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Principles

  • Dual Energy CT: Technical Approaches
    - Sequential acquisition
    - Rapid voltage switching
    - Dual-source CT
    - Layer detector
    - Quantum counting detectors
  • Dual Energy CT: Technical Approaches
    - Sequential acquisition
    - Rapid voltage switching
    - Dual-source CT
    - Layer detector
    - Quantum counting detectors
  • Dual Energy CT: Technical Notes on Dual Source CT
    - 2 x-ray tubes at 90 degrees to each other
    - Simultaneous acquisition of data on 2 x-ray systems
    - FOV is 33 cm as one tube is smaller
    - Latest systems are dose neutral compared with single energy CT scanning
  • Single-source with fast kilovoltage switching
    - GE Discovery CT 750HD
    - Single x-ray source with fast switching between two kilovoltage settings (80 and 140 kVp) at 0.5 msec intervals during a single gantry rotation to generate high and low energy spectra
    - Detector system with a fast response and a data acquisition system with a fast sampling capability are used to capture the alternating high and low energy data
  • Dual Source CT vs Single Source CT for Dual Energy
    - 33 cm field of view for DS while 50 cm field of view for SS
    - Limited spectral separation between high and low energy scans on SS when compared with DS
    - DS allows one to easily equalize dose and noise between high and low energy scans by modulating tube current for each tube which can not be done on SS
  • “ Dual energy CT permits a variety of image reconstructions for the depiction and characterization of vascular disease. Techniques include visualization of low and high peak kilovoltage spectra image datasets and also material specific reconstructions combining both low and high kilovoltage data.”
    Dual-Energy CT: Vascular Applications
    Vlahos I et al.
    AJR 2012;199:S87-S97
  • "These capabilities are promising for improved detection and characterization of lesions in the abdomen and pelvis and for evaluation of vascular structures."

    Dual-Energy Multidetector CT: How Does It Work, What Can It Tell Us, and When Can We Use It In Abdominalpelvic Imaging?
    Coursey CA et al.
    RadioGraphics 2010; 30:1037-1055

     

  • "Reductions in radiation dose are possible with dual energy CT if the need for true unenhanced datasets is elimnated,and if low tube currents are used, radiation doses delivered in dual energy CT are similar to those used in single energy CT."

    Dual-Energy Multidetector CT: How Does It Work, What Can It Tell Us, and When Can We Use It In Abdominalpelvic Imaging?
    Coursey CA et al.
    RadioGraphics 2010; 30:1037-1055

  • Dual Energy Scanner Technique
    - Dual source CT scanner (2 x-ray tubes and 2 detector arrays)
    - Single x-ray tube
  • Dual Energy facts
    - 80 kVp and 140 kVp vs 100 kVp and 140 kVp
    - At the lower kVp (80 or 100) photons have an energy closer to K edge of iodine (33.2) so the contrast in vessels is enhanced. This is typically by a factor of around 2x 
  • K edges and Atomic Numbers of Key Materials

    substance

    K edge (keV)

    Atomic Number (Z)

    Hydrogen

    0.01

    1

    Carbon

    0.28

    6

    Nitrogen

    0.40

    7

    Oxygen

    0.53

    8

    Calcium

    4.0

    20
    Iodine

     

    33.20

    53

    Barium

    37.45

    56

    Gadolinium

    50.20

    64


  • Dual Energy: Facts
    - The energy dependence of the photoelectric effect and the variability of K edges forms the basis for dual energy techniques
    - K edge refers to the spike in attenuation that occurs at energy levels just greater than that of the K-shell binding because of the increased photoelectric absortion at these energy levels
    - K edge values vary for each element and they increase as atomic number increases
  • Dual Energy CT: Basic Advantages in Practice
    - Provides information on how material behaves at different energy levels
    - Ability to generate virtual unenhanced CT datasets
    - Improved detection of iodine containing substances on low energy images
  • "Dual-energy CT could be an important tool for the diagnosis of various pulmonary diseases. Iodine perfusion maps and xenon ventilation imaging allow visualization of regional lung perfusion and ventilation and may facilitate the diagnosis of pulmonary embolisms and ventilation abnormalities."

    Dual-Energy CT: Clinical Applications in Various Pulmonary Diseases
    Kang MJ et al.
    RadioGraphics 2010; 30;685-698

  • Dual Energy Technology
    - Dual source CT: 2 x-ray tubes run at different kVps so data is perfectly aligned
    - Single source CT: rapid kVp switching is needed to get the two series aligned
  • Imaging at Lower kVp (80 or 100 kvp vs 120 or 140 kVp): The Bad News
    - Increase in image noise
    - MPR and 3D quality made be limited
  • Imaging at Lower kVp (80 or 100 kvp vs 120 or 140 kVp): The Good News
    - Iodinated contrast shows an approximately 80% increase in CT attenuation at 80 kVp compared with 140 kVp
    - Lower radiation dose
    - Less IV contrast needed for select examinations
    - Reduction in artifacts like pseudoenhancement

  • What is Dual Energy CT?

    "Material decomposition at dual energy CT can differentiate renal stones by their composition, quantify tissue iron stores, improve the detection of pathologic hyperenhancement, and reduce contrast material and radiation dose compared with conventional CT."

    Dual-Energy and Low-kVp CT in the Abdomen
    Yeh BM et al.
    AJR 2009; 193:47-54

  • What is Dual Energy CT?

    "Low peak tube voltage (kVp) settings provide high conspicuity of contrast materials at CT but may result in high image noise, particularly in larger patients."

    Dual-Energy and Low-kVp CT in the Abdomen
    Yeh BM et al.
    AJR 2009; 193:47-54

  • What is Dual Energy CT?

    The use of dual energy in a CT scan is to help create a new technique for data acquisition and display in order to optimize data extraction from complex datasets. Goals include data display, analysis and post processing.