Transcript Waves

XRAY
US
X
rays
Basic
principles
Sacco Simone
X Rays
X rays
Electromagnetic Waves.
- In Physics "wave" = “perturbation that
originates from a source and spreads out
through the space, carrying out energy
displacement of matter"
- May propagate both through the matter
and the vacuum.
Wave length
Y = Amplitude
Space
X rays
X-rays: same nature than visible light but with a
different wave-length.
Electromagnetic Waves Spectrum
Tra 10-9m e 10-12m
X rays
Electromagnetic Waves
The energy propagates through the space-time in the form of
the electromagnetic radiation generating an electric and a
magnetic field
Remember that the electromagnetic radiation has a quantized
nature fully described only with quantum mechanics, with the
double feature of wave and photons beam, that travels in the
vacuum at the speed of light.
A short History…
Discovery of x-rays:
Roentgen discovered the X rays during the night
of November 8 1895. He published this
breakthrough in December 28, 1895 to the
Physical-Medical Society of Wurzburg in a paper
entitled "A new species of rays.“
Roentgen showed that the ionizing radiation
emitted by a cathode within the ray tube is
capable to cross an opaque body and impress a
photographic film. The Radiology was born…
Wilhelm Conrad Röntgen
Remscheid, 27 marzo 1845 – Monaco di Baviera, 10 febbraio 1923
The first medical radiography performed by
Roentgen December 22, 1895 at the left
hand of his wife Anna Berthe.
The wedding ring is also visible
X rays – production
They are generated in the Rontgen’s tube after the
collision of the electrons produced on a hot filament in
the cathode into the anode releasing energy as
radiation X.
Remember…
• The higher the intensity of the electric current
(measured in milli-amperes) the greater is the
number of electrons produced
• The greater is the potential difference supplied to
the tube (measured in Kilovolt), much more
violent is the collision of electrons against the
plaque of tungsten and the shorter and the
wavelength of the radiation generated.
X Rays - properties
1) They pass through objects made of various
composition. (Law of absorption)
2) Ability to impress radiographic films
3) Ability to change the physical and chemical
state of matter (Radiotherapy)
Absorption Law
The absorption is:
1. Directly proportional to the atomic number
of the object.
2. Directly proportional to the thickness of the
object.
3. Directly proportional to the wavelength of
the radiation.
Radiodiagnostic
• Analog radiogram: the X-ray image is
impressed on a sensitive film exposed to the
radiation beam emerging from the body part
examined:
Tissues that absorb more X-rays appear as
bright areas (radiopaque)
The tissues that absorb less radiation appear as
darker areas (radiolucent)
Radiodiagnostic
Digital radiogram: the X-ray image is impressed on
sensitive detectors exposed to the radiation
beam emerging from the body and is then
analized and elaborated by a computer that
displays the image on the monitor:
The tissues that absorb more X-rays appear as light
areas (radiopaque) on the monitor
The tissues that absorb the radiation to a lesser
extent appear as darker areas on the monitor
Remember
• The radiologist looks at the patient's face.
Right
Left
Radiodiagnostic
• Projection: Path of radiation in the body
• It is expressed with two adjectives: The first
indicates the entry point of radiation,
according to the exit point.
• At least two more to represent the three
dimensions of space !!!
Radiodiagnostic
• X rays
Where???
Chest.
Abdomen.
Skeleton.
Other (urography, cystography)
Radiodiagnostic
Radiodiagnostica.
• Xray skeleton:
When???
-To Confirm the clinical suspect of fracture, define the type and
location
or evaluate the dislocation of a joint.
-To Ensure that a fracture has been properly treated and stabilized
-To Assess the damage caused by bone or joint infections, arthritis,
abnormal bone growth and bone diseases like osteoporosis
- To highlight skeletal malformations or degenerative processes.
- To identify and locate foreign bodies.
- To confirm the suspect of neoplasia.
- To estimate the physiological age based on bone growth
Fractures.
Fractures and controls after treatment.
Radiodiagnostic.
• RX Chest:
Why?
- Study of the Lung: Pneumonia, primary or
secondary malignancies, pleural effusion
- Study of the heart: Heart disease in general,
cardiogenic pulmonary edema, the study of
vascular structures, coarse study of the aorta and
the pulmonary arteries, the study of bone
structures rib.
Example
Radiodiagnostic.
• Xray Abdomen:
When?
•Basal (direct abdomen): Acute abdominal pain
(STAT); e.g. Subocclusive state post-surgery
• Contrast: Today infrequently used
A) Barium:
- enema> colonoscopy / CT
- Ileum> endoscopy.
B) Iodinated: Cystoscophy, Urography.
Basic
principles
Sacco Simone
Definition
ULTRASOUND
• Diagnostic imaging procedure that utilizes high-frequency mechanical
waves based on the principle of the echo transmission
• Ultrasound travels in the form of waves produced by an object (e.g.
speaker) that pushes forward the surrounding air causing small
changes in air pressure
Acustic wave
Wave lenght λ
λ = v T = v/F
Freq = 1/T
High
pressure
Low
pressure
Acustic wave
The humans can perceive acustic waves from 20 and 20000 hz
Ultrasounds are acustic waves above 20000 hz
PHYSICS
4.The
Thepiezoelectric
piezoelectriceffect
effect
"Piezo", derived from the Greek piezein, which means to squeeze or press
Piezo electricity refers to the charge which accumulates in certain solids in
response od a mechanical stress
PHYSICS
4.The
Thepiezoelectric
piezoelectriceffect
effect
Conversely, when an electric field runs a piezoelectric
material, this one contracts or expands.
If the electric field is an alternating current, the effect
will be a vibration of the piezoelectric material
tension
compression
PHYSICS
4.The
Thepiezoelectric
piezoelectriceffect
effect
When the current is switched on, the
probe produces ultrasounds which
travel through the body
Transmission time = 80 nanoseconds
When the current is switched off, the
reflection of the utrasounds stimulates
the piezoelectric cristals generating a
current, which is used to create the
image
Listening : 200-300 milliseconds
PROPERTIES
2. Wve parameters
The ultrasound to propagate needs to move a
certain quantity of matter (they do not
propagate in the vacuum)
Their speed varies depending on the density of
the medium
Velocity (m/s)
Air
300
fat
1430
liver
1500
muscle
1545
bone
2000-4000
In the soft tissues the velocity is approximated constant at 1540 m/s
PROPERTIES
• The ultrasound to propagate needs to move a certain
quantity of matter
• Like any other type of wave phenomenon ultrasound they are
subject to the phenomena of reflection, refraction and
diffraction
• These phenomenon are exploited to produce the ultrasound
image
Reflection
6. Types of reflections
Specular reflection is
responsible of the bright
appearance of fibrous or
hard structures, such as
tendons, ligaments or cortical
bone surface.
Large reflector
Specular reflection
Diffraction
6. Types
of reflections
Scattered reflection is characteristic
of soft tissues: small amounts of
energy are absorbed and
retransmitted in all directions
Small reflectors
scattering
Acoustic Impedence
Acoustic impedence is the physical property exploited to create contrast
between tissues
Impedance: how difficult it is for sound to penetrate a material).
•
It depends on the density and on the speed of the sound in the material
•
The amount of sound which is transmitted or reflected depends on the
difference of impedance between the 2 materials (greater difference,
more reflection)
Medium
Impedance (standard unit)
air
0,000429
water
1,50
blood
1,59
Fat
1,38
muslcle
1,70
bone
6,50
Acoustic impedence
Acoustic impedence ( how difficult it is for sound to
penetrate a material.
Because of the great
difference of impedance
between air and skin, a gel
is applied on the skin of the
patient to reduce the
impedence and facilitate
the transmission of US
Diagnostic frequencies
•
2 - 6 mhz
– abdominal ultrasound, obstetrical and gynecological
exam, echocardiography, trans-cranial Doppler
•
7.5 - 14 mhz
– small parts, vascular Doppler, musculoskeletal ultrasound
•
10 - 20 MHz
– ophthalmology, special vascular examimations
•
20 - 50 MHz
– endoluminal exam, ultrasound biomicroscopy
(ophthalmology, dermatology)
Diagnostic frequencies
Creation of an image
5. Creation of an image
• A-mode
• B-mode or 2D mode: In B-mode (brightness mode) ultrasound, a linear
array of transducers simultaneously scans a plane through the body that
can be viewed as a two-dimensional image on screen.
• M-mode: In M-mode (motion mode) ultrasound, pulses are emitted in
quick succession – each time, either an A-mode or B-mode image is
taken. Over time, this is analogous to recording a video.
• Doppler mode: This mode makes use of the Doppler effect in measuring
and visualizing blood flow
• Color Doppler: Velocity information is presented as a color-coded overlay
on top of a B-mode image
A - MODE
5. Creation of an image
Amplitude (A-scan) or monodimensional.
Each spike represents a signal reflected by a different anatomic
structure after some time, which is related to a certain distance to the
probe
amplitide
time
B - MODE
5. Creation of an image
B-scan (brightness)
The amplitude of each returning signal controls the brightness of a
spot which represents the reflection.
The largest reflection gives back the largest amplitude and
brightness
REAL TIME B-MODE
5. Creation of an image
Real time B-scan
In the modern ultrasound an array of piexoelectric cristals act as
individual transmitters and receivers
The image is build up from these multiple signals
Appearance of tissues
TISSUE
APPEARANCE
WATER
BLACK
SOFT TISSUE
Shades of gray
BONE
Reflecting
white boundary
AIR
BAD!
Appearance of tissues
Muscle fibers
fat
Muscle tissue is dark on ultrasound, but the aspect is msrbled due to the fat
inside the muscle and the interface fat-muscle fiber which is bright
7. Appearance
Appearance
of of
tissues
tissues
Bone appearance presents a remarkably bright line due to the interface soft
tissue-bone, and delow is completely black because of the complete
reflection of ultrasound from the cortical bone
Appearance of tissues
7. Appearance of tissues
Fluid, blood effusion or cyst appear
usually black, because of the small
reflection of the ultrasound. Fluid for
this property is called anechoic.
EXAMPLES
5.
of an image
B- Creation
MODE IN ABDOMINAL
REGION
5. Creation of an image
B- MODE IN OBSTETRICS
5. Creation of an image
B- MODE IN MUSCULOSKELETAL ULTRASOUND
Meniscal Tear
Doppler effect
When the ultrasound beam encounters a moving structures
(blood in the vessels), the echo received by the probe have
a phase shift
If the object (blood flow) is moving towards the probe, the
phase shift will be positive
If the blood flow is moving away the phase shift will be
positive
Faster is the object moving, greater the phase shift
Conventional doppler techniques
continous
pulsed
Applications of doppler
Arterial examinations
• Stenosis
• Aneurism
• Dissections
Colour flow mapping
Venous thrombosis
Colour
mapping
Colour
flow flow
mapping
Mass vascularization