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What is the primary function of the imaging system?

  • To produce X-rays, shape and filter the X-ray beam, and convert the transmitted photons into digital information (correct)
  • To produce digital information from the patient's cross-section
  • To record and store the image
  • To display the final image to the radiologist

    • What is the purpose of the filtration component in the CT imaging system?

  • To filter the X-ray beam to reduce radiation exposure (correct)
  • To shape the X-ray beam to pass through only a defined cross-section of the patient
  • To produce X-rays
  • To convert the X-ray beam into digital information

    • What is the Gantry in a CT scanner?

  • The computer system that processes the image
  • The detector assembly that converts photons into digital information
  • The X-ray tube that produces X-rays
  • The ring-shaped part of the CT scanner that houses many components (correct)

    • What is the function of the collimators in the CT imaging system?

    <p>To shape the X-ray beam to pass through only a defined cross-section of the patient</p> Signup and view all the answers

    What is mounted on a rotating scan frame in the Gantry?

    <p>The components necessary to produce and detect X-rays</p> Signup and view all the answers

    What is the purpose of the detectors in the CT imaging system?

    <p>To convert photons into digital information</p> Signup and view all the answers

    What is the function of the X-ray tube and generator in the CT imaging system?

    <p>To produce X-rays</p> Signup and view all the answers

    What is the component that houses many of the components necessary to produce and detect X-rays?

    <p>The Gantry</p> Signup and view all the answers

    What is the primary function of the X-ray generator in a CT scanner?

    <p>To produce high-voltage electricity to the X-ray tube</p> Signup and view all the answers

    What is the benefit of using high-frequency generators in CT scanners?

    <p>They are smaller and more compact than conventional generators</p> Signup and view all the answers

    Why are cooling mechanisms included in the gantry?

    <p>To prevent temperature fluctuations from affecting imaging components</p> Signup and view all the answers

    What is the purpose of filtration in CT scanners?

    <p>To create a more uniform beam intensity</p> Signup and view all the answers

    What is the advantage of using rotating anode X-ray tubes in CT scanners?

    <p>They have a higher output</p> Signup and view all the answers

    Where is the filter typically positioned in a CT scanner?

    <p>Between the X-ray tube and the patient</p> Signup and view all the answers

    What is the purpose of the X-ray generator in a CT scanner?

    <p>To produce X-rays</p> Signup and view all the answers

    What is the benefit of continuous rotation of the gantry frame?

    <p>It eliminates the need to straighten twisted system cables</p> Signup and view all the answers

    What is the purpose of the aperture in a CT scanner?

    <p>To properly center the body part of interest</p> Signup and view all the answers

    What was the limitation of early CT scanners that used recoiling system cables?

    <p>Limited gantry rotation times</p> Signup and view all the answers

    What is the function of the positioning lights in a CT scanner?

    <p>To properly center the body part of interest</p> Signup and view all the answers

    What is the purpose of the slip rings in a CT scanner?

    <p>To provide continuous electrical power and electronic communication</p> Signup and view all the answers

    What is the range of aperture size in a CT scanner?

    <p>70 to 90 cm</p> Signup and view all the answers

    What is the function of the emergency button in a CT scanner?

    <p>To stop every mechanical movement and x-ray emission</p> Signup and view all the answers

    How many positioning lights are typically mounted on the gantry?

    <p>Three to four</p> Signup and view all the answers

    What is the purpose of the microphone embedded in the gantry?

    <p>To allow communication between the patient and technologist</p> Signup and view all the answers

    What is the primary function of pre-patient collimators in CT?

    <p>To restrict the beam to the slice thickness</p> Signup and view all the answers

    What is the term for the ability of a detector to capture, absorb, and convert X-ray photons to electrical signals?

    <p>Efficiency</p> Signup and view all the answers

    Which of the following detector characteristics is essential for CT image production?

    <p>Efficiency</p> Signup and view all the answers

    What is the primary function of pre-detector collimators in CT?

    <p>To improve image quality by limiting scatter radiation</p> Signup and view all the answers

    What is the term for the ability of a detector to detect a broad range of X-ray transmission data?

    <p>Dynamic range</p> Signup and view all the answers

    What is the process by which a scintillation detector converts X-ray energy to electrical energy?

    <p>X-ray to light and then light to electrical signal</p> Signup and view all the answers

    What is the component of a solid-state detector that releases electrons when struck by light?

    <p>Photocathode</p> Signup and view all the answers

    What is the purpose of the photomultiplier tube in a scintillation detector?

    <p>To amplify the electrical signal</p> Signup and view all the answers

    What is the primary function of the electrical signal sent to the computer in a CT scanner?

    <p>To determine the attenuation of the X-ray beam by the body and generate an image</p> Signup and view all the answers

    What is the result of ionization of the xenon gas when X-rays fall on it?

    <p>Production of both positive and negative ions</p> Signup and view all the answers

    What is the characteristic of solid-state crystal detectors?

    <p>Sensitive to temperature and moisture, with high photon absorption</p> Signup and view all the answers

    What is the main difference between single-slice CT (SSCT) and multi-slice CT (MSCT) detectors?

    <p>The detector arrays, with SSCT having a one-dimensional array and MSCT having a two-dimensional array</p> Signup and view all the answers

    What is the detection efficiency of pressurized xenon gas detectors?

    <p>45%</p> Signup and view all the answers

    How do the positive ions migrate in the gas detector?

    <p>They migrate to the negatively charged plate</p> Signup and view all the answers

    What is the characteristic of MSCT detectors?

    <p>They are divided into several smaller detectors along the z-axis, forming a two-dimensional array</p> Signup and view all the answers

    What is the minimum number of rows of detectors in current CT scanners used in hospitals?

    <p>64</p> Signup and view all the answers

    Study Notes

    CT Imaging System Components

    • The CT scanner has several components:
      • Imaging system
      • Computer system
      • Image display, recording, storage, and communication system

    Gantry

    • The gantry is the ring-shaped part of the CT scanner that houses many components necessary to produce and detect X-rays.
    • It is mounted in the scanning room and has a rotating scan frame.
    • The gantry includes:
      • X-ray tube
      • Filter
      • Slip ring
      • High-voltage generator
      • Data acquisition system (collimator, detectors)

    Outside Components

    • Display panel: shows the reading of the gantry tilt, table height, and position of landmark.
    • Control panel: incorporates several buttons to control the movements of the gantry and table.
    • Emergency button: stops every mechanical movement and X-ray emission.
    • Positioning lights: red laser lights used for positioning the patient.
    • Aperture: the opening through which the patient passes.

    Slip Rings

    • Early CT scanners used recoiling system cables to rotate the gantry frame, which limited the scan method to the step-and-shoot mode.
    • Alternative to cabling system: slip-ring, which uses a brush to provide continuous electrical power and electronic communication across a rotating surface.
    • Slip rings serve three functions:
      • Supply of high-voltage electricity to the X-ray tube.
      • Supply of low-voltage electricity to various control mechanisms.
      • Enable the transmission of data from detector to computer system.

    X-ray Generator

    • CT scanners use high-frequency generators, which are small, compact, and more efficient than conventional generators.
    • The generator produces high kV (generally 120-140 kV) to increase the intensity of the beam, which increases the penetrating ability.

    Cooling Systems

    • Cooling mechanisms are included in the gantry to prevent temperature fluctuations from affecting imaging components.

    X-ray Tube

    • The X-ray tube is responsible for X-ray production.
    • Rotating anode X-ray tubes have become common in CT due to the demand for increased output.
    • These tubes produce a heterogeneous X-ray beam.

    Filtration

    • Filtration serves a dual purpose:
      • Remove long wavelength X-rays that do not play a role in CT image formation but contribute to patient dose.
      • Create a more uniform beam intensity, improving the CT image by reducing artifacts.
    • Two commonly used filters are:
      • Flat filter
      • Bowtie filter

    Collimation

    • Collimation is used to restrict the beam to the slice thickness and reduce scatter radiation.
    • There are two types of collimators:
      • Pre-patient collimators
      • Pre-detector collimators

    Detector Characteristics

    • The detector must exhibit several characteristics essential for CT image production:
      • Efficiency: refers to the ability to capture, absorb, and convert X-ray photons to electrical signals.
      • Stability: refers to the steadiness of detector response.
      • Response time: refers to the speed with which the detector can detect an X-ray event and recover to detect another event.
      • Dynamic range: detectors must be sensitive enough to measure a broad range of X-ray transmission data.

    Types of Detectors

    • Scintillation detector: converts X-ray to light and then light into electrical signals.
    • Gas ionization detector: converts X-ray energy directly to electrical energy.

    Detector Characteristics

    • Scintillation detectors:
      • Solid-state detectors made of a scintillation crystal and a photomultiplier tube.
      • When X-ray falls onto the crystal, flashes of light or scintillation are produced.
      • Light from the crystal strikes the photocathode of the photomultiplier tube, which then releases electrons.
    • Gas detectors:
      • When X-rays fall onto the xenon gas, ionization of the gas results and produces positive and negative ions.
      • Positive ions migrate to negatively charged plate, whereas negative ions are attracted to positively charged plate.
      • This migration of ions causes a small signal current that is related directly to the number of photons absorbed.

    Single (SSCT) and Multiple (MSCT) Detector

    • The main difference between SSCT and MSCT is the detector arrays.
    • SSCT uses detectors that form a one-dimensional array.
    • MSCT is divided into several smaller detectors along the z-axis, forming a two-dimensional array.
    • The CT scanners currently used in hospitals have at least 64 rows of detectors that provide a very high resolution.

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