PROJECTION GEOMETRY

PROJECTION GEOMETRY

is used to maximize radiographic image quality and facilitate accurate radiographic diagnoses

focal spot size and relative positions of the object and image receptor (digital sensor or film) on image clarity, magnification, and distortion.

five basic principles of projection geometry

conventional radiograph

a twodimensional projection image of a threedimensional object

1. use of small effective focal spot

2. use of long, open ended cylinder

3. minimize the distance between the object and image receptor

3 METHODS TO MINIMIZE THE LOSS OF IMAGE CLARITY

1.0mm or less

nominal focal spot size of intraoral

0.3mm

nominal focal spot size of extraoral

long, open ended cylinder

increases the source-to-object distance which reduces geometric unsharpness

long, open ended cylinder

increases the distance between the source and the object

long, open ended cylinder

reduces the magnification of images on a periapical view

long, open ended cylinder

also improves image sharpness by increasing the distance between the focal spot and the object

16 inches

ang usual distance between the subject to the focal spot

IMAGE SIZE DISTORTION

Often happens while using paralleling technique

IMAGE SIZE DISTORTION

s the increase in size of the image on the radiograph compared with the actual size of the object

Increasing the source-to object distance and decreasing the object-to-image receptor distance

__ minimizes image magnification

IMAGE SHAPE DISTORTION

Often happens when using bisecting technique

IMAGE SHAPE DISTORTION

ELONGATION & FORESHOERTENING.

elongation

result when the x-ray beam is oriented at right angles to the object but not to the image receptor

elongation

object appearing longer on the image receptor than its actual length

elongation

negative angulation

foreshortening

the result when there is an unequal distances of the various parts of the object from the image receptor

foreshortening

causes the radiographic image to be shorter than the object

foreshortening

positive angulation

RIGHT TUBE TECHNIQUE

Using 2 different radiographic films (# 1/2 panoramic x-ray and 4) and 2 techniques that is done

RIGHT TUBE TECHNIQUE

Examine two images projected at right angles to each other.

# 1/2 panoramic x-ray and 4

ginagamit for right tube technique

buccal object rule and clark’s rule

other name of slob technique

SLOB TECHNIQUE

Using only the same/one film

SLOB TECHNIQUE

SLOB TECHNIQUE

Done by shifting the central ray (mesial or distal) together with the object (film) where the subject (dot) is placed lingually/distally

digital receptor or film #2

ginagamit for slob technique

same lingual

pag kunware minove yung central ray mesially tas sumunod yung obect

opposite buccal

pag minove yung central ray mesially’distally at hindi sumunod yung object