Brain Imaging

Question 1

Which brain imaging modality uses a rotating x-ray beam?

Answer 1

Computed Axial Tomography (CAT) Scan

Question 2

How are attenuation variations in tissue detected in CT Scan?

Answer 2

X-ray source and X-ray detector move circularly and the detector picks up radiodensity information from several directions to reconstruct a 3D Image. Patient moving through scanner slowly allows more information to be detected.

Question 3

CT enhances visualization of what in the brain?

Answer 3

• bony anatomy

- elements with high atomic numbers(Ca, Fe,I, Ba, Pb)

Question 4

What pathologies are often detected by CT ?

Answer 4

Infarction, Tumors, Calcification, hemorrhage, acute stroke, and bone trauma

Question 5

In a CT Scan Tumor is detected by:

Answer 5

swelling and anatomical distortion

Question 6

In a CT Scan, a hypodense (dark) structure indicates:

Answer 6

Edema and infarction (differences in grey matter appear and differences in gray/white differentiation disappear)

Question 7

In a CT Scan, a hyperdense sturcture (bright) can indicate:

Answer 7

calcifications and hemorrhage

Question 8

Bone trauma is detected in a CT Scan by observation of:

Answer 8

bone disjunctions in bone windows

Question 9

Loss of blood suppply and oxygen to portion of the brain is known as :

Answer 9

An Infarct

Question 10

Spatial Resolution is greater in CT or MRI?

Answer 10

CT (several mm); MRI (1mm)

Question 11

TBI diagnosis and prognosis is significantly affected by what clinical finding?

Answer 11

Intracranial bleeding

Question 12

Heme and other blood products released during trauma lead to what pathologies?

Answer 12

• Subarachnoid Hemorrhages
• Intraparenchymal Contusion (bruising of brain tissue)
• Hematomas (bleeding in or around brain)
• Intrinsic Cellular Injury

Question 13

Which brain imaging modality uses Nuclear Magnetic Resonance?

Answer 13

Magnetic Resonance Imaging (MRI)

Question 14

What is the advantage of using MRI?

Answer 14

No radiation is used; Frequency waves are used instead of X-rays

Question 15

What are the advantages of using CT scans?

Answer 15

It is faster and less expensive than MRI thus can be used as an initial screening and assessment tool

Question 16

Does a CT Scan or MRI have better contrast difference (high resolotion and detailed visualization) between soft tissues?

Answer 16

MRI

Question 17

What pathologies can best be detected on MRI and why?

Answer 17

demyelinating and infectious diseases because MRI has special ability to visualize anatomy- gray, white matter, CSF

Question 18

What in a proton produces a magnetic field?

Answer 18

The Spin

Question 19

How much of the body is made of hydrogen atoms?

Answer 19

63%

Question 20

Describe the response of a protein spin to an external magnetic field.

Answer 20

It aligns against or with the field. It wobbles or “precess” at a frequency proportional to the field. This leads to a net magnetization of the tissue.

Question 21

What is the purpose of applying the radiofrequency pulse?

Answer 21

It tips the protons away from the direction of magnetaization allowing a more readily detection of magnetization. The RF signal is picked up by an antennae and is formed by the energy decay that occurs when a proton realigns with the field when the radiofrequency pulse is turned off. Rate of decay differs by tissue type.

Question 22

Fourier transform algorithms purpose:

Answer 22

to decode RF signal into images.

Question 23

What does a numerical index represent in Digital Image Construction?

Answer 23

Gray-scale level represented by Tissue composition of the particular pixel

Question 24

Timing of RF pulse can be varied. How and what are the effects/

Answer 24

Rapid repetitions of RF pulse enhange gray-white contrast. Infrequent repetitions enhances signal from water which is increased in pathological conditions (like lesions).

Question 25

What are the components of a MRI Scanner?

Answer 25

Magnet (Increased strength in Teslans-1.5T is common- high is 7- increases contrast), Gradient Coil, RF Coil. T2 Flair enhances lesion presence

Question 26

Anatomic MRI can be used to diagnose what diseases?

Answer 26

``` Inflammatory Diesease (Multiple Sclerosis) Neoplsatic Disease (Tumors) Epilepsy Cerebrovascular Disease (stroke) ```

Question 27

Magnetic Resonance Spectroscopy allows us to study ________

Answer 27

chemical structures of brain and derive concentrations and ratios of chemicals.

Question 28

MRS separates out components of the following chemical structures in the brain

Answer 28

N-acetylaspartate (neuronal marker located in cell bodies and dendrites) Choline( demyelination marker; cell membrane synthesis and degradation) Creatinine (glial marker) Lactate (found following ischemic events)

Question 29

In MRS, application of a RF pulse causes

Answer 29

the emission of a specific frequency by each chemical component (metabolite)

Question 30

What determines the size of the peak produced in the conentration of each metabolite in a MRS?

Answer 30

the size of the peak produced from Fourier transforms analysis

Question 31

How can we study a lesion using MRS?

Answer 31

Study its evolution and type (discriminate normal tissue from tumor tissue)

Question 32

Diffusion Weighted Imaging and Diffusion Tensor Imaging allows us to ...

Answer 32

visualize and measure the integrity of white matter tracts in the brain

Question 33

What are three gradient-directions in a DWI? its purpose?

Answer 33

alignment of magnetic fielld in 3 different directions to estimate the trace of the diffusion tensor or "average diffusivity" a measure of edema.

Question 34

What reflects the bet estimate of rate of water diffusion at the location in a DWI?

Answer 34

Intenstiy of each image element (Voxel)

Question 35

Measurement of water diffusion along different orientations within axons is known as

Answer 35

Ansiotropy (Fractional Ansiotropy is calculated based on both axial and radial diffusivity)

Question 36

What restricts the flow of water in an axon?

Answer 36

cell membranes and meylin (in the perependicular direction)

Question 37

Measurement of diffusion in a DWI is

Answer 37

along length of longitiduinal axis of the axon. the larger the coefficient, the greater diffusion

Question 38

Radial diffusiivity is

Answer 38

the diffusion along the perpendicular axes of voxel, in both directions

Question 39

Color Coding DTI:

Answer 39

red- transverse- lateral to medial green-longitudinal-anterior to posterior blue - horizontal- superior to inferior

Question 40

Functional Magnetic Resonance Imaging allows us to ..

Answer 40

acquire images of the brain while patients are performing cognitive tasks in MIR scanner.

Question 41

Clinical advantages of fMRI

Answer 41

It shows plasticity in brain . one can understand - neural sysgtems that make performance of cognitive tasks possible - understand changes in brain function with disorders and aging - understand sites of neural reorganization following stroke or injury

Question 42

How is increased neural activity detected in fMRI?

Answer 42

INcreased blood flow to region of the brain with increased activity- changes in local cerebral blood volume and oxyhemoglobin (paramagnetic)

Question 43

changes in intensity of values on MR images

Answer 43

BOLD signal- measured during baseline and experimental conditions

Question 44

Hemodynamic peak response occurs over what time duration?

Answer 44

4-6 s

Question 45

Control condition in fMRI is

Answer 45

taks has all features of the experimental task except the specific cognitive variable of interest

Question 46

fMRI experimental condition:

Answer 46

TASK IS COMPRISED OF TEH SPECIFIC COGNITIVE VARIABLE OF INTEREST

Question 47

Activation Maps are__________ on brain images

Answer 47

superimposed

Question 48

Limitations of fMRI

Answer 48

- limitations of temporal and spatial resolution | - relation between neuronal activity, blood flow and fMRI signals not definitely established

Question 49

This brain imaging modualtiy usees cyclotorn to prepare radioactive isotorpe tracers incorportated int a biolgoically acctive molecule in physiological sites

Answer 49

Positron Emission Tomography

Question 50

When does the scannner image postiron-emitting tracer

Answer 50

upon its decay

Question 51

Name too findings in fMRI scan for amygdal, prefrontal cortex, and left parietla low grade astroctyoma

Answer 51

Amygdala present different in emotions and PFC regions are improtant for memory formation but have prolonged maturational trejectory- mesial temporal lobe/ S[eecj areas areas defined in astrocytoma afftected patient. 2 languages can be in 2 different areas

Question 52

PET applications

Answer 52

Blood flow and perfusion Metabolism (traces glucose and oxygen uptake) Neurotransmitter Integrity: Ligand/ Neuroreceptor imaging (dopamine synthesis and reuptake- radiotracers bind to rpe and psost synaptic neuroreceptors)

Question 53

PET advantages over CT or MRI:

Answer 53

Functional Imaging Physiologcial variables can be determined It can distinguish radiation necrosis from tumor recurrence(hypermetabolic) with a high specificity. Radiation necrosis is hypometabolic of FDG-{ET

Question 54

Which matter is lost in Alzheimer's Disease?

Answer 54

Grey; Brain activity correlates with memory decline

Question 55

Which gene and allele carriers increased brain activation during memory tasks in AD?

Answer 55

APOE 4gene/ Brain activity correlates with memory decline

Question 56

What disorders can be detected with PET?

Answer 56

Psychiatric/ Addictive/ Degenerative Disorders and Epilepsy It is also useful in grading brain tumors nad determining their progonsis.

Question 57

Measurements provided by MRI

Answer 57

Brain structure Vasculature Chemical Structure Fiber Tracts

Question 58

MRI disadvantages

Answer 58

Long study duration No ferromagentic or electronic devices Clasutrophobic

Question 59

PET disadvantages

Answer 59

Ionizing radiation Costly limted access tracer production