Imaging Principles

Boomerang filter

placed behind patient used for superior shoulder & upper thoracic spine improved visualization of soft tissues

The positioning term that describes the general and specific body position is

positon

Density controlling factors

primary controlling factor.mAs: quantity of x-rays produced & duration of exposure kV: controls energy of x-ray beam

equivalent dose

quantifies the risk for different types of radiation using the same relative scale given in unites of sieverts (Sv) or rem

ALARA principles

(1) always wear a personnel monitor device (2) Mechanical holding devices: restraint devices or retention bands should be used whenever possible, and only as a last resort should anyone stay in the room to restrain patients - should NEVER be radiography personnel (3) practice the use of close collimation, filtration of primary beam, optimum kV techniques, high speed image receptors, and minimize repeat exams (4) follow the three cardinal principles of radiation protection: time, distance, and shielding

types of compensating filters

- wedge filter - trough filter -boomerang filter

Primary factors of Distortion

-SID -OID -Object IR alignment -CR alignment or centering

image quality factors for digital images(6)

-brightness - intensity of light that represents the individual pixels. -contrast - difference in brightness between light & dark areas of an image. -Spatial resolution -recorded sharpness or detail of structures on the image Factors - acquisition pixel size (the smaller the greater resolution) & display matrix (display capabilities- the larger display matrix the higher resolution) -distortion - misrepresentation of object size or shape as projected onto radiographic recording media. -Exposure indicator - numeric value that is representative of the exposure that the IR has received. Checking the exposure indicator is key in verifying that acceptable quality digital radiographic images have been obtained w/ the least possible dose to patient. -Noise - random disturbance that obscures or reduces clarity. A high signal to noise ratio is more desirable as the signal (mAs) is greater than the noise.

Primary controlling factors of Spatial resolution

-geometric factor -focal spot size -SID -OID -motion (involuntary & voluntary) -Film screen speed

Grid issues (4)

-off center grid -off level grid -off focus grid -upside down grid

Fluoroscopy Safety Practices

1) bucky slot cover 2) lead drape 3)0.5 mm lead apron 4) exposure limit: 10 R/min

Patient protection

1) minimum repeat radiographs 2) correct filtration 3) accurate collimation 4) specific area shielding 5)protection of fetus 6)optimum imaging system speed 7) select projections & techniques factors appropriate for the examination

controlling factors of distortion (4)

1) source image receptor distance (SID) 2) object image receptor distance (OID) 3) object image receptor alignment 4)central ray alignment/centering

ALARA

As Low As Reasonably Achievable

kilovoltage (kV)

Controls the energy (penetrating power) of the x-ray beam. Also referred to as Kilovoltage Peak (kVp): maximum electrical potential used to create the x-ray photons within x-ray tube.

Milliamperage (mA)

Controls the quantity or number of x-rays produced

Air kerma

Indicates the amount of energy transferred to a mass of air by the photons. unit of measurement is the gray (Gy) or rad

influencing factors of density

Source image receptor distance (SID): distance of x-ray source from IR . If sid is doubled at IR, the intensity of x-ray beam is reduced to one-fourth, which then reduces the radiographic density to 1/4

shadow shield

Suspended from above the radiographic beam-defining system, this device hangs over the area of clinical interest to cast a shadow in the primary beam over the patient's reproductive organs.

exposure latitude

The range of exposure over which a film produces an acceptable image.

When the anode heel rule is applied, the thicker aspect of the anatomy should be placed under the cathode end of x-ray tube.

True

trough filter

Used for chest imaging; mounts on the collimator thicker peripheral portions of filter paced to correspond to less dense lungs thinner portion of filter corresponds to mediastinum

Object image receptor alignment

[Controlling factor of distortion] -object/IR alignment -object (anatomy) parallel to IR the greater the angle of inclination of the object or IR, the great amount of distortion (the plane of the body part that is being imaged must be as near parallel to the plane of ir as possible)

object image receptor distance (OID)

[Controlling factor of distortion] decreased OID reduces distortion. The closer the object is to the IR, the less magnification & shape distortion. and better quality.

wedge filter

a type of compensating filter used to even out densities (placed towards the least dense part) mounts on the collimator ex: AP foot, AP thoracic spine, axiolateral hip

protection of fetus

all child bearing age women should be screened before hand critical during the first 2 months of pregnancy if pregnant- consult with radiologist before hand. If mother is at risk but image is need. go through with procedure but use the protection practices, especially careful collimation

Effective dose equivalent

allows comparisons of the relative risk from various imaging procedures. Given in sieverts (Sv) or rem

Absorbed dose

amount of energy deposited per unit mass by the interaction of ionizing radiation with tissue. given in gray (Gy) or rad

off-level grid

angling across grid lines results in grid cutoff ; also occurs if grid is tilted, CR hits the lead lines at an angle w/ angling, the CR must be angled along the long axis of the lead strips

off focus grid

at the wrong focal distance, the farther the distance, the worse the cutoff. Cut off is more severe toward edges of film. This is more important with high grid ratios a focused grid must be used at a specified SID if grid cutoff is to be prevented portable grid ratio - 6:1 or 8:1 compared with 12:1 for bucky grids

Landscape (crosswise)

broader lateral borders

Which of the following is NOT a type of compensating filter? a) wedge b)boomerang c)slotted d)trough

c: slotted

Central ray alignment

centering. CR has no divergence. Projects at 90 degrees or perpendicular

postprocessing image enhancement

changing or enhancing the electronic image for the purpose of improving its diagnostic quality.

minimum repeat radiographs

clear instructions & accurate positioning & exposure factors

Source Image receptor distance (SID)

controlling factor of distortion increased SID reduces distortion. Less magnification occurs at great SID (which is why a chest xray is at a minimum sid of 72 instead of 40.

Exposure time (ms)

controls the duration of the exposure ; usually expressed in milliseconds

Involuntary motion (can't control)

identified by localized unsharpness or blurring. minimized by: clear explanation. decrease exposure and increase mA

4 quality factors of film-based images

density ; contrast ; spatial resolution ; distortion

radiographic contrast

difference (variation) in density between adjacent areas of radiographic image differences in # of grays controlling factor- kV

short scale/ high contrast

fewer number of different grays 50kV [800mAs] lower kV=higher contrast

Compensating filters

filter out a portion of the primary beam toward the thin or less dense part of the body that is being imaged

contact shield

flat gonadal shields - most common in recumbent positions 1mm lead equivalent absorbs 95-99% of primary rays in 50 to 100kV range

Controlling factors of spatial resolution

geometric factors, the film-screen (fast system = short exposure times) , & motion small focal spot, increase in SID, & decrease in OID result in less geometric unsharpness & increase resolution.

upside down grid

grid turn upside down (the line running down the center of the grid is the tube side and is the same direction of the grid strips) extreme cuttoff

Distortion

image quality factor The misrepresentation of object size and shape on a radiograph caused by x-ray beam divergence. Distortion increases as the angle of divergence increases. Center point of x-ray beam (central ray) has no divergence (least amount of distortion). All other aspects hit the IR at an angle, with the angle divergence increasing to the outermost portion of xray beam.

spatial resolution

image quality factor (film based) the recorded sharpness of structures on the image. lack of definition is blur or unsharpness

Density

image quality factor (film-based) amount of "blackness" on the processed radiograph. (high density, less light)

anode heel effect

intensity of radiation emitted from the cathode end of the x-ray tube is greater than that emitted at the anode end (more intense under cathode [greater kV])

What is the primary controlling factor for radiographic contrast?

kV

off-center grid

lateral decentering: the more the CR is off center from the centerline of the gris, the greater cutoff CR must be centered along the center axis of the grid -exception: decubitus-short dimension (SD) ; grid is placed lengthwise w/ patient , but CR is centered along crosswise axis of grid to prevent cutoff

Accurate collimation

limiting the size & shape of the x-ray field to the area of clinical interest close four-side collimation one of the best ways to reduce patient exposure remember divergence of x-ray beam

spatial resolution is expressed and measured by?

line pairs per millimeter (lp/mm) for general imaging its 5 to 6 lp/mm

Portrait (lengthwise)

long axis of body part is aligned w/ longest dimension of the IR

mAs

mA x time =mAs refers to the number of x-rays and duration of exposure

The primary controlling factor for density is?

mAs (mA & time)

Personnel monitoring

measurement of the amount of radiation dose received by occupationally exposed individuals

exposure

measures amount of ionization created in air by x-rays, which is expressed in units of roetgen (R) or coulomb per kilogram (C/kg)

long scale/ low contrast

more number of different grays 110kV (20mAs) higher kV=less contrast

what is the greatest deterrent of spatial resolution?

motion. 2 types: voluntary/ involuntary

specific area shielding

shadow and contact shields

application of anode heel effect

thicker parts at cathode

Voluntary motion (can control)

visualized as generalized blurring of linked structures minimized by: controlled breathing, patient immobilization. Also by use of high mA and short exposure

What is is usually indicated by measurements of exposure

x-ray tube output, patient entrance exposure, and scattered radiation levels.