MRI-based prostate brachytherapy seed localization

Abstract

A magnetic resonance imaging (MRI) pulse sequence and a corresponding image processing algorithm to localize prostate brachytherapy seeds during or after therapy are presented. InversionRecovery with ON-resonant water suppression (IRON) is an MRI methodology that generates positive contrast in regions of magnetic field susceptibility, as created by prostate brachytherapy seeds. Phantoms comprising of several materials found in brachytherapy seeds were created to assess the usability of the IRON pulse sequence for imaging seeds. Resulting images show that seed materials are clearly visible with high contrast using IRON, agreeing with theoretical predictions. A seed localization algorithm to process IRON images demonstrates the potential of this imaging technique for seed localization and dosimetry.

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.…”

Pulse sequence considerations for simulation and postimplant dosimetry of prostate brachytherapy

“…It is possible that additional optimization of the MR pulse sequences, concentration of the seed markers, or different types of markers will further improve the signals in the different types of images (such as CISS images), providing even better localization of the seed markers and visualization of the anatomy. Other pulse sequences (39,40) under development may also be able to provide accurate and direct localization of the seeds without relying on the signal-generating seed markers.…”

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.…”