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Radiation_Protection_in_Medical_Imaging_(Part 6)

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Modern helical or spiral CT (Computed Tomography) units are constructed using slip ring technology that allows the X-ray tube to rotate 360 degrees around the patient as the table moves through the gantry. A helical unit can complete an entire dynamic study in less than one minute. But the primary beam is on the entire time. Because of the continuous exposure of the beam, patient dose and CT can be significantly higher than in radiography. For occupational dose however is generally the opposite. Most CT technologists receive little or no radiation exposure because they are usually behind the secondary barrier of the control room wall while the beam is on. Helical units are used for special procedures performed by a radiologist or other physician using the guidance of CT images to place a needle for tissue biopsy of a drainage tube for an abscess. All units can image the same 20 millimeters of tissue at given intervals to check for needle placement. Some CT units are also capable of fluoroscopy which can reduce the length of the procedure because it provides real time imaging. However, CT fluoroscopy also can raise the patient's exposure if the radiologist or other physician does not use the fluoroscopy pedal carefully. As in radiography, raising patient exposure produces a greater amount of scatter which increases occupational exposure for technologists and other personnel who may be assisting in the exam room. Wraparound lead and thyroid shield should be worn with leaded glasses if needed by any technologist or who must assist the patient with the exam. Interventional radiology is performed by specialized radiologists using invasive procedures under fluoroscopic guidance for diagnostic or therapeutic purposes. The equipment used in interventional radiology looks similar to a c-arm used in the O.R. and although it differs in some aspects to regular diagnostic equipment, the X-ray beam and result in scatter are the same. Interventional radiology procedures generally require more time, up to several hours more than fluoroscopy procedures conducted in the diagnostic radiology department. Because of the length of time the technologist is exposed to the beam, working in the interventional radiology suit generally carries the greatest risk of occupational radiation exposure, up to 15 times more than general radiography. To minimize their exposure, technologists should follow all shielding guidelines and they should also be rotated between the exam room and the control room. Radiation safety and radiation therapy is quite different from radiation protection and radiography, C.T. or fluoroscopy. For treatment procedures that use live radioactive sources, the fundamental concepts of time, distance and shielding apply. But because of the very powerful X-rays used in therapeutic applications, it is not practical for a radiation therapist to spend any amount of time in the treatment room or to try to increase their distance from the source. Shielding is the only effective way for radiation therapists to protect themselves. A therapist must leave the room during the room and rely in the shielding built into the structure of the treatment room for protection. Depending on the strength of the X-ray beam being used, the thickness the walls of a radiation therapy room often exceed 3 feet of solid concrete. The thickness of the wall can be reduced if materials of higher density are used, such as lead. All members of a diagnostic radiology department may be called to assist with transferring a patient to an exam table or transporting a patient between modalities. Therefore, all technologist should understand the differences in radiation safety requirements between radiography and nuclear medicine. The machinery used in nuclear medicine does not emit radiation and poses no risk to patient or technologist. Any risk of exposure to a nuclear medicine technologist comes from radiopharmaceuticals which are radioactive isotopes combined with particular drugs to pinpoint the body part of interest. Exposure can happen either before or after the radiopharmaceuticals are administered to a patient. Radioactive isotopes are stored in special containers in a clearly marked room per NRC standards. The dosage of any particular isotope is based on it's half-life or the amount of time it will take for the radioactivity to be halved. Once the correct patient does, measured in millicuries (mCi), is calculated, the nuclear medicine technologist administers the radiopharmaceutical to the patient while following established department protocol. The radiopharmaceuticals travel through the patient's body where it is either diffused or concentrated in a particular organ or disease process, depending on the tagging characteristic of the radiopharmaceutical used for that test. The patient and it's gamma rays and beta particles that are used to produced the diagnostic image and can be a source of radiation exposure to others. Transport of the radiopharmaceutical to the patient also depends on the nature of the test. If a technologist needs to leave the nuclear medicine department to inject the patient, the syringe containing the isotope is transported in a lead lined box. The syringe may also have a lead equivalent shield to protect the hands of a nuclear medicine technologist. No one other than a technologist should handle the box or the syringe. Once the isotope is administered to the patient, the weight before the actual nuclear medicine test begins can be anywhere from 30 min to an entire day. Patients and caregivers, if present, receive explicit instructions regarding radiation safety if there is any danger of radiation exposure to others. Although there are some isotopes used in medical imaging that may take days to completely decay, most do so within a few hours to a day. Generally patient radiation exposure from a nuclear medicine test is equivalent to that of other modalities in diagnostic radiology. As with other modalities, time, distance and shielding are the best way for nuclear medicine technologists to avoid radiation exposure from a patient injected with a radioactive isotope. One hour after injection of a radioactive isotope, exposure rates at a one meter distance from the patient vary from 0.54 mrem to 1.5 mrem. A notable exception is any test that uses iodine 131 which can have a rate of up to 45 mrem per hour, depending on the dose. However, NRC regulation state that patients given a radioactive iodine only may be released from isolation if they emit less than 5 mrem per hour at a distance of 1 meter. The nuclear medicine technologist is charged with keeping personnel aware of any danger from patient exposure. It has been more than 100 years since Wilhelm Röntgen discovered most of the properties of X-rays. His medical imaging has advanced so has the need to stay up to date on the protection standards that keep our patients and ourselves safe in the medical imaging department. Educating everyone involved in medical imaging on the basics of radiation production, the damage potential for human tissue and the ways in which they can protect themselves are minimum standards that should be enforced in diagnostic imaging departments. Radiologic technologists are the experts in the medical imaging and radiation therapy departments and therefore it is the responsibility of radiologic technologists to ensure that all radiation safety policies and procedures are closely followed so that quality imaging can be performed and patient dose and occupational radiation exposure can be kept as low as reasonably achievable.

Video Details

Duration: 8 minutes and 15 seconds
Country: United States
Language: English
License: All rights reserved
Views: 49
Posted by: omar.hassan on Oct 23, 2015

Radiation_Protection_in_Medical_Imaging_(Part 6)

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