Radiographic Math Flashcards

These vocabulary flashcards cover essential radiographic mathematics concepts, including exposure basics, the 15% rule, inverse square law, grid conversion factors, and magnification formulas.

$mAs$ (Milliampere Seconds)

The product of $mA$ (current) and time in seconds; it controls the quantity of x-ray exposure without affecting the quality.

Effect of Increase in $mAs$

Leads to increased exposure (more x-rays reach the image receptor) and results in a brighter image.

15% Rule

A formula used to maintain image receptor exposure when changing $kVp$: increasing $kVp$ by $15\%$ requires decreasing $mAs$ by $50\%$, while decreasing $kVp$ by $15\%$ requires doubling the $mAs$ ($100\%$ increase).

Inverse Square Law

The mathematical relationship expressed as $\frac{I_1}{I_2} = \left(\frac{D_2}{D_1}\right)^2$, where intensity is inversely proportional to the square of the distance from the source.

Inverse Square Law: Doubling Distance

When the distance ($SID$) is doubled ($2\times$), the exposure intensity decreases by $75\%$ to $\frac{1}{4}$ ($25\%$) of the original exposure.

Inverse Square Law: Halving Distance

When the distance ($SID$) is halved ($\frac{1}{2}$), the exposure intensity increases by $4\times$ ($400\%$) of the original exposure.

Grid Conversion Factor ($GF$) Formula

The formula used to adjust technique when changing grids: $\text{mAs with Grid} = \text{mAs without Grid} \times GF$.

Grid Factor for $8:1$ Ratio

The specific $GF$ for an $8:1$ grid ratio is $4$.

Grid Factor for $16:1$ Ratio

The specific $GF$ for a $16:1$ grid ratio is $6$.

$SID$ (Source-to-Image Distance)

The distance from the x-ray tube to the image receptor.

$SOD$ (Source-to-Object Distance)

The distance from the x-ray tube to the anatomy (object).

$OID$ (Object-to-Image Distance)

The distance from the anatomy (object) to the image receptor; keeping this as small as possible reduces magnification.

Magnification Factor ($MF$)

The ratio that determines how much an image is enlarged, calculated as $MF = \frac{\text{Image Size}}{\text{Object Size}}$ or $MF = \frac{SID}{SOD}$.

Effect of Distance on Magnification

Increasing $OID$ or decreasing $SID$ increases magnification, while decreasing $OID$ or increasing $SID$ decreases magnification.