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Title: SU-G-IeP1-01: A Novel MRI Post-Processing Algorithm for Visualization of the Prostate LDR Brachytherapy Seeds and Calcifications Based On B0 Field Inhomogeneity Correction and Hough Transform

Abstract

Purpose: This study aims at developing an MRI-only workflow for post-implant dosimetry of the prostate LDR brachytherapy seeds. The specific goal here is to develop a post-processing algorithm to produce positive contrast for the seeds and prostatic calcifications and differentiate between them on MR images. Methods: An agar-based phantom incorporating four dummy seeds (I-125) and five calcifications of different sizes (from sheep cortical bone) was constructed. Seeds were placed arbitrarily in the coronal plane. The phantom was scanned with 3T Philips Achieva MR scanner using an 8-channel head coil array. Multi-echo turbo spin echo (ME-TSE) and multi-echo gradient recalled echo (ME-GRE) sequences were acquired. Due to minimal susceptibility artifacts around seeds, ME-GRE sequence (flip angle=15; TR/TE=20/2.3/2.3; resolution=0.7×0.7×2mm3) was further processed.The induced field inhomogeneity due to the presence of titaniumencapsulated seeds was corrected using a B0 field map. B0 map was calculated using the ME-GRE sequence by calculating the phase difference at two different echo times. Initially, the product of the first echo and B0 map was calculated. The features corresponding to the seeds were then extracted in three steps: 1) the edge pixels were isolated using “Prewitt” operator; 2) the Hough transform was employed to detect ellipses approximately matching themore » dimensions of the seeds and 3) at the position and orientation of the detected ellipses an ellipse was drawn on the B0-corrected image. Results: The proposed B0-correction process produced positive contrast for the seeds and calcifications. The Hough transform based on Prewitt edge operator successfully identified all the seeds according to their ellipsoidal shape and dimensions in the edge image. Conclusion: The proposed post-processing algorithm successfully visualized the seeds and calcifications with positive contrast and differentiates between them according to their shapes. Further assessments on more realistic phantoms and patient study are required to validate the outcome.« less

Authors:
 [1];  [2]; ;  [3];  [2];  [3];  [2];  [4];  [2];  [1];  [1];  [2];  [2];  [2]
  1. Reyrson University, Toronto, Ontario (Canada)
  2. (Canada)
  3. Sunnybrook Research Institute, Toronto, Ontario (Canada)
  4. Sunnybrook Health Sciences Centre, Toronto, Ontario (Canada)
Publication Date:
OSTI Identifier:
22649319
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 43; Journal Issue: 6; Other Information: (c) 2016 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES; 61 RADIATION PROTECTION AND DOSIMETRY; ALGORITHMS; BRACHYTHERAPY; CORRECTIONS; IMAGES; IODINE 125; NMR IMAGING; PHANTOMS; PROSTATE; RADIATION SOURCE IMPLANTS; SPIN ECHO

Citation Formats

Nosrati, R, Sunnybrook Health Sciences Centre, Toronto, Ontario, Soliman, A, Owrangi, A, Sunnybrook Health Sciences Centre, Toronto, Ontario, Ghugre, N, University of Toronto, Toronto, ON, Morton, G, University of Toronto, Toronto, ON, Pejovic-Milic, A, Song, W, Sunnybrook Research Institute, Toronto, Ontario, Sunnybrook Health Sciences Centre, Toronto, Ontario, and University of Toronto, Toronto, ON. SU-G-IeP1-01: A Novel MRI Post-Processing Algorithm for Visualization of the Prostate LDR Brachytherapy Seeds and Calcifications Based On B0 Field Inhomogeneity Correction and Hough Transform. United States: N. p., 2016. Web. doi:10.1118/1.4956961.
Nosrati, R, Sunnybrook Health Sciences Centre, Toronto, Ontario, Soliman, A, Owrangi, A, Sunnybrook Health Sciences Centre, Toronto, Ontario, Ghugre, N, University of Toronto, Toronto, ON, Morton, G, University of Toronto, Toronto, ON, Pejovic-Milic, A, Song, W, Sunnybrook Research Institute, Toronto, Ontario, Sunnybrook Health Sciences Centre, Toronto, Ontario, & University of Toronto, Toronto, ON. SU-G-IeP1-01: A Novel MRI Post-Processing Algorithm for Visualization of the Prostate LDR Brachytherapy Seeds and Calcifications Based On B0 Field Inhomogeneity Correction and Hough Transform. United States. doi:10.1118/1.4956961.
Nosrati, R, Sunnybrook Health Sciences Centre, Toronto, Ontario, Soliman, A, Owrangi, A, Sunnybrook Health Sciences Centre, Toronto, Ontario, Ghugre, N, University of Toronto, Toronto, ON, Morton, G, University of Toronto, Toronto, ON, Pejovic-Milic, A, Song, W, Sunnybrook Research Institute, Toronto, Ontario, Sunnybrook Health Sciences Centre, Toronto, Ontario, and University of Toronto, Toronto, ON. Wed . "SU-G-IeP1-01: A Novel MRI Post-Processing Algorithm for Visualization of the Prostate LDR Brachytherapy Seeds and Calcifications Based On B0 Field Inhomogeneity Correction and Hough Transform". United States. doi:10.1118/1.4956961.
@article{osti_22649319,
title = {SU-G-IeP1-01: A Novel MRI Post-Processing Algorithm for Visualization of the Prostate LDR Brachytherapy Seeds and Calcifications Based On B0 Field Inhomogeneity Correction and Hough Transform},
author = {Nosrati, R and Sunnybrook Health Sciences Centre, Toronto, Ontario and Soliman, A and Owrangi, A and Sunnybrook Health Sciences Centre, Toronto, Ontario and Ghugre, N and University of Toronto, Toronto, ON and Morton, G and University of Toronto, Toronto, ON and Pejovic-Milic, A and Song, W and Sunnybrook Research Institute, Toronto, Ontario and Sunnybrook Health Sciences Centre, Toronto, Ontario and University of Toronto, Toronto, ON},
abstractNote = {Purpose: This study aims at developing an MRI-only workflow for post-implant dosimetry of the prostate LDR brachytherapy seeds. The specific goal here is to develop a post-processing algorithm to produce positive contrast for the seeds and prostatic calcifications and differentiate between them on MR images. Methods: An agar-based phantom incorporating four dummy seeds (I-125) and five calcifications of different sizes (from sheep cortical bone) was constructed. Seeds were placed arbitrarily in the coronal plane. The phantom was scanned with 3T Philips Achieva MR scanner using an 8-channel head coil array. Multi-echo turbo spin echo (ME-TSE) and multi-echo gradient recalled echo (ME-GRE) sequences were acquired. Due to minimal susceptibility artifacts around seeds, ME-GRE sequence (flip angle=15; TR/TE=20/2.3/2.3; resolution=0.7×0.7×2mm3) was further processed.The induced field inhomogeneity due to the presence of titaniumencapsulated seeds was corrected using a B0 field map. B0 map was calculated using the ME-GRE sequence by calculating the phase difference at two different echo times. Initially, the product of the first echo and B0 map was calculated. The features corresponding to the seeds were then extracted in three steps: 1) the edge pixels were isolated using “Prewitt” operator; 2) the Hough transform was employed to detect ellipses approximately matching the dimensions of the seeds and 3) at the position and orientation of the detected ellipses an ellipse was drawn on the B0-corrected image. Results: The proposed B0-correction process produced positive contrast for the seeds and calcifications. The Hough transform based on Prewitt edge operator successfully identified all the seeds according to their ellipsoidal shape and dimensions in the edge image. Conclusion: The proposed post-processing algorithm successfully visualized the seeds and calcifications with positive contrast and differentiates between them according to their shapes. Further assessments on more realistic phantoms and patient study are required to validate the outcome.},
doi = {10.1118/1.4956961},
journal = {Medical Physics},
number = 6,
volume = 43,
place = {United States},
year = {Wed Jun 15 00:00:00 EDT 2016},
month = {Wed Jun 15 00:00:00 EDT 2016}
}
  • Purpose: To propose a new method that provides a positive contrast visualization of the prostate brachytherapy seeds using the phase information from MR images. Additionally, the feasibility of using the processed phase information to distinguish seeds from calcifications is explored. Methods: A gel phantom was constructed using 2% agar dissolved in 1 L of distilled water. Contrast agents were added to adjust the relaxation times. Four iodine-125 (Eckert & Ziegler SML86999) dummy seeds were placed at different orientations with respect to the main magnetic field (B0). Calcifications were obtained from a sheep femur cortical bone due to its close similaritymore » to human bone tissue composition. Five samples of calcifications were shaped into different dimensions with lengths ranging between 1.2 – 6.1 mm.MR imaging was performed on a 3T Philips Achieva using an 8-channel head coil. Eight images were acquired at eight echo-times using a multi-gradient echo sequence. Spatial resolution was 0.7 × 0.7 × 2 mm, TR/TE/dTE = 20.0/2.3/2.3 ms and BW = 541 Hz/pixel. Complex images were acquired and fed into a two-step processing pipeline: the first includes phase unwrapping and background phase removal using Laplacian operator (Wei et al. 2013). The second step applies a specific phase mask on the resulting tissue phase from the first step to provide the desired positive contrast of the seeds and to, potentially, differentiate them from the calcifications. Results: The phase-processing was performed in less than 30 seconds. The proposed method has successfully resulted in a positive contrast of the brachytherapy seeds. Additionally, the final processed phase image showed difference between the appearance of seeds and calcifications. However, the shape of the seeds was slightly distorted compared to the original dimensions. Conclusion: It is feasible to provide a positive contrast of the seeds from MR images using Laplacian operator-based phase processing.« less
  • Purpose: To identify and analyze the appearance of calcifications and brachytherapy seeds on magnitude and phase MRI images and to investigate whether they can be distinguished from each other on corrected phase images for application to prostate and breast low dose rate (LDR) implant dosimetry. Methods: An agar-based gel phantom containing two LDR brachytherapy seeds (Advantage Pd-103, IsoAid, 0.8mm diameter, 4.5mm length) and two spherical calcifications (large: 7mm diameter and small: 4mm diameter) was constructed and imaged on a 3T Philips MR scanner using a 16-channel head coil and a susceptibility weighted imaging (SWI) sequence (2mm slices, 320mm FOV, TR/more » TE= 26.5/5.3ms, 15 degree flip angle). The phase images were unwrapped and corrected using a 32×32, 2D Hanning high pass filter to remove background phase noise. Appearance of the seeds and calcifications was assessed visually and quantitatively using Osirix (http://www.osirix-viewer.com/). Results: As expected, calcifications and brachytherapy seeds appeared dark (hypointense) relative to the surrounding gel on the magnitude MRI images. The diameter of each seed without the surrounding artifact was measured to be 0.1 cm on the magnitude image, while diameters of 0.79 and 0.37 cm were measured for the larger and smaller calcifications, respectively. On the corrected phase images, the brachytherapy seeds and the calcifications appeared bright (hyperintense). The diameter of the seeds was larger on the phase images (0.17 cm) likely due to the dipole effect. Conclusion: MRI has the best soft tissue contrast for accurate organ delineation leading to most accurate implant dosimetry. This work demonstrated that phase images can potentially be useful in identifying brachytherapy seeds and calcifications in the prostate and breast due to their bright appearance, which helps in their visualization and quantification for accurate dosimetry using MR-only. Future work includes optimizing phase filters to best identify and delineate seeds and calcifications.« less
  • Purpose: To evaluate the accuracy of interstitial catheter reconstruction with 0.35T MRI images for MRI-based HDR prostate brachytherapy. Methods: Recently, a real-time MRI-guided radiotherapy system combining a 0.35T MRI system and three cobalt 60 heads (MRIdian System, ViewRay, Cleveland, OH, USA) was installed in our department. A TrueFISP sequence for MRI acquisition at lower field on Viewray was chosen due to its fast speed and high signal-to-noise efficiency. Interstitial FlexiGuide needles were implanted into a tissue equivalent ultrasound prostate phantom (CIRS, Norfolk, Virginia, USA). After an initial 15s pilot MRI to confirm the location of the phantom, planning MRI wasmore » acquired with a 172s TrueFISP sequence. The pulse sequence parameters included: flip angle = 60 degree, echo time (TE) =1.45 ms, repetition time (TR) = 3.37 ms, slice thickness = 1.5 mm, field of view (FOV) =500 × 450mm. For a reference image, a CT scan was followed. The CT and MR scans were then fused with the MIM Maestro (MIM software Inc., Cleveland, OH, USA) and sent to the Oncentra Brachy planning system (Elekta, Veenendaal, Netherlands). Automatic catheter reconstruction using CT and MR image intensities followed by manual reconstruction was used to digitize catheters. The accuracy of catheter reconstruction was evaluated from the catheter tip location. Results: The average difference between the catheter tip locations reconstructed from the CT and MR in the transverse, anteroposterior, and craniocaudal directions was −0.1 ± 0.1 mm (left), 0.2 ± 0.2 mm (anterior), and −2.3 ± 0.5 mm (cranio). The average distance in 3D was 2.3 mm ± 0.5 mm. Conclusion: This feasibility study proved that interstitial catheters can be reconstructed with 0.35T MRI images. For more accurate catheter reconstruction which can affect final dose distribution, a systematic shift should be applied to the MR based catheter reconstruction in HDR prostate brachytherapy.« less
  • Purpose: To assess image quality and artifact extent of a novel direction modulated brachytherapy (DMBT) tandem applicator on a 3T MRI using various clinical imaging sequences. Methods: The tandem applicator is composed of a tungsten alloy with 6 peripheral grooves covered with a PEEK tip. An MR-compatible phantom with similar dimensions to the female pelvis was manufactured. To visually assess the spatial shift of the applicator’s tip, a mountable radial-fiducial with 4 plastic rods, each of 3mm diameter, was designed to tightly fit on the applicator. The rods are separated by 16 mm and mounted at 90-degree relative to onemore » another. The pelvis phantom was filled with a solution of MnCl2 to mimic T2 relaxation time of the cervix (60-80 ms at 3T).Imaging was performed on a 3T Philips Achieva using a 16-channel Torso coil array. Four MR sequences were tested: T2-weighted fast spin-echo (T2w-FSE), proton density weighted FSE (PDw-FSE), T1-weighted FSE (T1w-FSE) and T1 weighted spoiled gradient echo (T1w-GE). The spatial resolution was kept the same between all sequences: 0.6 × 0.6 × 3 mm{sup 3} with no slice gaps. Para-sagittal images were acquired with the applicator fixed at a 30-degree angle anterior to the B0- field to mimic clinical settings. Results: Minimal artifacts were observed on T2w-FSE, PDw-FSE and T1-FSE, while significant artifacts were seen on T1w-GE images. Artifacts induced in all 3 FSE sequences did not hinder accurate localisation of the tip and the applicator boundaries. The drift of the applicator’s centreline from the radial fiducials was measured and found to be < 1 mm for the 3 FSE sequences. Conclusion: The tungsten–based DMBT applicator can be potentially used on 3T with various clinical sequences without inducing significant artifacts. Further validation on patients as well as the evaluation of relative SNR among the different sequences is required.« less
  • Purpose: To propose a novel framework for accurate model-based dose calculations using only MR images for LDR prostate and breast seed implant brachytherapy. Methods: Model-based dose calculation methodologies recommended by TG-186 require further knowledge about specific tissue composition, which is challenging with MRI. However, relying on MRI-only for implant dosimetry would reduce the soft tissue delineation uncertainty, costs, and uncertainties associated with multi-modality registration and fusion processes. We propose a novel framework to address this problem using quantitative MRI acquisitions and reconstruction techniques. The framework includes three steps: (1) Identify the locations of seeds(2) Identify the presence (or absence) ofmore » calcification(s)(3) Quantify the water and fat content in the underlying tissueSteps (1) and (2) consider the sources that limit patient dosimetry, particularly the inter-seed attenuation and the calcified regions; while step (3) targets the quantification of the tissue composition to consider the heterogeneities in the medium. Our preliminary work has shown that the seeds and the calcifications can be identified with MRI using both the magnitude and the phase images. By employing susceptibility-weighted imaging with specific post-processing techniques, the phase images can be further explored to distinguish the seeds from the calcifications. Absolute quantification of tissue, water, and fat content is feasible and was previously demonstrated in phantoms and in-vivo applications, particularly for brain diseases. The approach relies on the proportionality of the MR signal to the number of protons in an image volume. By employing appropriate correction algorithms for T1 - and T2*-related biases, B1 transmit and receive field inhomogeneities, absolute water/fat content can be determined. Results: By considering calcification and interseed attenuation, and through the knowledge of water and fat mass density, accurate patient-specific implant dosimetry can be achieved with MRI-only. Conclusion: The proposed framework showed that model-based dose calculation is feasible using MRI-only state-of-the-art techniques.« less