Brain Imaging Flashcards
1
Q
intro
A
modern imaging modalities provide information about the living brain
- essential to understanding effect of both development and disease on:
- structure of the brain
- how structures are integrated as coherent networks
- which networks subserve diverse cognitive linguisitc and emotional systems
- how they are altered by disease
2
Q
CT
A
- computed axial tomography
- rotating X ray beam
- images the brain from several directions
- rate of attenuation varies by tissue
- radiodensity information is detected
- used to reconstruct a 3D image
3
Q
clinical applications of CT
A
- enhances visualization of
- bony anatomy
- acute hemorrhage or stroke
- elements with high atomic numbers show up better-Calcium, iron, iodine, barium, lead
- advantages-faster and less expensive then MRI, can be used as an initial screening and assesment tool
- disadvantages-use of Xray, less contrast differences between soft tissues, lower spatial resolution, several mm in CT vs 1 in MRI
- used for infarction, tumors, calcifications, hemorrhage, bone trauma
- hypodense-edema/infarction
- tumors from anatomical distortion or surrounding edema
4
Q
TBI
A
- heme released, causes sub-arachnoid hemorrhages, intraparenchymal contusions, hematomas
- intrinsic cellular injury
5
Q
anatomic MRI
A
- based on principles of nuclear magnetic resonance
- produces high resolution images of the brain and spine
- no radiation, radio frequency waves used
6
Q
clinical applications of MRI
A
- high resolution and detailed visualization of soft tissue
- visualizes anatomy (gray and white matter, CSF)
- identifies a wide range of pathological processes
7
Q
physics of MRI
A
- body comprised of 63% hydrogen atoms
- protons in hydrogen atoms spin like a top
- spin produces small magnetic field
- spinning proton placed within a large external magnetic field will align with or against the external field
- it will also precess (wobble) at a frequency proportional to the magnetic field
- slightly more protons will eventually align with the external field
- net magnetization of the tissue
- to detect magnetization, apply radiofrequency pulse which tips protons away from the direction of magnetization
- when the pulse is off, they realign
- the energy that each spinning proton absorbed from the RF decays
- signal emitted
- decoded into images with Fourier transform algorithms
8
Q
digital image construction
A
- the spin of the proton decays, and emits RF signals, at different rates depending on the composition of the tissue in which they are located
- each pixel of the image is encoded with a numerical index that represents the relative strength of the RF signal in the area of the brain to which that pixel corresponds
- each numerical index is assigned a gray scale value
9
Q
pulse sequences
A
- the clinician can vary the timing of the RF pulse which accentuates the tissue they are most interested in
- rapid repetitions of the RF enhance gray/white contrast
- lesions-best imaged with infrequent repetitions of RF pulse-enhanced signal from water, which is usually increased in pathological conditions
10
Q
equipment for MRI
A
- magnet
- gradient coil
- RF coil
11
Q
diagnostic applications of MRI
A
- inflammatory disease-MS
- neoplasms
- epilepsy
- cerebrovascular disease- stroke
12
Q
magnetic resonance spectroscopy
A
- permits us to study chemical structure of the brain
- separates out components of chemical mixtures in brain
- N-acetylaspartate (NAA)
- choline
- creatine (Cr)
- lactate
- can derive concentrations and ratios of chemicals
13
Q
how does MRS work?
A
- an RF pulse is applied, after which each chemical component emits a specific frequency
- the signals are analyzed with Fournier transforms to generate NMR spectra
- the concentration of each chemical component of interest is represented by the size of the peak that is produced
14
Q
NAA
A
-located in cell bodies of dendrites, considered a neuronal marker
15
Q
choline
A
- cell membrane synthesis and degradation
- marker for demyelination
