Computed Tomography (CT) Overview
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Questions and Answers

What is the abbreviation for Computerized Axial Tomography?

CAT

A CT scan takes multiple two-dimensional images of the area being scanned to generate a three-dimensional image.

True (A)

What is the unit of measurement for the CT numbers?

Hounsfield Units (HU)

What is the approximate range of CT numbers for the human body?

<p>-1000 to +1000</p> Signup and view all the answers

What is the primary difference between a narrow window and a wide window in CT imaging?

<p>A narrow window enhances contrast in a specific region, while a wide window provides an overview of the entire image.</p> Signup and view all the answers

A CT scanner is capable of producing images of the entire body.

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

What is the approximate maximum weight limit for a CT scanner?

<p>450 pounds (204 kg)</p> Signup and view all the answers

CT scanners are typically capable of tilting up to 60 degrees.

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

What is the typical aperture of a CT scanner?

<p>70 cm.</p> Signup and view all the answers

What is the difference between a VOXEL and a PIXEL in CT imaging?

<p>A VOXEL is an element of volume in a 3D image, while a PIXEL represents an individual element in a 2D image.</p> Signup and view all the answers

What is meant by attenuation in the context of a CT scan?

<p>Attenuation refers to the weakening of an X-ray beam as it passes through different tissues.</p> Signup and view all the answers

What factor(s) play a role in the attenuation of an X-ray beam?

<p>Beam energy, atomic number, and tissue density.</p> Signup and view all the answers

CT scanners do not rely on the use of a computer for image processing.

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

What is the purpose of windowing in CT imaging?

<p>It optimizes the contrast in images to highlight specific structures of interest.</p> Signup and view all the answers

Which of the following best describes the function of window level in CT imaging?

<p>Determines the center of the displayed range of Hounsfield Units (C), Adjusts the brightness of the image (D)</p> Signup and view all the answers

A narrow window enhances contrast.

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

A wide window enhances brightness.

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

A narrow window displays more details of a specific region.

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

A wide window is useful for evaluating a specific structure in detail.

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

CT scanners are a type of X-ray device.

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

A CT scan is a non-invasive diagnostic procedure.

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

CT scans are typically used for brain imaging.

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

CT scans are only used for diagnosis.

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

All CT scans are the same.

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

CT scans are always safe.

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

CT scans are only used for humans.

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

Flashcards

What is Computed Tomography?

A medical imaging technique that uses X-rays and computer processing to create cross-sectional images (slices) of the body.

What is a CT scanner?

A device that uses X-rays to produce detailed images of the inside of the body, allowing doctors to see bones, organs, and soft tissues.

What is a voxel?

A three-dimensional volume element in the object being scanned using CT.

What is a pixel?

A two-dimensional element in the CT image that represents a voxel.

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What is the field of view (FOV)?

The diameter of the body region being imaged by CT.

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How is pixel size determined?

By dividing the field of view (FOV) by the matrix size. Most CT scanners use a 512x512 matrix.

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What are the factors that affect voxel size?

Voxel size is determined by the field of view (FOV), matrix size, and slice thickness.

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What is attenuation?

The reduction in intensity of the X-ray beam as it passes through the body.

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What factors affect attenuation?

Factors that affect attenuation include the energy of the X-ray beam and the atomic number of the tissues being scanned.

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What are CT numbers?

Numbers in the image matrix that represent the X-ray attenuation in each voxel.

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What are Hounsfield Units (HU)?

Units used to measure the X-ray attenuation of different tissues, with water having a value of 0 HU.

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What is the range of CT numbers?

The range of CT numbers is typically 2000 HU, with some modern scanners having a range of 4000 HU.

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What is windowing?

The process of using CT numbers to create an image by assigning different shades of gray to different HU values.

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What is a narrow window?

A small range of HU values used to highlight specific structures in the image.

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What is a wide window?

A large range of HU values used to view a wider range of tissues in the image.

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How are liver windows used?

To evaluate the liver by distributing shades of gray over a narrow range of HU values, typically centered around 70 HU.

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How are bone windows used?

To view bone structures by using a wide window to encompass the full range of HU values within the bone.

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What does window level (WL) control?

The brightness of the image by determining the center of the range of HU values.

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What does window width (WW) control?

The contrast of the image by determining the total range of HU values displayed.

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What is the gantry?

The main part of the CT scanner that houses the X-ray tube, detectors, and other components.

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What is the patient couch?

The table that the patient lies on during the CT scan.

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What is the X-ray tube?

The component in the gantry that produces the X-ray beam.

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What are collimators?

Devices that restrict the X-ray beam to a specific size and shape.

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What are detectors?

Components that measure the intensity of the X-ray beam after it has passed through the body.

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What is the tilting range of a CT scanner?

The range of angles that the gantry can be tilted, typically +30 to -30 degrees.

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What is the aperture of a CT scanner?

The diameter of the opening in the gantry, typically around 70 cm.

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What is the weight limit of the patient couch?

Typically around 450 pounds (204 kg), distributed weight.

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What is the scannable range of the patient couch?

The distance that the couch can move, typically from head to thigh (162 cm).

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Study Notes

Computed Tomography (CT)

  • CT scanners were first introduced in 1971 for brain studies.
  • Developed under the leadership of Sir Godfrey Hounsfield, an electrical engineer at EMI.
  • Early CT scanners used a single detector.
  • Modern CT scanners have multiple detectors and shorter scan times.

What is a CT Scanner?

  • An X-ray device that creates cross-sectional images (slices) of the patient.
  • This enables detailed 3D visualizations of internal structures.

Why Use CT?

  • Traditional radiography shows overlapping 2D images of structures.
  • CT has good low-contrast resolution, allowing for the detection of small tissue changes.
  • CT provides accurate diagnostic information about the body's structure distribution.

Tomography Principles

  • Tomography is a non-invasive medical imaging method.
  • It combines X-rays and computer processing to generate tomographic slices of scanned areas.
  • Tomos = slice; Graphein = to write
  • A CT scanner images an object by analyzing its slices.
  • Another name for CT is CAT (Computerized Axial Tomography).
  • There are also Spiral CT (SCT) and Multi-Slice CT (MSCT)

Matrix and Voxels

  • A CT image is represented as a matrix of numbers.
  • Matrixes are 2-dimensional arrays of numbers arranged in rows and columns.
  • Each element (number) in the image matrix represents a 3-dimensional volume element called a voxel.
  • A voxel is represented as a 2-dimensional pixel (picture element) in the image.
  • Field of View (FOV) is the body region diameter being imaged (e.g., 25 cm for head, 40 cm for abdomen).
  • CT pixel size is determined by dividing the FOV by the matrix size (typically 512x512 in CT).

Pixel vs Voxel

  • Pixel size depends on matrix size and FOV.
  • Voxel size depends on FOV, matrix size, and slice thickness.

Attenuation

  • Attenuation is the reduction in X-ray beam intensity as it passes through matter.
  • Attenuation happens due to photon absorption or deflection (scatter).
  • Factors influencing attenuation include beam energy and absorber's atomic number.

CT Numbers

  • CT numbers (Hounsfield Units, HU): represent X-ray attenuation within each voxel.
  • They are assigned different shades of gray on a gray scale.
  • Water has an attenuation value of 0 HU.
  • Bone has an HU range of +400 to +1000.
  • Air has an HU value of -1000.
  • Modern CT scanners can show a wider range of HU values.

Hounsfield Values (HU)

  • HU values provide a quantitative measurement of tissue density.
  • Refer to a chart for specific HU values for different materials (like bone, water, fat, etc.).
  • Examples of HU values are given on a chart.

Windowing

  • Windowing is a technique used for image adjustments.
  • It maps HU values to 256 different shades of gray, allowing for better visualization of structures.
  • Window level is the center of the displayed HU range.
  • Window width determines the range of HU values displayed as shades of gray.
  • A narrow window enhances inherent contrast.
  • Window level determines the brightness of the image.

Imaging System Components

  • Scanner
  • Gantry
  • X-ray tube
  • Generator
  • Filter
  • Collimators
  • Detectors
  • Patient couch (450 pounds/204kg distributed weight limit & scan range from head to thigh/162 cm)

Gantry Characteristics

  • Tilting range: ±30 degrees (most scanners)
  • Aperture: 70 cm (most scanners)

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Computed Tomography PDF

Description

Explore the history, principles, and applications of Computed Tomography (CT) in medical imaging. This quiz delves into the development of CT scanners, their functionality, and the advantages over traditional radiography. Understand how CT technology revolutionized the visualization of internal structures.

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