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Modalities > CT > Flashcards

CT Flashcards

1
Q

name 3 types of contrast media used

A
  • oral
  • intravenous
  • air or CO2
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2
Q

what is the use of contrast media?

A

to assist in providing visual representations of information from within the body

aid in providing additional information

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3
Q

why is iodinated contrast media used?

A

iodine has high atomic number –> ability to absorb X-ray

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4
Q

what are the 4 basic principles of contrast media

A
  • iodinated CM
  • osmolarity and viscosity of CM
  • ionicity of CM
  • properties of an ideal CM
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5
Q

describe osmolality of CM

A

measurement assessing the number of particles dissolved in 1kg of water

osmolality of CM should be as close as possible to human plasma (300 mOsm/kg H2O)

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6
Q

what are the 3 classifications of CM osmolality

A
  • high osmolar (1000- over 2400 mOsm/kg H2O; 5-8x)
  • low-osmolar (900 mOsm/kg H20; 3x)
  • iso-osmolar (290 mOsm/kg H2O)
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7
Q

explain osmolar toxicity

A

when too high osmolar CM is given, fluids in patient’s cell leave the intracellular compartment and enter the extracellular space –> causing cell shrinkage –> crenation of RBC –> impaired cell functioning

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8
Q

describe viscosity of CM

A

a measure of friction or resistance of liquid to flow

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9
Q

factors affecting viscosity of CM

A

size and shape of solute particle
temperature

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10
Q

describe ionicity of CM

A

property of a molecule to break into positively charged cations and negatively charged anions

presence of ionicity: ionic
absence of ionicity: non-ionic

ionic contrast can disturb the normal dynamic ionic equilibrium of the body

ionic toxicity can affect physiological processes such as heart rate, BP and neurotransmission

therefore, non-ionic CM are preferred

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11
Q

how many iodine atoms are in a benzene molecule

A

3 (tri-iodinated benzenes ring)

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12
Q

how to differentiate between ionic and non-ionic CM molecular structures

A

ionic molecular structures will contain ions at the R-group, showing positive and negative charges

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13
Q

describe the distribution of CM

A
  • ICM does not cross cellular membrane easily, and is primarily distributed in the bloodstream
  • pathological tissue contains membranes that are less obstructive, thus more permeable to ICM (allow CM to enter the cell)
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14
Q

describe neurotoxicity of ionic CM

A
  • may cause seizures in susceptible patients
  • high risk of neurotoxicity in patients with disrupted BBB
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15
Q

properties of an ideal CM

A
  • water soluble
  • biologically inert
  • low viscosity
  • non-ionic
  • low or iso-osmolar
  • increase sensitivity and enhance differentiation of different soft tissues
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16
Q

4 types of risk associated with IV contrast scan

A
  • adverse reactions
  • contrast induced nephropathy (CIN) or contrast induced acute kidney injury (CIAKI)
  • metformin induced lactic acidosis
  • extraversation
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17
Q

probability of acute adverse reaction event occurring with high osmolar CM

A

5-15%

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18
Q

probability of acute adverse reaction event occurring with low osmolar CM

A

0.2-0.7%

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19
Q

probability of severe adverse reactions occurring with low osmolar CM

A

0.04%

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20
Q

how long does it take for the reactions to take place

A

manifest <1hour
can start to manifest within 5 mins after contrast injection
majority of the life-threatening events <20mins

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21
Q

what are some of the mild reactions signs and symptoms

A
  • vomiting
  • warm feeling
  • urtcaria
  • nausea
  • headache
  • sweat
  • cough
  • itching
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22
Q

what are some of the moderate reaction signs and symptoms

A
  • tachycardia
  • bradycardia
  • hypertension
  • hypotension
  • dyspnea
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23
Q

what are some severe reaction signs and symptoms

A
  • convulsions
  • cardiac arrest
  • unresponsiveness
  • profound hypotension
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24
Q

risk factors for adverse reactions

A
  • previous history of adverse reaction to CM
  • hx of allergic rxn that required medical intervention
  • hx of asthma
  • hx of significant cardiac diseases
  • multiple drug allergy
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25
Q

what is the usual premedication for adverse reaction

A

prednisolone 30mg 12hours and 2hours before CT scan

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26
Q

what is given for premedication for adverse reaction in the event of emergency

A
  • if scan can wait, prepare IV hydrocortisone 100/200mg every 4 hours until time of scan; with/without IV diphenhydramine 50mg 1hr prior to scan
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27
Q

risk factor for CIN

A

eGFR + :
- age >60
- hx of kidney disease as an adult, including tumour and transplant
- family hx of kidney failure
- diabetes treated with insulin or other prescribed med
- hypertension
- paraproteinemia syndromes or disease (eg myeloma)
- current use of nephrotoxic medications

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28
Q

metformin use for ICM

A
  • eGFR >45 - continue metformin
  • eGFR >30 - stop metformin 48hrs before CM injection and resume after 48hrs in the absence of deteriorating renal function
  • eGFR<30 - metformin is contraindicated and should be avoided
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29
Q

how does body weight affect iodine dose

A

body weight increase = iodine concentration decrease

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30
Q

how does cardiac output affect the arterial peak enhancement

A

poorer CO = longer time for heart to pump = peak gets pushed back

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31
Q

how does contrast volume affect the iodine concentration

A

contrast volume increase = iodine concentration increase

contrast volume increase = longer time to inject CM = peak gets pushed back

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32
Q

how does injection flowrate affect iodine concentration

A

injection FR increase = iodine flux increase = iodine peak is higher

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33
Q

characteristic of saline chaser

A
  • pushes contrast in tubing and peripheral veins into central veins
  • allows reduction in contrast vol
  • increases peak attenuation
  • reduced streak artifacts from veins and right heart
  • simpler to implement with dual head injectors
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34
Q

what are some patient preparation for IV contrast scan

A
  • risk of physiologic and allergic-like adverse reactions
  • premedication for adverse reactions
  • risk of CIN
  • fasting
  • IV cannula
  • metformin induced lactic acidosis
  • explained risk of extravasation
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35
Q

what is included in a CT protocol

A
  • region/scan range
  • any use of contrast
  • phases/sequences
  • scan details
  • recon details/phases
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36
Q

difference between epidural hematoma and subdural hematoma

A

epidural hematoma:
- occurs between the skull and dura mater
- convex shape

subdural hematoma:
- occurs between the dura mater and the arachnoid
- concave shape

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37
Q

how does infarction appear on CT

A
  • appears hypodense
  • due to disruption of blood supply to the brain
  • causing necrosis
  • brain tissue replaced by fluids
38
Q

how does bleed appear on CT

A
  • acute bleeding appears white and overtime becomes less dense, eventually shrinking
39
Q

describe the patient positioning for a brain CT scan

A
  • remove any metals from head
  • supine
  • head first
  • chin angled down slightly to bring orbits away from radiation
  • arms by patient side
  • velcro straps or pads used to immobilise head
40
Q

what is a localiser radiograph

A
  • needs to be performed first
  • to plan scan range and FOV
41
Q

what needs to be included in a brain CT

A

brain stem
- medulla, pons, midbrain

limbic system
- diencephalon (thalamus and hypothalamus)

cerebellar

cerebrum

42
Q

how does mA, kV, pitch and rotation time affect radiation dose

A
  • increase mA and kV = increase radiation dose
  • increase pitch = table move faster = decrease scan time = decrease radiation dose
  • increase rotation time = increase radiation dose
43
Q

what are the differences between thin and thick slices

A

thin:
- acquired when reformatted images required
- provide excellent definition of the temporal bones, pituitary fossa, focial bones and foramina
- improve spatial resolution
- decreased SNR –> require increase in mAs and kV = increase radiation dose

thick:
- increase the definition of gray and white matter in the brain
- used to improve visualization of herniated lumbar disk in larger patients

44
Q

what is the window width and window level for bone and brain window

A

brain window:
WW80-150/WL40

bone window:
WW2000-4000/WL300-400

45
Q

what is the formula to calculate the upper and lower grey level

A

WL +/- (WW/2)

46
Q

what are some indication for CT orbits

A

plain:
- foreign body
- trauma

contrast:
- tumour

47
Q

what are some indications for CT temporal bone

A

plain:
- loss of hearing
- otalgia
- acute otitis media
- cholesteatoma
- trauma
- tinnitus (non pulsating)

contrast:
- glomus tumour
- malignant otitis externa
- tinnitus (pulsating)

48
Q

what should be included in the scan range in CT orbits

A

roof of orbit, floor of orbit and zygoma

49
Q

what are the advantages of orbital CT imaging

A
  • radiopaque FB accurately localised
  • improved characterizing of orbital mass lesions
  • allows imaging in multiple planes
50
Q

what are some indications for CT neck/C-spine

A

plain:
- trauma/ degenerative changes
- ? FB (contrast if necessary)

contrast:
- infection
- tumours/masses
- abscess
- nodule
- vocal cord paralysis

51
Q

what is the scan range for neck/C-spine

A

base of skull to level of T4

52
Q

why is the scan range up to the level of T4

A

to include nasophraynx, oropharynx and laryngopharynx + lymphatic system of the neck

53
Q

what are the 4 types of scan for a CT chest/thorax

A
  • non-contrast
  • arterial
  • venous
  • delayed
54
Q

patient postioning for CT chest/thorax

A
  • remove any metal from the thorax
  • supine
  • head/feet first
  • arms above head
  • velcro straps or pads can be used to immobilise patients or stop from falling off the table
  • breathing instructions
55
Q

what is the scan range for a CT chest/thorax

A

apex of lungs to adrenal gland or mid kidney

56
Q

what are some indications for a CT chest/thorax

A

plain:
- ?FB

contrast (venous):
- persistent cough
- hemoptysis
- dyspnea
- chest pain
- pneumonia
- mediastinum indications
- metastasis

57
Q

what should be included in a CT thorax

A
  • thoracic cage
  • sternum
  • lungs
  • hilum of lungs
  • bronchus
  • mediastinal compartments
  • thymus glands
  • lymph nodes
  • pulmonary vessels
  • SVC tributaries
  • adrenals
58
Q

what indication will require the use of a high resolution CT

A

interstitial lung disease (ILD)
- to detect and characterise disease affecting the pulmonary parenchyma and airways

59
Q

why HRCT

A
  • ability to detect lung disease in symptomatic patients with a normal CXR
  • provide more specific diagnosis or exclude certain disease in patients with non-diagnostic findings on CXR
  • ability to detect or evaluate specific problems or diagnoses
60
Q

what are the 4 common types of ILD

A
  1. tree in bud
  2. ground glass opacity
  3. consolidation
  4. brochectasis
61
Q

what is tree in bud

A

it represents dilated and impacted (mucus or pus filled) bronchioles

62
Q

what is ground glass opacity

A
  • filling of the alveolar spaces with pus, edema, hemorrhage, inflammation or tumour cells
  • thickening of the interstitium or alveolar walls
63
Q

what is consolidation

A

when the air that usuallly fills the small airways in the lungs is replaced with something else

64
Q

what is bronchiectasis

A

localised bronchial dilatation
- signet-ring sign
- bronchial wall thickening
- visibility of airways in the peripheral lung
- mucus retention in the bronchial lumen

65
Q

why are some CT chest done in prone instead of supine

A

essential in the context of distinguishing dependent density (atelectasis) from pulmonary inflammation or fibrosis-atelectasis detected on supine scan

66
Q

what are some indications for CT abdomen

A

plain:
- ?FB

contrast:
- ?metastasis
- abdo pain / IO
- inflammation/ infection/ abscess
- appendicitis
- LOW/LOA
- sepsis

67
Q

patient positioning for CT Abdomen

A
  • remove any metals from the abdo pelvis
  • supine
  • head/feet first
  • arms above head
  • velcro straps or pads can be used to immobilise patients or stop from falling off the table
  • breathing instructions
68
Q

what is oral CM used for

A

to provide adequate distention of bowel loops

69
Q

why need to administer OCM

A
  • absence of OCM can result in under-distended bowel loops which can give false impression of a mass lesion or mask lesion
  • optimal differentiation of lymph nodes from bowel loops becomes difficult without bowel distention
70
Q

what are the 3 different types of OCM

A

neutral/gray - water
white - barium or iodine
black - air

71
Q

benefit of neutral/gray OCM

A
  • allow assessment of luminal pathology (within) and bowel wall
  • excellent for upper GIT if scanned at appropriate time
72
Q

limitations of neutral OCM

A
  • transits rapidly, absorbed distally
  • suboptimal distention can mask or mimic lesion
73
Q

benefit of positive OCM

A
  • extra luminal findings are more confidently identified
  • peritoneal metastatic lesions cannot be optimally differentiated from bowel loops or ascetic fluid with the use of neutral OCM
74
Q

limitation of positive OCM

A
  • obscuration of bowel wall enhancement
  • ischemic bowel or inflammatory small bowel disease
  • radiologists need to assess bowel wall enhancement. NOCM should be served instead
  • when POCM not properly diluted, can result in streaking artifact to the liver
75
Q

what is rectal contrast

A

given in case of suspected bowel perforation or anastomosis leakage (150-250ml)

76
Q

when to avoid rectal contrast

A
  • oncologic patients on chemotherapy –> develop neutropenia from chemo
  • rectal cancer cases - already diagnosed
  • anal fissure and perianal fistulas –> very painful
77
Q

scan range for CT abdo pelvis

A

above diaphragm to below SP

78
Q

what is included in a abdomen pelvis scan

A
  • abdominal viscera
  • peritoneum and retroperitoneal
  • adrenals
  • vasculature
  • lymph nodes
79
Q

what is included in the abdominal viscera

A

stomach
intestine
liver and biliary system
pancreas
spleen
kidneys
ureters
suprarenal glands

80
Q

what is CT angiography

A

radiographic technique using CT to investigate the vessels and organs after the introduction of ICM

81
Q

CT Angiography techniques

A
  • high flowrate
  • 18 or 20G cannula
  • test bolus or bolus track
  • 3D recon; peak arterial enhancement
  • lower kV
  • high speed table, wider detector coverage
82
Q

factors affecting arterial phase of contrast bolus

A
  • time-to-peak enhancement (differs for different target arteries)
  • distance from venous access site
  • individual cardiac output
  • diseases or disorders with the blood vessels
  • high speed table, wider detector coverage
83
Q

4 steps that create 3D images

A
  • data acquisition
  • image post processing
  • 3D rendering
  • image display and analysis
84
Q

patient positioning for CTA COW and carotid

A
  • remove any metals from head
  • supine
  • head first
  • chin angled down slightly
  • arms by patient’s side
  • velcro straps or pads can be used to immobilise patient’s head
  • follow CTA carotid, instruct patient to stop swallowing during the scan
85
Q

indications for a CT COW

A
  • ? aneurysm
  • acute stroke
  • trauma
  • arterial venous malformation (AVM)
  • arterial venous fistula (AVF)
86
Q

patient positioning for CT aortogram

A
  • remove any metal from thorax and abdo pelvis
  • supine
  • head/feet first
  • arms above head
  • velcro straps or pads can be used to immobilise patients or stop from falling off the table
87
Q

indications of CT aorta

A
  • ? aneurysm
  • dissection
  • surgical planning
88
Q

patient positioning for CTA UL

A
  • remove any metal from the affected UL
  • supine
  • head first
  • affected arms above head
  • velcro straps or pads can be used to immobilise patients or stop from falling off the table
89
Q

patient positioning for CTA LL

A
  • remove any metal from the affected LL
  • supine
  • feet first
  • arms above head
  • velcro straps or pads can be used to immobilise patients or stop from falling off the table
90
Q

scan range for CTA LL

A
  • CTA may be acquired in 2 blocks:
    1. above diaphragm to below knee
    2. above knee and clear both feet

Modalities (5 decks)

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