Dr Simon J DoranCRUK-EPSRC Cancer Imaging Centre, Institute of Cancer Research, Sutton, Surrey

Department of Physics, University of Surrey

MRI: Seeing inside people!

• Brief history of medical imaging

• A few basic principles

• The human brain as seen by MRI

• What else can MRI do?

Summary of today’s talk

• There is a lot of evidence that the ancient Greeks performed major surgery as early as 150 BC.

• But how did they know what was inside the body?

History of medical imaging

• Up until the very end of the 1800’s, the only way to find out about what was inside the human body was to find somebody who was already dead and cut them up.

History of medical imaging

• This is not very useful if you want to find out what is wrong with somebody who is alive and cure them!

“The Anatomy Lecture of Dr. Nicolaes Tulp” [1632] by Rembrandt

History of medical imaging

• Things changed for ever in 1895 with the discovery of X-rays by Wilhelm Roentgen.

Modern x-ray Data: Mayo ClinicMrs Roentgen’s hand Painting of woman having an x-ray (1896)

History of medical imaging

• In 1972, Sir Godfrey Hounsfield made the breakthrough that earned him the Nobel Prize.

Sir Godfrey Hounsfield and his x-ray CT scanner

• The problem with x-ray imaging is that you can only see flat 2-D images.

• By shining x-rays through the body at a variety of different angles all round the body, we can reconstruct images that are three-dimensional.

History of medical imaging

• X-ray CT is particularly good for seeing bones and blood vessels.

X-ray CT visualisation: Vital ImagesData :Toshiba AmericaVisuals : Vital Images

Data source : SMIS LtdSir Peter Mansfield and Paul Lauterbur, Photo: AFP

History of medical imaging

• Just two years later (1974), these two men invented the MRI scanner

• They got the Nobel Prize, too, but they had to wait till 2003.

• MRI is really good at taking pictures of the brain.

Data : ToshibaVisuals : Vital Images

Data: Mayo Clinic

Why use different methods of imaging?

• Plane-film X-ray maps the total attenuation of X-rays along a path through the body, giving a projection image. Good for bone structure in accidents.

• X-ray CT measures the X-ray attenuation coefficient of the body at each point. True 3-D images.

• Ultrasound maps the reflection and attenuation of sound.

Data: Clearview Ultrasound

Data source: SMIS Ltd

• MRI maps the distribution and “environment” of water molecules in the body.

• PET maps the distribution of radioactively labelled compounds.

• MEG maps directly the magnetic fields generated by currents flowing in the brain.

Data: CSUA, Berkeley

Data: FORENAP, Rouffach

Why use different methods of imaging?

Image sources : GE Medical Systems, VA Imaging Centre, University of Florida

What is the tunnel into which the patient slides?

• Resonant frequency is related to the magnetic field.

f B

x

BHeadFeet

• If we vary the magnetic field across the sample, then the frequency of emitted radio waves varies.

What happens in a scan?

• By looking at the frequency spectrum of the signal, we can find out how many spins are where.

• A gradient coil is just like a big loudspeaker (i.e., a large coil of wire sitting in a magnetic field).

• As we change the current passing through the coil the whole gradient assembly (many tons) tries to move.

• It is held in place very securely, yet still vibrates a little, particularly at certain frequencies.

• An expert can tell what imaging scan is being done by listening to the sound the gradients make.

Why do MRI scanners make a noise?

Scout T1-W gradient echo EPI

The Human Brain as seen by MRI

Data: The Whole-brain Atlas, K. A. Johnson and J. A. Becker, Harvard

Data: Christopher Nimsky, Neurosurgery, Erlangen, Germany

Where are we heading with anatomical MRI?

Data source: SMIS

Data source: Gachon University, Seoul

7 T

Where are we heading with anatomical MRI?

Data source: Roger Ordidge, UCL

4.7 T

1.5 T

Stained section

MRI in research: Functional imaging

• We acquire one image of the brain in a “resting” state.

• We follow this by a corresponding image where the brain is active.

• Any differences between these two images correspond to places where the brain is working.

• We can see you think!!

Data source: http://www.youtube.com/watch?v=alS3GeRxYGY

MRI in research: Functional imaging

• Typical base data (greyscale) at 4.7 T, leading to the activation time course (right) and subsequent overlaying of activated areas on images (yellow-red scale)

Data source: Roger Ordidge, UCL

Nerve fibre

• MR images can be sensitised to the rate of diffusion of water molecules.

MRI in research: neural fibre tracking

• Water diffuses faster along nerve fibres than perpendicular to them.

• This allows us to map the local direction of a fibre and create a map of the fibres.

Data source: Geoff Parker, University of Manchester

• MR images can be sensitised to the rate of diffusion of water molecules.

MRI in research: neural fibre tracking

• Water diffuses faster along nerve fibres than perpendicular to them.

• This allows us to map the local direction of a fibre and create a map of the fibres.

Data source: Wilde et al. 2008

• Finally, we can overlay them on a high-resolution 3-D image of the head.

MRI in research: neural fibre tracking

Data source: Wakana et al., Radiology 2004; 230:77–87

MRI in research: neural fibre tracking

Data source: András Jakab. (University of Debrecen)

MRI-guided neurosurgery• State-of-the-art neurosurgery unit at Erlangen, Germany.

• MRI is completely integrated into the operating theatre and used in conjunction with digital images captured from an operating microscope.

Data source : Christopher Nimsky, Neurosurgery, Erlangen, Germany

MRI-guided brain surgery• The surgeon can see both the patient and MR image on

the same display.

Data source : Christopher Nimsky, Neurosurgery, Erlangen, Germany

So, what else can we do with MRI?

MRI-guided thermotherapy

• Basic premise: Heating tumour tissue in vivo can destroy tumours by “cooking them”

• The basic requirements of the system are:.

a heating device

a method of monitoring the heating in 3-D

a method of controlling the heating based on feedback from the monitoring

Data source : Chrit Moonen, University of Bordeaux, France

fzx

• The MR signal can be made sensitive to temperature, allowing a temperature map to be made over a 3-D region in a matter of seconds.

• The heating source is a focused ultrasound transducer, built into the scanner’s patient table.

Data source : Chrit Moonen, University of Bordeaux, France

MRI-guided thermotherapy

MR image with temperature map overlaid

Colours indicate temperature distribution

Muscle

Water

Transducer

Planned temperature change, with measured values

Data source : Chrit Moonen, University of Bordeaux, France

MRI-guided thermotherapy

MRI-guided surgery: catheter placement

Schematic of homebuilt catheter Realisation of catheter

Data source : Stefan Petersson, Malmö, Sweden

Ø = 2 mm

Data source : Stefan Petersson, Malmö, Sweden

TrueFISP pulse sequence (linear)TR/TE/FA 5.1 ms / 2.6 ms / 70o

Pixelsize 2.0 x 2.0 x 200.0 mm3

Matrix 64x 128Scan time 300 ms / projectionOff-line reconstruction

13C MR guided renal intervention

MRI-guided surgery: catheter placement

Iron-oxidenanoparticles

cell

factor 50 higher iron content

MRI in research: Stem cell imaging

Unlabelled stem cells

Magnetically labelled cellsData source: Peter Jakob, University of Wurzburg, Germany

MRI can image much more than just the brain ...

Data source : Siemens Medical

MRI can image much more than just the brain ...

Data: David Lomas, Addenbrokes HospitalData: www.journey-with-crohns-disease.com

A virtual tour of the human colon ...

Sports injuries ...

Data: www.imaios.com/en/e-Anatomy/Limbs/Knee-MR

Data: Paul Debevec

… and the diagnosis, Mr Beckham ...

Data source: American Radiology Services

Conclusion

• It is money — the human brain is a very valuable thing — which has led to the incredible developments that we see today.

• It is study of basic Physics (electromagnetism, nuclear physics, mechanics) which has discovered the principles.

• The different methods tell us different things.

• There are many different ways of imaging the human body.

The End

Thank you for listening!

Any questions?