Clinical magnetic resonance imaging of the equine foot: An investigation of factors influencing image quality and image interpretation

Magnetic resonance imaging (MRI) is a fundamental imaging modality for evaluation of the equine foot. Optimising image quality and observer pathology identification is important to maximise the diagnostic value of MRI. There is limited information investigating factors that influence magnetic resonance (MR) image quality in live equine patients in a clinical setting. In addition, agreement between observers assessing pathology on clinical MRI studies of the equine foot has not been investigated. This project aimed to evaluate the influence of patient general anaesthesia (which encompasses the potential effects of motion and weight-bearing) and field strength on clinical MR image quality. In addition, the project aimed to determine the agreement between expert observers for pathology assessment of clinically important anatomical structures of the equine foot. A total of fifteen routine equine MRI foot studies were acquired from the clinical databases of three different MRI systems: low-field standing, low-field under general anaesthesia and high-field under general anaesthesia. Ten experienced observers (diploma or associate level) assessed entire MRI studies and seven key individual anatomical structures of the equine foot. Observers used an online image assessment platform to grade subjective image quality (briefly, grade 1: textbook quality, grade 2: high diagnostic quality, grade 3: satisfactory diagnostic quality, grade 4: non‐diagnostic), pathology, and their confidence in pathology assessment. Statistical analysis was performed to assess the influence of anaesthesia and field strength on image quality, and to document inter-observer agreement in pathology assessment. Observers deemed most clinical MRI foot studies to be of diagnostic quality, regardless of acquisition system. There were no significant differences in image quality between low-field standing and low-field under general anaesthesia (for both groups all individual structure image quality median grades= 3). Conversely, high-field under general anaesthesia studies had significantly greater image quality for entire studies and all individual anatomical structures (median grades= 1 for 5/7 structures and 2 for 2/7 structures) compared to low-field under general anaesthesia (all individual structure median grades= 3). There was a general trend of agreement between observers for pathology assessment of anatomical structures of the equine foot. Although absolute agreement for pathology assessment grading was generally low, relative agreement (accounting for the ranking of study pathology grading) was greater. Agreement was lowest for the distal interphalangeal joint (Kendall’s coefficient of concordance= 0.19) and greatest for the navicular bone (Kendall’s coefficient of concordance= 0.70). Importantly there were instances of marked variation in pathology assessment for individual MRI studies. In general, agreement was greater at the extremes of pathology. The findings indicate that field strength is a more important influencer of image quality than general anaesthesia for MRI of the equine foot in clinical patients. However, the reasons described for reduced image quality appear to differ between MRI systems. There was a general tendency of agreement between observers for pathology assessment. However, there can be notable variation in pathology assessment for individual MRI studies, even when interpretation is performed by experienced observers. Future work is needed to evaluate the influence of image quality factors when imaging other regions of the equine limb and to investigate the processes of lesion identification and subsequent diagnostic decision making by those interpreting MRI images of the equine foot

Assessment of Magnetic Resonance Imaging Artefacts Caused By Equine Anaesthesia Equipment:A Cadaver Study

Acquisition of magnetic resonance images of the equine limb is still sometimes conducted under general anaesthesia. Despite low-field systems allow the use of standard anaesthetic equipment, possible interferences of the extensive electronic componentry of advanced anaesthetic machines on image quality is unknown. This prospective, blinded, cadaver study investigated the effects of 7 standardised conditions [Tafonius positioned as in clinical cases, Tafonius on the boundaries of the controlled area, anaesthetic monitoring only, Mallard anaesthetic machine, Bird ventilator, complete electronic silence in the room (negative control), source of electronic interference (positive control)] on image quality through the acquisition of 78 sequences using a 0.31T equine MRI scanner. Images were graded with a 4-point scoring system, where 1 denoted absence of artefacts and 4 major artefacts requiring repetition in a clinical setting. A lack of STIR fat suppression was commonly reported (16/26). Ordinal logistic regression showed no statistically significant differences in image quality between the negative control and either the non-Tafonius or the Tafonius groups (p = 0.535 and p = 0.881, respectively), and with the use of Tafonius compared to the other anaesthetic machines (p = 0.578). The only statistically significant differences in scores were observed between the positive control and the non-Tafonius (p = 0.006) and the Tafonius groups (p = 0.017). Our findings suggest that anaesthetic machines and monitoring do not appear to affect MRI scan quality and support the use of Tafonius during acquisition of images with a 0.31T MRI system in a clinical context

Equine emergency upper airway management

Respiratory distress due to acute upper respiratory tract obstruction is an uncommon emergency in equine practice. However, clinicians should be confident with the approach to this truly life-threatening scenario. Clinical signs are obvious at rest and include increased respiratory effort, loud respiratory noise and recumbency as asphyxiation progresses. Many cases of upper respiratory tract obstruction involve the pharynx or larynx, though obstruction in other regions of the upper respiratory tract and other causes of respiratory distress should be considered. Generally, the obstruction can be bypassed by placing a nasotracheal tube under endoscopic guidance or by making a temporary tracheotomy to ensure a patent airway. Following this stabilisation, further investigation into the cause of airway obstruction can be performed. Endoscopy is usually the most valuable diagnostic tool, though other imaging modalities can be useful. Further empirical treatment is often required, though the specific management will vary depending on the pathology present

Modes of Random Lasers

In conventional lasers, the optical cavity that confines the photons also determines essential characteristics of the lasing modes such as wavelength, emission pattern, ... In random lasers, which do not have mirrors or a well-defined cavity, light is confined within the gain medium by means of multiple scattering. The sharp peaks in the emission spectra of semiconductor powders, first observed in 1999, has therefore lead to an intense debate about the nature of the lasing modes in these so-called lasers with resonant feedback. In this paper, we review numerical and theoretical studies aimed at clarifying the nature of the lasing modes in disordered scattering systems with gain. We will discuss in particular the link between random laser modes near threshold (TLM) and the resonances or quasi-bound (QB) states of the passive system without gain. For random lasers in the localized regime, QB states and threshold lasing modes were found to be nearly identical within the scattering medium. These studies were later extended to the case of more lossy systems such as random systems in the diffusive regime where differences between quasi-bound states and lasing modes were measured. Very recently, a theory able to treat lasers with arbitrarily complex and open cavities such as random lasers established that the TLM are better described in terms of the so-called constant-flux states.Comment: Review paper submitted to Advances in Optics and Photonic

Large fibrosarcoma of the equine distal limb treated by surgical excision using a harmonic scalpel

An 18-year-old Warmblood gelding was presented for investigation of a large, firm mass over the medial and plantar aspect of the left distal metatarsal and fetlock region. The mass was first identified 4 months prior to referral, following a traumatic incident, and had over time gradually increased in size. Clinical examination and diagnostic imaging revealed a large soft tissue mass adjacent to the metatarsophalangeal joint and digital flexor tendon sheath, with no overt involvement of underlying bone. The mass was surgically excised under general anaesthesia using a harmonic scalpel with limited margins to avoid compromise of adjacent anatomical structures. Following histology, the mass was diagnosed as a fibrosarcoma. Twelve months after surgical resection, no signs of recurrence were evident. This report demonstrates that fibrosarcoma of the equine distal limb may be successfully managed with surgical excision. The use of a harmonic scalpel should be considered as an alternative to sharp excision when treating fibrosarcoma or other infiltrative tumours, particularly those located in regions where only limited surgical margins may be achieved

Clinical magnetic resonance image quality of the equine foot is significantly influenced by acquisition system

Background: Investigation of image quality in clinical equine magnetic resonance (MR) imaging may optimise diagnostic value. Objectives: To assess the influence of field strength and anaesthesia on image quality in MR imaging of the equine foot in a clinical context. Study design: Analytical clinical study. Methods: Fifteen equine foot studies (five studies per system) were randomly selected from the clinical databases of three MR imaging systems: low‐field standing (LF St), low‐field anaesthetised (LF GA) and high‐field anaesthetised (HF GA). Ten experienced observers graded image quality for entire studies and seven clinically important anatomical structures within the foot (briefly, grade 1: textbook quality, grade 2: high diagnostic quality, grade 3: satisfactory diagnostic quality, grade 4: non‐diagnostic). Statistical analysis assessed the effect of anaesthesia and field strength using a combination of the Pearson chi‐square test or Fisher’s exact test and Mann‐Whitney test. Results: There was no difference in the proportion of entire studies of diagnostic quality between LF St (90%, 95%CI 78‐97%) and LF GA (88%, 76‐95%, p = 0.7). No differences were evident in the proportion of diagnostic studies or median image quality gradings between LF St and LF GA when assessing individual anatomical structures (both groups all median grades=3). There was a statistically significant difference in the proportion of entire studies of diagnostic quality between LF GA and HF GA (100%, 95% CI lower bound 94%, p = 0.03). There were statistically significant differences in median image quality gradings between LF GA (all median grades=3) and HF GA (median grades=1 (5/7 structures) or 2 (2/7 structures) for all individual anatomical structures (all P<0.001). The reasons reported for reduced image quality differed between systems. Main limitations: Randomised selection of cases from clinical databases. Individual observer preferences may influence image quality assessment. Conclusions: Field strength is a more important influencer of image quality than anaesthesia for magnetic resonance imaging of the equine foot in clinical patients

Variations in the application of equine prosthetic laryngoplasty: a survey of 128 equine surgeons

Objective: To document variations in the application of equine prosthetic laryngoplasty among equine surgeons. Study design: Cross-sectional survey. Sample population: Six hundred and seventy-eight equine surgeons performing prosthetic laryngoplasty. Methods: An online questionnaire was sent to equine surgeons, including diplomates of the American College of Veterinary Surgeons and European College of Veterinary Surgeons. Questions focused on participant profile, surgical technique, antimicrobial therapy, and concurrent procedures. Descriptive statistical analysis was performed on the survey output. Results: Complete responses were received from 128/678 individuals, mostly from experienced surgeons. Most participants used 2 prostheses (106/128, 82.8%) and a single loop was the most common method used to anchor the prosthesis in the cricoid (95/128, 74.2%) and arytenoid (125/128, 97.7%) cartilages. Use of general anesthesia was common, although 46/128 (35.9%) participants now performed most laryngoplasty surgery with standing sedation. The material used as a prosthesis varied among surgeons, although participants typically aimed to achieve grade 2 intraoperative arytenoid abduction. Participants most commonly administered perioperative systemic antimicrobial therapy for 1-3 days (57/128, 44.5%) and 48/128 (37.5%) used local antimicrobial therapy. Conclusion: Most surgeons performed laryngoplasty with 2 prostheses, a single loop construct at the muscular process of the arytenoid cartilage and systemic antimicrobial therapy. There was variation in the preferred method of surgical restraint, prosthesis material selection, and use of local antimicrobial therapy. Clinical significance: Long-established techniques remain popular in clinical practice despite evidence that variations offer advantages, particularly in relation to biomechanics. Other factors are also likely to influence technique selection in a clinical context

An Assemblage of Lava Flow Features on Mercury

In contrast to other terrestrial planets, Mercury does not possess a great variety of volcanic features, its history of volcanism instead largely manifest by expansive smooth plains. However, a set of landforms at high northern latitudes on Mercury resembles surface flow features documented on Earth, the Moon, Mars, and Venus. The most striking of such landforms are broad channels that host streamlined islands and that cut through the surrounding intercrater plains. Together with narrower, more sinuous channels, coalesced depressions, evidence for local flooding of intercrater plains by lavas, and a first-order analysis of lava flow rates, the broad channels define an assemblage of flow features formed by the overland flow of, and erosion by, voluminous, high-temperature, low-viscosity lavas. This interpretation is consistent with compositional data suggesting that substantial portions of Mercury's crust are composed of magnesian, iron-poor lithologies. Moreover, the proximity of this partially flooded assemblage to extensive volcanic plains raises the possibility that the formation of these flow features may preface total inundation of an area by lavas emplaced in a flood mode and that they escaped complete burial only due to a waning magmatic supply. Finally, that these broad channels on Mercury are volcanic in nature yet resemble outflow channels on Mars, which are commonly attributed to catastrophic water floods, implies that aqueous activity is not a prerequisite for the formation of such distinctive landforms on any planetary body

Abiotic versus biotic iron mineral transformation studied by a miniaturized backscattering Mössbauer spectrometer (MIMOS II), X-ray diffraction and Raman spectroscopy

Searching for biomarkers or signatures of microbial transformations of minerals is a critical aspect for determining how life evolved on Earth, and whether or not life may have existed in other planets, including Mars. In order to solve such questions, several missions to Mars have sought to determine the geochemistry and mineralogy on the Martian surface. This research includes the two miniaturized Mössbauer spectrometers (MIMOS II) on board the Mars Exploration Rovers Spirit and Opportunity, which have detected a variety of iron minerals on Mars, including magnetite (Fe2+Fe3+2O4) and goethite (α-FeO(OH)). On Earth, both minerals can derive from microbiological activity (e.g. through dissimilatory iron reduction of ferrihydrite by Fe(III)-reducing bacteria). Here we used a lab based MIMOS II to characterize the mineral products of biogenic transformations of ferrihydrite to magnetite by the Fe(III)-reducing bacteria Geobacter sulfurreducens. In combination with Raman spectroscopy and X-ray diffraction (XRD), we observed the formation of magnetite, goethite and siderite. We compared the material produced by biogenic transformations to abiotic samples in order to distinguish abiotic and biotic iron minerals by techniques that are or will be available onboard Martian based laboratories. The results showed the possibility to distinguish the abiotic and biotic origin of the minerals. Mossbauer was able to distinguish the biotic/abiotic magnetite with the interpretation of the geological context (Fe content mineral assemblages and accompanying minerals) and the estimation of the particle size in a non-destructive way. The Raman was able to confirm the biotic/abiotic principal peaks of the magnetite, as well as the organic principal vibration bands attributed to the bacteria. Finally, the XRD confirmed the particle size and mineralogy

Synovial sepsis of unknown origin in the adult Thoroughbred racehorse

Background: Synovial sepsis of unknown origin is a rare cause of lameness in the adult horse, and a haematogenous pathogenesis has been proposed in previous cases. Objectives: To describe the features and outcome of synovial sepsis of unknown origin in adult Thoroughbred racehorses. Study design: Retrospective case series. Methods: Hospital records for admissions between 2005 and 2015 were reviewed to identify adult horses diagnosed with synovial sepsis of unknown origin. Presentation, clinicopathological, microbiological and diagnostic imaging findings were recorded. Treatment methods, surgical findings, complications and long-term outcome were evaluated. Results: Eleven cases were identified over the study period. Diagnosis was established from clinical examination and clinicopathologic findings, which were comparable to other aetiologies of synovial sepsis. Affected structures included synovial joints, tendon sheaths and bursae. Concurrent osteochondritis dissecans or articular cartilage lesions were evident during arthroscopic surgery in three cases. Significant intrasynovial haemorrhage was not identified. Microbial culture of synovial fluid or synovial biopsy was positive in 6/11 of cases, with all isolates being Gram-positive cocci. Of the 6 positive microbial cultures, all isolates demonstrated in vitro sensitivity to a cephalosporin antimicrobial agent. A concurrent remote wound was present in a single case. No other potential origins of bacteraemia were identified. Treatment methods included endoscopic surgery, standing multineedle lavage, intravenous regional limb perfusion, intrasynovial medication and/or systemic antimicrobial administration. All horses survived to hospital discharge. For the 6/11 cases that raced following synovial sepsis, the median period for return to racing was 221 days. Main limitations: A small study population, which was retrospectively reviewed. Conclusions: Synovial sepsis of unknown origin is rare in the adult Thoroughbred racehorse and can affect a range of synovial structures. A concurrent potential source of bacteraemia is rarely identified. With appropriate management, the prognosis to return to racing is fair