Numerical modeling of needle tip artifacts in MR gradient echo imaging

Abstract

Exact determination of needle tip position is obsolete for interventional procedures under control of magnetic resonance imaging (MRI). Exact needle tip navigation is complicated by the paramagnetism of microsurgical instruments: Local magnetic field inhomogeneities are induced resulting in position encoding artifacts and in signal voids in the surrounding of instruments and especially near their tips. The artifacts generated by the susceptibility of the material are not only dependent on the material properties themselves and on the applied MRI sequences and parameters, but also on the geometric shape of the instruments and on the orientation to the static magnetic field in the MR unit. A numerical model based on superposition of induced elementary dipole fields was developed for studying the field distortions near paramagnetic needle tips. The model was validated by comparison with experimental data using field mapping MRI techniques. Comparison between experimental data and numerical simulations revealed good correspondence for the induced field inhomogeneities. Further systematic numerical studies of the field distribution were performed for variable types of concentric and asymmetric tip shapes, for different ratios between tip length and needle diameter, and for different orientations of the needle axis in the external static magnetic field. Based on the computed local inhomogeneities of the magnetic field in the surroundings of the needle tips, signal voids in usual gradient echo images were simulated for a prediction of the artifacts. The practically relevant spatial relation between those artifacts and the hidden tip of the needle was calculated for the different tip shapes and orientations in the external field. As needle tip determination is crucial in interventional procedures, e.g., in taking biopsies, the present model can help to instruct the physician prior to surgical interventions in better estimating the needle tip position for different orientations and needle tip shapes as they appear in interventional procedures. As manufacturing prototypes with subsequent measurements of artifacts in MRI are a costly procedure the presented model may also help to optimize shapes of needle tips and of other parts of MR-compatible instruments and implants with low expense prior to production if some shape parameters can be chosen freely.

Effect of Spatial Distribution of Magnetic Dipoles on Lamor Frequency Distribution and MR Signal Decay – a Numerical Approach Under Static Dephasing Conditions

“…We modified an already published numerical model [26,27] that has been used for computing the field distribution in the presence of an arbitrarily shaped paramagnetic material in a homogeneous external field as based on the superposition of elementary dipoles. The program flow chart is shown in Fig.…”

Magnetic susceptibility effects on the accuracy of MR temperature monitoring by the proton resonance frequency method

“…Field distortions caused by the RF needle were computed using an elementary dipole model (18) (Fig. 2).…”

Accurate Localization of Metal Electrodes Using Magnetic Resonance Imaging

“…Previous studies have been focused on needle sheath, so they set electrode parallel to B0 field because it makes the sheath have minimal artifact (2)(3)(4)(5)(6). However, there is another artifact at a needle tip called blooming artifact (4).…”

“…Metallic materials severely distort the main magnetic field (B0) and this inhomogeneity causes image artifacts. Aspects of susceptibility artifacts have been described well (2) and several groups experimentally and numerically examined the field perturbation and image artifact due to electrode (3)(4)(5), but it is still difficult to find accurate location of metal electrode.…”