Ability to read and understand brain imaging results is a critical skill for a neuropsychologist.  The most commonly used brain imaging procedures are magnetic resonance imaging (MRI), computerized tomography (CT), functional imaging and neuroangiography. 


Computerized tomography (CT) measures tissue density, in a similar manner to x-rays.  During a CT scan, a patient lies on a long table that moves them through a ring-shaped scanner that shoots multiple slices of the brain.  The word “tomography” refers to the multiple angles from which the x-rays are shot.  Detectors on the opposite side of the machine receive the energy and a computer uses this information to construct horizontal slices showing the density of brain tissue in each slice.  As with X-rays, hyperdense structures such as bone appear white in CT scans, and hypodense substances like air appear black. 


CT is less expensive than MRI and requires only a fraction of the time. (5-10 minutes)  CT is the preferred brain imaging procedure for patients with skull fractures, head trauma, calcified lesions, fresh hemorrhages, or mass effect.  Unlike MRI, it can be used with patients who have metallic implants such as pacemakers or aneurism clips.


Magnetic resonance imaging (MRI), is a more detailed form of brain scanning which is preferred for conditions such as old hemorrhages, brainstem lesions and subtle infarcts, tumors and demylination.  Unlike CT, which look at tissue density, MRI images use water and fat content to determine brightness on brain images.


T1 weighted images look like brain slices and are best for identifying anatomy.  Water appears dark, grey matter appears grey and white matter appears white on T1 images.  T2 weighted images look like negatives from T1 images.  CSF appears white, white matter appears grey and grey matter appears white.  T2 images are usually preferred to M1 when looking for pathological changes in the brain such as fresh infarcts.  Proton density, PD, images enhance visibility of subtle abnormalities in the parenchyma such as edema and infarctions near CSF.  These three modalities are compared below.
























Functioning neuroimaging (FN) is an area of growing interest because it helps describe physiological functioning around areas of neuroanotomical importance.  FN procedures typically rely on the detection of either electrical signals or brain metabolism to reveal information about brain functioning.


EEG was the first method of FN to gain popularity.  It relied upon the measurement of weak electric brain signals through the use of electrodes placed upon the scalp.  It proved useful for the evaluation of epilepsy and widespread brain abnormalities.  Eventually new methods for measuring electrical signals in the brain were developed.  These methods, quantitative EEG analysis and magnetoencephalography (MEG) are used mostly for research purposes.


Additional imaging procedures were developed that relied on brain metabolism to speculate about brain functions.  Some procedures that rely on brain metabolism either measure bloodflow and volume.  Procedures that fall into this category include blood oxygen level-dependent functional MRI (BOLD fMRI), single photon emission computerized tomography (SPECT), positron emission tomography (PET), Xenon regional cerebral blood flow mapping (Xe rCBF) and dynamic contrast functional MRI (perfusion MRI).


Additional functional MRI procedures have been developed which include perfusion MRI, BOLD MRI.















































To learn more about brain imaging I recommend visiting The whole brain atlas.

 

Brain Imaging

CT scan

fat

congealed blood

water

CSF

white matter

air

bone

grey matter

Anagram for when CT was generated concerning brain.

T1

T1

T2

PD

           Ferritin                  White Matter, CA2+                Water, CA2+

  Grey Matter, Gliosis                                                       White Matter

Edema, Demylination

                

                                                 Grey Matter                      Grey Matter