A brief description of the history and physics behind MRI scanning.

1. M Y E X P E R I E N C E W I T H M R I S C A N N E R S A N D
T H E P H Y S I C S B E H I N D T H E M
Magnetic Resonance Imaging
RASA SADOUGHI

2. MRI Scanner at Eastbourne DGH
 Visited the MRI scanner as part of
my work experience in the
Radiology department
 1.5 T MRI Scanner
 Used to help diagnose brain
tumours, torn ligaments, cancers
and many other medical issues.
 Scanner is stored in a container
outside of the hospital, which
allows for portability and
transport to other hospitals.
All photos taken by myself unless specified

3. History of MRI and MRI Scanning
 Late 1930’s – Dr Isidor Rabi discovers Nuclear Magnetic
Resonance and is awarded the Nobel prize in 1944 for his
discovery.
 1971 – Paul C. Lauterbur invents MRI and uses it to distinguish
heavy water from normal water; a feat which no other imaging
technique at the time could achieve.
 1977 – Dr Raymond Damadian invents the first Magnetic
Resonance Scanning Machine and volunteers to be the first
experimental subject.
 He was the first to suggest its uses for identifying differences in
tissue and tumours, which could be used for diagnosing cancers.
 After 5 hours, the machine was able to produce an image, though
nowadays a scan can take anywhere from 15 to 90 minutes based
on the area being scanned.
Photos from (http://creationwiki.org/Raymond_Damadian) (https://en.wikipedia.org/wiki/Raymond_Vahan_Damadian#/media/File:Damadian_MRI.jpg) (14/11/15)

4. Inside an MRI Scanner
Diagram from (http://bmeng.blogspot.co.uk/2009/07/mri-machine-mri-image-block-diagram-of.html) (14/11/15)
Formed of two types of magnet:
- Superconductor coil (Blue)
- Gradient coils (Orange)

5. Superconductor Coil
 The largest and strongest magnet in the machine, which
produces a large and stable magnetic field.
 Strength of 0.3 – 9T (Standard MRI Scanners are 1.5T)
 1.5 T is 15000 gauss, which is huge when compared to the
Earth’s magnetic field which is about 0.5 gauss.
 Strong enough to lift a car!
 Achieves this strength by using loops of a superconductive
wire, creating an electromagnetic field.
 Due to superconductivity, the resistance of the wire can be
reduced to nearly zero when cooled.
 Wires are continuously bathed in liquid helium at -269.1◦C and
the entire magnet is insulated by a vacuum.
 This makes the system expensive (about £300,000) but
increases the quality of the images produced.
 Picture is of an Emergency Stop button in the scanning room.
 Causes a shut down of the transformer used to power the
machine and release of all liquid helium, which demagnetizes
the coil. Reasons why this may occur will later be highlighted.
Diagram from (http://mriquestions.com/superconductive-design.html) (14/11/15)

6. Gradient Coils
 Located within the bore of the superconducting
magnet.
 Three different coils which provide the ability
to scan in three planes.
 Create variable magnetic fields which allow for
a specific part of the body, called a “slice” to be
scanned only.
 Move within the machine based on software
built in to the computer, which positions the
magnets around the specific body parts being
scanned using a laser guided system.
 Don’t require cooling as they are not
superconductors and are much less powerful
(0.018 – 0.027T)
 Allow the scanner to image in the Axial (top-
down), Sagittal (side-side) and Coronal (end –
end) planes, and form 3D images.

7. RF Transmitters and Receivers
 Also stored in the bore of the superconducting magnets, on the inside of the
gradient coils.
 Release radiofrequency pulses into the patients body and detect any
radiofrequency pulses released by the body.
 This information is what is used to form the final image during the MRI scan,
and this process is explained on the following slides.
 RF coils are connected to a powerful computer which receives the signals from
the coils and uses this data to form a detailed 2D image of the body part(s)
being scanned.
 The computer can also use a complex mathematical equation known as the
Fourier Transform to create 3D images based on signals gathered when
scanning multiple planes of the “slice”.

9. BEFORE
AFTER
ENERGY
SPIN-UP
SPIN-DOWN

10. The process of MRI
http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/Articleimage/2012/CS/c1cs15248c/c1cs15248c-f2.gif 14/07/16

11. FAT
LongitudinalMagnetization
TIME
H2O
TransverseMagnetization
FAT
TIME
H2O

12. Interpreting the signal
 The voltage induced in the coil is interpreted by the
computer.
 Computer can identify tissue based on the magnetic
component of the pulse, as the time taken for the
pulse to be emitted and the longitudinal
magnetisation of the pulse is different for each
tissue:
 By emitting multiple pulses and recording the
energies of the pulses received, the MRI scanner can
build a 2D image of the body part being scanned.
 A mathematical equation called the Fourier
Transform can be used, as images from different
planes (which can be achieved by rotating the
gradient coils around the slice) enables the scanner
to build 3D models of body parts as well.
 Tumours can be identified by using injectable
contrast and dyes to alter the local magnetic field in
the tissue being examined, as normal and abnormal
tissue will react differently to this alteration.
 The MRI System can display more than 250 shades
of grey to depict varying tissue.
 This allows doctors to visualise tissue abnormalities
better as the image can be easily compared to that of
a normal tissue.
FAT
LongitudinalMagnetization
TIME
H2O
EXAMPLES OF IMAGES PRODUCED
Photos from (http://www.mr-tip.com/serv1.php?type=img&img=Sagittal%20Knee%20MRI%20Images%20T1%20Weighted) (http://www.brainfacts.org/about-
neuroscience/technologies/articles/2014/brain-scans-technologies-that-peer-inside-your-head/) (14/11/15)

13. Improving the image
 The image produced can be greatly improved by
using localized RF Transmitters and Receivers.
 These are modelled to fit certain body parts
perfectly, and move the RF Transmitters and
Receivers as close to the tissue as possible, so
that the least possible distortion occurs, and the
most useful image can be produced.
 This also means that the whole person doesn’t
have to enter the scanner, and the patient would
only have to put the limb being scanned into the
machine. This is a great benefit to those with
claustrophobia or who are obese and may not fit
into a regular MRI Scanner.
 Also, larger MRI Scanners are available for those
who have sever claustrophobia or are obese,
which are either open at the top or have a larger
bore, but they are weaker (0.3T), and scans often
take longer and produce less detailed images.

14. Issues with the Scanner
 Since the scanner is very sensitive, the whole
scanning room must be surrounded by a Faraday
cage, to prevent electromagnetic pulses from
outside the room distorting the images produced.
Just leaving the door open can cause lines to
appear on the image!
 Also, slight movements during the imaging process
means that there will be blurring and warping in
the final image, so often young children will have
to be anaesthetised first, as they move too much
during the scanning process.
 Due to the strength of the magnet, no magnetized
metal objects are allowed in the scanning room
whilst a scan is taking process. This also means
that patients with metal fillings, stems or older
pacemakers can’t have an MRI scan, as the risk for
harm is too high. Those with metal implants must
also have their body parts strapped down, as they
are often pulled towards the magnet or begin to
vibrate!
Photos from (http://radiopaedia.org/articles/zipper-artifact) (14/11/15)

15. Photos from (http://www.intechopen.com/books/imaging-and-radioanalytical-techniques-in-interdisciplinary-research-fundamentals-and-cutting-edge-applications/assessment-of-safety-standards-of-magnetic-resonance-imaging-at-the-korle-bu-teaching-hospital-kbth-)
(http://www.ar15.com/archive/topic.html?b=1&f=5&t=41108) (http://my.firefighternation.com/forum/topics/mri-hazards-what-happens-when?q=forum/topics/mri-hazards-what-happens-when) (14/11/15)

16. Any Questions?

17. Thank you!
Cartoon from (https://www.cartoonstock.com/directory/m/mri.asp) 14/11/15