7 Tesla MRI protocol development

The quality of magnetic resonance imaging (MRI) has been improved considerably
since it was first applied in the medical arena. A major contributor to this
development is the surge for an increase in magnetic field strength: two years
ago 1.5 Tesla was still the clinical standard, now 3.0 Tesla has shown much
higher quality especially for neuro-imaging. A stronger magnetic field leads to
higher quality images and enables new kind of measurements not feasible at low
or medium field strength MRI scanners. At the moment a 7.0 Tesla MRI scanner is
being installed at the LUMC. This brings the LUMC the potential to take the
quality of MR images to the next level. However, the technology of the 7.0
Tesla is not fully developed yet and therefore the 7.0 Tesla scanner should be
regarded as a research scanner. Most scan techniques need further development
before they can successfully be employed in clinical research or patient care.
It is essential to be able to scan normal volunteers to enable this
optimization. Techniques that will be optimized are:
- Anatomical imaging (T1,T2, PG, angiography, high resolution imaging, etc)
- Functional imaging (brain activation, perfusion, diffusion)
- Metabolic status (MR spectroscopy)
Whereas the main focus will be brain imaging, it is also anticipated that
research will be performed on the knee, ankle, heart, and carotid arteries.

To further optimize 7.0 Tesla MRI techniques and to develop new MRI techniques
that will enable state-of-the-art clinical and cognitive research leading to
improved patient care. Whereas some applications of 7.0 Tesla MRI already show
improvements compared to clinical scanners, the potential of ultra-high field
MRI is much higher. Typical applications that will be studied are: ultra high
resolution anatomical imaging (MR microscopy), hemodynamic imaging,
susceptibility weighted imaging, quantitative MRI techniques, MR spectroscopy,
fMRI and DTI techniques. Since the underlying technical problems are comparable
for all these techniques, the development of these techniques will be performed
parallel to each other. From the technical viewpoint, the goals of this study
will be to develop imaging pulses insensitive to RF and magnetic field
inhomogeneities, optimization of imaging parameters, design of optimal shimming
techniques, study interactions between tissue and RF, limit artifacts from
physiological processes, and to develop more homogeneous RF distribution.

Studies will be designed like normal MR physics research. Several stages can be
identified:
1. Characterization
Measuring basic tissue properties that determine MRI contrast, like T1, T2* and
proton density for the region of interest. Secondly, this stage employs
state-of-the-art imaging as based on literature to identify current quality.
2. Assessment of quality and identification of potential technical problems
Image quality is assessed during consensus meetings by radiologists and MR
physicists and if image quality is deemed insufficient, hypotheses are
generated about the origin of the artifacts or limited signal-to-noise ratio.
3. Improvements in acquisition-parameters or pulse sequence
Most artifacts in MRI can be resolved by means of tuning of acquisition
parameters. Based on the hypotheses of the origin of the artifacts,
optimization of acquisition parameters is performed in vivo by systematically
changing the MR parameters involved. Such optimization procedures should be
performed in several subjects to obtain robust settings that are subject
independent. Whenever tuning of acquisition parameters does not yield enough
improvement, redesign of the pulse sequence should be performed.
After each step in the optimization process, one should go back to step 2 and
conduct a quality survey with a radiologist.
4. Evaluation study
Finally, a newly developed sequence should be subject of a small pilot study
and compared to the starting sequence, to a comparable sequence at 3.0 Tesla,
to a physiological test (e.g. detection of brain activity) or literature
values.

In 1997 an 8 Tesla MRI scanner was installed in Ohio State University. Early
research focussed on the safety of ultra-high field MRI. They especially
focussed on cardiovascular effects (first in pigs, later on humans) and on more
subjective signs of comfort. Literature shows furthermore studies on cell
reproduction, cell function, thrombolysis, nerve function, cardiovascular
effects, body temperature change, magnetophosphenes, and cell alignment. None
of these studies show conclusive evidence for irreversible, hazardous side
effects to acute, short-term and long term exposure to a static magnetic field
(see a recent publication by the World Health Organization, ISBN 92 4 157232
9). We refer to the project proposal for a more detailed description of the
safety aspects of ultra-high field MRI. Post-exam interviews of the first 100
volunteers showed that approximately 30-40% volunteers experienced some
dizziness when positioned inside the scanner. These effects last only shortly.