Ultrasound imaging (ultrasonography)
Introduction
Ultrasound is a mechanical vibration which is used for medical or diagnostic
purposes. The frequencies of ultrasound lay above 20 000 Hz and during its
application to human body there is no electric current going through tissues.
When the ultrasound is applied for a therapy purpose it cause
micromassage and local increase of the temperature. This has various
physiological effects:
improvement of human metabolism
increase of capillary permeability
decrease of symphatetic activity = improved blood perfusion
leading to better muscle relaxation
improvement of tissue regeneration
Ultrasound imaging
Nowadays, ultrasound imaging is a basic and widely used diagnostic method.
Moreover, if necessary, the diagnostic is possible at the patients bed. The medical
examination can be stored by each frame at specialized photo paper or on the data
storage. The examination by ultrasound can be done without any special preparation,
however in the case of abdominal cavity organs it is recommend to examine patient
on an empty stomach – the results are much better. Slim people are easier to
examine.
Principles of ultrasound examination (screening)
Ultrasound waves with frequency 2,5-10 MHz are generated by piezoelectric probe
and penetrating to the certain depth into the tissue (approx. 4-25 cm). In soft tissues
the ultrasound is propagating with only small looses and its best propagation is in the
liquid. On the tissue boundaries the waves are reflected, mostly form the bone
surfaces and similar structures such as renal stones. Similar barrier for the ultrasound
is also an air contained in the stomach and intestine. Presence of the air swallowed
during eating or during flatuance is the biggest obstacle of this diagnostic method.
The final image is constructed using signals reflected from various tissues back to the
probe. Each medium, including tissues, has different propagation speed of
ultrasound, acoustic impedance and damping (which depends on the ultrasound
frequency).
Type of ultrasound imaging
Type A – one dimensional – reflections are modulating the amplitude (today used only
in ophthalmology)
Type B – static – not used anymore
- dynamic - the series of images are created in examined area which allows to
observe the movement
Type M – was developed for cardiologic diagnostics. It displays a moving object of type
A which causes a so called flowing echo from which we can recognize the movement
boundaries.
(Higher) Harmonic imaging – an intensive ultrasound pulse of basic frequency f 0 is
emitted from the probe, however the reflected signal is detected at frequency 2f 0. This
increases the image contrast
Excercise ultrasound diagnostics
1.Ultrasound imaging on model
Attention – protect the ultrasound probes from any shock, work carefully,
after the operation put each probe back to the holder
1. Turn on the power switch.
2. Select the imaging probe – firstly the linear probe (A), than the sector probe (B) (see
Fig. 1).
3. Select the imaging mode type (B mode). – see Fig. Mode B selection.
4. Take the probe and place it perpendicularly to the model with applied gel. Slowly
move with the probe and watch the image on the screen.
5. There are different objects inside the model.
6. Fix the image with the fixation button (see Fig. 1).
7. Press the button B DIST for distance measurement (see Fig. 1)
The cross appears and it can be moved by trackball and fixed by button CHANNEL 1.
8. Distance measurement – Move the cross into the position from which you want to
measure the distance and press CHANNEL 1. Move the cross using the trackball into
the final position and press CHANNEL 1. On the right side of the image you will read
the distance D in mm.
D =……mm
If you want to correct the positions, press CHANEL 1.
9. Area measurement – Press button B TRACE fror area measurement. Move the
cross to the position from which you want to start. Press CHANEL 1 for the cross
fixation. Move the corss around the area you want to measure until the value A in
mm2 and value L in mm will appear on the right side of the image. If the values will
not appear, press CHANNEL 1.
10. Investigate the objects in the model and write down the values D, L, and A. Make a
sketch of each object.
Imaging probe selection
A linear left
B sector right
Cross fixing
button
B mode selection
Distance
measuremen
t
Area
measuremen
t
Trackball
Fig. 1.
Image
fixing
button
2. Abdominal imaging by ultrasonography
Ultrasonography became the dominant diagnostic method of gall bladder. Gallstones
are easily visible and for medical doctor is very important the opportunity to examine
the width of gall paths. Another organ which is easily visible by ultrasonography is liver.
One can easily recognize its enlargement and tumors inside (including metastases).
Kindnesses are also easily examined, however pancreas, situated deep in the
abdominal cavity, is difficult to observe by ultrasonography (especially in the case of
obese people). In the abdominal cavity we can also examine spleen and large vessels.
Ultrasonography also reveals relatively small amount of liquid in abdominal cavity,
which appears during heart or liver failure.
1.Take the probe , apply a gel on the right side area under the ribs of one student in
the group and observe the ultrasound image.
Write down which organs you observed and which of them are suitable for examination
by ultrasound.