Transcript PERFUSION MRI IMAGING Dr. Mohamed El Safwany, MD.

PERFUSION
MRI IMAGING
Dr. Mohamed El Safwany, MD.
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Intended learning outcome
• The student should learn at the end of this
lecture principles of Perfusion MRI studies.
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Perfusion imaging
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Definitions
Principles
Some more definitions
Perfusion technique
Applications
Future
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Definitions
• Perfusion is refer to the delivery of oxygen
and nutrients to the cells via capillaries
• Perfusion is identified with blood flow
which is measured in milliliters per minute
per 100 g of tissue
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Principles
After injection of a contrast agent
• In normal brain, the paramagnetic contrast agent
remains enclosed within the cerebral vasculature
because of the blood brain barrier
• The difference in magnetic susceptibility between the
tissue and the blood results in local magnetic field
finally to large signal loss
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Some more Definitions
• rCBF “ the rate of supply of Gd chelate to a specified
mass ” ( ml / 100g / min)
• rCBV - “ the volume of distribution of the Gd chelate
during its first passage through the brain ” ( % or ml /
100g )
• MTT - “ the average time required for any given
particle to pass through the tissue, following an idealised
input function ” (min or s)
MTT = rCBV / rCBF
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► Passage
of Gd. can be followed by the changes in
the relaxation rates concentration of local
contrast.
► Linear
relation bet. concentration and rates of
signal changes can be expressed as curve.
► Tissue
contrast concentration time curve can be
used to determine tissue micro vascularity,
volume and flow.
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At each voxel we observe :
slice n
~ ‘mean transit time’
time
Integral:=
cerebral blood volume
intensity
time
Principles
• Each one of these effects is linearly proportional to
the concentration of the paramagnetic agent
• To date, this technique results in non-quantitative
perfusion parameters (like rCBV,rCBF or MTT)
because of the ignorance of the arterial input
function
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Dynamic MR perfusion
• Hemodynamics
• Aim
Bl. volume
Bl. flow
1. Diagnosis
2. Monitoring management
3. Understanding intracranial lesions
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rCBV
rCBV, processed with “Negative Enhancement Integral”(NEI)
is related to area under curve
MTT
MTT is related to the time to peak and to the width of the peak ; it
is processed with “Mean Time to Enhance“(MTE)
Cerebral blood perfusion by bolus
tracking
Requires very high power injector - Gadolium
speed imaging
5ml/sec
Procedure :
1 - Start Imaging
2 - Inject Contrast*
3 - Continue Imaging
10 slices - 50 images of each slice - TOTAL time 1:34 min
* Push Gadolinium with 20 cc of saline flush
Applications of Perfusion MRI
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Neurology
Neuro-oncology
Neurophysiology
Neuropharmacology
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Stroke
Perfusion Imaging: Findings in Infarction
• CBV
– regional perfusion deficit
– compensatory increased volume
• MTT
– regional prolongation of transit time
Findings with Perfusion imaging
for Neuro-oncology
• Critical imaging to BBBB imaging of neoplasm
– many tumors have high rCBV
– regions of increased rCBV correlate with areas of
active tumor.
– heterogeneous patterns of perfusion suggest high
grade
– radiation necrosis typically demonstrates low rCBV
• Lesion characterization may be possible
– meningiomas have very high CBV in contrast to
schwannomas
Neuro-oncology
rCBV maps
• low rCBV in tumour
infers low grade glioma
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Text Book
• David Sutton’s Radiology
• Clark’s Radiographic positioning and
techniques
Assignment
• Two students will be selected for
assignment.
Question
• Describe the rCBF, rCBV & MTT?