1. DIFFUSION & PERFUSION MRI IMAGING
Dr. Wael Darwish

2. DIFFUSION MRI IMAGING

3. - History -
The feasibility of diffusion images was demonstrated in the middle 1980s
Demonstration on clinical studies is more recent ; it corresponds with the availability of EPI on MR system
A single shot EPI sequence can freeze the macroscopic pulsating motion of the brain or motion of the patient’s head

4. Diffusion Weighted Image
Core of infarct = irreversible damage
Surrounding ischemic area  may be salvaged
DWI: open a window of opportunity during which ttt is beneficial
DWI: images the random motion of water molecules as they diffuse through the extra-cellular space
Regions of high mobility “rapid diffusion”  dark
Regions of low mobility “slow diffusion”  bright
Difficulty: DWI is highly sensitive to all of types of motion (blood flow, pulsatility, bulk patient motion,……).

5. - Diffusion contrast -
Diffusion gradients sensitize MR Image to motion of water molecules
More motion = Darker image
Freely Diffusing Water = Dark
Restricted Diffusion = Bright

6. - Principles - Velocities and methods of measurement

7. - Principles - About the b factor
b is a value that include all gradients effect (imaging gradients + diffusion gradients)
The b value can be regarded as analogous to the TE for the T2 weighting

8. Medium
High
Low
“b = 500”
“b = 1000”
“b = 5”

9. - Principles - About ADC
The ADC value does not depend on the field strength of the magnet or on the pulse sequence used (which is different for T1 or T2)
The ADC obtained at different times in a given patient or in different patients or in different hospitals can be compared

10. - Principles - Isotropic and Anisotropic diffusion
Diffusion is a three dimensional process, but molecular mobility may not be the same in all directions
In brain white matter, diffusion’s value depends on the orientation of the myelin fiber tracts and on the gradient direction*

11. Anisotropic diffusion : Individual direction weighted
X Diffusion - Weighting
Y Diffusion - Weighting
Z Diffusion - Weighting

12. Isotropic diffusion - + x / Isotropic Diffusion- Individual Diffusion
Weighted Image
Individual Diffusion
Directions
Mathematical Combination
(Sorensen et al., MGH)
- + x /

13. Diffusion weighted image

14. Short TE DWI gives more SNR
Characteristics of diffusion’s contrast
Short TE DWI gives more SNR
TE=100ms
SR 120
b = 1000 s/mm 2
TE=75ms
SR150

15. Characteristics of diffusion’s contrast
Higher b value increases sensitivity MS
Higher CNR helps
distinguish active lesions
Stroke
Higher CNR
Vasogenic edema
Cytotoxic Edema
Tumor
Vasogenic edema
b = b= 3000

16. Mathematical Processing
Diffusion-weighted
ADC
map

17. Mathematical Processing
Diffusion-weighted
ADC
map
Exponential ADC

18. Diffusion Imaging Processing
Exponential ADC (ratio of Isotropic DWI/T2)
eliminates T2 shine through artifacts and may
distinguish subacute from acute stroke

19. Arachnoid Cyst
b=0
b=1000
ADC
eADC

20. Clinical Application

21. MR Images of 60-Year-Old Man with Glioblastoma Multiforme. 2.
Figures 1, 2. On (1) T2-weighted fast spin-echo and (2) contrast-enhanced T1-weighted spin-echo images, the differential diagnosis between glioblastoma and abscess is impossible.

22. 3. 4. .
central hypointensity on diffusion-weighted image and hyperintensity on ADC map, consistent with the diagnosis of tumor.

23. MR Images of 57-Year-Old Woman with Cerebral Metastasis5. 6.

24. 7. 8.
central hypointensity on diffusion-weighted image and hyperintensity on ADC map, consistent with the diagnosis of tumor.

25. MR Images of 70-Year-Old Man with History of Recent Vertigo and Disequilibrium1. 2.

26. 3. 4.
A brain abscess with Streptococcus anginosus was found at surgery.

27. 5. 6.
MR Images of 57-Year-Old Woman with Cerebral Metastasis
the differential diagnosis between metastasis and abscess is impossible.

28. 7. 8.
Central hypointensity is seen on the diffusion-weighted image and hyperintensity on the ADC map, consistent with the diagnosis of tumor.

29. APPLICATIONS
SPINE

30. BENIGN VERSUS MALIGNANT FRACTURE

31. This finding indicates that the lack of signal reduction in malignant vertebral fractures is caused by tumor cell infiltration
Different diffusion effect is caused by more restriction or hindrance in densely packed tumor cells compared with more mobile water in extracellular volume fractions in fractures

32. diffusion-weighted spin-echo sequences could differentiate benign fracture edemas and fractures caused by tumor infiltration due to higher restriction of water mobility in tumor cells.

33. T2-weighted MR image shows ovoid hypointense mass in spinal canal.

34. T1-weighted sagittal MR image after infusion of gadolinium contrast material shows diffuse signal enhancement of mass.

35. T1-weighted transverse MR image after infusion of contrast material shows extent of tumor in spinal canal and C4-C5 neural foramen

36. Diffusion-weighted sagittal MR image using peripheral pulse gating and navigator correction shows signal intensity of mass (open arrows) to be intermediate, less than that of brainstem (large solid arrow) and greater than that of vertebral bodies (small solid arrows).

37. ADC map shows mass (arrows) as structure of intermediate intensity.
MENINGIOMA

38. In that study, tumors with high cellularity had low mean ADC values, and tumors with low cellularity had high mean ADC values.
In addition, the relatively high ADC value seen in our patient corresponded to a low degree of cellularity, such as has been reported in cerebral gliomas.

39. Perfusion imaging Definitions Principles Some more definitions
Perfusion technique
Applications
Future

40. 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

41. 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

42. 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

43. 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.

44. At each voxel we observe :
slice n
~ ‘mean transit time’
time
Integral:=
cerebral blood volume
intensity
time

45. 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

46. Principles - + x / Dynamic Susceptibility Contrast Imaging First Pass
Extract time-intensity
curves
Perform mathematical
manipulation
Generate functional
maps + +
NEI
- + x /
MTE
Negative Enhancement
Integral Map(NEI)
Qualitative rCBV map
Mean Time to
Enhance (MTE)Map
Ischaemic Penumbra
First Pass
Contrast bolus

47. Hemodynamics Bl. volume Bl. flow
Dynamic MR perfusion
Hemodynamics Bl. volume
Bl. flow
Aim Diagnosis
2. Monitoring management
3. Understanding intracranial lesions

48. rCBV rCBV, processed with “Negative Enhancement Integral”(NEI)
is related to area under curve

49. 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)

50. Cerebral blood perfusion by bolus tracking
Requires very high
speed imaging
power injector - Gadolium
5ml/sec
Procedure :
1 - Start Imaging
2 - Inject Contrast*
3 - Continue Imaging
10 slices images of each slice - TOTAL time 1:34 min
* Push Gadolinium with 20 cc of saline flush

51. Applications of Perfusion MRI
Neurology
Gerontology
Neuro-oncology
Neurophysiology
Neuropharmacology

52. Perfusion Imaging: Findings in Infarction
Stroke
Perfusion Imaging: Findings in Infarction
CBV
regional perfusion deficit
compensatory increased volume
MTT
regional prolongation of transit time

53. Head Trauma T2 image showing bifrontal volume loss
FLAIR image showing bifrontal gliosis and encephalomalacia

54. Head trauma:Hypo-perfusion
rCBV MAP
Tc-HMPAO SPECT
Hypo-perfusion

55. E.g. 1 : Left hemisphere stroke, 4.5 hrs after onset of symptoms
3D-TOF Vascular
FSE-T2W
FSE-FLAIR

56. Same patient with DWI and FLAIR
EPI
FLAIR
4.5 hrs
24 hrs
Diffusion imaging shows lesion early.
b=0
b=800
FLAIR shows enhanced changes after 24 hrs.
4.5 hrs

57. Isotropic diffusion image
Apparent diffusion coefficient ADC
ADC map
Isotropic diffusion image
b=800

58. Contrast enhanced perfusion imaging
24 slices
3 seconds/acquisition
Time/intensity graph

59. Mean Time To Enhance delayed compensatory hyperperfusion
delayed hypoperfusion

60. Diffusion Coefficient*
EPI Diffusion and Perfusion mapping
MTT
Mean Time To Enhance
CBV
Negative Enhancement
Integral
ADC
Diffusion Coefficient*
EPI Diffusion
EPI Perfusion

61. Findings with Perfusion Imaging for Infarction
Changes seen almost immediately after the induction of ischemia
more sensitive than conventional MRI
Perfusion findings often more extensive than those on DW-EPI in early stroke
more accurately reflects the amount of tissue under ischemic conditions in the hyperacute period than DW EPI
Abnormal results correlate with an increased risk of stroke
PerfEPI - DWEPI = tissue at risk

62. Findings with Perfusion imaging for Gerontology
Alzheimer’s disease
FDG PET
marked temporo-parietal hypometabolism
Tc-HMPAO SPECT
marked temporo-parietal hypoperfusion
DSC MRI
correlates well with SPECT

63. Findings with Perfusion imaging for Neurophysiology and pharmacology
Traumatic brain injury
focal rCBV deficits that correlate with cognitive impairment
Schizophrenia
decreased frontal lobe rCBV
HIV/ AIDS
multiple discrete foci of decreased CBV
Polysubstance abuse
New Jersey Neuroscience Institute

64. 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
New Jersey Neuroscience Institute

65. Intracranial neoplasm N.B angiogenesis usually = aggressiveness
Dynamic MR perfusion
Clinical applications:-
Intracranial neoplasm
N.B angiogenesis usually = aggressiveness
Exceptions:- 1. Meningioma
2.Choroid plexus papilloma
1.Glioma Grading
Biopsy
D.D recurrence from radiation necrosis

66. 2.Metastasis
Can differentiate solitary metastasis from 1ry brain neoplasm (glioma) by measuring the peritumoral relative blood volume.
3.1ry cerebral lymphoma
Can help in differentiating lymphoma from glioma as lymphoma is much less vascular

67. 4. Meningioma
Hypervascular Extra axial
Has leaky and permeable capillaries causing no recovery of T2* signal to basline.
5. Tumor mimicking lesions e.g.
cerebral infections
tumefactive demyelinating lesions
less commonly infarcts

68. 6.Tumefactive demyelinating lesions
No neo-vascularization in demyelinating lesions
To conclude
MR perfusion should be included in routine evaluation of brain tumor as it improve diagnostic accuracy.

73. Neuro-oncology
rCBV maps
low rCBV in tumour infers low grade glioma

74. Eg2 Diffused tumor: Abnormal capillary density
Glioblastoma multiform
Hyper perfusion
Excised region
Before surgery MTSE shows blood brain / barrier breakdown (bbbb)
After surgery rCBV map shows diffuse disease in right frontal lobe

75. Eg3 tumor vs.radiation necrosis
CBV
Conventional T2
Non specific changes
Recurrent Tumor