**1. Background**

Since the discovery of X-rays accidentally by Professor Wilhelm Roentgen (from March 27, 1845 to February 10, 1923), a German scientist, Rector of Wurzburg University on Friday, November 8, 1895, a huge development was occurred in the technology of X-ray machines and its applications [1]. He provisionally called these as X-rays. Afterward, he and other scientists performed systemic scientific research to define the newly discovered X-rays. Few months later, in February 1896, in recognition of his discovery, the scientific community named these X-rays as Roentgen rays [2]. Later in 1901, Roentgen awarded the first Nobel Prize in Physics in recognition of his discovery. Recently in 2004, the International Union of Pure and Applied Chemistry, in honor of Roentgen, named the highly radioactive element with atomic number 111 Roentgenium (280Rg111) (**Figure 1**) [6].

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

The first X-ray image of a human was the hand of Wilhelm Roentgen's wife Bertha Roentgen on December 22, 1895. This opened the door for medical applications of X-rays (**Figure 2**). At that time, X-rays were only known as a form of electromagnetic radiation (photons) with

nanometer.

**1.** Penetration: X-rays can penetrate most objects, and the penetration ability depends on photon energy (tube voltage (kVp)) and the object medium characteristics (thickness, density and the atomic number). The X-ray penetration ability is inversely dependent on

**2.** Ionization and excitation of atoms: X-rays have sufficient energy to ionize air, i.e., eject electron from an atom, producing positive ion and free electron. As hydrogen is the atom with a minimal binding energy (−13.5 eV), which considered the threshold energy between ionizing and nonionizing radiation, photons of energy higher than 13.5 eV are ionizing radiation. Excitation occurs when the orbital electron absorbed energy less that its binding energy, which resulted in raising electrons to higher energy levels. Ionization of gas is the

**3.** Fluorescence: X-rays can cause certain materials such as calcium tungstate to emit visible light. This is one of the major characteristics of X-rays used in medical imaging, which resulted in reduction of patient radiation dose by using intensifying screens and conversion of X-rays to visible light. Fluoroscopy is used to obtain dynamic images for diagnostic and/or therapeutic purposes.

with silver bromide (AgBr) or silver iodide (AgI) (photosensitive materials which are sensitive to X-rays and light). This effect is invisible (latent imaging) and can be converted to visible image via development or processing. X-rays have different shades of gray based on the X-ray beam absorption in the body. The conventional X-ray film consists of 98% AgBr and 2% AgI. **5.** Chemical effect: X-rays can produce chemical alterations in certain materials. This chemical change in living organism can lead to biological effect (see list 7). The accurate quantification of the chemical change in the absorbing material enabled scientists to measure the

**6.** Thermal effects: when a medium is exposed to X-rays, tiny amount of energy is converted to heat, and thus increases the medium temperature. If a suitable calorimeter is used, the

**7.** Biological effect: One of the major effects of radiation is the ability to cause damage to cells, organs, or organisms. Thus, patients, staff, and public protection are major concerns in medical imaging. On the other hand, these biological effects are used to destroy cancerous

absolute absorbed dose can be estimated in relation to medium temperature.

) and an electron when they interact

Medical Imaging and Image-Guided Interventions http://dx.doi.org/10.5772/intechopen.76608 35

to 10−<sup>9</sup>

short wavelength ranged from 10−<sup>2</sup>

**2. Characteristics of X-rays**

medium characteristics.

Other main characteristics were revealed including:

oldest method of radiation detection and dosimetry.

**4.** Photographic effect: X-rays can produce a silver ion (Ag<sup>+</sup>

absolute radiation dose (Fricke dosimeter).

cells and cure patients with fatal diseases.

**Figure 1.** William Roentgen.

**Figure 2.** The first X-ray image (left hand of Bertha Roentgen)*.*

The first X-ray image of a human was the hand of Wilhelm Roentgen's wife Bertha Roentgen on December 22, 1895. This opened the door for medical applications of X-rays (**Figure 2**). At that time, X-rays were only known as a form of electromagnetic radiation (photons) with short wavelength ranged from 10−<sup>2</sup> to 10−<sup>9</sup> nanometer.
