MRI has become an integral imaging tool over the last 20 years. It uses magnetic fields and radio waves to create detailed images of organs and tissues without exposing patients to ionizing radiation. Different pulse sequences (T1, T2, proton density etc.) along with contrast agents allow MRI to characterize soft tissues and pathology. It is commonly used to image the brain, spine, joints, soft tissues, and for angiography. Recent advances include diffusion MRI, spectroscopy, and functional MRI. MRI has good soft tissue contrast but is more expensive than other modalities.

1. Magnetic
resonance
imaging
Roll no 0954

2. Over the last 20 years, MRI has become an
integral part of the imaging arsenal with ever-
expanding indications.
Technique that
uses a magnetic
field and radio
waves to create
detailed images
of the organs
and tissues
within the body.

3. History Nikola Tesla
discovered the
Rotating Magnetic
Field in 1882
 1969: Raymond
Damadian
proposed the first
human body
scanner using
MRI/Spectroscopy
 1977:Paul
Lauterbur

4. MRI scanner
 device in which the patient lies within a large, powerful
magnet where the magnetic field is used to align the
magnetization of some atomic nuclei in the body
 radio frequency magnetic fields are applied to
systematically alter the alignment of this magnetization.

6. By using gradients in different directions, 2D images or
3D volumes can be obtained in any arbitrary

8. Principle
Nuclei containing an odd number of protons or
electrons
have a characteristic motion in a magnetic field
(precession)
and produce a magnetic moment as a result of this
motion.
atoms of hydrogen in water and lipids
In a strong uniform magnetic field such as a MRI
scanner, these nuclei align themselves with the main
magnetic field and result in a net magnetic moment.

9. A brief radiofrequency pulse is applied at 90 0 to alter the
motion of the nuclei.
Radiofrequency pulse is removed
Nuclei realign themselves with the main magnetic field
(relaxation)
emit a radiofrequency signal that can be recorded,
spatially encoded and used to construct a grey-scale
image

11. In the absence of a strong magnetic field, hydrogen nuclei
are randomly aligned as in (a). When the strong magnetic
field, , is applied, the hydrogen nuclei precess about the
direction of the field as in (b).

12. RF pulse causes the net magnetic moment of the nuclei, ,
to tilt away from original field . (b) When the RF pulse
stops, the nuclei return to equilibrium again parallel to M .
During realignment, the nuclei lose energy and a
measurable RF signal

14. Spince relaxation/ Longitudinal
relaxation
Application of RF Protons at low energy
levels excited to higher energy levels
Absorbed energy used as protons relax back to
original energy level
Time, measured in milliseconds, for 63% of
the hydrogen protons to return to their
normal equilibrium state
It is exponential and referred to by time
constant T1

15. Spin- spin relaxation/ transverse
relaxation
 When RF pulse is applied, protons precess
together in synchronism or in phase with each
other
 During relaxation- they go quickly out of phase
due to small variations in local magnetic fields
 time for 63% of the protons to become
dephased owing to interactions among nearby
protons.
 Exponential

16. T1-weighted images
TR and TE relatively short.
superior in the delineation of anatomy,
Fat, methaemoglobin and mucinous fluid are
bright
T2-weighted images
longer TR and TE times
highlight pathology better.
water and thus most pathological processes
which tend to increase tissue water content, are
bright
Cortical bone, air, haemosiderin and

17. Intraspinal cysticercosis, lumbar area. Multiple large cystic lesions within the
subarachnoid space, isointense to spinal fluid. MRI sagittal plane. (A) T1-weighted
and (B) T2-weighted images

18. Spin density/proton density weighted MRI
 have no contrast from either T2 or T1 decay, the only
signal change coming from differences in the amount of
available spins (hydrogen nuclei in water).
(a) A proton density (PD) weighted MR image slice. (b) The same T2-weighted slice

19. Depending on specific tissue characteristics
under study, T1 and T2 relaxation times will
differ, giving differences in image
MRI image (signal intensity) depends on:
T1 relaxation time
T2 relaxation time
Proton density
Blood flow

20. Sagittal T2-weighted magnetic resonance
imaging scan of the lumbar spine demonstrates
disc herniation in a patient with acute back
pain.

21. agentGadolinium -basis of all currently approved
intravenous MR contrast agents
paramagnetic substance- reduces the T1 and T2
relaxation times of nearby water protons, resulting in a
high signal on T1W images and a low signal on T2W
images
Adverse effects:
allergic reactions
nephrogenic systemic fibrosis (NSF), in patients with
renal insufficiency
widespread fibrosis of the skeletal muscle, bone,
lungs, pleura, pericardium, myocardium, kidney,
muscle, bone, testes, and dura.

22. GFR assessment obtained in patients with a history
of:
 Renal disease (including solitary kidney, renal
transplant, renal tumor)
 Age >60 years
 History of hypertension
 History of diabetes
 History of severe hepatic disease/liver
transplant/pending liver transplant

23. Transverse gadolinium-enhanced images in a 71-
year-old man with multiple hepatocellular
carcinomas and moderate cirrhosis

24. It has traditionally been used extensively in the
assessment
of intracranial, spinal and musculoskeletal disorders
allowing a global assessment of bony and soft-tissue
Structures.
Sequential sections from an MRI of the brain,
concurrently showing slices through transverse,
sagittal, and coronal planes

25. Herniated disc

26. Coronal magnetic resonance imaging scan of the knee
demonstrating extensive serpiginous areas of altered signal
intensity in the distal femur and proximal tibia in a patient with
bone infarcts secondary to oral corticosteroids.

27. Acl tear

28. T2-weighted axial magnetic resonance
imaging scan of the head in a patient with a
large left-sided oligodendroglioma.

29. Today, MRI is commonly used in oncological
imaging -rectal carcinoma

30. Gynaecological malignancies

31. Breast cancer
•many false positive results
•lacks specificity

32.  Mammographically subtle or occult
malignancy(lobular carcinoma)
 Differentiates scar tissue from cancer-local
recurrence
 Response to neoadjuvant chemotherapy
 Breast with implants, dense breasts, pregnancy

33. Characterisation and identification of
hepatic masses

34. Magnetic Resonance Angiography
 general term describing several MR techniques that result
in vascular-weighted images.
 provide a vascular flow map rather than the anatomic
map shown by conventional angiography.
•atherosclerosis,
•Aneurysms
• abnormal vascular
anatomy
•PVD

35. MRA demonstrating the abdominal aorta, common
and external iliac arteries as well as parts of the
pulmonary, mesenteric and renal vasculature.

37. A short-segment high-grade stenosis is present
in the middle of the left superficial femoral

38. Magnetic resonance
cholangiopancreatography
noninvasive technique for evaluating the
intrahepatic and extrahepatic bile ducts and the
pancreatic duct
does not require contrast material to be
administered into the ductal system.
Fluid naturally present in the ducts serves as a
contrast substance.
morbidity associated with endoscopic procedures
and contrast materials is avoided

40. Dilated central intrahepatic bile ducts and a stricture of
the common bile duct in a patient with obstructive
jaundice and cholangiocarcinoma.

41. Intraductal Papillary Mucinous
Neoplasm- Pancreas

42. Uses
 examine diseases of the liver, gallbladder, bile ducts,
pancreas and pancreatic duct. These may include
tumors, stones, inflammation or infection.
 evaluate patients with pancreatitis to detect the
underlying cause.
 help to diagnose unexplained abdominal pain.
 provide a less invasive alternative to ERCP

43. Absolutecontraindications
Ocular metallic foreign bodies
Pacemakers
Cochlear implants
Cranial aneurysm clips
prosthetic heart valves
Defibrillators
Ferromagnetic IVC filters, coils, stents—safe 6 weeks
after implantation
Relative contraindications
First trimester of pregnancy
Claustrophobia
Patients with joint replacements can be studied safely

44.  Ferromagnetic implants (aneurysm clips) may
torque within the magnet  damage to vessels and
even death.
 Screening for ocular metallic fragments -history of
metal work or ocular metallic foreign bodies.
 May move and cause intraocular hemorrhage
 Implanted cardiac pacemakers -the risk of induced
arrhythmias
 some newer pacemakers -safe.

45. Movement of patients may produce artefacts
Respiratory ,cardiac motion, bowel
peristalsis
respiratory and cardiac gating

46. Pulsatile cerebro spinal
fluid flow produces ghost
artifacts that are
superimposed in the
flow compensation
shows the artifact
reduction

47. Magnetic resonance spectroscopy
 measures the levels of different metabolites in
body tissues.
 The MR signal produces a spectrum of
resonances that corresponds to different
molecular arrangements of the isotope being
"excited“
 metabolic disorders, tumor metabolism.

49.  malignant brain lesion with corresponding alteration of the
chemical levels

50. Diffusion MRI
 measures the diffusion
of water molecules in
biological tissues.
 diagnoses of
conditions (e.g.,
stroke) or neurological
disorders (e.g.,
multiple sclerosis)
 helps better
understand the
connectivity of white

52. Functional magnetic resonance
imaging
 measures brain activity by detecting associated
changes in blood flow
 relies on the fact that cerebral blood flow and
neuronal activation are coupled.

53. Echo-Planar MR Imaging
 fast gradients are switched on and off at high speeds
to create the information used to form an image.
 reduces patient and organ motion
 useful in early detection of ischemic injury of the
brain

54. Magnetic Resonance Neurography
 detects increased signal in irritated,
inflamed, or infiltrated peripheral nerves.
 indicated in patients with radiculopathy
whose conventional MR studies of the
spine are normal, suspected peripheral
nerve entrapment or trauma.

56. Strengths
Non invasive
No ionising radiation
Excellent soft-tissue contrast
multiplanar imaging, as
images can be acquired in
any plane
No bone/air artefact
Best imaging technique for
Intracranial lesions,Spine,Bone
marrow and joint lesions
Evolving use
Staging
MRCP
MR angiography
Breast malignancy
Pelvic malignancy
Cardiac imaging

57. Disadvantages
Limited availability
Expensive
Due to variety of protocol options during scanning
final image is highly operator dependent and
requires expert technical staff
Poor bone and calcium detail

58. Long scan times so
patients may not be
able to keep still,
especially if in pain
Time consuming
with respect to
image acquisition
and interpretation.