Did you see the letters mAs mentioned on your radiology report? Or are you starting as a radiographer or radiology resident? This article explains what mAs in radiology stands for and what it means.

mAs = Milliampere-Seconds

mAs is the product of the electrical current applied to the X-ray tube (in milliamperes) and the exposure time (in seconds). It determines the total amount of X-rays produced during an imaging procedure.

What Is mAs or Milliampere-Seconds? More Details Please!

mAs Simply Explained

To obtain X-ray or CT images, the X-ray machine needs an electrical current to generate X-rays. This current is measured in milliamperes (mA). When you multiply this current by the exposure time in seconds (s), you get mAs. Essentially, mAs determines how many X-ray photons are produced during the exposure.

• Higher mAs means more X-ray photons are generated, resulting in a clearer image.
• Lower mAs means fewer X-ray photons are produced, which can lead to a grainier image.

What Is the Difference Between Lower and Higher mAs?

For X-ray and CT images, changing the mAs affects how the images look:

• More mAs means more X-ray photons will travel through the body and reach the detector, resulting in better image quality with less image noise (graininess).
• Less mAs means fewer X-ray photons reach the detector, which can increase image noise and make the image appear grainy.

This balance is crucial for radiologists to obtain clear images while minimizing the radiation dose to the patient.

Does Higher mAs Mean More Radiation?

In brief (Answer! STAT!): If no other parameters are changed, than yes. Increasing the mAs increases the radiation dose to the patient.

For example, doubling the mAs will roughly double the radiation dose if all other factors remain the same.

However, radiologists and radiographers aim to use the lowest mAs possible that still provides a clear image, following the ALARA principle (As Low As Reasonably Achievable) to minimize radiation exposure.

What Is mAs in Radiology – A More Complex Explanation

As you may know, the X-ray tube requires both a tube current (in milliamperes, mA) and an exposure time (in seconds, s). The product of these two factors is the mAs. Here’s how it works:

• Tube Current (mA): Determines how many electrons flow from the cathode to the anode per second.
• Exposure Time (s): Determines how long the tube current is applied.

The mAs controls the total quantity of X-ray photons produced during the exposure. Adjusting mAs influences:

• Image Quality: Higher mAs reduces image noise and improves image clarity.
• Radiation Dose: Higher mAs increases the radiation dose to the patient.

Radiology professionals adjust mAs to find the optimal balance between obtaining a diagnostic-quality image and minimizing radiation exposure.

Further reading:

• What does STAT mean in radiology?
• What does attenuation mean in radiology?
• What is kVp in Radiology? Simply Explained!