Magnetic Resonance Imaging of Brain Tumor

Brain tumor

A brain tumor is an assortment of irregular cells that develops in or around the brain. It represents a hazard to the sound brain by either attacking or pulverizing typical cerebrum tissue or by compressing the brain. Brain tumors are of two types. Brain tumors can be malignant (cancerous) or benign (non-cancerous cells). (1)

Primary and secondary tumors

Some originate in the brain itself, in which case they are termed primary. Others spread to this area from elsewhere in the body through metastasis, and are named secondary. Primary brain tumors do not spread to other body sites and can be malignant or benign. Secondary brain tumors are always malignant. Both types are potentially disabling and life-threatening. (2)

Cause of cancer-related deaths

Brain tumors are, in fact, the second leading cause of cancer-related deaths in children and young adults. Gliomas are the most widely recognized dangerous brain tumors. Gliomas are typically associated with low survival. This is due to a combination of factors, including high relapse rates, which hinder successful treatment. Magnetic resonance imaging (MRI) utilizes a strong magnetic field, radiofrequency pulses and a PC to create pictures of organs, delicate tissues, bone, and practically all other inner body structures. X-ray gives detailed pictures that can distinguish brain abnormalities from the norm, for example, tumors and disease. X-ray has a high affectability for recognizing tumors. (3)

MRI Use in Brain Tumor

Magnetic resonance imaging (MRI) utilizes a strong magnetic field, radiofrequency pulses and a PC to create pictures of organs, delicate tissues, bone, and practically all other inner body structures. X-ray gives detailed pictures that can distinguish brain abnormalities from the norm. Every MRI picture comprises a T1 component and a T2 component. It is possible to turn off the majority of one of either component, making a T1 weighted or T2 weighted picture individually.MR imaging is an important diagnostic tool in the evaluation of intracranial tumors. (3)

Effectiveness

Its effectiveness is due to its inherent high sensitivity to pathologic alterations of normal(2, 4)

Parenchymal water content, as demonstrated by abnormal high or low signal intensity on T2- or T1-weighted images, respectively. It gives more data about tumor type, position, and size. For this reason, MRI is the imaging study of choice for the diagnostic workup and, thereafter, for surgery and monitoring treatment outcomes. (3)

MRI Signal Generation

Conventional MRI uses three physical properties of tissue protons to create signals that are seen as areas of different contrast, which mirror the anatomy and physiology of the organ. Protons are positively-charged particles inside the nucleus of elements’ atoms. To understand how the MRI signal is generated, we can imagine this proton as a minute magnet bar that moves like a spinning top. This tiny magnet bar can be described as a two-dimensional (2D) vector–also called a spin vector–with respect to a Cartesian coordinate system. Without a magnetic field, the spin vector is haphazardly orientated.(2) However, when placed in a strong static magnetic field (B0), such as that generated by MRI scanners, the spin vector tends to align parallel with B0. As a result, its component along the y-axis (longitudinal magnetization) is different from zero but the one along the x-axis (transverse magnetization) is zero, and no signal can be produced. (1)

MRI Image Generation

The time needed to recover 63% of the longitudinal magnetization is called T1-relaxation time. The time taken for 63% of the transverse magnetization to be lost is called T2-relaxation time. T1-and T2-relaxation times are specific to different types of tissue and increase as the magnet’s field strength increases. Both T1 and T2 are components of the MRI signal. A third part is proton density; that is, the quantity of hydrogen protons per unit volume of the tissue being imaged. All three contribute to contrast generation. But, because they do it simultaneously, the image would be confusing and difficult to interpret. The issue is kept away from by weighting the difference toward one of the three signal segments. As a result, the following images can be obtained: T1-weighted, T2-weighted, and proton density-weighted.(1, 3)

Bright and dark areas

In all three types of images, bright areas correspond to tissue with high signal intensity (i.e., large transverse magnetization) and are referred to as hyperintense, whereas dark areas correspond to low signal intensity (i.e., small transverse magnetization) and are referred to as hypointense. This means that high-fat-content tissues appear as bright areas in T1-weighted images, whereas high-water-content tissues appear as dark areas. The opposite is true for(3)T2-weighted images. Since most diseases are characterized by increased water content in tissues, T2-weighted images are particularly useful for pathological investigations. In contrast, T1-weighted images are best for anatomical studies, although they can be used for pathology if combined with contrast enhancement. Currently, the standard contrast agent is gadolinium (G d), due to its ability to cross the blood-brain barrier (BBB). In proton-weighted images, bright areas indicate high proton-density tissues, such as the cerebrospinal fluid, and dark areas indicate low-proton-density tissues, such as cortical bone. Proton-density pictures are commonly used to show anatomy and some pathology. While the interpretation of gadolinium-enhanced T1- weighted images and T2-weighted images remains the mainstay of brain tumor diagnosis, this approach has limitations. For example, it is sometimes difficult to differentiate new from old tumors, or tumors from non-tumoral lesions, like ischemia. Evaluating, checking of tumor progression, treatment reaction appraisal, and recognition of lingering tumor after medical procedure may likewise be risky. Techniques other than T1- and T2-weighted MRI can help overcome these limitations. (4)

Conclusion:

MRI is the favored imaging study for brain tumor finding, giving point by point data on injury type, size, and area. Gadolinium-enhanced T1-weighted images and T2-weighted images are the MRI modalities of choice for the initial assessment. (4)

References

1. Gerstner ER, Chen P-J, Wen PY, Jain RK, Batchelor TT, Sorensen G. Infiltrative patterns of glioblastoma spread detected via diffusion MRI after treatment with cediranib. Neuro-Oncology. 2010;12(5):466-72.

2. Shukla G, Alexander GS, Bakas S, Nikam R, Talekar K, Palmer JD, et al. Advanced magnetic resonance imaging in glioblastoma: a review. Chinese clinical oncology. 2017;6(4).

3. Weber MA, Zoubaa S, Schlieter M, Jüttler E, Huttner HB, Geletneky K, et al. Diagnostic performance of spectroscopic and perfusion MRI for distinction of brain tumors. Neurology. 2006;66(12):1899.

4. Dandy WE. THE DIAGNOSIS AND LOCALIZATION OF SPINAL CORD TUMORS. Ann Surg. 1925;81(1):223-54.