Image Radiation Biology of Medical Imaging

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The electron may act either directly on DNA direct action or affect but may also interact on a water molecule resulting in a free radical, which in turn can damage DNA indirect action or affect. DNA damage results in either single stranded breaks or double stranded breaks. Single stranded breaks are usually well repaired with minimum bioeffects. Breaks in both strands of DNA which are in close proximity are more problematic to repair and underlie disruptive function that can result in cell death or in impaired cellular function resulting in the development of cancer.

These inappropriate repairs with resultant stable aberrations can initiate one of the multi-step processes in radiation induced carcinogenesis. Of note, there are some chemicals, which serve as radioprotectants, primarily in the setting of radiation oncology that have recently been reviewed While not yet applicable to general diagnostic imaging, these DNA stabilizing agents provide a model for radiation protection at the cellular level.. Radiation results in two biological effects: deterministic and stochastic effects.

For virtually all diagnostic imaging CT, nuclear medicine, and radiography and fluoroscopy radiation doses are at the levels which are stochastic. Stochastic effects are generally disruptions that result in either cancer or heritable abnormalities. For diagnostic imaging, the discussion is limited almost exclusively to the potential for cancer induction; heritable effects i. For a stochastic effect, the risk increases with the dose but the severity of the effect i.

There is also no threshold for this risk see following discussion on models of radiation risks based on dose.

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The other biological effect is deterministic. Deterministic effects include cataracts, dermatitis skin burns , and epilation hair loss. With the deterministic effect, the amount of radiation determines the severity of effect. For example, the greater amount of radiation, the more extensive the hair loss. With deterministic effects, there is a threshold. Below this threshold the injury does not occur. Deterministic effects can be seen with extensive interventional procedures, and certainly with doses delivered from radiation oncology.

Deterministic effects are, except for very unusual circumstances, including imaging errors, not encountered in during diagnostic medical imaging examinations.. A brief review of radiation units will be helpful for the subsequent material. First, radiation can be measured as exposure; however this is not useful in determining risks since it says nothing about what the organs at risk actually receive.

Individual patient risk for organ specific cancer can be determined if the absorption of the radiation, the absorbed dose, measured in Gray Gy , is known. Obviously, this cannot be determined during routine medical imaging for an individual patient but there are estimations for organ doses.

Radiation risk from medical imaging - Harvard Health

The biological impact on the tissue may vary depending on the type of radiation delivered. For diagnostic imaging, this is the x-ray, and the waiting factor ends up being 1. The final unit of import is the effective dose in Sv, or mSv in the range of diagnostic imaging which is commonly used metric in discussions of diagnostic imaging radiation dose. It is formally determined by the sum of the exposed organs and their equivalent doses in mSv multiplied by weighting factors which depend on the differing radiosensitive of those organs that are exposed.

The effective dose is a very general dose unit. It could be similar to say an average rainfall for a country per year. This average rainfall takes into account regional and seasonal variations into a single number, but there is no way to extract from the average rainfall the specific data on the coastal rainfall in summer months. Effective dose derived from experiments and models of organ doses since, again we cannot practically measure internal organ doses during medical imaging represents an equivalent whole body dose like the yearly average rainfall from what may be regional exposures.

For example, a brain CT may result in an effective dose of 2.


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A pelvic CT may result in an effective dose of 4. This means that the pelvic CT equivalent for the whole body exposure is twice that of a brain C T. However, it is easy to see that any potential risks from the brain CT to the lens of the eye for example are going to be greater than the pelvic CT. While the effective dose continues to be the most commonly used metric in discussing ionizing radiation dose from imaging modalities in the clinical realm, it is still problematic and often misunderstood measure The doses for imaging modalities can vary widely, more than a factor of a hundred.

In general, radiography of the extremities such as the ankle, wrist, or elbow provide very low doses, and computed tomography and nuclear imaging studies tend to provide relatively higher doses. Again, these are effective doses, or whole body equivalents that, allow the various imaging modalities to be compared with respect to an overall population risk but not an individual patient risk.

Doses will depend on the various technical factors used for various imaging studies.

In particular, fluoroscopy and angiography doses may vary depending on the indication for the evaluation, or various findings during the procedure. An upper gastrointestinal series with a small bowel follow through will in general have a higher fluoroscopic dose than a simple fluoroscopic cystogram in children. Doses for nuclear medicine studies can be quite low or relatively high 11 , Single imaging doses in children from a single CT examination may be as low as less than 1.

Overall, there are nearly 4 billion diagnostic imaging evaluations that use ionizing radiation performed worldwide Given the current world population, this means more than one examination for every individual in the world is performed every other year.

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Radiation in Medicine: Medical Imaging Procedures

Obviously, not everyone has an examination and various populations of patients will have significant number of examinations per year. If one looks at medical imaging use in the United States, it has substantially increased over the past 30 years Previously, about 3. Before , an effective dose of approximately 0. This is now 3. Nearly half of this is from CT and the vast majority of medical radiation is due to combination of CT and nuclear imaging. This is largely due to increase in medical imaging, rather than higher doses per procedure.

The reasons for this increased use are complex but, as noted before, CT has provided an increasingly valuable tool in a number of settings, including evaluation of trauma, especially brain injury, in the setting of cardiovascular disease, including thromboembolism, and other cardiovascular abnormalities such as acquired and congenital heart disease in children , and in the clinical setting of acute abdominal pain, such as appendicitis..

Currently, in the United States, nearly 80 million CT examinations are performed per year 25 which equates to about one CT evaluation performed per year for every four individuals. In the U. For example, Dorfman et al noted that out that over a three year period in a U. Larson noted a five-fold increase in the number of CT examinations from , to over 1. While these data do indicate that the use of medical imaging in children has increased substantially over the past few decades, some other data indicate that at least the use of CT imaging in children has declined over the past few years 28 , 29 , and further investigations will need to determine if this is a sustained trend..

In general, risk estimations for medical imaging in both adults and children come from four sources consisting of studies of populations exposed to atomic bombs the Radiologic Effects Research Foundation-RERF , occupational exposures, medical exposures, and environmental exposures, such as the Chernobyl accident. Rather than a detail discussion of the limitations of the BEIR VII Report, it is probably more worthwhile to just understand that estimations of cancer risks, such as the levels provided by medical imaging, continue to be speculative.

We also estimate the dose provided by imaging recall effective dose discussion above , so that there are many estimations involved in determining risks. We do know that at effective doses greater than mSv, there is a significant risk of cancer. Below that, and the range of medical imaging examinations, there is a debate 10 , 14 , The model most widely accepted for cancer induction risk related to dose estimations is a linear no threshold model LNT 31 , It is important that a modern CT scanner is used for children, and that the operator adjusts the imaging parameters to reduce the radiation dose to an acceptable level.

The information for parents and carers page includes access to videos and interactive games. What is a whole body MIBI myeloma scan?


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A whole body MIBI myeloma scan is a nuclear medicine scan which…. A nuclear medicine thyroid scan uses a radioactive medication radiopharmaceutical to take pictures or images of the thyroid gland. What is an arthrogram?

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An arthrogram is an X-ray image or picture of the inside of a joint e. A Nuclear Medicine NM cardiac stress test involves a scintigraphic radioactive isotope …. It issues no invitation to any person to act or rely upon such opinions, advices or information or any of them and it accepts no responsibility for any of them. The content of this publication is not intended as a substitute for medical advice.

Some of the tests and procedures included in this publication may not be available at all radiology providers. Each person should rely on their own inquires before making decisions that touch their own interests. Find information about a clinical radiology procedure or test: Refine search Reset.

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Health professional information. Nuclear Medicine Thyroid Scan A nuclear medicine thyroid scan uses a radioactive medication radiopharmaceutical to take pictures or images of the thyroid gland. The… Read more. Arthrogram What is an arthrogram? Scroll Up. Refine search. Principles, practices and policies of the health care organization s will be examined, in addition to the professional responsibilities of the radiographer. Students will be oriented to the administrative structure of the Radiology Department and to professional organizations significant to radiology.

Routine and emergency patient care procedures will be described, as well as infection control procedures utilizing standard precautions. The role of the radiographer in patient education will be identified. A word-building system will be introduced and abbreviations and symbols will be discussed. Also introduced will be an orientation to the understanding of radiographic orders and interpretation of diagnostic reports.


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Related terminology is addressed. This course will introduce an overview of the principles of radiation protection, including the responsibilities of the radiographer for patients, personnel and the public. Devices used for protection will be presented. Radiation health and safety requirements of federal and state regulatory agencies, accreditation agencies and health care organizations are incorporated.

The fundamental skills necessary to adapt studies to specific patient needs will be introduced as well as concepts related to pathology with emphasis on radiographic appearance. Laboratory and clinical experience will be used in conjunction with seminars to facilitate mastery of skills necessary for the beginning medical imaging student.

The basic knowledge of atomic structure and terminology, nature and characteristics of radiation, x-ray production, the fundamentals of photon interactions with matter, and the design and function of the radiographic equipment are explored. The concepts of radiographic density, contrast, latitude, detail and distortion are analyzed with respect to how they affect the image production process.

Ideal technique formulation and selection, troubleshooting and error correction is examined.