Question

A radiograph of the hand is underexposed and must be repeated. The original technique used was 55 kV 2.5 mAs and the technologist decides to keep the mAs at the same level but increase radiographic density. How much increase in kV is required to double the density?

Answer 1

An approximate 6 kV increase from the original setting of 55 kV would be required to double the radiographic density, according to the rule of thumb that a 10-15% increase in kV doubles the radiographic density.

Step-by-step explanation:

To double the radiographic density without changing the mAs value, we need to understand how kV affects the density of an x-ray image. An increase in kilovoltage (kV) results in an increase in the energy of x-ray photons which in turn increases the penetration power and reduces the absorption of x-rays by the subject tissue, therefore increasing the radiographic density of the image.

The rule of thumb for radiographic exposure is that an increase of kV by 10-15% will double the radiographic density. In this case the original technique was 55 kV. If we use the lower end of the rule, an increase of 10% of 55 kV is needed. Therefore, we need an additional 5.5 kV rounding up a 6 kV increase might be required, resulting in a new setting of approximately 61 kV to achieve the desired effect.