MRI

Magnetic Resonance Imaging (MRI) is the most preferred technology to scan brain tumors as it is not as harmful as the other X-ray based Imaging modalities. In addition to that, MRI images have better resolution and better contrast, which helps with a better distinction between grey and white. This makes MRI the best tool for brain scans. 

As our body is mainly composed of water, the protons of water molecules can be adjusted by a strong magnetic field. With a radio frequency that precesses the protons, the setting causes a phase shift of some of them. As the protons tend to go back to the aligning with the string magnetic field again, they undergo a relaxation, which induces current in the inner-cell magnetic field created by its spins. This current is measured, sampled and stored for producing the image.

The most vital signals for MRI are the relaxation times T1 and T2. The current flow indicates the relaxation of the signal, so it is easy to take the relevant timestamps. By Fourier Transformations, these time signals are converted into digital signals. Scannings from different angles are then composed to a single MRI image.

                                                        [Signal processing of MRI]

CT

Computer Tomography, short CT, extends ordinary x-ray images with the computation power of computers in a way that multiple images are combined to a single picture e.g. of a brain. The CT scanner has to rotate around the to-be-scanned body in order to produce enough images. 

           [CT images of a brain tumor]

In the CT image above, the yellow arrows show a brain tumor. Noticable is the contrast difference between image A and B, which enables a better recognition of the tumor.

MRA

Angiography, short as MRA, is a special version of MRI and is used to track the presence and position of blood vessels in the brain. Although a contrast dye is helpful, it is not necessary.

[Angiography of a human brain]

Dynamic CT/ Dynamic MRI

MEG

Magnetoencephalography, short as MEG, is used to detect the magnetic field created by nerve cells. A physical contact is unnecessary, which is the big advantage of this method.

                                                      [source]

PET/ SPECT

Both of these methods are additional imaging techniques. They are not used to get diagnosis about brain tumors, but can give additional information to data from other imaging techniques. PET can be helpful for tumor grading because the tracer is absorbed by surrounding tissue, whereas SPECT is mainly used to detect blood flow.

                                                       [PET and SPECT captions of the human brain]

fMRI

By increasing the speed of producing MRI images, the ability of recogizing oxygen usage in brain is acquired. 

                          [Oxygen flow in brain regions by fMRI method]

DTI(Diffusion Tensor Imaging)

Various DTI is also an extension to conventional MRI in order to get physiological and functional features. With the diffusion tensor images, the orientation and the architecture of tissue microstructure at the voxel level are acquired.

                       [Diffusion Tensor Image of a human brain]

MRS (Magnetic Resonance Spectrography) 

Focussing of the function, not a shape of a to-be-examined tissue is the key point to Magnetic Resonance Spectrography, short as MRS. The advancedness of a tumor can be reviewed by this approach, which is also an indication for dispersal in the brain.

                                 [components of a brain tumor tissue]

Biopsy

To determine the real brain tumor type and to assure a certain guess, doctors decide to perform a surgery and take some brain tumor cells from brain tissue. This process is called biopsy. Identifying the right tumor is essential, as medication and treamtment planning differs from tumor to tumor. By this means, performing a biopsy is vital. 

Three types of biopsies can be utilized: The needle biopsy is made by a small cut to drill into the skull. After penetrating the bones level, the needle removes tumor tissue at its tip. 

With the help of CT or MRI, the biopsy is called stereotactic, as this assistance leads to accurate information about the tumors position and its location in the brain. If a biopsy is performed during a surgery and tumor cells are spotted, it is called open biopsy.

In all three cases, the collected tissue are sent to pathologists who analyse them and give their reports back to the treating doctors.

                                  [set-up for a biopsy]