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Basics of Chest Sonography
and Anatomy of Chest Wall
By
Gamal Rabie Agmy , MD , FCCP Professor of Chest Diseases ,Assiut University
ERS National Delegate of Egypt
• Diagnostic ultrasonography
is the only clinical imaging
technology currently in use
that does not depend on
electromagnetic radiation.
Ultrasound Transducer
Speaker
transmits sound pulses
Microphone
receives echoes
• Acts as both speaker & microphone Emits very short sound pulse
Listens a very long time for returning echoes
• Can only do one at a time
Physical Principles
Cycle • 1 Cycle = 1 repetitive periodic oscillation
Cycle
Frequency
• # of cycles per second
• Measured in Hertz (Hz)
-Human Hearing 20 - 20,000 Hz
-Ultrasound > 20,000 Hz
-Diagnostic Ultrasound 2.5 to 10
MHz
(this is what we use!)
frequency 1 cycle in 1 second = 1Hz
1 second
= 1 Hertz
High Frequency
• High frequency (5-10 MHz)
greater resolution
less penetration
• Shallow structures
vascular, abscess, t/v gyn,
testicular
Low Frequency
• Low frequency (2-3.5 MHz)
greater penetration
less resolution
• Deep structures
Aorta, t/a gyn, card, gb, renal
Wavelength
• The length of one complete cycle
• A measurable distance
Wavelength
Wavelength
Amplitude
• The degree of variance from the normal
Amplitude
The Machine
Ultrasound scanners
• Anatomy of a scanner:
– Transmitter
– Transducer
– Receiver
– Processor
– Display
– Storage
Transmitter
• a crystal makes energy into sound waves and then receives sound waves and converts to energy
• This is the Piezoelectric effect
• u/s machines use time elapsed with a presumed velocity (1,540 m/s) to calculate depth of tissue interface
• Image accuracy is therefore dependent on accuracy of the presumed velocity.
Transducers
• Continuous mode
– continuous alternating current
– doppler or theraputic u/s
– 2 crystals –1 talks, 1 listens
• Pulsed mode
– Diagnostic u/s
– Crystal talks and then listens
Receiver
• Sound waves hit and make voltage
across the crystal-
• The receiver detects and amplifies
these voltages
• Compensates for attenuation
Signal Amplification
• TGC (time gain
compensation)
– Manual control
– Selective enhancement or suppression of sectors of the image
– enhance deep and suppress superficial
*blinders
• Gain
– Manual control
– Affects all parts of the image equally
– Seen as a change in “brightness” of the images on the entire screen
*glasses
Changing the TGC
Changing the Gain
Displays
• B-mode
– Real time gray scale, 2D
– Flip book- 15-60 images per second
• M-mode
– Echo amplitude and position of moving
targets
– Valves, vessels, chambers
“B” Mode
“M” Mode
Image properties
• Echogenicity- amount of energy reflected back from tissue interface
– Hyperechoic - greatest intensity - white
– Anechoic - no signal - black
– Hypoechoic – Intermediate - shades of gray
Hyperechoic
Hypoechoic
Anechoic
Image Resolution
• Image quality is dependent on
– Axial Resolution
– Lateral Resolution
– Focal Zone
– Probe Selection
– Frequency Selection
– Recognition of Artifacts
Axial Resolution
• Ability to differentiate two objects along
the long axis of the ultrasound beam
• Determined by the pulse length • Product of wavelength λ and # of cycles in
pulse
• Decreases as frequency f increases
• Higher frequencies produce better
resolution
Axial Resolution
• 5 MHz transducer
– Wavelength 0.308mm
– Pulse of 3 cycles
– Pulse length
approximately 1mm
– Maximum resolution
distance of two objects
= 1 mm
• 10 MHz transducer
– Wavelength 0.15mm
– Pulse of 3 cycles
– Pulse length
approximately 0.5mm
– Maximum resolution
distance of two objects
= 0.5mm
Axial Resolution
body
screen
Lateral Resolution
• The ultrasound beam is made up of
multiple individual beams
• The individual beams are fused to
appear as one beam
• The distances between the single
beams determines the lateral resolution
Lateral resolution
• Ability to differentiate objects along an
axis perpendicular to the ultrasound
beam
• Dependent on the width of the
ultrasound beam, which can be
controlled by focusing the beam
• Dependent on the distance between the
objects
Lateral Resolution
body
screen
Focal Zone • Objects within the focal zone • Objects outside of focal zone
Focal zone Focal zone
Probe options • Linear Array
• Curved Array
Ultrasound Artifacts
• Can be falsely interpreted as real
pathology
• May obscure pathology
• Important to understand and appreciate
Ultrasound Artifacts
• Acoustic enhancement
• Acoustic shadowing
• Lateral cystic shadowing (edge artifact)
• Wide beam artifact
• Side lobe artifact
• Reverberation artifact
• Gain artifact
• Contact artifact
Acoustic Enhancement
• Opposite of acoustic shadowing
• Better ultrasound transmission allows
enhancement of the ultrasound signal
distal to that region
Acoustic Enhancement
Acoustic Shadowing
• Occurs distal to any highly reflective or
highly attenuating surface
• Important diagnostic clue seen in a
large number of medical conditions
– Biliary stones
– Renal stones
– Tissue calcifications
Acoustic Shadowing
• Shadow may be more prominent than
the object causing it
• Failure to visualize the source of a
shadow is usually caused by the object
being outside the plane of the
ultrasound beam
Acoustic Shadowing
Acoustic Shadowing
Lateral Cystic Shadowing
• A type of refraction artifact
• Can be falsely interpreted as an
acoustic shadow (similar to gallstone)
X
Lateral Cystic Shadowing
Beam-Width Artifact
• Gas bubbles in the duodenum can
simulate a gall stone
• Does not assume a dependent posture
• Do not conform precisely to the walls of
the gallbladder
Beam-Width Artifact
Beam-width artifact Gas in the duodenum simulating stones
Side Lobe Artifact
• More than one ultrasound beam is
generated at the transducer head
• The beams other than the central axis
beam are referred to as side lobes
• Side lobes are of low intensity
Side Lobe Artifact
• Occasionally cause
artifacts
• The artifact by be
obviated by
alternating the angle
of the transducer
head
Side Lobe Artifact
Reverberation Artifacts
• Several types
• Caused by the echo bouncing back and
forth between two or more highly
reflective surfaces
Reverberation Artifacts
• On the monitor parallel bands of
reverberation echoes are seen
• This causes a “comet-tail” pattern
• Common reflective layers
– Abdominal wall
– Foreign bodies
– Gas
Reverberation Artifacts
Reverberation Artifacts
Gain Artifact
Contact artifact
• Caused by poor probe-
patient interface
Traditionally, air has been considered the
enemy of ultrasound and the lung has been
considered an organ not amenable to
ultrasonographic examination. Visualizing the
lung is essential to treating patients who are
critically ill.
Lines written on ultrasound in the five
Light’s editions
43
78
102
122
278
1983 1990 1995 2001 2008
1998 -2008
2009
2010
V SCAN
Probes
A high-resolution linear transducer of 5–10 MHz is suitable for imaging the thorax wall and the parietal pleura (Mathis 2004). More recently introduced probes of 10–13 MHz are excellent for evaluating lymph nodes (Gritzmann 2005), pleura and the surface of the lung.
For investigation of the lung a convex or sector probe
of 3–5 MHz provides adequate depth of penetration.
Transthoracic Sonography
Scanning Positions for Chest Sonography
Normal Anatomy
Normal lung surface
Left panel: Pleural line and A line (real-time). The pleural line is located 0.5 cm below the rib line in the adult. Its visible length between two ribs in the longitudinal scan is approximately 2 cm. The upper rib, pleural line, and lower rib (vertical arrows) outline a characteristic pattern called the bat sign.
Normal Chest Ultrasound
Superficial tissues
ribs
Poste
rior a
coustic
shadow
ing
Impure
acoustic
shadow
ing
Pleural line
Muscle
Fat
Pleura
Lung
the "seashore sign" (Fig.3).
Duplex Doppler sonogram of a 5 x 3 cm hypoechoic mass
(adenocarcinoma) in upper lobe of left lung shows blood flow
at margin of tumor near pleura. Spectral waveform reveals
arteriovenous shunting: low-impedance flow with high
systolic and diastolic velocities. Pulsatility index = 0.90,
resistive index = 0.51, peak systolic velocity = 0.47 m/sec, end
diastolic velocity =0.23 m/sec, peak frequency shift = 3.8 kHz,
Duplex Doppler sonogram in 67-year-old man with pulmonary
tuberculosis in lower lobe of left lung shows several blue and
red flow signals in massiike lesion. Spectral waveform reveals
high-impedance flow. Pulsetility index = 4.20, resistive index =
0.93, peak systolic velocity = 0.45 m/sec, end diastolic
velocity = 0.03 m/sec, Doppler angle = 21#{
Alveolar-interstitial
syndrome
(Chest. 2008; 133:836-837)
© 2008 American College of Chest
Physicians
Ultrasound: The Pulmonologist’s New
Best Friend
Momen M. Wahidi, MD, FCCP
Durham, NC
Director, Interventional Pulmonology, Duke
University Medical Center, Box 3683,
Durham, NC 27710
