Which statement is true regarding SID and spatial resolution?

Which statement is true regarding SID and spatial resolution?

• A. Short SID yields better spatial resolution
• B. Long SID yields better spatial resolution
• C. SID has no effect on spatial resolution
• D. Only OID affects resolution

Answer: (B)

In radiography, sharpness of detail (spatial resolution) is governed by geometric factors: focal spot size, source-to-image distance (SID), and object-to-image distance (OID). Increasing SID reduces geometric blur because the beam hits the image receptor at a steeper angle, producing less magnification and edge blur. The amount of blur is roughly proportional to the focal spot size times OID divided by SID, so as SID grows, that blur decreases and edges appear sharper. That’s why a longer SID yields better spatial resolution. Shorter SID increases magnification and blur, worsening resolution. It’s also incorrect to say SID has no effect, and while OID matters, the improvement from a longer SID is real and beneficial when feasible.

In radiography, sharpness of detail (spatial resolution) is governed by geometric factors: focal spot size, source-to-image distance (SID), and object-to-image distance (OID). Increasing SID reduces geometric blur because the beam hits the image receptor at a steeper angle, producing less magnification and edge blur. The amount of blur is roughly proportional to the focal spot size times OID divided by SID, so as SID grows, that blur decreases and edges appear sharper. That’s why a longer SID yields better spatial resolution. Shorter SID increases magnification and blur, worsening resolution. It’s also incorrect to say SID has no effect, and while OID matters, the improvement from a longer SID is real and beneficial when feasible.