What if I want to Scan...?

Common CT Scanning Inquiries

People often ask us about size limitations, accuracy/resolution and the ability to scan mixed material parts. While CT scanning is capable of providing geometric and density data on a range of size and materials, not all scanners are created equal. A couple of the factors to consider are maximum voltage and size of the scanning envelope.

Different scanners have different sized scanning envelopes. A scanning envelope is the area that can be captured by the x-ray beams. Data can be acquired for any part or piece of a part that fits within that area. If you have a larger x-ray cone or are willing to compromise resolution, you can achieve larger scanning envelope areas. Based on the scanning envelope size and the part size, multiple parts of the same or varying geometries can be scanned at the same time. For us, the envelope is 5 inches in height by 5 inches in diameter. By understanding the importance of the scanning envelope, we can provide the best inspection services for our customers.

Other inquiries are made concerning accuracy and resolution. We offer an accuracy of 5-7 microns that is guaranteed by metrology software algorithms that take voxel size into account. Voxels are the units used to determine resolution. A voxel represents a value on a regular grid in three dimensional space, and is a combination of “volume” and “pixel”. Smaller voxels equate to higher resolution. The size of a voxel depends on its proximity to the x-ray source. As a part gets farther from the x-ray origin, the resolution will become lower. The accuracy won’t change but the picture will lose some of its crispness.

Mixed material parts can present challenges when scanning due to the ways x-rays react when they encounter different densities and compositions. The x-rays can be absorbed or deflected and scattered to different degrees. High-density materials, such as steel, offset x-rays much more than low density materials like plastic. CT scanning requires x-ray activity to be captured by computerized detectors that generate 3D images. There are filters available to correct for some scatter effect, but when the density difference between two materials causes too much of a scatter effect, non-linearities are amplified by the computer’s reconstruction algorithm which will result in streaking. Alternatively, the lower density material can be “washed out” if the voltage has to be increased too high in an effort to penetrate the higher density material. For the most complete and accurate data, the density difference should be within 2.5 g/cm3.

We take all of these factors into consideration when discussing projects with our customers. Our goal is to provide you with the results you need to make better decisions. Whether that requires high resolution scans or the best possible mixed material scans, we will work to the best of our ability to achieve the information that you need.

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