MRI in Orthopaedics

1. MRI in Orthopaedics
Dr. Debesh Shrestha
PG resident
GMC
19th September 2019

2. History
 Awarded Nobel Prize for physics in 1952 for the
discovery of Nuclear Magnetic Resonance (NMR)
spectroscopy
FELIX BLOCH
EDWARD
PURCELL

3. History
 1971- Damadian
discovered that NMR
could differentiate
between healthy and
cancerous tissues
 1976- Damadian
produced the first NMR
image of a living mouse
 1977- produced the first
human image Dr. Raymond V.
Damadian

5. 1st NMR Scanner

6. July 3, 1997

7.  Mid 1980s

8. MAGNET
1. Resistive (electromagnet)
2. Permanent
3. Superconductive – most common

9. Temperatur
e –
Absolute
zero

10. Super magnet

11. MRI gantry

12. MAGNET
 SI unit– Tesla
 1 Tesla= 10,000 Gauss (G)
1. Ultra high field > 4 T
2. High field 1.5-4 T
3. Medium field 0.5-1 T
4. Low field 0.1- 0.5 T
5. Ultra low field <0.1 T

13. Paramagnetic vs Ferromagnetic
 Para-magnetic substance is weakly attracted
towards the strongest region of the magnetic field
 Appear bright on T1 weighted image
1. Hydrogen
2. Gadolinium (contrast enhancing agent)

14. Ferromagnetic substance
 Strongly attracted toward the strongest region of
the magnetic field
 Iron, Cobalt, Nickel

15. Image generation
 Interaction of hydrogen protons with an external
magnetic field
 Abundance of hydrogen proton inside living tissue

16. Normally, protons in human body
are in random orientation

17. When an external magnetic field is
applied, protons align themselves either
in parallel or antiparallel direction relative
to the magnetic field

18. When a radiofrequency pulse
(RF) is applied, atoms are
excited to a higher energy
state

19. When RF is removed, the protons realign
and release energy
Signal is deteced by the transmitter
and the computer produces the
image

20.  RF pulses are repeated several times
 The interval between two pulses is the repetition
time (TR)-- ms
 Time interval between the pulse and the detection
of magnetic resonance signal is the echo time
(TE)-- ms
 Manipulation of TE and TR produces various
image characteristics

22.  Hyperintense : relatively increased signal intensity
– white
 Hypointense : relatively decreased signal
intensity – black
 Isointense – relatively equal in signal intensity
-- gray

24. Basic pulse sequences in MSK

25. T1 weighted image
 Short TR and short TE
 Excellent anatomic information
 Fat image
 Fat is hyperintense
 Water is hypointense
 Short scan time
 Enhancement after the administration of
gadolinium
 Detects bone marrow pathologies and meniscal
pathologies
 Weakness– low sensitivity for soft tissue edema
and pathology

28. T2 weighted image
 Long TR and long TE
 Water image
 Water is hyperintense
 Detects fluid/edema
 Detects pathology such as tumor,
infection,inflammation, fractures and bone contusions
 Good for evaluating cartilage, tendon,ligaments and
fluid filled structures such as cysts
 Weakness– long image acquisition time
inability to detect marrow pathology
when not combined with fat suppression techniques

31. Proton density weighted image
 Long TR and short TE
 Characteristics of both T1 and T2
 Excellent for detecting anatomic detail
 Fat suppressed proton density image used to
evaluate menisci and articular cartilage
 Not sensitive for fluid or marrow pathology

32. Fat suppressed proton
density image of knee
Tear of posterior horn of
medial meniscus

33. Fat suppressed /STIR images
 Suppress the signal coming from fat
 Fat becomes darker
 Achieved by spectral fat suppression or a STIR
technique
 STIR- Short Tau Inversion Recovery

34. Fat suppressed image
 When combined with T2 weighted image or
proton density image– detects bone bruises and
osseous stress injury
 Accentuates the increase in T2 weighted signal
which may otherwise be missed
 Bone marrow edema and edema due to
pathologic processes – more conspicuous

35. T2 weighted image of
pelvis
Fat suppressed T2 weighted
image showing marrow
edema

36. Bone contusion distal
femur
Fat
suppressed
T2 weighted

37.  When combined with T1 weighted image–
differentiates the fat containing mass (lipoma)
from other tissue that may contain elements of
increased intensity (hemorrhage)
 Increase the conspicuity of enhancing masses on
contrast enhanced T1 weighted image

38. T1
weighted
(gadolinium
T1 weighted with fat
suppression (gadolinium)–
inflamed synovium

39. Disadvantages :
 Requires higher
strength magnets >
1T
 Incomplete fat
suppression due to
local magnetic field
inhomogeneities esp.
in curved surfaces
such as shoulder and
ankle, in presence of
metal or air

40. Contrast enhanced imaging
 Gadolinium is commonly used intravenously and
intra-articularly
 Tissues that show increased vascularity–
enhanced
 Often combined with fat suppression

41. T1 weighted image
Post gadolinium T1 weighted
image – mass is more
conspicuous

42. Indirect MR arthrography
 IV injection of gadolinium
 Joint movement through ROM
 Imaging of joint after 5-10 mins

43. Direct MR arthrography
 Direct injection of
gadolinium into the
joint
 Advantages
1. Ligamentous injuries
2. Labral tears
3. TFCC injuries
4. Meniscal tears
5. Articular cartilage
injuries
6. Loose bodies
 Disadvantages
1. Invasive
2. Air bubbles that
simulate loose
bodies
3. Leakage of contrast
into peri-articular
tissue that obscures
or mimics pathology

44.  Post gadolinium fat
suppressed T1
weighted image
 Rotator cuff tear

45. Contra-indications
 Large patient (>300 pounds)– too large to fit
 Claustrophobia
 Aneurysm clips
 Intra-ocular foreign body
 Cardiac pacemakers
 Implanted neuro-stimulators
 Prosthetic heart valves
 Cochlear implants
 Tattoed eye-liner and other make-ups
 First trimester pregnancy

46. Artifacts in MRI

47. Motion artifact

48. Truncation artifact
 Distortion of adjacent
tissues at parallel high
contrast interfaces
high signal in the
center and dark
edges of the spinal
cord

49. Magic angle effect
Magic angle effect– prolongation of T2 within tissues
that are at 55 degrees angle relative to the main
magnetic field

50. Susceptibility artifact
 local field
inhomogeneities
within the scan field–
areas of focal signal
loss– due to metal,
air, calcium, blood
products within the
tissue being imaged

51. Reading Musculoskeletal MRI
 Step 1. Identifying the pulse sequence

53. T1 or T2 ??

54. T1 or T2 ??

55. TR value
 T1—TR is 300- 800 ms
 T2– TR is 2000-5000 ms
 If TR is in 100s –T1
 If TR is in 1000s- T2

56. 2. Evaluation of T2 weighted
image
 Begin with sagittal images for spine, knee, elbow
and ankle
 Begin with coronal or coronal oblique images for
hip and shoulder
 Look for any areas of increased T2 weighted
signal that should not have increased T2
weighted signal – indicates pathology

58. 3. Evaluation of T1 weighted
image
 Optimal evaluation of anatomic detail
 Correlate the areas of increased T2 weighted
signal with the same region on T1 weighted
image

59. 4. Evaluation of specialized pulse sequences
 Fat suppressed T2/ STIR images
 Post- gadolinium T1 images
5. Correlation of MRI with history and clinical
examination to make a definitive diagnosis

61. References
 Essentials of Skeletal Radiology- 3rd edition
Yochum and Rowe
 MRI for Orthopaedic Surgeons – A.J. Khanna
 www.radiopedia.org