General Notes/ Overview Flashcards
What three headings can factors that increase the risk to the patient in Radiology fall under ?
- Due to radiation
- Due to contrast medium
- Due to the technique
What are the two headings of radiation effects on humans and their definitions ?
- Hereditary - revealed in the offspring of the exposed individual
- Somatic - suffered by the exposed person
What two groups can somatic effects of radiation be divided into ? (Explain each)
- Deterministic - results in loss of tissue function (eg. Skin erythema and cataracts). If distributed over period of time, tissue repair is allowed (greater tolerance than if it was given at once)
- implies threshold dose
So above a certain limit tissue will be damaged due to radiation exceeding capabilities of cell repair mechanisms.
- Stochastic — refers to random modifications to cell components like DNA (can occur at any radiation dose)
- implies no threshold
(cancer produced by small dose is same as that produced by a high dose, but frequency of occurrence is less with a small dose)
With comparatively low doses, how is the risk of radiation induced cancer and hereditary disease assumed to increase?
Linearly with increasing radiation dose, with no threshold dose
(Linear no threshold model)
What are the most important factors which influence the risk of developing cancer after exposure to ionizing radiation?
- Genetics - mutations and family history
- Age at exposure - children more radiosensitive than adults
- Gender - slight increased risk in females
- Fractionation (separation into different portions- characterized by dose per exposure and number of times exposed )and protraction (the longevity - total duration of exposure ) of exposure -
- The higher dose and dose rate increase the risk due to influence of DNA damage
What are the legal regulations which guide the use of diagnostic radiation?
- Justification that a proposed examination is of net benefit to the patient (eg. Pregnant-teratogenic and carcinogenic effects to the fetus - risk depends on GA and absorbed dose)
- ALARP - dose should be kept ‘As Low As Reasonably Practicable’ with economic and social factors being taken into account
When is the developing fetus most vulnerable to radiation effects on the CNS ?
Between 8 to 15 wks GA
Exposure to ionizing radiation doses of less than how much units has not been shown to be associated with teratogenic risk?
50 mGy (milligray - one thousandth of a Gray or 0.1 rad)
What is the risk of the general population developing childhood cancer for an exposure of 30 mGy ?
1 in 500
What is the amount of mGy that most diagnostic procedures will lead to fetal absorbed dose of, not irradiating the maternal/pelvis vs doing so or using nuclear imaging ?
1 mGy vs < 10 mGy
What are the four groups a female of reproductive age should be assigned to for an exam in which the primary beam irradiates the pelvic area or a procedure involving radioisotopes ?
(After she is asked if she is or might be pregnant or if her menstrual period is overdue)
- No possibility of pregnancy - Proceed with examination
- Definitely or probably pregnant - consider if justified , decide if to defer until after delivery if doesn’t cause greater risk to fetus, keeping in mind that benefit to mother might indirectly benefit fetus. If justified to keep fetal dose to minimum consistent with diagnostic purpose
- Low-dose examination, pregnancy cannot be excluded - fetal dose likely < 10 mGy. If menses not overdue- proceed, if overdue - treat as probably pregnant
- High-dose examination, pregnancy cannot be excluded - fetal dose > 10 mGy eg. CT maternal abdomen/pelvis - may double risk of childhood cancer after 3-4 wks GA. Small risk still if earlier.
What are the two courses that can be adopted to minimize the likelihood of inadvertent exposure of an unrecognized pregnancy (with high dose exam)
- Females of childbearing potential can always be booked for these exams during the first 10 days of their menstrual cycle, when conception is unlikely to have occurred.
OR
- They are booked in the normal way but are not examined and rebooked if, when they attend, they are in the ( second half of their menstrual cycle and in whom pregnancy cannot be excluded)
If a radiation examination is deemed necessary in pregnancy what is important to practice?
Evaluation of the fetal dose and associated risks by a medical physicist should be arranged.
A technique that minimizes the number of views and absorbed dose of the examination should also be utilized as long as the quality of the exam is not reduced to a level where the diagnostic value is impaired
Which 4 categories of people do clinical radiologists carry a responsibility for the protection from unnecessary radiation?
- Patients
- Themselves
- Other members of staff
- Members of public (incudes relatives and carers)
What are the types of consent that a patient may take for radiological procedures?
- Implied consent - very low risk procedures - patient actions at the time indicate consent
- Written consent - must for procedures with significant risk
- Expressed consent - intermediate risk procedures eg. Barium enema - verbal or written
What does ability to consent depend on?
To understand :
- nature of investigation
- purpose of investigation
- possible consequences of investigation
- possible consequences of non investigation
How can excessive bowel gas be reduced prior to a radiological exam ?
- By keeping the patient ambulant before the exam
- If the patient routinely takes laxatives, by informing them to continue to do so
What factors should be considered in preparing a patient for a radiological procedure?
8 factors - PWH CARB
- Hospital admission needed or not
- Woman of childbearing age
- Consent
- Anticoagulant therapy in the case of IR procedures that carry risk of bleeding
- Bowel preps to cleanse bowel needed or not
- Review of prior imaging and notes
- Premedication
Why is it important to still review if patients are being treated with new anticoagulants such as factor Xa inhibitors when. rivaroxaban (Xarelto) vs warfarin?
Because their anticoagulant effects are unreliable reflected in assays of clotting time
What are the purpose of preliminary images?
- To make final adjustments in exposure, centering, collimation and patient position
- To exclude prohibitive factors such as residual barium from a previous examination or excess faecal loading
- To demonstrate, identify and localize opacities which may be obscured by contrast medium
What concentrations of what solutions can be used for aseptic technique?
0.5% chlorhexidine in 70% industrial spirit (denatured alcohol) or its equivalent 5% povidone -iodine (Betadine) less toxic and similar effectiveness than 10%