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A Technical Seminar On
X-RAY AND CT SCAN
Introduction
X-rays were discovered by the German physicist Will
elm Konrad Rontgen in November 1895. He called
the 'new kind of ray' or X-rays, X for the unknown.
their usefulness to visualize the internal anatomy of
humans was established. Today, imaging with X-rays
is perhaps the most commonly used diagnostic tool
with the medical profession, and the techniques from
a simple chest radiography to a digital subtraction
angiography or computer tomography depend on the
use of X-rays.
Properties of x-ray
The main properties of X-rays, which make them
suitable for the purposes of medical diagnosis, are
their:
• Capability to penetrate matter coupled with
differential absorption observed in various
materials; and
• Ability to produce luminescence and its effect
on photographic emulsions.
Principle of Working
X-rays are produced in: specially constructed glass
tube, which basically comprises.
(i) A source for the production 0: electrons,
(ii) a energy source to accelerate the electrons,
(iii) a free electron path,
(iv) a means of focusing the electron beam and
(v) a device to stop the electrons.
Stationary mode tubes and rotating anode tubes are
the two main types of X-ray tubes:
Fig. Construction of stationary anode X-ray tube
Failure of X-ray
There are two main limitations of using conventional X-rays
to examine internal structures of the body.
•
Firstly, the super-imposition of the three-dimensional
information onto a single plane makes diagnosis
confusing and often difficult.
•
Secondly, the photographic film usually used for making
radiographs has a limited dynamic range and, therefore,
only objects that have large variations in X-ray absorption
relative to their surroundings will cause sufficient contrast
differences on the film to be distinguished by the eye.
CT-SCAN
Principles of Working of CT SCAN
In principle, computed tomography involves the
determination of attenuation characteristics for each
small volume of tissue in the patient slice, which
constitute the transmitted radiation intensity
recorded from various irradiation directions. It is
these calculated tissue attenuation characteristics
that actually compose the CT image.
For a monochromatic X-ray beam, the tissue
attenuation characteristics can be described by
It = Io e- x
I0 = Incident radiation intensity
It = Transmitted intensity
x = Thickness of tissue
 = Characteristic attenuation coefficient of tissue
System Components
All computed tomography systems consist of the following
four major sub-systems:
i. Scanning system—This takes suitable readings for a
picture to be reconstructed, and includes X-ray source and
detectors.
ii. Processing unit—This converts these readings into
intelligible picture information.
iii. Viewing part—It presents this information in visual form
and includes other manipulative aids to assist diagnosis.
iv. Storage unit—This enables the information to be stored
for subsequent analysis.
Conclusion
Ever since the CT technology was developed, rapid
developments in computer hardware and detector
technology have been witnessed. Modern CT systems
acquire the projection data required for one
tomographic image in approximately one second and
present the reconstructed image on a 1024 x 1024
matrix display within a few seconds. The images
represent high quality tomographic maps of the X-ray
linear attenuation coefficients of the Patient tissues.