FUNDAMENTALS OF IMAGING

RAD 206

Geometric factors

What is focal spot? andWhat is effective focal spot ?

The smaller the beam towards the patient

The better the detail of image produced

FOCAL-SPOT BLURDependent on the size of the effective focal spotSmaller the effective focal spot results in:

• less Blur and •better spatial resolution

Focal spot Blur is the most important factor in determining spatial resolution

Smaller x-ray beam width will produce a sharper imageFine detail = small focal spot ( for small parts of the body )General radiography of large areas uses large focal spot

Experiment and compare between beam from a penlight with a beam from a flood light

Focal-Spot Blur is caused by the effective size of the focal spot, which is larger towards the cathode side of the image

Anode cathode

Effect of focal spot size on: PenumbraAnd Resolution

Anode cathode

Focal Spot Blur is smaller when the OID is smaller

OBJECT SHAPEObjects with structures coincide (aligned) with the x-ray beam has maximum detail