kV & Distance in Radiography

Vocabulary flashcards covering kilovoltage, contrast scale, 15% rule, generator heat units, and distance calculations.

Kilovoltage (kV)

The exposure factor that primarily affects beam quality and secondarily affects beam quantity, while controlling radiographic contrast.

15% Rule

A rule stating that increasing the $kV$ by $150\%$ doubles the exposure of the image, while a $150\%$ decrease in $kV$ cuts exposure in half.

Exposure Maintenance Technique

A technique modification where increasing the $kV$ by $150\%$ requires decreasing the $mAs$ to $\frac{1}{2}$ to maintain the same image exposure.

Short Scale Contrast

A scale of radiographic contrast associated with high contrast, exhibiting major differences between adjacent density areas.

Long Scale Contrast

A scale of radiographic contrast associated with low contrast, displaying a wide range of subtle density shades.

Optical Density Perception Threshold

The minimum percentage change in $kV$ required to perceive a visible change in optical density, which is a $40\%$ change.

High kV Techniques

Radiographic technique selections that lower patient radiation exposure and decrease heat unit production in the x-ray tube.

Efficient Generator Heat Unit Formula

The formula used to calculate heat units for three-phase or high-frequency x-ray generators, defined as $\text{HU} = \text{mA} \times \text{time} \times \text{kV} \times 1.41$.

Inverse Square Law

A law stating that radiation intensity is inversely proportional to the square of the distance from the radiation source ($\frac{I_1}{I_2} = \frac{D_2^2}{D_1^2}$).

Direct Square Law

A law stating that $mAs$ is directly proportional to the square of the distance ($\frac{\text{mAs}_1}{\text{mAs}_2} = \frac{D_1^2}{D_2^2}$).

Roentgen (R or mR)

The unit of measurement used to quantify x-ray radiation intensity in air.