Diagnosis Of Brain Tumors
Diagnosis Of Brain Tumors
Diagnosis Of Brain Tumors, Of the conventional X-ray examinations , the X-ray examination of the skull has only significance as preparation for the operation, but not for the detection of a brain tumor. Angiography (angiography) is only performed in selected individual cases for the diagnosis of brain tumors or for the preparation of the operation. For the determination of space requirements in the cranial cavity, computer tomography (CT) and primarily magnetic resonance tomography (MRI) are suitable.
Diagnosis Of Brain Tumors – Computer tomography (CT)
It is an x-ray cutting method, in which disks of the body perpendicular to the body longitudinal axis are irradiated by an X-ray beam in the form of a circular rotation. A series of detectors is arranged opposite the x-ray tube, which during such circular movement measures the radiation not absorbed by the body. From these values, the density of the transmitted tissue can be calculated, and a gray value in a digital image is assigned to the respective density given in Hounsfield units (named after the inventor of the method, Godfrey Hounsfield).
Magnetic resonance tomography (MRI)
In magnetic resonance tomography , the magnetization of hydrogen atoms, which are everywhere present in biological tissue, is altered by irradiation of a radiowave. Upon completion of this excitation by the radio pulse, the corresponding energy is released again as a wave, and this is different depending on the type of tissue. The energy delivered is displayed as a gray value in an image.
One differentiates according to the chosen measuring conditions different sequences, of which the most important are the T1-weighted and the T2-weighted picture. Both images provide important and different information about the tissue under investigation.
Diagnosis Of Brain Tumors – Normal brain
Brain tumors differ from normal brain by a different density and different content and binding of hydrogen atoms, so they are recognizable by both methods within the brain. Through the growth, tumors displace the surrounding brain, which can not escape in the skull indefinitely. This is called mass displacement. Pressure is applied to the nerve water spaces (ventricles and brain furrows). The pressure of the tumor on the surrounding brain often leads to a water storage around the tumor called brain edema.
CT and MRT
All these effects can be detected with CT and MRT. In addition, many brain tumors and also brain metastases of tumors in the body lead to a diseased disturbance of a normal barrier between the blood vessels and the brain (hemophilia barrier). Such a disturbance of the blood barrier can be made visible after administration of a suitable contrast medium (iodine-containing for CT and gadolinium-containing MRI) in that the contrast agent accumulates in the disturbed area and becomes visible. The detection and the extent of contrast medium uptake into the tumor can provide evidence of the type of tumor.
Not only because of the radiation exposure through the CT as an X-ray examination, but also because of the clearly better recognizability of different soft tissue qualities in the MRT is the MRI given priority for clarification of brain tumors. Decreases in the brain membranes in brain tumors as well as in tumors in the body are significantly better with the MRT detectable than with the CT. MRI is almost exclusively suitable for examining the spinal canal. Comparable results can not be obtained with the CT even after administration of contrast medium into the nerve water.
Diagnosis Of Brain Tumors – Tumor possible
However, the MRI also has limitations. A patient with the most common cardiac pacemaker should not be examined by MRI. Also, other electronic devices or metal foreign bodies in the body of the subject to be examined can be a considerable obstacle so that an MRI can not be performed. In the case of restless patients, meaningful pictures are often not possible due to the disturbance caused by movement. Seriously ill patients are difficult to monitor in their life functions. For women in early pregnancy, an MRI is not recommended for safety reasons. In the detection of calcifications the MRT has a considerable disadvantage compared to the CT. These, even if they are large, can sometimes not be seen. Therefore, it may be useful to perform additional CT imaging in potentially calcified tumors. Currently, CT is better able to assess the cell density of tumors than with MRI, which also makes conclusions about the type of tumor possible.
Specialized methods such as magnetic resonance spectroscopy (MRS), diffusion-weighted MRI and blood flow measurements of the brain with CT and MRI allow a more detailed classification of the type of a space requirement or the evaluation of a brain tumor during the course of the treatment. Since inflammatory changes such as an abscess or changes in CT or MRI caused by irradiation or chemotherapy can also look like a brain tumor, these methods are used for more reliable classification. With the so-called functional MRT, important functions (speech, movement) can be assigned anatomically.
Diagnosis Of Brain Tumors- biopsy
However, in the initial diagnosis of a brain tumor, in almost all cases it is not possible to dispense with the diagnosis by means of tissue sampling during surgery or stereotactic biopsy.
Positron emission tomography
In the last decade, positron emission tomography (PET) with amino acids (fluoroethylthyrosine, methionine) has established itself as a procedure that allows additional information about the metabolic activity of the tumor. This method, in addition to magnetic resonance tomography, offers the possibility to clarify whether there is any tumor at all. In some hereditary tumors, PET can complement nuclear MRI to identify rapidly growing sites in slow-growing tumors. The detection of such areas (“hot spots”) is important in order to get the sample in the correct place during a sampling. PET has become an important part of the diagnostic repetoires in numerous centers specializing in neuro-oncology.