Quality assessment of anterior segment OCT images: Development and validation of quality criteria

BACKGROUND

The utility of medical imaging is dependant on image quality. We aimed to develop and validate quality criteria for ocular anterior segment optical coherence tomography (AS-OCT) images.

METHODS

We undertook a cross-sectional study using AS-OCT images from patients aged 6-16. A novel three-level grading system (good, limited or poor) was developed based on the presence of image artefact (categorised as lid, eyelash, cropping, glare, or movement artefact). Three independent experts graded 2825 images, with agreement assessed using confusion matrices and intraclass correlation coefficients (ICC) for each parameter.

RESULTS

There was very good inter-grader IQA agreement assessing image quality with ICC 0.85 (95 %CI: 0.84-0.87). The most commonly occurring artefact was eyelash artefact (1008/2825 images, 36 %). Graders labelled 621/2825 (22 %) images as good and 384 (14 %) as poor. There was complete agreement at either end of the confusion matrix with no 'good' images labelled as 'poor' by other graders, and vice versa. Similarly, there was very good agreement when assessing presence of lash (0.96,0.94-0.98), movement (0.97,0.96-0.99), glare (0.82,0.80-0.84) and cropping (0.90,0.88-0.92).

CONCLUSIONS

The novel image quality assessment criteria (IQAC) described here have good interobserver agreement overall, and excellent agreement on the differentiation between 'good' and 'poor' quality images. The large proportion of images graded as 'limited' suggests the need for refine this classification, using the specific IQAC features, for which we also report high interobserver agreement. These findings support the future potential for wider clinical and community care implementation of AS-OCT for the diagnosis and monitoring of ocular disease.

Broadly applicable methods for the detection of artefacts in electroencephalography acquired simultaneously with hemodynamic recordings

Electroencephalography (EEG) data, acquired simultaneously with magnetic resonance imaging (MRI), must be corrected for artefacts related to MR gradient switches (GS) and the cardioballistic (CB) effect. Canonical approaches require additional signal acquisition for artefact detection (e.g., MR volume onsets, ECG), without which the EEG data would be rendered uncleanable from these artefacts.•We present two broadly applicable methods for artefact detection based on peak detection combined with temporal constraints with respect to periodicity directly from the EEG data itself; no additional signals are required. We validated the performance of our methods versus the two canonical approaches for detection of GS/CB artefact, respectively, on 26 healthy human EEG-functional MRI resting-state datasets. Utilising various performance metrics, we found our methods to perform as well as - and sometimes better than - the canonical standard approaches. With as little as one EEG channel recording, our methods can be applied to detect GS/CB artefacts in EEG data acquired simultaneously with MRI in the absence of MR volume onsets and/or an ECG recording. The detected artefact onsets can then be fed into the standard artefact correction software.

Magnetic resonance imaging artefacts caused by orthodontic appliances and/or implant-supported prosthesis: a systematic review

OBJECTIVES

Dental materials, including orthodontic appliances and implants, are commonly mentioned as a possible source of artefacts in magnetic resonance imaging (MRI). The aim of the present study was to undertake a systematic review of the relevant literature on MR image artefacts due to dental materials, limited to orthodontic appliances and implant-supported dental prosthesis, on both technical and diagnostic levels.

METHODS

The MEDLINE (PubMed) bibliographic database was searched up to September 2020. The search was limited to studies published in English, using the search string: (MRI or magnetic resonance) and (artefact or artifact) and (dental or ortho or implant or restoration or restorative). The studies were assessed independently by three reviewers, focusing on the following parameters: MRI sequences, tested materials, assessed parameters, efficacy level and outcome.

RESULTS

The search strategy yielded 31 studies, which were included in this systematic review. These studies showed that metallic dental materials, commonly present in orthodontic appliances and implant-supported dental prosthesis led to diverse types/severities of artefacts in MR images. Fifteen studies were in vivo, based on human subjects. The studies differed substantially in terms of tested materials, assessed parameters, and outcome measurements.

CONCLUSIONS

Metallic dental materials cause artefacts of diverse types and severities in MR images of the head and neck region. However, the diagnostic relevance of the investigated artefacts for the diverse MRI applications is yet to be studied.

The effect of metallic dental restorations and implants in causing patient discomfort and artefacts during magnetic resonance imaging of the head and neck

Context

Patients with metallic dental objects in their oral cavity are often associated with discomfort or artefacts during magnetic resonance imaging (MRI) of the head and neck.

Aim

This study was conducted to evaluate the effects of metallic dental objects in causing patient discomfort and artefacts during MRI of the head and neck region.

Design

This is an observational study including 538 participants from various specialized MRI centres in Kozhikode.

Methods and Material

MRI records of 538 participants who underwent head and neck MRI as a part of their medical treatment were collected. With the help of questionnaire and clinical examination, the type of metallic dental object in the patient's oral cavity was identified. After examining the MRI images, four categories of artefacts were established. In MRI brain, artefacts in three different sequences were also studied.

Statistical Analysis Used

The significance of the difference between proportions was analysed by the Chi-square test.

Results

Artefacts were found in 65 cases with metallic dental objects but none of the participants had experienced any kind of discomfort. The artefact formation significantly depended on the type of metallic dental restoration in the patient's oral cavity. Orthodontic braces and titanium bone plate created severe artefacts in head and neck MRI making interpretation almost impossible. In the MRI brain, diffusion-weighted imaging is most sensitive to artefact followed by fluid-attenuated inversion recovery.

Conclusions

Artefacts were found in 65 cases with metallic dental restorations but none of the participants had experienced any kind of discomfort.

Metal artefact reduction in the oral cavity using deep learning reconstruction algorithm in ultra-high-resolution computed tomography: a phantom study

OBJECTIVES

This study aimed to improve the impact of the metal artefact reduction (MAR) algorithm for the oral cavity by assessing the effect of acquisition and reconstruction parameters on an ultra-high-resolution CT (UHRCT) scanner.

METHODS

The mandible tooth phantom with and without the lesion was scanned using super-high-resolution, high-resolution (HR), and normal-resolution (NR) modes. Images were reconstructed with deep learning-based reconstruction (DLR) and hybrid iterative reconstruction (HIR) using the MAR algorithm. Two dental radiologists independently graded the degree of metal artefact (1, very severe; 5, minimum) and lesion shape reproducibility (1, slight; 5, almost perfect). The signal-to-artefact ratio (SAR), accuracy of the CT number of the lesion, and image noise were calculated quantitatively. The Tukey-Kramer method with a p-value of less than 0.05 was used to determine statistical significance.

RESULTS

The HR_DLR visual score was better than the NR_HIR score in terms of degree of metal artefact (4.6 ± 0.5 and 2.6 ± 0.5, p < 0.0001) and lesion shape reproducibility (4.5 ± 0.5 and 2.9 ± 1.1, p = 0.0005). The SAR of HR_DLR was significantly better than that of NR_HIR (4.9 ± 0.4 and 2.1 ± 0.2, p < 0.0001), and the absolute percentage error of the CT number in HR_DLR was lower than that in NR_HIR (0.8% in HR_DLR and 23.8% in NR_IR). The image noise of HR_DLR was lower than that of NR_HIR (15.7 ± 1.4 and 51.6 ± 15.3, p < 0.0001).

CONCLUSIONS

Our study demonstrated that the combination of HR mode and DLR in UHRCT scanner improved the impact of the MAR algorithm in the oral cavity.

ST elevation myocardial infarction, or not - This is the question

We present an artefactual ECG created by a digital ECG-recording machine, caused by deletion of the first 80 ms of the QRS complex immediately following the pacing spike in a patient with complete atrio-ventricular block, biventricular pacing and chronic atrial fibrillation. The artefact was mistaken for inferior ST elevation myocardial infarction and the patient underwent unnecessary urgent coronary angiogram. We are not aware of this particular artefact pattern being previously reported in the literature.

Diagnostic Utility of CUSA Specimen in Histopathological Evaluation of Tumors of Central Nervous System

Introduction

Cavitron Ultrasonic Surgical Aspirator (CUSA) is a technique used for the surgical treatment of tumors that aids the surgeon in highly selective tumor sampling with minimal injury to surrounding tissues. The utility of the tissue obtained from CUSA for histopathological diagnosis of central nervous system tumors is not as well-known as its surgical benefits. Even though a few studies have evaluated the diagnostic accuracy of CUSA specimen, these have dealt with very few cases.

Methodology

In this study, we nil analysed 73 cases of CNS tumors (glial and non-glial) where CUSA specimen was available for histopathological examination and compared with findings on conventional samples as gold standard.

Results

Most frequent types of artefacts induced by CUSA included tissue breakdown resembling necrosis, empty spaces in tissues, and crush artefacts particularly in cellular tumors, that interfered with interpretation. CUSA samples were found optimal for diagnosis of non-glial tumors (45/73), (mainly mesenchymal), wherein the diagnostic utility was comparable to the conventional samples. Difficulties were encountered in glial neoplasms, medulloblastomas and meningiomas. In glial neoplasms (28/73), accurate grading was not possible (9/28, 32%) utilising CUSA samples alone as necrosis and mitosis were not represented. Similarly in meningiomas, mitosis and brain invasion, essential for grading, was not recognizable in CUSA samples. In medulloblastomas, extensive crush artefacts interfered with diagnosis and histological subtyping making it mandatory to examine conventional tissue samples and CUSA. Immunohistochemistry results were optimal with CUSA tissue, wherever performed.

Conclusion

The greatest benefits of CUSA, is its ability to sample multiple areas enhancing the yield in heterogenous tumors like gliosarcomas and its utility in tumors at surgically inaccessible sites. As a policy, we recommend that it is beneficial that all surgically excised tissues including those from the CUSA bottle and suction be sent for histopathological analysis for optimising diagnostic accuracy.

Learning about construction behaviour from observing an artefact: can experience with conspecifics aid in artefact recognition?

Observation of or interaction with the enduring products of behaviour, called 'social artefacts' (e.g. an abandoned nest) is a potential source of social information. To learn from an artefact, that artefact needs to be recognized as the product of a behaviour that can provide relevant information (i.e. the artefact should be recognized as a nest). We used zebra finches (Taeniopygia guttata) to experimentally test whether observing a conspecific using a nest facilitates recognition of a future artefact as a source of social information. We manipulated the opportunity to form an association between a conspecific and their nest: half the subjects observed a pair of birds incubating eggs in a nest, the control subjects did not get this opportunity. Then, subjects observed an artefact made of their non-preferred colour and finally were allowed to build a nest. We predicted that the subjects given the opportunity to associate a nest with conspecifics would copy the colour of the artefact (i.e. use social information). We found that subjects who had the opportunity to learn what a nest is used social information obtained from the artefact by increasing their use of the artefact-material colour after artefact observation, while control birds did not. These data suggest that forming an association between conspecifics and their nest facilitates recognition of an artefact as a nest affecting how first-time builders use social information. This finding is important because it demonstrates that social learning is not limited to observing behaviour, but rather inferring behaviour from an artefact.

Deep learning for detection and segmentation of artefact and disease instances in gastrointestinal endoscopy

The Endoscopy Computer Vision Challenge (EndoCV) is a crowd-sourcing initiative to address eminent problems in developing reliable computer aided detection and diagnosis endoscopy systems and suggest a pathway for clinical translation of technologies. Whilst endoscopy is a widely used diagnostic and treatment tool for hollow-organs, there are several core challenges often faced by endoscopists, mainly: 1) presence of multi-class artefacts that hinder their visual interpretation, and 2) difficulty in identifying subtle precancerous precursors and cancer abnormalities. Artefacts often affect the robustness of deep learning methods applied to the gastrointestinal tract organs as they can be confused with tissue of interest. EndoCV2020 challenges are designed to address research questions in these remits. In this paper, we present a summary of methods developed by the top 17 teams and provide an objective comparison of state-of-the-art methods and methods designed by the participants for two sub-challenges: i) artefact detection and segmentation (EAD2020), and ii) disease detection and segmentation (EDD2020). Multi-center, multi-organ, multi-class, and multi-modal clinical endoscopy datasets were compiled for both EAD2020 and EDD2020 sub-challenges. The out-of-sample generalization ability of detection algorithms was also evaluated. Whilst most teams focused on accuracy improvements, only a few methods hold credibility for clinical usability. The best performing teams provided solutions to tackle class imbalance, and variabilities in size, origin, modality and occurrences by exploring data augmentation, data fusion, and optimal class thresholding techniques.

Artifacts in Optical Coherence Tomography Angiography

We performed a comprehensive search of the published literature in PubMed and Google Scholar to identify types, prevalence, etiology, clinical impact, and current methods for correction of various artifacts in optical coherence tomography angiography (OCTA) images. We found that the prevalence of OCTA image artifacts is fairly high. Artifacts associated with eye motion, misidentification of retinal layers, projections, and low optical coherence tomography signal are the most prevalent types. Artifacts in OCTA images are the major limitations of this diagnostic modality in clinical practice and identification of these artifacts and measures to mitigate them are essential for correct diagnosis and follow-up of patients.

Cone-beam Computed Tomographic-based Assessment of Filled C-shaped Canals: Artifact Expression of Cone-beam Computed Tomography as Opposed to Micro-computed Tomography and Nano-computed Tomography

INTRODUCTION

The present study investigated the assessment of root canal fillings in a series of cone-beam computed tomographic (CBCT) images obtained from endodontically treated mandibular molars with C-shaped canals.

METHODS

Clinically comparable high (HR) and normal (NR) resolution protocols were selected in 3D Accuitomo 170 (J Morita Corporation, Kyoto, Japan), NewTom VGi evo (Cefla QR Verona, Verona, Italy), ProMax 3D Max (Pro; Planmeca, Helsinki, Finland), and Pax-i3D Green Premium (Pax; Vatech, Gyeonggi, South Korea). Micro-computed tomographic and nano-computed tomographic images were considered as the reference standard. The set of images was evaluated according to beam hardening artifact patterns (dark streaks, hypodense areas, and volume distortion).

RESULTS

Regarding dark streaks, the Fleiss kappa test showed that Pax HR and NR and Pro HR images showed the highest artifact expression. Hypodense areas were detected in 100% and 99.1% of the images obtained using Pax HR and NR, respectively. Kappa tests showed highest distortion for images derived from the Pax and Pro CBCT devices. Root canal filling assessment was considered appropriate in 100% of the 3D Accuitomo 170 HR, NewTom VGi evo NR, micro-computed tomographic, and nano-computed tomographic images.

CONCLUSIONS

The present study confirms the large variability in CBCT-derived artifact expression. Highlighting the increased artifact expression for particular CBCT systems, it may be concluded that for diagnosis of endodontically filled molars with C-shaped canals, the choice of CBCT unit and protocol is essential.

Conductive heating mattress leads to ECG changes that mimic pacemaker spikes

Hypothermia is a common perioperative complication. To prevent perioperative hypothermia amongst other things electrical heating mattresses are used. We have made an observation with the use of an electrical heating mattress that may confuse users. In this case the ECG monitoring suddenly showed spikes that looked like spikes from an implanted pacemaker. When turning off the heating mattress the spikes disappeared and returned after turning on the heating mattress again.

Artifacts in Macular Optical Coherence Tomography

Purpose:

To identify and explain different artifacts in macular optical coherence tomography (OCT).

Methods:

For this comprehensive review, a PubMed and Google Scholar (January 1995–October 2018) search was conducted by the researchers, using the keywords such as OCT, artifacts, artefact, and macula.

Results:

We reviewed the main OCT artifacts including software break-down or misidentification of retinal layers, incomplete segmentation error, complete segmentation failure, mirror artifact (inverted artifact), cut edge artifact, degraded image scan, out-of-register artifact, off-center artifact, motion artifact, foveal duplication, segmentation shift, blink artifact, static or fixed image artifact, linear artifact, and perfluorocarbon liquid-producing artifact.

Conclusions:

There are various artifacts in OCT image scans. The identification of these artifacts may help in accurate interpretations of OCT images in clinical settings that can affect the diagnosis and management of different retinal disorders.

Inter-slice leakage and intra-slice aliasing in simultaneous multi-slice echo-planar images

Simultaneous multi-slice (SMS) imaging is a popular technique for increasing acquisition speed in echo-planar imaging (EPI) fMRI. However, SMS data are prone to motion sensitivity and slice leakage artefacts, which spread signal between simultaneously acquired slices. Relevant to motion sensitivity, artefacts from moving anatomic structures propagate along the phase-encoding (PE) direction. This is particularly relevant for eye movement. As signal from the eye is acquired along with signal from simultaneously excited slices during SMS, there is potential for signal to spread in-plane and between spatially remote slices. After identifying an artefact temporally coinciding with signal fluctuations in the eye and spatially distributed in correspondence with multiband slice acceleration and parallel imaging factors, we conducted a series of small experiments to investigate eye movement artefacts in SMS data and the contribution of PE direction to the invasiveness of these artefacts. Five healthy adult volunteers were scanned during a blinking task using a standard SMS-EPI protocol with posterior-to-anterior (P ≫ A), anterior-to-posterior (A ≫ P) or right-to-left (R ≫ L) PE direction. The intensity of signal fluctuations (artefact severity) was measured at expected artefact positions and control positions. We demonstrated a direct relationship between eye movements and artefact severity across expected artefact regions. Within-brain artefacts were apparent in P ≫ A- and A ≫ P-acquired data but not in R ≫ L data due to the shift in artefact positions. Further research into eye motion artefacts in SMS data is warranted but researchers should exercise caution with SMS protocols. We recommend rigorous piloting of SMS protocols and switching to R ≫ L/L ≫ R PE where feasible.

A Cautionary Tale: Endogenous Biotinylated Proteins and Exogenously-Introduced Protein A Cause Antibody-Independent Artefacts in Western Blot Studies of Brain-Derived Proteins

Antibodies are commonly used to detect or isolate proteins from biological samples. Much attention has been paid to the potential for poorly-characterized antibodies to lead to misleading results, but antibody-independent artefacts may also occur. Here, we recount two examples of antibody-independent artefacts that have confounded the interpretation of results in our search for molecular entities associated with memory loss in Alzheimer’s disease (AD). First, when using biotin-avidin systems for antibody detection, endogenous biotinylated proteins created spurious bands in Western blots of brain lysates from AD patients and transgenic mouse models of AD. These artefactual bands occurred in a transgene- and strain-dependent manner. A second, unexpected artefact occurred when Protein A-conjugated Sepharose beads were used to deplete lysates of endogenous immunoglobulins prior to immunopurification of target proteins. In these assays, Protein A shed from the beads, then bound to (and was eluted from) an immunoaffinity matrix designed to capture AD-related proteins. The Protein A then bound detection antibodies when the immunoaffinity eluates were analyzed by Western blot. Both of these artefacts–the endogenous biotinylated proteins and the Protein A artefact–can be monitored by including an “irrelevant” antibody as an experimental control (e.g., running a parallel protocol in which the antibody directed against the target of interest is replaced by a non-specific antibody).

Interaction of biologically relevant proteins with ZnO nanomaterials: A confounding factor for in vitro toxicity endpoints

The results of in vitro toxicological studies for manufactured nanomaterials (MNs) are often contradictory and not reproducible. Interference of the MNs with assays has been suggested. However, understanding for which materials and how these artefacts occur remains a major challenge. This study investigated interactions between two well-characterized ZnO MNs (NM-110 and NM-111) and lactate dehydrogenase (LDH), and two interleukins (IL-6 and IL-8). Particles (10 to 640 μg/mL) and proteins were incubated for up to 24 h in routine in vitro assays test conditions. LDH activity (OD_LDH), but not interleukins concentrations, decreased sharply in a dose-dependent manner within an hour after exposure (OD_LDH < 60% of OD_ref for both MNs at 10 μg/mL). A Freundlich adsorption isotherm was successfully applied, indicating multilayer adsorption of LDH. ZnO MNs and LDH had neutral to slightly negative surface charges in dispersion, precluding electrostatic attachment. Particle sedimentation was not a limiting factor. Fast dissolution of ZnO MNs was shown and Zn²⁺ could play a role in the OD_LDH drop. To summarize, ZnO MNs quickly reduced OD_LDH due to concentration-dependent adsorption and LDH inhibition by interaction with dissolved Zn. The control of particle interference in toxicological in vitro assays should become mandatory to avoid misleading interpretation of results.

24-hour oxygen saturation recordings in preterm infants: editing artefact

AIM

To create editing guidelines for artefact removal in preterm infant pulse oximetry recordings.

METHODS

38 preterm infants ready for discharge home from the neonatal intensive care unit underwent 24-hour pulse oximetry recording using the Masimo^® Rad-8 device. An expert panel determined editing rules based on clinical protocols. For each recording, three reports were generated, 'raw' no editing, 'auto' using the software editing feature and 'manual' reviewed and edited according to the rules. Primary outcome measures were desaturation indices including desaturation index 3% and 4%. Secondary measures included heart rate, mean oxygen saturation and time below 90%.

RESULTS

While all oximetry outcomes differed significantly between editing modes, the majority were not considered likely to influence clinical management. Use of the auto editing compared to no editing did alter by >5%: Time spent <90% oxygen saturation and Desaturation index 4% >10 seconds. The use of manual editing removed extremely low pulse values that were considered unphysiological in this group of otherwise healthy infants.

CONCLUSION

We recommend that oximetry recordings to determine cardiorespiratory stability in newborn infants ready for discharge from the neonatal unit have software editing features applied. This will remove artefact without consuming time in a busy unit.

Improved method for MR microscopy of brain tissue cultured with the interface method combined with Lenz lenses

MR in microscopy can non-invasively image the morphology of living tissue, which is of particular interest in studying the mammalian brain. Many studies use live animals for basic research on brain functions, disease pathogenesis, and drug development. However, in vitro systems are on the rise, due to advantages such as the absence of a blood-brain barrier, predictable pharmacokinetics, and reduced ethical restrictions. Hence, they present an inexpensive and adequate technique to answer scientific questions and to perform drug screenings. Some publications report the use of acute brain slices for MR microscopy studies, but these only permit single measurements over several hours. Repetitive MR measurements in longitudinal studies demand an MR-compatible setup which allows cultivation for several days or weeks, and hence properly functioning in vitro systems. Organotypic hippocampal slice cultures (OHSC) are a well-established and robust in vitro system which still exhibits most histological hallmarks of the hippocampal network in vivo. An MR compatible incubation platform is introduced in which OHSC are cultivated according to the interface method following Stoppini et al. In this cultivation method a tissue slice is placed onto a membrane with nutrition medium underneath and a gas atmosphere above, where the air-tissue interface perpendicular to the B₀ field induces strong artefacts. We introduce a handling protocol that suppresses these artefacts and increases signal quality significantly to acquire high resolution images of tissue slices. An additional challenge is the lack of available of MR microscopy equipment suitable for small animal scanners. A Lenz lens with an attached capacitor can dramatically increase the SNR in these cases, and wirelessly bring the detection system in close proximity to the sample without compromising the OHSC system through the introduction of wired detectors. The resultant signal gain is demonstrated by imaging a PFA-fixed brain slice with a 72 mm diameter volume coil without a Lenz lens, and with a broadband and a self-resonant Lenz lens. In our setting, the self-resonant Lenz lens increases the SNR 10-fold over using the volume coil only.

Orbital pathology - Iatrogenic findings and artefacts

The relationship between the ophthalmologist and ophthalmic pathologist is particularly important in orbital disease, as diagnosis is heavily dependent on correlation with clinical context. If the patient has previously had treatment to the orbit or an adjacent area, whether for the same or a different condition, tissue changes may occur which affect the histological appearance of any specimen taken. This article is an overview of therapeutic interventions which may cause either orbital pathology or an altered appearance of the tissue, either of which can pose a diagnostic challenge. The problem of artefact is also addressed as another factor which may alter the appearance of a specimen. It is hoped that the information provided in this brief review will help clinicians better evaluate what information may be relevant when submitting a specimen.

Polarisation vision: overcoming challenges of working with a property of light we barely see

In recent years, the study of polarisation vision in animals has seen numerous breakthroughs, not just in terms of what is known about the function of this sensory ability, but also in the experimental methods by which polarisation can be controlled, presented and measured. Once thought to be limited to only a few animal species, polarisation sensitivity is now known to be widespread across many taxonomic groups, and advances in experimental techniques are, in part, responsible for these discoveries. Nevertheless, its study remains challenging, perhaps because of our own poor sensitivity to the polarisation of light, but equally as a result of the slow spread of new practices and methodological innovations within the field. In this review, we introduce the most important steps in designing and calibrating polarised stimuli, within the broader context of areas of current research and the applications of new techniques to key questions. Our aim is to provide a constructive guide to help researchers, particularly those with no background in the physics of polarisation, to design robust experiments that are free from confounding factors.

Segmentation error in spectral domain optical coherence tomography measures of the retinal nerve fibre layer thickness in idiopathic intracranial hypertension

BACKGROUND

Optical Coherence Tomography (OCT) imaging is being increasingly used in clinical practice for the monitoring of papilloedema. The aim is to characterise the extent and location of the Retinal Nerve Fibre Layer (RNFL) Thickness automated segmentation error (SegE) by manual refinement, in a cohort of Idiopathic Intracranial Hypertension (IIH) patients with papilloedema and compare this to controls.

METHODS

Baseline Spectral Domain OCT (SDOCT) scans from patients with IIH, and controls with no retinal or optic nerve pathology, were examined. The internal limiting membrane and RNFL thickness of the most severely affected eye was examined for SegE and re-segmented. Using ImageJ, the total area of the RNFL thickness was calculated pre and post re-segmentation and the percentage change was determined. The distribution of RNFL thickness error was qualitatively assessed.

RESULTS

Significantly greater SegE (p = 0.009) was present in RNFL thickness total area, assessed using ImageJ, in IIH patients (n = 46, 5% ± 0-58%) compared to controls (n = 14, 1% ± 0-6%). This was particularly evident in moderate to severe optic disc swelling (n = 23, 10% ± 0-58%, p < 0.001). RNFL thickness was unable to be quantified using SDOCT in patients with severe papilloedema.

CONCLUSIONS

SegE remain a concern for clinicians using SDOCT to monitor papilloedema in IIH, particularly in the assessment of eyes with moderate to severe oedema. Systematic assessment and manual refinement of SegE is therefore important to ensure the accuracy in longitudinal monitoring of patients.

Neck injury and conjunctival petechiae in a woman who underwent cardiopulmonary resuscitation and subsequently died from meningococcal sepsis

Cardiopulmonary resuscitation (CPR) can create a range of unusual lesions and injuries, which may complicate forensic evaluation. Although potentially sinister findings, neck injury and conjunctival petechiae may also be seen in patients who have undergone CPR. We report a case of an individual with subcutaneous bruising and hemorrhage in the deep structures of the neck and florid conjunctival petechiae at autopsy that can be explained by cardiopulmonary resuscitation and meningococcal sepsis.

The effect of post-mortem computed tomography angiography (PMCTA) using water-soluble, iodine-based radiographic contrast on histological analysis of the liver, kidneys and left ventricle of the heart

The purpose of this study was to investigate the impact of post-mortem computed-tomography angiography (PMCTA) on the histology of the liver, kidneys and heart. Multiple tissue cores were collected from the liver, left and right kidneys and left ventricle utilizing CT-guided biopsy. Subsequent whole body PMCTA was performed using a solution of polyethylene glycol and iodinated radiographic contrast, and an embalming pump. Corresponding biopsy cores were collected at autopsy, and blinded histology analysis assessing for PMCTA-induced histology artefact was performed. The blinded analysis of pre-PMCTA and post-PMCTA biopsy samples demonstrated that whole body PMCTA had no effect on the histological analyses of the liver (0%, CI = 0-13.7%), left ventricle of the heart (0%, CI = 0-36.9%) and right kidney (0%, CI = 13.2%), however likely caused increased Bowman's capsule spaces in the left kidney of one case (4%, CI = 0.01-20.4%). Other artefactual histological changes identified included eosinophilic material in the liver, whiter interstitium and dilated tubules in kidney samples, and autolysis-related changes, however these could not be categorically attributed to the PMCTA procedure. PMCTA causes zero or minimal effect to the histological examination of the liver, left kidney, right kidney and left ventricle, and as such performing PMCTA prior to autopsy is unlikely to impact autopsy histological results in these organs.

The Dismal State of Pathology Laboratories in Dental Colleges - A Stitch in Time Can Save Nine!

Being a pathologist, we all are aware of the protocols which need to be followed in the histopathology laboratories. However, quite often due to our carelessness or busy schedules we tend to skip one or two steps in the protocol. These steps may appear to be insignificant at that time but later on they may take a toll on the diagnosis by creating an artefact. Here, we have presented a case of a similar artefact which tried to mask our diagnostic ability.

Intraoperative aberrant bispectral index values due to facial nerve monitoring

Bispectral index is an accepted depth of anaesthesia monitor for guiding intraoperative hypnotic agent administration. Frontalis EMG displayed on BIS monitor may increase due to twitching of frontalis muscle. EMG increases are also known to cause artefactual increases in BIS values. We report a case of artefactual increase of EMG and subsequently BIS values, due to electrical artefact from cranial nerve stimulator being used to identify the facial nerve. An explanation of the effect of stimulator signal on BIS EMG and BIS values has been provided.

Anthropogenic microfibres pollution in marine biota. A new and simple methodology to minimize airborne contamination

Research studies on the effects of microlitter on marine biota have become more and more frequent the last few years. However, there is strong evidence that scientific results based on microlitter analyses can be biased by contamination from air transported fibres. This study demonstrates a low cost and easy to apply methodology to minimize the background contamination and thus to increase results validity. The contamination during the gastrointestinal content analysis of 400 fishes was tested for several sample processing steps of high risk airborne contamination (e.g. dissection, stereomicroscopic analysis, and chemical digestion treatment for microlitter extraction). It was demonstrated that, using our methodology based on hermetic enclosure devices, isolating the working areas during the various processing steps, airborne contamination reduced by 95.3%. The simplicity and low cost of this methodology provide the benefit that it could be applied not only to laboratory but also to field or on board work.

Apparent elevated blood alcohol due to laboratory artefact: A potential cause of misinterpretation

Of all the drugs of forensic interest, none are more common or pervasive than alcohol. A thorough understanding of all aspects of alcohol pharmacokinetics and pharmacodynamics is essential for any clinical forensic practitioner. In rare cases interpretation of blood alcohol results may require questions to be asked about laboratory analysis. We present a case where an apparently positive blood alcohol result could have resulted in an unnecessary avenue of coronial investigation of a child death.

Rejecting deep brain stimulation artefacts from MEG data using ICA and mutual information

BACKGROUND

Recording brain activity during deep brain stimulation (DBS) using magnetoencephalography (MEG) can potentially help clarifying the neurophysiological mechanism of DBS. The DBS artefact, however, distorts MEG data significantly. We present an artefact rejection approach to remove the DBS artefact from MEG data.

NEW METHODS

We developed an approach consisting of four consecutive steps: (i) independent component analysis was used to decompose MEG data to independent components (ICs); (ii) mutual information (MI) between stimulation signal and all ICs was calculated; (iii) artefactual ICs were identified by means of an MI threshold; and (iv) the MEG signal was reconstructed using only non-artefactual ICs. This approach was applied to MEG data from five Parkinson's disease patients with implanted DBS stimulators. MEG was recorded with DBS ON (unilateral stimulation of the subthalamic nucleus) and DBS OFF during two experimental conditions: a visual attention task and alternating right and left median nerve stimulation.

RESULTS

With the presented approach most of the artefact could be removed. The signal of interest could be retrieved in both conditions.

COMPARISON WITH EXISTING METHODS

In contrast to existing artefact rejection methods for MEG-DBS data (tSSS and S(3)P), the proposed method uses the actual artefact source, i.e. the stimulation signal, as reference signal.

CONCLUSIONS

Using the presented method, the DBS artefact can be significantly rejected and the physiological data can be restored. This will facilitate research addressing the impact of DBS on brain activity during rest and various tasks.

Post-operative imaging in deep brain stimulation: A controversial issue

In deep brain stimulation (DBS), post-operative imaging has been used on the one hand to assess complications, such as haemorrhage; and on the other hand, to detect misplaced contacts. The post-operative determination of the accurate location of the final electrode plays a critical role in evaluating the precise area of effective stimulation and for predicting the potential clinical outcome; however, safety remains a priority in postoperative DBS imaging. A plethora of diverse post-operative imaging methods have been applied at different centres. There is neither a consensus on the most efficient post-operative imaging methodology, nor is there any standardisation for the automatic or manual analysis of the images within the different imaging modalities. In this article, we give an overview of currently applied post-operative imaging modalities and discuss the current challenges in post-operative imaging in DBS.

Missing head and color banding in low-count SPECT reconstructions

Due to low counts in an ¹¹¹In single photon emission computed tomography (SPECT) scan, a large part of the head was missing in the reconstructed images on Philips Extended Brilliance Workspace (EBW) and IntelliSpace Portal (ISP) workstations. This problem occurred for the ordered subsets expectation maximization (OSEM) algorithm with and without resolution recovery (Astonish), but not for filtered backprojection (FBP) or maximum likelihood expectation maximization (MLEM). There were also underflow problems because the images are stored as integers resulting in a loss of intensity resolution and color banding.

Philips EBW2.0 and ISP5.02 workstations upscale low-count images, but the result is not always optimal, for example, in the case of low counts in one part and more counts in another part of an image. On these workstations, the missing head artefact problem could be resolved by applying a Hann pre-filter (with a cutoff at the Nyquist frequency, which only influences the filtering) in the reconstruction process. Upscaling of the projection data prior to reconstruction did not recover the head in the images, neither did limiting the reconstructed volume to the low-count part of interest.

Underflow problems were partially solved by the new version 2.0 of the Philips EBW and ISP stations, although situations could arise where underflow still poses a problem. A solution for the underflow problems is to upscale the raw projection data before reconstruction. While this results in a pure upscaling of the FBP reconstruction, the effect in iterative statistical reconstruction is not only upscaling of the intensities because the assumption of Poisson statistics of the data is violated. However, the influence of this last matter seems limited.

Reconstruction of studies with low counts in relevant areas should be performed with care. Reconstruction artefacts and scaling issues can easily arise.

Imaging of lumbar spinal surgery complications

Abstract

Lumbar spine surgery for spinal stenosis is a frequently performed procedure and was the fastest growing type of surgery in the US from 1980 to 2000. With increasing surgical invasiveness, postoperative complications also tend to be higher. Cross-sectional imaging techniques (CT and MRI) are more sensitive than radiographs and play an increasingly important role in evaluation of patients with lumbar spine surgery. Their use in patients with metallic implants is somewhat limited by artefacts, which can obscure pathology and decrease accuracy and reader confidence. Metal artefact reduction techniques have been developed, which can significantly improve image quality and enable early detection of postoperative complications. Complications can occur throughout postoperative course. Early complications include hardware displacement, incidental durotomy, postoperative collections—most commonly seroma, and less likely haematoma and/or infection. Incidental durotomy with CSF leak causing intracranial hypotension has characteristic MR brain findings and diagnosis of occult leak sites have been improved with use of dynamic CT myelography. Haematomas, even when compressing the thecal sac, are usually asymptomatic. Early infection, with nonspecific MR findings, can be diagnosed accurately using dual radiotracer studies. Delayed complications include loosening, hardware failure, symptomatic new or recurrent disc herniation, peri-/epidural fibrosis, arachnoiditis, and radiculitis.

Teaching Points

• CT and MRI play an increasingly important role in evaluation of patients with lumbar spine surgery

• Complications can occur throughout the postoperative course and early detection is critical

• Artefact reduction techniques can improve image quality for early and improved detection of complications

19(4→3)-abeo-abietane diterpenoids from Scrophularia dentata Royle ex Benth

Five 19(4→3)-abeo-abietane diterpenoids, scrodentoids A-E (1-5), were isolated from the whole plant of Scrophularia dentata. Planar structures of scrodentoids A-E were elucidated mainly by using 1D, 2D NMR and MS data. The absolute configurations of compounds 1 and 2 were established using X-ray crystallographic analysis. The absolute configurations of other compounds were confirmed using HPLC-UV/CD detection. The immunosuppressive effects of compounds 1-5 were studied using a ConA-induced splenocyte proliferation model. These compounds significantly inhibited ConA-induced splenocyte proliferation, with IC50 values in the range of 3.49-133.86 μM. Compounds 1-5 (IC50>10 μM) showed no discernible cytotoxic activity against B16 or MCF-7 cells.

Electrically evoked compound action potentials artefact rejection by independent component analysis: procedure automation

BACKGROUND

Independent-components-analysis (ICA) successfully separated electrically-evoked compound action potentials (ECAPs) from the stimulation artefact and noise (ECAP-ICA, Akhoun et al., 2013).

NEW METHOD

This paper shows how to automate the ECAP-ICA artefact cancellation process. Raw-ECAPs without artefact rejection were consecutively recorded for each stimulation condition from at least 8 intra-cochlear electrodes. Firstly, amplifier-saturated recordings were discarded, and the data from different stimulus conditions (different current-levels) were concatenated temporally. The key aspect of the automation procedure was the sequential deductive source categorisation after ICA was applied with a restriction to 4 sources. The stereotypical aspect of the 4 sources enables their automatic classification as two artefact components, a noise and the sought ECAP based on theoretical and empirical considerations.

RESULTS

The automatic procedure was tested using 8 cochlear implant (CI) users and one to four stimulus electrodes. The artefact and noise sources were successively identified and discarded, leaving the ECAP as the remaining source. The automated ECAP-ICA procedure successfully extracted the correct ECAPs compared to standard clinical forward masking paradigm in 22 out of 26 cases.

COMPARISON WITH EXISTING METHOD(S)

ECAP-ICA does not require extracting the ECAP from a combination of distinct buffers as it is the case with regular methods. It is an alternative that does not have the possible bias of traditional artefact rejections such as alternate-polarity or forward-masking paradigms.

CONCLUSIONS

The ECAP-ICA procedure bears clinical relevance, for example as the artefact rejection sub-module of automated ECAP-threshold detection techniques, which are common features of CI clinical fitting software.

Comparison of monopolar and bipolar diffusion weighted imaging sequences for detection of small hepatic metastases

OBJECTIVE

To compare monopolar (MP) and bipolar (BP) diffusion weighted imaging (DWI) in detecting small liver metastases.

MATERIALS AND METHODS

Eighty-eight patients underwent 3-T MRI. The signal-to-noise ratios (SNR) of the liver parenchyma and lesions, the lesion-to-liver contrast-to-noise ratios (CNR), and the detection sensitivities were compared. The lesion distortion was scored (LDS) from 4 (no distortion) to 1 (excessive distortion), dichotomised as no-distortion and distortion, and the association between detected lesions for each reader in the MP or BP DWI group and the dichotomised lesion distortion degree was assessed.

RESULT

Forty-six hepatic metastases were confirmed. The CNR with BP images showed significantly higher values than with MP (P=0.017). The detection sensitivities of the three readers were higher in the BP sequence than in MP, and one reader detected significantly more hepatic lesions with BP images (P=0.04). LDS was significantly improved with BP sequence (P=0.002). In the no-distortion group, excluding the MP DWI assessments of one reader, detection sensitivities were significantly higher than in the distortion group (P<0.001 and P=0.002, respectively).

CONCLUSION

Reduced lesion distortion improves the detection of small liver metastases, and BP is more sensitive in detecting small liver metastases than MP DWI.

On a ghost artefact in ultra low field magnetic resonance relaxation imaging

Nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) are widely used techniques across numerous disciplines. While typically implemented at fields >1T, there has been continuous interest in the methods at much lower fields for reasons of cost, material contrast, or application. There have been numerous demonstrations of MR at much lower fields (from 1μT to 1mT), the so-called ultra-low field (ULF) regime. Approaches to ULF MR have included superconducting quantum interference device (SQUID) sensor technology for ultra-sensitive detection and the use of pulsed pre-polarizing fields to enhance the signal strength. There are many advantages to working in the ULF regime. However, due to the low strength of the measurement field, acquisition of MRI at ULF is more susceptible to ambient fields that cause image distortions. Imaging artifacts can be caused by transients associated with non-ideal field switching and from remnant fields in magnetic shielding, among other causes. In this paper, we introduce a general theoretical framework that describes effects of non-ideal measurement field inversion/rotation due to presence of these transient fields. We illustrate imaging artifacts via simulated and experimental examples.

Processing strategies to obtain clean interleaved ultrafast 2D NMR spectra

Ultrafast (UF) 2D NMR enables the acquisition of 2D spectra in a single-scan. In spite of its promising potential, the accessible spectral width is highly limited by the maximum gradient amplitude, which limits the general applicability of the method. A number of solutions have been recently described to deal with this limitation, among which stands the possibility to record several interleaved scans. However, this alternative acquisition scheme leads to numerous ghost peaks characteristic of interleaved acquisitions. These artefacts highly affect the readability of 2D spectra for structural elucidation, as well as their quantitative performance. Here, we propose several pre-FT or post-FT processing corrections to clean artefacts from interleaved ultrafast NMR spectra. Their performances are compared, and their potentialities are illustrated in a small organic molecule context. Post-FT processing corrections such as ArSub (Artefact Subtraction) or symmetrisation appear to be the most efficient ones in terms of artefact removal. While not purely single-scan, these strategies open new perspectives towards the routine use of UF 2D NMR for structural or quantitative analysis.

Electrocardiographic artefacts mimicking atrial tachycardia resulted in unnecessary diagnostic and therapeutic measures

Electrocardiographic (ECG) artefacts may closely simulate both supraventricular and ventricular tachycardias. We describe a case initially diagnosed as rapid atrial fibrillation, based on 12-lead surface ECG (especially the limb leads) and monitor tracing. The arrhythmia was resistant to beta blockers. Because of the at times apparently regular rhythm, an esophageal ECG recording was performed, and adenosine was administered. When the presumed atrial fibrillation terminated after sodium pentothal was administered while preparing for electrical cardioversion, the oesophageal ECG recordings and the ECGs during adenosine administration were reviewed. An ECG artefact diagnosis was suspected, and then confirmed, during relapse of the "arrhythmia," with simple palpation of the radial pulse and cardiac auscultation.

Small bowel MRI enteroclysis or follow through: Which is optimal?

AIM: To determine if a nasojejunal tube (NJT) is required for optimal examination of enteroclysis and if patients can be examined only in the supine position.

METHODS: Data were collected from all patients undergoing small bowel (SB) magnetic resonance imaging (MRI) examination over a 32-mo period. Patients either underwent a magnetic resonance (MR) follow-through (MRFT) or a MR enteroclysis (MRE) in the supine position. The quality of proximal and distal SB distension as well as the presence of motion artefact and image quality were assessed by 2 radiologists.

RESULTS: One hundred and fourteen MR studies were undertaken (MRFT-49, MRE-65) in 108 patients in the supine position only. Image artefact was more frequent in MRE than in MRFT (29.2% vs 18.4%), but was not statistically significant (P = 0.30). Adequate distension of the distal SB was obtained in 97.8% of MRFT examinations and in 95.4% of MRE examinations, respectively. Proximal SB distension was, however, less frequently optimal in MRFT than in MRE (P = 0.0036), particularly in patients over the age of 50 years (P = 0.0099). Image quality was good in all examinations.

CONCLUSION: All patients could be successfully imaged in the supine position. MRE and MRFT are equivalent for distal SB distension and artefact effects. Proximal SB distension is frequently less optimal in MRFT than in MRE. MRE is, therefore, the preferred MR examination method of the SB.