Abstract
The consistency of off-axis MRI with non-Cartesian sequences across a large number of scanners is highly variable. Improper timing alignment of the gradient fields, data acquisition system, and real-time frequency demodulation reference signal, which are necessary for off-axis imaging, is an important source of this variability. In addition, eddy currents and anisotropic gradient delays cause deviations in k-space trajectories that in turn make the demodulation reference signals inaccurate. A method is presented to quickly measure the timing error in the frequency demodulation reference signal and separate it from anisotropic gradient delays. k-Space deviations, as measured with a previous gradient calibration technique, are shown to be a second source of demodulation phase errors that degrade image quality. Using the timing delay and k-space deviations, a retrospective phase correction is applied to each k-space sample before the data are regridded during reconstruction. The timing delays of four MR scanners were measured to be 4.2-7.5 μs below the manufacturer's suggested delay. Significant degradation in 3D radial (3D projection reconstruction (PR)) knee and breast images are retrospectively corrected while a partial prospective correction is applied for spiral imaging. The method allows for more consistent performance of non-Cartesian sequences across multiple scanners without operator intervention.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 206-211 |
| Number of pages | 6 |
| Journal | Magnetic Resonance in Medicine |
| Volume | 57 |
| Issue number | 1 |
| DOIs | |
| State | Published - Jan 1 2007 |
| Externally published | Yes |
Fingerprint
Keywords
- k-space deviation
- Non-Cartesian
- Off-axis
- Real-time frequency demodulation
- Timing discrepancy
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging
Cite this
Consistent non-Cartesian off-axis MRI quality : Calibrating and removing multiple sources of demodulation phase errors. / Jung, Youngkyoo; Jashnani, Yogesh; Kijowski, Richard; Block, Walter F.
In: Magnetic Resonance in Medicine, Vol. 57, No. 1, 01.01.2007, p. 206-211.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Consistent non-Cartesian off-axis MRI quality
T2 - Calibrating and removing multiple sources of demodulation phase errors
AU - Jung, Youngkyoo
AU - Jashnani, Yogesh
AU - Kijowski, Richard
AU - Block, Walter F.
PY - 2007/1/1
Y1 - 2007/1/1
N2 - The consistency of off-axis MRI with non-Cartesian sequences across a large number of scanners is highly variable. Improper timing alignment of the gradient fields, data acquisition system, and real-time frequency demodulation reference signal, which are necessary for off-axis imaging, is an important source of this variability. In addition, eddy currents and anisotropic gradient delays cause deviations in k-space trajectories that in turn make the demodulation reference signals inaccurate. A method is presented to quickly measure the timing error in the frequency demodulation reference signal and separate it from anisotropic gradient delays. k-Space deviations, as measured with a previous gradient calibration technique, are shown to be a second source of demodulation phase errors that degrade image quality. Using the timing delay and k-space deviations, a retrospective phase correction is applied to each k-space sample before the data are regridded during reconstruction. The timing delays of four MR scanners were measured to be 4.2-7.5 μs below the manufacturer's suggested delay. Significant degradation in 3D radial (3D projection reconstruction (PR)) knee and breast images are retrospectively corrected while a partial prospective correction is applied for spiral imaging. The method allows for more consistent performance of non-Cartesian sequences across multiple scanners without operator intervention.
AB - The consistency of off-axis MRI with non-Cartesian sequences across a large number of scanners is highly variable. Improper timing alignment of the gradient fields, data acquisition system, and real-time frequency demodulation reference signal, which are necessary for off-axis imaging, is an important source of this variability. In addition, eddy currents and anisotropic gradient delays cause deviations in k-space trajectories that in turn make the demodulation reference signals inaccurate. A method is presented to quickly measure the timing error in the frequency demodulation reference signal and separate it from anisotropic gradient delays. k-Space deviations, as measured with a previous gradient calibration technique, are shown to be a second source of demodulation phase errors that degrade image quality. Using the timing delay and k-space deviations, a retrospective phase correction is applied to each k-space sample before the data are regridded during reconstruction. The timing delays of four MR scanners were measured to be 4.2-7.5 μs below the manufacturer's suggested delay. Significant degradation in 3D radial (3D projection reconstruction (PR)) knee and breast images are retrospectively corrected while a partial prospective correction is applied for spiral imaging. The method allows for more consistent performance of non-Cartesian sequences across multiple scanners without operator intervention.
KW - k-space deviation
KW - Non-Cartesian
KW - Off-axis
KW - Real-time frequency demodulation
KW - Timing discrepancy
UR - http://www.scopus.com/inward/record.url?scp=33846101573&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=33846101573&partnerID=8YFLogxK
U2 - 10.1002/mrm.21092
DO - 10.1002/mrm.21092
M3 - Article
C2 - 17139618
AN - SCOPUS:33846101573
VL - 57
SP - 206
EP - 211
JO - Magnetic Resonance in Medicine
JF - Magnetic Resonance in Medicine
SN - 0740-3194
IS - 1
ER -