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To understand what has been done in the area of x-ray imaging and computed tomography, it is first necessary to appreciate the terms many imaging modalities include in the sphere of x-ray. These terms are related to the various types of signals generated by the x-ray source and received by the imaging system. Physical process yielding the observed signal This is the fundamental concept behind imaging modalities and forms a basis of the concepts in this article.
Image contrast is often important to the diagnostician and it is related to the detected energy in the image. Energy detected in the image will be stronger for higher contrast image. Energy detected in the image is related to the energy deposited into the object. If the x-ray source is small, relatively large energy deposition may result in large signal. This is important to know in order to understand what happens to x-ray energy in materials. The ease with which energy can be deposited into a material depends on its density. For example the highest energy photons (those that have the shortest wavelength) are easier to deposit energy into a material than the lowest energy photons (those that have the longest wavelength). As the energy of the incident photon gets higher, there is a decreased probability of the photon being stopped by the object. If the x-ray energy is decreased (lower photon energy) the x-ray will be stopped more often by the object. This will likely deposit more energy into the object. Thus decreasing the x-ray energy will increase the density of the transmitted energy. This is why materials look darker for lower energy x-rays. Thus the amount of energy deposited in the tissue is proportional to the x-ray energy for a given x-ray energy wavelength.
The more condensed the object, the more energy that will be deposited into the object. The amount of energy deposit will depend on several other physical processes depending on the x-ray beam size, energy and material of the object, and for some objects such as bone and lipid, the interaction of the x-ray with the object. In its basic form, a photographic image results from the accumulation of energy deposited into the object.
The energy deposit is defined by the area of the x-ray beam which strikes the object. The area is referred to as the “beam area”. The beam area is not the same as the beam cross section area because the beam is not circular 0b46394aab