Image Sharpness

Sharpness plays a crucial role in image quality, as it determines the level of detail an imaging system can capture (Figure 11).

Figure 11. Image A is sharpness when compared to B.

Image sharpness is defined by the dimensions of an object’s partially shaded outer region, known as the penumbra. A broader penumbra results in a less sharp image (Figure 12).^1,^2,⁵

Figure 12. Shadow casting, umbra and penumbra.

We will only discuss the properties of shadow-casting and the penumbra width related to the x-ray tube and sensor. We will not factor in the patient-related sharpness of the image.

Several factors influence image sharpness. Each factor can be assessed individually while keeping others constant:

The apparent focal spot size: A larger focal spot increases the penumbra, reducing sharpness.^1,^3,^6,¹¹
Source-to-object distance: A greater distance decreases the penumbra, enhancing image sharpness.^1,^2,^4,^5,^8,¹¹
Object-to-receptor distance: A larger distance increases the penumbra, lowering image sharpness.^2-4,^7,^9,¹¹
X-ray tube motion-related un-sharpness: Movement of the tube during image acquisition enlarges the apparent focal spot, increasing the penumbra and reducing sharpness.^2,^5,¹²

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