Images & Quality

Radiographic Quality

OR: “MAKING PRETTY PICTURES” • Chris Ober, DVM,

PhD, DACVR

What is a Good Radiograph?

• You can see everything that you’re supposed to in a given study • Depends on the intent of the study

– Thoracic spine? – Heart and lungs?

• 10 February 2011

• Patient positioning important, but we’ll leave that for later discussions

Artifacts

• Component of image

– Not real structure AND/OR – Interferes with image interpretation

Perception

• Be aware of optical illusions • Mach lines

– Appear at interfaces of different opacities – Can be mistaken for fractures

• Can occur anywhere in the imaging process

– From the production of electrons to the storing of an image file or anything in between

• We’ll mostly talk about these in lab and in a couple of lectures

Reference to Consider

• Kirberger RM. Radiograph Quality Evaluation for Exposure Variables—A Review. Vet Radiol Ultrasound 40(3), 1999, pp 220-226.

The Grand Plan

• Image Geometry • Film Density • Radiographic Contrast • Image Detail • Exposure Technique • Quirks of Digital Radiography

Radiographic Quality

• Image Geometry • Film Density • Radiographic Contrast • Image Detail • Exposure Technique • Quirks of Digital Radiography

Basic Points

• Divergent Beam – Photons travel in all directions from the source (focal spot) • The source has dimensions – not just a point in space • Photons travel in straight lines

– Scatter radiation confounds this postulate, which is why scatter is troublesome

• Image is 2D representation of 3D object

Cathode

Basic Points

• Divergent Beam – Photons travel in all directions from the source (focal spot) • The source has dimensions – not just a point in space • Photons travel in straight lines

– Scatter radiation confounds this postulate, which is why scatter is troublesome

• Image is 2D representation of 3D object

Larger penumbra = more unsharpness

Inverse Square Law

• Intensity of X-ray beam

– Directly proportional to mAs – Inversely proportional to square of...