MR Perfusion Weighted Imaging Basic Principles and Physics Diagnostic values of MRP

1. MAGNETIC RESONANCE
PERFUSION
Rahman Ud Din
Lecturer Medical Imaging
NWIHS

2. Introduction
 Blood flow and metabolism of human tissues
 Studied in nuclear medicine with tracer
 Now it is still studied with PET
 But PET lack spatial and temporal resolution
 Also lack in specificity
 Recent methods introduced like CT & MRI
perfusion
 MR perfusion performed with
 Exogenous contrast agent (Gd)
 Endogenous contrast agent (no contrast
administration)

3. Principles of MRP Imaging
 Perfusion refers to passage of blood from
arterial supply to venous drainage through
microcirculation
 Perfusion is vital for nutritive supply to tissues
 For clearance of products as well
 Perfusion can be affect by various disease
processes
 Hence to detect such changes in perfusion
can help in diagnosis of certain diseases,
monitoring and assessing the treatment
response

4.  Gd (paramagnetic agents) cause shortening of
both T1 and T2 of the tissue or region in which
they go
 Decrease T1 relaxation time on T1-w images
results into increased signals or brightening
 Decrease in the T2 relaxation time on T2 or
T2*-w images results into signal drop or
blackening
 As Gd passes through the microvasculature in
high concentration there is decrease in signal
in surrounding tissues
 Signal drop (shows disease)

5. Before and after Gd adminitration
in T1-w Sequence

6. Technique of MRP with Exogenous
Contrast
 A dose of 0.1mmol/kg of Gd injected IV
 Using power injector at rate of 5ml/s
 Fast T2*-w EPI seq is run to catch first pass of the
contrast through microcirculation
 This seq: takes 15-20 slices from entire brain 1-2 s
 About 60 such run acquired before, during and after
dynamic injection of the contrast media
 Raw data images converted into various color coded
maps using software
 rCBV=relative Cerebral Blood Volume
 CBF= Cerebral blood flow
 TTP=Time to Peak
 MTT =Mean Transit Time

8. Permeability or Leakiness
 Areas of severe blood-brain barrier
break-down are seen in necrotic
tumor and irradiated tumor beds
 Increase in leakiness bcoz break in
BBB results in accumulation of Gd-
based contrast in extravascular
space
 T1-enhancing effects of
extravascular Gd may predominate
to counteract the T2 signal

9. Clinical Applications of MRP
 MRP performed in various clinical conditions
 Stroke
 Brain tumors
 Dementia
 Psychiatric illnesses
 Migraine
 Headaches
 Trauma
 Epilepsy
 Multiple sclerosis

10. MRP in Stroke
 Stroke is brain attack
 To detect brain ischemia & salvageable tissue
in early window period of 3-6 hours
 DWI and PWI or MRP effective for early
ischemia
 PWI more sensitive than DWI detecting
ischemia in early period of after onset of
arterial occlusion

12. MRP in Brain Tumours
Glioma
Glioblastoma

13. Other Clinical Conditions
 MRP used to assess ischemic or under
perfused areas
 Like moyamoya disease and CNS vasculities
CNS
vasculities