Contrast & Dosimetry Flashcards
(81 cards)
1
Q
How is CTDI calculated?
A
CTDIvol = CTDIw / Pitch
2
Q
How is DLP calculated?
A
DLP=CTDIvol x Scan Length
3
Q
Define absorbed dose
A
The amount of energy deposited by radiation in a mass
4
Q
What unit is absorbed dose measured in?
A
mGy
5
Q
Define equivalent dose
A
Dose calculated for individual organs based on absorbed dose to a single organ
6
Q
What unit is equivalent dose measured in?
A
mSv
7
Q
Define effective dose
A
Dose calculated for body adjusted to account for the sensitivity of organ to tissue weighting factors
8
Q
What unit is effective dose measured in?
A
mSv
9
Q
What is the Australian DRL for CT Brain?
A
880 DLP mGy
10
Q
What is the Australian DRL for CT Neck?
A
450 DLP mGy
11
Q
What is the Australian DRL for CT Chest?
A
390 DLP mGy
12
Q
What is the Australian DRL for CT Abdomen?
A
600 DLP mGy
13
Q
What is the effective dose for CT Brain?
A
2 mSv
14
Q
What is the effective dose for CT Chest?
A
1-8 mSv
15
Q
What is the effective dose for CT Abdomen?
A
10-14 mSv
16
Q
Name 7 scanner design factors that influence patient dose
A
Beam filtration, beam shaper, beam collimation, detector array, data acquisition system, spiral interpolation, adaptive filtration
17
Q
Name 8 clinical application factors that influence patient dose
A
kVp, mAs, tube current modulation, pitch, scan range, patient factors, image reconstruction, pathology
18
Q
What is the threshold of an embryo or fetus to expect detrimental radiation effects
A
100 mSv
19
Q
What scanning selection factor has the biggest influence on patient dose?
A
kVp
20
Q
Does kVp affect contrast or brightness?
A
Contrast
21
Q
Is the photoelectric effect likely to occur at higher or lower energies?
A
Higher
22
Q
How does mA effect dose?
A
mA has a linear affect on radiation dose
23
Q
How is effective mAs calculated?
A
Eff mAs = ratio of tube current to pitch
24
Q
What is k-edge?
A
The energy required to eject a k shell electron
25
What is the k-edge of iodine?
32kEv
26
What is the approximate average energy of the beam?
1/3 kVp
27
What is a linear attenuation co-efficient?
A constant that describes the fraction of attenuated incident photons in a monoenergetic beam per unit thickness of a material which is used to calculate hounsfield units
28
Describe ionic contrast
Ionic contrast dissociates in water and has high osmolality. It dissociates into 2 molecular particles resulting in higher risk of reaction
29
What is the molecular structure of ionic contrast?
Monomer
30
Describe non-ionic contrast
Non-ionic contrast does not dissolve into charged particles when entering the bloodstream with less chance of reaction
31
Describe low osmolar contrast and its molecular structure
Low osmolar contrast is a monomer with increased solubility in water
32
Describe iso osmolar contrast and its molecular structure
Iso osmolar contrast is a dimer that does not dissociate in water
33
What is a monomer?
A molecule that can be bonded to other identical molecules to form a polymer (single benzene ring)
34
What is a dimer?
A molecular complex consisting of two identical molecules linked together (double benzene ring)
35
What is the viscosity of Ultravist 370 @ 20 degrees?
22mPa.s
36
What is the viscosity of Ultravist 370 @ 37 degrees ?
10mPa.s
37
What is concentration of iodinated contrast expressed? Give an example
Concentration is expressed as milligrams of iodine per millilitre e.g Omnipaque 300 has 300mgI/mL
38
Define osmolality
The concentration of a solution expressed as the total number of solute particles per kg
39
What is the osmolality of blood?
275-295 mosm/kg
40
What is the osmolality of Ultravist 370?
770 mosm/kg
41
What is the osmolality of Visipaque 320?
290 mosm/kg
42
What is the osmolality of ionic contrast?
1220-1690 mosm/kg
43
What are the contraindications of oral contrast?
Perforation, GI bleed, allergy
44
What are the contraindications for IV contrast?
Previous allergy and assessment of severity of reaction, egfr below 30
45
What is contrast induced nephropathy?
Impairment of renal function with elevation of serum creatinine >25% from the baseline within 48 hours
46
What are the risk factors for CIN?
Known renal insufficiency, diabetes, malignancy, >65 years old, use of NSAIDs
47
What is eGFR?
Estimated glomerular filtration rate. How well the kidneys filter waste from the blood and is indicative of kidney damage
48
eGFR has not been accurately established in which groups?
Malnourished, amputees and frail patients
49
Which group is most at risk of CIN?
eGFR <30mL/min
50
What is the association of IV contrast and asthma?
This group experiences a 6x increased risk of hypersensitivity to reaction and is high in those with unstable disease
51
What is the association of IV contrast and beta blockers?
May increase severity of reaction
52
What is the association of IV contrast and hyperparathyroidism?
If TSH is abnormal but T3 and T4 are normal contrast can be administered. These patients cannot have radioactive thyroid treatment 8 weeks pre/post IV contrast
53
What is the association of IV contrast and sickle cell disease?
May experience temporary worsening pain
54
What is the association of IV contrast and pregnancy?
Infants born to patients who have had IV contrast during pregnancy should have heel prick test for neonatal hyperthyroidism
55
What is the association of IC contrast and breastfeeding?
No cessation of breast feeding or discarding required
56
What is the association of IV contrast and phaeochromocytoma?
None
57
What is the association of IV contrast and Myasthenia Gravis?
Possibility of worsening symptoms e.g. breathing difficulties
58
What is the association of IV contrast and Interleukin -2 (IL-2) immunotherapy?
Risk of delayed anaphylactic reaction if therapy has been within the past 6 months
59
Define anaphylaxis
A generalised allergic reaction which often involves more than one body system (e.g. skin, respiratory, gastrointestinal, cardiovascular) and can rapidly become life threatening
60
What is the chance of a severe reaction to IV contrast?
1 in 100,000
61
What is the chance of a fatal reaction to IV contrast?
1 in 170,000
62
What are the signs of a minor reaction?
Flushing, nausea, pruitus (itch), vomiting, headache, mild uritcaria (rash)
63
What treatments can be given for a minor reaction?
Non-sedating antihistamines (urticaria), anti-emetics (vomiting)
64
What are the signs of a moderate reaction?
Severe vomiting, marked urticaria, bronchospasm, other respiratory symptoms, facial/laryngeal oedema, vasovagal
65
What treatments can be given for a moderate reaction?
Non-sedating antihistamines and adrenaline (urticaria)
Adrenaline, salbutamol, oxygen (6-10L) (other symptoms)
Remain supine if possible and elevate legs, hartmanns IV (hypotension or vasovagal)
66
What are the signs of a severe reaction?
Hypovolaemic shock (rapid loss of blood or fluid), respiratory arrest, convulsions, cardiac arrest
67
What treatments can be given for a severe reaction?
Adrenaline, IV fluids, other drugs as required
| Remain supine, sit up (dyspnea), oxygen 6-10L, maintain airway and suction, ECG, observations
68
What is the time frame for a delayed contrast reaction?
1 hour to 1 week
69
What are the signs of a delayed reaction?
Maculopapular rash (hives), angioedema, urticaria, erythema, painful salivary gland swelling
70
What is the recommended pre-medication?
13 hours before: 50mg prednisolone
1 hour before: 25mg prednisolone
1 hour before: 25mg phenergen
1 hour before: 40mg cimetidine
71
What IV lines cannot be used for contrast administration?
PICC lines (not pressure rated), CVC
72
What IV lines can be used for contrast administration?
Power PICC, portacath
73
What is thyrotoxicosis?
Increased secretion of thyroid hormones due to IV contrast administration with hyperparathyroidism developing over the following 2-12 weeks
74
What groups are at risk of CT thyrotoxicosis?
Graves disease, multinodular goitre, elderly and endemic iodine deficiency
75
Although kV and dose is not linear, how are they related?
Dose is approximately the square root of the kV
76
What is the photoelectric effect?
Absorbed x-ray photons interact with inner shell electrons
77
How is the photoelectric effect proportional to kV?
Inversely proportional to third power of the kV (1/E)^3
78
How is the photoelectric effect proportional to the atomic number?
Directly proportional to the third power of the atomic number (Z^3)
79
How should mAs be modified from adult to newborn in CT brain?
Reduced a factor of 2-2.5
80
How should mAs be modified from adult to newborn in CT body?
Reduced by a factor of 4-5
81
When taking into account less intra-abdominal fat in paediatrics when can the mAs be halved?
For each 4-6cm reduction in body diameter
