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Chapter 11:
X-ray Radiation and Dose-Reduction Techniques
When x-ray radiation penetrates an object, part of its energy is transferred to the object and causes changes in the object's material. During the energy transfer, an x-ray can indirectly produce ion pairs in the tissue. The ion pairs react with other chemical systems and cause radiation damage. Alternatively, the x rays may strike and break molecular bonds, such as those in DNA, and cause direct damage. The level of acceptable dose for humans is greatly helped by the fact that humans have been exposed to natural radiation since the dawn of time. There are three main sources of natural radiation: cosmic rays (charged particles from outer space), external gamma rays (radioactivity in the earth's crust), and internal radiation (radioactive material present in our body, such as K-40 and radon). On average, the human average exposure to manmade radiation is roughly equal to the total amount of natural radiation and therefore, doubles the radiation level that humans have been subjected to for centuries. A general sensitivity to and awareness of the x-ray dose delivered to patients has increased steadily over the years. Many studies have been conducted on the subject. It is an understatement that the topic of CT x-ray dose has received much attention lately. Scientific journal publications, conference papers, and even articles in major newspapers present evidence and severe warnings about the adverse effects of CT radiation dose. Others strongly defend the benefits of CT and raise serious concerns about research methodologies that lead to concerns about x-ray dosages. Given the large number of CT procedures performed each year, it is not surprising that CT's impact on public health has received increasing scrutiny. It is estimated that about 62 million CT scans were performed in the U.S. alone in 2006, up from about 3 million in 1980. Regardless of the controversy, it is accurate to state that significant efforts have been made to reduce x-ray radiation from CT. These efforts come from three main sources: the research and clinical community, government agencies, and industry. In recent years, the clinical community has gradually adopted the ALARA (as low as reasonably achievable) principle. ALARA is based on the conservative assumption that every radiation dose can produce some level of detrimental effect that may be manifested as an increased risk of genetic mutations or cancer.
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Radiation effects


Computed tomography

Defense and security

Energy transfer

Gamma radiation

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