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%
What is the most common percentage of lidocaine used for radiological procedures ?
1 % (10 mg of lidocaine/ ml) - 1% of 1,000 mg
When is gonad protection not used for a radiological procedure?
When it obscures the region of interest
What headings can complications in radiological procedures be classified under?
- Due to anaesthesia
- Due to contrast medium
- Due to the technique
What categories can complications due to anesthesia be divided into ?
- Complications from GA
- Complications from local anaesthesia:
- toxic
- allergic (rare)
What is the recommended dose of lidocaine for local anaesthesia per patient, the onset and duration of action ?
Lidocaine:
3 to (4.5 mg/kg infiltrated /SC but up to 4 mg/kg IV regional) (but not to exceed 300 mg for anyone)
- (Max 2400 mg/24 hr- medicine.uiowa.edu
- so for a 70 kg person stick to maximum of 4 mg
Up to 7 mg/kg with epinephrine infiltration (not to exceed 500 mg)
Onset of action - 1-3 min by infiltration, 3-5 min topically
Duration of action: 30 min to 2 hrs (2 hrs to 4 hrs with vasoconstriction)
What is the recommended dose of bupivacaine per patient for local anesthesia, the onset and duration of action ?
Bupivacaine:
2 to 2.5 mg/kg infiltrated (but not to exceed 175 mg for anyone)
- (Max 400 mg/24 hr- medicine.uiowa.edu
2.5 - 3 mg/kg with epinephrine infiltration (not to exceed 225 mg)
Onset of action - 2-10 min by infiltration, not routine topical
Duration of action: 2 hrs to 2 hrs 45 min (3 hrs to 8 hrs with vasoconstriction)
What are the signs of local and systemic lidocaine (local anaesthetic) toxicity, how soon does it start and how do you prevent and treat it?
Manifestations typically appear 1-5 mins after injection. But can start from 30 seconds to an hour. Initial signs also vary.
Local:
- Irreversible conduction block within 5 mins
- Prolonged sensory and motor deficits ( low pH and sodium busulfite may cause)
- Reversible skeletal muscle damage
Systemic:
- CNS - early: circumoral/tongue numbness, metallic taste, lightheadedness, dizziness, visual/auditory disturbances, difficulty focusing, disorientation, drowsiness
CNS - late - CNS depression - muscle twitching to convulsions- tonic cloning to unconsciousness to coma to respiratory depression and arrest
CVS - usually precedes CNS symptoms put can be isolated (greater risk with lipophilic anaesthetic such as bupivacaine) -
lightheadedness, chest pain, SOB, palpitations, diaphoresis, hypotension, effects on cardiac conduction, syncope to CVS depression and collapse
Haematologic - cyanosis, skin discoloration, tachypnea, dyspnea, fatigue, dizziness, syncope weakness, exercise intolerance
Vs
Allergic- rash, urticaria,
anaphylaxis (wheezing, respiratory distress)
- Similar effects with Bupivacaine - but minimum toxic dose is lower at 1.6 mg/kg vs 6.4 mg/kg with lidocaine.
Similar effects with other agents also
Treatment:
- ABCs
- American Society of Regional Anesthesia and Pain Medicine (ASRA) guidelines recommend considering the use of lipid emulsion therapy at the first signs of systemic toxicity from local anesthetics, after airway management.
Lipid emulsion therapy is performed with a 20% solution.[35] The 2020 ASRA guidelines state that the order of administration (bolus or infusion) and the method of infusion are not critical. For patients who weigh less than 70 kg, administer a bolus of 1.5 mL/kg over 2 - 3 minutes.[36, 13, 2] or an infusion at a rate of 0.25 mL/kg/min.[2] For patients weighing < 40 kg, consider using a pump for infusion. For patients who weigh more than 70 kg, administer a bolus of 100 mL over 2-3 minutes or an infusion of 250 mL over 15-20 min.
(Keep in mind has own adverse effects) - CNS - Benziodiazipines to abort seizures
- CVS - ACLS guidelines - amoidarone for ventricular arrhythmias
- Allergies - mild skin reactions :DPH IV or oral 25 to 50 mg for adults 1 mg/kg for children. serious allergic reactions, administer subcutaneous epinephrine (0.3 mL of 1:1000 dilution) and closely monitor for further decompensation. Corticosteroids (125 mg methylprednisolone IV push, or 60 mg prednisone orally) should be given to the patient with severe allergic reactions (eg, respiratory distress, hypotension).
Prevention:
A careful injection method may help prevent toxic reactions. Perform high-volume (> 5 mL) injections slowly, in 3-mL increments. Stop to aspirate and observe for blood in the syringe after every 3 mL injected. Injecting local anesthetic in this manner reduces the chances of a large-volume intravascular injection.
What is the most frequent radionuclide used in nuclear medicine?
99m TC (metastable nuclear some of technetium-99- a 140 Kev gamma emitting radioisotope of the element technetium with a t 1/2 of 6 hrs
*Kev - electron volt
: a unit of energy equal to the energy gained by an electron in passing from a point of low potential to a point one volt higher in potential : 1.60 × 10−19 joule
What units are used to quantify radioactivity ?
SI unit - Megabecquerel (MBq)
Old - Millicuries (mCi)
1 mCi = 37 MBq
What are radiation doses quoted as ?
As the adult effective dose (ED) in millisieverts (mSv)
What is the resolution of gamma camera images critically dependent on?
The distance of the collimator surface from the patient , falling off approximately linearly with distance
What can monitor and possibly correct for movement artifact on SPECT CT?
Point marker sources attached to the patient away from areas being examined
What factors can affect image acquisition times in radionuclide imaging ?
- The sensitivity of the equipment
- The amount of activity injected
- The size of the patient
Compromise between time available, counts required for diagnostic imaging and ability of the patient to remain motionless
What are the most likely radionuclide substances to cause complications?
- Blood products
- Antibodies
- Substances of a particulate nature
What dose of 300 mg Iodine/mL contrast is used for the head?
50 mL
What dose of 300 mg Iodine/ml contrast is used for the chest or abdomen ?
100 mL
What are the scan times for each CT phase:
- Early arterial : 15 - 25 seconds post injection or immediately post bolus tracking (chest) - avg 20 seconds
- Late arterial : 30 - 40 seconds post injection or 15 - 20 seconds post bolus tracking (abdomen/pelvis) - avg 30 seconds - 35-40 seconds UHWI, 35 seconds routine venous phase for chest
- Portal venous (Hepatic/late portal) - 70 - 90 seconds post injection or 50 - 70 seconds post bolus tracking - avg 60 seconds - 65-70 seconds UHWI
- Nephrogenic - 85 - 120 seconds post injection or 80 seconds post bolus tracking - 80-100 seconds UHWI
- Delayed (excretory) 5/6 - 10 minutes post injection or 6-10 minutes post bolus tracking - 5 - 10 mins UHWI
- PE and aorta studies - bolus tracking
CTPA- ROI tracker place in pulmonary trunk or right atrium, when threshold of 150 HU is reached, patient is asked to breath in and the scan is started immediately
What is the use of saline chasers when administering IV contrast?
- Allows smaller volumes of contrast to be used
- Increases peak contrast enhancement
- Reduces streak artifact - eg. Thoracic scanning from the brachiocephalic veins and right side of the heart
What is the maximum total iodinated contrast dose that should be observed in children ?
2 mL/kg body weight (300 mg I/mL)
What causes comparable image noise in acquisitions performed at lower kilovolts?
- Volume-based reconstruction
- Greater detector fidelity
- utilizes the attenuation characteristics of the k-edge of iodine when paired with higher milliampere tube currents - allows lower contrast concentrations
What causes comparable image noise in acquisitions performed at lower kilovolts?
- Volume-based reconstruction
- Greater detector fidelity
- utilizes the attenuation characteristics of the k-edge of iodine when paired with higher milliampere tube currents - allows lower contrast concentrations
What volume of oral contrast medium should be diluted in what quantity of liquid?
20 ml medium (eg. Water soluble Urograffin 150 in 1 L orange squash and preflavoured Gastromiro in 1 L water)
- low density barium suspensions 2% w/v can also be used
What are the timing and volumes of oral contrast medium used in CT?
Adult
- Full abd/pel - 1000 ml gradually over 1 hr before scan
- Upper abdomen (eg. Pancreas) - 500 ml gradually over 30 min before scan
Child - To drink full dose 1 hr before scan then further half dose immediately prior scan
- Newborn - 60-90
- 1 month to 1 year - 120-240
- 1 year to 5 years - 240-360
- 5 years to 10 years - 360-480
- Over 10 years like adult
If large bowel needs to be opacified - start drinking night before or after t least 3-4 hrs before scan
What are the potential hazards of MRI to patients and staff?
Those due to:
- Electromagnetic fields :
-static magnetic field - strength measured in gauss or Tesla (T), 1 gauss = 10,00 Tesla. Earth’s magnetic field = 0.6 gauss
- biological effects
- temporary ECG changes (electrodynamic forces on moving ions in blood vessels)
- vertigo, nausea > 2 T
- nonbiological effects
- ferromagnetic materials (high susceptibility to magnetization) - may undergo rotational or translational movement (loose objects accelerated by the field (missile effect) - due to it trying to align with the magnetic field . POS op fibrosis > 6wks usually strong enough to anger iatrogenic placed materials.
- Electrical devices - cardiac pacemakers - most modern ones have sensing mechanism that can be bypassed by a magnetically operated relay triggered by a field as low as 5 gauss - must not enter controlled area. MRI conditional pacemakers are now available - still take care
-gradient magnetic field -
- biological effects
rapidly switched magnetic gradients used in MRI can induce electric fields in patients which may stimulate nerves or muscles (strength depends on rate of the field and size of the subject) - threshold for peripheral nerves lower than heart and brain
Therefore system must not have a gradient output that exceeds limit for peripheral nerve stimulation (which would also protect brain and prevent cardiac fibrillation) - can be intolerable and cause exam to end
- nonbiological effects
Rapidly varying fields can induce currents in conductors which can cause metal objects to heat up rapidly and cause tissue damage - partial to full thickness burns when conducting loops (ECG electrodes or surface imaging coils) come into contact with skin
-radiofrequency field - cause energy to be deposited throughout the blood as heat (avg - specific absorption rate - SAR) - areas of concern are hypothalamus and portly perfumed - lens of eye. Body temperature to not exceed 1 degree C, 0.5 in infants and circulatory impaired. Head < 38 C, Trunk < 39, Limbs < 40
- Noise - vibration of gradient coils and other areas of scanner due to varying magnetic fields. Amplitude depends on strength of magnetic field, pulse sequence and scanner design. Levels as high as 95dB, above statutory noise limits in industry (earplugs/headphones in most cases used)
- Inert gas quench - with superconducting magnets - coolant gases, liquid helium and liquid nitrogen could vaporize if the temperature accidentally rises - this potentially could lead to asphyxiation or exposure to extreme cold
Prevention - well-ventilated room with oxygen monitor to raise an alarm
- Claustrophobia
- IV contrast agents
What is the difference between MRI safe and MRI conditional
- MRI safe - no known hazard in all MRI environments
- MRI conditional - no known hazard in a specified MRI environment with specified conditions of use
What are the MRI zones ?
Zone 1 - Lobby
Zone 2 - Patient waiting area
Zone 3 - Control and equipment rooms
Zone 4 - Magnet room
Restricted - 5 gauss line
Controlled - Closer to scanner - 10 gauss line
- get rid of ferromagnetic materials - paper clips, pens, watches, credit cards, magnetic tape, wheelchairs,trolleys, specially adapted cleaning equipment, fire extinguishers, anaesthetic/monitoring equipment should be non ferromagnetic
What will increase the SAR and thus radiofrequency energy deposited as heat on the fetus in MRI?
- Increased static magnetic field strength
- Increased flip angle
- Increased number of radio frequency pulses
- Decreased spacing between pulses
What trimester of pregnancy should you avoid MRI unless an alternative would involve ionizing radiation and what area should pregnant staff be informed to stay outside of and what fields to avoid?
- First trimester
- 10 gauss line and avoid gradient and RF fields
What can allow optimal assessment of the gallbladder in ultrasound?
- Tell the patient to fast for 6-8 hrs so that the gallbladder can be dilated
What can help detailed assessment of the pancreas on ultrasound?
- Clear fluid filling the stomach to act as an acoustic window
What can help visualize pelvic contents optimally on ultrasound?
- Bowel gas must be displaced - facilitated by filling the urinary bladder to capacity, which acts as an acoustic window
- The patient should be told to drink 1 to 1.5 L of water during the hour
before scanning and to not empty their bladder. - oral intake of clear fluids will not promote gallbladder empty and so pelvic exams can often be combined with abdominal exams
What does it mean if dilation of the renal collecting system persists after a patient empties their bladder as noted on ultrasound?
The renal collecting system dilation is significant
How do you prepare a patient for yransesophageal echocardiography or examination of the oesoohagus ?
- Appropriately starved
- personal operator preference - anaesthesia and sedation - 10% lidocaine spray for the pharynx . 200 mg max. IV BZD maybe.
- Inform to avoid hot food and drink until anesthesia worn off (1-2 hrs) to avoid heat injury and potential aspiration
