ArtIfacts in usg Artifacts are part n parcel of any imagin modality .Us artifact can be avoidable and may be due to improper scanning technique. Recognition of these artifacts is important because they may be clues to tissue composition and aid in diagnosis.

ARTIFACTS Defined as a feature appearing in an ultrasound image that does not correspond to or represent an actual anatomical or pathological structure.

Classified into three types : 1. Related to the instrument. 2. Technique related. 3. Artifacts due to sound reaction with various tissues.

The ultrasound beam only travels in a straight line The ultrasound machine makes various assumptions in generating an image. These include: The ultrasound beam only travels in a straight line with a constant rate of attenuation. with constant speed speed (1540m/s.) as infinitely thin beam with all echoes originating from its central axis. in all body tissues The depth of a reflector is accurately determined by the time taken for sound to travel from the transducer to the reflector and return.

ARTIFACTS RELATED TO EQUIPMENT ARTIFACTUAL NOISE It is caused by electrical interference from nearby equipment.

MAIN BANG ARTIFACT Many echoes from the skin –transducer interface in the immediate subcutaneous tissue. More common with the old transducers. The matching layers in the new transducers prevent this. Too much Near Gain also causes the artifact. Disadvantages : The superficial lesions will be hidden.

Correction technique: Decrease the near gain. Use a higher frequency transducer, Use stand-off pads to evaluate superficial structures.

SIDE LOBES Produce confusing echoes that arise from sound beams that lie outside the main ultrasound beam. Create impression of structures or debris in fluid filled structures. Eliminated by repositioning the transducer and proper focusing. The ultrasound beam exits the transducer as a complex three-dimensional bowtie shape with additional off-axis low-energy beams. These off axis beams also reflect corresponding to imaging object and reach probe and so cause artefact. The ultrasound beam exits the transducer as a complex three-dimensional bowtie shape with additional off-axis low-energy beams, which are referred to as side lobes and grating lobes

Periodic spacing of elements by phased array, more commonly linear array. Grating lobe travel at an angle to the main beam . Depending on whether it hits after or before the main beam a curvilinear echo seen . Correction is by using different transducer or acoustic window GRATING LOBES

ARTIFACTS RELATED TO TECHNIQUE NOISE Noise is created by excessive Gain. Disadvantage: excessive gain causes artifactual echoes in the fluid filled structures. Correction is by the reduction of the gain.

TGC PROBLEMS Artifacts can occur due to poor TGC adjustments. It can lead to excessive or few echoes from a depth. A type of poor TGC technique is BANDING.

Correct adjustment

VEILING Bands of increased echogenicity seen at different depths. Occurs if multiple focal zones are utilized simultaneously. Disadvantage : Mass can be created or overlooked at the interfaces. Correction: Use only one focal zone. Adjust the TGC.

ARTIFACTS CAUSED BY MOVEMENT Breathing. Operator scanning speed. Operator pressure.

ARTIFACTS CAUSED BY SOUND-TISSUE ARTIFACTS CAUSED BY SOUND-TISSUE INTERACTION ARTIFACTS FROM STRONGLY REFLECTIVE STRUCTURES Gas and Bone do not conduct the sound well. When the sound strikes these structures two effects can occur: 1.SHADOWING. 2.REVERBERATION. The disadvantages are that the structures in the distal field are masked. It is however helpful in identifying structures like the calculi.

Reverberation Artifact. Reverberation artifact produces a series of parallel false images of flat interfaces that happen to lie parallel to the skin. They are the result of repeated reflections of the incident ultrasound pulse between the transducer and the flat surface or between two such surfaces within the body.

Shadowing Artifact Shadowing occurs when little or no ultrasound can penetrate an interface and results in a dark band over the deeper tissues. Causes of shadowing 1.Absorption: calculi eg. Shadowing by fibrous tissue like scars, scirrhous breast carcinoma, Fibroid in uterus. 2. Reflection: e.g. tissue-gas interface

PROPOGATION VELOCITY ARTIFACT When US beam passing through a fat containing lesion, delayed echo return. Delay in echo return interpreted as deeper target. The image shows a mis-registration artifact. Ex., Broken diaphragm sign of hepatic lipoma, Shadowing at areas of multiple interfaces ex renal medulla,

Propagation velocity artefact 2 More generally, the different velocities at multiple small tissue–fat interfaces produce minor deviations of the ultrasound beam that defocus and disperse it. The clinical effect of this is loss of contrast, the image appearing noisy and blurred.

Mirror Artefact Due to reflection by curved specular reflector surface. It is fallacy of usg machine misinterpreting that - all echoes returning to transducer arise from structure along the axis. -an echo returns to the transducer after a single reflection.

Enhancement Effect In area of low attenuation, stronger echoes arise from deeper tissue because they receive stronger pulses as compared to surrounding structures behind normal soft tissue that causes over amplification and bright echoes.

Comet Tail Artifact Occurs due to a very strong acoustic interface as gas bubble or metallic structure. It appears as a dense echogenic line extending through the image. It is diagnostically important in identifying surgical clips and air pockets

SPLIT IMAGE/REFRACTION ARTIFACT It is also known as the Refraction artifact. Bending of the sound beam occurs so that target not along the axis of transducer are insonated. There reflections are then detected and displayed in the image. Structures that lie outside the volume appear in the image. Example- vanishing twin phenomenon Correction is by Scanning from site other than midline

(a) shows the refraction of incident US beam as it travels between two adjacent tissues with different sound propagation velocities (C1 and C2). (b) The object in the path of the refracted portion of the beam is misplaced because the processor assumes a straight path of the beam.

Conclusion.. Artifacts are common in US. Artifacts are unavoidable and occur secondary to intrinsic physical properties of the ultrasound beam. Recognition of these unavoidable artifacts is important because they may be clues to tissue composition and aid in diagnosis. The ability to recognize and remedy potentially correctable artifacts is important for image quality improvement.

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