Physics, Artefacts and Shadows - Russell McLaughlin, Belfast
Physics, Artefacts and Shadows - Russell McLaughlin, Belfast
Physics, Artefacts and Shadows - Russell McLaughlin, Belfast
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
BMUS/CEM<br />
Focused<br />
Bedside<br />
Ultrasound<br />
Course<br />
<strong>Physics</strong>, <strong>Artefacts</strong><br />
<strong>and</strong> <strong>Shadows</strong><br />
<strong>Russell</strong> <strong>McLaughlin</strong><br />
Emergency Department<br />
Ulster Hospital<br />
<strong>Belfast</strong>
Objectives<br />
BMUS/CEM<br />
Focused<br />
Bedside<br />
Ultrasound<br />
Course<br />
• Describe Basic US <strong>Physics</strong><br />
• Describe artefact<br />
• Give examples of shadowing<br />
• Give examples of enhancement<br />
• Relate these issues to clinical practice
US <strong>Physics</strong><br />
BMUS/CEM<br />
Focused<br />
Bedside<br />
Ultrasound<br />
Course<br />
• Transduced Energy/ Piezo-electric<br />
Crystals<br />
• B Mode<br />
• Frequency 2-15MHz<br />
• Low 3.5-5.0MHz Better Penetration(Depth)<br />
Less Resolution<br />
• High 7-12 MHz Better Resolution Less<br />
Penetration (Depth)
US <strong>Physics</strong><br />
BMUS/CEM<br />
Focused<br />
Bedside<br />
Ultrasound<br />
Course<br />
• Transducers:<br />
• Low Frequency<br />
• Curved<br />
• Small Footprint<br />
• High Frequency<br />
• Linear<br />
• Orientation Marker
US <strong>Physics</strong><br />
BMUS/CEM<br />
Focused<br />
Bedside<br />
Ultrasound<br />
Course<br />
• Keyboard<br />
• Depth<br />
• Focus / Auto focus<br />
• Gain<br />
• Time Gain Compensation<br />
• Freeze
US <strong>Physics</strong><br />
BMUS/CEM<br />
Focused<br />
Bedside<br />
Ultrasound<br />
Course<br />
• Different Tissues have varying acoustic<br />
textures<br />
• Bone Cortex Highly Reflective : White/<br />
Hyperechoic<br />
• Fluid Transmits Sound: Black/ Anechoic<br />
• Soft Tissue is in between <strong>and</strong> appears Grey
US <strong>Physics</strong><br />
BMUS/CEM<br />
Focused<br />
Bedside<br />
Ultrasound<br />
Course
Artefact<br />
BMUS/CEM<br />
Focused<br />
Bedside<br />
Ultrasound<br />
Course<br />
• Echo information that does not<br />
correspond to anatomic information as it<br />
is positioned <strong>and</strong> reflected from within<br />
the patient.<br />
• Problematic<br />
• Diagnostic
Artefact Classification<br />
BMUS/CEM<br />
Focused<br />
Bedside<br />
Ultrasound<br />
Course
Shadow generation<br />
BMUS/CEM<br />
Focused<br />
Bedside<br />
Ultrasound<br />
Course<br />
• Sound wave encounters echo-dense<br />
structure.<br />
• Bone, Gallstones, Calcification.<br />
• Majority of energy is returned to<br />
transducer.<br />
• Structure appears bright.<br />
• Area beyond structure is “shadow”.
Acoustic Shadow<br />
BMUS/CEM<br />
Focused<br />
Bedside<br />
Ultrasound<br />
Course
Rib <strong>Shadows</strong><br />
BMUS/CEM<br />
Focused<br />
Bedside<br />
Ultrasound<br />
Course
Foreign Body: Look for<br />
BMUS/CEM<br />
Focused<br />
Bedside<br />
Ultrasound<br />
Course<br />
acoustic shadowing as<br />
indicator of FB
Posterior Acoustic<br />
BMUS/CEM<br />
Focused<br />
Bedside<br />
Ultrasound<br />
Course<br />
Enhancement<br />
• Sound wave encounters anechoic<br />
structure.<br />
• Fluid filled structure: GB, Bladder.<br />
• Majority of energy passes through<br />
structure.<br />
• Sound energy is reflected from beyond<br />
structure.<br />
• Acoustic window i.e pelvic USS.
Acoustic Enhancement<br />
BMUS/CEM<br />
Focused<br />
Bedside<br />
Ultrasound<br />
Course
Gas: Completely obscures useful<br />
information but may represent perforation<br />
or sub-cut emphysema.<br />
BMUS/CEM<br />
Focused<br />
Bedside<br />
Ultrasound<br />
Course
Reverberation<br />
BMUS/CEM<br />
Focused<br />
Bedside<br />
Ultrasound<br />
Course
Reverberation<br />
BMUS/CEM<br />
Focused<br />
Bedside<br />
Ultrasound<br />
Course<br />
• Sound emitted from transducer <strong>and</strong> reflected<br />
at tissue interface.<br />
• Some reflected sound is re-reflected from<br />
transducer <strong>and</strong> therefore travels from<br />
transducer to tissue twice or more.<br />
• USS machine assumes that sound arriving<br />
“late” after 2 nd pass is coming from separate<br />
identical tissue deep to initial tissue interface.
Reverberation<br />
BMUS/CEM<br />
Focused<br />
Bedside<br />
Ultrasound<br />
Course
Mirror<br />
BMUS/CEM<br />
Focused<br />
Bedside<br />
Ultrasound<br />
Course
Mirror<br />
BMUS/CEM<br />
Focused<br />
Bedside<br />
Ultrasound<br />
Course<br />
• Similar to reverberation<br />
• Usually occurs at tissue interfaces<br />
• Double image of organ created eg<br />
bladder/ liver<br />
• Can mimic free pelvic fluid<br />
• Should not persist through all planes<br />
• Will “shrink” as bladder empties
Mirror<br />
BMUS/CEM<br />
Focused<br />
Bedside<br />
Ultrasound<br />
Course
Technique: Gain too high<br />
BMUS/CEM<br />
Focused<br />
Bedside<br />
Ultrasound<br />
Course
Technique: Gain too low<br />
BMUS/CEM<br />
Focused<br />
Bedside<br />
Ultrasound<br />
Course
Other <strong>Artefacts</strong><br />
BMUS/CEM<br />
Focused<br />
Bedside<br />
Ultrasound<br />
Course<br />
• Motion<br />
• Side Lobes<br />
• Edge<br />
• Noise
BMUS/CEM<br />
Focused<br />
Bedside<br />
Ultrasound<br />
Course<br />
Revised Artefact Classification<br />
• Practitioner<br />
• Probe position, control settings.<br />
• Patient<br />
• Shadowing, enhancement, motion, gas,<br />
anatomy.<br />
• <strong>Physics</strong><br />
• Mirror, reverberation.
Summary<br />
BMUS/CEM<br />
Focused<br />
Bedside<br />
Ultrasound<br />
Course<br />
• Frequency, Resolution, Depth<br />
• Artefact can help as well as hinder<br />
• No substitute for sound clinical<br />
judgement
Change language