Purpose
Artifacts often change the information included in medical images. They are therefore to be studied thoroughly to prevent the images to be misinterpreted by the examining radiologist. As an example, needle tip artefacts are critical for correct localization of the needle tip during MR guided surgical procedures.
Methods and Materials
MR imaging was performed for a set of 7 Nitinol needles with different tip shape, 4 of them conical with angles 0, 1.85, 3.7 and 9.0 and 3 of them flat with angles 16.5, 7.2 and 3.7 (see Figs. 1 a-d andFigs. 1 e-g), at a 0.2 T Siemens Scanner (MAGNETOM-Concerto) and studied the image artifacts for GRE, TE and TSE sequences for different needle orientations with respect to the outer field B0 in a GdDTPA-H2O Phantom (0.66 ml GdDTPA per liter H2O) for different...
Results
We found that SE produces the smallest MR image artefacts, TSE produces slightly more artefacts and GRE produces the most image artefacts. This behaviour is theoretically well understood and reported in the literature. Within SE and TSE, the overall error is larger for frequency encoding perpendicular to the needle, where the needle tip position determination is better than for frequency encoding parallel to the needle (cf. Fig. 2).Sharpening the tip leads in a narrowing of the artefact which, especially within SE techniques, can lead to...
Conclusion
Needle tip artefacts show several specifics as follows:Needle tip shapes show a continuous reduction of diameter with reducing the physical diameter of the needle tip. The blooming ball artefact can only be guessed for needle orientation parallel B0 due to the resolution of the imaging sequence to be small compared to the needle diameter.The artefact grows with increasing TE within GRE due to intravoxel dephasing. On the other side, the artefact does not to depend on TE within SE and TSE due to the rephasing...
References
[1]Bernd Mller-Bierl et al., 'Measurement and Modeling of Susceptibility Artefacts using a numerical algorithm and the MAGSUS Sequence', Poster ECR 2003
Personal Information
Jens Brieger, PhDSara LozanoBernd Mller-Bierl, PhDGnter SteidleFritz Schick, MD, PhDSection of Experimental Radiology, University Hospital of Tbingen, Germany