Radiographic imaging

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Terms

Definitions

                                                                      Attenuation

     -Process by which   a beam of radiation is reduced in energy when passing through tissue or other   material
  -Absorption radiation + Scatter radiation
  -What left of the primary that reach the IR

Automatic   Rescaling

     Process by which   images are produced with uniform brightness and contrast, regardless of the   amount of exposure

Brightness

     the amount of   light emitted from a flat-screen monitor

Computed   Radiography (CR)

     cassette or   cassette-based digital radiography; the digital acquisition (su duoc, earn)   modality (quality) that uses storage phosphor plates to produce images

Contrast

     difference between   adjacent densities on a radiographic image

Density

     degree of   darkening or blackness of exposed and processed photographic or radiographic   film

Digital   Radiography (DR)

     cassette or   cassette-less image receptor system that convert x-ray energy into a digital   electronic signal for manipulation (handle) and display (show info.)

Direct Capture DR

     -devices that   convert incident x-ray energy directly into an electrical signal
  -x-ray-TFT (Thin-film transistor; amorphous selenium   material)-Electronic-digital signal

Exposure Index   (EI)

     a numeric   representation of the quantity of exposure received by a digital image   receptor

distortion

     -misrepresentation   of the true size or shape of an object

Grid

     device consisting   of thin lead strips designed to permit primary radiation to pass while   reducing scatter radiation

Fog

     undesirable   exposure to the image receptor

Exposure Latitude

     the range of   exposures that can be used and still result in the capture of a   diagnostic-quality image
  -EI (Exposure Index)

Half-Value Layer

     amount of   filtration necessary to reduce the intensity of the radiation beam to one   half its original value

Image Receptor   (IR)

     medium used to   capture the image for recording, such as x-ray film or a digital imaging   plate

Indirect Capture   DR

     -devices that   absorb x-rays and convert them into light;
  -X-ray-scintillator-Lt-TFT (thin-film-transistor)-Electronic-digital signal

Intensifying   Screen

     layer of   luminescent crystals placed inside a cassette to expose x-ray film   efficiently and thereby significantly reduce patient dose

Inverse Square Law

     mathematic formula   that describes the relationship between radiation intensity and distance from   the source of the radiation

     Source-to-Image   Distance (SID)

     the distance   between the source of the x-ray (usually the focal spot of the x-ray tube)   and the image receptor

     Window Level

     -is one of the   features of post processing
  -image manipulation parameter (a constant-not changing) that changes image   brightness on the display monitor, usually through the use of a mouse or   trackball
  -NOT RECOMMENDED

Radiopaque

     not easily   penetrable by x-rays or other forms of radiant energy

Radiolucent

     permitting the   passage of x-rays or other forms of energy with little attenuation

Penetrating   Ability

     ability of an   x-ray beam to pass through an object; controlled by the kVp of the beam

Primary Radiation

     x-ray beam after   it leaves the x-ray tube and before it reaches the object

Latent Image

     invisible image   created after exposure but before processing

Milliampere-Seconds   (mAs)

-is the   parameter that controls the amount of x-radiation produced by the x-ray tube;   it is the product of milliamperage (mA) multiplied by seconds
  -it determine the amount of x-ray are using
  -modern time, change mAs at least 30% to see image contrast for the naked   eyes to see
  -traditionally on film screen, change from 100 mAs to 200 mAs to see image
  -is directly proportional to density, meaning that double the mAs same as   double the density
  -Overexposure or underexposure it can effect image contrast

Kilovolt Peak   (kVp)

     -is a measure of   the electrical pressure forcing the current through the tube. It controls the   penetrating ability of the beam and primarily affects the quality but also   the quantity of the x-ray photons produced.

Photon

     quantum or   particle of radiant energy

Recorded Detail

     representation of   an object’s true edges

     Relative Speed

     relative   measurement of the speed of a radiographic film and Intensifying screen   system

Remnant Radiation

     -radiation   resulting after the x-ray beam exits the object or patients
  – This remnant radiation produces and image in the image receptor

Scatter Radiation

     -it the term   generally used to describe this type of non-diagnostic radiation
  -it can bound off or it can interact with patient tissue then reach the IR   but it wil be consider Fog.
  -it can bound off patient and hit radiographer or other matter.

Imaging

     -Is a general term
  -on campus aspect, difference factor that are effecting the x-ray beam/ or   changing the x-ray beam and how that can change the appearing of the image

Types of   absorption

     Bone- very dense,   lots absorption x-ray ( will appear white on the IR)
  Soft tisse- absorp some and some x-ray pass through the IR ( will appear gray   on the IR)
  Air/Gas- Not absorp x-ray ( will appear black on IR)

Image Quality   factor

     -acceptable range   of visuability that can pass on to the radiologist for properly   interpertation for accurate diagnosis
  -Diagnostic image or Not

Photographic   Qualities

     -visuability of   the image

     Geometric   Qualities

     -sharpness of the   structual line of the part that are imaging (Detail)
  -the accuracy of the part on the image that compare to how it is inside the   body

Density/IR   Exposure

     -Density is the   traditional term for Film screen
  -IR exposure for Digital system
  -the degree or the amount of blackening on an image
  -digital can adjust the brightness but are not recommend, film screen can not   adjust the brightness.

Films screen

     – if overexposure   or underexposure is very knowed able

Digital

     – cant tell if   over or underexposure because it had a features call Rescaling
  -Exposure Index (EI)

Rescaling

     – is an automatic   correction
  -too little radiation result will be quantum mottle (grainy)
  -too much radiation result will be effecting the image contrast and patients   exposure

Reciprocity

     -any combination   of mA and time producing equivalent mAs values should produce equivalent   exposures and therefore densities
  -purpose- for kids and in pain patients
  100 mA * 1 s = 100 mAs
  200 mA * .5 s = 100 mAs
  300 mA * 1/3 s = 100 mAs

Image contrast

-difference   between image side by side density
  -kVp is the control factor of image contrast
  -higher in kVp, 80 and up range give more shade of gray on image; not much   difference in density therefore, decrease or low amount of image contrast
  -lower in kVp, 50 and down range; more difference in density btw black and   white, therefore higher image contrast.

Patients

     -subject density
  -subject refering to the patient
  -pathology can effect density
  -Emphysema- Destructive will increase density of IR, less absorption
  -Respiratory syncytial Virus (RSV)- Additive will decrease density of IR,   more absorption
  -Muscular or obesity can effect density

SID

-Source to   Image distance
  -distance from the anode to image receptor
  -Two SID: 72″ inches and 40″ inches
  -Distance working by a factor of 4
  -Half SID, decrease density by 4x
  -Double SID, decrease density by 1/4 x
  -More SID, the less x-ray reach the patient, less x-ray exit patient, low   density/IR exposure

Beam Modification

     -collimation   increase- meaning decrease field side that reduces the amount of scatter   radiation
  -Increase collimation technically decrease density/IR exposure
  -decrease in scatter causes a decrease in IR exposure/density

Filtration

     -between x-ray   tube and collimator, from manufacture there a little thin strip aluminum
  -Strip Aluminum- functions is to absorp low engery and scatter energy from   x-ray tube, similar with the alumium window in the x-ray tube.
  -filtration will decrease density/IR exposure

Grid

     -Btw patient and   IR for larger part
  – same function as collimator
  -made out of lead, and it block or collect low energy x-ray
  -use grid will decrease density/IR exposure
  -increase mAs when using grid
  -Better with digital
  -humerus in, head down, knee up

Image Receptor

     -intensifying   screen- convert x-ray photon into light ( for film screen
  – Spectral matching

Spectral matching

     – film-screen   systems use a combination of intensifying screens that emit a specific color   light and radiographic film that is sensitive to the same color
  -mismatched combination result of poor image quality

Speed system

     -how much   radiation is require by this film screen system to produce a certain density   on an image
  -fast system requires less radiation
  -slower system generlly produce sharper (detail) images
  -meet in the middle for better image (400-600)
  -fast system speed 1000 and up
  -slower system speed 200 and down

Developer

-develop   from latent image (invisible) to visibel image
  -maintain- the developer must be at 95 degree
  -if too warm, like 0.5 degree higher than 95 degree the density increase
  -if too cold, like 0.5 degree lower than 95 degree it will decrease density
  – for film screen system, 6 to 8 week must be maintain
  and look at from a service tech.

contrast media

     -Iodine base   contrast and Barium
  -the higher the atomic # the material has, the more radiation it will absorb,   example: bone (calcium)
  -contrast media increase image contrast, make it more black and white

Motion

     -voluntary
  -involuntary

voluntary

     -can be controlled   by the use of careful instructions to the patient, suspension of patient   respiration during exposure short exposure times and judicious (sang suot) of   appropriate immobilization devices.

Focal spot size

     -small focal spot   used when fine detail
  -large focal spot is used for most general radiographic examinations

SID

     -larger SID,   better detail
  -Source to Image distance
  -distance from the anode to image receptor

OID

     -smaller OID,   better detail
  -object to image distance

Elongated

     -tube and beam
  -represent the part that is longer than what it really is

Foreshortened

     -part or IR
  -represent the part that is shorter than what it really is

shape distortion

     -the alignment btw   the x-ray beam, part and the IR
  ideally, the goal is to place the x-ray beam perpendicular to the part, the   part parallel to IR.

quantum mottle

     -too little   radiation result will be grainy

kVp 15% rule

     -radiography can   range from 30 to 150 kVp
  -increase kVp 15% will double density/IR exposure
  -decrease kVp 15% will be halve density/IR exposure
  -Increase kVp 15% and halve mAs
  -Decrease kVp 15% and double mAs

 

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2 thoughts on “Radiographic imaging

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    July 30, 2014 at 4:37 am

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    MR said:
    June 27, 2013 at 12:32 am

    Busy EDs, patient acuity drive ED imaging use variation

    Evan GodtJun 24, 2013

    – physicians

    Patient- and visit-level factors, as opposed to physician-level factors, are the predominant predictors of whether an imaging exam is ordered during an emergency department (ED) visit, according to a study published online June 25 in Radiology.

    ED physicians’ level of experience, residency training, annual workload and sex all failed to correlate with imaging use after a hierarchical logistic regression of possible imaging predictors, explained Hannah J. Wong, PhD, of York University, Toronto, and colleagues.

    Conclusions were based on an analysis of 88,851 ED visits at Massachusetts General Hospital (MGH) in Boston, in 2011. During the study period, imaging utilization in the ED was 45.4 percent, compared with the 2010 national average of 47.2 percent.

    A number of patient and visit factors were found to impact the likelihood of imaging during the ED visit, including prior ED visits, referral source to the ED, method of arrival and clinical reason for the visit, according to Wong and colleagues. A busy ED, another visit-level factor, was found to lead to more high-cost imaging, while less busy EDs increased the odds of low-cost imaging 11 percent.

    “We speculated that low-cost imaging may be performed more often when the ED is least busy because ED physicians would have more time to order and review the examinations during a comprehensive assessment,” wrote the authors, adding that ordering high-cost imaging early in the workup may free up more of the ED physician’s time in the short term, despite the fact that use of advanced imaging results in longer patients stays—and increased costs—overall.

    The unadjusted variation between physicians, measured as intraclass correlation coefficient (ICC), was 12.66 percent for low-cost imaging and 23.63 percent for high-cost imaging. However, after adjusting for patient- and visit-level characteristics, variation in imaging use attributable to the practice style of the physician was 0.97 percent for low-cost imaging and 1.07 percent for high-cost imaging across the ED as a whole.

    Four of the 46 ED physicians involved in the study would be considered high outliers for the use of imaging in their patients, but Wong and colleagues said the impact of other factors on utilization means focusing on physician-specific rates of ED imaging could lead to misclassification and limited results for utilization reduction efforts.

    “Discussion of quality and cost-control efforts is promoted by reporting interphysician variation for use of ED imaging in this manner,” they wrote. “However, we would urge caution in the use of such metrics to remediate outlier physicians because only about 1 percent (measured by ICC) of overall variation in ED imaging use is directly affected by physicians.”
    ….

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