What Causes X-Ray Tube Arcing and How Can You Avoid It?

CT X-Ray Tubes Can Fail Due to Arcing - Here’s How You Can Avoid It

CT scanners are complex machines that use X-Ray imaging to capture detailed anatomical diagnostic images. They are able to capture high-resolution images within a short period of time, which is why they are often used in ERs to accurately diagnose patients in need of emergency treatment. CT scanners tend to be expensive due to the technology needed to capture X-Ray images quickly and accurately.

For example, components like the X-Ray tube lend to the machine's initial expense. However, X-Ray tubes can experience damage due to normal wear and tear or improper use, or even fail completely, which means that they will need to be replaced at some point, and this can be quite expensive. One of the most common reasons that X-Ray tubes fail is X-Ray arcing. Fortunately, X-Ray arcing can be mitigated  if you take the necessary precautions.

The Function of CT X-Ray Tubes

CT scanners depend on X-Ray tubes to convert electrical input power into actual X-Rays. The way X-Ray tubes work is by accelerating electrons to high energies. This causes the electrons to hit a metal target out of which the X-rays are produced. The CT scanner's X-Ray tube must be energized to produce the X-rays.

Energizing the X-Ray tube takes a lot of electrical energy--only some of which is actually converted into producing the X-Rays. The remainder of that energy is turned into heat. As a result, X-Ray tubes have to be specially built for CT scanners to withstand that heat, which is one of the reasons they are so expensive to manufacture and to replace.

There are several different types of X-Ray tubes built specifically for CT scanners. These X-Ray tubes vary greatly in their design. For example, Philips' Maximum Rotalic Ceramic X-Ray tube is manufactured with a spiral groove that makes use of liquid metal alloy as a lubricant to cool its rotating anode directly, whereas the Aquilion X-Ray tube is an air-cooled tube that uses a straddle bearing structure and a grounded anode.

Although the designs of an X-Ray tube varies greatly from one manufacturer to another, they have two main things in common. They are designed to withstand the massive amount of heat that a CT scanner's X-Ray tubes are exposed to and they are vulnerable to potential X-Ray arcing if the proper precautions are not taken.

What Is X-Ray Tube Arcing?

An electrical arc is the electrical breakdown of a gas that generates a continuous electrical discharge. An arc occurs in an X-Ray tube because of a short-circuit within the tube, generally from the cathode to the tube envelope. When an X-Ray arc occurs, it results in the loss of X-Ray output and in a localized artifact.

Most short circuits that occur within X-Ray tubes occur due to the presence of impurities that obstruct the path of electrons produced by the cathode before they reach the anode; this causes the momentary loss of X-Ray output. These impurities often form as a result of tungsten evaporation, which is caused by a faulty anode rotor. However, short circuits within the X-Ray tube are not always the result of impurities. In some cases, they may be caused by a defective transformer supplying voltage to the rotating anode's rotor.

What Happens When Arcing Occurs?

Depending on the severity of the short circuit, electrical arcing within the X-Ray tube can have a varying effect on the image captured. Artifacts may show up in the image, making it difficult to make an accurate diagnosis. These artifacts tend to look like alternating hypodense streaks throughout the transaxial image.

Because a CT scanner is a high voltage machine, some arcing is normal. It's such a common occurrence that many CT scanners are designed with the application of a correction algorithm that helps to smooth minor artifacts over in the event that arcing does occur. This is done using either synthesized projections created using unaffected slices, by using a partial data interpolation method, or by using an adaptive filtering scheme.

Although newer CT scanners can smooth out any artifacts caused by minor to moderate arcing, more serious arcing cannot be corrected. Frequent arcing will also cause wear and tear to the X-Ray tube, thereby shortening its lifespan and increasing the risk of tube failure.

How To Avoid Arcing

There are a few precautions you can take to prevent arcing. First, checking the casing of the X-Ray tube itself on a regular basis can help ensure that there are no impurities present. Such preventative maintenance can go a long way towards helping to keep your X-Ray tubes in good condition and preventing wear and tear from shortening its lifespan.

Secondly, if arcing is occurring as a result of an issue with the transformer that's causing surges in voltage, look for any error messages that are popping up. You may need to have your transformer inspected, although one potential way to solve the problem is by using your CT scanner at a slightly lower voltage. For example, changing the acquisition from 140 kV to 120 kV.

What to do if You Experience X-Ray Tube Arcing

Even though minor arcing may not result in artifacts due to your CT scanner's correction capabilities, any electrical arcing that occurs within your X-Ray tubes should not be ignored. X-Ray tubes are expensive and even minor arcing can cause enough wear and tear to require a replacement sooner than it should. If arcing occurs, have a field service engineer inspect your CT scanner's X-Ray tubes as well as the transformer. When it comes to your X-Ray tubes, it's better to be safe than sorry.