Live pulmonary endoscopy Transthoracic ultrasound pulmonary endoscopy Transthoracic ultrasound AIMS: Transthoracic ultrasound is a helpful tool for investigating clinical problems
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ERS International Congress Amsterdam
26–30 September 2015
Live pulmonary endoscopy
Transthoracic ultrasound
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There is no real or perceived conflicts of interest that relate to this presentation:
This event is accredited for CME credits by EBAP and EACCME and speakers are required to disclose their potential conflict of interest. The intent of this disclosure is not to prevent a speaker with a conflict of interest (any significant financial relationship a speaker has with manufacturers or providers of any commercial products or services relevant to the talk) from making a presentation, but rather to provide listeners with information on which they can make their own judgments. It remains for audience members to determine whether the speaker’s interests, or relationships may influence the presentation. The ERS does not view the existence of these interests or commitments as necessarily implying bias or decreasing the value of the speaker’s presentation. Drug or device advertisement is forbidden.
6
Oxford
Pleural
Unit Overview
1. Physics and Principles
2. Basics of Scanning
3. Evidence and Training
4. Abnormal Appearances
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Oxford
Pleural
Unit
1. Physics and Principles
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Oxford
Pleural
Unit What is ultrasound
• A longitudinal wave - particles move in
the same direction as the wave.
• A succession of rarefactions and
compressions transmitted due to elastic
forces between adjacent particles
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Oxford
Pleural
Unit What is Ultrasound
• Audible sound has frequency 20 Hz to 20 kHz
• Most diagnostic ultrasound has frequencies in
range 2-20 MHz
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Oxford
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Unit Important equation!
• Frequency of oscillations inversely
proportional to wavelength
• f = c/ (c ≈ 1540 m s-1 in soft tissue)
• Diagnostic ultrasound of 2-20MHz,
wavelength• = approximately 1 - 0.1 mm in tissue
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Oxford
Pleural
Unit Generation of Ultrasound
• US generated by piezoelectric crystal
• Commonest material is lead zirconate titanate
(PZT).
• Electric field applied:
• crystal rings at a resonant frequency
• determined by its thickness
• Same or similar crystal used as receiver:
• produces electrical signal when struck by the returning
ultrasound wave
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Oxford
Pleural
UnitUltrasound Transducer
Matching layer
Piezoelectric crystalAcoustic insulator
Converts electricity to sound and vice versa
Backing
block
Co-axial cable
Plastic housing
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Oxford
Pleural
Unit Speed of ultrasound in tissue
• Speed of US in tissue depends on:
• Stiffness
• Density
• Stiffer material (more solid) transmits
ultrasound faster
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Oxford
Pleural
Unit Speed of ultrasound in tissue
Medium Speed of sound
(ms-1)
Air 331
Muscle 1,585
Fat 1,450
Soft Tissue (average) 1,540
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Pleural
Unit Interaction of US with tissue
Ultrasound which enters tissue may :
• Transmit
• Attenuate
• Reflect
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Oxford
Pleural
Unit Attenuation
• If particles in a tissue are small enough:• Move as a single entity
• Transmit sound in an orderly manner
• Coherent vibration
• Sound
• If large molecules are present:• Chaotic vibration
• Heat
• Loss of coherence loss of ultrasound energy
• Alter with gain control on machine
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UnitGain too high
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Unit Gain reduced
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UnitAbsorption of
ultrasound / gain
• Absorption of ultrasound:
• Lower tissues return less ultrasound
• Some absorbed as heat
• Some reflected/refracted out of field of probe.
• To ensure a uniform picture
• (so deeper areas not darker)
• Use Time Gain Compensation (TGC).
• TGC:
• Applies progressively increasing amplitude to later
echoes in proportion to their depth
• i.e differential amplification
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Unit TGC
• TGC can be varied by users
• Used to compensate for artefactual increased
brightness
• Beware previous user adjusting TGC controls
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Unit TGC incorrect
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Unit TGC corrected
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Unit
• Absorption proportional to ultrasound
frequency
• Higher frequency probes:
• Smaller depth penetration
• Better resolution
• Many US machines allow user to alter
frequency up to maximum/minimum allowed
Attenuation and
depth penetration
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Unit
Pleura on 3.5 MHz
curvilinear probe
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Unit
Pleura on high resolution
linear probe
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Unit
Reflection
Importance of Reflection:• Allows generation of the ultrasound signal
• Leads to loss of ultrasound signal
• Determines the appearance of tissue
• Can cause artefacts
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Unit Reflection
Reflection occurs when:
• Ultrasound crosses an interface between two tissues with
different impedance
• Amount depends on difference in impedance
• Ultrasound which is not reflected:
• Continues
• Is used to image deeper structures
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Oxford
Pleural
Unit Reflection
Interface Reflection co-efficient
(%)
Soft Tissue - Air 99
Soft Tissue - Bone 66
Fat - Muscle 1.08
Muscle - Liver 1.5
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Unit Ribs preventing
US transmission
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Unit US avoiding ribs
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Unit
Reflection –
consequences
1. Need coupling material between probe
and patient skin
2. Cannot see through aerated lung
3. Cannot see through bone
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Unit Artefacts
Mirror artefact• Occurs at smooth curved surfaces eg
diaphragm
• Reflection occurs
• Projects image of organ under diaphragm eg liver, above diaphragm
• Reflections of liver into chest can give false impression consolidated lung
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Pleural
Unit Acoustic shadowing
• Artefact:• Causing shadowing behind certain structures
• Prevents user seeing beyond them
• Caused by absorption or reflection
• Occurs at fibrous tissue eg scars and fat (eg fatty liver)
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Pleural
Unit Fatty liver
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Unit Gas shadows
• Proportion of incident US reflected
• Unable to continue through the tissue for imaging
• At gas-tissue interfaces:• Almost all US is reflected
• Lung:• Clean shadow
• Bowel gas shadows:• ‘Dirty shadows’
• Partly filled by reverberant echoes due to multiple gas-tissue reflectors
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Unit Gas shadows
‘Clean’ Shadow ‘Dirty’ Shadow
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Unit
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Unit
2. Basics of Scanning
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Unit Equipment
• Machine able to achieve depth of at least 10cm
• Dynamic range of transducer:• Low Hz (3-5MHz) probe better for depth (e.g. abdominal)
• High Hz (7-12MHz) better for detail (e.g. small parts)
• Shape of transducer:• Linear
• Curvilinear
• Small footprint
• Machines much the same for standard use
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Scanning Position
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Image Orientation
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F
D
VP
PP
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Oxford
Pleural
Unit Normal Appearance
Thoracic structures:• Ultrasound unable to see through air
• Ribs are in the way
• Unable to penetrate normal lung• “Comet tails”
• Lung sliding
Other organs• Liver
• Spleen
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Unit
Normal Appearance
Costophrenic angle
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L
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L
50
51
L
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Unit
Normal Appearance
Mid thorax
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Unit Normal Lung
Diagnosis of aerated lung:• “Comet tails”
• Lung sliding
Caution:• Unable to comment on what is below
• “Lung” not really seen - artefact
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Unit Normal Subdiaphragm
Liver Spleen
Recognition of normal structure is key to safe practice57
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Unit SummaryKey points:
• US relies on sound creation, reflection and detection
• In tissues, US can transmit / attenuate / reflect
• Decrease attenuation by increasing power (gain)
• Higher frequency, better penetration
• Interface of tissues determines how much is reflected
• Artefacts:• Mirror• Shadowing
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Pleural
Unit Ultrasound tips
• Use highest frequency for necessary depth penetration
• Use tissue harmonics for larger patients
• Try moving patient into different positions eg to move ribs apart/move bowel gas out of way
• Use ‘optimise’ button
• Reduce size of sector for improved resolution
• More jelly and press harder
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Unit
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Unit
3. Evidence and Training
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Unit Thoracic US
• Should physicians perform thoracic US?
• Evidence
• Training
• Equipment
• Examples
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Unit Thoracic US
Advantages:• Higher sensitivity for the detection of pleural fluid
• Smaller volumes of pleural fluid detectable
• Locules detectable
• Intervention safer:• Marking
• Real-time procedures
• Diagnostic value (PTx / malignancy)
Disadvantages:• Training required
• Support required
• Limitations of technique and operator need to be known
conflicts of interest that relate to this presentation.
This event is accredited for CME credits by EBAP and speakers are required to disclose their potential conflict of interest going back 3 years prior to this presentation. The intent of this disclosure is not to prevent a speaker with a conflict of interest (any significant financial relationship a speaker has with manufacturers or providers of any commercial products or services relevant to the talk) from making a presentation, but rather to provide listeners with information on which they can make their own judgment. It remains for audience members to determine whether the speaker’s interests or relationships may influence the presentation.Drug or device advertisement is strictly forbidden.
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INTRODUCTION
AIMS
• Establish why thoracic US is important
• Explore practical applications of respiratory physician-
delivered thoracic US
• Highlight limitations, cautions and tips
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THORACIC ULTRASOUND
Advantages:• Higher sensitivity for the detection of pleural fluid
• Smaller volumes of pleural fluid detectable
• Locules detectable
• Intervention safer:» Marking
» Real-time procedures
• Diagnostic value (PTx / malignancy)
Disadvantages:• Training required
• Support required
• Limitations of technique and operator need to be known
• Evidence suggests thoracic US improves safety and
accuracy of pleural procedures
• Know its limitations and, more importantly, your limitations
• Use of US in untrained/ inexperienced hands provides false confidence and may be harmful – access to machines with level 1 certificate or under supervision only
• Radiologists are highly trained in ultrasound – work closely and maintain a mentor after achieving basic training
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Additional course resources
Readings, guidelines and E-learning resources
1. Solomon SD1, Saldana F., Point-of-care ultrasound in medical education--stop listening and
look, N Engl J Med. 2014 Mar 20;370(12):1083-5. doi: 10.1056/NEJMp1311944
2. Von Groote-Bidlingmaier F., Koegelenberg C.F.N., A practical guide to transthoracic
ultrasound, Breathe 2012 Dec2012 9, no 2. Doi: 10.1183/20734735.024112
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Faculty disclosures
There are no faculty disclosures for this session.