Radiation measuring units

Radiation measuring units

Radiation in the air is a measure of radiation intensity.

These measurements include exposure and the air KERMA.

Radiation in tissue is a measure of the dose.

These measurements include absorbed dose, equivalent dose, and effective dose.

All of these measurements are different but related.

Here's an example.

If we wanted to, we could measure each of these values during a single x-ray exposure.

The intensity of the x-ray beam is usually measured as the exposure or the air KERMA.

These values tell us how much radiation is coming out of the x-ray tube and is directed at the patient.

We could also use the air KERMA and exposure to measure the leakage radiation escaping the tube housing.

The dose to the patient, or the radiography, or anyone is first measured as the absorbed dose.

But then the absorbed dose can be calculated and converted into the equivalent dose.

An equivalent dose can be converted into the effective dose.

So why do we need these two categories and five

different ways to measure radiation?

First of all, you should know there's actually more than five

ways to quantify radiation.

But the main reason is that each of these measurements

is used in several ways and tell us

something different about radiation exposure.

For example, absorbed dose tells us how much radiation energy is absorbed in the patient

or in the worker.

We can use this number to evaluate the risk of short-term radiation effects, like skin erythema or hair loss.

But absorbed dose tells us very little about the risk

of long-term effects like cancer.

And that's why we need another dose measurement, which is the effective dose.

Effective dose is used to evaluate the long-term effects, like cancer or genetic conditions.

But it is not used to calculate the total absorbed energy in the patient.

And we cannot use it to predict short-term effects, like erythema or appellation.

So even though these dose measurements might be used in different ways, they're also related in some ways.

For example, if we increase the mA, this will increase the beam intensity, which will increase the exposure and the air KERMA.

And that is going to result in an increase in the absorbed dose, the equivalent dose, and the effective dose.

The same thing is true for kVp.

If we increase the kVp, this is going to increase the beam intensity.

This is going to result in a measurable increase in the exposure and air KERMA.

And if that increases, it's also going to increase the absorbed dose to the person and their equivalent dose and effective dose.

We could also change the distance

and the result is different.

If we increase the distance between the person and the x-ray source, this is going to result in a decrease in the intensity of the x-ray beam according to the inverse square law, which then will result in a measurable decrease in the exposure and air KERMA.

And if those things are decreasing, the absorbed dose, the equivalent dose,

and the effective dose also all decrease.

It's good to know that all of these measurements are related to each other.

Here's a practice question to make sure you

understand these concepts.

Which of those radiation measurements is commonly wont to evaluate the intensity of the x-ray beam within the air?

Select multiple answers.

Take a minute to see if you can figure out what you think the answer is.

Since we're looking to measure the intensity of the x-ray beam in the air, this question has only two correct answers.

If we're measuring the x-ray beam in air, we can measure the air KERMA or we could measure the exposure.