Final Review: Beam Restriction Flashcards
Increased kVp affect on interactions:
-increased transmission
-decreased photoelectric absorption
-increased Compton Scatter
affects the penetrability of beam
kVp
**i know we already know this shit but hey nothings wrong with repetition lol
Volume of irradiated material
-Field Size
-Patient Thickness
Decreased kVp affect on interactions
-Decreased transmission
-increased photoelectric absorption
-decreased Compton Scatter
increased kVp affect on patient dose:
-decreased dose
(decreased photoelectric absorption and increase in kVp typically accompanied by reduction in mAs)
Increased kVp affect on image quality
-lower amount of contrast if using film/scree receptor System
-not as pronounced in digital systems, due to image post processing
Decreased kVp affect on interactions:
Decreased transmission
increased photoelectric absorption
Decreased Compton Scatter
Decreased kVp affect on patient dose:
Increased dose
(increased photoelectric absorption and decrease in kVp usually accompanied by increase in mAs which increases dose even more)
Decreased kVp affect on image quality
-Higher image contrast if using film/screen receptor system
-Not as pronounced in digital systems, due to image post processing
Decreased FS decreases beam quantity
-decreases scatter
-decreases amount of remnant radiation hitting receptor
-can increase image noise without mAs compensation
Increased FS increases volume of tissue irradiated
Results in increased scatter
Decreasing FS, fewer photons reach IR
-image receptor exposure decreased
-increases in mAs must accompany significant reduction in FS to maintain image receptor exposure
More matter=
more scatter
Compression devices used to improve spacial resolution and contrast
-decreases patient thickness
-results in lower patient dose
-brings tissue closer to receptor
-routinely used in mammography
Using beam restricting devices
-usually beam restrictors decrease FS to anatomy of interest
-unnecessary tissue exposure decreases
-scatter decreases
-scale of contrast shortens
-visibility of detail increases
Beam Restrictors
-aperture diaphragms, cones, and cylinders
-collimators
ancillary devices
-modern equipment feature
-light localizing field light
(provides indication of midpoint of central ray)
-two sets of shutters that permits infinite number of field sizes (length and width of field independently controlled)
Collimator
Bottom shutters
Reduce Penumbra
Occurs from areas of xray tube other than focal spot area
Off focus radiation
Upper shutters
reduce off focus radiation reaching IR
produces images beyond exposed field of radiation
-image shadows
Off focus radiation
-uses light reflected off mirror to project coverage of xray beam
-proper adjustment of mirror necessary to accurately display location of exposure field
-light field/xray beam coincidence testing should be part of quality control program
-needs to be accurate within +/= 2% of SID
-mirror adds to system inherent filtration
Light Field
what is your first step for beam restricting
Collimating
what do the lead lined shutters decrease
decreases scatter going on to patient
Automatically collimates beam to size of image receptor
Positive Beam Limitation (PBL)
Ancillary Devices
Lead Blockers (shields)
Lead masks(attach to collimator)
Is receptor exposure increased or decreased when there is more absorption in the body
Decreases
What does decreasing field size do to the beam
decreasing field size makes the beam more concentrated
Patient factors
-body habitus
-part thickness affects (beam attenuation, exposure reaching IR, scatter production and image contrast)
-pediatric patients
hypersthenic
sthenic
hyposthenic
asthenic
hypersthenic- larger build
sthenic-averge
hyposthenic-slender
asthenic-very slender
Special considerations:
-projections and positions
-casts and splints
-pathology
-soft tissue imaging
-contrast media
5 xray densisties
air
fat
muscle
bone
metal
Positive contrast agents
Iodine or barium
because of their high atomic number (ability to attenuate the beam)
iodine is 53
barium is 56
This disease breaks bone down; you need less kvp to penetrate it
degenerative disease
is arthritis additive or degenerative
degenerative
is emphysema additive or degenerative
degenerative disease
With this disease , you may need more kvp to penetrate it
Additive disease
is pneumonia additive or degenerative
additive
is pleural effusion additive or degenerative
additive
Reduction in xray photons remaining in beam after passing through given thickness of material
Attenuation
increased part thickness and material density results in:
increased attenuation
radiographers greatest variable
the patient
-result of photoelectric absorption
-result of Compton scattering(provides no useful info and contributes to occupational dose)
-exponential process
attenuation
-Effective atomic number :7.78 (greater than fat or muscle)
-low tissue density
-absorbs few photons
results in increased area of exposure on ir
radiolucent
Air
composition of human body determines its radiographic appearance
gas(air)
fat surrounding kidney
muscle (water density)
bone (mineral)
-Soft tissue
-effective atomic number and tissue density similar to water
-effective atomic number slightly less than muscle
-fat as a tissue density less than muscle and therefore will contrast with muscle on images
Fat
-Soft tissue
-slightly higher atomic number and tissue density than fat
considered essentially a water density
Muscle
-Composed of calcium and phosphorous salts
-calcium among highest atomic number of elements found in body
-greatest tissue density of four basic tissue substances
-high absorption of photons
-large percentage of PE interactions
-decreased area of exposure on ir
-results in areas considered radiopaque
Bone
IR exposure will be altered by changes in amount or type of tissue being irradiated
Subject density
-Degree of differential absorption resulting from differing absorption characteristics of tissues in body
-dependent upon the tissue composition as a body part
Subject contrast
low subject contrast body part
breast, abdomen
high subject contrast body part
Skill, spine, knee
Recorded detail of anatomical structures dependent upon:
-anatomical location within body
-bodys placement in relationship to ir
-increased distance of anatomical structures from receptor yields less detail of anatomy
subject detail
-misrepresentation of the size of anatomy due to its orientation to path of xray beam
-unless patient is positioned specifically to demonstrate a particular structure, may not be accurately represented on image receptor
Subject Distortion
Can alter thickness and composition of patients tissue density
Pathology
increase tissue thickness, effective atomic number and/or tissue density
Additive conditions
which condition (additive or destructive) permits less exposure to receptor, without technique compenstation
less exposure
does destructive or additive increase attenuation
ex. edema, abcess, effusion, tumor
Additive
for additive conditions what do you do to technique
increase kvp
for destructive what do you do to the technique
decrease mAs
is additive condition increased absorption or transmission
increased absorption
is destructive condition increased absorption or transmission
increased transmission
Destructive or additive
atelectasis
-collapse lung
additive
Destructive or additive
Bronchiectasis
additive
Destructive or additive
cardiomegaly
heart enlargement
additive
Destructive or additive
CHF
additive
Destructive or additive
empyema
additive
Destructive or additive
pleural effusion
additive
Destructive or additive
pneumoconiosis
-inhalation of dust particles
additive
Destructive or additive
pnemonia
additive
Destructive or additive
pneumoectomy
additive
removal of a lung
Destructive or additive
pulmonary edema
blood
additive
Destructive or additive
tuberculosis
additive
Destructive or additive
Aortic aneurysm
additive
Destructive or additive
ascites
additive
Destructive or additive
cirrhosis
enlargement of liver
additive
Destructive or additive
Acromegaly
additive
Destructive or additive
Chronic osteomyelitis
hydrocephalus
osteoblastic metastases
osteochondroma
pagets disease
sclerosis
additive
atrophy
weakness of muscles
pagets disease
calcified spots
emaciation
vomitting a lot
Destructive or additive
anorexia nervosa
atrophy
emaciation
Destructive
Destructive or additive
emphysema
large pneumothroax
COPD
Destructive
-air
Destructive or additive
Aerophagia
bowel obstruction
ileus
Destructive
aerophagia
swallowing air
ileus
obstruction air
Destructive or additive
Active osteomyelitis
Aseptic necrosis
carcinoma
Destructive
Destructive or additive
degenerative arthritis
fibrosarcoma
gout
Destructive
Destructive or additive
hyperparathyroidism
multiple myeloma
osteolytic metastases
Destructive
Destructive or additive
osteomalacia
osteoporosis
Destructive
