Highly localized positive contrast of small paramagnetic objects using 3D center‐out radial sampling with off‐resonance reception

Abstract

In this article, we present a 3D imaging technique, applying center-out RAdial Sampling with Off-Resonance reception, to accurately depict and localize small paramagnetic objects with high positive contrast while suppressing long T 2 * components. The center-out RAdial Sampling with Off-Resonance reception imaging technique is a fully frequency-encoded 3D ultrashort echo time acquisition method, which uses a large excitation bandwidth and off-resonance reception. By manually introducing an offset, Df 0 , to the central reception frequency (f 0 ), the typical radial signal pileup observed in 3D center-out sampling caused by a dipolar magnetic field disturbance can be shifted toward the source of the field disturbance, resulting in a hyperintense signal at the magnetic center of the small paramagnetic object. This was demonstrated both theoretically and using 1D time domain simulations. Experimental verification was done in a gel phantom and in inhomogeneous porcine tissue containing various objects with very different geometry and susceptibility, namely, subvoxel stainless steel spheres, a puncture needle, and paramagnetic brachytherapy seeds. In all cases, centerout RAdial Sampling with Off-Resonance reception was shown to generate high positive contrast exactly at the location of the paramagnetic object, as was confirmed by X-ray computed tomography. Magn Reson Med 65:146-156,

Registration free automatic identification of gold fiducial markers in MRI target delineation images for prostate radiotherapy

“…37 Other means of improving the detection accuracy of GFM could be by magnetic susceptibility mapping or by providing positive contrast in the vicinity of the marker using off-resonance signals. [29][30][31][32]47 As MEGRE is a generic and available sequence on multiple vendor platforms this should be further explored for both automatic and manual GFM identification.…”

“…27,28 The use of more exotic sequences to even enable a positive contrast of the metal has been developed. [29][30][31][32] The use of multiple dedicated MRI sequences for prostate RTP is common. The proposed MRI only workflows for EBRT of prostate present in the literature all depend on separate MRI sequences for GFM identification, target delineation, and sCT generation.…”

Iron Oxide Nanoparticles Imaging Tracking by MR Advanced Techniques: Dual-Contrast Approaches

“…orthopedic MR imaging as well as MR-PET attenuation correction. A 3D imaging technique (Seevinck, 2011) from the group in University Medical Center Utrecht, The Netherlands, applying center-out RAdial Sampling with Off-Resonance reception (co-RASOR) by the using of UTE technique (for the minimization of subvoxel dephasing at locations with high magnetic field gradients in the vicinity of the magnetized objects), and a hard, nonselective RF block pulse and radial sampling of k-space, was also presented to depict and accurately localize small paramagnetic objects with high positive contrast but ideally without background signal.…”

Effect of pulse sequence parameter selection on signal strength in positive‐contrast MRI markers for MRI‐based prostate postimplant assessment

“…By taking advantage of the seeds' high magnetic susceptibility, recent efforts in seed visualization on MRI images include the use of an inversion-recovery with ONresonant water suppression (IRON) prepulse to spectrally select off-resonant protons, 20 the use of ultrashort-TE sequences to preserve signal before rapid transverse dephasing, 21 the postprocessing use of homodyne high-pass filters of various sizes, 22,23 the use of susceptibility gradient mapping using the original resolution (SUMO) by filtering in k-space, 24 the use of a kernel deconvolution algorithm with regularized L 1 minimization 25 (the dipole kernel 26 and a nominal seed kernel 27 have been explored), as well as the use of centerout radial sampling with off-resonance reception (co-RASOR) that moves the radial signal pile-up to the seed's center (using multiple acquisitions 28 and only a single acquisition 29 ). However, imaging susceptibility may be inconsistent across MRI slices, difficult to locate accurately, and more challenging in heterogeneous tissue.…”

“…23 Ultimately, MRI-only postimplant dosimetry allows for superior soft tissue contouring, no extraneous radiation dose, image-acquisition flexibility, and possible integration of functional imaging. Regardless of whether MRI-only postimplant dosimetry is achieved using markers 6 or the other solutions [18][19][20][21][22][23][24][25][26][27][28][29] described above, the next step is to explore the impact of MRI soft tissue contrast on the accuracy and precision of anatomical contouring on patient images, so as to examine the correlation of dose deposited in the prostate and normal tissue to tumor control and normal tissue complications. Ultimately, in future patient studies comparing MRI-only to MRI-CT fusion-based postimplant dosimetry, we need to evaluate the improvements in the accuracy and precision of contouring prostate and organs at risk, the accuracy and precision of seed localization, as well as the subsequent accuracy and precision of dose volume histogram parameters, apart from accounting from fusion uncertainties.…”