IMAGE PROCESSING OF CONVENTIONAL X-RAY IMAGES
Dr. Khalil I. Jassam,
Researcher, The Institute of Islamic Medicine for Education and Research, Panama City, FL
and Visiting Professor, Department of Surveying Engineering, University of Maine, Orono, ME
USA, Commission No: VII
ABSTRACT:
The goal of this paper is to outline the procedure of obtaining sharper and more visible images from a
rejected X-ray. This process will improve X-ray image quality and produce image data that is more
effectively displayed for a later visual imaging diagnosis. Image processing enhances image contrast
thus increasing image visibility, helping both physicians and radiologists to make more accurate
diagnoses and to decrease the need to retake X-rays. This in turn reduces the risk of radiation
exposure and increases economical benefits by lessening the number of rejected X-rays. Different
spectral and spatial enhancement techniques were used both in the spatial and frequency domain. The
obtained X-ray images are sharper, more visible and recognizable, and provide much more
information.
Key Words: X-ray Imaging, Image Processing, Medical Imaging.
INTRODUCTION
The discovery of X-rays revolutionized the diagnosis
procedure, and its importance can not be overemphasized.
Radiographic quality refers to both image visibility and
recognizability. The visibility of the image is best when its
density is sufficient, its noise is minimal, and its contrast is
maximum. It is most recognizable when its geometry is
maintained, which takes place when sharpness is
maximized and image distortion and magnification are
minimized. Several factors affect the image quality, some
of which are the focal-spot size, milliampere-seconds,
kilovoltage, field size limitation, patient status, contrast
media, and film quality. Over the years the optimum
parameters for a specific examination have been empirically
determined by a large number of practitioners.
Tremendous efforts have been invested in upgrading X-ray
image quality. A variety of techniques were developed,
which were mainly concerned with hardware improvement,
but their effects were limited. In the last decade computed
tomography (CT) was developed. This system represents
the state of the art in modern X-ray imaging. The CT
system has major advantages as well as disadvantages. It
maximizes both image visibility and recognizability, and it
has a better resolution when compared to the conventional
X-ray. The main disadvantage of the CT system is that it is
too expensive to buy and operate, and only major clinics
can afford it. In addition, it is less safe due to higher
radiation levels and more expensive to the patiants. For
these reasons, the need for the conventional X-ray will
continue for the next decade.
This paper expands the use of image processing techniques
to improve the quality of conventional X-ray images
without hardware modification. The only additional
hardware needed is a digitizing device and a personal
computer.
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BACKGROUND
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 affect
photographic film in the same way as light. On the other:
hand, they were 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 10 5cm. 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
(figure 1).
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-
ray is then directed to the human body. The number of X-
rays that interact with the patient depend 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 radiations. 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.