TC Artifacts

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PRESENTAtion

ct artefacts

Esther Costumero, Alvaro Ferrero, Pablo Muñoz, Pedro Sanchez, Manuel Sanchez .

Introduction

Kinds of Artifacts

Motion Artifact

Transient interrumption of contrast

Clothing Artifact

Jewlry Artifact

Tube Arcing

Beam Hardening

Partial Volume Averaging

Photon Starvation

Aliasing

Truncation Artifact

Ring Artifact

Conclusion

Bibliography

ÍNDICE

CT Artefacts

Introduction

Computed Tomography (CT) is a widely used medical technique to obtain detailed images of the inside of the body. However, sometimes artifacts can appear, which are distortions or errors in the images. These artifacts can make it difficult to interpret the results correctly and are caused by various factors, such as patient movement or issues with the equipment. Understanding the types of artifacts that can occur and how to avoid them is important for improving the accuracy of medical diagnoses.

Photon Starvation

Aliasing

Jewlry Artifact

Beam Hardening

Partial Volume Averaging

Ring Artifact

Tube Arcing

Truncation Artifact

Motion Artifact

Transient interrumption of contrast

Clothing Artifact

Kinds of artefacts

motion artifact

Motion artifact is a patient-based artifact. It occurs with voluntary or involuntary movement during image acquisition. They appear as blurring, streaking, or shading, and are caused by patient movement during a CT scan. Blurring also occurs with patient movement during radiographic examinations. If patient movement is voluntary, patients may require immobilization or sedation to prevent this. Involuntary motion, such as respiration or cardiac motion, may cause artifacts that mimic pathology in surrounding structures.

transient interruption of contrast

The temporary interruption of the contrast bolus is an error that can affect the opacification of the pulmonary arteries in angiographic studies. It occurs when blood without contrast flows from the inferior vena cava, which can lead to uncertain results or incorrect diagnoses of pulmonary embolism.

clothing artifact

Clothing artifacts, are a regular feature on imaging examinations but generally are recognized for what they are, either when the radiographer takes the image or later by the reporting radiologist. The radiographer will often either retake the image after the patient has removed the offending garment, or more commonly they will label the image with a warning that clothing artifact is present to avoid misinterpretation. Removing clothing that corresponds to the area of interest is important, in particular, In the literature are good examples of cases in which clothing has mimicked potentially more serious pathology 4,5.

Jewlery artifact

It's common to see jewelry artifacts on imaging examinations, where they can produce unhelpful artifacts that may obscure important structures and preclude confident diagnostic evaluation. These include:

• body piercing in many different anatomical location

• most commonly earrings

• nose studs/rings

• nipple rings

• cleavage rings

• umbilical rings

• genital rings

• also tongue, lips, eyebrows, chin, etc.

• necklaces, bracelets, anklets, chains etc.

• finger and - much more rarely - toe rings

beam hardening

Beam hardening is the phenomenon that occurs when an X-ray beam comprised of polychromatic energies passes through an object, resulting in selective attenuation of lower energy photons. The effect is similar to a high-pass filter in that only higher energy photons are left to contribute to the beam, and thus, the mean beam energy is increased ("hardened")This same phenomenon is exploited in radiography and CT by the use of metal filters "pre-harden" the X-ray spectrum and minimize low-energy photons CT, beam hardening from a very dense target (bone or iodinated contrast) may result in characteristic artifacts. CT beam hardening artifacts have 2 manifestations: streaking (dark bands) and cupping artifacts.

partial volume averaging

Partial volume artifact occurs when tissues of widely different absorption are encompassed on the same CT voxel producing a beam attenuation proportional to the average value of these tissues. Partial volume averaging is particularly problematic in CT angiography (e.g. misdiagnosis of an apparent contrast filling defect caused by the artifact as PE). Therefore the use of thin section reconstructions (1-1.5 mm) are recommended where the impact of this artifact is negligible 2.

photon starvation

Photon starvation is one source of streak artifacts which may occur in CT. It is seen in high attenuation areas, particularly behind metal implants. Because of high attenuation, insufficient photons reach the detector. During the reconstruction process, the noise is greatly magnified in these areas leading to characteristic streaks In some applications, namely low-dose CT protocols, the increased noise due to photon starvation is normally encountered as a trade-off between low patient radiation dose and acceptable image quality. The artifact can be reduced by automatic tube current modulation (increased mAs) and adaptive filtration via applying the local filter. Use of iterative reconstruction techniques can also significantly reduce image noise caused by this artifact.

Aliasing

Aliasing artifact, otherwise known as undersampling, in CT refers to an error in accuracy proponent of analog to digital converter (ADC) during image digitization. Image digitization has 3 distinct steps: scanning, sampling, and quantization. When sampling, brightness of each pixel in the image is measured, and via a photomultiplier, creates an output analog signal that is then due to undergo quantization. The more samples that are taken the more accurate the representation of the signal will be, hence if a lack of sampling has occurred the computer will process an inaccurate image resulting in an aliasing artifact.

Axial cut of a rodent CT scan with truncated projections. The red arrow points to the bright artifact caused by truncation.

truncation artifact

When part of the sample is outside the field of view (FOV), incomplete projections are obtained, leading to a truncation artifact. Several methods have been proposed to compensate for the missing data, based on extrapolating the projections, but none can fully recover the truncated data.

tube artifact

These artifacts are unwanted changes in the image that do not reflect the actual structure of human anatomy being scanned, often caused by issues in how the X-rays are generated or detected.The most common causes of tube artifacts include: - Instability in the X-ray Tube. - Geometric Misalignment. - Beam Hardening. - Detector Issues. - Electrical Interference or Noise. Reducing or eliminating tube artifacts often requires technical adjustments, such as recalibrating the equipment, improving alignment, or using advanced software to correct for distortions.

ring artifact

It is caused by a misalignment in the detectors (due to movement and/or play in the rails of the crane that moves the gantry components). Therefore, these detectors must be calibrated periodically, which reduces the occurrence of this type of artifact.

conclusion

In conclusion, artifacts are those that can make it harder to diagnose the disease. So, we should try to avoid them or, at least, make the image the most clear possible for the radiographers so they can do their job properly.

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• https://pubs.rsna.org/doi/abs/10.1148/rg.246045065?journalCode=radiographics

bibliography

Contextualiza tu tema con un subtítulo

• https://radiopaedia.org/articles/aliasing-artifact-ct?lang=us