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Part II Image Quality 1  Image Quality  Photographic Quality  Geometric Quality 2.

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Presentation on theme: "Part II Image Quality 1  Image Quality  Photographic Quality  Geometric Quality 2."— Presentation transcript:

1

2 Part II Image Quality 1

3  Image Quality  Photographic Quality  Geometric Quality 2

4 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.

5 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

6 Image quality Density Contrast Detail Distortion 5

7 Resolution, ability to distinguish shapes, ability to distinguish lines on image detail 6

8 RECORDED DETAIL  The degree of sharpness in an object’s borders and structural details.  How “clear” the object looks on the radiograph 7

9 Recorded detail  Image sharpness  Spatial resolution  Smallest separation of two lines or edges  Measured by lp/mm 8

10 RESOLUTION TEST TOOLS LINE PAIRS/ MM Depicts how well you can see the differences in structures More lines=more detail 9

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13 Recorded Detail  SID  Focal spot size  OID  Image receptor type  Motion Factors that affect detail

14 Focal Spot Geometry Angle of anode size

15 Focal Spot Geometry Focal spot is not really a single point Dependent on filament size and anode angle.

16 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

17 Recorded Detail: Penumbra and SID

18 Recorded Detail: Penumbra and Focal Spot Size

19 Recorded Detail: Penumbra and OID

20 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

21 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.

22 Recorded Detail: Image Receptor Type Film/Screen Imaging excellent spatial resolution-smallest detail that can be detected in an image Computed Radiography (cassettes) Digital Radiography (cassette-less) improved contrast resolution

23 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

24 23 Blurring of image due to patient movement during exposure.

25 Misrepresentation of size or shape of anatomic part; when part is distorted, detail is reduced distortion 24

26 Distortion An increase of decrease in the size of an object : magnification or reduction Three types: size, shape, placement of part in body

27 Types of Distortion  SID-size distortion  OID-size distortion  Beam Angulation-shape distortion  Body Part-Beam alignment- shape distortion FACTOR INFLUENCING DISTORTION

28 Distortion: SID

29 40” SID VS 72” SID Which one is which? 28

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31 Distortion: OID

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38 Elongation Foreshortened Normal 37

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