Description of MRI | Thesis Guidance Chandigarh

MRI scanners for medical IP came into use in the 1980s. However, discovery of the MRI machine was around 65 years ago and was first recognized and identified by physicists. Presently, it has become a common and important medical imaging tool for modern science. When compared to CT scans images, MRI produces higher quality images with lots of detailed information of the human body and its organs. High resolution and contrast of the brain will not be detailed by other techniques. CT scan is an X-ray based test that will not give details of some of the brain diseases. MRI is an important diagnosing technique in predicting brain diseases in medical images, which gives a clear image of soft tissues. This computer-aided analysis of disease will reduce doctors‟ workload and also increase the accuracy of para-medical analysis .The principle and brief description of MRI machine is shown in figure.

Figure : Overview of an MRI Scan

In MRI, the image is represented as a map of the local transverse magnetization of the hydrogen nuclei. Transverse magnetization that depends on intrinsic properties of the tissues in the human body is represented by this. MRI is based on the principles of Nuclear Magnetic Resonance (NMR). NMR depends on the primary property that combination of protons and neutrons make up a nucleus and have an angular momentum intrinsically. Nuclei with even number of protons and neutrons will not have a net spin, while nuclei with odd number of protons and neutrons have a net spin. The proton is a positive charge, a current loop perpendicular to the rotation axis is formed. This rotation generates a magnetic field and the joint effect of the self-generated magnetic field and the angular moment, gives the proton a magnetic dipole moment parallel to the rotation axis.

There are many novel techniques such as Positron Emission Tomography (PET), CT, EEG, and so on, constantly being developed to investigate brain diseases, so as to provide robust solutions and ensure accuracy and satisfy requirements. Among these, the greatest revolutionary technique in medical imaging is MRI. MRI scanners use powerful magnets to stimulate hydrogen nuclei i.e., stimulate the water molecules in human tissues and thus, produce electrical signals which will be decoded, and images are produced as an output of these electric signals. Electromagnetic fields in MRI mainly have three uses, of which, first stimulates hydrogen nuclei which is a strong static magnetic field and it is also called as static field; second, is for spatial encoding, which uses weaker time known as gradient field for encoding; and the last is for manipulating hydrogen nuclei - a weak Radio Frequency (RF) field is used and thus, it produces measurable signals collected with the help of RF antenna. MRI is challenging, expensive, and a time consuming task. In spite of all these, MRI predicts and identifies many diseases and it is very useful in the field of neuroscience and radiological applications.

Figure : Different Planes of MRI Brain

MRI is the most important imaging technique in diagnosing tumor, studying various characteristics of the brain such as location of suspected region, size, shape, presence of gray matter and white matter and so on. In spite of other imaging methods, MRI identifies bone abnormalities also. MRI scanner scans the brain and produces the resultant image in three different planes with detailed description. MRI scanner provides various scanning images of the brain from different directions. Above figure shows the different planes of MRI of the brain.

Table 1: Different Types of MRI Images

One is axial plane which slices the brain into two halves and provides information about it; the second one is the coronal plane, which divides the brain into front and back (with the spinal cord) and gives information. The third, is the sagittal plane which divides the brain into right side and left side. The midsagittal plane would divide the right and left sides of the brain into two equal parts as shown in figure.

Imaging protocols of MRI brain images should meet several criteria, which are,
 It must provide all the information for clinical questions.
 The provided or the required information should be complete in all aspects.
 The time spent by the patient in the magnet should be as short as possible.
 The resultant imaging protocols should be reproducible and must be a standard one.
 MRI studies of the brain should include at least two imaging planes.

MRI of the brain is taken inorder to acquire more information than CT scan brain images provide. CT scan shows only mass lesion, whereas, MRI will identify each and every lesion, however minute they are. With the help of MRI of the brain, radiologists are able to answer whether the lesion is a tumor or not and also can identify the tumor affected region. Several imaging types of MRI of the brain exist and the some of the standard categorisation of MRI brain images are discussed in table1.

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