FEDER ERENTO ES 
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X rays range from 10° * to 19 ( um) 
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Figure 1.The electomagnetic spectrum, 
Yo = 
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= Gamma rays 
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Because their directions are unrelated to the position of the 
focal spot, these scattered X-rays do not carry any useful 
information about the patient and serve only to reduce X- 
ray contrast. Unfortunately, the interaction of diagnostic 
X-rays with soft tissue is mainly by the Compton process, 
and specific stratagems must be employed to prevent 
"scatter" from reaching the imaging device. The X-ray 
image is determined by the intensity distribution in the X- 
ray beam as it emerges from the patient. The quality, i.e. 
visibility and recognizability of the X-ray image, depends 
upon the focal-spot size, the incident X-ray spectrum, and 
the composition of the patient. Over many years the 
optimum parameters for a specific examination (e.g. X-ray 
tube potential, beam filtration, exposure time, infection of 
contrast media) have been empirically determined by a large 
number of practitioners. 
At average diagnostic kilovoltage levels, about 5% or less 
of the primary radiation traverses completely through the 
patient's body, without interacting with any of the atoms in 
the patient, and strikes the film. In addition, about 15% of 
the primary radiation interacts with atoms resulting in the 
production of the secondary photons which make it out of 
the patient and strike the film. The remaining 80% of the 
primary beam is totally absorbed within the patient. Figure 
2 illustrates the attenuation of an X-ray beam by the various 
tissues within the patient, resulting in a variation of 
transmitted radiation. The pattern of transmitted radiation 
may be expressed in terms of variations in photon fluency, 
variations in energy fluency or variations in exposure. 
X-ray images are formed in a manner similar to the regular 
black and white pictures. Body parts which have higher 
resistances to X-ray penetration ( bones) result in less light 
reaching the film, and consequently brighter image on the 
X-ray transparency which is nothing more than a negative 
image. On the other hand, soft tissues have less resistance 
to X-rays, so more X-rays pass through them, resulting in 
more radiation reaching the film and producing darker tone. 
In most cases the bones are the brightest and gases are the 
darkest. 
; Film 
Patient 
    
X rays 
Source 
Responses 
Figure 2. Formation of radiological image 
THE REJECTED X-RAY PICTURES 
Rejected X-ray pictures are the ones which do not satisfy 
the initial intended purpose. They are usually thrown away 
or destroyed, and the radiographs have to be retaken. X- 
ray images may be rejected for more than one reason, for 
example: over or under exposure, patient movement, poor 
film development, and other causes which result in poor 
contrast. (Figures 3 and 4 show examples of rejected X- 
ray images.) 
Rejected images account for 15 to 20 percent of the X-rays 
taken per year. This in turn costs public and private 
hospitals and clinics millions of dollars and exposes 
patients to unnecessary radiation which is a major public 
concern. They also slow down the diagnostic process and 
increase the cost which is passed on to the patients. 
. Presently, the only solution radiologists and physicians 
offer is to destroy X-rays and take new ones. This has 
been and probably will be, the trend for the next decade. 
With the growing public concern of insurance cost, and 
with increase in computer capabilities both in software and 
hardware, the medical community have to find a better and 
more reasonable solution.