TMS
Didactic Muse
Page 14
Imaging Ultrasound Cont.
A sector with seven
ultrasound lines.
the mechanic probe sends one ultrasound beam and waits to receive the echoes from the interfaces it passes through. After it has received all the echoes, the crystal is moved to another position and sends again another ultrasound beam and again waits to receive the echoes from the interfaces. This
process is repeated until the whole sector image is done. (Fig. 11) shows
a sector with seven ultrasound lines. There are many lines needed to fill the
sector image. According to the first line, after sending the first pulse, the
ultrasound beam collided with four interfaces. The pulses represent echoes
shown in the interfaces I1,I2,I3,and I5 of the figure 10, the first and the
third pulses represent echoes coming from interfaces of the same difference of
acoustic impedance because the amplitude are the same. The third pulse
represents an echo from an interface with bigger difference acoustic impedance than interfaces 1 and 3, and the fourth pulse represents an echo from an
interface that reflects all the ultrasound beam. In this interface, bone or air is
present. After the four echoes are received a motor moves the crystal from
line 1 to line 2, and the process done in line 1 is repeated until reaching
line 7 and the complete image is done. Then the motor moves the crystal back
to line 1 to begin the formation of another image. To illustrate the process (fig.12) shows two figures scanned. Each time the ultrasound beam
goes through an interface of these figures an echo is produced, and it is represented in a screen as a point as is shown in (fig.13). This information is not
enough because it only gives an approximation of the real figures. A real
representation of the figures scanned is needed to give a right medical diagnosis. This lack of information happens because of the spaces between lines
in the sector, so the spaces in between have no echoes. For solving this lack
of information, processing digital signal are used to fill the empty spaces between lines generating points with the most approximated level of brightness
in the space they are located. If the position of the point is between an original black point and an original white point, the point generated ought to have the
half bright of the two original originals points. If the empty space is between
a white color and a gray brightness, the resulting new point generated
ought to be of a lighter gray brightness, and vice versa. (Fig 14) shows the
image on screen after being processed; the points generated appear in red and
the original in black.
Two figures scanned,
each time the ultrasound
beam goes through an
interface of these figures
an echo is produced.
(Continued)