Part II

Image Quality

1

Image Quality

Image Quality Photographic Quality Geometric Quality

2

3

Why you see what you see…

The films or images have different levels of density – different shades of gray

X-rays show different features of the body in various shades of gray.

The gray is darkest in those areas that do not absorb X-rays well – and allow it to pass through

The images are lighter in dense areas (like bones) that absorb more of the X-rays.

Terminology Density, contrast Detail Distortion Image Sharpness spatial resolution Lp/mm Blur Motion SID OID Focal spot size

Image receptor Magnification Penumbra Size distortion Shape distortion Focal Spot size

Image quality5

Resolution, ability to distinguish shapes, ability

to distinguish lines on image

detail

6

RECORDED DETAIL

The degree of sharpness in an object’s borders and structural details.

How “clear” the object looks on the radiograph

7

Recorded detail Image sharpness Spatial resolution Smallest separation

of two lines or edges Measured by lp/mm

8

RESOLUTION TEST

TOOLS

LINE PAIRS/ MM

Depicts how well you can see the differences in structures

More lines=more detail

9

10

11

Recorded Detail

SID Focal spot size OID Image receptor type Motion

Factors that affect detail

Focal Spot Geometry

Angle of anodesize

Focal Spot Geometry

Focal spot is notreally a single point

Dependent on filament size and anode angle.

SID

Shine a flashlight on a 3-D object, shadow borders will appear “fuzzy”

-On a radiograph called penumbra

Penumbra (fuzziness) obscures true border

Farther the flashlight from object = sharper borders. Same with radiography.

15

Recorded Detail: Penumbra and SID

Recorded Detail: Penumbra and Focal Spot Size

Recorded Detail: Penumbra and OID

19

The position of the structure in the body will influence how magnified it will be seen on the image

The farther away – the more magnified

20

Recorded Detail: OID and Penumbra

The closer the object to the film, the sharper the detail.

OID , penumbra , sharpness OID , penumbra , sharpness

Structures located deep in the body, radiographer must know how to position to get the object closest to the film.

Recorded Detail: Image Receptor Type

Film/Screen Imagingexcellent spatial resolution-smallest

detail that can be detected in an imageComputed Radiography (cassettes)Digital Radiography (cassette-less)

improved contrast resolution

22

Motion Can be voluntary or involuntary

Best controlled by short exposure times

Use of careful instructions to the patient

Suspension of patient respiration

Immobilization devices

23

Blurring of image due to patient movement during exposure.

Misrepresentation of size or shape of anatomic part; when part is distorted,

detail is reduced

distortion

24

Distortion

An increase of decrease in the size of an object : magnification or reductionThree types: size, shape, placement of part in body

Types of Distortion

SID-size distortion OID-size distortion Beam Angulation-

shape distortion Body Part-Beam

alignment-shape distortion

FACTOR INFLUENCING DISTORTION

Distortion: SID

40” SID VS 72” SID Which one is which?

28

29

Distortion: OID

31

Elongation Foreshortened Normal

37

38