Visibility Of Markers Research Articles

Use of detachable coils without the need of a double marker microcatheter: Technical note

When using detachable coils for cerebral aneurysm embolization, it is necessary to place a microcatheter with radiopaque markers at 2 sites (tip and 3 cm proximal from the tip) in most cases. Detachable coils that can be positioned independently from the proximal marker may facilitate new applications utilizing their characteristics. Herein, we report 2 cases that were treated with new applications. Detachable coils that function to electrically detect the moment they come out of the microcatheter were used. In one patient with a large aneurysm with an irregular shape, coil embolization was applied by advancing the catheter more than 3 cm from the aneurysm neck to the caudally protruded compartment near the proximal end of the neck, which was difficult to reach with the coil. In the other patient with cerebral arteriovenous malformation (AVM), microcatheters for AVM without a proximal marker were used for coil embolization before Onyx injection: Coil embolization was applied through one microcatheter to a site more proximal than the tip of the other microcatheter, followed by Onyx injection through the distal catheter, by which the nidus was continuously penetrated from the initiation of injection, obtaining an effect similar to that of the plug and push technique. Through the use of detachable coils, which are not dependent on the visibility of the proximal marker, the limitation of catheter positioning is reduced and the applicable types of catheter increase, which may facilitate to enable its use for new clinical indications.

Tailoring four-dimensional cone-beam CT acquisition settings for fiducial marker-based image guidance in radiation therapy.

Use of four-dimensional cone-beam CT (4D-CBCT) and fiducial markers for image guidance during radiation therapy (RT) of mobile tumors is challenging due to the trade-off among image quality, imaging dose, and scanning time. This study aimed to investigate different 4D-CBCT acquisition settings for good visibility of fiducial markers in 4D-CBCT. Using these 4D-CBCTs, the feasibility of marker-based 4D registration for RT setup verification and manual respiration-induced motion quantification was investigated. For this, we applied a dynamic phantom with three different breathing motion amplitudes and included two patients with implanted markers. Irrespective of the motion amplitude, for a medium field of view (FOV), marker visibility was improved by reducing the imaging dose per projection and increasing the number of projection images; however, the scanning time was 4 to 8min. For a small FOV, the total imaging dose and the scanning time were reduced (62.5% of the dose using a medium FOV, 2.5min) without losing marker visibility. However, the body contour could be missing for a small FOV, which is not preferred in RT. The marker-based 4D setup verification was feasible for both the phantom and patient data. Moreover, manual marker motion quantification can achieve a high accuracy with a mean error of [Formula: see text].

Calcium Phosphate Cement Paste Injection as a Fiducial Marker of Cervical Cancer

Calcium phosphate cement (CPC) is used to fill bone voids in dental, orthopedic, and craniofacial applications. This study evaluated CPC marker as an injectable non-metallic fiducial marker. Six patients received 3-5 injections of CPC paste placed at a depth of 10 mm into tumors of the cervix before treatment planning CT (TPCT). Patients were treated with external-beam radiotherapy (EBRT) and high-dose rate brachytherapy (BT). We investigated marker visibility on cone-beam CT (CBCT), T2-weighted MRI, and interfraction of the marker motion for cervical cancer patients. Of a total of 22 visible CPC markers at TPCT, 17 CPC markers were visible on the first CBCT. Excluding one patient, all markers were visible on CBCT during EBRT. Of 16 visible CPC markers on CBCT, 13 CPC markers were visible on the magnetic resonance imaging (MRI) obtained before BT. For CPC marker centroid movement, the mean-of-means/systematic variation/random variation were 0.2/0.4/1.4, -1.6/5.1/4.1, and -3.4/2.1/2.8 mm for the left-right, dorsal-ventral, and cranial-caudal directions, respectively. This is the first report of a CPC marker injected into tumors of the cervix. It can be visualized on CBCT and MRI with reductions in marker loss and artifacts.

Quantification of MRI visibility and artifacts at 3T of liquid fiducial marker in a pancreas tissue-mimicking phantom.

X-ray-based position verification of the target volume in image-guided radiation therapy (IGRT) of patients with pancreatic ductal adenocarcinoma (PDAC) is currently performed on solid fiducial markers that are implanted under endoscopic ultrasonography. A new biodegradable liquid fiducial marker has recently been introduced. To assess its potential use for magnetic resonance imaging (MRI)-guided photon or proton radiotherapy of PDAC, the MRI visibility and artifacts of this marker were quantified and compared against solid gold markers. Different spherical volumes (10 μL, 25 μL, 50 μL, and 100 μL) of a biodegradable liquid fiducial marker as well as seven differently sized and oriented solid gold (0.35 mm diameter; 5 mm and 10 mm length) and iron-gold alloy fiducial markers (0.28 mm diameter; 1 cm and 2 cm length) were implanted in a spherical gel phantom, mimicking the proton spin relaxation properties of healthy pancreatic tissue at 3 Tesla. MR relaxometry was performed to quantify the size and magnitude of the decrease in the effective transversal relaxation time T2∗ and relative proton density ρ(H) as a measure of potential visibility and to quantify the size and magnitude of the increase in magnetic field inhomogeneity ΔB0 as a measure of potential signal artifacts. The phantom was scanned in a 3.0 T PET/MR scanner with an eight-channel head coil. The solid fiducial markers showed a direct linear relationship between the potentially visible size and artifact size. The liquid fiducial marker showed a tendency toward a potentially visible size at smaller artifacts. Liquid markers from 25 to 100 μL generated visible volumes comparable to the size of the solid markers. The magnitude of visibility was the highest for the liquid fiducial marker with volumes of 25-100 μL showing no correlation with the magnitude of artifact. The solid markers showed a strong nonlinear correlation between magnitude of visibility and artifact, whereas the solid marker consisting of a gold-iron alloy induced the strongest artifacts. The liquid fiducial marker causes signal voids on MRI due to its absence of water hydrogen atoms without strongly affecting the magnetic field in the surrounding tissue. The alteration of the static magnetic field was found to be the main effect leading to the visibility of the solid fiducial markers. Hence, especially when a low level of image distortion is required, MRI characteristics of the liquid marker surpass those of solid gold markers currently being used for IGRT of PDAC.

Visibility of an iron-containing fiducial marker in magnetic resonance imaging for high-precision external beam prostate radiotherapy.

Visualization of fiducial gold markers is critical for registration on computed tomography (CT) and magnetic resonance imaging (MRI) for imaging-guided radiotherapy. Although larger markers provide better visualization on MRI, they tend to generate artifacts on CT. MRI is strongly influenced by the presence of metals, such as iron, in the body. Here we compared efficacies of a 0.5% iron-containing gold marker (GM) and a traditional non-iron-containing marker. Twenty-seven patients underwent CT/MRI fusion-based intensity-modulated radiotherapy. Markers were placed by urologists under local anesthesia. Gold Anchor (GA; diameter: 0.28mm; length: 10mm), an iron-containing marker, was placed on the right side of the prostate using a 22-G needle and VISICOIL (VIS; diameter: 0.35mm; length: 10mm), a non-iron-containing marker, was placed on the left side using a 19-G needle. T2*-weighted images MRI sequences were obtained. Two radiation oncologists and a radiation technologist evaluated and assigned scores for visual quality on a five-point scale (1, poor; 5, best visibility). Artifact generation on CT was slightly greater with GA than with VIS. The mean marker visualization scores on MRI of all three observers were significantly superior for GA than for VIS (3.5 vs 3.2, 3.9 vs 3.2, and 4.0 vs 2.9). The actual size of the spherical GA was about 2mm in diameter, but the signal void on MRI was approximately 5mm. Although both markers were well visualized and can be recommended clinically, the results suggest that GA has some subtle advantages for quantitative visualization that could prove useful in certain situations of stereotactic body radiotherapy and intensity-modulated radiotherapy.

Visibility of fiducial markers used for image-guided radiation therapy on optical coherence tomography for registration with CT: An esophageal phantom study.

Optical coherence tomography (OCT) is of interest to visualize microscopic esophageal tumor extensions to improve tumor delineation for radiation therapy (RT) planning. Fiducial marker placement is a common method to ensure target localization during planning and treatment. Visualization of these fiducial markers on OCT permits integrating OCT and computed tomography (CT) images used for RT planning via image registration. We studied the visibility of 13 (eight types) commercially available solid and liquid fiducial markers in OCT images at different depths using dedicated esophageal phantoms and evaluated marker placement depth in clinical practice. We designed and fabricated dedicated esophageal phantoms, in which three layers mimic the anatomical wall structures of a healthy human esophagus. We successfully implanted 13 commercially available fiducial markers that varied in diameter and material property at depths between 0.5 and 3.0 mm. The resulting esophageal phantoms were imaged with OCT, and marker visibility was assessed qualitatively and quantitatively using the contrast-to-background-noise ratio (CNR). The CNR was defined as the difference between the mean intensity of the fiducial markers and the mean intensity of the background divided by the standard deviation of the background intensity. To determine whether, in current clinical practice, the implanted fiducial markers are within the OCT visualization range (up to 3.0 mm depth), we retrospectively measured the distance of 19 fiducial markers to the esophageal lumen on CT scans of 16 esophageal cancer patients. In the esophageal phantoms, all the included fiducial markers were visible on OCT at all investigated depths. Solid fiducial markers were better visible on OCT than liquid fiducial markers with a 1.74-fold higher CNR. Although fiducial marker identification per type and size was slightly easier for superficially implanted fiducial markers, we observed no difference in the ability of OCT to visualize the markers over the investigated depth range. Retrospective distance measurements of 19 fiducial markers on the CT scan of esophageal cancer patients showed that 84% (distance from the closest border of the marker to the lumen) and 53% (distance from the center of the marker to the lumen) of the fiducial markers were located within the OCT visualization range of up to 3.0 mm. We studied the visibility of eight types of commercially available fiducial markers at different depths on OCT using dedicated esophageal phantoms. All tested fiducial markers were visible at depths ≤3.0 mm and most, but not all, clinically implanted markers were at a depth accessible to OCT. Consequently, the use of fiducial markers as a reference for OCT to CT registration is feasible.

PO-0866: Visibility, image artifacts and proton dose perturbation of fiducial markers

PO-0866: Visibility, image artifacts and proton dose perturbation of fiducial markers

Evaluation of ceramic marker for the treatment of ocular melanoma with proton therapy

BioMarc SecureTM, a fiducial marker with ceramic core (zirconium oxide) and carbon coating, was evaluated for use in the localization and alignment of ocular melanoma targets using proton pencil beam scanning (PBS). Measurements and Monte Carlo (MC) simulations were performed to estimate the dose attenuation behind the marker. Imaging tests were performed to evaluate the visibility of marker for x-ray based alignment. An anthropomorphic phantom with implanted fiducial marker was scanned to obtain two-dimensional kilo-voltage (kV) x-ray and three-dimensional computed tomographic (CT) images. For dose shadow measurements, an in-house phantom was constructed using solid water, Styrofoam and EBT3 gafchromic film. Dose attenuation behind the marker was measured at multiple depths and for three cardinal orientations: parallel, perpendicular, and transverse. The measurements were performed at the proton pencil beam gantry at the Seattle Cancer Care Alliance Proton Therapy center. A beam model for pencil beam gantry was created in the validated MC simulation toolkit GATE (GEANT4 Applications for Tomographic Emission). MC simulations were set up to mimic the measurement geometry and dose attenuation behind the marker was studied for a single layer PBS beam. Additional simulations were performed in water using the clinical relevant spread out Bragg peak (SOBP) beam. Qualitative analysis of the planar kV images showed excellent visibility of marker. Reconstruction artifacts in the form of light and dark streaks were present on the CT images. The film and MC simulations showed significant dose attenuation behind the marker that worsened when marker was placed close to the distal edge. Dose shadows of up to 45% and range loss of up to 1.1 mm were seen behind the marker. The transverse marker orientation in the clinical SOBP beam showed dose reduction of up to 61% and range pull-back of 2.4 mm. The dose attenuation was found to be a function of marker orientation and location within the SOBP. The analysis showed that small volumes behind the marker can see severe under-dosing. This effect should be taken into account during the planning of treatment. Comparing the results of this study to published results for tantalum marker, the BioMarc Secure marker was found to be inferior due to its greater dose attenuation and extended dose shadow on larger underlying volume. Furthermore, its bigger physical size may mean more discomfort to patient.

Longitudinal Changes in Active Bone Marrow for Cervical Cancer Patients Treated With Concurrent Chemoradiation Therapy

The aim of this study was to evaluate a calcium phosphate cement (CPC) marker as an injectable nonmetallic fiducial marker. We investigated interfraction cervical motion with cone beam CT (CBCT) images using a CPC marker and marker visibility on T2-weighted MRI for cervical cancer patients. Our commercially available CPC, widely used as a bone substitute, was prepared by mixing a powder component and liquid. A volume of 0.1-0.2 cc of the paste was injected by a disposable syringe with a 19-gauge long needle. This paste was self-hardening and recrystallizes to calcium hydroxyapatite in a living body. Six patients received 3-4 injections of CPC paste placed at a depth of 10 mm into a tumor of the cervix before planning CT. Patients were first treated with external beam radiation therapy to the whole pelvis with a total prescribed dose of 48.6-50.4 Gy delivered in 27-28 fractions. Three fractionated high-dose rate brachytherapy treatments were performed with a prescribed dose per fraction of 6 Gy to Point A. Concurrent chemotherapy was delivered to all except one patient. In each fraction, a CBCT scan was acquired before dose delivery. Position verification was based on registration of the bony structures in the CBCT images corresponding to planning CT images. Systematic and random displacement of the marker centroid analysis were performed in 3 directions. Visibility of the markers using T2-weighted MRI before final brachytherapy was also assessed. The procedure was well-tolerated. There was no interruption of the implantation due to pain or hemorrhage. There were no other procedure-related complications during or after CPC marker injection. Comparing the initial and final CBCT images, one patient had lost all three markers and one patient lost one marker. Gross tumor volumes (GTV) before radiation therapy of these patients were 250.7 and 91.7 cc, and GTV before final brachytherapy were 7.5 and 1.1 cc, respectively. The initial GTV of patients with no marker loss ranged from 49.1-67.2 cc, and GTV before the final brachytherapy ranged from 2.4-8.4 cc. Of 15 markers in the final CBCT images, 11 markers with a size >0.15 cc on planning CT images were visible on T2-weighted MRI. For CPC marker movement with rigid bony anatomy registration, the mean-of-means/systematic variation/random variation were 0.6/2.4/0.5, 1.5/4.6/1.9, and 3.4/2.6/1.1 mm for the left-right, anterior-posterior, and cranial-caudal directions, respectively. The injection of CPC paste into the cervix was feasible and safe. More than 0.15 cc of CPC paste was required to be visualized with T2-weighted MRI. For patients with a large cervical tumor, technical improvements in CPC marker placement are necessary.

WE‐DE‐BRA‐04: A Cost‐Effective Pixelated EPID Scintillator for Enhanced Contrast and DQE

Purpose:Beams‐eye‐view imaging applications such as real‐time soft‐tissue motion estimation and MV‐CBCT are hindered by the inherently low image contrast of electronic portal imaging devices (EPID) currently in clinical use. We investigate a cost effective scintillating glass that provides substantially increased detective quantum efficiency (DQE) and contrast to noise ratio (CNR).Methods:A pixelated scintillator prototype was built from LKH‐5 glass. The array is 12mm thick; 42.4×42.4cm2 wide and features 1.51mm pixel pitch with 20µm separation (glue+septa). The LKH‐5 array was mounted on the active matrix flat panel imager (AMPFI) of an AS‐1200 (Varian) with the GdO2S2:Tb removed. A second AS‐1200 was utilized as reference detector. The prototype EPID was characterized in terms of CNR, modulation transfer function (MTF) and DQE. Additionally, the visibility of various fiducial markers typically used in the clinic as well as a realistic 3D‐printed lung tumor model was assessed. All items were placed in a 12cm thick solid water phantom. CNR is estimated using a Las Vegas contrast phantom, presampled MTF is estimated using a slanted slit technique and the DQE is calculated from measured normalized noise power spectra (NPS) and the MTF.Results:DQE(0) for the LKH‐5 prototype increased by a factor of 8× to about 10%, compared to the AS‐1200 equipped with its standard GdO2S2:Tb scintillator. CNR increased by a factor of 5.3×. Due to the pixel size the MTF50 decreased by about 55% to 0.23lp/mm. The visibility of all fiducial markers as well as the tumor model were however markedly improved in comparison to an acquisition with the same parameters using the GdO2S2:Tb scintillator.Conclusion:LKH‐5 scintillating glasses allow the cost effective construction of thick pixelated scintillators for portal imaging which can yield a substantial increase in DQE and CNR. Soft tissue and fiducial marker visibility was found to be markedly improved.The project was supported in part by NIH grant R01CA188446‐01 and a grant from Varian Medical Systems.

Clinical implementation of a novel applicator in high-dose-rate brachytherapy treatment of esophageal cancer.

PurposeIn this study, we present the clinical implementation of a novel transoral balloon centering esophageal applicator (BCEA) and the initial clinical experience in high-dose-rate (HDR) brachytherapy treatment of esophageal cancer, using this applicator.Material and methodsAcceptance testing and commissioning of the BCEA were performed prior to clinical use. Full performance testing was conducted including measurements of the dimensions and the catheter diameter, evaluation of the inflatable balloon consistency, visibility of the radio-opaque markers, congruence of the markers, absolute and relative accuracy of the HDR source in the applicator using the radiochromic film and source position simulator, visibility and digitization of the applicator on the computed tomography (CT) images under the clinical conditions, and reproducibility of the offset. Clinical placement of the applicator, treatment planning, treatment delivery, and patient's response to the treatment were elaborated as well.ResultsThe experiments showed sub-millimeter accuracy in the source positioning with distal position at 1270 mm. The digitization (catheter reconstruction) was uncomplicated due to the good visibility of markers. The treatment planning resulted in a favorable dose distribution. This finding was pronounced for the treatment of the curvy anatomy of the lesion due to the improved repeatability and consistency of the delivered fractional dose to the patient, since the radioactive source was placed centrally within the lumen with respect to the clinical target due to the five inflatable balloons.ConclusionsThe consistency of the BCEA positioning resulted in the possibility to deliver optimized non-uniform dose along the catheter, which resulted in an increase of the dose to the cancerous tissue and lower doses to healthy tissue. A larger number of patients and long-term follow-up will be required to investigate if the delivered optimized treatment can lead to improved clinical outcomes.

Clinical applicability of a new 3D portable stereo-photogrammetric opto-electronic device

s / Gait & Posture 42S (2015) S1–S27 S5 Fig. 1. (a) Reference image. Model generated after the manual identification of the relevant anatomical landmarks. (b) Tracked model in a dynamic frame. They wore an underwear garment with a coloured patch applied, and uniformly coloured ankle socks used as segmentalmarkers (for pelvis and feet, respectively). A RGB video camera (Vicon Bonita 720C, 60 fps) was placed laterally to the walkway. Synchronous 3D marker positions were captured with a Vicon system (Bonita10). Markers were positioned according to the Davis protocol [3] (GS). The proposed ML methodology requires a preliminary model calibration step, performed on a reference image of the subject standing upright (Fig. 1a), from which a foot contour model template is automatically identified, while the lateral malleolus, lateral epicondyle and greater trochanter are manually identified [2]. Model templates of the shank and thigh segments are defined bymeans of technical reference points identified on the silhouette contour. The pelvis orientation is assumed to coincidewith the orientation of the segment obtained by interpolating the points extracted from the pelvis patch. For eachgait trial, the silhouette contourof themoving subject was extracted using a background subtraction technique, and the foot and pelvis segmental markers were identified using colour filters. The foot orientation was determined by matching the foot template with the foot current image. The shank and thigh reference points on the deformed silhouette contour were identified for each frame, and the corresponding templates fitted using a SVD procedure (Fig. 1b) [2]. The kinematic estimations provided by theMLmethodwere compared to the GS in terms of correlation coefficient (CC) and root mean square deviation (RMSD). Results: The CC (and RMSD) between the ML and the GS estimations ranged from 0.91 (4.9◦) to 0.98 (7.3◦) for the hip flexextension, from0.94 (5.4◦) to 0.97 (8.3◦) for the knee flex-extension and from0.74 (5.9◦) to0.84 (9.9◦) for theankledorsi-plantarflexion. Discussion: Joint kinematics estimatedusingML showed a good correlation with the GS joint kinematics (0.74≤CC≤0.98), however the relevant errors are clearly larger than those found in healthy adults [2] (up to 9.9◦). This difference can be attributed partly to the children’s body segments small size (particularly for the foot) and in some cases to the presence of the arm swing that reduces the visibility of the pelvis segmental marker. Therefore, the extraction of the segmental markers will have to be improved in order for this method to be applied in clinical settings.

Application of a markerless gait analysis methodology in children with cerebral palsy: Preliminary results

s / Gait & Posture 42S (2015) S1–S27 S5 Fig. 1. (a) Reference image. Model generated after the manual identification of the relevant anatomical landmarks. (b) Tracked model in a dynamic frame. They wore an underwear garment with a coloured patch applied, and uniformly coloured ankle socks used as segmentalmarkers (for pelvis and feet, respectively). A RGB video camera (Vicon Bonita 720C, 60 fps) was placed laterally to the walkway. Synchronous 3D marker positions were captured with a Vicon system (Bonita10). Markers were positioned according to the Davis protocol [3] (GS). The proposed ML methodology requires a preliminary model calibration step, performed on a reference image of the subject standing upright (Fig. 1a), from which a foot contour model template is automatically identified, while the lateral malleolus, lateral epicondyle and greater trochanter are manually identified [2]. Model templates of the shank and thigh segments are defined bymeans of technical reference points identified on the silhouette contour. The pelvis orientation is assumed to coincidewith the orientation of the segment obtained by interpolating the points extracted from the pelvis patch. For eachgait trial, the silhouette contourof themoving subject was extracted using a background subtraction technique, and the foot and pelvis segmental markers were identified using colour filters. The foot orientation was determined by matching the foot template with the foot current image. The shank and thigh reference points on the deformed silhouette contour were identified for each frame, and the corresponding templates fitted using a SVD procedure (Fig. 1b) [2]. The kinematic estimations provided by theMLmethodwere compared to the GS in terms of correlation coefficient (CC) and root mean square deviation (RMSD). Results: The CC (and RMSD) between the ML and the GS estimations ranged from 0.91 (4.9◦) to 0.98 (7.3◦) for the hip flexextension, from0.94 (5.4◦) to 0.97 (8.3◦) for the knee flex-extension and from0.74 (5.9◦) to0.84 (9.9◦) for theankledorsi-plantarflexion. Discussion: Joint kinematics estimatedusingML showed a good correlation with the GS joint kinematics (0.74≤CC≤0.98), however the relevant errors are clearly larger than those found in healthy adults [2] (up to 9.9◦). This difference can be attributed partly to the children’s body segments small size (particularly for the foot) and in some cases to the presence of the arm swing that reduces the visibility of the pelvis segmental marker. Therefore, the extraction of the segmental markers will have to be improved in order for this method to be applied in clinical settings.

Optical tracking with two markers for robust prospective motion correction for brain imaging.

Prospective motion correction (PMC) during brain imaging using camera-based tracking of a skin-attached marker may suffer from problems including loss of marker visibility due to the coil and false correction due to non-rigid-body facial motion, such as frowning or squinting. A modified PMC system is introduced to mitigate these problems and increase the robustness of motion correction. The method relies on simultaneously tracking two markers, each providing six degrees of freedom, that are placed on the forehead. This allows us to track head motion when one marker is obscured and detect skin movements to prevent false corrections. Experiments were performed to compare the performance of the two-marker motion correction technique to the previous single-marker approach. Experiments validate the theory developed for adaptive marker tracking and skin movement detection, and demonstrate improved image quality during obstruction of the line-of-sight of one marker when subjects squint or when subjects squint and move simultaneously. The proposed methods eliminate two common failure modes of PMC and substantially improve the robustness of PMC, and they can be applied to other optical tracking systems capable of tracking multiple markers. The methods presented can be adapted to the use of more than two markers.

SU‐E‐J‐42: Evaluation of Fiducial Markers for Ultrasound and X‐Ray Images Used for Motion Tracking in Pancreas SBRT

PurposeUltrasound tracking of target motion relies on visibility of vascular and/or anatomical landmark. However this is challenging when the target is located far from vascular structures or in organs that lack ultrasound landmark structure, such as in the case of pancreas cancer. The purpose of this study is to evaluate visibility, artifacts and distortions of fusion coils and solid gold markers in ultrasound, CT, CBCT and kV images to identify markers suitable for real‐time ultrasound tracking of tumor motion in SBRT pancreas treatment.MethodsTwo fusion coils (1mm × 5mm and 1mm × 10 mm) and a solid gold marker (0.8mm × 10mm) were embedded in a tissue–like ultrasound phantom. The phantom (5cm × 12cm × 20cm) was prepared using water, gelatin and psyllium‐hydrophilic‐mucilloid fiber. Psylliumhydrophilic mucilloid acts as scattering medium to produce echo texture that simulates sonographic appearance of human tissue in ultrasound images while maintaining electron density close to that of water in CT images. Ultrasound images were acquired using 3D‐ultrasound system with markers embedded at 5, 10 and 15mm depth from phantom surface. CT images were acquired using Philips Big Bore CT while CBCT and kV images were acquired with XVI‐system (Elexta). Visual analysis was performed to compare visibility of the markers and visibility score (1 to 3) were assigned.ResultsAll markers embedded at various depths are clearly visible (score of 3) in ultrasound images. Good visibility of all markers is observed in CT, CBCT and kV images. The degree of artifact produced by the markers in CT and CBCT images are indistinguishable. No distortion is observed in images from any modalities.ConclusionAll markers are visible in images across all modalities in this homogenous tissue‐like phantom. Human subject data is necessary to confirm the marker type suitable for real‐time ultrasound tracking of tumor motion in SBRT pancreas treatment.

Visibility and artifacts of gold fiducial markers used for image guided radiation therapy of pancreatic cancer on MRI.

In radiation therapy of pancreatic cancer, tumor alignment prior to each treatment fraction is improved when intratumoral gold fiducial markers (from here onwards: markers), which are visible on computed tomography (CT) and cone beam CT, are used. Visibility of these markers on magnetic resonance imaging (MRI) might improve image registration between CT and magnetic resonance (MR) images for tumor delineation purposes. However, concomitant image artifacts induced by markers are undesirable. The extent of visibility and artifact size depend on MRI-sequence parameters. The authors' goal was to determine for various markers their potential to be visible and to generate artifacts, using measures that are independent of the MRI-sequence parameters. The authors selected ten different markers suitable for endoscopic placement in the pancreas and placed them into a phantom. The markers varied in diameter (0.28-0.6 mm), shape, and iron content (0%-0.5%). For each marker, the authors calculated T2 (∗)-maps and ΔB0-maps using MRI measurements. A decrease in relaxation time T2 (∗) can cause signal voids, associated with visibility, while a change in the magnetic field B0 can cause signal shifts, which are associated with artifacts. These shifts inhibit accurate tumor delineation. As a measure for potential visibility, the authors used the volume of low T2 (∗), i.e., the volume for which T2 (∗) differed from the background by >15 ms. As a measure for potential artifacts, the authors used the volume for which |ΔB0| > 9.4 × 10(-8) T (4 Hz). To test whether there is a correlation between visibility and artifact size, the authors calculated the Spearman's correlation coefficient (Rs) between the volume of low T2 (∗) and the volume of high |ΔB0|. The authors compared the maps with images obtained using a clinical MR-sequence. Finally, for the best visible marker as well as the marker that showed the smallest artifact, the authors compared the phantom data with in vivo MR-images in four pancreatic cancer patients. The authors found a strong correlation (Rs = 1.00, p < 0.01) between the volume of low T2 (∗) and the volume with high |ΔB0|. Visibility in clinical MR-images increased with lower T2 (∗). Signal shift artifacts became worse for markers with high |ΔB0|. The marker that was best visible in the phantom, a folded marker with 0.5% iron content, was also visible in vivo, but showed artifacts on diffusion weighted images. The marker with the smallest artifact in the phantom, a small, stretched, ironless marker, was indiscernible on in vivo MR-images. Changes in T2 (∗) and ΔB0 are sequence-independent measures for potential visibility and artifact size, respectively. Improved visibility of markers correlates strongly to signal shift artifacts; therefore, marker choice will depend on the clinical purpose. When visibility of the markers is most important, markers that contain iron are optimal, preferably in a folded configuration. For artifact sensitive imaging, small ironless markers are best, preferably in a stretched configuration.

Simulation of a Bead Placement Protocol for Follow-up of Thoracic Spinal Fusion Using Radiostereometric Analysis

Study DesignComputer simulation to detect intervertebral motion enabling future follow-up of spinal fusions performed on patients with multilevel thoracic scoliosis. ObjectivesTo propose a method using computer simulation to evaluate a radiostereometric analysis (RSA) marker placement protocol for visibility and redundancy and validate the performance of the developed RSA system in detecting intervertebral motion. Summary of Background DataRadiostereometric analysis is a stereo x-ray technique in which clusters of tantalum markers are implanted to label well-defined landmarks and measure the relative motion between rigid bodies. MethodsA model of the spine with the instrumentation and the RSA markers was developed. The vertebrae were aligned to mimic multilevel thoracic scoliosis after correction. The researchers performed virtual segment motion to validate the performance of the developed system. X-ray images were simulated and RSA was used to evaluate the proposed marker placement protocol and detect virtual motion. The authors performed a physical phantom study to evaluate marker visibility. ResultsAll markers were located and matched between simulations and the condition numbers were well below the recommended value of 100. Based on computer simulation, average translational accuracy was 0.14, 0.01, and 0.24 mm along the x, y, and z axes, respectively, and average rotational accuracy was 0.23°, 0.12°, and 0.11° about the x, y, and z axes, respectively. The translational and rotational precision of the simulated RSA system was generally high. The physical phantom study agreed with the computer simulation and validated marker visibility. ConclusionsComputer simulation is a powerful tool that can be used to facilitate the development and refinement of an RSA system before its application in patients, particularly when the anatomy involved is complex. The proposed marker placement protocol yielded translational and rotational accuracy below the limits of clinical significance, which enables future follow-up of multilevel thoracic scoliosis with Lenke classification 1AN.

PD-0457: Visibility of gold markers on optical coherence tomography for registration with CT: an esophageal phantom study

PD-0457: Visibility of gold markers on optical coherence tomography for registration with CT: an esophageal phantom study

In vitro evaluation of a novel fiducial marker for computed tomography and magnetic resonance imaging of soft tissues in small animals.

To construct and optimize a fiducial marker suitable for both CT and MRI. Fiducial markers containing serial dilutions of iopamidol mixed with water. IV tubing sets were infused with serial dilutions (0% to 100%; increments of 10%) of iopamidol. Tubing ends were sealed; additional seals were added to create an equilateral triangle. A reference point was created by placing a crimp in 1 side. Markers were fixed to a gelatin soft tissue-attenuating phantom and evaluated by use of CT and MRI. For CT, simple linear regression analysis was used to assess the relationship between the percentage of marker contrast medium and quantitative variables, including marker attenuation, attenuation changes in the phantom, and beam-hardening artifact length. A subjective grading scheme for artifact creation on CT images and marker visibility on MRI images was used. Measurements were obtained by investigators who were unaware of the contents of each marker. Percentage of contrast medium in each marker was strongly correlated with marker attenuation (r(2) = 0.96), artifact length (r(2) = 0.765), and mean attenuation changes within the phantom (r(2) = 0.826) for CT. Subjective CT scores indicated that concentrations of contrast medium > 50% resulted in excessive artifacts. Markers with concentrations of iopamidol > 50% had poor subjective MRI visibility scores. No artifacts were seen on MRI. A marker containing a 10% solution of iodinated contrast medium mixed with water provided ideal contrast for both CT and MRI.

Qualitative Evaluation of Fiducial Markers for Radiotherapy Imaging

To evaluate visibility, artifacts, and distortions of various commercial markers in magnetic resonance imaging (MRI), computer tomography (CT), and ultrasound imaging used for radiotherapy planning and treatment guidance. We compare 2 solid gold markers, 4 gold coils, and 1 polymer marker from 3 vendors. Imaging modalities used were 3-T and 1.5-T GE MRIs, Siemens Sequoia 512 Ultrasound, Phillips Big Bore CT, Varian Trilogy linear accelerator (cone-beam CT [CBCT], on-board imager kilovoltage [OBI-kV], electronic portal imaging device megavoltage [EPID-MV]), and Medtronic O-ARM CBCT. Markers were imaged in a 30 × 30 × 10 cm(3) custom bolus phantom. In one experiment, Surgilube was used around the markers to reduce air gaps. Images were saved in Digital Imaging and Communications in Medicine (DICOM) format and analyzed using an in-house software. Profiles across the markers were used for objective comparison of the markers' signals. The visibility and artifacts/distortions produced by each marker were assessed qualitatively and quantitatively. All markers are visible in CT, CBCT, OBI-kV, and ultrasound. Gold markers below 0.75 mm in diameter are not visible in EPID-MV images. The larger the markers, the more CT and CBCT image artifacts there are, yet the degree of the artifact depends on scan parameters and the scanner itself. Visibility of gold coils of 0.75 mm diameter or larger is comparable across all imaging modalities studied. The polymer marker causes minimal artifacts in CT and CBCT but has poor visibility in EPID-MV. Gold coils of 0.5 mm exhibit poor visibility in MRI and EPID-MV due to their small size. Gold markers are more visible in 3-T T1 gradient-recalled echo than in 1.5-T T1 fast spin-echo, depending on the scan sequence. In this study, all markers are clearly visible on ultrasound. All gold markers are visible in CT, CBCT, kV, and ultrasound; however, only the large diameter markers are visible in MV. When MR and EPID-MV imagers are used, the selection of fiducial markers is not straightforward. For hybrid kV/MV image-guided radiotherapy imaging, larger diameter markers are suggested. If using kV imaging alone, smaller sized markers may be used in smaller sized patients in order to reduce artifacts. Only larger diameter gold markers are visible across all imaging modalities.