Final Review: Beam Restriction Flashcards by Melissa Unknown

Increased kVp affect on interactions:

-increased transmission
-decreased photoelectric absorption
-increased Compton Scatter

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affects the penetrability of beam

kVp

**i know we already know this shit but hey nothings wrong with repetition lol

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Volume of irradiated material

-Field Size
-Patient Thickness

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Decreased kVp affect on interactions

-Decreased transmission
-increased photoelectric absorption
-decreased Compton Scatter

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increased kVp affect on patient dose:

-decreased dose
(decreased photoelectric absorption and increase in kVp typically accompanied by reduction in mAs)

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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

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Decreased kVp affect on interactions:

Decreased transmission
increased photoelectric absorption
Decreased Compton Scatter

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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)

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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

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Decreased FS decreases beam quantity

-decreases scatter
-decreases amount of remnant radiation hitting receptor
-can increase image noise without mAs compensation

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Increased FS increases volume of tissue irradiated

Results in increased scatter

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Decreasing FS, fewer photons reach IR

-image receptor exposure decreased
-increases in mAs must accompany significant reduction in FS to maintain image receptor exposure

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More matter=

more scatter

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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

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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

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Beam Restrictors

-aperture diaphragms, cones, and cylinders
-collimators
ancillary devices

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-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

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Bottom shutters

Reduce Penumbra

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Occurs from areas of xray tube other than focal spot area

Off focus radiation

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Upper shutters

reduce off focus radiation reaching IR

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produces images beyond exposed field of radiation
-image shadows

Off focus radiation

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-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

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what is your first step for beam restricting

Collimating

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what do the lead lined shutters decrease

decreases scatter going on to patient

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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