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REMOVAL OF RANDOM NOISE FROM CONVENTIONAL 
DIGITAL X-RAY IMAGES 
Dr. Khalil I. Jassam, Researcher, the Institute of Islamic Medicine for Education and 
Research Panama City, FL. and a visiting professor, and Maureen Carr, Department of 
Surveying Engineering University of Maine Orono, ME. USA 
Commission No: VII 
ABSTRACT: 
Conventional X-ray imaging is the fastest, most common, and least expensive diagnostic 
imaging system available. Production of digital X-rays from pictorial radiographs is 
becoming a common practice to maximize information and reduce the number of rejected 
X-rays. Secondary radiation, film processing and handling, and digitization are the main 
sources of noise in digital X-ray images. The aim of this paper is to present the best 
procedure for noise suppression in digital X-ray images by applying conventional noise 
filtering techniques in the spatial and frequency domains. The resulting X-ray images are 
more visible, although fine details may be lost. In addition, filtering in the frequency 
domain appears to maintain image integrity better than that of the spatial domain. 
Key Words: X-ray imaging, Image Processing, Medical Imaging, Noise removal 
INTRODUCTION 
X-rays were discovered in 1895 by the German physicist 
Roentgen and were so named because their nature was 
unknown at the time. Unlike ordinary light, these rays are 
invisible, but they travel in straight lines and effect 
photographic film in the same way as light. On the other 
hand, they are much more penetrating than light and could 
easily pass through the human body, wood, and other 
"opaque" objects. We know today that X-rays are 
electromagnetic radiation of exactly the same nature as 
light but of very much shorter wavelength. The unit of 
measurement in the X-ray region is the angstrom (À), equal 
to 108 cm. X-rays, used in diffraction, have wavelengths 
lying approximately between the range of 0.5 - 2.5 A 
where the wavelength of visible light is on the order of 
6000 A. X-rays, therefore, occupy the region between 
gamma and ultraviolet rays in the electromagnetic 
spectrum. 
The method employed to produce X-rays is essentially the 
same as that used at the time of its discovery. A beam of 
electrons, accelerated by high voltage to a velocity 
approaching the speed of light, is rapidly decelerated upon 
colliding with a heavy metal target. In the process of 
slowing down, X-ray photons are emitted; the emitted X- 
rays are then directed to the human body. The number of 
X-rays that interact with the patient depends upon the 
thickness and the composition of the various tissues. 
Diagnostic X-rays interact primarily by the photoelectric 
and Compton processes. Photoelectric interactions are the 
most important for image formation because of the strong 
dependence of the photoelectric effect on the atomic 
composition of the absorber and the absence of long-range 
secondary radiation. Compton interactions are generally 
detrimental in that the likelihood of their occurrence 
depends mainly on tissue density, and the scattered X-rays 
produced in Compton collisions have a high probability of 
escaping from the patient and crossing the image plane. 
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 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. The 
attenuation of an X-ray beam by the various tissues within 
the patient results 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 regular 
black and white pictures. Body parts which have higher 
resistance 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 
tones. In most cases the bones are the brightest and gases 
are the darkest.