11/13/24, 7\:33 PM Guide | MRI interpretation

MRI interpretation

Table of contents

Introduction

Magnetic resonance imaging (MRI) is a topic that is delivered in a variety of di
therefore students and healthcare professionals alike may receive di
types, viewing planes, and a large range of associated pathologies to visualise.
These complexities may make students intimidated by MRI interpretation. Here, we provide a brief overview of MRI
fundamentals, approach, and interpretation. Whilst we won’t be able to turn you into a radiologist, we may be able to help you
look less confused when you next get quizzed by one.

Why do we need to use MRIs?

Generally, MRI is used less commonly than plain
tissues. MRI is particularly helpful in patients with suspected neurological or musculoskeletal pathology, however, they can be
used in many other specialities too. It takes slightly longer to acquire MR images and they are more expensive. MRI is
contraindicated in patients who have ferromagnetic metal implants or foreign bodies. 1
Consideration should be given to
patients who are claustrophobic as well.

How do they work?

MRI machines work by exploiting the interaction of the magnetic
put a patient in a strong magnetic
change the direction of alignment of these hydrogen ions. When the RF pulse is turned o
with the magnetic
that the hydrogen ion is in.
1
Using these principles, you can adjust the machine to detect signals of varying ranges and from varying planes of
magnetisation – this is where the “weighted imaging” comes in. We can also tell the machine to disregard certain values of
signals to “suppress” them when it comes to viewing the pictures – these are known as “fat suppression” sequences.
2
MRI can also be used as a dynamic imaging tool. For example, di
weighted imaging (DWI), or macroscopic movement of blood can be studied, in the case of MR angiographic techniques.

MRI Images and sequences

There are many factors that lead to the production of a
di
T1-weighted and T2-weighted imaging (T1WI and T2WI)
DWI and ADC
FLAIR
STIR
… and many others.

T1 and T2 weighted images

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T1 and T2 images demonstrate di
need to be aware of are\:
T1 – ONE tissue is bright\: fat
T2 – TWO tissues are bright\: fat and water (WW2 – Water is White in T2)
T1 is the most ‘anatomical’ image (Figure 1). Conversely, the cerebrospinal
T2 is generally the more commonly used, but T1 can be used as a reference for anatomical structures or to distinguish
between fat vs. water bright signals.
Figure 1. Normal brain MR shows di
Additional features of T1/T2 weighted images
Fat suppressed
The fat signal can be suppressed to enable a better view of pathology in and around anatomical structures – particularly
oedema. This is useful in adrenal tumours or bone marrow pathology, where the image will appear homogenous with
surrounding tissue due to fat content.
Gadolinium-enhanced
Gadolinium enhances vasculature (i.e. arteries) or pathologically-vascular tissues (e.g. intracranial metastases, meningiomas).
This process involves injecting 5-15ml of contrast intravenously, with images taken shortly thereafter. Gadolinium appears bright
in signal, allowing for detection of detailed abnormalities (e.g. intracranial pathologies). Typical intracranial abscesses have a
“ring-enhancement” pattern, while metastases enhance homogeneously. Meningiomas will have a homogenous enhancement
after the contrast, but will also have a “dural tail,
” meaning the lesion appears continuous with the dura (Figure 2).
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Figure 2. Meningioma is shown more clearly by gadolinium contrast with a dural tail [5]
Inversion recovery (IR) sequences
These types of images are manipulations of T1 and T2. They nullify certain tissue types based on their inversion timings, thereby
stopping tissues such as fat and CSF from appearing as bright signals. This is helpful to identify pathological signals. The two
main types are discussed below.
Short tau inversion recovery (STIR)
STIR is based on a T2 image, but the image is manipulated in a way that results in fat (and any other materials with similar
signals) being nulli4
As previously
discussed, fat can make the interpretation of oedematous areas and bone marrow di
signal can assist with the identi
Figure 3. STIR highlighting marrow oedema in L1 vertebra, indicative of a fracture [6]
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Fluid attenuated inversion recovery (FLAIR)
FLAIR is also similar to T2, however, the CSF signal is nulli
nervous system (CNS), including the periventricular areas, sulci, and gyri. For example, FLAIR can be used to identify plaques in
multiple sclerosis, subtle oedema after a stroke, and pathology in other conditions whereby CSF may interfere with
interpretation (Figure 4).
1
Figure 4. Multiple sclerotic plaques in periventricular regions and corpus collosum [7]

Di

DWI is an imaging modality that combines T2 images with the di
within minutes of it occurring (Figure 5). This is because DWI has a high sensitivity for water di
physiological changes that happen immediately after a stroke.
Figure 5. Recent right-sided ischaemic stroke [8]
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ADC should be used alongside DWI in order to con
from T2. The table below explains the key di
DWI ADC
Measures purely di
combination
Measures abnormal di
ALSO combines it with the T2 image
Structures that are bright on a T2 image can shine through into DWI
images
Provides con
DWI
High signal in early ischaemia, but lowers after several weeks
Low signal at
several weeks and stays high
Very sensitive (e.g. if CT is normal, but stroke is still suspected)
Always use DWI in conjunction with ADC

A systematic approach to MRI interpretation

Verify details
Begin by verifying the following details\:
Patient details (i.e. name, date of birth, hospital number)
Image details (i.e. date, type)
Make sure it is the most recent image for the correct patient
Look for previous cross-sectional imaging (if available)
Look at the T2 weighted images
Inspect the T2 weighted images\:
Look at each available plane (axial, coronal, sagittal)
Check for abnormal MRI signals
Work through the anatomy of the areas you are looking at to make sure nothing is missed/abnormal
Comparing both sides of an image (if possible) can reveal clear areas of abnormal signalling
Shape, size, location, and intensity of the signal
Compare di
Compare the available MRI image sequences to help di
Comparing fat sensitive images (e.g. T1) vs water-sensitive images (e.g. T2 or STIR) can help di
ischaemia and in
Post-contrast enhancement is useful for vascular pathology or pathologically-vascular tissue.
Learn why each image type is used - this will enable you to know what you are looking for (e.g. for MR brain it’s useful to look
at T2, then FLAIR, then DWI/ADC, as this will help distinguish between most di
Compare against other imaging modalities
Compare the MRI images to other imaging modalities (e.g. ultrasound, CT, plain
Can you view the pathology on other imaging modalities?
Plain
Compare against previous images
Compare the current MRI images to previous MRI scans if available\:
Are the abnormal signals new or old?
Are there any changes in the size/shape/brightness of the abnormal signals?
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Consider the clinical context
Finally, place your
Are the symptoms acute or chronic?
How unwell is the patient?
Does the imaged pathology correlate with the presenting symptoms?

Summary

In this article, we have outlined the basics of di
has not, but this will give you a good understanding of the fundamentals of MRIs.
The key points are as follows\:
MRIs are a superior imaging modality for viewing soft tissues.
T1 and T2 weighted images represent the core types of MR images.
T1 and T2 images may be adjusted\: fat-suppressed, gadolinium-enhanced and inversion recovery.
The di
and the clinical history, we can make a diagnosis.
Anatomy, as with all scans, is key. MRIs produce a very clear view of structures, therefore strong anatomical knowledge is
particularly helpful.
Spend time looking at normal scans. The more you become familiar with what is normal, the easier it is to see when things
are abnormal.
Always compare both sides of the scan – pathology is rarely bilateral.
Be methodical!

Reviewer

Dr Muiz Shari
Radiology Registrar

References

1. Westbrook, C., Roth, C. K. & Talbot, J. MRI in practice. Published in 2005. Available from\: [LINK]
2. Bitar, R. et al. MR pulse sequences\: What every radiologist wants to know but is afraid to ask. Published in 2006. Available from\:
[LINK]
3. Dr Hidayatullah Hamidi. Normal brain MR shows di[CC BY-SA]. Available from\:
[LINK]
4. Andrew Murphy, et al. MRI sequences (overview). Radiopaedia.org, the wiki-based collaborative Radiology resource. [Internet]
(Accessed\: 21st March 2020). Available from\: [LINK]
5. Assoc Prof Frank Gaillard. Meningioma shown more clearly by gadolinium contrast with a dural tail. Licence\: [CC BY-SA].
Source\: geekymedics.com
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