1 / 40

Welcome to Belgium!!!

Welcome to Belgium!!!. US Imaging Artifacts. Dominique Penninck, DVM, DVSc. Missing. Improperly located. Artifacts = structure made by external action. Not real. Improper brightness, shape, or size. CONTENTS. Name of the artifact Cause/explanation of the artifact Cure or palliation.

keala
Download Presentation

Welcome to Belgium!!!

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Welcome to Belgium!!!

  2. US Imaging Artifacts Dominique Penninck, DVM, DVSc

  3. Missing Improperly located Artifacts = structure made by external action Not real Improper brightness, shape, or size

  4. CONTENTS • Name of the artifact • Cause/explanation of the artifact • Cure or palliation

  5. Baseline Assumptions: • Sound travels in a straight line at 1540 m/sec • For each pulse, all echoes are received before the next pulse is emitted • The imaging plane is extremely thin • Sound travels directly to a reflector and back to the transducer • The maximum depth imaged unambiguously is determined by the Pulse Repetition Frequency

  6. Axial Resolution Higher frequency transducers produce shorter pulses than lower frequency transducers. Pulse length determines axial resolution but directly depends on the wavelength of the beam. The ability to resolve the cyst is dependent on the pulse length and the distance between walls. Axial resolution cannot be better than one half of the pulse length. In the example, only the 7.5 MHz transducer can resolve the 0.5 mm cyst.

  7. Lateral Resolution Lateral resolution depends on the beam’s diameter. In focused US beams, the diameter of the beam is narrowest at the focal point (B). The distance between the transducer and the focal point is the focal distance (FD). Acceptable lateral resolution is obtained for a short distance along the beam’s axis on either side of the focal point within the focal zone (FZ). Increased beam width at other distances from the transducers (A, C) results in poorer lateral resolution.

  8. Elevational resolution Slice-thickness artifact

  9. Commonly seen artifacts Section thickness Reverberation Refraction Mirror image Side and Grating lobe Comet tail (ring down) Propagation speed error Range ambiguity Shadowing (edge) shadowing Enhancement (through transmission) (Focal enhancement) Electronic noise Aliasing

  10. Operator and Machine Settings • Inadequate patient preparation • Inadequate gain or TGC • Focal Enhancement (banding) • Electronic noise

  11. Poor Contact

  12. Patient preparation

  13. Gain Adjustment Normal High Low Normal

  14. TGC setting Adequate Inadequate Inadequate US beam attenuation:0.5 dB/cm/MHz (round trip)

  15. Electronic noise *Due to electromagnetic or radiofrequency interference from devices Located near the US machine *Can be seen with or without probe contact on the patient

  16. Reverberation • External or internal reflective interface • Series of bright interfaces

  17. Comet-tail (ring-down artifact) = Series of small bright interfaces (closely spaced reverberations) * Discrete echoes cannot be identified * Mechanism unknown; may be resonance phenomenon associated with gas bubbles

  18. Mirror Image • Erroneous location of an organ or structure • Near a large, curvilinear reflector • Common at diaphragm/lung interface

  19. Refraction Reflector improperly displayed

  20. Refraction Improper image display because the US beam is deviated after passing between 2 tissues of different speed of sound, or through an oblique reflector

  21. Duplication

  22. Non constant speed artifacts Erroneous location or shape of a structure due to sound traveling at a different speed than 1540 m/sec.

  23. Side and grating lobes artifact Two strong reflective points (actual position) within one of the side lobes return a significant amount of energy that is erroneously displayed on the axis of the main beam (perceived position). Presence of low-level echoes in the dorsal aspect of the bladder lumen is due to “slice- thickness” artifact (arrow). This pattern is also called pseudo-sludge.

  24. Decreased gain

  25. True sludge A B • “True” sludge in gallbladder. The interface (arrows) between anechoic bile and sludge is linear when the animal is scanned in a recumbent position. • B. The same interface (arrows) appears oblique when the animal is standing, showing the gravity-dependency of true sludge, unlike the pseudo-sludge.

  26. Anisotropism *Due to suboptimal transducer orientation (not 90˚to the axis of the structure evaluated) *Decreased specular echoes and increased scatter result in decreased returning echoes (hypoechogenicity) Solution: once the artifact is identified, correct the angle

  27. Range Ambiguity Cause: a new sound pulse is transmitted BEFORE energy from previous pulse is received The returning echo is registered as a new pulse Image from reflector located deeply may appear superficially Correction: Decrease PRF, select higher transducer, decreased filed of view, reduce number of focal zones 7.5 MHz curvilinear transducer 6 focal zones 10 cm depth of field Frame rate of 12 Hertz O’Brien RT, et al 2001

  28. Shadowing • Low echoes amplitude behind a highly attenuating structure • Gas, mineral, some foreign bodies • Dirty (sound reflecting-gas) versus clean (sound absorbing-bone) shadowing?

  29. Edge Shadowing • Reduced intensity of echoes distal to the lateral margins of rounded cystic structures • US beam is reflected off the curved surface • Gallbladder, bladder, renal medulla, any round to oval shaped structure

  30. Edge Shadowing

  31. EnhancementThrough transmission • Increased echoes amplitude behind a weakly attenuating structure • Gallbladder

  32. EnhancementThrough transmission Unexpected apparent enhancement: All 4 combinations of high and low echogenicity, and high and low attenuation in lesions can occur

  33. Focal Enhancement Focal hyperechoic band centered on the focal zone Solution: correct the gain distribution modify focal area

  34. Focal Enhancement

  35. Doppler related Artifacts • Incorrect gain, wall filtering, velocity scale setting • Beam width: spectral gate is not infinitely thin, and adjacent flow can be erroneously detected • Attenuation: detection of low flow decreases with depth • Reflection: improper location of vessels (“ghost”) • Refraction: “displaced” flow signals • Vascular motion can create flow variation • Moving non vascular structures can cause Doppler shift • Doppler angle near 90° can create directional ambiguity • Grating/side lobes

  36. Aliasing • Due to low PRF unable to adequately sample the Doppler shift If the Doppler shift frequency exceeds 1/2 PRF, aliasing occurs

  37. Aliasing Artifact Displayed as reverse flow

  38. Aliasing Correction Scale change+baseline adjustment Increase PRF …but can result in range ambiguity Increase Doppler angle (decrease Doppler shift) Lower frequency transducer Use continuous wave Doppler but loose depth localization

  39. Color Aliasing =Color of reversed flow with central band of higher laminar velocity Correction: Reduced color gain, Increase PRF

  40. Questions ???

More Related