CT image production post course assessment

What CT scanning mode may induce patient motion artifact from several stops and starts of the gantry table during data acquisition?

axial mode

measuring a pathology in the x-axis could be accomplished with which of the following imaging planes?

axial only

Which of the following computed (CT) artifacts is caused by a significant increase in the average energy of the X-ray beam?

beam hardening artifact

Pitch is defined as a ratio between table movement to the

beam width

which the following statements correctly describes the flow of electrons through an X-ray tube?

cathode to anode

Which of the following correctly describe the anatomical data within the scan field of view (SFOV)?

data from SFOV is saved in the CT computer system.

Consider a computed tomography (CT) image that was initially displayed with a 300 window width (WW) and a 30 window level (WL). DECREASING the window level from 30 to 0 will have what effect on the image?

decreased brightness

What is the main DISADVANTAGE of using thick detector rows?

decreased contrast resolution

Which of the following is a disadvantage of accessing the PACS server through the internet on a basic desktop computer 1. decreased image quality 2. inability to access archived studies 3. increased archived retrieves time

decreased image quality

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:

decreased patient dose in this situation the detector has been changed to used 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.

What is the primary reason for decreasing the detector thickness for CT angiography examination

increased spatial resolution

compared to axial scanning helical scanning provides for all of the following advantages EXCEPT:

increased spatial resolution for most imaging procedures helical scanning is preferred for two reasons: decreased scan time and better post processing. the scan is faster because the patient moves continuously through the scan. the scan allow for better post process since one large volume is created rather than several sequential volumes.

increasing mA in CT has the effect of:

increasing dose to the patient increasing exposure to the detector elements increasing the intensity of the beam

During spiral scanning, attenuation data from the patient is first organized in a helical pattern. The process of converting this information into axial sections is accompanied by through:

interpolation

Computed tomography (CT) imaging of the temporal bones often calls for a very low pitch (less than 1). One effect of using a pitch of less than one is increased?

spatial resolution

Ring artifact can be the result of

using a large display field of view

xray tubes in CT are very similar to those used in diagnostic radiography.

true

what axis position has changed in this series of axial images 1. X 2. Y 3. Z

Z AXIS

What controls the physical size of the X-ray beam?

Pre patient collimators

Calculate the pitch based on the following variables. Acquisition thickness=1 mm beam width=10 mm rotation time = 0.5 sec tube current = 0.8 mm

0.8 mm table movement/beam width

What difference in image processing accounts for the visible difference between the following two images of the brain?

Back projection filter

What artifact is visible in the image below in the posterior portion of the patient's abdomen?

Beam hardening artifact

What two computed tomography (CT) artifacts are demonstrated in the following image? (Select two)

Beam hardening artifact Ring artifact

A common kVp setting used in CT is

-120 kVp Most CT scanners are equipped with a limited number kVp options, which includes 80, 100, 120, and 140 kVp. Higher and low kVp settings are not possible.

An 8-slice scanner has:

-8 detector rows When a scanner is referred to as an "8 slice scanner", the number refers specifically to the number of detector rows.

reconstructed image data is produced by the

-Computer system The computer system is the last step in the data transformation process when the raw digital data is reconstructed into image data that can be viewed on the monitor and sent to PACS for reading and archival.

the signal produced by a detector is a(n):

-Analog electrical signal When detectors capture remnant 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.

the principal advantage of thin detector rows is:

-Higher spatial resolution 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.

Acquisition thickness refers to:

-The thickness of active detector rows The acquisition thickness is the same as the thickness of active detector rows. If the detector rows are 25 mm thick, we would say the acquisition thickness is 1.25 mm.The acquisition thickness can be changed by combining detector rows. Realize that the acquisition thickness is not necessarily the same as the reconstruction slice thickness.

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 - The number of active detector rows 2 - The thickness of active detector rows the total anatomical coverage depends on the total width or collimation of the X-ray beam. the width of the X-ray beam is dependent on the number of active detector rows and thickness of those rows. the total beam coverage is calculated as the number of rows multiplied by the row thickness. PITCH applied to ONLY HELICAL SCANNING!

During what CT acquisition mode does the patient table move between x-ray exposures? 1. Axial scanning 2. Helical Scanning 3. Volume scanning

1. Axial scanning

What CT scanning mode activates the x-ray tube only while the patient table is stationary? 1. Axial scanning 2. Helical Scanning 3. Volume scanning

1. Axial scanning 3. Volume scanning Unlike helical scanning axial and volume scanning activate the x ray tube only when the patient table is stationary. with axial scanning one section of the data is acquired and the patient moves to the next position so the next section can be scanned with volume scanning the entire area to be imaged is scanned with just one rotation of the tube.

a PACS network is used to connect which of the following? 1. Radiologist reading stations 2 Imaging equipment 3. PACS servers

1. Radiologist reading stations 2 Imaging equipment 3. PACS servers

Which of these statements concerning the scan field of view (SFOV) are true? (choose 2) 1. The SFOV is usually larger than the display field of view (DOFV) 2. Data in the SFOV is sent to the radiologist 3. Data in the SFOV is saved on the CT computer system 4. The size of the SFOV is set by the technologist using the scout images

1. The SFOV is usually larger than the display field of view (DOFV) 3. Data in the SFOV is saved on the CT computer system

Production of X-rays int he ct machine requires: 1. a source of electrons 2. a means of rapid accelerations of electrons 3. a means of rapid deceleration of electrons

1. a source of electrons 2. a means of rapid accelerations of electrons 3. a means of rapid deceleration of electrons

Which of these statements correctly describes the DFOV in CT imaging 1. data in the DFOV is reconstructed for viewing 2. data in the DFOV is sent to the radiologist 3.Data in the DFOV is converted to image data 4. The size of the DFOV is set by the tech using the scout images. 5. all the statements

1. data in the DFOV is reconstructed for viewing 2. data in the DFOV is sent to the radiologist 3.Data in the DFOV is converted to image data 4. The size of the DFOV is set by the tech using the scout images.

consider two identical scanning protocols, except one protocol uses a pitch of 0.73 and the other uses a pitch of 0.87. the protocol using a pitch of 0.87 will have 1. decreased scan time 2. increased spatial resolution 3. decreased patient dose

1. decreased scan time 3. decreased patient dose

Compared to a pitch of 1, a pitch of 1.137 will demonstrate what three differences? (Select three) 1. decreased scan time 2. decreased pt. dose 3. decreased spatial resolution

1. decreased scan time 2. decreased pt. dose 3. decreased spatial resolution

increasing the mA and kVp of a CT scan will usually result in: 1. increased patient dose 2. increased image quality 3. increased processing time

1. increased patient dose 2. increased image quality increasing the mA and kVp of CT scan will usually improve the image quality, but this is at the expense of increased pt dose. the ideal mA and kVp should be the lowest possible dose that still results in a diagnostic scan. changes in mA and kVp have no effects on processing time.

an increase of which of the following exposure factors would increase the total number of X-ray photons exposing the detectors 1. mA 2. kVp 3. rotation time

1. mA 2. kVp 3. rotation time increased mA increases the total number of photons produced increase penetration ability of those phones increase rotation time without changing the mA results in a longer exposure (per rotation) and more total photons exposing the detectors.

Physical components located inside the CT gantry typical includes: 1. xray tube 2. high voltage generator 3. computer system

1. xray tube 2. high voltage generator

If the pitch is equal to 1.1, how far is the patient table moving during each rotation of the tube?

1.1 times the beam width

calculate the total beam width of a CT scan using 32 detector rows, 0.5mm detectors, 100 mA and 140 kVp:

16mm the beam width is calculated as: 32rows X (0.5mm)/row = 16mm beam width

During which acquisition mode is the patient table in constant motion? 1 axial scanning 2 helical scanning 3 volume scanning

2 helical scanning

The width of the X-ray beam is controlled by: 1 kVp setting 2. collimators 3. pixel dimensions

2. collimatiors the shape of the X-ray beam as it leaves the X-ray tube is controlled by the pre patient collimators. -- pixel dimensions and other technical factors have no influence on this. only the collimator change the actually width/geometry of the beam.

Which of these matirix sizes will have the smallest pixels?

2048X2048

What number represents the z axis?

3

from the list below, identify the CT scanning method that requires a large detector array with numerous data collection channels 1. Axial scanning 2. Helical Scanning 3. Volume scanning

3. Volume scanning requires a detector array with enough data channels to image In entire organ with just one rotation of the tube.

under what circumstances would it be impossible to reconstruct the additional brain anatomy missing from the image below? 1. the missing anatomy is outside the original DFOV 2. the original image data has been deleted from the CT computer system 3. the original scan data has been deleted from the CT computer system 4. the missing anatomy is outside of the original SFOV

3. the original scan data has been deleted from the CT computer system 4. the missing anatomy is outside of the original SFOV The missing anatomical information in this patients brain can probably be retrieved from raw data saved on the CT computer. This would be impossible only if the original raw data has been deleted or if the missing anatomy is outside the SFOV.

Which of the following detector configurations has the most total beam coverage?

3mm X 7 rows

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

4mm X 4rows thicker detector rows allow for a decrease in radiation and patient dose.

What portion of the CT data collected during a scan is saved by the scanner but NOT reconstructed for viewing?

Any portion of the patient within the scan field of view but outside of the display field of view the DFOV is sometimes the same size as the SFOV but not always. if the DFOV is smaller there will be some portions of the patient with in the SFOV but not within the DFOV. these portions of the patient are still included in the raw data and saved on the scanner but they will no the viewed within the image data .

Which part of the PACS system houses all of the historic digital image data along with the current digital data being generated by the modalities?

Archive server

Assuming that all other factors remain constant, which reconstruction algorithm is expected to result in the most image noise?

Bone algorithm

Adjusting the window level (WL) of a computed tomography (CT) image will affect which two of the following?

Brightness of the displayed image Contrast of the displayed image WL does NOT change the Hounsfield values

Increasing the acquisition thickness of a CT scan means:

Combining detector rows together to function as one detector row the acquit ion thickness refers to the thickness of detector rows. the only way to change this thickness is to combine detector rows together so they function as one detector.

Reconstruction of raw data into image data occurs within which component of the CT system?

Computer system

What data process is used to smooth or sharpen image data for better visualization of the desired anatomy?

Convolution

Which two types of reconstruction algorithm should be used to view bony injuries to the thorax? (Select two)

Edge enhancing algorithms Smoothing algorithms

ideally, the patient worklists on imaging equipment should be automatically populated from examination request placed though the:

Electronic medical record ( EMR)

An ROI placed on the parotid abnormality in this image produced a HU reading of -48. This abnormality is mostly likely a:

Fatty tumor

The contrast resolution of a CT system is recorded with which of these units?

HU

Which computed tomography (CT) scanning technique collects scan data while the patient table is in motion? 1. axial scanning 2.helical scanning 3. Volume scanning

Helical scanning

The following sagittal reformation of the cervical spine shows LESS detail than expected. Based on the appearance of the image, it could be a result of creating the reformation from:

Images reconstructed in the standard algorithm.

Compared to a pitch of 1.2, a pitch of 1 will demonstrate what two differences? (Select two) 1. Increased dose 2. increased spatial resolution 3. increased total scan time

Increased dose Increased spatial resolution

Which procedural change will increase the potential spatial resolution in a computed tomography (CT) image?

Increased matrix size

One advantage of using a small reconstruction slice thickness is:

Increased spatial resolution

The following image shows excessively high contrast. Improving the contrast could be accomplished by:

Increasing the WW

In this coronal reformation of the abdomen, the most likely cause of the blurry appearance is that it was:

It was reformatted from thick axial images?

When reviewing a computed tomography (CT) of the bony pelvis, the technologist notices that the trabecular bone looks blurry. this is a quality control issue related to:

Linearity

What quality control (QC) test in computed tomography (CT) ensures that the CT numbers increase proportionally with increasing physical density?

Linearlity

A region-of-interest (ROI) indicating an average Hounsfield unit (HU) of -697 mostly likely corresponds to which of the following?

Lung

The purpose of the detector array in CT is to:

Measure and convert transmitted radiation into electrical signal.

In this images the streaking around the patient's diaphragm is resulted of:

Patient breathing

The artifact visible in the image below is a result of:

Patient motion

What is the principle function of the data acquisition system (DAS) in CT?

Reconstruct raw data into image data

After performing a thoracic spine scan for trauma the radiologist requests images to include the entire lumbar spine as well. The raw data is still saved on the CT scanner. This will require:

Rescanning the patient.

If the pitch is greater than one, this results in:

Scan data without overlap or missing views

Compared to a soft tissue algorithm, a bone algorithm will have more: (Select two)

Sharpness Brightness?

Which of these algorithms will yield 3D images will the least amount of image noise?

Standard algorithm

Compared to general radiography, CT xray tube require:

a larger heat capacity

Consider a PACS network running through a traditional internet network. What is the primary advantage of this network architecture?

The PACS archive server can be accessed from any internet-connected computer

Consider a voxel which includes these tissue types lung, bone, fat, and muscle. What computed tomography (CT) number will be displayed by the pixel in the reconstructed image?

The average of all tissues will be displayed by the pixel.

When using a CT scanner with non-uniform detector rows, which of the following statements is true:

The inner rows have the highest spatial resolution

"Matrix size" in computed tomography (CT) refers to which of the following?

The number of pixels in the matrix

CT angiography imaging of the heart is sometimes performed with the CT scanner in the volume acquisition mode. these means

The scan data is acquired in one rotation of the xray tube Volume scanning is the preferred way to image the heart. this scan is quite rapid bc the entire heart is imaged in just one rotation of the xray tube there are no additional sequences.

When considering the following variables, which of statement describes how the resulting views comprise scan data? Pitch = 1 acquisition thickness = 1.5mm rotation time = 1 sec max tube current = 300mA

There will be no overlap or missing views in the scan data.

A technologist review a patient's EMR for evidence of a gadolinium allergy prior to performing a scan with contrast. is this a hippa violation?

This is NOT a hippa violation

A radiography department uses a shared computer for EMR access that does NOT required a password for sign in. is this is violation of HIPPA law?

This is a HIPPA violation.

The phantom pictured below contains only water. Based on the ROI readings what problem should be reported to the medical physicist?

Unacceptable uniformity

Cone beam artifact is increased under what circumstances?

Use a wide X-ray beam

Consider the following scenario. Several QC tests were performed on four different scanners. Based on the results of these tests, which scanner has the highest spatial resolution?

Water phantom average = - 0.5 HU Water phantom standard deviation = 1.2 Line pairs = 12 lp/cm

when imaging a patient in CT what portion of the patient is processed for viewing on the technologist's computer monitor?

any part of the patient within the DFOV

what portions of a patient receive radiation exposure during CT scanning?

any portion of the patient within the scanner gantry

the specific process that accelerates electron in an X-ray tube is

application of a voltage

What is the relationship between acquisition thickness and spatial resolution?

as acquisition thickness increases spatial resolution decreases the acquisition thickness is the same as the thickness of the detector rows. thinner rows more spatial resolution

Partial volume averaging is an error caused by:

averaging multiple tissues types into one voxel

What CT data acquisition mode collects a series of adjacent axial sections? 1. axial 2. helical 3. volume

axial Axial scanning collects a series of adjacent axial slices, one section at a time. when the table is stationary the scanner collects one section data. the patient table slides the patient to the next portion and the next section is acquired. this continues until the full scan is complete.

What is the function of output devices in a CT imaging system?

display and store image data

if mA is decreased by a factor of 2, how is the radiation dose to the patient changed? Assume all other factors remain unchanged?

dose is decreased by a factor of 2

During helical scanning, if the table moves a greater distance than the width of the beam the pitch will be:

greater than 1

The helical acquisition mode is the most common technique used for imaging all of the following body sections EXCEPT:

head Helical scanning mode is the most common mode for essentially all body sections except for the head. however some institutions use helical mode for the head and virtually all exams.

Pitch is an acquisition variable defined for which acquisition mode? 1. axial mode 2. helical mode 3. volume mode

helical mode

What CT data acquisition mode is described in this illustration?

helical mode

What CT scanning mode forms a spiral of scan data during imaging? 1. axial 2. helical 3. volume

helical scanning

Which of the following images is displayed with a window width (WW) of 2500 and window level (WL) of 600?

image b

what technical change is expected to increase the penetrating ability of an X-ray beam?

increased kVp

if the rotation time of a scan decreased, what other exposure parameter should be changed to maintain image quality

increased mA

If a routine helical scan of the chest is pre-programmed to use a 16 detector rows and a pitch of 1.13, this will result in:

missing views in the scan data

Compared to a 2mm reconstruction slice thickness a 1mm slice thickness will result in 1. decreased image noise 2. decreased spatial resolution 3. more total image slices

more total image slices

After completing a routine scan of the chest the radiologist request a sagittal image series with 5mm slices. this request can be completed using which of these imaging techniques?

multiplaner reformation

what portion of the patient can be visualized through the process of retrospective reconstruction?

only parts of the patient within the scan field of view Any portion of the patient with in the SFOV can be visualized with retrospective reconstruction. this is true if those portions of the patient were not represented in the original images. For example it is common to accidentally clip portions of the patient from the DFOV. this can be corrected through retrospective reconstructions as long as those portions of the patient are inside the SFOV.

The bright areas on the edges of this image are an example of:

out of field artifact

a CT scanning protocol is st to use a pitch of 0.79 this will result in

overlap in the scan data

a single "view" acquired during a CT scan is also called a

projection a ct scanner collects several projections as the tube and detector spin around the patient. each of these projections represent a unique view of the anatomy that is eventually complied together to form the 3D volume of data.

the main difference between image production in CT compared to image production in radiography is:

projections are compiled into a 3d volume of data

after completing a CT of the abdomen you notice that your images do not include the entire abdomen. how can this missing information be retrieved?

retrospective reconstruction RT side of the ab is cut off bc it is outside the DFOV. more than likely this missing information is within the SFOV and saved as raw data on the computer. Through the process of retrospective reconstruction the tech can reconstruct new image data with the pt more appropriately centered in a large DFOV

Raw data is also called

scan data

Some pathologies of the chest maybe visualized by rendering a multi planar reformation as minimum intensity projections. In a minimum intensity projection, what CT number will be displayed for a voxel that contains portions of lung air and a contrast filled artery?

the average CT number within the voxel

The sequential acquisition mode is described by which of these statements?

the patient couch moves only between x ray exposures

When pitch is less than one

there is overlap in the scan data

A new CT protocol calls of imaging the entire Circle of Willis in one X-ray exposure in one tube rotation. what scanning mode would meet this requirement? 1 Axial scanning 2 Helical scanning 3 volume scanning

volume scanning

Which of these windowing options will produce a displayed image with the longest scale of contrast in a CT image of the abdomen?

window width = 40, window level = -30

What part of the patient's anatomy is saved as raw data in the computed tomography (CT) computed system includes any portion of the patient that is:

within the scan field of view (SFOV)

What axis portion has changed in this series of sagittal images?

x axis postion

What axial position has changed in the following series of coronal images? x axis position y axis position z axis position

y axis position

Changing the slice thickness of an axial reconstruction changes the dimensions of the image data in what data in what axis?

z-axis The z-axis runs longitudinally through the scanner, when the slice thickness change this changes the dimensions of the image data z axis.