CT Radiation Dose and Image Quality

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CT radiation dose

What is radiation dose? How is it measured? What terminology has been developed specifically to characterize CT radiation dose?

Radiation dose is a measure of the amount of energy imparted by ionizing radiation to a small mass of material. The unit of absorbed dose in the International System of Units (SI) is the gray (Gy), which is the deposition of 1 joule of energy by ionizing radiation into 1 kg of material. Some of us (including the author) were around before the formal establishment of the

CT dose index

Instead of measuring the MSAD for a CT acquisition of multiple CT slices, a method was developed using the principles of calculus to measure the radiation dose distribution from only one CT slice and then to calculate the dose for multiple slices. This is called the CT dose index (CTDI), described in a paper by Shope and colleagues [17]. The CTDI value is the integral of the radiation dose distribution profile in the z-axis (along the axis of the patient table) of a single CT slice (Eq. 1)CTDI=1

Effective dose

CTDIVol does provide a reasonable estimate of radiation dose but it does not provide information on radiation risk. For this purpose the concept of effective dose was introduced by the International Commission on Radiological Protection (ICRP) to provide a risk-based dose from the nonhomogeneous irradiation of human beings [22]. In the context of CT examinations, the effective dose is a weighted sum of the dose to the various organs and tissues from the CT study to a limited patient volume,

Appropriate CT scan protocols

How are the current CT scan protocols in a department established? Almost invariably they are supplied by the CT manufacturer and then modified by an applications specialist and a lead CT operator at the time of CT installation. Periodic software updates generally are supplied by the manufacturer and CT protocol modification often is made at this time. How many times has someone in a department sat down and reviewed all of the CT protocols with the lead CT technologist? Is it ever done in

Summary

Image quality is proportional to radiation dose. Improvements in image quality come only at a cost of increased radiation dose. This is a continuing challenge in CT imaging. Because of technologic improvements, CT scanners are more robust today than they were even 5 years ago. The x-ray tubes are capable of producing high levels of almost continuous radiation for rapid CT volume acquisitions and angiographic studies. All parameters of modern CT scanners have been technologically turbo-charged

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References (35)

  • M. McNitt-Gray

    Radiation issues in computed tomography screening

    Semin Roentgenol

    (2003)
  • W. Kalender et al.

    Spiral volumetric CT with single-breath-hold technique, continuous transport and scanner rotation

    Radiology

    (1990)
  • C. McCollough et al.

    Performance evaluation of a multi-slice CT system

    Med Phys

    (1999)
  • E. Nickoloff et al.

    Radiation exposures to patients from CT: reality, public perception and policy

    AJR Am J Roentgenol

    (2001)
  • S. Golding et al.

    Radiation dose in CT: are we meeting the challenge

    BJR

    (2002)
  • Report to the General Assembly with scientific annexes, vol. 1, sources, annex D

  • J. Haaga

    Radiation dose management: weighing risk versus benefit

    AJR Am J Roentgenol

    (2001)
  • J.R. Haaga et al.

    Effect of MAS variation upon CT image quality

    Radiology

    (1991)
  • L. Rogers

    Dose reduction in CT: how low can we go?

    AJR Am J Roentgenol

    (2002)
  • D. Brenner et al.

    Estimated risks of radiation-induced fatal cancer form pediatric CT

    AJR Am J Roentgenol

    (2001)
  • A. Paterson et al.

    Helical CT of the body: are settings adjusted for pediatric patients?

    AJR Am J Roentgenol

    (2001)
  • L. Donnelly et al.

    Minimizing radiation dose for pediatric body applications of single-detector helical CT: strategies at a large children's hospital

    AJR Am J Roentgenol

    (2001)
  • ICRU report 10a

    (1962)
  • E. McCullough et al.

    Patient dose in computed tomography

    Radiology

    (1978)
  • E. McCullough et al.

    Radiation dose

  • Rothenberg L., Pentlow K. CT dosimetry and radiation safety. RSNA categorical course in diagnostic radiology physics:...
  • T. Shope et al.

    A method for describing the doses delivered by transmission x-ray computed tomography

    Med Phys

    (1981)
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