The size of the focal spot influences the image resolution.

• A. Radiation Dose
• B. Image Resolution
• C. Field of View
• D. Contrast

Answer: (B)

Focal spot size controls geometric unsharpness in radiographic images. Because X-rays emanate from a finite area, rays from different parts of the focal spot create a small blur, called penumbra, along edges. A smaller focal spot minimizes this blur, producing crisper edges and higher spatial resolution (the ability to distinguish small details). A larger focal spot increases the penumbra, making edges blurrier and lowering resolution. This effect is most evident when the image is formed with minimal magnification, though it remains a primary determinant of sharpness regardless of other factors. Dose, field of view, and contrast are influenced by other aspects of technique and equipment, so the focal spot size mainly governs image sharpness and resolution.