Central Nervous System Recording Presentation

Computed
Tomography(CT)Scan
 Greek word
 Tomos (slice)
 Graphein (to write)
 Large series of two-dimensional X-ray
images taken around a single axis of
rotation
 Images generated are in axial or transverse
plane
 Modern scanners allow this volume of data
to be reformatted in various planes or even
as volumetric (3D)

History
 Invented by Godfrey Newbold Hounsfield
in Hayes, England using X-rays in 1972
 “The greatest legacy” of the Beatles (the
massive profits from their record sales
enabled EMI to fund scientific research)
 Allan McLeod Cormack of Tufts University
independently invented a similar process
and they shared a Nobel Prize in medicine
in 1979

Prototype
 Took 160 parallel readings through 180
angles, each 1° apart, with each scan taking
a little over five minutes
 The images from these scans took 2.5
hours to be processed
 This scanner required the use of a water-
filled Perspex tank with a pre-shaped
rubber “head-cap” at the front, which
enclosed the patient's head
 The water-tank was used to reduce the
dynamic range of the radiation reaching
the detectors

History (Cont..)
 First EMI-Scanner was installed in Atkinson
Morley's Hospital in Wimbledon, England
 First patient brain-scan was made in 1972
 In the U.S., the first installation was at the
Mayo Clinic
 The images were relatively low resolution,
being composed of a matrix of only 80 x 80
pixels

CVA & Hemorrhages
 Diagnosis of cerebrovascular accidents
and intracranial hemorrhage
 Is the most frequent reason for a "head
CT" or "CT brain
 Scanning is done with or without
intravenous contrast agents
 Does not exclude infarct in the acute
stage of a stroke, but is useful to
exclude a bleed

Tumors
 Detection of tumors
 CT scanning with IV contrast is
occasionally used but is less sensitive
than magnetic resonance imaging

ed Intra-Cranial
Pressure
 Can also be used to detect increases in
intracranial pressure
 Before lumbar puncture or to evaluate
the functioning of a
ventriculoperitoneal shunt

Vascular & BB Barrier
IV contrast helps reveal vascular
anomalies like
 Arteriovenous malformations
 Aneurysms
Lesions producing abnormalities of Blood
Brain Barrier like
 Abscesses
 Certain Tumors
 Demyelinating Lesions

Neuropsychiatric
 Widely used in neuropsychiatric
research for the calculation of
“ventricular-to-brain” ratio

Other Indications
 Setting of trauma for evaluating facial and
skull fractures.
 In the head/neck/mouth area, CT scanning
is used for
 Surgical planning for craniofacial and
dentofacial deformities
 Evaluation of cysts and some tumors of the
jaws/paranasal sinuses/nasal cavity/orbits
 Diagnosis of the causes of chronic sinusitis,
and for planning of dental implant
reconstruction.

Advantages over
projection Radiography
 Completely eliminates the superimposition of
images of structures outside the area of interest
 Because of the inherent high-contrast resolution
of CT, differences between tissues that differ in
physical density by less than 1% can be
distinguished
 Data from a single CT imaging procedure can be
viewed as images in the axial, coronal, or
sagittal planes, depending on the diagnostic
task

Radiation exposure
 Regarded as a moderate to high
radiation diagnostic technique
 radiation dose depends on:
 Volume scanned
 Patient build
 Number and type of scan sequences
 Desired resolution and image quality
 In children, produces increases in the
probability of lifetime cancer mortality

Adverse reactions to
contrast agents
 Certain patients may experience severe
and potentially life-threatening allergic
reactions to the contrast dye
 May induce kidney damage (contrast
nephropathy)
 Contraindicated in Moderate Renal
Failure
 However can be done in severe renal
failure requiring dialysis

Contra-Indication Of CT-
Scan
Pregnancy (involve doses of ionizing
radiation and may increase the risk of
malignancy, especially in a fetus)

Limitations Of Old CT-
Scan
 Unable to visualize structures immediately
adjacent to bone because of artifacts
 Inferior surface of frontal and temporal
lobes as well as entire posterior fossa is
not best visualized

Process
 X-ray slice data is generated using an X-ray
source that rotates around the object
 X-ray sensors are positioned on the
opposite side of the circle from the X-ray
source
 Many data scans are progressively taken as
the object is gradually passed through the
framework
 They are combined together by the
mathematical procedure known as
Tomographic reconstruction

Mechanism
 An X-ray tube and detector are
physically rotated
 An electron beam is produced by X-Ray
Tube and is deflected in a hollow funnel
shaped vacuum chamber
 X-rays are generated when the beam
hits the stationary target
 The detector is also stationary

Spiral CT
 Can process not only individual cross
sections but continuously changing cross
sections as the gantry, with the object to
be imaged, is slowly and smoothly slid
through the X-ray circle.
 Their computer systems integrate the data
of the moving individual slices to generate
three dimensional volumetric information
(3D-CT scan)

3D Reconstruction
 It is possible for a software program to
build a volume by “stacking” the individual
slices one on top of the other
 A volume is built by stacking the axial slices.
 The software then cuts slices through the
volume in a different plane

Segmentation
 Procedure that removes the unwanted
structures from the image
 For Example, The bones are whiter than
the surrounding area. Blood vessels
also show brightly when injected with
iodine-based contrast agent
 By segmentation, bone can be removed
and blood vessels can be seen in detail

 The bones are
whiter than the
surrounding
 Note the blood
vessels (arrowed)
showing bright

Brain
vessels
reconstruct
ed in 3D
after bone
has been
removed by
segmentati
on

History
 Inventor of MRI was Paul Lauterbur
 Named it – “zeugmatography”
 A Greek term meaning “that which is used
for joining”
 The term referred to the interaction
between the static and the gradient
magnetic fields necessary to create an
image
 But, this name never caught on

History (Cont..)
 Later named as Nuclear Magnetic
Resonance Imaging (NMRI)
 But, the word “nuclear” has been
associated with ionizing radiation
exposure
 So, to prevent patients from making a
negative association between MRI and
ionizing radiation, the word has been
almost universally removed

Technique
 Relies on the relaxation properties of excited
hydrogen nuclei (proton) in water and lipids.
 Patient head is placed in a magnetic field that
forces protons in the brain to align
 Series of radio frequency pulses are then applied
perpendicular to this field
 Causes protons to change their alignment briefly
 Then, emit energy as they relax back to previous
alignment
 As the high-energy nuclei relax and realign they
emit energy at rates which are recorded to
provide information about the material they are
in

Parameters of MRI
 Image is created by using a selection of
image gaining parameters which include
1.The Spin proton Density – {No Relaxation
time}
2.T1 or Spin-Lattice relaxation time
3.T2 or Spin-Spin Relaxation time

 Proton density reflects the numbers of
protons present in a tissue sample
 T1 and T2 values are tissue specific
 Imaging sequences can be varied to
highlight the T1 or T2 component of
signal

T1
 The realignment of nuclear spins with the
magnetic field is termed “longitudinal
relaxation”
 Time required for a certain percentage of the
tissue's nuclei to realign in longitudinal
fashion is termed “Time 1” or T1
 Typically about 1 second
 T1 causes the nerve connections of white
matter to appear white, neurons of gray
matter to appear gray, while CSF appears
dark

T2
 T2-weighted imaging relies upon local
dephasing of spins following the application
of the transverse energy pulse
 The transverse relaxation time is termed
"Time 2" or T2
 Typically < 100 ms for tissue
 T2 causes the nerve connections of white
matter to appear dark, and the congregations
of neurons of gray matter to appear white,
while cerebrospinal fluid appears white

Commonly Used Sequences
The two most common sequences in
clinical use are
1.Inversion recovery
2.Spin-echo

Inversion recovery
 Rely heavily on the T1 component
 Produce the best gray-white resolution
 Best for visualizing anatomical detail
 Very sensitive to differences between
normal and abnormal tissue

Spin-echo
 Sequences are usually T2 weighted
 Best for detecting small focal lesions
(e.g., multiple sclerosis plaques)
 Increased signal intensity or image
brightness is associated with
 Increased proton density (i.e., water
content)
 Decreased T1 values
 Increased T2 values

Resultant Images
 Water content tends to increase with
most brain pathology, resulting in
increased T1 and T2 signals
 High T1 signals appear black (as CSF
does on a CT scan)
 High T2 signals appear white

Resultant Images
(Cont..)
 Some tissue components appear almost the
same with either T1 or T2-weighted images
 Air, calcium, and bone all have low proton
density and appear dark in either type of
image
 Fat, with its short T1 and long T2 values,
appears bright in either type of image
 What may appear at first to be skull bone
surrounding the brain on MRI is actually fat in
the bone marrow that causes a bright signal

Advantages of CT
 Superior for detection of calcifications and
bone abnormalities (because it uses X-rays)
 Can be done rapidly to rule out
hemorrhagic conditions
 Cost is typically less than half that of MRI
 Good spatial resolution (the ability to
distinguish two structures an arbitrarily
small distance from each other as separate)

Advantages of MRI
 No ionizing radiations (Safe in pregnancy )
 Superior for detection of demyelinating
lesions, posterior fossa lesions, and small
infarctions
 Better imaging procedure in most cases to
scan for temporal-lobe lesions
 Provides comparable resolution with far
better contrast resolution (the ability to
distinguish the differences between two
arbitrarily similar but not identical tissues)

Principal
 Diffusion MRI measures the diffusion of
water molecules in biological tissues
 Water Molecule inside the axon of a
neuron have a low probability of
crossing the myelin membrane
 Therefore the molecule will move
principally along the axis of the neural
fiber

Uses
 Enables researchers to make brain
maps of fiber directions to examine the
connectivity of different regions in the
brain
 Examine areas of neural degeneration
and demyelinaton in diseases like
Multiple Sclerosis

Uses (In Ischemic
Stroke)
 In ischemic stroke there is increase in
restriction (barriers) to water diffusion, as a
result of cytotoxic edema (cellular swelling)
 Responsible for the increase in signal
 Appears within 5-10 minutes of the onset
of stroke symptoms (as compared with CT,
which often does not detect changes of
acute infarct for up to 4-6 hours)
 Remains for up to two weeks

Uses (In Ischemic
Stroke)
 Researchers can highlight regions of
"perfusion/diffusion mismatch"
 Those regions may indicate regions
capable of salvage by reperfusion
therapy
 If available, then test of choice in
ischemic strokes

Principal
 fMRI measures signal changes in the brain
that are due to changing neural activity
 Increased neural activity causes an
increased demand for oxygen
 Vascular system actually overcompensates
for this, increasing the amount of
oxygenated hemoglobin relative to
deoxygenated hemoglobin.
 Deoxygenated hemoglobin attenuates the
MR signal

Principal (Cont..)
 Vascular response leads to a signal
increase that is related to the neural
activity.
 This mechanism is referred to as the
BOLD (blood-oxygen-level dependent)
effect

This example of
fMRI data shows
regions of
activation including
primary visual
cortex, extrastriate
visual cortex and
lateral geniculate
body in a
comparison
between a task
involving a
complex moving
visual stimulus and
rest condition.

Contra-Indications and
side-effects of MRI

Contra-Indications
 Pacemakers – (they can cause arrhythmia)
 Other forms of medical or bio-stimulation
implants (Vagus nerve stimulators,
implanted cardio-defibrillators, insulin
pumps, cochlear implants etc.)
 Ferromagnetic foreign bodies (e.g. shell
fragments)
 Metallic implants (e.g. surgical prostheses,
aneurysm clips)

Side-Effects
 Hyperthermia – A powerful radio transmitter
is needed for excitation of proton spins. This
can heat the body significantly
 Twitching in extremities - The rapid
switching (on and off) of the magnetic field
is capable of causing nerve stimulation
 High acoustic noise – may reach 130 dB
(equivalent to a jet engine at take-off)
 Asphyxia – If Helium is not properly
dissipated through vents

Use in Pregnancy
 Safe in pregnancy
 However, as a precaution, pregnant
women undergo MRI only when
essential (particularly in the first
trimester )
 Contrast agents (like gadolinium
compounds) should be avoided

Claustrophobia
 Potentially unpleasant to lie in (which is
often a long, narrow tube even up to one
hour)
 Potential solutions include
 Visiting the scanner to see the room and
practice lying on the table
 Watching DVDs with a Head-mounted display
while in the machine
 The use of open MRI
 Use of sedation
 For the most severe cases, general anesthesia

Positron Emission
Tomography (PET Scan)

PET Scan
 It is a Nuclear medicine medical
imaging technique which produces a
three-dimensional image or map of
functional processes in the body

Principal of PET
 A short-lived radioactive tracer isotope – which
decays by emitting a positron – is injected
 There is a waiting period while the
metabolically active molecule becomes
concentrated in tissues of interest
 Then the patient is placed in the imaging
scanner
 The molecule most commonly used for this
purpose is fluorodeoxyglucose (FDG), a sugar,
for which the waiting period is typically an hour.

Procedure
 As the radioisotope undergoes positron
emission decay (also known as positive beta
decay), it emits a positron (the antimatter
counterpart of an electron)
 After travelling up to a few millimeters the
positron encounters and annihilates with an
electron
 Producing a pair of annihilation (gamma)
photons moving in almost opposite
directions

Procedure (Cont..)
 These are detected when they reach a
scintillator material in the scanning device
 Creating a burst of light which is detected
by photomultiplier tubes or silicon
avalanche photodiodes
 The technique depends on simultaneous or
coincident detection of the pair of photons
 Photons which do not arrive in pairs are
ignored

 This figure shows how during the
annihilation process two photons are
emitted in diametrically opposing directions.
 These photons are registered by the PET as
soon as they arrive at the detector ring
 After the registration, the data is forwarded
to a processing unit which decides if two
registrered events are selected as a so-
called coincidence event.
 All coincidences are fowarded to the image
processing unit where the final image data
is produced via image reconstruction
procedures

Radioisotopes used in
PET
 Typically isotopes with short half lives
such as
 11C (~20 min)
 13N (~10 min)
 15O (~2 min)
 18F (~110 min)
 Incorporated into compounds
normally used by the body such as
glucose, water or ammonia (these
compounds are known as radiotracers)

Uses
 Clinical oncology (medical imaging of
tumors and the search for metastases)
 Various types of dementias
 Tool to map normal human brain function
 Changing of regional blood flow in various
anatomic structures

Use in Neurology
 Brain is normally a rapid user of glucose
 Brain pathologies such as Alzheimer's
disease greatly decrease brain metabolism
of both glucose and oxygen in tandem
 Standard FDG-PET of the brain (which
measures regional glucose use) is used to
differentiate Alzheimer's disease from other
dementing processes, and also to make
early diagnosis of Alzheimer's disease

Pet Scan of Brain
Red areas show
more
accumulated
radioactivity
and blue areas
are portions
where low to
no activity was
accumulated

Use in Neuropsychology
 To examine links between specific
psychological processes or disorders
and brain activity

Use in psychiatry
 Numerous compounds that bind selectively to
neuro-receptors of interest in biological
psychiatry have been radiolabeled with 11C or
18F
 Radioligands that bind to dopamine receptors ,
serotonin receptors, opioid receptors (mu) and
other sites have been studied
 Studies have been performed examining the
state of these receptors in patients of
schizophrenia, substance abuse, mood
disorders and other psychiatric conditions

Safety
 PET scanning is non-invasive, but it
does involve exposure to ionizing
radiation
 So should be avoided in pregnancy

Single photon emission
computed tomography
(SPECT) Scan

Principal
 Imaging technique using gamma rays
 Image obtained by a gamma camera
image is a 2D view of 3D distribution of a
radionuclide.
 SPECT imaging is performed by using a
gamma camera to acquire 2D images from
multiple angles
 A computer is then used to apply a
tomographic reconstruction of the multiple
projections, yielding a 3-D dataset

Procedure
 The gamma camera is rotated around the
patient
 Projections are acquired at every degree
and full 360 degree
 The time taken to obtain each projection is
about 15 – 20 seconds
 Total scan time of 15-20 minutes

Uses
 Tumor imaging
 Infection (leukocyte) imaging
 Thyroid imaging
 Bone imaging
 Information about localized function in
internal organs
 Functional cardiac (diagnosis of ischemic
heart disease )
 Brain imaging (dementia)

Central Nervous System Recording Presentation

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