scan length D. Increase mA

A

Reconstructed image data is produced by the: A. Computer system B. Data acquisition system C. Detector array D. Display monitor

A

What technical change is expected to increase the penetrating ability of an x-ray beam? A. Increased kVp B. Increased mA C. Increased rotation time D. Decrease mAs

A

When imaging a patient in CT, what portion of the patient is processed for viewing on the technologist's computer monitor? A. Any part of the patient within the DFOV B. Any part of the patient within the SFOV, but outside of the DFOV C. Any part of the patient outside of the SFOV D. Any part of the patient within the scanner gantry

A

If the pitch is = 1, what happens to the spatial resolution? Dose? scan time?

All areas are considered modest **there is no overlap in the scan, but there are no missing views either. This is standard for most protocols.

A single view acquired during a CT scan is also called a: A. Slice B. Projection C. Detector D. Attenuation reading

B

Acquisition thickness refers to: A. The number of active detector rows B. The thickness of active detector rows C. The thickness of reconstructed slices D. The number of data collection channels

B

After completing a CT of the abdomen, you noticed that your images do not include the entire abdomen. How can this missing information be retrieved? A. Increase the SFOV B. Increase the DFOV C. Increase the reconstruction slice thickness D. Increase the acquisition slice thickness

B

Increasing the window level of a CT image will result in: A. Increased brightness B. Decreased brightness C. Increases contrast D. Decreased contrast

B

Patient records are shared between medical providers using: A. Picture Archiving and Communication System (PACS) B. Electronic Health Record (EHR) C. International Classification of Diseases, 10th Edition (ICD-10) D. Digital Imaging and Communication in Medicine (DICOM)

B

What software program is used for digital documentation of all patient health information? A. Picture Archiving and Communication System (PACS) B. Electronic Medical Record (EMR) C. International Classification of Diseases, 10th Edition (ICD-10) D. Digital Imaging and Communication in Medicine (DICOM)

B

A CT myelogram calls for a 2100 window width and a 700 window level. What pixel values will be displayed as black? A. CT numbers above 1750 B. CT numbers below -350 C. CT numbers above 2800 D. CT numbers below -1400

B. The window level is the center point of all displayed pixel values. The window width is the total number of displayed pixel values, with half being above the window level and half being below the window level. Pixel values below the lowest portion of the window width will be displayed as black. To find this number, subtract half of the window width from the window level. 700 - 1050 = -350.

Using edge-enhanced images for volume rendering is expected to result in: A. Loss of contrast B. Image noise C. Poor spatial resolution D. Partial volume averaging

B. Volume rendered images should always be created with smoothing algorithms, like the standard algorithm. Failure to do so will result in significant image noise in the 3D images. This is true even when creating volume rendered images of bones.

Before convoluted information can be viewed, it must undergo another reconstruction process called?

Back-projection

______ is detrimental to spatial resolution, where _______ is detrimental to contrast resolution

Blur/noise

Physical components located inside the CT gantry typical includes: 1 X-ray tube 2 High-voltage generator 3 Computer system A. 1 only B. 2 only C. 1 and 2 only D. 1, 2, and 3

C

The main difference between image production in CT compared to image production in radiography is: A. X-ray photons are collected by detectors. B. An unprocessed digital signal is converted to image data C. Projections are compiled into a 3D volume of data. D. The x-ray beam is partially attenuation by the patient

C

mA & time have NO effect on ______________

energy

Computer monitors, PACS, etc.

operator's console