Radiography history, image production Flashcards
when was xrays discovered by Roentgen:
1895
how was it discovered:
- Crookes tube
- fogging of photographic plate
- no visible ligt emitted from tube
x in xray stands for:
- unknown
list (9) properties of xrays discovered:
- EM waves
- 1/10,000 wavelength of visible light
- can’t penetrate lead
- attenuation of xray beam depends on substance
- causes certain substances to fluoresce
- produces biological changes
- can ionise gases
yr of first medical use of xrays in diagnosis and therapy:
- 1896
- Hall-Edwards, Frost, Lyle
exposure times of ‘shadow graphs’ initially and effects
- 30min (long)
- low voltage
- blurred images w high radiation dose
intensifying screen in 1896 sig:
- reduced time to take image
1898 Edison’s fluoroscope:
- xray tube under table
- xray enters viewing device
- able to visualise moving images in real time
most sig discoveries to improve image quality:
- collimation
- filtration
when was Coolidge xray tube dev:
1913
coolidge tube sig: list (5)
- basis of xray tubes today
- hot cathode xray tube
- vacuum tube: allowed xray intensity, energy to be selected separately
- used snook transformer to increase current, voltage
- start of modern radiology
1917 cellulose nitrate film: sig
- due to lack of glass in WWI
- better than glass but highly flammable
1918 double emulsion film: sig
- exposure time halved
- image enhanced
soluble iodine contrast media used in:
1920
1921 Potter-bucky grid intro: sig
- improved image contrast
1922 Compton scatter rays: sig
- large cont to image fogging
modern radiology: 1923 ‘safety’ film intro- sig
- cellulose acetate
- not flammable
modern radiology: 1928 defined xray intensity units in
roentgen
modern radiology: 1929 rotating anode into- sig
- extended tube life
modern radiology: 1930 tomography dev- sig
- ability to image structures at certain depth in body
- allowed visualisaiton of structures without overlying structures obscuring anatomy
modern radiology: 1953 defined unit of absorbed dose as
rad
modern radiology: 1960 more durable film used-
- polyester
modern radiology: diagnostic ultrasound intro
1966
modern radiology: first CT scanner
1972
modern radiology: first MRI prod
1973
modern radiology: rare-earth intensifying screens
1974
modern radiology: digital fluoroscopy
1979
modern radiology: SI units of radiation
1980
modern radiology: 1982 PACS available– sig
- picture archiving and communication sys
radiation injury: Edison, Morton, Tesla warned
- radiation injury
- reported eye irritations from experimenting w xrays
first xray fatality in:
1904
radiation injury: list effects (5)
- skin damage
- burns
- loss of hair
- anaemia common in early yrs
- all due to long exposure time
radiation injury: 1910 controlled radiation techniques-
- biological effects of xrays began to be studied
- collimation
- filtration
- shielding
radiation injury: decreased injuries due to intro of
- coolidge tube
- snook transformer
- less exposure
radiation injury: radiologists found to have higher rate of- and solution
- aplastic anemia
- leukaemia
- lead-lined protective devices being used
radiation injury: list (3) guidlines to minimise radiation exposure
- time
- distance
- shielding
radiation injury: radiographic guidelines- time= time/lvl of exposure
- decrease time/lvl of exposure: coolidge tube, snook transformer, intensifying screens, double emulsion film
radiation injury: radiographic guidelines- time= repeat exposures
- decrease
- shorter time
- potter-bucky grid
- positioning
- procedure
radiation injury: radiographic guidelines- time= inappropriate imaging
- clinical guidlines
radiation injury: radiographic guidelines- distance
- inverse square law: when 2x distance, xray intensity drops by 1/4
radiation injury: radiographic guidelines- shielding
- lead shielding
- collimation
- filtration
analogue vs digital xrays: list image prod concepts (5)
- kV and mA
- film type
- filters
- processing and dev
- storage
analogue vs digital xrays: safety issues btw modes
- digital usually assoc w less repeat exposures
sig of xray vs CT/MRI:
- not obsolete
- minimal visualisation of soft tissues BUT:
- better bone visualisation than MRI
- cheaper, quicker
- less radiation than CT
- often rec 1st line of imaging prior to further imaging
radiographic image: features
- xray beam emerges from tube as uniform beam
- beam is attenuated as pass through patient
- exit beam is varied in intensity depending on characteristics of tissue through which it passed
- exit beam interacts w image receptor to form radiographic image
radiographic image: define attenuation
reduction of xray beam intensity, resulting from:
- absorption
- scattering
xray attenuation: thicker/thinner body parts attenuate more xrays
thicker
xray attenuation: increase of 4cm of soft tissue=
- decreases exit radiation by factor of 2
xray attenuation: list (5) from least to most attenuated material
- air
- fat
- water
- bone
- metal
exposure parameters: why?
- proper exposure in necessary to produce diagnostic radiograph
- exposure parameters determine xray quantity and quality
- correct selection enables creation of high quality xrays of good diagnostic value
exposure parameters: list 1˚ parameters (2)
- kV
- mAs
exposure parameters: list 2˚ parameters (2)
- distance
- filtration
optical density: define image density
- amount of BLACKENING of processed image
- greater image density, less light can pass through image
optical density: higher image density =
blacker image
optical density: equation
OD = log(Ii/It)
optical density: OD of 0=
clear image
optical density: OD of 4=
black image
optical density: OD in diagnostic radiology range from
0.25 - 2.5
optical density: useful diagnostic range
0.5 - 1.25
optical density: just possible to read newspaper through film w OD of
1
xray quantity: define and measured in
- output intensity of xray imaging sys
- measured in mGy
xray quantity: also aka (2)
- xray intensity
- radiation exposure
same as xray quantity
xray quantity: directly affects
optical density
mAs: mA?
exposure current:
- current determines no. of xrays prod
- controls xray beam quantity
mAs: s?
exposure time:
- controls time xray beam prod for
- controls xray beam quantity
mAs: features (controls? doesn’t affect?)
- exposure current (mA) x exposure time (s)
- controls xray beam quantity
- does NOT affect beam quality
- controls OD on radiograph
xray intensity is directly proportional to:
mAs
mAs: meaning when mAs is 2x?
- no. electrons striking tube target 2x
= no. xrays emitted 2x
mAs: the higher mAs, higher/lower image density?
higher
mAs: mAs and xray intensity ratio
i1 / i2 = mAs 1 /mAs 2
mAs: must be at particular lvl to achieve correct-
optical density
mAs: if mAs remains constant, same OD can be achieved through combo of (2)
- exposure current
- time
mAs: if mAs remains constant, same OD can be achieved- techniques (2)
- kept short as possible= min movement blur
- decreased time, needs increase in current to ensure sufficient quantity
maintaining OD: equation
mA1 x s1 = mA2 x s2
mAs: eg (1) technique req increased time to allow for movement- compensation?
- autotomography
- mA must be decreased proportionally to allow for constant OD
autotomography: eg. (2)
- controlled patient movement can blur overlying structures (ribs, scapulae) through breathing
- flapping jaw technique
distance: SID affects
source to image distance (SID): influences xray beam quantity at image receptor
distance: SID no effect on
xray beam quality
distance: relatively fixed at
- 100cm/ 180cm depending on anatomical region
distance: increased SID increases/reduces xray beam quantity?
reduces quantity
distance: inverse square law aka
- xray intensity (quantity) varies inversely w distance from xray tube-> target (SID)2
distance: inverse square law equation
i1/i2 = (d2/d1)2
the square law: when SID increased, what needs to be increased to maintain constant OD?
mAs must also be increased
corollary to inverse square law: equation
mAs 2/mAs 1 = (d2/d1)2
the square law: if 2x SID, mAs must be increased by factor of: to keep OD same
mAs increased by factor of 4
image contrast: define
degree of diff in density btw 2 areas on xray image
image contrast: features
- contrast reflects no. of shades of grey btw lightest/darkest areas
image contrast: high contrast image
- fewer shades grey
- more diff btw them
image contrast: low contrast image
- many shades of grey
- less diff btw them
xray quality: aka the
energy
xray quality: if energy increases, so does
penetrability
xray quality: define penetrability
- xrays range within tissue
- able to pass through tissue
xray quality: high energy xrays can
- penetrate deeper tissue, ‘hard’ xrays
xray quality: low energy xrays can
- penetrate far less
- termed ‘soft’ rays
xray quality: xray energy (quality) identified numerically by
- half value layer (HVL)
xray quality: higher the HVL, =
higher xray quality/penetrability/energy
HVL: define
- HVL of xray beam is thickness of absorbing material necessary to reduce xray intensity to 1/2 og value (attenuation)
HVL: diagnostic xray beam range for soft tissue?
3 - 6cm
HVL: affected by (2)
- kV (kilovoltage)
- added filtration
HVL: xray quality is also affected by
- kV
- filtration
HVL: factors affecting beam quality also influence
radiographic contrast
HVL: radiation quality NOT affected by
- distance
- mAs
kV: define
- kilovoltage
- 1˚ control of xray beam/penetrability
kV: influences
xray beam quantity
kV: increasing kV effects- (5)
increases:
- xrays emitted (increases quantity)
- energy of xrays
- penetrability
- Compton effect, scatter radiation
decreases:
- contrast
kV: controls
- image contrast
- image density
kV: if kV increased and so does xray beam quality, what else?
- increases penetrability = HVL
kV: when increased xray beam can penetrate more/less tissue
- more tissue
kV: low kV effect of beam
- aka low quality xray beam
- beam largely attenuated by most tissue (white parts)
- beam only penetrates low density tissues (=black parts)
- v white/ v black image
= HIGH CONTRAST IMAGE
kV: high kV effect of beam
- aka high quality xray beam
- beam able to penetrate most of tissues
- degree of attenuation will differ depending on tissue density and thickness
- many shades of grey
LOW CONTRAST IMAGE
kV: what varies rapidly w changes in kV and is proportional to kV2?
xray quantity
kV: xray quantity change is proportional to what of kV?
- proportional to square of kV
- ie. if kV 2x, xray intensity increases by factor of 4
kV: intensity and kV equation
i1/i2 = (kV1/kV2) 2
kV: density linked to ? which can be manipulated to highlight..
- contrast
- highlight particular image qualities
kV: if kV increased, will increase/decrease image contrast, and increase/decrease image density
- decrease image contrast
- increase image density
kV: 15% rule
- 15% increase in kVp will increase density
- same as 2x mAs
- 2x OD
filtration: features
- reduces no. of low energy xray that reach patient
filtration: low energy xray sig
- cont nothing useful to image
- only increases patient dose
filtration: increasing beam quality and penetrability will increase/decrease contrast?
decrease contrast
filtration: decreasing beam quality will increase/decrease density
decrease density
filtration: inherent features
- affects all xray beams
- glass/metal envelope of xray tube, collimator, additional Al filter btw xray tube housing and collimator
- required total filtration of 2.5mm Al
filtration: added features
- additional filtration may be used for examination of tissues w higher subject contrast: extremities, joints, chest
- requires diff radiographic technique charts
- not required w digital imaging
parameters affecting density and contrast: mA increase
- increase density
- unchanged contrast
parameters affecting density and contrast: mA decrease
- decreases density
- unchanged contrast
parameters affecting density and contrast: time increase
- increase density
- unchanged contrast
parameters affecting density and contrast: time decrease
- decrease density
- unchanged contrast
parameters affecting density and contrast: kVp increase
- increase density
- decreases contrast
parameters affecting density and contrast: kVp decrease
- decrease density
- increase contrast
parameters affecting density and contrast: SID increase
- decrease density
- unchanged contrast
parameters affecting density and contrast: SID decrease
- increase density
- unchanged contrast
parameters affecting density and contrast: filtration increase
- decreases density
- decrease contrast
parameters affecting density and contrast: filtration decrease
- increase density
- increase contrast
