What are artifacts in radiology? Artifacts can be represented in many ways, such as an abnormal shadow or a reduced image quality due to hardware failure in the radiograph or improper handling and errors. Simply, artifacts are when the radiograph does not correspond to the anatomy shown. Artifacts can be caused by improper handling of a film, errors during processing a film and patient motion while the radiographer takes the image. This will result in a distorted image. X-rays can be taken in computed radiography, digital radiography, computed tomography and magnetic resonance imaging. One of the most common artifacts is radiopaque objects on the internal or external surface of the patient. This artifact can be presented in any radiograph. Radiopaque objects are objects that block radiation rather than passing it through and this objects can be metals that contain compounds such as barium sulfate, bismuth, and tungsten. So radiopaque items can be necklaces, piercing, and heart stents. Overall preventing artifacts is vital, because it can prevent incorrect diagnosis for the physician.
First of all, there are artifacts in Computed radiography and this type of radiographs use photostable storage phosphors. An increasing number of Computed radiography machines are being installed in third world countries and developing countries due to the magnificent image quality of radiographs. But artifacts such as fogging, foreign bodies and double exposure have been seen throughout this images and many of this artifacts can resemble diseases to the radiologist. One of the artifacts in (CR) Computed radiography is called fog. Fogging is when imaging plate is exposed to extraneous radiation when you use dynamic range. The fog creates an unwanted darkness and it is caused by exposure to white light, radiation scattering improper safe lighting and using expired film. Fogging creates an unwanted increase in density and can reduce the radiographic contrast. CR can create the light bulb effect. Light bulb effect is another artifact that can appear and it happens when the lower and peripheral portions of the film are darker than rest of the image. It can be caused by black scattered radiation entering the imaging plate and it is most frequently shown when exposure is increased or not collimated entirely in overweight patients. Like the fogging, this artifact is induced by the dynamic range and sensitivity of the image plate. This image can misrepresent disease such a pneumothorax or pneumoperitoneum. This image can obscure abnormalities with contrast and brightness This artifact can be prevented by lowering the kilovoltage and using exact combination of the anatomy. Double exposure is another serious obstruction that is viewed on the image. Double exposure occurs due to the radiographer’s error. Double exposure is when the same film is exposed twice and may lead to superimposition of the anatomy and duplication of the images. Proper knowledge of the X-ray equipment can prevent this errors. Foreign bodies such as dust and other foreign material can obstruct the image plate and result as an artifact. Some examples can include of spillage of liquid on the imaging plate that can result in calcification when viewed. This type of artifact can be prevented by cleaning the reader using proper technique. Lastly, in CR hardware or equipment malfunction can result in multiple artifacts. One of the hardware in the CR is called imaging plate. The imaging plates can have cracks which will lead to artifacts and manufacturers recommend changing the imaging plate every 5 years. Also, there are software induced artifacts known as image transmission errors. This artifact will be due to power failure when the image is being transmitted to the reader. This results in a corrupt image or missing pixels of the image. Overall, this is the main artifacts caused in the CR and it is vital to prevent artifacts so that patient would not have to be exposed again and prevent confusion of diseases or obscuring diseases such as the Light Bulb effect.
Secondly, there are artifacts in digital radiography(DR). Digital radiography is an automatic digital x-ray detector that is much more efficient than the CR. The DR system produces better quality images with faster image acquisition. There are similar artifacts in DR and CR and there are many unique artifacts seen in DR. Some artifacts in CR and DR is under and overexposure called does creep and collimation issues. In DR detector may experience an artifact called image lag or ghosting. Lag refers to the trapped charge. Ghosting is used to describe the change of sensitivity, because of excessive exposure. DR systems can produce images at a faster rate than their detectors can detect. This offset can signal one exposure into a readout of many exposures. This artifact can cause to expose outside the skin line to the unattended x-ray beam. The second exposure will produce residual signals from other objects and can affect the image mimicking a disease. After the first exposure is taken a ghost image of the first exposure will appear clearly on the second image obstructing the anatomy. Many steps can be approached to stop this artifact from happening. The radiology technologist can reduce the exposure level and colmation because lag increases with exposure. Secondly, we can decrease this artifact and lag by increasing the time interval between exposures causes lag decreases with increased time. Lastly, when you do multiple images, we have to increase the exposure in the larger area of attenuated radiation, would allow time before the next X-ray. Many DR system may have lag, but in many cases, it may not be clinically relevant, because it may have elapsed time between exposures. Image compositing is another major artifact in DR. During Dr an image a single x-ray exposure may be used to expose two or three plates all at once. Image composting is when the anatomy of the top and bottom are included in two images. When the picture is combined and the two images will overlap which may result in artifacts. For example, if a stitched screw was taken of scoliosis the image. It may seem as if the screw was loose or displaced , because of the acquired superimposition the screw images when the machine was in different depth. To avoid this incident you can acquire source images before the image compositing is taken. Also, it has been clinically proven that these images can be taken by pivoting the X-ray tube at the focal spot and aligning to match the detector for each exposure. When doing this image since the anatomy is imaged on the same alignment no artifacts can be created. Lastly, another important artifact that obstructs the image is called backscatter. Backscatter can contaminate many images and are acquired by portable radiographs that use higher exposure for more obese people. This creates a significant amount of scattered radiation and inappropriate collimation creates scattered radiation. Scattered radiation on the back of the detector produces an image of the electronic components on the radiograph. This would be noted as a hardware failure for the DR and this artifact can be reduced by having an extra lead on the back of the detector.
Lastly, there are many artifacts in CT, MRI and film radiographs. Streak artifacts in CT machine are when there is a high attenuation of metal objects in the field of views such as surgical plates, screws, and bands. In MRI machines magnetic fields are magnetic fields are used and magnetic field can be distorted when metal objects such as dental implants containing metal are imaged. This metal artifacts can affect CT and MRI machines because it will obstruct pathology and the anatomy of the patient. But some MRI imaging of implanted metals is okay to image if they made of low magnetic abilities. While there are many more artifacts that can be produced by the machine or operator the metal items interfere with the machines creating a magnitude amount of artifacts. Overall, metals are a major reason for the artifacts on CT and MRI machines. While film radiography is rarely used in hospitals today there are many artifacts that have shown up. Film radiography can have finger mark artifacts. This artifact happens when the operator touches the image. Some common artifacts in film radiography are called static electricity, black film, and clear spots. Static electricity is when there is forced flexing of the film. This results in black marks on the image that is similar to electricity. Black film artifact is when the film is exposed to complete exposure of the light and this event makes the film turn black unable to see the image. The clear spot is an artifact on the image created by dirt on the intensifying screen or air bubbles sticking on the film when you process the image.
In conclusion, artifacts should be prevented and precautions should be taken in order to prevent it. Artifacts are dangerous to the radiologist at times because they can mimic diseases or disorders. It is vital for the radiologic technologist to prevent artifacts because an artifact can cause the image to be taken again increasing unnecessary radiation to the patient and staff. Proper equipment maintenance and proper procedures will help prevent artifacts.