What Is a CT Scan?
A CT scan or Computed Tomography (CT) examination refers to a diagnostic procedure that utilizes X-rays.
Following the discovery of X-rays by the German physicist Wilhelm Röntgen in 1895, the utility of X-ray imaging was recognized in various industries. Currently, X-ray imaging (referred to as X-ray inspection) is widely employed in diverse fields.
In industrial applications, X-ray inspections are primarily categorized into two types: transmission inspections and CT scans.
Transmission inspections follow the same principles as conventional X-ray examinations conducted in hospitals, capturing two-dimensional images by detecting X-rays that have been attenuated based on the material, density, and thickness of the transmitting substance using a film or detector on the receiving surface.
On the other hand, Computed Tomography, or CT scan, involves capturing multiple transmission images around 360° and utilizing computer-based reconstruction calculations to generate cross-sectional images and three-dimensional models of the subject. It is a digital X-ray inspection method.
The reconstructed 3D images allow observation of the subject’s interior at any cross-section, facilitating tasks such as defect and foreign object detection within products and measurement of material thickness. Additionally, the obtained 3D models can be output as data, enabling comparisons with Computer-Aided Design (CAD) data and utilization in reverse engineering.
Uses of CT Scan
In the industrial sector, CT scans (Computed Tomography) serve as a widely used non-destructive testing (NDT) method for quality control and product development.
Industries such as automotive, aerospace, energy, and electronics manufacturing use CT scans for tasks like detecting internal defects in cast components and welded parts, inspecting foreign objects within products, and measuring the geometrical dimensions of assembled components.
In manufacturing, CT scans play a crucial role in product development and quality control, contributing to design verification, prototype evaluation, and investigations into the durability and reliability of products.
Principles of CT Scan
CT scans utilize X-rays, also known as ionizing radiation.
X-rays, having a very short wavelength and high energy, can penetrate objects. However, during the transmission through objects, they collide with electrons orbiting around atomic structures, causing attenuation. Materials with high density, such as metals, exhibit a high attenuation rate, whereas materials with low density, like air or plastic, show a lower attenuation rate.
The basic principle of X-ray inspection lies in the detection of attenuated X-rays based on the material, density, and thickness of the transmitting subject. CT scans extend this principle by applying computer-based calculations to reconstruct three-dimensional physical distributions of the subject using multiple transmitted information (projection data, transmission images).
While conventional X-ray inspections produce 2D images, CT scans leverage multiple transmission data for the calculation of image reconstruction, enabling the acquisition of 3D information about the subject.
When obtaining CT scan images, it is essential to consider both hardware and reconstruction algorithms. The configuration and reconstruction algorithm of the hardware can vary based on the method of acquiring image data, impacting the time required for obtaining a single set of data compared to traditional X-ray inspections.
Structure of CT Scan
The components of an X-ray CT device include the following three main elements:
- X-ray Tube (and High-Voltage Generator)
- Detector
- Drive System Hardware, such as Rotation Stages
1. X-ray Tube (and High-Voltage Generator)
The X-ray tube comes in various types depending on the required output dose. For industrial X-ray applications, there are mini-focus X-ray tubes with a focal size of several millimeters suitable for large parts in X-ray CT. Conversely, micro-focus X-ray tubes with micron-level focal sizes and nano-focus X-ray tubes with extremely small foci in the nanometer range are suitable for X-ray CT of small products, such as semiconductor and chip components. The choice depends on the output energy and the imaging requirements.
2. Detector
Various types of detectors exist, but in industrial X-ray CT, Line Detector Array (LDA) sensors and Flat Panel Detector (FPD) sensors are commonly used. LDA sensors, consisting of linearly arranged elements, capture only slice images. While they produce low-noise images less affected by scattered radiation, capturing the entire subject requires capturing multiple-slice images, making it time-consuming for whole-scan applications.
FPD sensors, on the other hand, feature elements arranged planarly, capturing a wide area in a single scan. While allowing quick scans compared to LDA sensors, they are more susceptible to scattered radiation, resulting in slightly noisier images.
3. Drive System Hardware
In X-ray CT, the drive system hardware for rotating the subject is indispensable. By rotating the subject 360° while irradiating it with X-rays and detecting transmission information, X-ray CT images are obtained. The precision of the drive system significantly influences the accuracy of CT images and the level of noise. Additionally, the drive speed affects the capture time, making the hardware crucial in X-ray CT.
Other Information on CT Scan
1. Trends in CT Scan
In recent years, with advancements in CT scans, smaller focal points of X-ray sources have enabled the creation of even higher-resolution CT scan images. The availability of detailed CT scan images, coupled with the reduction in computation time for reconstruction due to improved processing capabilities, has led to diverse applications across various fields.
Innovative applications include evaluating and structurally analyzing prototypes of batteries installed in hybrid and electric vehicles. There is also an increasing number of cases involving detailed analysis and troubleshooting of electronic circuit boards using micro-focus X-ray CT and nano-focus X-ray CT.
The visualization of internal structures has led to the non-destructive testing of Glass Fiber Reinforced Plastics (GFRP) and Carbon Fiber Reinforced Plastics (CFRP). CT scans have become valuable in these cases, where, previously, inspections were performed by destroying products to analyze the orientation of glass or carbon fibers.
2. Reverse Engineering
In reverse engineering applications, CT scan images serve as a basis for creating 3D data from CT scan images for tools such as CAD. Comparing design data with the actual shape and dimensions of products aids in product design changes and process improvements. The ability to construct CAD data from CT scan images allows for compatibility with 3D printers, enabling the realization of product shapes using 3D printers, especially for products without design blueprints.
Moreover, CT scans are applied in fields previously untouched, such as analyzing the foam structure of materials like sponges and foam urethane, scanning the interiors of Buddhist statues in archaeology, and digitizing the skeletons of living organisms, including fish.
3. Workflow of CT Scan
CT scans typically involve the steps of imaging, evaluation, and analysis.