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Brain Imaging

Authors: Judy Zhu and Cassie Wang


CT Scan

Computerized axial tomography (CT or CAT) is the most common imaging test. It combines

a series of X-ray images taken from different angles around your body and uses computer

processing to create cross-sectional images (slices) of the bones, blood vessels and soft

tissues inside your body. When used for detecting brain injury, it produces a series of images

showing cross-sections of the brain. It is particularly good for hemorrhage, trauma and




The amount of radiation you get when having a CT scan is greater than you would get during a plain X-ray because the CT scan gathers more-detailed information. The low doses of radiation used in CT scans have not been shown to cause long-term harm, although at much higher doses, there may be a small increase in your potential risk of cancer.


In certain cases, your doctor may recommend that you receive a special dye called contrast material, which can be something to drink before your CT scan, or something that is injected into a vein in your arm or inserted into your rectum. Although rare, the contrast material can cause medical problems or allergic reactions. Most reactions are mild and result in a rash or itchiness. In rare instances, an allergic reaction can be serious, even life-threatening.



Magnetic resonance imaging (MRI) employs powerful magnets which produce a strong magnetic field that forces protons in the body to align with that field. When a radiofrequency current is pulsed

through the patient, the protons are stimulated and spin out of equilibrium, straining

against the pull of the magnetic field. When the radiofrequency field is turned off, the MRI

sensors are able to detect the energy released as the protons realign with the magnetic field.

The time it takes for the protons to realign with the magnetic field, as well as the amount of

energy released, changes depending on the environment and the chemical nature of the

molecules, which allows physicians to tell the difference between various types of tissues.


Because MRI does not use x-rays or other radiation, it is the imaging modality of choice when frequent imaging is required for diagnosis or therapy, especially in the brain. The brain can be seen much more clearly with MRI than with regular x-rays and CT. In the brain, MRI can differentiate between white matter and grey matter. However, MRI is more expensive than x-ray imaging or CT.



It employs a strong magnetic field that extends beyond the machine and exerts very powerful forces on objects of iron, some steels, and other magnetizable objects. Patients should notify their physicians of any form of medical or implant prior to an MRI scan.

DTI Scan

Diffusion tensor imaging (DTI) is a specialized type of MRI that measures the movement

of water in the brain, detecting areas where the normal flow of water is disrupted. This

test is particularly useful to image the white matter fiber tracts, or neurons, of the brain.

Disadvantages of X-rays, MRIs, and CTs

X-rays, MRIs, and CT scans can detect fractures, hemorrhages, swelling, and certain kinds of tissue damage, but they do not always detect traumatic brain injury. This is because TBI, especially in its milder forms, often involves subtle trauma to the brain that causes chemical and physical changes to brain tissues rather than structural damage. These changes often cannot be found with standard imaging procedures.



Single-photon emission computerized tomography (SPECT) scan is a type of nuclear

imaging test. It involves the injection of a small amount of short-lived radioactive particles

into the blood. A special camera capable of detecting these particles then rotates around

the patient and takes pictures from many angles. A computer then uses these pictures to

form a cross-sectional image. A SPECT scan is particularly useful in detecting blood flow

and showing what areas of your brain are more active or less active.



If you receive an injection or infusion of radioactive tracer, you may experience:

  • Bleeding, pain or swelling where the needle was inserted in your arm

  • Rarely, an allergic reaction to the radioactive tracer

For women who are pregnant or breast-feeding, the radioactive tracer may be passed to the developing fetus or the nursing baby.

You are exposed to a small amount of radiation, but it is not associated with any long-term health risks.


PET Scan

Positron emission tomography (PET) uses short-lived radioactive substances to produce three-dimensional colored images. It studies metabolic activity or body function of substances

functioning within the body. The scan uses a special dye containing radioactive
tracers. These tracers are either swallowed, inhaled, or injected into a vein in

your arm depending on what part of the body is being examined. The tracer will

collect in areas of higher chemical activity, which is helpful because certain

tissues of the body, and certain diseases, have a higher level of chemical activity.

These areas of disease will show up as bright spots on the PET scan.



The PET scan involves radioactive tracers, but the exposure to harmful radiation is minimal.



An angiogram is used to examine blood vessels. When diagnosing a brain injury,

the test involves injecting dye into an artery that supplies blood to the brain,

usually through a catheter inserted in the groin. The dye highlights the blood

vessels on x-ray, and shows any leakage from those vessels.


  • stroke (if the catheter loosens plaque inside a blood vessel)

  • damage to the blood vessels, including puncturing an artery

  • blood clots, which can form around the catheter tip


ICP Monitor

Intracranial pressure monitoring (ICP) is a device used to measure

pressure within the skull. It is used in two ways. One way is to place a

small, hollow tube (catheter) into the fluid-filled space in the brain

(ventricle). Other times, a small, hollow device (bolt) is placed through

the skull into the space just between the skull and the brain.



An electroencephalogram (EEG), is a safe and painless test

used to measure brain activity. During an EEG, numerous

electrodes in the form of patches are applied to the head.

These electrodes detect the electrical activity in the brain,

and a graph of that activity is generated.




Magnetoencephalography (MEG) 

MEG also uses magnetic forces to detect ionic current changes during brain

activity. It is usually used when performing visual, auditory, sensory and motor

tasks in studies and shows the specific location of activity. 

Compared to MRI, a MEG scanner is a helmet fixed on the head and it does not

make noise. Individuals can move around during MEG scans but have to lie still

on MRI scanners. Moreover, it provides more detailed information in higher

resolution than fMRI. 


Transcranial Magnetic Stimulation (TMS) 

TMS, like MRI and MEG, measure the function of the human

brain via magnetic field. But what makes TMS unique is that

it stimulates specific areas of interest by inducing minimal

electric currents to activate neurons. TMS is not frequently

used for clinical diagnosis, although some studies showed

that TMS has the potential to be implemented as a treatment

of depression, stroke and other neurological diseases.


Wikipedia contributors. “Neuroimaging.” Wikipedia, 7 Jan. 2021,,medicine%2C%20neuroscience%2C%20and%20psychology.

“Traumatic Brain Injury - Imaging Tests.” Traumatic Brain Injury,,which%20may%20require%20immediate%20treatment. Accessed 25 Mar. 2021.

“CT Scan - Mayo Clinic.” Mayo Clinic, 28 Feb. 2020,,than%20plain%20X%2Drays%20do.

“Magnetic Resonance Imaging (MRI).” National Institute of Biomedical Imaging and Bioengineering, Accessed 25 Mar. 2021.

“SPECT Scan - Mayo Clinic.” Mayo Clinic, 28 Dec. 2019,,to%20create%203%2DD%20pictures.

“What Is a PET Scan?” Healthline, Accessed 3 Apr. 2021.

“Intracranial Pressure Monitoring (ICP).” Stanford Health Care, 12 Sept. 2017,

What is Magnetoencephalography (MEG)? (n.d.). Retrieved from


Images: “CT Brain with or without Contrast.” Cedars-Sinai, Accessed 25 Mar. 2021.

Wikipedia contributors. “Magnetic Resonance Imaging of the Brain.” Wikipedia, 31 Dec. 2020,

SIMON FRASER/SCIENCE PHOTO LIBRARY. “Brain Tumour, DTI Scan - Stock Image - C006/8342.” Science Photo Library, 7 Aug. 2019,

“Brain SPECT | Brain Scan | Amen Clinics.” Amen Clinics, Accessed 3 Apr. 2021.

Bahrampour, Tara, et al. “PET Scans Show Many Alzheimer’s Patients May Not Actually Have the Disease.” Washington Post, 19 July 2017,

“Cerebral Angiography.” Healthline, 8 July 2017,

Czosnyka, M. “Monitoring and Interpretation of Intracranial Pressure.” Journal of Neurology, Neurosurgery & Psychiatry, vol. 75, no. 6, 2004, pp. 813–21. Crossref, doi:10.1136/jnnp.2003.033126.

“Free EEG Data Database Freely ERP Data Publicly Available.” Accessed 4 Apr. 2021.

Kozak, Sarah. “How Does Transcranial Magnetic Stimulation (TMS) Work?” Mysite, 24 July 2017,

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