3 - History -The feasibility of diffusion images was demonstrated in the middle 1980sDemonstration on clinical studies is more recent ; it corresponds with the availability of EPI on MR systemA 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 damageSurrounding ischemic area may be salvagedDWI: open a window of opportunity during which ttt is beneficialDWI: images the random motion of water molecules as they diffuse through the extra-cellular spaceRegions of high mobility “rapid diffusion” darkRegions of low mobility “slow diffusion” brightDifficulty: 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 moleculesMore motion = Darker imageFreely Diffusing Water = DarkRestricted 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
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 directionsIn 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 - WeightingY Diffusion - WeightingZ Diffusion - Weighting
12 Isotropic diffusion - + x / Isotropic Diffusion- Individual Diffusion Weighted ImageIndividual DiffusionDirectionsMathematical Combination(Sorensen et al., MGH)- + x /
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 Metastasis 5.6.
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 Disequilibrium 1.2.
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 Metastasisthe 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.
31 This finding indicates that the lack of signal reduction in malignant vertebral fractures is caused by tumor cell infiltrationDifferent 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 techniqueApplicationsFuture
40 DefinitionsPerfusion is refer to the delivery of oxygen and nutrients to the cells via capillariesPerfusion 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 barrierThe difference in magnetic susceptibility between the tissue and the blood results in local magnetic field finally to large signal loss
42 Some more DefinitionsrCBF “ 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’timeIntegral:=cerebral blood volumeintensitytime
45 PrinciplesEach one of these effects is linearly proportional to the concentration of the paramagnetic agentTo 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-intensitycurvesPerform mathematicalmanipulationGenerate functionalmaps++NEI- + x /MTENegative EnhancementIntegral Map(NEI)Qualitative rCBV mapMean Time toEnhance (MTE)MapIschaemic PenumbraFirst PassContrast bolus
48 rCBV rCBV, processed with “Negative Enhancement Integral”(NEI) is related to area under curve
49 MTTMTT 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 highspeed imagingpower injector - Gadolium5ml/secProcedure :1 - Start Imaging2 - Inject Contrast*3 - Continue Imaging10 slices images of each slice - TOTAL time 1:34 min* Push Gadolinium with 20 cc of saline flush
51 Applications of Perfusion MRI NeurologyGerontologyNeuro-oncologyNeurophysiologyNeuropharmacology
52 Perfusion Imaging: Findings in Infarction StrokePerfusion Imaging: Findings in InfarctionCBVregional perfusion deficitcompensatory increased volumeMTTregional 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 MAPTc-HMPAO SPECTHypo-perfusion
55 E.g. 1 : Left hemisphere stroke, 4.5 hrs after onset of symptoms 3D-TOF VascularFSE-T2WFSE-FLAIR
56 Same patient with DWI and FLAIR EPIFLAIR4.5 hrs24 hrsDiffusion imaging shows lesion early.b=0b=800FLAIR shows enhanced changes after 24 hrs.4.5 hrs
59 Mean Time To Enhance delayed compensatory hyperperfusion delayed hypoperfusion
60 Diffusion Coefficient* EPI Diffusion and Perfusion mappingMTTMean Time To EnhanceCBVNegative EnhancementIntegralADCDiffusion Coefficient*EPI DiffusionEPI Perfusion
61 Findings with Perfusion Imaging for Infarction Changes seen almost immediately after the induction of ischemiamore sensitive than conventional MRIPerfusion findings often more extensive than those on DW-EPI in early strokemore accurately reflects the amount of tissue under ischemic conditions in the hyperacute period than DW EPIAbnormal results correlate with an increased risk of strokePerfEPI - DWEPI = tissue at risk
62 Findings with Perfusion imaging for Gerontology Alzheimer’s diseaseFDG PETmarked temporo-parietal hypometabolismTc-HMPAO SPECTmarked temporo-parietal hypoperfusionDSC MRIcorrelates well with SPECT
63 Findings with Perfusion imaging for Neurophysiology and pharmacology Traumatic brain injuryfocal rCBV deficits that correlate with cognitive impairmentSchizophreniadecreased frontal lobe rCBVHIV/ AIDSmultiple discrete foci of decreased CBVPolysubstance abuseNew Jersey Neuroscience Institute
64 Findings with Perfusion imaging for Neuro-oncology Critical imaging to BBBB imaging of neoplasmmany tumors have high rCBVregions of increased rCBV correlate with areas of active tumor.heterogeneous patterns of perfusion suggest high graderadiation necrosis typically demonstrates low rCBVLesion characterization may be possiblemeningiomas have very high CBV in contrast to schwannomasNew Jersey Neuroscience Institute
65 Intracranial neoplasm N.B angiogenesis usually = aggressiveness Dynamic MR perfusionClinical applications:-Intracranial neoplasmN.B angiogenesis usually = aggressivenessExceptions:- 1. Meningioma2.Choroid plexus papilloma1.Glioma GradingBiopsyD.D recurrence from radiation necrosis
66 2.MetastasisCan differentiate solitary metastasis from 1ry brain neoplasm (glioma) by measuring the peritumoral relative blood volume.3.1ry cerebral lymphomaCan help in differentiating lymphoma from glioma as lymphoma is much less vascular
67 4. MeningiomaHypervascular Extra axialHas leaky and permeable capillaries causing no recovery of T2* signal to basline.5. Tumor mimicking lesions e.g.cerebral infectionstumefactive demyelinating lesionsless commonly infarcts
68 6.Tumefactive demyelinating lesions No neo-vascularization in demyelinating lesionsTo concludeMR perfusion should be included in routine evaluation of brain tumor as it improve diagnostic accuracy.