GEOMETRIC FACTORS

• optimal geometric quality - Can be achieved by

  Maximizing recorded detail and minimizing image distortion.
• Recorded detail - refers to the distinctness or sharpness of the structural lines that make up the recorded image.
• 3 types of recorded detail

  • Geometric unsharpness
  • Receptor unsharpness
  • Motion Unsharpness
• types of distortion is size and shape
• RECORDED DETAIL - ability of a radiographic image

  to demonstrate sharp lines will determine the quality of the

  recorded detail.
• Resolution - is the ability of the

  imaging system to resolve or

  distinguish between two adjacent

  structures.
• Resolution can be expressed in the unit of (Lp/mm)
• greater the number of line pairs per

  millimeter resolved, the greater the resolution and recorded detail. True or False?

  True
• (Lp/mm) stands for - line pairs per millimeter
• line pairs per millimeter - Depicts how well you can see the differences in structures.
• Spatial resolution - refers to the

  smallest detail that can be detected in

  an image
• Contrast resolution - refers to the ability

  of the imaging system to distinguish

  between small objects having similar

  subject contrast
• The unit of resolution is line pairs

  per millimeter (lp/mm) or - cycles per

  mm
• resolution tool - is read by

  discerning the point at which the

  finest lines are visible as separated

  from one another.
• Most human visual acuity is limited

  to the range of 5-10 lp/mm
• The higher the number, the smaller is the object that can be imaged and the better is the spatial resolution.
• Very fast screens can resolve 7 lp/mm
• fine-detail screens can resolve 15 lp/mm.
• Direct exposure film can resolve 50

  lp/mm.
• The objective of radiography involves controlling the degree of unsharpness so that it does not interfere with image diagnosis
• Evaluation of resolution is best accomplished when an image has high contrast and a diagnostic quality density
• The amount of geometric unsharpness is the result of the relationship among the size of the focal spot, SID and OID
• Focal spot - is the region of the anode target in which electrons interact to produce x-rays.
• Line Focus Principle - is used to reduce the effective area of the focal spot for better resolution.
• decreased angle is = decreased focal spots
• narrower useful beam - smaller anode angle
• wider useful beam is greater anode angle
• The physical dimensions of the focal spot on the anode target in x-ray tubes used in standard radiographic applications usually range from 0.5 to 1.2mm
• Focal spot size is determined by the

  filament size
• Small focal spot sizes are usually- 0.5 or 0.6mm

  large focal spot size are usually- 1.0 or 1.2mm
• focal spot size only affects recorded detail
• Focal spot size - influences the amount of unsharpness recorded in the image
• Increasing the SID decreases the amount of unsharpness
• Increasing the OID increases the amount of unsharpness
• Unsharpness resulting from patient motion can be classified as voluntary (within patient’s control) or involuntary (outside patient’s control)
• physical immobilization, such as

  sandbags, tape, or other devices, as

  deemed necessary.
• Distortion - Results from the radiographic misrepresentation of either size

  (magnification) or shape of the anatomic part
• magnification refers to an increase in object’s image size compared with its true, or actual size
• SID is inversely related to magnification
• MAGNIFICATION FACTOR - indicates how much

  size distortion or magnification is demonstrated on

  a radiograph