Radiology and contrast agents Flashcards

1
Q

how are radiographs produced

A
  • X-rays transmitted through a patient
  • X-rays projected through body onto a detector
  • image formed based on which rays pass through ad are deteted versus those that are absorbed or scattered in patient and not detected
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2
Q

digital radiography and EOS imaging

A
  • X-rays strike sensors that convert the signals generated into digital information which is transmitted and converted into an image displayed on a computer
  • in DR the sensors are shaped like a plate
  • in EOS a linear sensor vertically scans the patient
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3
Q

examples of diseases diagnosed by plain radiography

A
  • various types of arthritis
  • pneumonia
  • bone tumours
  • fractures
  • congenital skeletal abnormalities
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4
Q

applications of low energy projectional radiography

A
  • mammography for breast cancer evaluation
  • DXA for osteoporosis evaluation
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5
Q

fluoroscopy and angiography

A
  • fluorescent screen and image intensifier tube connected to a closed circuit television system
  • allows real-time imaging of structures in motion or augmented with a radiocontrast agent
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6
Q

why are radiocontrast agents used

A
  • to delineate anatomy and functioning of blood vessels, genitourinary system or the gastrointestinal tract
  • they strongly absorb or scatter X-rays and in conjunction with the real-time imaging allow demonstration of dynamic processes such as peristalsis in the GI tract or blood flow in arteries and veins
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7
Q

barium sulphate (BaSO4) as a radiocontrast agent

A
  • given orally or rectally
  • evaluation of the GI tract
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8
Q

iodine as a radiocontrast agent

A
  • given by oral, rectal, vaginal, intra-arterial or intravenous routes
  • concentrated in abnormal areas more or less than in normal tissues and make abnormalities like tumours and cysts more conspicuous
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9
Q

gases as contrast agents

A
  • air for the GI system
  • carbon dioxide in the venous system
  • the agent attenuates the X-ray radiation less than surrounding tissues
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10
Q

computed tomography (CT)

A
  • uses X- rays in conjunction with computing algorithms to image the body
  • X-ray tube opposite an X-ray detector in a ring-shaped apparatus rotates around the patient producing cross-sectional images
  • radiocontrasts often use for enhanced delineation of anatomy
  • detects more subtle variations in attenuation of X-rays than radiographs
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11
Q

examples of conditions diagnosed using CT

A
  • cerebral haemmorhage
  • pulmonary embolism
  • aortic dissection
  • appendicitis
  • diverticulitis
  • obstructing kidney stones
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12
Q

nuclear medicine

A
  • administration of radiopharmaceuticals labelled with radioactive tracer into the patient
  • substances consist of material with an affinity for specific body tissues
  • anatomical detail is limited
  • useful in displaying physiological function so can measure excretory function of kidneys, iodine-concentrating ability of thyroid, blood flow to heart muscle
  • gamma camera and PET scanner detect radiation emitted by tracer in body and with computer processing display it as an axial, coronal or sagittal image as SPECT or PET
  • most images can be fused with CT scan so physiological information can be overlaid with anatomical structures to improve diagnostic accuracy
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12
Q

commonly used radioactive tracers

A
  • technetium-99m
  • iodine-123
  • iodine-131
  • gallium-67
  • indium-111
  • thallium-201
  • 18F-fluorodeoxyglucose (18F-FDG)
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13
Q

positron emission tomography (PET)

A
  • positrons annihilate to produce two opposite travelling gamma rays to be detected coincidentally
  • radioactive, biologically active substance (often 18F-FDG) is injected into patient and radiation emitted is detected to produce multi-planar images
  • more metabolically active tissues such as cancer cells concentrate the active substance more than normal tissues so can be imaged
  • PET images can be combined with CT imaging to improve diagnostic accuracy
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14
Q

interventional radiology

A
  • minimally invasive procedures are performed using image guidance for diagnostic (eg. angiogram) or treatment (eg. angioplasty) purposes
  • often performed with patient fully awake with little or no sedation
  • primary instruments used are needles and catheters
  • images provide maps that allow the clinician to guide the instruments through the body to the areas containing disease
  • peripheral interventions can reduce infection rates, recovery times and hospital stays
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15
Q

what is a contrast agent

A
  • chemical agent administered to the patient for a scan
  • improves contrast resolution (ability to differentiate between different types of tissue)
  • helps characterise pathology
16
Q

what types of scans are contrast agents used for

A
  • CT
  • MRI
  • gastrogaffin in abdominal x-rays
  • angiograms
  • GI fluoroscopy
  • ultrasound
17
Q

how can contrast be given

A
  • orally
  • rectally
  • intravenously
  • intraarterial
  • any cavity
18
Q

types of contrast

A

X-ray
- positive contrast is more radiopaque, tend to be heavy elements such as iodine or barium
- negative contrast is more radiolcent, tend to be lighter materials such as air or CO2

MRI
- gadolinium based agents are used as it interferes with how protons behave in a magnetic field

ultrasound
- microbubbles interact with sound waves

19
Q

ideal characteristics of contrast agents

A
  • biologically inert
  • safe and non-toxic
  • stable for storage and within body
  • low osmolality and viscosity
  • soluble in water
  • cost-effective
20
Q

idiosyncratic reactions to contrast agents

A
  • acute (<1hour), can range from mild to life threatening
  • higher risk if previous reaction to contrast, asthma or other allergies
  • severe reactions very rare
21
Q

non-idiosyncratic reactions to contrast agents

A
  • contrast extravasation, metallic taste or warm sensation
  • nausea and vomiting, vasovagal syncope and other CVS effects
  • can be delayed reactions (1 hour-1 week), commonly skin reactions
22
Q

what does idiosyncratic reaction mean

A
  • cannot be explained by drug’s known mechanism of action
  • do not occur at any dose in most patients
  • mostly unpredictable
23
Q

severity of idiosyncratic reactions to contrast agents

A
  • mild: flushing, itching, mild urticaria
  • moderate: marked urticaria, bronchospasm, angioedema, laryngeal oedema
  • severe: anaphylaxis, cardiopulmonary arrest