Substantial Artifacts Research Articles

Dual-electrode motion artifact cancellation for mobile electroencephalography

Objective. Our purpose was to evaluate the ability of a dual electrode approach to remove motion artifact from electroencephalography (EEG) measurements. Approach. We used a phantom human head model and robotic motion platform to induce motion while collecting scalp EEG. We assembled a dual electrode array capturing (a) artificial neural signals plus noise from scalp EEG electrodes, and (b) electrically isolated motion artifact noise. We recorded artificial neural signals broadcast from antennae in the phantom head during continuous vertical sinusoidal movements (stationary, 1.00, 1.25, 1.50, 1.75, 2.00 Hz movement frequencies). We evaluated signal quality using signal-to-noise ratio (SNR), cross-correlation, and root mean square error (RMSE) between the ground truth broadcast signals and the recovered EEG signals. Main results. Signal quality was restored following noise cancellation when compared to single electrode EEG measurements collected with no phantom head motion. Significance. We achieved substantial motion artifact attenuation using secondary electrodes for noise cancellation. These methods can be applied to studying electrocortical signals during human locomotion to improve real-world neuroimaging using EEG.

Cadaveric Study of the Safety and Device Functionality of Magnetically Controlled Growing Rods After Exposure to Magnetic Resonance Imaging

Study DesignCadaveric study. ObjectiveTo establish the safety and efficacy of magnetically controlled growing rods (MCGRs) after magnetic resonance imaging (MRI) exposure. Summary of Background DataMCGRs are new and promising devices for the treatment of early-onset scoliosis (EOS). A significant percentage of EOS patients have concurrent spinal abnormalities that need to be monitored with MRI. There are major concerns of the MRI compatibility of MCGRs because of the reliance of the lengthening mechanism on strongly ferromagnetic actuators. MethodsSix fresh-frozen adult cadaveric torsos were used. After thawing, MRI was performed four times each: baseline, after implantation of T2–T3 thoracic rib hooks and L5–S1 pedicle screws, and twice after MCGR implantation. Dual MCGRs were implanted in varying configurations and connected at each end with cross connectors, creating a closed circuit to maximize MRI-induced heating. Temperature measurements and tissue biopsies were obtained to evaluate thermal injury. MCGRs were tested for changes to structural integrity and functionality. MRI images obtained before and after MCGR implantation were evaluated. ResultsAverage temperatures increased incrementally by 1.1°C, 1.3°C, and 0.5°C after each subsequent scan, consistent with control site temperature increases of 1.1°C, 0.8°C, and 0.4°C. Greatest cumulative temperature change of +3.6°C was observed adjacent to the right-sided actuator, which is below the 6°C threshold cited in literature for clinically detectable thermal injury. Histologic analysis revealed no signs of heat-induced injury. All MCGR actuators continued to function properly according to the manufacturer's specifications and maintained structural integrity. Significant imaging artifacts were observed, with the greatest amount when dual MCGRs were implanted in standard/offset configuration. ConclusionsWe demonstrate minimal MRI-induced temperature change, no observable thermal tissue injury, preservation of MCGR-lengthening functionality, and no structural damage to MCGRs after multiple MRI scans. Expectedly, the ferromagnetic actuators produced substantial MR imaging artifacts. Level of EvidenceLevel V.

The Performance of a Zirconium-based Root Filling Material with Artifact Reduction Properties in the Detection of Artificially Induced Root Fractures Using Cone-beam Computed Tomographic Imaging

IntroductionLimited field of view cone-beam computed tomographic (CBCT) imaging has been used to augment clinical testing of vertical root fractures (VRFs); however, the presence of gutta-percha (GP) in the canal space generates substantial imaging artifacts that make fracture detection difficult. The purpose of this study was to evaluate the influence of a zirconium (Zr)-based root filling material with radiologic properties that reduce beam hardening (BH) artifacts using CBCT imaging in the in vitro diagnosis of VRFs. MethodsOne hundred seventy-six single-rooted mandibular premolar teeth were obtained, and half of these teeth were filled with GP or Zr (CPoint; EndoTechnologies, LLC, Shrewsbury, MA). VRFs were induced in 44 decoronated teeth in each group using an Instron (Norwood, MA) Universal Testing Machine. Each root was then placed in a dry human mandible and imaged with the Carestream 9000 3D CBCT system (Carestream Dental, Atlanta, GA). The images were evaluated by 6 oral maxillofacial radiologists (OMRs) and residents. ResultsThe sensitivity was greater for detecting VRFs in the Zr group than the GP group (P = .035). However, the specificity was greater for the GP group than the Zr group (P = .028). Receiver operating characteristic area under the curve values were greater for the Zr group than the GP group, but these differences were not statistically significant. The OMRs outperformed the residents in the detection of VRFs in the Zr group with respect to specificity (P = .006) and positive predictive value (P = .012). ConclusionsThe reduced BH of the Zr group improved the sensitivity of the detection of artificially induced VRFs. The ability to detect VRFs in the Zr group was further enhanced by clinical experience.

Dynamic PET image reconstruction integrating temporal regularization associated with respiratory motion correction for applications in oncology

Respiratory motion reduces both the qualitative and quantitative accuracy of PET images in oncology. This impact is more significant for quantitative applications based on kinetic modeling, where dynamic acquisitions are associated with limited statistics due to the necessity of enhanced temporal resolution. The aim of this study is to address these drawbacks, by combining a respiratory motion correction approach with temporal regularization in a unique reconstruction algorithm for dynamic PET imaging.Elastic transformation parameters for the motion correction are estimated from the non-attenuation-corrected PET images. The derived displacement matrices are subsequently used in a list-mode based OSEM reconstruction algorithm integrating a temporal regularization between the 3D dynamic PET frames, based on temporal basis functions. These functions are simultaneously estimated at each iteration, along with their relative coefficients for each image voxel. Quantitative evaluation has been performed using dynamic FDG PET/CT acquisitions of lung cancer patients acquired on a GE DRX system. The performance of the proposed method is compared with that of a standard multi-frame OSEM reconstruction algorithm.The proposed method achieved substantial improvements in terms of noise reduction while accounting for loss of contrast due to respiratory motion. Results on simulated data showed that the proposed 4D algorithms led to bias reduction values up to 40% in both tumor and blood regions for similar standard deviation levels, in comparison with a standard 3D reconstruction. Patlak parameter estimations on reconstructed images with the proposed reconstruction methods resulted in 30% and 40% bias reduction in the tumor and lung region respectively for the Patlak slope, and a 30% bias reduction for the intercept in the tumor region (a similar Patlak intercept was achieved in the lung area).Incorporation of the respiratory motion correction using an elastic model along with a temporal regularization in the reconstruction process of the PET dynamic series led to substantial quantitative improvements and motion artifact reduction. Future work will include the integration of a linear FDG kinetic model, in order to directly reconstruct parametric images.

Excavation of a medieval burgh ditch at East Market Street, Edinburgh

In 2015 excavation works undertaken in preparation for a new hotel development at East Market Street, Edinburgh (NGR: NT 26242 73758), encountered the remains of a substantial ditch feature likely relating to previously excavated ditches in the medieval burghs of Edinburgh and Canongate. A substantial stratified artefact assemblage including both animal bone and ceramics was recovered and the waterlogged deposits in the base of the ditch also offered the opportunity for macroplant analysis. These waterlogged deposits afforded the preservation of artefacts including a textile garment, the first of its kind in the British Isles, and leather shoe soles boasting slender waists and turned out, pointed toes. These finds were both attributed to the 14th to 15th centuries, contributing to a vivid picture of the inhabitants of Edinburgh and Canongate in the medieval period. Analysis of both the artefact and ecofact assemblage revealed two phases of use, from the construction of the ditch in the late 12th–13th century to its eventual disuse in the latter half of the 15th century.

Suggestion of the Relative Artifact Index for Noise-independent Evaluation of the Streak Artifact

The aim of this study was to inspect the usefulness of relative artifact index (AIr), which divided artifact index (AI) by standard deviation of the noise image for noise-independent evaluation of the streak artifact in computed tomography images. A water phantom without/with a cylindrical phantom filled with diluted contrast medium was scanned with different tube voltages (100/120/140 kV) and radiation doses (5/10/20 mGy), then images were reconstructed with different kernels (B10/30/50f). AI, location parameter in Gumbel method and AIr were measured in each condition and compared. The higher tube voltage or radiation dose or lower spatial resolution kernel, the lower quantitative values were presented by both AI and Gumbel method. AIr showed quantitative values independent of radiation dose and kernel, and substantial artifact amounts affected only by tube voltage. Our results showed AIr can evaluate quantitative artifact amount independent of image noise.

Calculating the prominence and isolation of every mountain in the world

A global-scale calculation identifies peaks in a digital elevation model (DEM) and computes their isolation and topographic prominence. A new DEM is presented that covers the entire globe at 90 meter resolution with no substantial voids or artifacts. All peaks with at least 1 kilometer of isolation are found, and the closest higher ground is identified. For prominence, all peaks with at least ∼30 meters are found, and the key saddle is identified. The prominence algorithm uses results from Morse–Smale topology to run in parallel on standard, freely available elevation data. Thirteen previously unknown “ultra-prominent” mountains with at least 1500 meters of prominence are listed.

Genome-scale detection of positive selection in nine primates predicts human-virus evolutionary conflicts.

Hotspots of rapid genome evolution hold clues about human adaptation. We present a comparative analysis of nine whole-genome sequenced primates to identify high-confidence targets of positive selection. We find strong statistical evidence for positive selection in 331 protein-coding genes (3%), pinpointing 934 adaptively evolving codons (0.014%). Our new procedure is stringent and reveals substantial artefacts (20% of initial predictions) that have inflated previous estimates. The final 331 positively selected genes (PSG) are strongly enriched for innate and adaptive immunity, secreted and cell membrane proteins (e.g. pattern recognition, complement, cytokines, immune receptors, MHC, Siglecs). We also find evidence for positive selection in reproduction and chromosome segregation (e.g. centromere-associated CENPO, CENPT), apolipoproteins, smell/taste receptors and mitochondrial proteins. Focusing on the virus–host interaction, we retrieve most evolutionary conflicts known to influence antiviral activity (e.g. TRIM5, MAVS, SAMHD1, tetherin) and predict 70 novel cases through integration with virus–human interaction data. Protein structure analysis further identifies positive selection in the interaction interfaces between viruses and their cellular receptors (CD4-HIV; CD46-measles, adenoviruses; CD55-picornaviruses). Finally, primate PSG consistently show high sequence variation in human exomes, suggesting ongoing evolution. Our curated dataset of positive selection is a rich source for studying the genetics underlying human (antiviral) phenotypes. Procedures and data are available at https://github.com/robinvanderlee/positive-selection.

The effect of concomitant fields in fast spin echo acquisition on asymmetric MRI gradient systems.

To investigate the effect of the asymmetric gradient concomitant fields (CF) with zeroth and first-order spatial dependence on fast/turbo spin-echo acquisitions, and to demonstrate the effectiveness of their real-time compensation. After briefly reviewing the CF produced by asymmetric gradients, the effects of the additional zeroth and first-order CFs on these systems are investigated using extended-phase graph simulations. Phantom and in vivo experiments are performed to corroborate the simulation. Experiments are performed before and after the real-time compensations using frequency tracking and gradient pre-emphasis to demonstrate their effectiveness in correcting the additional CFs. The interaction between the CFs and prescan-based correction to compensate for eddy currents is also investigated. It is demonstrated that, unlike the second-order CFs on conventional gradients, the additional zeroth/first-order CFs on asymmetric gradients cause substantial signal loss and dark banding in fast spin-echo acquisitions within a typical brain-scan field of view. They can confound the prescan correction for eddy currents and degrade image quality. Performing real-time compensation successfully eliminates the artifacts. We demonstrate that the zeroth/first-order CFs specific to asymmetric gradients can cause substantial artifacts, including signal loss and dark bands for brain imaging. These effects can be corrected using real-time compensation. Magn Reson Med 79:1354-1364, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Automatic motion correction for in vivo human skin optical coherence tomography angiography through combined rigid and nonrigid registration.

When using optical coherence tomography angiography (OCTA), the development of artifacts due to involuntary movements can severely compromise the visualization and subsequent quantitation of tissue microvasculatures. To correct such an occurrence, we propose a motion compensation method to eliminate artifacts from human skin OCTA by means of step-by-step rigid affine registration, rigid subpixel registration, and nonrigid B-spline registration. To accommodate this remedial process, OCTA is conducted using two matching all-depth volume scans. Affine transformation is first performed on the large vessels of the deep reticular dermis, and then the resulting affine parameters are applied to all-depth vasculatures with a further subpixel registration to refine the alignment between superficial smaller vessels. Finally, the coregistration of both volumes is carried out to result in the final artifact-free composite image via an algorithm based upon cubic B-spline free-form deformation. We demonstrate that the proposed method can provide a considerable improvement to the final en face OCTA images with substantial artifact removal. In addition, the correlation coefficients and peak signal-to-noise ratios of the corrected images are evaluated and compared with those of the original images, further validating the effectiveness of the proposed method. We expect that the proposed method can be useful in improving qualitative and quantitative assessment of the OCTA images of scanned tissue beds.

Rapid monoisotopic cisplatin based barcoding for multiplexed mass cytometry

Mass cytometry presents an exceptional opportunity to interrogate the biology of highly heterogeneous cell populations, owing to the ability to collect highly parametric proteomic data at a single cell level. However, sample-to-sample variability, due to antibody staining and/or instrument sensitivity, can introduce substantial artifacts into the data, which can in turn lead to erroneous conclusions. This variability can be eliminated by sample barcoding which enables samples to be pooled, stained and run simultaneously. Existing mass cytometry barcoding approaches require time intensive labeling, reduce the number of biologically meaningful parameters and/or rely on expensive reagents. We present an approach utilizing monoisotopic cisplatin to perform cell barcoding that does not require cell permeabilization, can be completed in 10 minutes and can be utilized in combination with existing barcoding techniques to greatly increase the number of samples which can be multiplexed to improve throughput and consistency.

Comparison of contrast media for visualization of the colon of healthy dogs during computed tomography and ultrasonography

OBJECTIVE To evaluate contrast agents for their ability to improve visualization of the colon wall and lumen during CT and ultrasonography. ANIMALS 10 healthy adult Beagles. PROCEDURES Food was withheld from dogs for 36 hours, after which dogs consumed 250 mL of polyethylene glycol solution. Dogs were then anesthetized, a contrast agent (tap water, diluted barium, or air; order randomly assigned) was administered rectally, iodine contrast medium (880 mg of I/kg) was administered IV, and CT and ultrasonography of the colon were performed. After a 1-week washout period, this process was repeated with a different contrast agent until all agents had been evaluated. Two investigators reviewed the CT and ultrasonographic images for colon wall thickness, conspicuity, artifacts, wall layering, and degree of lumen dilation at 4 sites. RESULTS Thickness of the colon wall was greatest in CT and ultrasonographic images with water used as contrast agent, followed by barium and then air. The CT images obtained after water administration had a smooth appearance that outlined the colonic mucosa and had the highest score of the 3 contrast agents for wall conspicuity. Although no substantial artifacts related to any of the contrast agents were identified on CT images, barium- and gas-induced shadowing and reverberation artifacts hindered wall evaluation during ultrasonography. For ultrasonography, the degree of conspicuity was highest with barium in the near-field wall and with water in the far-field wall. In contrast to CT, ultrasonography could be used to distinguish wall layering, and the mucosal and muscular layers were distinct with all contrast agents. CONCLUSIONS AND CLINICAL RELEVANCE Use of water as a contrast agent for both CT and ultrasonography of the colon in dogs compensated for each imaging modality's disadvantages and could be beneficial in the diagnosis of colon disease.

Conductive Plastic Electrodes Reduce EEG Artifact During Pediatric ECMO Therapy.

Extracorporeal membrane oxygenation (ECMO) is a life-saving heart and lung bypass procedure that can cause substantial EEG artifact. Continuous EEG monitoring is nonetheless a helpful neuromonitoring tool for patients receiving ECMO therapy because neurologic complications are frequent, but factors such as sedation, neuromuscular blockade, and hemodynamic instability limit clinical and radiographic evaluation. We examined whether using conductive plastic electrodes in place of conventional gold electrodes reduces artifact in clinical EEG studies of pediatric ECMO patients. Four masked electroencephalographers assessed artifact and its impact on overall EEG interpretation in samples from 21 consecutive EEGs recorded during ECMO therapy (14 gold and 7 plastic). A spectral power analysis then quantified 50- to 70-Hz artifact in a larger group of 14 gold and 34 plastic electrode studies during ECMO and 4 non-ECMO gold electrode studies. The masked electroencephalographers identified less artifact (P < 0.001) and indicated greater confidence in the accuracy of EEG interpretation (P < 0.001) among studies recorded with plastic electrodes. In quantitative analyses, ECMO was associated with greater 50- to 70-Hz power among studies using gold electrodes (P < 0.001) and gold electrodes exhibited greater 50- to 70-Hz power than plastic electrodes (P < 0.001). Contrasting studies in which most of the electroencephalographers believed that interpretation was (n = 12; 7 gold and 5 plastic) or was not (n = 7; all gold) compromised by artifact, 50- to 70-Hz power was similarly higher among the compromised studies (P < 0.001). Plastic electrodes substantially reduce the burden of electrical artifact in EEG studies performed on pediatric ECMO patients and improve confidence in EEG interpretation.

Motion artefact detection in structured illumination microscopy for live cell imaging.

The reconstruction process of structured illumination microscopy (SIM) creates substantial artefacts if the specimen has moved during the acquisition. This reduces the applicability of SIM for live cell imaging, because these artefacts cannot always be recognized as such in the final image. A movement is not necessarily visible in the raw data, due to the varying excitation patterns and the photon noise. We present a method to detect motion by extracting and comparing two independent 3D wide-field images out of the standard SIM raw data without needing additional images. Their difference reveals moving objects overlaid with noise, which are distinguished by a probability theory-based analysis. Our algorithm tags motion-artefacts in the final high-resolution image for the first time, preventing the end-user from misinterpreting the data. We show and explain different types of artefacts and demonstrate our algorithm on a living cell.

Motion correction for functional MRI with three-dimensional hybrid radial-Cartesian EPI.

PurposeSubject motion is a major source of image degradation for functional MRI (fMRI), especially when using multishot sequences like three‐dimensional (3D EPI). We present a hybrid radial‐Cartesian 3D EPI trajectory enabling motion correction in k‐space for functional MRI.MethodsThe EPI “blades” of the 3D hybrid radial‐Cartesian EPI sequence, called TURBINE, are rotated about the phase‐encoding axis to fill out a cylinder in 3D k‐space. Angular blades are acquired over time using a golden‐angle rotation increment, allowing reconstruction at flexible temporal resolution. The self‐navigating properties of the sequence are used to determine motion parameters from a high temporal‐resolution navigator time series. The motion is corrected in k‐space as part of the image reconstruction, and evaluated for experiments with both cued and natural motion.ResultsWe demonstrate that the motion correction works robustly and that we can achieve substantial artifact reduction as well as improvement in temporal signal‐to‐noise ratio and fMRI activation in the presence of both severe and subtle motion.ConclusionWe show the potential for hybrid radial‐Cartesian 3D EPI to substantially reduce artifacts for application in fMRI, especially for subject groups with significant head motion. The motion correction approach does not prolong the scan, and no extra hardware is required. Magn Reson Med 78:527–540, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

TH-AB-209-06: An Investigation of the Feasibility of Malignant Lesion Detection During Routine Breast Cancer Screening Using a Prototype Acousto-Optic Transmission Ultrasound Imaging System

Purpose: To investigate the feasibility of malignant lesion detection during routine breast cancer screening using an acousto-optic (AO) transmission ultrasound imaging system, particularly in premenopausal women with high breast density. Methods: A full-field, single-projection ultrasound imaging system was developed that uses a high-resolution AO detector to convert the acoustic intensity transmitted through the compressed breast into a visual image by virtue of the AO effect in nematic liquid crystals. In this work, a comprehensive system model was proposed to describe the AO imaging process, including the generation of the incident acoustic field by the transducer, the propagation of the field through the breast tissue, and the conversion of the transmitted acoustic field intensity into a visual image. Validation of the imaging model was achieved through comparison of actual AO breast phantom images with simulated images based on the proposed model. Malignant lesion detectability studies were subsequently performed in simulation using homogeneous and heterogeneous numerical breast phantoms. Results: Comparison of actual AO breast phantom images with simulated images based on the proposed system model showed strong agreement, with an RMSE less than 4%. Lesion detectability studies using homogeneous numerical breast phantoms demonstrated excellent visibility for breast lesions as small as 0.5 cm and source frequencies on the order of 4 MHz. Though lesion detectability proved immune to spatial variations in mass density (2%) and attenuation (15%) in the breast parenchyma, minor variations in parenchymal sound speed (1.3%) resulted in substantial refraction artifacts that compromised the diagnostic utility of the prototype system. Conclusions: Differences in acoustic absorption may overcome refraction and enhance lesion visibility at conventional breast ultrasound frequencies (10 to 15 MHz). However, provided the FDA limit on the incident acoustic intensity (1 W/cm2) is employed, such high-frequency imaging will require improvements in the current AO detector sensitivity (10−6 W/cm2). Department of Defense (DOD) Breast Cancer Research Program IDEA Award W81XWH-11-1-0332; National Institutes of Health (NIH) Grant T32 EB002103-24 from the National Institute of Biomedical Imaging and Bioengineering (NIBIB)

TU‐AB‐BRA‐04: An Investigation of Metal Artifact Effects in Multi‐Modalities: Development of MRI‐CT Heterogeneous Head and Neck Phantom for MRI‐CT Registration

Purpose:The purpose of this investigation was to develop an CT‐MR head and neck phantom which can investigate dose calculation differences between density‐assigned MRI and CT, and to compare non‐implant inserted registered MR‐CT registered image with artifact reduced image of MR‐CT registered image. It is to identify potential limitations related to dental implants of MR image and CT image and maximize the advantages to find interactive method to use registered image.Methods:The phantom comprises half‐circled shape which shaped to simulated the anatomical structures of a human head and neck. Through applying various clinical cases, the developed phantom is closely allied to human. Developed phantom can be verified in to opened‐mouth and closed‐mouth phantom. The case of the phantom was made of acrylic, which introduces a 0.003 parts per million (ppm) phase shift, whereas the Teflon results in a 0.03 ppm shift measured at 3T which represents human bone. Both materials are considered acceptable for MR field measurements. The phantom was filled with a solution of nickel chloride and sodium chloride. The implants and teeth were imaged by means of 3T MRI system.Results:In MRI image, the metal artifact reduced and the results in improved image quality and reduction of susceptibility artifacts originate in MR images. CT and MR artifact correction method resulted in substantial artifact reduction, both quantitatively and qualitatively. On head and neck CT images, it remained anatomical conformation but it has reduced streak and dark artifact which appeared around the dental restoration. The artifact reduced MR‐CT image improved image quality and calculation accuracy for patients with severe CT artifacts.Conclusion:By using MRI/CT and the artifact‐free slice location of the phantom, we demonstrated that the proposed artifact reduction method can effectively remove streak artifacts from a metal object.

Quantifying the accuracy of the tumor motion and area as a function of acceleration factor for the simulation of the dynamic keyhole magnetic resonance imaging method.

The dynamic keyhole is a new MR image reconstruction method for thoracic and abdominal MR imaging. To date, this method has not been investigated with cancer patient magnetic resonance imaging (MRI) data. The goal of this study was to assess the dynamic keyhole method for the task of lung tumor localization using cine-MR images reconstructed in the presence of respiratory motion. The dynamic keyhole method utilizes a previously acquired a library of peripheral k-space datasets at similar displacement and phase (where phase is simply used to determine whether the breathing is inhale to exhale or exhale to inhale) respiratory bins in conjunction with central k-space datasets (keyhole) acquired. External respiratory signals drive the process of sorting, matching, and combining the two k-space streams for each respiratory bin, thereby achieving faster image acquisition without substantial motion artifacts. This study was the first that investigates the impact of k-space undersampling on lung tumor motion and area assessment across clinically available techniques (zero-filling and conventional keyhole). In this study, the dynamic keyhole, conventional keyhole and zero-filling methods were compared to full k-space dataset acquisition by quantifying (1) the keyhole size required for central k-space datasets for constant image quality across sixty four cine-MRI datasets from nine lung cancer patients, (2) the intensity difference between the original and reconstructed images in a constant keyhole size, and (3) the accuracy of tumor motion and area directly measured by tumor autocontouring. For constant image quality, the dynamic keyhole method, conventional keyhole, and zero-filling methods required 22%, 34%, and 49% of the keyhole size (P < 0.0001), respectively, compared to the full k-space image acquisition method. Compared to the conventional keyhole and zero-filling reconstructed images with the keyhole size utilized in the dynamic keyhole method, an average intensity difference of the dynamic keyhole reconstructed images (P < 0.0001) was minimal, and resulted in the accuracy of tumor motion within 99.6% (P < 0.0001) and the accuracy of tumor area within 98.0% (P < 0.0001) for lung tumor monitoring applications. This study demonstrates that the dynamic keyhole method is a promising technique for clinical applications such as image-guided radiation therapy requiring the MR monitoring of thoracic tumors. Based on the results from this study, the dynamic keyhole method could increase the imaging frequency by up to a factor of five compared with full k-space methods for real-time lung tumor MRI.

Robust power spectral estimation for EEG data

BackgroundTypical electroencephalogram (EEG) recordings often contain substantial artifact. These artifacts, often large and intermittent, can interfere with quantification of the EEG via its power spectrum. To reduce the impact of artifact, EEG records are typically cleaned by a preprocessing stage that removes individual segments or components of the recording. However, such preprocessing can introduce bias, discard available signal, and be labor-intensive. With this motivation, we present a method that uses robust statistics to reduce dependence on preprocessing by minimizing the effect of large intermittent outliers on the spectral estimates. New methodUsing the multitaper method (Thomson, 1982) as a starting point, we replaced the final step of the standard power spectrum calculation with a quantile-based estimator, and the Jackknife approach to confidence intervals with a Bayesian approach. The method is implemented in provided MATLAB modules, which extend the widely used Chronux toolbox. ResultsUsing both simulated and human data, we show that in the presence of large intermittent outliers, the robust method produces improved estimates of the power spectrum, and that the Bayesian confidence intervals yield close-to-veridical coverage factors. Comparison to existing methodThe robust method, as compared to the standard method, is less affected by artifact: inclusion of outliers produces fewer changes in the shape of the power spectrum as well as in the coverage factor. ConclusionIn the presence of large intermittent outliers, the robust method can reduce dependence on data preprocessing as compared to standard methods of spectral estimation.

Moving average template subtraction to remove stimulation artefacts in EEGs and LFPs recorded during deep brain stimulation

BackgroundDeep brain stimulation (DBS) is a well established therapy to treat movement disorders such as Parkinson's disease. More recently it has also been discussed as a therapy for certain psychiatric diseases. However, during active DBS the recordings of local field potentials (LFP) and the electroencephalogram (EEG) can be corrupted by substantial spike-type artefacts which need to be removed before any analysis. New methodHere, we present a new method that we term ' Moving Average Subtraction' (MAS) that removes DBS artefacts by subtracting adaptive DBS artefact templates from the artefact contaminated data. In particular we have developed a resampling technique which is more efficient than upsampling for a precise reconstruction of the artefact shape without the need to oversample the EEGs. ResultsBy applying this method we can derive undistorted signals even in case of the low sampling frequencies that are usual in clinical recordings. We applied the new technique to 12 data sets recorded at the surface and in various brain structures [subthalamic nucleus (STN), pedunculo pontine nucleus (PPN), Globus pallidus internus (GPi)] with 7 patients. Our results demonstrate the suppression of artefact related activity at the basic and harmonic frequencies of DBS. Comparison with existing method(s)The new technique outperforms the non-adaptive template subtraction technique for the removal of high frequency artefact residuals without producing the spectral dips that occur with notch filter approaches. ConclusionsThe new technique facilitates the analysis of higher frequency bands (Gamma activity) in LFPs and EEGs recorded during active DBS.