CT Boot Camp Section 1 Flashcards

Questions and Answers

What is the primary benefit of the reconstruction process?

A reduction in patient dose while increasing image quality.

The acquisition thickness is the same as the?

Detector row thickness

If the reconstruction slice thickness is set to 3.0 mm, what is a true statement?

The image data is 2.0 mm thick

The image data is 4.0 mm thick

The image data is 3.0 mm thick (correct)

The image data is 5.0 mm thick

Using a larger reconstruction slice thickness results in which of the following?

Decreased image noise Signup and view all the answers

What is a negative effect when decreasing slice thickness from 2.5 mm to 1.25 mm?

Increased image noise Signup and view all the answers

Compared to a 1.25 mm image data, what will 3.75 mm image data demonstrate?

Decreased spatial resolution Signup and view all the answers

Which CT protocol generally uses thin slices?

Circle of Willis for arterial-venous malformation Signup and view all the answers

In reconstructed image data, what is defined as the distance from the start of one slice to the start of the next slice?

Slice interval Signup and view all the answers

Thick reconstruction slices (greater than 3 mm) are NOT suitable for which of the following?

Multiplanar reformations Signup and view all the answers

What scenario will result in gaps in the reconstructed image information?

When the slice interval is greater than the slice thickness. Signup and view all the answers

What reconstruction algorithm should be used to create detailed images of the bony trabeculae?

Edge-enhancing algorithms Signup and view all the answers

Which parameters can be changed retrospectively?

Scan start and end locations Signup and view all the answers

After a thoracic spine scan, what is required to obtain images of the entire bony thorax?

Retrospectively reconstructing images with a different display field-of-view Signup and view all the answers

What is required when raw data is not saved on the CT scanner after an abdominal scan?

Rescanning the patient Signup and view all the answers

An ROI indicating an average HU of +39 corresponds to which substance?

Blood Signup and view all the answers

An ROI over an abnormal lesion with an average CT number of -52 is likely composed of?

Fat Signup and view all the answers

What is a possible reason the initial image series of the temporal bones was rejected?

Incorrect reconstruction algorithm Signup and view all the answers

The difference in appearance of CT images can be attributed to what factor?

Using a different number of projections Signup and view all the answers

What could explain the visible difference between two CT images?

Different slice thickness Signup and view all the answers

What is a likely explanation for poor image quality in coronal reformations?

Incorrect reconstruction slice thickness in the axial data set Signup and view all the answers

What CT artifact may result from excessive absorption of the x-ray beam?

Beam hardening artifact Signup and view all the answers

What error may result from an overly concentrated bolus of IV contrast?

Beam hardening artifact Signup and view all the answers

How can beam-hardening artifact be prevented during a chest scan?

By placing the patient's arms above his/her head Signup and view all the answers

What may cause ring artifact in axial images during a chest scan?

Incorrectly calibrating the detector array Signup and view all the answers

What can result from leaving an EKG line in the exposure field?

Beam hardening artifact Signup and view all the answers

The appearance of streaks extending from lead pellets in the nasal cavity is known as?

Beam hardening artifact Signup and view all the answers

What is the primary reason for decreasing the detector thickness for CT angiography examinations?

Increased spatial resolution Signup and view all the answers

What is a result of changing a CT detector configuration from 0.625 mm x 16 rows to 1.25 mm x 8 rows?

Decreased patient dose Signup and view all the answers

What is the relationship between acquisition thickness and spatial resolution?

As acquisition thickness increases, spatial resolution decreases Signup and view all the answers

When using a CT scanner with non-uniform detector rows, which rows have the highest spatial resolution?

The inner rows Signup and view all the answers

Which detector configuration would best suit a new low-dose CT protocol for patients less than 30 pounds?

4 mm x 4 rows Signup and view all the answers

Increasing the acquisition thickness of a CT scan means what?

Combining detector rows together to function as one detector row Signup and view all the answers

What is pitch defined as in CT scanning?

The ratio of the table movement to the beam width Signup and view all the answers

Calculate the pitch given these variables: Acquisition thickness = 0.5 mm, Detector rows = 20, Rotation time = 0.8 seconds, Tube current = 250 mA, Table movement = 10 mm

1 Signup and view all the answers

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 Signup and view all the answers

A CT scanning protocol is set to use a pitch of 0.79. What will this result in?

Overlap in the scan data Signup and view all the answers

What happens if a routine helical scan of the chest is pre-programmed to use 16 detector rows and a pitch of 1.13?

Missing views in the scan data Signup and view all the answers

When the pitch is less than one, there will be overlap in the scan data.

True Signup and view all the answers

In comparing two identical scanning protocols, which one using a pitch of 0.87 will have advantages?

Decreased scan time and decreased patient dose Signup and view all the answers

What is the effect of the table moving a greater distance than the width of the beam during helical scanning?

The pitch will be greater than 1 Signup and view all the answers

Which statements concerning the scan field-of-view (SFOV) are true? Choose two.

Data in the SFOV is saved on the CT computed system Signup and view all the answers

What portion of the patient is processed for viewing on the technologist's computer monitor?

Any part of the patient within the display field-of-view Signup and view all the answers

Which statements correctly describe the display field-of-view (DFOV) in CT imaging? Choose all that apply.

All statements are correct Signup and view all the answers

What number represents the Z-axis?

3 Signup and view all the answers

What axis position has changed in this series of axial images?

3 only Signup and view all the answers

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

1 only Signup and view all the answers

After completing a CT of the abdomen, how can missing information be retrieved?

Retrospective reconstruction Signup and view all the answers

Under what circumstances would it be impossible to reconstruct the additional brain anatomy missing from the image?

The missing anatomy is outside of the original scan field-of-view Signup and view all the answers

What CT data acquisition mode is described in this illustration?

Helical mode Signup and view all the answers

Where is raw CT data stored?

In the CT computer system Signup and view all the answers

What does the process of reconstruction in the CT computer system create?

Image data Signup and view all the answers

Estimating an unknown value in a series of known values is called what?

Interpolation Signup and view all the answers

Which image-processing technique in CT is used only in helical scanning?

Interpolation Signup and view all the answers

The mathematical filtration of CT data to enhance specific tissue types is known as what?

Convolution Signup and view all the answers

What process assigns a specific level of edge-enhancement to CT image data?

Reconstruction algorithms Signup and view all the answers

Which algorithms are preferred for viewing bone?

Edge-enhancing algorithms Signup and view all the answers

Select algorithms that would be useful for viewing soft tissue changes around the cranium. Multiple correct answers are available.

Smoothing algorithms Signup and view all the answers

What filter will best demonstrate structural damage to the eye?

Smoothing algorithms Signup and view all the answers

What mathematical process prevents star-like artifacts from appearing on the CT images?

Back-projection filter Signup and view all the answers

What does iterative reconstruction help to achieve?

Reduce patient dose Signup and view all the answers

A single 'view' acquired during a CT scan is also called a:

Projection Signup and view all the answers

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

Projections are compiled into a 3D volume of data. Signup and view all the answers

Physical components located inside the CT gantry typically includes:

X-ray tube Signup and view all the answers

Increasing the mA and kVp of a CT scan will usually result in:

Increased image quality Signup and view all the answers

A common kVp setting used in CT is

120 kVp Signup and view all the answers

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

Analog electrical signal Signup and view all the answers

An 8-slice scanner has:

8 detector rows Signup and view all the answers

The principal advantage of thin detector rows is:

Higher spatial resolution Signup and view all the answers

Calculate the total beam width of a CT scan using 32 detector rows, 0.5 mm detectors:

16 mm Signup and view all the answers

The width of the x-ray beam is controlled by:

Collimators Signup and view all the answers

Reconstructed image data is produced by the:

Computer system Signup and view all the answers

X-ray tubes in CT are very similar to those used in diagnostic radiography.

True Signup and view all the answers

Compared to general radiography, CT x-ray tubes require:

A larger heat capacity Signup and view all the answers

Production of x-rays in a CT machine requires:

A means of rapid deceleration of electrons Signup and view all the answers

Which of the following statements correctly describes the flow of electrons through an x-ray tube?

Cathode to anode Signup and view all the answers

The specific process that accelerates electrons in an x-ray tube is:

Application of a voltage Signup and view all the answers

Increasing mA in CT has the effect of:

Increasing dose to the patient Signup and view all the answers

An increase of which of the following exposure factors would increase the total number of x-ray photons exposing the detectors?

mA Signup and view all the answers

If mA is decreased by a factor of 2, how is the radiation dose to the patient changed?

Dose is decreased by a factor of 2 Signup and view all the answers

What technical change is expected to increase the penetrating ability of an x-ray beam?

Increased kVp Signup and view all the answers

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

Increase mA Signup and view all the answers

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

Z-axis Signup and view all the answers

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

Data from the SFOV is saved in the CT computer system Signup and view all the answers

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 display field-of-view Signup and view all the answers

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 Signup and view all the answers

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

Any portion of the patient within the scanner gantry Signup and view all the answers

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 Signup and view all the answers

What CT scanning mode forms a spiral of scan data during imaging?

Helical scanning Signup and view all the answers

What CT scanning mode activates the x-ray tube only while the patient table is stationary?

Volume scanning Signup and view all the answers

What CT data acquisition mode collects a series of adjacent axial sections?

Axial scanning Signup and view all the answers

During an axial scan, the total amount of anatomical coverage per tube rotation is dependent on which of these variables?

The thickness of active detector rows Signup and view all the answers

During what CT acquisition mode does the patient table move between x-ray exposures?

Axial scanning Signup and view all the answers

From the list below, identify the CT scanning method that requires a large detector array with numerous data collection channels.

Volume scanning Signup and view all the answers

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

Head Signup and view all the answers

During which acquisition mode is the patient table in constant motion?

Helical scanning Signup and view all the answers

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

Axial mode Signup and view all the answers

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

The patient couch moves only between x-ray exposures Signup and view all the answers

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

The scan data is acquired in one rotation of the x-ray tube Signup and view all the answers

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

Increased spatial resolution Signup and view all the answers

Acquisition thickness refers to:

The thickness of active detector rows Signup and view all the answers

Study Notes

CT Imaging Fundamentals

Projection: A single view acquired during a CT scan, vital for data compilation into a 3D volume.
Differences from Radiography: CT uses multiple projections to create a 3D image while traditional radiography results in a 2D image from a single projection.
Essential Components of CT Gantry: Includes x-ray tube, high-voltage generator (often housed within the gantry), and computer system (typically outside the gantry, responsible for data reconstruction).

Image Quality and Patient Dose

Increasing mA and kVp generally improves image quality but raises patient dose; ideal settings minimize dose while ensuring diagnostics.
Common kVp Setting: 120 kVp is commonly utilized in CT scans for optimal performance.
Detector Signal: An analog electrical signal generated when x-ray photons are captured; depends on the number of photons, influencing the image quality.

Scanner Specifications

8-slice scanners refer to 8 detector rows, crucial for determining image resolution.
Thin detector rows enhance spatial resolution, allowing for imaging of smaller anatomical details, but increase patient dose due to higher tube output requirements.
Beam Width Calculation: Total beam width can be determined by multiplying the number of detector rows by individual detector width (e.g., 32 rows x 0.5 mm = 16 mm total width).

Image Reconstruction and Data Handling

Reconstruction of image data occurs via the computer system, transforming raw data into viewable formats for diagnosis.
The effectiveness of CT x-ray tubes is attributed to their larger heat capacity, accommodating longer exposures, and higher mA settings.
Necessary requirements for x-ray production include a source of electrons (cathode), means for rapid acceleration (kVp), and means for rapid deceleration (anode).

Technical Specifications and Effects

Changes in mA directly affect patient dose and exposure to detectors; increasing mA results in higher intensity x-ray beams and necessitates careful handling.
Decreasing mA by a factor of 2 reduces patient dose similarly by a factor of 2, illustrating the direct proportionality of dose and mA.
Increasing kVp is the only change that enhances the penetrating ability of x-ray beams; other factors like mA and rotation time do not alter photon energy.

Scanning Techniques

Axial Scanning: Entails a series of stationary x-ray exposures; patient table moves between scans, which can lead to potential motion artifacts.
Helical Scanning: Offers continuous motion of the patient table with simultaneous x-ray acquisition, creating a spiral path of data; ideal for detailed imaging and less likely to induce artifacts.
Volume Scanning: Fast acquisition method requiring a large detector array, allowing comprehensive imaging of organs in a single tube rotation.

Image Processing and Field of View

Scanned data is stored in the scan field of view (SFOV) and processed for viewing in the display field of view (DFOV), with only the latter being utilized for image reconstruction.
Retrospective reconstruction allows visualization of areas in the scan field of view not initially included in the display field of view.

Radiation Exposure Considerations

Radiation exposure occurs in any part of the patient within the scanner gantry, emphasizing the importance of minimizing unnecessary exposure.
Portions of data collected but not reconstructed generally relate to areas in the SFOV that do not appear in the DFOV.

Acquisition and Detector Details

Acquisition thickness correlates with the thickness of detector rows; thinner rows enhance spatial resolution.
A change in detector configuration affects patient dose; using thicker rows with equivalent beam coverage can reduce the required radiation for a quality signal.
Spatial resolution diminishes with increased acquisition thickness, highlighting the trade-off between visualization of small features and the ability to image larger areas.

Non-Uniform Detector Rows

Using non-uniform detector rows allows the inner rows to provide higher spatial resolution, while outer rows cater to faster scan times and lower doses.### CT Protocols and Configurations
A new low-dose CT protocol for patients under 30 pounds can utilize 4 mm x 4 row detector configurations to minimize radiation exposure due to larger surface area for absorbing radiation.
Increasing acquisition thickness in CT scans is achieved by combining detector rows, resulting in decreased patient dose but reduced spatial resolution.

Understanding Pitch in CT

Pitch describes the ratio of table movement to beam width; a pitch of 1 indicates movement equal to beam width, while a pitch over 1 indicates faster scanning with potential missing views.
A calculated pitch of 1 is derived when the table moves 10 mm and the beam width is also 10 mm.
If the pitch is set to 1.1, the patient table is moving 1.1 times the beam width during each tube rotation.

Field-of-View and Image Processing

A pitch less than one, such as 0.79, results in overlapping scan data for high-resolution imaging, while a pitch greater than one leads to missing views in the scanned data.
The scan field-of-view (SFOV) is typically larger than the display field-of-view (DFOV), with important data saved from SFOV but only DFOV data sent for viewing and analysis.
Patient anatomy within the display field-of-view is what is processed for viewing on screens, making it crucial for accurate diagnostics.

Image Reconstruction Techniques

Image reconstruction in CT transforms raw data into viewable image data, utilizing algorithms like first-rate reconstruction and mathematical filters to enhance specific tissue types.
Edge-enhancing algorithms are ideal for visualizing bone, while smoothing algorithms are preferred for soft tissue evaluation.
Iterative reconstruction techniques can effectively reduce patient dose while enhancing image quality by reducing artifacts, such as star-like appearances.

Slice Thickness and Image Quality

The acquisition thickness is synonymous with detector row thickness and can be adjusted by combining rows.
Thicker reconstruction slices lead to decreased spatial resolution but less image noise, as more data is averaged together.
For protocols requiring high detail, such as angiographic imaging, thin slices under 3 mm are essential to avoid quality loss.

Special Considerations in CT Imaging

When specialized protocols, like Circle of Willis for vascular evaluation, are employed, the use of thin slices is critical for capturing intricate anatomy.
Gaps in reconstructed image information can arise from pitch settings or slice interval discrepancies, impacting diagnostic accuracy.

Key Takeaways

Selection of pitch and slice thickness is vital to balance image quality and patient safety during CT scans.
Different scanning modes and reconstruction techniques should be chosen based on the specific anatomical focus and clinical objectives of the imaging study.### Slice Interval and Thickness
Slice interval typically set equal to slice thickness to avoid data gaps.
Increased slice interval over slice thickness creates gaps in data, analogous to gaps in a loaf of bread.

Reconstruction Algorithms

Edge-enhancing algorithms are crucial for creating detailed images of bony trabeculae.
Best spatial resolution achieved with thin slices and edge-enhancing algorithms, increasing image noise but highlighting smaller structures.

Retrospective Changes in CT Imaging

Parameters that can be changed retrospectively include scan start/end locations, slice thickness, display field-of-view, reconstruction algorithm, and slice interval.
Scan field-of-view and acquisition thickness cannot be altered retrospectively; acquiring new raw data requires rescanning.

Thoracic Spinal Scan

Raw data can be retrospectively reconstructed for the entire bony thorax if still available on the CT scanner.
This process involves changing the display field-of-view without rescanning the patient.

Abdominal Scan for Trauma

If raw data from an abdominal scan is not saved, the patient must be rescanned for new image reconstructions.

Hounsfield Units

An average Hounsfield unit (HU) of +39 typically corresponds to blood.
A lesion yielding an average CT number of -52 is likely composed of fat, since only a few tissues show negative Hounsfield values.

Image Reconstruction and Quality

Incorrect reconstruction algorithm leads to poor-quality images; clear edges require the correct edge-enhancing algorithm.
Different numbers of projections affect CT image quality; more projections yield better representation of objects.

Image Noise and Thickness

Thicker slices in CT imaging create less noise, resulting in smoother images, while thinner slices introduce more image noise.

Temporal Bone Scans

Blurriness in images from incorrect slice thickness governs the quality of reformations; thin slices produce better images.

CT Artifacts

Beam hardening artifacts occur due to excessive absorption of the X-ray beam and can be caused by dense objects or concentrated IV contrast.
Preventing beam hardening during chest scans can be achieved by positioning the patient's arms above the head, diminishing dense bone exposure.

Ring Artifact Prevention

Regularly calibrating the detector array can prevent ring artifacts in CT imaging.

EKG Lines in Imaging

Leaving EKG lines within the exposure field may cause beam hardening artifacts due to metal wires.

Metal Artifact from Density

Streaks in CT images from metal fragments, like lead pellets, are classified as beam hardening artifacts resulting from dense materials absorbing significant radiation.

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Description

Test your knowledge on key terms and concepts from Section 1 of the CT Boot Camp. This quiz covers fundamental terminology related to CT scanning, including projections and image production. Perfect for students and professionals looking to reinforce their understanding of CT technology.