1. MAGNETIC RESONANCEMAGNETIC RESONANCE
IMAGINGIMAGING
Dr.Shahzad Ahmad DaulaDr.Shahzad Ahmad Daula
MID,DMLT,DDC
The University of LahoreThe University of Lahore

2. MRIPRINCIPLEMRIPRINCIPLE
 MRI isbased on theprincipleof nuclear magnetic resonance.MRI isbased on theprincipleof nuclear magnetic resonance.
 Two basic principlesof NMRTwo basic principlesof NMR
1.1. Atomswith an odd number of protonsor neutronshavespinAtomswith an odd number of protonsor neutronshavespin
2.2. A moving electric charge, beit positiveor negative, producesamagnetic fieldA moving electric charge, beit positiveor negative, producesamagnetic field
 Body hasmany such atomsthat can act asgood MR nucleiBody hasmany such atomsthat can act asgood MR nuclei
((11
H,H, 1313
C,C, 1919
F,F, 2323
Na)Na)
 Hydrogen nuclei isnot only positively charged, but also hasHydrogen nuclei isnot only positively charged, but also has
magnetic spinmagnetic spin
 MRI utilizesthismagnetic spin property of protonsof hydrogen toMRI utilizesthismagnetic spin property of protonsof hydrogen to
elicit imageselicit images

3. WHY HYDROGEN IONS ARE USEDWHY HYDROGEN IONS ARE USED
IN MRI?IN MRI?
an unpaired proton which ispositively charged
Every hydrogen nucleusisatiny magnet which
producessmall but noticeablemagnetic field.
Hydrogen atom istheonly major speciesin the
body that isMR sensitive
Abundant in thebody in theform of water and fat
MRI ishydrogen (proton) imaging

4. BODY IN AN EXTERNALBODY IN AN EXTERNAL
MAGNETIC FIELD (MAGNETIC FIELD (BB00))
•In our natural stateIn our natural state Hydrogen ions in bodyHydrogen ions in body
are spinning in a haphazard fashion, andare spinning in a haphazard fashion, and
cancel all the magnetism.cancel all the magnetism.
•When an external magnetic field is appliedWhen an external magnetic field is applied
protons in the body align in one direction.protons in the body align in one direction.

5. NETMAGNETIZATION
 Half of the protons align along the magnetic field and restHalf of the protons align along the magnetic field and rest
are aligned opposit.are aligned opposit.
 At room temperature, theAt room temperature, the
population ratio of anti-population ratio of anti-
parallel versus parallelparallel versus parallel
protons is roughly 100,000protons is roughly 100,000
to 100,006 per Tesla ofto 100,006 per Tesla of BB00
 These extra protons produce net magnetization vector (M)These extra protons produce net magnetization vector (M)

6. MANIPULATING THENETMANIPULATING THENET
MAGNETIZATIONMAGNETIZATION
 Manipulated by changing themagnetic fieldManipulated by changing themagnetic field
environment (static, gradient, and RF fields)environment (static, gradient, and RF fields)
 RF wavesareused to manipulatethemagnetization ofRF wavesareused to manipulatethemagnetization of
H nucleiH nuclei
 Externally applied RF wavesperturb magnetizationExternally applied RF wavesperturb magnetization
into different axis(transverseaxis). Only transverseinto different axis(transverseaxis). Only transverse
magnetization producessignal.magnetization producessignal.
 When perturbed nuclei return to their original stateWhen perturbed nuclei return to their original state
they emit RF signalswhich can bedetected with thethey emit RF signalswhich can bedetected with the
help of receiving coilshelp of receiving coils

7. T1 ANDT2 RELAXATION
 When RFpulse is stopped higherenergy gained byWhen RFpulse is stopped higherenergy gained by
proton is retransmitted and hydrogen nuclei relax byproton is retransmitted and hydrogen nuclei relax by
two mechanismstwo mechanisms
 T1 orspin lattice relaxation- by which originalT1 orspin lattice relaxation- by which original
magnetization begins to recover.magnetization begins to recover.
 T2 relaxation orspin spin relaxation - by whichT2 relaxation orspin spin relaxation - by which
magnetization in X-Y plane decays towards zero in anmagnetization in X-Y plane decays towards zero in an
exponential fashion. It is due to incoherence of Hnuclei.exponential fashion. It is due to incoherence of Hnuclei.
 T2 values of CNS tissues are shorterthan T1 valuesT2 values of CNS tissues are shorterthan T1 values

8. T1 RELAXATIONT1 RELAXATION
After protonsare
Excited with RF pulse
They moveout of
Alignment with B0
But oncetheRF Pulse
isstopped they Realign
after someTimeAnd
thisiscalled t1 relaxation
T1 is defined as the time it takes for the hydrogen nucleus
to recover 63% of itslongitudinal magnetization

9. T2 relaxation time is the time for 63% of the protons to become dephased
owing to interactions among nearby protons.

10. TR AND TE
 TE (echo time) : time interval in which signals are measuredTE (echo time) : time interval in which signals are measured
after RF excitationafter RF excitation
 TR (repetition time) : the time between two excitations isTR (repetition time) : the time between two excitations is
called repetition timecalled repetition time
 By varying theTR and TE onecan obtain T1WI and T2WIBy varying theTR and TE onecan obtain T1WI and T2WI
 In general ashort TR (<1000ms) and short TE (<45 ms) scan isIn general ashort TR (<1000ms) and short TE (<45 ms) scan is
T1WIT1WI
 Long TR (>2000ms) and long TE (>45ms) scan isT2WILong TR (>2000ms) and long TE (>45ms) scan isT2WI
 Long TR (>2000ms) and short TE (<45ms) scan is protonLong TR (>2000ms) and short TE (<45ms) scan is proton
density imagedensity image

11. Different tissues have differentDifferent tissues have different
relaxation times. These relaxationrelaxation times. These relaxation
time differences is used to generatetime differences is used to generate
image contrast.image contrast.

12. TYPES OF MRI
IMAGINGS
 T1WIT1WI
 T2WIT2WI
 FLAIRFLAIR
 STIRSTIR
 DWIDWI
 ADCADC
 GREGRE
 MRAMRA
 MRVMRV
 MRSMRS
 MTMT
 Post-Gd imagesPost-Gd images

13. T1 &T2 W IMAGING

14. GRADATION OF INTENSITYGRADATION OF INTENSITY
IMAGING
CT SCAN CSF Edema White
Matter
Gray
Matter
Blood Bone
MRI T1 CSF Edema Gray
Matter
White
Matter
Cartilage Fat
MRI T2 Cartilage Fat White
Matter
Gray
Matter
Edema CSF
MRI T2
Flair
CSF Cartilage Fat White
Matter
Gray
Matter
Edema

15. CT SCAN
MRI T1 Weighted
MRI T2 Weighted
MRI T2 Flair

16. DARK ON T1DARK ON T1
Edema,tumor,infection,inflammation,hemorrhageEdema,tumor,infection,inflammation,hemorrhage
Low proton density ,calcificationLow proton density ,calcification
Flow voidFlow void

17. BRIGHT ON T1BRIGHT ON T1
 Fat,subacute hemorrhage,melanin,protein rich fluid.
 Slowly flowing blood
 Paramagnetic
substances(gadolinium,copper,manganese)
 9

18. BRIGHT ON T2
 Edema,tumor,infection,inflammation,subduralEdema,tumor,infection,inflammation,subdural
collectioncollection
 Methemoglobin in late subacute hemorrhageMethemoglobin in late subacute hemorrhage

19. DARK ON T2DARK ON T2
 Low proton density,calcification,fibrous tissueLow proton density,calcification,fibrous tissue
 Paramagnetic substances (deoxy hemoglobin,Paramagnetic substances (deoxy hemoglobin,
methemoglobin,ferritin,hemosiderin,melanin.methemoglobin,ferritin,hemosiderin,melanin.
 Protein rich fluidProtein rich fluid
 Flow voidFlow void

20. WHICHSCAN BESTDEFINES THEWHICHSCAN BESTDEFINES THE
ABNORMALITYABNORMALITY
T1 WImages:T1 WImages:
SubacuteHemorrhageSubacuteHemorrhage
Fat-containing structuresFat-containing structures
Anatomical DetailsAnatomical Details
T2 WImages:T2 WImages:
EdemaEdema
DemyelinationDemyelination
InfarctionInfarction
Chronic HemorrhageChronic Hemorrhage
FLAIRImages:FLAIRImages:
Edema,Edema,
DemyelinationDemyelination
Infarction esp. in Periventricular locationInfarction esp. in Periventricular location

21. FLAIR & STIRFLAIR & STIR

22. CONVENTIONALICNVERSION
RECOVERY
- 180° preparatory pulse180° preparatory pulseis applied to flip the net magnetizationis applied to flip the net magnetization
vector 180° andvector 180° andnull the signal from a particular entitynull the signal from a particular entity
(eg, water in tissue).(eg, water in tissue).
- When the RF pulse ceases, the spinning nuclei begin to relax.When the RF pulse ceases, the spinning nuclei begin to relax.
When the net magnetization vector for water passes theWhen the net magnetization vector for water passes the
transversetransverseplane (the null point for that tissue), theplane (the null point for that tissue), the
conventional 90°conventional 90°pulse is applied, and the SE sequence thenpulse is applied, and the SE sequence then
continues as beforecontinues as before..
- The interval between the 180° pulse and the 90°- The interval between the 180° pulse and the 90° pulse is thepulse is the
TI ( Inversion Time).TI ( Inversion Time).

23. Contd:Contd:
 At TI, thenet magnetization vector of water isvery weak, whereasthat
for body tissuesisstrong. When thenet magnetization vectorsare
flipped by the90° pulse, thereislittleor no transversemagnetization
in water, so no signal isgenerated (fluid appearsdark), whereassignal
intensity rangesfrom low to high in tissueswith astronger NMV.
 Two important clinical implementationsof theinversion recovery
concept are:
 Short TIinversion-recovery (STIR) sequence
 Fluid-attenuated inversion-recovery (FLAIR) sequence.

24. SHORT TI INVERSION-RECOVERY
(STIR)
 an inversion-recovery pulseisused to nullan inversion-recovery pulseisused to null thesignal from fat (180° RFthesignal from fat (180° RF
Pulse).Pulse).
 When NMVWhen NMV of fat passesitsnull point , 90° RF pulseisapplied. Asof fat passesitsnull point , 90° RF pulseisapplied. As
littleor no longitudinallittleor no longitudinal magnetization ispresent and thetransversemagnetization ispresent and thetransverse
magnetizationmagnetizationisinsignificant.isinsignificant.
 It istransversemagnetization thatIt istransversemagnetization that inducesan electric current in theinducesan electric current in the
receiver coil so no signal isgenerated from fat.receiver coil so no signal isgenerated from fat.
 STIRSTIRsequencesprovideexcellent depiction of bonemarrow edemasequencesprovideexcellent depiction of bonemarrow edema
which may betheonly indication of an occult fracture.which may betheonly indication of an occult fracture.
 UnlikeUnlikeconventional fat-saturation sequencesSTIRconventional fat-saturation sequencesSTIRsequencesarenotsequencesarenot
affected by magnetic field inhomogeneities,affected by magnetic field inhomogeneities,so they aremoreefficientso they aremoreefficient
for nulling thesignal from fatfor nulling thesignal from fat

25. Comparison of fast SE and STIR sequences
for depiction of bone marrow edema
FSE STIR

26. FLUID-ATTENUATED INVERSION
RECOVERY
(FLAIR)
 First described in 1992 and has become one of the corner
stones of brain MR imaging protocols
 An IR sequence with a long TR and TE and an inversion
time (TI) that is tailored to null the signal from CSF
 In contrast to real image reconstruction, negative signals are
recorded as positive signals of the same strength so that the
nulled tissue remains dark and all other tissues have higher
signal intensities.

27.  Most pathologic processesshow increased SI on T2-WI, and the
conspicuity of lesionsthat arelocated closeto interfacesb/w brain
parenchymaand CSF may bepoor in conventional SE or FSE T2-WI
sequences.
 FLAIR imagesareheavily T2-weighted with CSF signal suppression,
highlightshyperintenselesionsand improvestheir conspicuity and
detection, especially when located adjacent to CSF containing spaces

28.  In addition to T2- weightening, FLAIR possesses
considerableT1-weighting, becauseit largely dependson
longitudinal magnetization
 Assmall differencesin T1 characteristicsareaccentuated,
mild T1-shortening becomesconspicuous.
 Thiseffect isprominent in theCSF-containing spaces,
whereincreased protein content resultsin high SI (eg,
associated with sub-arachnoid spacedisease)
 High SI of hyperacuteSAH iscaused by T2 prolongation in
addition to T1 shortening

29. Clinical Applications:
 Used to evaluate diseases affecting the brain parenchyma neighboring
the CSF-containing spaces for eg: MS & other demyelinating
disorders.
 Unfortunately, less sensitive for lesions involving the brainstem &
cerebellum, owing to CSF pulsation artifacts
 Helpful in evaluation of neonates with perinatal HIE.
 Useful in evaluation of gliomatosis cerebri owing to its superior
delineation of neoplastic spread
 Useful for differentiating extra-axial masses eg. epidermoid cysts from
arachnoid cysts. However, distinction is more easier & reliable with
DWI.

30.  Mesial temporal sclerosis: m/c pathology in patients with partial
complex seizures.Thin-section coronal FLAIR is the standard
sequence in these patients & seen as a bright small hippocampus on
dark background of suppressed CSF-containing spaces. However,
normally also mesial temporal lobes have mildly increased SI on
FLAIR images.
 Focal cortical dysplasia of Taylor’s balloon cell type- markedly
hyperintense funnel-shaped subcortical zone tapering toward the
lateral ventricle is the characteristic FLAIR imaging finding
 In tuberous sclerosis- detection of hamartomatous lesions, is easier
with FLAIR than with PD or T2-W sequences

31.  Embolic infarcts- Improved visualization
 Chronic infarctions- typically dark with a rim of high signal. Bright peripheral zone
corresponds to gliosis, which is well seen on FLAIR and may be used to distinguish
old lacunar infarcts from dilated perivascular spaces.

32. T2 W
FLAIR

33. Subarachnoid Hemorrhage (SAH):
 FLAIR imaging surpasseseven CT in thedetection of traumatic supratentorial SAH.
 It hasbeen proposed that MR imaging with FLAIR, gradient-echo T2*-weighted,
and rapid high-spatial resolution MR angiography could beused to evaluatepatients
with suspected acuteSAH, possibly obviating theneed for CT and intra-arterial
angiography.
 With theavailability of high-quality CT angiography, thisapproach may not be
necessary.

34. FLAIR
FLAIR

35. DWI & ADC

36. DIFFUSION-WEIGHTEDMRI
 Diffusion-weighted MRI is a example of endogenous contrast, using
the motion of protons to produce signal changes
 DWI images is obtained by applying pairs of opposing and
balanced magnetic field gradients (but of differing durations and
amplitudes) around a spin-echo refocusing pulse of a T2 weighted
sequence. Stationary water molecules are unaffected by the paired
gradients, and thus retain their signal. Nonstationary water
molecules acquire phase information from the first gradient, but are
not rephased by the second gradient, leading to an overall loss of the
MR signal

37. • The normal motion of water molecules within living tissues is
random (brownian motion).
• In acute stroke, there is an alteration of homeostasis
• Acute stroke causes excess intracellular water accumulation,
or cytotoxic edema, with an overall decreased rate of water
molecular diffusion within the affected tissue.
• Reduction of extracellular space
• Tissues with a higher rate of diffusion undergo a greater loss of
signal in a given period of time than do tissues with a lower
diffusion rate.
• Therefore, areas of cytotoxic edema, in which the motion of
water molecules is restricted, appear brighter on diffusion-
weighted images because of lesser signal losses

38. descriptio
n
T1 T2 FLAIR DWI ADC
White
matter
high low intermediat
e
low low
Grey
matter
intermediat
e
intermediat
e
high intermediat
e
intermediat
e
CSF low high low low high

39.  DW images usually performed with echo-planar sequences which
markedly decrease imaging time, motion artifacts and increase sensitivity to
signal changes due to molecular motion.
 The primary application of DW MR imaging has been in brain imaging,
mainly because of its exquisite sensitivity to early detection of ischemic
stroke

40.  The increased sensitivity of diffusion-weighted MRI in
detecting acute ischemia is thought to be the result of the
water shift intracellularly restricting motion of water
protons (cytotoxic edema), whereas the conventional T2
weighted images show signal alteration mostly as a
result of vasogenic edema

41. • Core of infarct = irreversible damage
• Surrounding ischemic area  may be salvaged
• DWI: open a window of opportunity during which Tt is beneficial
• 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, patient motion).

44.  Ischemic Stroke
 Extra axial masses: arachnoid cyst versus epidermoid tumor
 Intracranial Infections
Pyogenic infection
Herpes encephalitis
Creutzfeldt-Jakob disease
 Trauma
 Demyelination

45. APPARENT DIFFUSIONAPPARENT DIFFUSION
COEFFICIENTCOEFFICIENT
 It is a measure of diffusion
 Calculated by acquiring two or more images with a different gradient
duration and amplitude (b-values)
 To differentiate T2 shine through effects or artifacts from real ischemic
lesions.
 The lower ADC measurements seen with early ischemia,
 An ADC map shows parametric images containing the apparent diffusion
coefficients of diffusion weighted images. Also called diffusion map

46.  The ADC may be useful for estimating the lesion age and
distinguishing acute from subacute DWI lesions.
 Acute ischemic lesions can be divided into hyperacute lesions (low
ADC and DWI-positive) and subacute lesions (normalized ADC).
 Chronic lesions can be differentiated from acute lesions by
normalization of ADC and DWI.
 a tumour would exhibit more restricted apparent diffusion compared
with a cyst because intact cellular membranes in a tumour would
hinder the free movement of water molecules

47. NONISCHEMIC CAUSES FOR
DECREASED ADC
 Abscess
 Lymphoma and other tumors
 Multiple sclerosis
 Seizures
 Metabolic (Canavans )

48. 65 year male- Rt ACA Infarct

49. EVALUATION OF ACUTE STROKE ONEVALUATION OF ACUTE STROKE ON
DWIDWI
 The DWI and ADC maps show changes in ischemic brain
within minutes to few hours
 The signal intensity of acute stroke on DW images increase
during the first week after symptom onset and decrease
thereafter, but signal remains hyper intense for a long period
(up to 72 days in the study by Lausberg et al)
 The ADC values decline rapidly after the onset of ischemia and
subsequently increase from dark to bright 7-10 days later .
 This property may be used to differentiate the lesion older
than 10 days from more acute ones (Fig 2).
 Chronic infarcts are characterized by elevated diffusion and
appear hypo, iso or hyper intense on DW images and
hyperintense on ADC maps

51. DW MR imaging characteristics of Various Disease Entities
MR Signal Intensity
Disease DW Image ADC Image ADC Cause
Acute Stroke High Low Restricted Cytotoxic edema
Chronic Strokes Variable High Elevated Gliosis
Hypertensive
encephalopathy
Variable High Elevated Vasogenic edema
Arachnoid cyst Low High Elevated Free water
Epidermoid mass High Low Restricted Cellular tumor
Herpes encephalitis High Low Restricted Cytotoxic edema
CJD High Low Restricted Cytotoxic edema
MS acute lesions Variable High Elevated Vasogenic edema
Chronic lesions Variable High Elevated Gliosis

52. CLINICAL USES OF DWI & ADCCLINICAL USES OF DWI & ADC
Stroke:
 Hyperacute Stage:- within one hour minimal hyperintensity seen in DWI
and ADC value decrease 30% or more below normal (Usually <50X10-4
mm2
/sec)
 Acute Stage:- Hyperintensity in DWI and ADC value low but after 5-
7days of ictus ADC values increase and return to normal value
(Pseudonormalization)
 Subacute to Chronic Stage:- ADC value are increased (Vasogenic edema)
but hyperintensity still seen on DWI (T2 shine effect)

53. GRE

54. GRE
 In a GRE sequence, an RF pulse is applied that partly
flipsthe NMV into the transverse plane (variableflip
angle).
 Gradients, as opposed to RF pulses, are usedto dephase
(negative gradient) and rephase (positive gradients)
transverse magnetization.
 Because gradients donot refocus field inhomogeneities,
GRE sequences with long TEsare T2* weighted
(because of magnetic susceptibility) ratherthan T2
weighted like SE sequences

55. GRE Sequences contd:
 This feature of GRE sequences is exploited- in detection of
hemorrhage, as the iron in Hb becomesmagnetized locally (produces
its own local magnetic field) andthus dephases the spinning nuclei.
 The technique is particularlyhelpful for diagnosing hemorrhagic
contusions such as thosein the brain and in pigmented villonodular
synovitis.
 SE sequences, on the other hand- relativelyimmune from magnetic
susceptibility artifacts, and also lesssensitive in depicting
hemorrhage and calcification.

56. GREFLAIR
Hemorrhage in right parietal lobe

57. GRE Sequences contd:
Magnetic susceptibility imaging-
 - Basis of cerebral perfusionstudies, in which the T2* effects (ie,
signal decrease) createdby gadolinium (a metal injected intravenously
as a chelatedion in aqueous solution, typically in the form of
gadopentetatedimeglumine) are sensitively depicted by GRE
sequences.
 - Also used in blood oxygenationlevel–dependent (BOLD) imaging,
in which the relativeamount of deoxyhemoglobin in the cerebral
vasculature is measuredas a reflection of neuronal activity. BOLD MR
imaging is widelyused for mapping of human brain function.

58. GRADIENT ECHO
Pros:
 fast technique
Cons:
 More sensitive to magnetic susceptibility artifacts
 Clinical use:
 eg. Hemorrhage , calcification

59. Axial T1 (C), T2 (D), and GRE (E) images show corresponding T1-hyperintense and GRE-
hypointense foci with associated T2 hyperintensity (arrows).

60. MRS & MT-MRI

61. MR SPECTROSCOPY
 Magnetic resonance spectroscopy (MRS) is a means of
noninvasive physiologic imaging of the brain that
measures relative levels of various tissue metabolites
 Purcell and Bloch (1952) first detected NMR signals from
magnetic dipoles of nuclei when placed in an external
magnetic field.
 Initial in vivo brain spectroscopy studies were done in the
early 1980s.
 Today MRS-in particular, IH MRS-has become a valuable
physiologic imaging tool with wide clinical applicability.

62. PRINCIPLES:
 The radiation produced by any substance is dependent on its atomic
composition.
 Spectroscopy is the determination of this chemical composition of a
substance by observing the spectrum of electromagnetic energy emerging
from or through it.
 NMR is based on the principle that some nuclei have associated magnetic
spin properties that allow them to behave like small magnet.
 In the presence of an externally applied magnetic field, the
magnetic nuclei interact with that field and distribute themselves to
different energy levels.
 These energy states correspond to the proton nuclear spins, either
aligned in the direction of (low-energy spin state) or against the applied
magnetic field (high-energy spin state).

63.  If energy is applied to the system in the form of a radiofrequency
(RF) pulse that exactly matches the energy between both states. a
condition of resonance occurs.
 Chemical elements having different atomic numbers such as
hydrogen ('H) and phosphorus (31P) resonate at different
Larmor RFs.
 Small change in the local magnetic field, the nucleus of the atom
resonates at a shifted Larmor RF.
 This phenomenon is called the chemical shift.

64. TECHNIQUE:
Single volume and Multivolume MRS.
1) Single volume:
 Stimulated echo acquisition mode (STEAM)
 Point-resolved spectroscopy (PRESS)
 It gives a better signal-to noise ratio
2) Multivolume MRS:
 chemical shift imaging (CSI) or spectroscopic imaging (SI)
 much larger area can be covered, eliminating the sampling error to an extent
but significant weakening in the signal-to-noise ratio and a longer scan time.
 Time of echo: 35 ms and 144ms.
 Resonance frequencies on the x-axis and amplitude (concentration) on the y-
axis.

65. OBSERVABLE METABOLITES
Metabolite Location
ppm
Normal function Increased
Lipids 0.9 & 1.3 Cell membrane
component
Hypoxia, trauma, high
grade neoplasia.
Lactate 1.3
TE=272
(upright)
TE=136
(inverted)
Denotes anaerobic
glycolysis
Hypoxia, stroke, necrosis,
mitochondrial diseases,
neoplasia, seizure
Alanine 1.5 Amino acid Meningioma
Acetate 1.9 Anabolic
precursor
Abscess ,
Neoplasia,

66. PRINCIPLE METABOLITESMetabolite Location
ppm
Normal
function
Increased Decreased
NAA 2 Nonspecific
neuronal
marker
(Reference for
chemical shift)
Canavan’s
disease
Neuronal loss,
stroke,
dementia, AD,
hypoxia,
neoplasia,
abscess
Glutamate ,
glutamine,
GABA
2.1- 2.4
Neurotransmit
ter
Hypoxia, HE Hyponatremia
Succinate 2.4 Part of TCA
cycle
Brain abscess
Creatine 3.03 Cell energy
marker
(Reference for
metabolite
ratio)
Trauma,
hyperosmolar
state
Stroke, hypoxia,
neoplasia

67. Metabolite Location
ppm
Normal
function
Increased Decreased
Choline 3.2 Marker of
cell memb
turnover
Neoplasia,
demyelination
(MS)
Hypomyelinat
ion
Myoinositol 3.5 & 4 Astrocyte
marker
AD
Demyelinatin
g diseases

68. METABOLITE RATIOS:
Normal abnormal
NAA/ Cr 2.0 <1.6
NAA/ Cho 1.6 <1.2
Cho/Cr 1.2 >1.5
Cho/NAA 0.8 >0.9
Myo/NAA 0.5 >0.8

69. MRS
Dec NAA/Cr
Inc acetate,
succinate,
amino acid,
lactate
Neuodegene
rative
Alzheimer
Dec
NAA/Cr
Dec NAA/
Cho
Inc
Myo/NAA
Slightly inc Cho/ Cr
Cho/NAA
Normal Myo/NAA
± lipid/lactate
Inc Cho/Cr
Myo/NAA
Cho/NAA
Dec NAA/Cr
± lipid/lactate
Malignancy
Demyelinatin
g disease Pyogenic
abscess

70. CLINICAL APPLICATIONS OF
MRS:
 Class A MRS Applications: Useful in Individual Patients
1) MRS of brain masses:
 Distinguish neoplastic from non neoplastic masses
 Primary from metastatic masses.
 Tumor recurrence vs radiation necrosis
 Prognostication of the disease
 Mark region for stereotactic biopsy.
 Monitoring response to treatment.
 Research tool
2) MRS of Inborn Errors of Metabolism
Include the leukodystrophies, mitochondrial disorders, and enzyme defects that
cause an absence or accumulation of metabolites

71. CLASS B MRS APPLICATIONS: OCCASIONALLY
USEFUL IN INDIVIDUAL PATIENTS
1) Ischemia, Hypoxia, and Related Brain Injuries
 Ischemic stroke
 Hypoxic ischemic encephalopathy.
2)Epilepsy
Class C Applications: Useful Primarily in Groups of Patients (Research)
 HIV disease and the brain
 Neurodegenerative disorders
 Amyotrophic lateral sclerosis
 Multiple sclerosis
 Hepatic encephalopathy
 Psychiatric disorders

72. MAGNETIZATION TRANSFER (MT) MRI
 MT is a recently developed MR technique that alters contrast of tissue on
the basis of macromolecular environments.
 MTC is most useful in two basic area, improving image contrast and tissue
characterization.
 MT is accepted as an additional way to generate unique contrast in MRI
that can be used to our advantage in a variety of clinical applications.

73. Magnetization transfer (MT) contd:-
 Basis of the technique: that the state of magnetization of an atomic nucleus can be
transferred to a like nucleus in an adjacent molecule with different relaxation
characteristics.
 Acc. to this theory- H1
proton spins in water molecules can exchange magnetization
with H1
protons of much larger molecules, such as proteins and cell membranes.
 Consequence is that the observed relaxation times may reflect not only the properties
of water protons but also, indirectly, the characteristics of the macromolecular
solidlike environment
 MT occurs when RF saturation pulses are placed far from the resonant frequency of
water into a component of the broad macromolecular pool.

74. Magnetization transfer (MT) contd:-
 These off-resonance pulses, which may be added to standard MR pulse
sequences, reduce the longitudinal magnetization of the restricted
protons to zero without directly affecting the free water protons.
 The initial MT occurs between the macromolecular protons and the
transiently bound hydration layer protons on the surface of large
molecules’
 Saturated bound hydration layer protons then diffuse and mix with the
free water proton pool
 Saturation is transferred to the mobile water protons, reducing their
longitudinal magnetization, which results in decreased signal intensity
and less brightness on MR images.

75. Magnetization transfer (MT) contd:-
 The MT effect is superimposed on the intrinsic contrast of the baseline image
 Amount of signal loss on MT images correlates with the amount of macromolecules
in a given tissue and the efficiency of the magnetization exchange
 MT characteristically:
Reduces the SI of some solid like tissues, such as most of the brain and spinal cord
Does not influence liquid like tissues significantly, such as the cerebrospinal fluid
(CSF)

76. MT Effect

77. CLINICAL APPLICATION
• Useful diagnostic tool in characterization of a variety of CNS infection
• In detection and diagnosis of meningitis , encephalitis, CNS tuberculosis ,
neurocysticercosis and brain abscess.
TUBERCULOMA
• Pre-contrast T1-W MT imaging helps to better assess the disease load in CNS
tuberculosis by improving the detectability of the lesions, with more number
of tuberculomas detected on pre-contrast MT images compared to routine SE
images
• It may also be possible to differentiate T2 hypo intense tuberculoma from T2
hypo intense cysticerus granuloma with the use of MTR, as cysticercus
granulomas show significantly higher MT ratio compared to tuberculomas

78. T1 T2
MT
PC
MT

79. NEUROCYSTICERCOSIS
Findings vary with the stage of disease
 T1-W MT images are also important in demonstrating perilesional gliosis in
treated neurocysticercus lesions
 Gliotic areas show low MTR compared to the gray matter and white matter.
So appear as hyperintense
BRAIN ABSCESS
 Lower MTR from tubercular abscess wall in comparison to wall of
pyogenic abscess(~20 vs. ~26)

80. Magnetization transfer (MT) contd:-
Qualitative applications:
 MR angiography,
 postcontrast studies
 spine imaging
 MT pulses have a greater influence on brain tissue (d/t high conc.
of structured macromolecules such as cholesterol and lipid) than
on stationary blood.
 By reducing the background signal vessel-to-brain contrast is
accentuated,
 Not helpful when MR angiography is used for the detection and
characterization of cerebral aneurysms.

81. GRE images of the cervical spine without (A) and with (B) MT
show improved CSF–spinal cord contrast

82. Magnetization transfer (MT) contd:-
Quantitative applications:
 Multiple sclerosis: discriminates multiple sclerosis & other
demyelinating disorders, provides measure of total lesion load,
assess the spinal cord lesion burden and to monitor the response
to different treatments of multiple sclerosis
 systemic lupus erythematosus,
 CADASIL (cerebral autosomal dominant arteriopathy with
subcortical infarcts and leuko encephalopathy),
 Multiple system atrophy,
 Amyotrophic lateral sclerosis,
 Schizophrenia
 Alzheimer’s disease

83. MTR Quantitative applications contd:
 May be used to differentiate between progressive multifocal leukoencephalopathy
and HIV encephalitis
 To detect axonal injury in normal appearing splenium of corpus callosum after head
trauma
 In chronic liver failure, diffuse MTR abnormalities have been found in normal
appearing brain, which return to normal following liver transplantation

84. Thank you