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Radiology Artifacts: References and resources for radiology theory/practical exams:

This is a set of 10 radiology artifacts spotters set. These cases are contributed by Dr. M Venkatesh! Here are instructions about radiology cases and spotters: General instructions for spotters Radiology Artifacts are commonly asked in theory exam as a long question. Some viva examiners also like to ask questions about artifacts during practical exams. I am also posting relevant theory resources for various radiology artifacts. Most of the articles are available for free. You can request the ones that are not available or any other article for that matter in our radiology telegram group.

Radiology Artifacts: X-ray / RadioGraphy (Courtesy Dr. Mangal Mahajan):

Definition An unintended, unwanted visual aberration in an x-ray image Types of artifacts Positive density x-ray artifacts. They are DARK marks Generally, they occur in the developer step Negative density x-ray artifacts They are a LIGHT mark They can occur in any step in processing Transmitted x-ray artifacts These marks generally show up best looking through them on a view box Usually occurs in any processing step Reflected x-ray artifacts These are marks that show best by looking at light reflected off of the film Most commonly a washing problem Positive density x-ray artifacts Black Streaks Black Bands Black Spots Watermarks Developer streaks Black Streaks/Black Bands /Black Spots Cause Black streaks sometimes are a result of developer streaks Black bands and streaks are due to exposure of films to light Leak in the cassette If the film packet is kept open in the darkroom and the lights are put on accidentally Black spots could be a result of mottle or due to spillage of the developer on the film Power failure when the film is processed in an auto processor leading to dark wide band formation If these are due to cassette leak then it would appear at the same side of the film Light-exposed films from packet would show this defect mainly at the top of the films Watermarks Caused by water droplets on the film surface Appear-round dark spots of various sizes because of migration of silver particles How to avoid dark spots Improvement in dark room handling will solve the majority of these artifacts However, for mottle, replacement is the only option. Change of cassettes in case they are defective will eliminate this problem Developer streaks These appear as brown or black streaks or clouds appearing on the film Sometimes they can cover the entire film surface Usually not observed in all films in a packet, only some films will show such artifacts They are usually prominent in the white portion (specifically of chest radiographs) of X-ray film Causes Exact cause is not known Failure to agitate the films in the developer Failure to rinse the films adequately Failure to agitate the film when first immersed in the fixer Failure to stir the processing solution thoroughly after replenishment Seen very rarely in automatic processors, which clearly indicates this defect has a relationship to manual processing only Use of ice in developer tank can sometimes give rise to these streaks due to the formation of temperature as well as different concentration zones of developer How to avoid developer streaks Agitate film vigorously in stop bath or rinser for 10 to 15 secs to stop the action of developer completely Change water in stop bath every day. Dilution of high activity developer. Negative density artifacts (white spots) Appearance As diffused white spots (diffused negative kinks are sometimes misinterpreted as white spots) Shiny white spots with black centers Small white spots running parallel from edges of the film (white streaks)   Generalized white spots all over the film sometimes alternating with tiny black spots Cause Moisture   It is the most common cause of diffused white spots Incidences of such spots may increase during or immediately after monsoon Cassette marks Caused by dust, hair, fragments of paper etc or by screen defects Appear - Corresponding white mark on the radiograph Grid marks This gives rise to thin parallel white lines on the film Cause  Using the grid upside down When the grid remains fails to move i.e. remains stationary during film exposure If the grid ratio is too high If the x-ray tube & the film distance is less the grid cut-off will be more Screen marks Any deposit on the surface of intensifying screen like dust particles, fluff, hair, surface scratches etc Image artifact-appears white on the radiograph Photoactivation of interleaving paper This causes Shiny white spots However, they will appear as tiny spots, as compared to dust spots Contamination of the interleaving paper or due to moisture absorption by interleaving paper Causes White Streaks These can be easily identified from the rest of the types of white spots since they would appear at one specific site and one specific dimension on the film Paper mottling artifact During manual loading of the film in the cassette in the darkroom the yellow paper remains along with it (towards the tube side of the cassette) & the film is exposed in this situation Air-bell marks Formation of air bubbles in the developer solution, which prevents the developer from reaching the underlying film Splashing of water drops on the film during manual handling Appear as small clear circular spot on the radiograph Aging of the screen After five years or so, the fluorescent crystals on the intensifying screens begin to lose their ability to fluoresce, leaving small areas of non-exposure (lack of black) which we see as "white" dots diffusely spread over the film. How to avoid Buy new intensifying screens It is possible to put new screens in old cassettes, but it is not recommended Finger marks Handling the surface of the film with fingers especially contaminated by contact of chemicals or metal causes transfer of moisture modifying the action of the developer during processing Manual handling carries the risk of spotting or splashing film surface with developer, fixer or water. Avoided by - Automated film handling How to avoid Proper storage under air-conditioned atmosphere and controlled humidity is the key Regular cleaning of screens will help to remove dust Usually, the inner pouch of films has enough margins to fold it back. A slight effort to fold it back after taking out the film would help minimize entry of moisture to some extent. This can avoid pre-exposure of films also White spots due to screens would appear due to a damaged super coat. In such cases, change of screens will eliminate such defects Transmitted x-ray film artifacts Positive transmitted x-ray film artifacts Pressure marks Static marks Slap lines Crescents Light Fog Pressure marks Occur due to the application of undue pressure to the film emulsion before or during the development Larger usually white marks Pressure damage before the exposure-white mark Pressure damage after exposure-dark mark The magnitude of pressure is also determinative in the appearance of the pressure marks Cause Pressure marks due to improper storage: Stacking of boxes of film on top of one other Pressure mark during developing in an auto processor: Usually, occur during the developer step when the swollen rollers press over the film emulsion too hard Pressure marks during the manufacturing process: Stress suffered by emulsion during film manufacturing How to avoid pressure mark Do not stack the cassettes one above other instead keep them vertical sidewise Check the rollers in the auto processor if they are swollen Static marks Cause Handling of the film by machine or operator produce static electricity  during friction between the film & other objects like intensifying screen, loading bench etc that triggers chemical changes in the emulsion mimicking exposure Occur in the following situations - During film manufacture Film transport system of rapid film changes Feed mechanism of the film processors Cassette loading or unloading activities. Synthetic clothing materials like nylon Appearance Tree static Crown static Pin static Crows feet How to avoid static marks Use an antistatic mat, clean cassettes and feed tray with antistatic cleaner Regular cleaning of screens with antistatic screen cleaning solution helps to reduce incidences of branch static Ideally, screens should be cleaned once in 15 days Application of screen cleaner should be carried out as per instructions given on the bottle While cleaning screens, one should never use concentrated 'soap' solution Put a few drops of screen cleaner on a soft cloth (should not be a fibrous cloth), apply evenly on screens, and keep the cassette open for 10 minutes Allow the solution to dry completely and then close the cassette Handle the films gently Loading bench should be grounded to prevent the build-up of static electricity Slap lines Appearance A single dark line appearing at 1-2” from leading or trailing edge of the film (perpendicular to the direction of transport) How to avoid Check guide shoe alignment in developer rack and that the crossovers aren't slowing down the transport Crimp mark / crinkle marks / crescents / nail marks Cause Occurs due to careless handling in the darkroom due to acute bending of the films over the end of the finger especially the larger films Appears Curved black or white lines about 1cm in length How to avoid Proper handling, films should always be held from two diagonally opposite ends to avoid such artifacts Automatic daylight film handling system Fog It is the generalized darkening of the film Types Exposure to light - because Light leakage in the darkroom The safelight contains too large a bulb The safelight housing /filter is cracked The safelight filter series is incorrect Exposure of the film to the safelight is prolonged especially at short distances Light accidentally put on in the darkroom while box is open Leakage in cassette Film box accidentally being kept open Light leakage through pass box Do not allow light until the films have been fixed for at least one minute Exposure to x-rays or radionuclides The film should be shielded from this by sufficient distance & sufficient thickness lead Chemical fog - because  Development for a long time  Development at high temperature  Using oxidized developer (it also stains the film brown)  Prolonged or repeated inspection of the films during development  Contamination from corroded tanks Age fog - because Outdated films (mottled or uniform fogging) Films stored under high temperatures Films stored under excessive humidity Negative transmitted x-ray film artifacts Pickoff Scratches Blocked screen Pickoff Cause Almost always a guide shoe alignment problem or swollen rollers forcing film into the shoes Appearance Small white specks where the emulsion has been removed on the film Appears anywhere on the film Scratches / Surface damage Cause Usually a guide shoe or loose hardware in one of the racks. May occur in any step of processing Abrasions to the film emulsion due to badly adjusted processor film transport system Appearance Appears parallel to the direction of transport Long parallel lines that may stretch the entire length of the film Pi marks Suggestive of damage produced by one of the transport rollers in the film processor Detected by - view radiograph under reflected and transmitted light, locate any roughness by fingers Reticulation / Frilling                                             Partial or complete detachment of the emulsion from the base exposing the glossy base material due to the adverse processing condition Blocked screen Cause Usually when the radiation strikes the screen in the cassette it glows, exposing the film to blue or green light. A damaged or dirty screen will not glow properly so it is called a blocked screen Appearance Light spots or speckles will be seen on the processed film Reflected x-ray film artifacts Algae Improper washing Algae Appearance Appears as dark random marks on the film May scratch off with your fingernail How to avoid Drain wash tank when not in use Observe regular cleaning intervals using algaecide on the wash rack Clean rack and working tank with a strong bleach solution. Rinse well, rinse more. Adjust water supply so more water circulates through the tank. Use caution not to overflow the wash tank drain. Drain water when not in use Consider photo brome, but be aware this may damage some processors Always consult manufacturer before Improper washing Appearance The film may come out looking quite dirty or even sticky or wet. How to avoid Check that fixer and wash tanks are full of the appropriate fluid Stains They develop after months and years of storage Brown Use of oxidized developer Variegated color pattern Inadequate rinsing Grayish-yellow or brown Excessive fixation or use of exhausted hypo fixer agent which becomes firmly bound to the emulsion so that it cannot be removed, staining the film brown) followed by inadequate washing. Grayish-white scum Incomplete washing Presentation Courtesy Dr A.P. Jaganathan  Images and further reading: Pictorial Review of Digital Radiography Artifacts General Radiography Artifacts

Radiology Artifacts: USG (Courtesy Dr. Hemanth)

 https://www.youtube.com/watch?v=WrzisTDAZcM Further reading: US Artifacts - RadioGraphics Primer and Clinical Significance of Artifacts in Ultrasound

Radiology Artifacts: Doppler

Doppler has become the mainstay of diagnostic modality in imaging venous system, abdominal, pelvic and in obstetric scanning. Continuous wave Doppler. Pulsed wave Doppler. Colour Doppler. Power Doppler. Doppler Effect: Measures a change in the reflected sound frequency generated by the motion of the source or the detector. Doppler shift: Doppler signal is a shift or difference in frequency between the transmitted and the received ultrasound pulse. It displays the direction and speed of motion of detectors. An accurate signal is achieved when the motion is parallel to the ultrasound beam and no signal is generated when the motion is perpendicular to it. Doppler Shift formula. ΔF= Fr –ft = 2 x Ft x V/C x Cos θ. Fr= Reflected frequency. ft = Transmitted frequency. V= Blood flow velocity. C= Speed of sound in human tissue. θ = Beam Vessel Angle When the beam is angled 90 degrees to the vessel axis the frequency shift equals zero i.e. no signal is detected even if the flow is present. This difference falls in the frequency range detectable by the human ear and after amplification, this Doppler shift is the audible signal. This magnitude of Doppler shift is not only proportional to the frequency of the original signal but is also proportional to. Blood flow velocity Speed of sound in human tissue. Angle of the ultrasound beam relative to the long axis of the vessel. Various technical parameters should be in optimal range to prevent many artifacts in Doppler study. They are 1. Transducer Frequency. For superficial structures, 7-10MHZ is used. For deep abdominal structures – 3MHZ – 5MHZ is optimal. Choice of transducer frequency is paramount because the intensity of the scattered sound varies in proportion to the fourth power of the Doppler frequency. 2. Doppler Angle. Unlike in grayscale ultrasound imaging whereby the best image is obtained perpendicular to the US beam, in Doppler ultrasound, the strongest signals (and best spectra) result when the motion is parallel to the beam. Strongest signals of Doppler results when the motion is parallel to the beam A Doppler angle of 90 degrees does not display flow because no component of the frequency shift is directed back towards the transducer. Ideally, the angle should be 60 degrees and always less than 70 degrees. The larger the angle greater the correction is needed and more prone to errors. 3. Sample Volume. Ideal sample volume should be about two-thirds of the vessel width positioned in the center of the vessel. If the sample volume is more: - Spectral broadening happens (that may be incorrectly interpreted as post-stenotic turbulence). If the sample volume is less: Measured velocity is too low. Definition:-The sample volume is the three-dimensional space from which the Doppler frequency shifts are measured. 4. Wall Filters. Cut off of the low-frequency noises, a cleaner high-velocity blood flow signal is displayed. If it is set too high the blood flow is discarded if set low noise will be more. 5. Doppler Gain. Controls the amplitude of the color display in color or power Doppler mode and the spectral display in pulse Doppler mode. If the gain is too low, the flow may be present but not visualized. If the gain is high color or power signals may overwrite grayscale clot. 6. Velocity scale. Controls the range of frequencies displayed and it is critical in color and spectral Doppler imaging. If the scale is too high (similar to a too wide window in CT) the dynamic range is too large and low-velocity signals are missed simulating an area of thrombosis, particularly in low flow vessels such as the portal vein. If the scale is too low the dynamic range is too small to display the high-velocity signals accurately resulting in aliasing. The above-mentioned parameters are very important for optimal Doppler study. If these are inaccurate artifacts results in Doppler study. These are grouped into three broad categories. 1. Artifacts caused by technical limitations Aliasing. Blooming artifact /color Bleed. Directional ambiguity. Partial volume artifact. The absence of flow due to high-velocity settings. 2. Artifacts caused by Patient Anatomy. Pseudo flow. Flash artifact. Mirror image artifact. 3. Artifacts Caused by Machine Factors Edge artifact---Along cortical bone. Twinkling artifact----Beneath Calculi. Aliasing Artifact. It is an inaccurate display of color or spectral Doppler velocity when the velocity range exceeds the scale available to display it. Nyquist Limit: Accurate depiction of frequency shifts requires a scale that is twice as large as the maximum velocity. If the scale is too small, large shifts exceed the available range and are displayed as multiples of small shifts. Practically, the display “wraps around” the scale and overwrites the existing data. In spectral Doppler flow velocity peak is cut off at the top of the scale and the missing portion is written from the lowest portion of the scale back toward the top. In color Doppler, if the scale is low, aliasing within a vessel is displayed as adjacent colors from red to yellow to light blue to dark blue. Solutions: To reduce aliasing first drop the baseline or increase the available velocity range. If the scale is still inadequate, decrease the Doppler frequency shift by using a lower frequency or by increasing the Doppler angle. Power Doppler has no aliasing because it has no directional or velocity component. Disadvantage:- Disadvantage of aliasing is high velocity may not be accurately measured. Advantage: - 1. Aliasing is useful for localizing the highest velocity region. 2. It is used in identifying the abnormal area in transjugular intrahepatic portosystemic shunt, and in localizing arteriovenous fistulae. 2. Blooming Artifact (Colour Bleed). In this artifact, the color spreads out from within the vessel and bleeds beyond the wall into adjacent areas. It is caused by abnormally high gain settings. This causes the obscuration of thrombus or plaques in the vessel. This is also seen with ultrasound contrast agents and occurs soon after the bolus injection at the time the increase in signal strength is the highest. 3. Directional Ambiguity. Refers to a spectral Doppler tracing in which the waveform is displayed with nearly equal amplitude above and below the baseline in a mirror image pattern. This results when the interrogating beam intercepts the vessel at a 900 angle and is most commonly seen in small vessels, especially those that may be traveling in and out of the imaging plane. This artifact adversely affects transcranial Doppler blood flow velocities. This artifact should not be confused for bidirectional flow where the flow is never simultaneously symmetric above and below the baseline. The flow direction varies within the cardiac cycle. Eg: Blood actually flows in two directions, such as in the neck of pseudoaneurysm. Another type of bidirectional flow occurs in the setting of high resistance organ flow. (Eg torsion, venous thrombosis, or other causes of parenchymal edema) and is represented as diastolic flow reversal. 4. Partial volume artifact. It results from a slice thickness that is not infinitely thin. Echoes and Doppler signal are acquired from the objects that may be partly within the slice and partly outside of it. These signals in the US slice are summed together and the echoes produced are attributed to the structure in the assumed thin scan plane. In color flow imaging e.g. of this artifact is the visualization of a portion of the iliac artery within ovary giving the impression of abnormal cyst wall flow. This artifact is produced by grating lobes or side lobes. These generate information outside the expected path of the main beam. This is a transducer related artifact and depends on the crystal element size and the spacing of the array elements (seen mainly with the high frequency tightly curved, convex, linear arrays used in endocavitary probes.) Echoes returning from either of these additional lobe sources are displayed as though they originated from main beam. 5. Pseudo flow: Is defined as the presence of the flow of a fluid other than blood. It mimics real blood flow with color or power Doppler ultrasound, but no true vessel containing the fluid exists. The signal appears as long as fluid motion continues. These artifacts may be misinterpreted as flow unless Doppler spectral analysis is used. The spectral Doppler tracing does not exhibit a normal arterial or venous waveform. Pseudo flow is seen in ascites, amniotic fluid, and urine (bladder jets) 6. Flash Artifact It is a sudden burst of random color that fills the frame, obscuring the grayscale image. This artifact is caused by object motion or transducer motion. It is seen in the left lobe of the liver due to cardiac pulsation and in hypoechoic areas such as cysts and fluid collections. Flash artifact can be used to denote the fluid nature of solid appearing material. Power Doppler is more susceptible to this artifact because of longer time to build the image. Perivascular artifact or color bruit is a tissue motion artifact where motion is generated within an organ. This appears as a random color mosaic in the soft tissue due to vascular tissue vibration. Useful in detecting anastomotic sites, stenotic arteries or arteriovenous fistulae. 7. Mirror Image artifact : This artifact displays objects on both sides of a strong reflector, though they are located only on one side of it. The reflectors (diaphragm, pleural surface, and aortic wall) directs some of the echoes to a second reflector before it returns them to the transducer resulting multipath reflection. The machine assumes that the echoes comes from the initial transducer beam and from a distance corresponding to the actual time of flight. This results in a display of echoes deeper I the image than they should be. The resulting artifact shows up as the virtual object, deep to the original image but identical to it thus the term mirror. Duplication of subclavian artery (pleura reflector) and common carotid arteries are noted (carotid ghost) 8. Edge Artifact Refers to the Doppler signal generated at the margin of a strong, smooth, specular reflector displayed on imaging as persistent color along the rim of calcified structures, such as gallstones or cortical bone, and may mimic vascularity unless to spectral tracing is obtained (spectral noise). This is caused by low PRF on velocity scale and low wall filter setting. This is more common with power Doppler than with color Doppler ultrasound because of a larger dynamic range. 9. Twinkling artifact It is a mosaic of rapidly changing colors located deep to an echogenic reflector which is granular e.g: Renal Calculi, bladder calcification and cholesterol crystals in the gall bladder. In power Doppler signal location is the same but color is uniform. This is caused by a narrow band of intrinsic machine noise called phase jitter. To produce this artifact high colour write priority should be selected and grayscale gain kept to a minimum. This artifact is useful in identifying the small stones which do not produce acoustic shadowing but shows twinkling artifact. Stones made up of calcium oxalate dihydrate and calcium phosphate calculi produce the twinkling artifact. Calcium oxalate monohydrate and urate lack a twinkling artifact. Foreign bodies like iron filings, emery paper, ground chalk, wire mesh, aneurysm coil produce this artifact. On spectral Doppler, only noise is noted. Guidelines for an optimal color flow Doppler examination. The colour flow box should be kept as small as possible to allow better frame rate for better resolution and sensitivity. Adjust the gain and filter settings to obtain an optimal color signal and minimal color noise. Adjust the velocity scale (PRF) and baseline according to the flow conditions. A low scale is used for low flows and velocities; however, it may produce aliasing. A high scale reduces aliasing but is less sensitive for slow flows. Obtain an optimal Doppler angle by adjusting the beam steering and probe position. The angle should be 600 or less if velocity measurements are to be made. Adjust the pulsed Doppler sample volume size (gait) appropriately (2/3rd of the velocity diameter) to obtain accurate velocities. Avoid transducer motion. https://www.youtube.com/watch?v=cYx4vK_KU30 https://www.youtube.com/watch?v=JRecm5CwT78 https://www.youtube.com/watch?v=qpMZGmGev68 Further reading: Spectral and color Doppler artifacts Doppler Artifacts Doppler Artifacts and Pitfalls

Radiology Artifacts: Computed Tomography (Courtesy Dr. Ameet Mudda)

 https://www.youtube.com/watch?v=ZMjhPo8KDTo Further reading: CT artifacts: Causes and reduction techniques Artifacts in CT: Recognition and Avoidance- Radiographics CT artifacts Radiology Physics Common artifacts in computerized tomography: A review

Radiology Artifacts: MRI (Courtesy Dr. Shalini)

https://www.youtube.com/watch?v=x05ZWlzr2no Further reading: An Image-based Approach to Understanding the Physics of MR Artifact MR artifacts

Radiology Artifacts: Mammography