This document provides an overview of MRI basics including: 1) How MRI scanners work by using magnetic fields and radio waves to produce images mapping proton distribution and energy. 2) The differences between T1- and T2-weighted images and how they highlight different tissues. 3) How specialized sequences like STIR, FLAIR, and DWI provide additional clinical information. 4) The use of contrast agents and their role in identifying abnormal tissues. 5) The importance of a systematic approach to MRI interpretation and relating findings to clinical information. 6) Key safety considerations for MRI scanning.

1. Radiology Department
National institute of diabetes and endocrinology
Cairo, Egypt
Basics of MRI interpretation
Kareem Alnakeeb, M.B., B.Ch.

2. Contents
• Application of MRI
• MRI scanner
• MRI images & signal production
• T1 VS T2 images
• Specialized MRI sequences
• Contrast agents
• Systematic approach
• MRI safety

3. Application of MRI
• MRI is often incorrectly considered a superior imaging modality to other imaging
techniques.
• The successful application of MRI depends on the clinical question in mind, and the body
part to be imaged
• MRI provides exquisite images of body parts that do not move, such as the brain, and
anatomical structures that can be kept still, such as parts of the musculoskeletal system.
• With some applications of MRI, drugs may be given to help reduce movement and
improve image quality

4. MRI scanner
• An electric current sent once through the
ultra-cold conducting coil will
and create a
magnetic field. The magnet in an MRI
scanner is
• The patient lies on the scanner couch (1)
which slides into the bore of the scanner (2)
• Within the bore of the scanner there is a
powerful magnetic field
• The scanner produces radiofrequency
to ‘excite’ protons in the body
• As the excited protons in the body ‘relax’
after each pulse, they give off radiofrequency
‘ ’ which is detected by the receiver (3)
• The receiver is placed around or near the
body part being imaged

5. Scanner Schematic
• The produces the intense
and stable magnetic field around the
patient.
help make the magnetic field
more homogeneous.
• The are lower strength
than the main magnetic field and produce
a variable field adjusted to different body
parts.
direct a pulse
toward the area to be examined and are
also adjusted for different body parts.
• The scanner bore is the horizontal tube
in which the patient rests. The actual
magnets reside inside the gantry housing.

6. What are MRI images?
• X-ray and CT images are maps of density
of tissues in the body
white = high density
• MRI images are a map of proton energy
within tissue of the body
white = high signal

7. • Free protons within molecules of the body
are orientated randomly, spinning on a
North-South magnetic axis
• On entering the scanner, the protons align
with the axis of the magnetic field (blue
arrows) within the bore of the scanner
MRI signal production

8. • A radiofrequency is applied to
‘excite’ the protons
• Protons are aligned at an angle to the
magnetic field
• The radiofrequency pulses also cause the
protons to spin in phase with each other
creating 'resonance'
• Milliseconds after removal of each
radiofrequency pulse the excited protons
'relax', giving off radiofrequency
which is detected by the scanner

9. Steps in the excitation and relaxation of the hydrogen protons
in producing the T1 and T2 relaxation times
Caption

10. Longitudinal (spin-lattice relaxation) (T1)
• a process responsible for the from RF-excited protons into their molecular environment
or “lattice.”
• T1 relaxation time is a measure of time required for Mz to return to 63% of its equilibrium magnetization (M0).
Transverse (spin-spin relaxation) (T2)
• a process that progressively reduces order after an excitation pulse.
• Individual components of magnetization lose their alignment and rotate at various rates in the transverse plane
( ).
• T2 relaxation time is a measure of the time required for 63% of the initial magnetization to dissipate.
• T2 is usually much shorter than T1.

11. 1. Realignment of protons with the magnetic field
2. Dephasing of spinning protons (loss of resonance)
• T1 signal relates to the speed of realignment with the magnetic field
the quicker the protons realign, the greater the T1 signal
Tissues that have a will be .
• T2 signal relates to the speed of proton spin dephasing
the slower the dephasing, the greater the T2 signal
Tissues with a will be .

13. Tissue differentiation - Fat vs water
• Protons in the body realign and
dephase with varying rapidity
depending on the tissue type
• Detecting the signal after different time
intervals allows different tissue types to
be highlighted
• Protons in fat realign quickly with high
energy and produce high T1 signal;
• 'T1-weighted' images highlight fat in
tissues of the body
• Protons in water dephase slowly ;
• 'T2-weighted' images highlight water
in tissues of the body

14. Structures normally appear in all MR images due to:
Motion of protons (H+):
1. Cortical bone
2. Mature fibrous tissue - ligaments and tendons in the body
3. Calcifications
4. Flowing blood
Amount of protons (H+): Minimal
MRI sequences

15. T1 images – 1 tissue type is bright – FAT
T2 images – 2 tissue types are bright – FAT and WATER
• Therefore, when looking at any MR image, first try to find something you know
is such as in the ventricles and spinal canal or in the
bladder, for example.
If the fluid is , it is probably a -weighted sequence
If the fluid is , it is probably a -weighted image
T1 VS T2

16. • T1 images can be thought of as a map of proton energy within fatty tissues
• Fatty tissues include and of the vertebral bodies
• contains no fat – so it appears black on T1-weighted images
T1-weighted image – Anatomy (spine)

17. • T2 images are a map of proton energy within fatty water-based tissues of the body
• Anything that is bright on the T2 images but dark on the T1 images is tissue
is white on this T2 image and dark on the T1 image because it is free fluid and contains no fat
is black – it gives off no signal on either T1 or T2 images because it contains no free protons
T2-weighted image – Anatomy (spine)

18. • Loss of the normal high signal in the bone marrow indicates:
loss of normal fatty tissue and increased water content
• Abnormal low signal on T1 images frequently indicates:
a pathological process such as trauma, infection, or cancer
T1 weighted image – Pathology (spine)

19. • Same areas are whiter than usual on this T2 image indicating: increased water content
• Abnormal brightness on a T2 image indicates:
a disease process such as trauma, infection, or cancer
• This patient had
T2 weighted image – Pathology (spine)

20. Bright on T1-weighted tissues & structures
• Fat: subcutaneous and
intraabdominal fat, fat within yellow
bone marrow, fat-containing tumors
• Hemorrhage: although this varies
depending on the of the
hemorrhage
• Proteinaceous fluid:
proteinaceous fluid in renal or
hepatic cysts, cystic neoplasms
• Melanin (e.g., melanoma)
• Gadolinium and other
paramagnetic substances
(manganese, copper)
• Sagittal T1-weighted image of the brain demonstrates a bright mass
in the frontal lobe representing metastatic melanoma.
• Notice that both the yellow bone marrow within the skull
and the overlying subcutaneous fat are bright.
• We can tell that this is a T1-weighted image because the CSF in the lateral
ventricles is dark

21. Bright on T2-weighted tissues & structures
• Fat: subcutaneous and
intraabdominal fat, fat within
yellow bone marrow, fat-
containing tumors
• Hemorrhage: although this
varies depending on the of
the hemorrhage
• Water, edema, inflammation,
infection, cysts
• Axial T2-weighted image demonstrates bright vasogenic-type edema
surrounding a large, lobulated frontal lobe mass
representing glioblastoma multiforme, an aggressive brain tumor.
• A few bright areas of cystic degeneration appear within
this mass.
• The frontal horns of the lateral ventricles are compressed .

22. Suppression
• It is the ability to the signal from certain tissues selectively, thus
making that tissue look on the image
is often suppressed
• It is used to identify such as ovarian dermoid cysts,
adrenal myelolipomas, and liposarcomas, as they will appear to change from
on the non–fat-suppressed images to on the fat-suppressed
images.
• It is also essential for evaluation of tissues the administration of
.

23. • (A) Axial T1-weighted image of the scrotum demonstrates a bright, heterogeneous right scrotal mass
. The left testis is unremarkable and the right testis is not visualized. Note that
subcutaneous fat is normally bright
• (B) Axial T1-weighted, fat-suppressed, gadolinium-enhanced image demonstrates that the bright signal in the right
scrotal mass is now dark, consistent with fat . The subcutaneous fat is also dark on the fat-
suppressed image This was an unusual malignancy of the spermatic cord derived from fat cells.

24. STIR image
• STIR images are highly water-sensitive and the
timing of the pulse sequence used acts to
suppress signal coming from fatty tissues – so
is bright
• A combination of standard T1 images and STIR
images can be compared to determine the
amount of fat or water within a body part
• In these MRI images, abnormal signal is seen in
the vertebral bodies and intervertebral disc;
Abnormal low signal on the T1 image and
abnormal high signal on the STIR image –
indicates abnormal fluid
• These are typical appearances of
(also known as )
‘Short Tau Inversion Recovery’

25. FLAIR images
‘Fluid Attenuated Inversion Recovery’
• FLAIR images are commonly used in brain
imaging
• The signal from free fluid – such as in the
ventricles – is suppressed (compare with the T2
image)
• High signal seen on these images indicates:
a pathological process such as infection,
tumour, or areas of demyelination – as in this
patient with

26. T2* images
‘gradient echo’ images
• Pronounced ‘T2 star’
• It can be used to highlight the presence of
• such as in this
( )

27. DWI & ADC
‘Diffusion Weighted Imaging’ & ‘Apparent Diffusion Coefficient’
• Areas of high signal on DWI images and
low signal on ADC images indicate
'restricted diffusion' - an indicator of a
pathological process of such
as infarction, cancer, or abscess
formation
• Restricted diffusion in a
region of the brain ( ) is a
characteristic finding of a
• These images also show smaller areas
of restricted diffusion due to
( )

28. Contrast agents
• The most common contrast agent is gadolinium, a para-magnetic substance
which produces T1 signal
• It can be given or injected into a body part such as a joint
• Abnormal tissue may
than surrounding normal tissue following IV gadolinium
gadolinium than normal tissue

29. MRI with gadolinium (brain)
• The pre-gadolinium image
shows only an
in the left cerebral
hemisphere.
• The post-gadolinium image of
the brain shows
–
in this case due to a

30. Cardiac MRI
• This image was acquired after
following intravenous
injection of gadolinium
• An area of the myocardium remains
‘enhanced’ ( )
• This ‘delayed enhancement’ indicates
in this area of the heart
following
• A normal example is shown for
comparison – gadolinium is not
retained by normal myocardial tissue
( )

31. MRI arthrogram – shoulder
• Fluid containing gadolinium has
been injected into the shoulder
joint revealing
in
this patient with recurrent
shoulder dislocation
• G = Glenoid of scapula
• H = Head of humerus

32. Systematic approach
• Start by checking the
• Look at all the available
• Compare the with the images looking for
abnormal signal
• Correlate the MRI appearances with available
• Relate your findings to the

33. Image and patient information
• Check that the images are of
the
• Check the to
ensure you are looking at the
most up to date images
• Check you are looking at the
– and the
if dealing with the
limbs

34. MRI planes
• Check all images planes
•
•
•
• oblique

35. MRI sequences
• Look at the
images which often provide
good of the
area being studied
• Compare with the
images – such as the
T2-weighted or STIR images

36. Abnormal MRI signal
• Determine the of the signal
change – abnormal fat or fluid?
• Note the anatomical
of the abnormality
• The combination of standard T1
images (fat sensitive) and STIR
images (water sensitive) can be
compared to determine the
within a body part
• In this pair of images, the high signal
mass seen on the T1 image is dark on
the STIR image – confirming it
contains fat and no water
• These are typical signal characteristics
of a

37. Previous imaging
• Correlate the images with previous
imaging – either previous MRIs or
other imaging modalities
• For some body parts correlation with
should be
considered part of the routine
assessment of the MRI images
• This plain X-ray gives a good
overview of the and shows
good detail of the
• The MRI provides no detail of the
cortical bone, but shows the
and structures –
such as the cruciate ligaments – not
visible on the X-ray image

38. The clinical question
• Relate your findings to the clinical
features and the specific clinical question
• Both of these images show an area of
within the grey and
white matter of the brain
• gradually worsening
headaches and seizures – diagnosis =
• sudden onset left hemiplegia –
diagnosis =
• Although the MRI appearances provide
information regarding the position and
size of the areas of abnormality, it is the
which provide
the strongest clues to the diagnosis in
both cases

39. MRI safety
• MRI safety issues apply to the scanning room
• A typical MRI magnet has a local magnetic field which is the
strength of the earth's magnetic field
• can become projectile and cause serious injury or
death to patients or staff
• All staff must abide by MRI department safety rules
• Persons entering the scanning room must complete a
prior to being escorted in by trained MRI staff

40. MRI safety precautions
• When referring a patient for an MRI scan, the clinician is usually required to complete
some initial safety checks.
patients may need sedation, or other imaging tests can be considered.
• Up-to-date results are required for patients having a scan with gadolinium.
• Before entering the MRI room patients are again asked a set of safety questions by a
radiographer.
• Patients with or , such
as pacemakers or cochlear implants, should not enter the MRI scanning room.
• Any person with an , such as a vascular aneurysm clip or
prosthetic heart valve, can only enter the MRI scanner room once it has been established
that the device is . If there is doubt, then the person must not enter.

41. MRI safety warnings
• The magnetic field itself is not
harmful to patients.
• However, the machine is very noisy
and patients are provided with
.
• You must never enter an MRI room
unless qualified to do so.
• You are not permitted to enter even
if a patient has had a .
• The patient must be from
the room by MRI department staff
can start

42. MRI in pregnancy
• Generally, MRI is not advised in pregnancy, especially during the
• Discussion with the Radiology Department will be required.
• Contrast agents are avoided in patients who are pregnant or breast feeding.

43. Key Points
• A basic understanding of MRI physics helps in the interpretation of MRI
images
• MRI produces detailed images of many body parts but is not always the best
imaging modality
• A wide range of different MRI images can be produced to help answer
specific clinical questions
• A systematic approach is required for MRI image interpretation
• There are important safety issues regarding the use of MRI

44. References
• Radiology Masterclass; “Basics of MRI interpretation” Tutorial
https://www.radiologymasterclass.co.uk/tutorials/mri/mri_scan
• Basics of MRI - Prof. Mamdouh Mahfouz
https://youtu.be/KRVHZysiYt4
• Learning Radiology: Recognizing the Basics, 4E ;
CHAPTER 21: Magnetic Resonance Imaging: Understanding the Principles and
Recognizing the Basics
• Primer of diagnostic imaging, 6E ; Magnetic Resonance Imaging Physics