Maths and video game graphics help develop live MRI of beating heart
2 Sept 2010
Magnetic resonance imaging taking just one fiftieth of a
second have been recorded by researchers at the Max Planck Institute for
Biophysical Chemistry, Göttingen.
With this breakthrough, the dynamics of organs and joints can be
filmed 'live' for the first time, including the beating heart, the
bending knee, and movements of the eye and jaw.
The new MRI method promises to add important information about
diseases of the joints and the heart. In many cases MRI examinations
may also become easier and more comfortable for patients.
The recording of cross-sectional images of the body by magnetic
resonance imaging (MRI) required several minutes until well into the
1980s, but now only takes a matter of seconds. This was enabled by
the FLASH (fast low angle shot) method developed by Göttingen
scientists Jens Frahm and Axel Haase at the Max Planck Institute for
FLASH revolutionised MRI and was largely responsible for its
establishment as a most important modality in diagnostic imaging.
MRI is completely painless and, moreover, extremely safe. Because
the technique works with magnetic fields and radio waves, patients
are not subjected to any radiation exposure, as is the case with
At present, however, the procedure is still too slow for the
examination of rapidly moving organs and joints. For example, to
trace the movement of the heart, the measurements must be
synchronised with the electrocardiogram (ECG) while the patient
holds the breath. Afterwards, the data from different heart beats
have to be combined into a film.
Real-time MRI of the heart with a measurement
time of 33 milliseconds per image and 30 images per second. The
spatial resolution is 1.5 millimetres in the image plane (section
thickness 8 millimetres). The eight successive images show the
movement of the heart muscle of a healthy subject for a period of
0.264 seconds during a single heartbeat. The images range from the
systolic phase (arrow, top left: contraction of the heart muscle) to
the diastolic phase (arrow, bottom right: relaxation and expansion).
The bright signal in the heart chambers is the blood.
Future prospect: extended diagnostics for diseases
The researchers working with Jens Frahm, Head of the non-profit
Biomedizinische NMR Forschungs Gmb”, succeeded in further
accelerating the image acquisition process. The new MRI method
developed by Jens Frahm, Martin Uecker and Shuo Zhang reduces the
image acquisition time to one fiftieth of a second (20
milliseconds), making it possible to obtain live recordings of
moving joints and organs at so far inaccessible temporal resolution
and without artefacts.
Filming the dynamics of the jaw during opening and closing of the
mouth is just as easy as filming the movements involved in speech
production or the rapid beating of the heart.
“A real-time film of the heart enables us to directly monitor the
pumping of the heart muscle and the resulting blood flow — heartbeat
by heartbeat and without the patient having to hold the breath,”
The scientists believe that the new method could help to improve
the diagnosis of conditions such as coronary heart disease and
myocardial insufficiency. Another application involves minimally
invasive interventions which, thanks to this discovery, could be
carried out in future using MRI instead of X-rays.
“However, as it was the case with FLASH, we must first learn how
to use the real-time MRI possibilities for medical purposes,” says
Frahm. “New challenges therefore also arise for doctors. The
technical progress will have to be ‘translated’ into clinical
protocols that provide optimum responses to the relevant medical
Less is more: acceleration through better image
To achieve the breakthrough to MRI measurement times that only
take very small fractions of a second, several developments had to
be successfully combined with each other.
Whilst still relying on the FLASH technique, the scientists used
a radial encoding of the spatial information which renders the
images insensitive to movements. Mathematics was then required to
further reduce the acquisition times.
“Considerably fewer data are recorded than are usually necessary
for the calculation of an image. We developed a new mathematical
reconstruction technique which enables us to calculate a meaningful
image from data which are, in fact, incomplete,” explains Frahm.
In the most extreme case it is possible to calculate an image of
comparative quality out of just 5% of the data required for a normal
image — which corresponds to a reduction of the measurement time by
a factor of 20. As a result, the Göttingen scientists have
accelerated MRI from the mid 1980s by a factor of 10000.
Although these fast MRI measurements can be easily implemented on
today’s MRI devices, something of a bottleneck exists when it comes
to the availability of sufficiently powerful computers for image
Physicist Martin Uecker explains: “The computational effort
required is gigantic. For example, if we examine the heart for only
a minute in real time, between 2000 and 3000 images arise from a
data volume of two gigabytes.”
Uecker consequently designed the mathematical process in such a
way that it is divided into steps that can be calculated in
parallel. These complex calculations are carried out using fast
graphical processing units that were originally developed for
computer games and three-dimensional visualization.
“Our computer system requires about 30 minutes at present to
process one minute’s worth of film,” says Uecker. Therefore, it will
take a while until MRI systems are equipped with computers that will
enable the immediate calculation and live presentation of the images
during the scan. In order to minimise the time their innovation will
take to reach practical application, the Göttingen researchers are
working in close cooperation with Siemens Healthcare.
1. Martin Uecker, Shuo Zhang, Dirk Voit, Alexander Karaus, Klaus-Dietmar
Merboldt, Jens Frahm. Real-time MRI at a resolution of 20 ms.
NMR in Biomedicine 23. doi:10.1002/nbm.1585 (Online 27 August
2. Shuo Zhang, Martin Uecker, Dirk Voit, Klaus-Dietmar Merboldt,
Jens Frahm. Real-time cardiovascular magnetic resonance at high
temporal resolution: radial FLASH with nonlinear inverse
reconstruction. Journal of Cardiovascular Magnetic Resonance
12, 39 (2010). doi:10.1186/1532-429X-12-39