Type:
Educational Exhibit
Keywords:
Radiographers, MR physics, MR, Education, Physics, Technical aspects, Education and training, Artifacts
Authors:
V. G. Syrgiamiotis1, V. Maliakas2, T. Thomas1, L. G. Astrakas2, M. Argyropoulou2, A. Ploussi1; 1Athens /GR, 2Ioannina/GR
DOI:
10.1594/ecr2018/C-0027
Findings and procedure details
The degree to which matter interacts with electric and magnetic fields can be described by three parameters:i) Magnetic permeability (μ).(ii) Electrical permeability (e).iii) Electrical conductivity (σ).For weakly conductive dielectric materials such as those of the human body,
the internal RF field is disturbed by a jump current (JC) and displacement current flux (JD) that can be described by Ampère's law with the Maxwell correction ∇ X B = μJC + μJD = μσE + iεεEIn human tissues,
the RF frequencies used in JC and JD are of the same order of magnitude.
As the frequency increases,
the dielectric term (JD) becomes more important.
Even in 7.0T (300 MHz) static field magnetic field tomography,
the conduction / displacement current ratios for fat,
gray matter,
muscles and CSF are about 0.4,
0.6,
0.7 and 1.7 respectively.
To avoid the heterogeneous distribution of RF in the anatomical area under consideration,
many ≥3.0T magnetic resonance imaging systems use the "MultiTransmit" technology,
which catalyzes the prevention of dielectric phenomenon expression as a dielectric shadow
In 3.0T systems without Multi Transmit technology,
dielectric shading effects may occur depending onthe patient,
particularly in body imaging.
To avoid this,
it is recommended to use the body-coordinated CLEAR technique - a B1 special filter designed to eliminate the inconsistencies in the body imaging