Radiography/Projection Geometry/ hand

define radiography

conventional technique/process of using x-rays to produce a static, 2D image of internal structures of the body (radiograph; plain or projection view)

define imagining chain

components that contribute to radiographic image formation and display

what are components of the imaging chain

x-ray source: produces x-ray

image receptor: receives/detects data

image display device (for digital imaging): shows the radiograph/image

the path of radiation (x-ray beam) must include…

anatomy of interest, and receptor

radiographic image is essentially a map of…

beam attenuation

what is attenuation

reduction in x-ray beam intensity as it travels through the anatomy

the thicker and denser the structure, the more x-rays are absorbed and the ______ the beam is attenuated

more

key features of x-rays beams

• consists of many x-ray photons

• x-rays travel in straight lines

• x-ray beam is divergent

incident beam is differentially attenuated by structures of different _______

densities

rank the following things in order of dec density: fat, air, dentin/cementum, metal, enamel, muscle, bone

metal > enamel > dentin/cementum > bone > muscle > fat > air

less attenuated structures = _____ (high/low) density

low

high attenuated structures = _______ (high/low) density

high

less attenuated structures have what appearance in radiograph formation

black: more intense transmitted beam- radiolucent

more attenuated structures have what appearance in radiograph formation

white: less intense transmitted beam- radiopaque

define density

degree of darkening or opacity of an exposed film or receptor

density depends on…

the number of x-ray photons absorbed by the receptor

in terms of density, the more x-ray photons (more intense transmitted beam)…

inc density → darker image

define contrast

range of densities on an image defined as the difference in densities between the light and dark regions

does this image have high or low contract

low

does this image have high or low contract

high

what are the two types of radiographs

intraoral and extraoral

what are the types of intraoral radiographs

PA, BWX, O

what are the types of extraoral radiographs

PANO, cephalometric and skull projections

reliability of an image in its representation of the…

true state of anatomy examined

what are the parameters of radiographic image quality (5)

• image sharpness

• spatial resolution

• contrast resolution

• magnification

• distortion

image should have __________ magnification and distortion and ________ contrast and spatial resolution for the dx task

minimal; adequate

image sharpness and resolution are distinct but ___________ parameters

independent

what does sharpness measure

how well a boundary between two areas of different radiodensity is revealed

what does spatial resolution measure

how well an image reveals small objects that are close together

what is image size distortion

difference between object size on image an actual object size

what is magnification

inc of size of object on image compared to the actual size of object

what is magnification caused by

divergent paths of x-ray photons in a beam

what is image shape distortion

different in appearance of object shape on image compared to actual object shape

what is the image shape distortion a result of

unequal magnification of different parts of the same object

what are the principles of projection geometry

based on effects of focal spot size and relative positions of the object and image receptor on image clarity, magnification and distortion

when thinking of the principles of projection geometry, the focal spot should…

be as small as possible

when thinking of the principles of projection geometry, the source-receptor distance should…

be as long as possible

when thinking of the principles of projection geometry, the object-receptor distance should…

be as small as possible

when thinking of the principles of projection geometry, the receptor should be __________ (parallel/perpendicular) to the long axis of the object

parallel

when thinking of the principles of projection geometry, the central beam should be ____________ (parallel/perpendicular) to the object and receptor

perpendicular

what is a focal spot

the area on the target of the x-ray tube where x-rays are produced

x-rays originate from all points within…

the area of the focal spot

what is the focal spot range for dental PANOs and/or CT machines

0.4-0.8

a smaller focal point yields a _________ image

sharper

x-rays travel in what way

a straight line

x-rays produced at different points in the focal spot that pass through the same point on an object…

will NOT hit the same spot on the receptor causing blurring of object edges

what are the blurring edges of the object called that are caused by the x-ray being produced at different points in the focal spot

geometric unsharpness/penumbra/adumbration

a large focal spot creates…

wider zone of geometric unsharpness → loss of image sharpness

distances between the source and object and the object and recptor impact…

image sharpness and magnification

what should the source-object distance and the object-receptor distance be to get: reduced x-ray beam divergence, reduced geometric unsharpness, minimal image magnification

inc source-object distance and dec object-recptor distance

what is the magnification equation

SID= source to image (receptor) distance

SOD= source to object distance

intraoral radiographic image magnification is usually less than…

10%

magnification caused by an inc object-receptor can be minimized by inc…

the source to object distance

when does image shape distortion occur

when not all the parts of an object are at the same source-to-object and/or object-to-receptor distance

you can minimize shape distortion by…

• aligning the object and image receptor parallel w each other

• aligning the central ray perpendicular to both the object and image receptor

physical shape of an object may prevent optimal orientation, resulting in…

some shape distortion (max molar root divergence prevents placing all roots parallel- palatal root appears disproportionally longer)

what is foreshortening

radiographic image of object is shorter than the true object

what can cause foreshortening

• the object is not parallel to the receptor

• the central ray is perpendicular to receptor but not to the object

what is elongation

radiographic image of an object is longer than true object

what can cause elongation

• object is not parallel to the receptor

• central ray is perpendicular to the object but not the receptor

to maximize image sharpness… (3)

• use a small focal spot as practical (determined by manufacture)

• inc the source-object distance

• minimize the object-receptor distance

define selection criteria

circumstances that suggest a need for dx imaging

imaging is needed/indicated when…

• there is clinical evidence of abnormality that cannot be fully assessed by only a physical exam

  • there is a high probability of disease that is not clinically evident

before taking images, you should… (3)

• know your dx objectives

• determine which images will help achieve the goals

• have justification for why you expose your pt to ionizing radiation

what are the three quality criteria for radiographs

• record the complete area of interest in the image

• have the least possible amount of distortion

• have optimal density and contrast to facilitate interpretation

what is the backbone of dental dx imaging

intraoral radiographs

what is a periapical radiograph (PA)

projections show entire tooth length and surrounding peri-radicular bone

what are the two projection techniques of periapical x-rays, which is preferred?

paralleling and bisecting angle; parallel is preferred

what is the paralleling technique (AKA right-angle, long-cone or extension cone technique)

position receptor parallel to the long axis of the tooth; use receptor holding instrument to hold receptor in place and guide ring to aid in cone alignment

to achieve the parallel technique, the receptor placement must be placed…

away from the teeth toward the midline

when trying to accomplish the parallel technique, there may be anatomical constraints such as…

shallow palate or vestibule, tori

the use of the parallel technique has inc ________________ distance; what can be used to compensate for this inc distance

object-receptor; a long cone positioning indicating device (PID)

what is a bitewing radiograph (BWX)

projections show only the crowns of the teeth and adjacent alveolar crests

what is an occlusal radiograph

projections show an area of teeth and bone larger than PA images

what is a full-mouth radiographic series (FMX)

includes a “survey” of the whole mouth intended to display the crowns and the roots of all teeth, PA areas, interproximal areas and alveolar bone (including edentulous areas); consists of PAs and BWXs; 18-20 images- 4 BWXs and 14-16 PAs

what are the types of x-ray sources

• wall/ceiling mounted

• hand-held

what is the difference w the operator in a wall/ceiling mounted vs hand-held x-ray source

wall/ceiling: exposure is made while operator is outside of the operatory

hand-held: operator is in the room holding the source wh

what is a position indicating device (PID)

attached to tubehead aperture to direct x-ray beam, usually an open-ended cylinder: “cone” or “aiming cylinder”

what is the job of the receptor

detects/records x-rays; only 1 active side that needs to face the source

what are the two types of receptors

film and digital

what are the two types of digital receptors

direct and indirect

what is the difference between direct vs indirect digital receptors

indirect receptors first convert X-rays to light, then to an electrical signal, while direct receptors convert X-rays directly into an electrical signal

is photostimulable phosphor plate (PSP) direct or an indirect digital receptor

indirect receptor

is solid state, direct digital sensor (CCD/CMOS, corded) a direct or indirect digital receptor

direct receptor

size 0 receptor

pediatric

size 1 receptor

pediatric, small mouth, narrow arch (anterior teeth)

size 2 receptor

most used; posterior teeth

size 4 receptor

occlusal

is the bisecting or the parallel technique used more

parallel

what is the bisecting technique generally

useful when parallel cannot be applies; receptor is placed as close to the tooth as possible and use your imagination to make a bisecting angle between the long axis of teeth and the long axis of the receptor, and align the x-ray tubehead to be positioned at a right angle to the bisecting line

what is vertical angulation

angle between the x-ray bean and line parallel to floor/occlusal plane

what does positive angulation mean

cone points downward

what is negative angulation

cone points upward

what is elongation, what is it caused by

vertical angle too small; under-anggulation

what is foreshortening, what is it caused by

vertical angle too large; over-angulation

what is the PA orientation of an anterior tooth

long axis of the image receptor is vertical

what is the PA orientation in posterior teeth

long ais of the image receptor is horizontal

paralleling advantages and disadvantages

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