Fluke Biomedical 76-903 - Manual (Page 5)

Introduction
Introduction
1
1-1
Section 1
Introduction
1.1 Introduction
This phantom is designed for comprehensive evaluation of critical imaging parameters of magnetic
resonance imaging (MRI) in a time efficient manner. Particular attention was paid to obtaining all the
necessary image quality information with a minimum number of imaging sequences. It is designed to
study parameters unique to multi-slice two-dimensional and three-dimensional Fourier imaging.
The overall dimensions of the phantom adjust so that it can be positioned in each of the three major
imaging planes: axial, coronal and sagittal.
The phantom can be used for the measurement of absolute values for calibration purposes. However, its
design is optimized for time efficient daily quality assurance.
The performance parameters that can be evaluated using the phantom include: slice orientation, slice
thickness, interslice distance, aspect ratio, magnetic field uniformity, radio-frequency signal uniformity,
spatial resolution, T
1
and T
2
values, and modulation transfer function. The phantom can also be used to
evaluate such parameters as resonant frequency, radio frequency power setting, radio frequency
quadrature setting, magnetic field gradient calibration, slice off-set parameters, image off-set, and other
image artifacts peculiar to MRI.
1.2 Orientation Imaging Method
In a two-dimensional Fourier transform (2DFT) imaging of MRI, the data is collected in two orthogonal
directions, i.e., encoding and readout.
In some imaging sequences, the spatial resolution may be different in the two directions. The star pattern
is designed to study such asymmetric resolution as well as qualitative modulation transfer function (MTF)
in MR images. For this reason, it is important to properly orient the star pattern. Note four lines or dots on
the wall of the phantom.
Place the phantom in the imaging system SO that one is in either the phase encoding or frequency
readout direction.
1.3 Choosing Echo Time
Any clinical multi-slice imaging sequence can be used. Often, however, the imaging sequences with the
shortest echo time (TE), largest number of slices possible within the pulse repetition time (TR), and single
excitation (no averaging) will demonstrate the performance of an imaging system under one of the most
demanding situations. For a daily QA program, it is important to record all the important imaging
parameters. An example of such a table of imaging parameters can be found in Table 1-1.