# Image-Guided Surgical and Pharmacotherapeutic Routines as Part of Diligent Medical Treatment
## 3 MRI Field Components  
The image produced in an MRI is created by signals resulting from the interaction of magnetic fields and biological tissues. In an imaging progression, three magnetic fields of different natures are used to form 3D images. The first type is a high static field generating a magnetization vector in biological tissues aligning the tissue particles (protons) and measuring their density. The second type corresponds to three low-frequency space gradient fields locating aligned protons in tissues and forming a 3D spatial reconstruction of different tissue divisions in images. The third one is a radiofrequency field stimulating the magnetization vector to permit its detection by the scanner and the conversion of tissue assets into images [95]. Indeed, MRI, in principle, is used to image the nuclei of hydrogen atoms that are confined within the human body. A nucleus (a proton, for hydrogen), is a positive charge mass which rotates around an axis on itself. In the body tissues, protons are arbitrarily oriented and do not spin together. Consequently, they exhibit zero resultant magnetic field (the human body has no magnetization) and they perform out of phase. Reflecting the principle of MRI, protons need three essential organizations inside the explored fragment of the body tissue: to align all the protons in a fixed direction, to rotate them all together in the tissue, and to localize their distinctive origin in the space. Proton alignment could be realized by the insertion of the fragment of the body tissue in a high-strength magnet to drive them together in the axial orientation of its static magnetic field B\({}_{0}\). In order to achieve protons spinning together, an excitation by supplying wave radiofrequency B\({}_{1}\) with a frequency equal to the protons' rotation natural frequency f\({}_{\rm L}\) (Larmor frequency of protons) could be used allowing such action of resonance. In order to localize protons distinctive positions in the space, one may use their associated magnetic field's distinctive values. For this, a 3D space gradient G(x, y, z) with pulsations of very low-frequency repetition could be applied to the field B\({}_{0}\), allowing the position distinctive values of B\({}_{0d}\) (x, y, z) = B\({}_{0}\) + G(x, y, z). The MRI system uses three different fields, B\({}_{0}\), B\({}_{1}\), and G(x, y, z), to determine imaging of the examined fragment of the body in the following way. The value of the Larmor frequency of protons f\({}_{\rm L}\) is dependent of the static field value and equal to 42.5 MHz per tesla. The corresponding position distinctive values f\({}_{\rm Ld}\) (x, y, z) are functions of B\({}_{0d}\) (x, y, z). An excitation of protons by radiofrequency (RF) wave energy followed by a relaxation restoring this energy permit the corresponding signal detection by a suitable tuned RF antenna coil. These signals correspond to values of B\({}_{1}\) of frequencies of f\({}_{\rm Ld}\) (x, y, z), which  
Figure 6: Representation of IG-RDD: (**a**) a collaborative self-governed IG-RDD scheme, (**b**) scanned safe brain (**left**), and affected brain (**right**) with a troubled indicated zone (the circle on the right side). allow coding of a spatial imaging for the concerned body part. Note that the frequency of B\({}_{1}\) is equal to f\({}_{L}\), which is usually tuned to value of f\({}_{Ld}\) (x, y, z) in the center of the examined body fragment. The three different fields employed in the MRI system are very different in nature with respect to their magnitude, frequency, and existence during system operation: B\({}_{0}\): 0.2-10T, 0 Hz, always present, gradient: 0-50 mT/m, 0-10 kHz, multiple pulses of few ms, B\({}_{1}\): 0-50 \(\upmu\)T, 8-300 MHz, (amp. mod. pulses) of few ms. These fields are produced by the strong magnet, gradient coils, and RF coil, respectively. The most popular RF coil comes in the form of a birdcage and is used as tuned RF antenna.