CT Image Quality Quiz

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Questions and Answers

What is the primary purpose of Maximum Intensity Projection (MIP) in CT imaging?

  • To average pixel values for better image quality
  • To display the lowest value pixels along a line
  • To create a full 3D image using all data points
  • To reconstruct images using the highest value pixels along any line (correct)

Which view does the Multiplanar Reconstruction (MPR) NOT allow?

  • Saggital
  • Rectangular (correct)
  • Coronal
  • Transverse

How does the Shaded Volume Display (SVD) enhance image quality compared to Shaded Surface Display (SSD)?

  • By focusing on surface boundaries only
  • By limiting the viewing angle
  • By utilizing the entire data set (correct)
  • By using only selected pixels

What is one limitation of using Maximum Intensity Projection (MIP)?

<p>It may miss small vessels passing through a voxel (D)</p> Signup and view all the answers

Which of the following is NOT a type of image representation mentioned in the content?

<p>Image Averaging Display (IAD) (A)</p> Signup and view all the answers

What distinguishes the Shaded Surface Display (SSD) from other imaging techniques?

<p>It creates images that appear as organ surfaces (B)</p> Signup and view all the answers

In what way does Multislice helical CT excel?

<p>In 3D Multiplanar Reconstruction (MPR) (D)</p> Signup and view all the answers

What is the main advantage of the Shaded Volume Display (SVD) compared to other imaging methods?

<p>It produces better image quality and more information (C)</p> Signup and view all the answers

Which method measures the scanner's ability to separate two adjacent objects?

<p>Spatial resolution (A)</p> Signup and view all the answers

What does a low spatial frequency represent in CT imaging?

<p>Large objects (D)</p> Signup and view all the answers

How does slice thickness affect spatial resolution in CT imaging?

<p>Thinner slices improve spatial resolution (C)</p> Signup and view all the answers

What reflects the ability to distinguish soft tissues in CT imaging?

<p>Contrast resolution (C)</p> Signup and view all the answers

What is the primary cause of image noise in CT systems?

<p>Pixel size (B)</p> Signup and view all the answers

Linearity in CT imaging refers to which of the following?

<p>The relationship between CT numbers and linear attenuation (D)</p> Signup and view all the answers

What type of object tends to drift in CT imaging measurements?

<p>Uniform objects like water (D)</p> Signup and view all the answers

Which technique is used to increase image accuracy by manipulation of raw data?

<p>Image reconstruction (B)</p> Signup and view all the answers

What effect does high noise have on CT images?

<p>It causes graininess (C)</p> Signup and view all the answers

What is the primary benefit of solid-state detectors compared to film in CT imaging?

<p>Better differentiation of similar densities (B)</p> Signup and view all the answers

What does a high noise level in CT images typically indicate?

<p>Reduced image clarity (A)</p> Signup and view all the answers

What effect does image filtering have on CT images?

<p>Improves soft tissue discrimination (B)</p> Signup and view all the answers

Which parameter directly affects the uniformity of CT images?

<p>Consistent calibration of the system (D)</p> Signup and view all the answers

Flashcards

MPR (Multiplanar Reconstruction)

A computer program that transforms images from axial/transverse views into coronal, sagittal, and oblique views.

Coronal View

A view of a body part from front to back.

Sagittal View

A view of a body part from left to right.

MIP (Maximum Intensity Projection)

A 3D image reconstruction technique that uses the highest intensity pixels along a line to create an image.

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Shaded Surface Display (SSD)

A 3D display technique that shows an organ's surface, defined by operator-selected values.

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Shaded Volume Display (SVD)

A 3D image technique that uses the entire dataset for a more detailed and high-quality display.

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Multislice Helical CT

A type of CT that excels in creating 3D MPR (Multiplanar Reconstruction) images.

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Partial Volume Averaging

A phenomenon where small vessels, or other structures that pass obliquely through a voxel, might be obscured in MIP (Maximum Intensity Projection) based 3D images.

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Spatial Resolution

The ability of a CT scanner to distinguish between two closely spaced objects.

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Spatial Resolution Factors

Pixel size, slice thickness, and detector element size influence spatial resolution.

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Contrast Resolution

Ability to distinguish between tissues with similar densities.

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Contrast Resolution and HU

CT excels at differentiating tissues with similar densities using Hounsfield Units (HU).

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Noise in CT

Variation in CT numbers around the true value, resulting in image graininess.

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Noise Factors

kVp, filtration, pixel size, slice thickness, and detector efficiency affect noise.

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Linearity in CT

Relationship between CT numbers and the linear attenuation coefficient of tissues.

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Uniformity in CT

Consistency of CT values for a uniform material (like water).

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Localizer Scan (Scout)

Initial CT images to position anatomy correctly before the main scan.

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Image Filtering

Algorithms modifying the image to enhance detail or reduce noise, improving image quality.

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Window Width (WW)

Image setting that controls the range of CT numbers displayed.

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Window Level (WL)

Image setting that controls the center of the range of CT numbers displayed.

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Image Reconstruction

Process of manipulating raw CT data to create different image outputs.

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Line Pairs per cm (lp/cm)

Unit for measuring spatial resolution, showing how many pairs of lines can be resolved per centimeter.

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Attenuation Coefficient

Measure of how much X-rays are absorbed by a tissue.

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Study Notes

CT Image Quality

  • Five methods are used to measure CT image quality: spatial resolution, contrast resolution, noise, linearity, and uniformity.

Spatial Resolution

  • Spatial resolution measures how well a CT image can differentiate small objects.
  • Blurring of sharp interfaces in images is inversely proportionate to spatial resolution.
  • Smaller pixel sizes result in better spatial resolution.
  • Spatial resolution depends on pixel size.
  • Low spatial frequencies represent large objects, while high frequencies represent small objects.
  • Resolution is related to the detector element size; thinner slices and smaller voxel sizes improve resolution.
  • Spatial resolution is expressed as line pairs per centimeter (lp/cm).

Contrast Resolution

  • Contrast resolution refers to the ability to differentiate tissues with similar densities.
  • Multislice helical CT excels in this area.
  • The attenuation coefficient depends on x-ray energy and the atomic number of the tissue.
  • CT utilizes x-ray absorption to determine tissue density.
  • Amplified contrast scales improve differentiation of adjacent tissues.
  • Contrast resolution is affected by image noise and the uniformity of the object.

Noise

  • CT image noise appears as graininess.
  • Noise is affected by various factors such as kVp, filtration, pixel size, slice thickness, detector efficiency, and patient radiation dose.
  • Low noise appears smooth, while high noise appears spotty or blotchy.
  • Variation in CT numbers from the ideal zero value is a measure of noise.
  • Image noise limits the resolution of low-contrast objects.

Linearity

  • Linearity refers to the relationship between CT numbers and the linear attenuation of the imaged object.

Uniformity

  • Uniformity ensures consistent CT number values for a uniform material (e.g., water).
  • CT values for water can vary slightly from day to day or hour to hour.

CT Image Manipulation and Display

  • Localizer scans (scout images) are used to position the patient and verify anatomy in the CT scan field of view.
  • These scans are performed with the x-ray tube stationary.
  • Image enlargement reduces resolution.
  • Image filtering techniques smooth the image and, in some cases, enhance edges.
  • Contrast is improved by adjusting window width and level.

Image Manipulation

  • Image reconstruction is the process of manipulating raw CT data
  • various image manipulations and filters produce modified images (e.g., MIP, MPR)
  • Various manipulation techniques include different filters, display field of view, multiplanar reconstructions, and maximum intensity projection.

3D Imaging

  • Multiplanar reconstruction (MPR) is a method to generate sagittal, coronal, and oblique views from axial images.
  • Other 3D image manipulations allow for volume and surface rendering, maximizing intensity projections, and shaded surface/volume displays.

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