John Magnussen

A Mathematical Model of Human Semicircular Canal Geometry: A New Basis for Interpreting Vestibular Physiology

We report a precise, simple, and accessible method of mathematically measuring and modeling the three-dimensional (3D) geometry of semicircular canals (SCCs) in living humans. Knowledge of this geometry helps understand the development and physiology of SCC stimulation. We developed a framework of robust techniques that automatically and accurately reconstruct SCC geometry from computed tomography (CT) images and are directly validated using micro-CT as ground truth. This framework measures the 3D centroid paths of the bony SCCs allowing direct comparison and analysis between ears within and between subjects. An average set of SCC morphology is calculated from 34 human ears, within which other geometrical attributes such as nonplanarity, radius of curvature, and inter-SCC angle are examined, with a focus on physiological implications. These measurements have also been used to critically evaluate plane fitting techniques that reconcile many of the discrepancies in current SCC plane studies. Finally, we mathematically model SCC geometry using Fourier series equations. This work has the potential to reinterpret physiology and pathophysiology in terms of real individual 3D morphology.

Effect of weight loss on upper airway size and facial fat in men with obstructive sleep apnoea

Background Obstructive sleep apnoea (OSA) is commonly associated with obesity and can be improved by weight loss. Changes in upper airway size related to regional fat loss may mediate the improvement in OSA. This study aimed to assess changes in upper airway size and regional facial and abdominal fat with weight loss and their association with OSA improvement. Methods Middle-aged obese men with moderate-to-severe OSA underwent a 24-week sibutramine-assisted weight loss trial. Polysomnography and CT of the head and neck were performed at baseline and 24u2005weeks. The upper airway lumen and facial and parapharyngeal fat were measured with image analysis software. Results Post-intervention there was a significant reduction in weight (−7.8±4.2u2005kg, p<0.001) and apnoea-hypopnoea index (AHI) (−15.9±20.5u2005events/h, p<0.001). Velopharyngeal airway volume significantly increased from baseline (5.3±0.4 to 6.3±0.3u2005cm3, p<0.01) and facial and paraphayngeal fat volume significantly reduced. A reduction in upper airway length was associated with improvement in AHI (r=0.385, p=0.005). The variance in AHI improvement was best explained by changes in upper airway length and visceral abdominal fat (R2=0.31, p=0.004). Conclusions Weight loss increases velopharyngeal airway volume, but changes in upper airway length appear to have a greater influence on the reduction in apnoea frequency. Inter-individual variability in the effects of weight loss on OSA severity cannot be explained in terms of changes in upper airway structure and local fat deposition alone.

Airway dimensions measured from micro-computed tomography and high-resolution computed tomography

Volume averaging results in both over- and underestimation of airway dimensions when they are measured by high-resolution computed tomography (HRCT). The current authors calibrated computerised measurements of airway dimensions from HRCT against a novel three-dimensional micro-computed tomography (CT) standard, which has a 50-fold greater resolution, as well as against traditional morphometry. Inflation-fixed porcine lung cubes were scanned by HRCT and micro-CT. A total of 59 lumen area (Ai), 30 wall area (Aaw) and 11 lumen volume (Vi) measurements were made. Ai was measured from the cut surface of 11 airways by morphometry. Airways in scanned images were matched using branching points. After calibration, the errors of Ai, Aaw and Vi HRCT measurements were determined. The current authors found a systematic, size-dependent underestimation of Ai and overestimation of Aaw from HRCT measurements. This was used to calibrate an HRCT measurement algorithm. The 95% limits of agreement of subsequent measurements were ±3.2u2005mm2 for Ai, ±4.3u2005mm2 for Aaw, and ±11.2u2005mm3 for Vi with no systematic error. Morphometric measurements agreed with micro-CT (±2.5u2005mm2) without systematic error. In conclusion, micro-computed tomography image data from inflation-fixed airways can be used as calibration standards for three-dimensional lumen volume measurements from high-resolution computed tomography, while morphometry is acceptable for two-dimensional measurements. The image dataset could be used to validate other developmental three-dimensional segmentation algorithms.

Click-evoked vestibulo-ocular reflex: Stimulus–response properties in superior canal dehiscence

Background: An enlarged, low-threshold click-evoked vestibulo-ocular reflex (VOR) can be averaged from the vertical electro-oculogram in a superior canal dehiscence (SCD), a temporal bone defect between the superior semicircular canal and middle cranial fossa. Objective: To determine the origin and quantitative stimulus–response properties of the click-evoked VOR. Methods: Three-dimensional, binocular eye movements evoked by air-conducted 100-microsecond clicks (110 dB normal hearing level, 145 dB sound pressure level, 2 Hz) were measured with dual-search coils in 11 healthy subjects and 19 patients with SCD confirmed by CT imaging. Thresholds were established by decrementing loudness from 110 dB to 70 dB in 10-dB steps. Eye rotation axis of click-evoked VOR computed by vector analysis was referenced to known semicircular canal planes. Response characteristics were investigated with regard to enhancement using trains of three to seven clicks with 1-millisecond interclick intervals, visual fixation, head orientation, click polarity, and stimulation frequency (2 to 15 Hz). Results: In subjects and SCD patients, click-evoked VOR comprised upward, contraversive-torsional eye rotations with onset latency of approximately 9 milliseconds. Its eye rotation axis aligned with the superior canal axis, suggesting activation of superior canal receptors. In subjects, the amplitude was less than 0.01°, and the magnitude was less than 3°/second; in SCD, the amplitude was up to 60 times larger at 0.66°, and its magnitude was between 5 and 92°/second, with a threshold 10 to 40 dB below normal (110 dB). The click-evoked VOR magnitude was enhanced approximately 2.5 times with trains of five clicks but was unaffected by head orientation, visual fixation, click polarity, and stimulation frequency up to 10 Hz; it was also present on the surface electro-oculogram. Conclusion: In superior canal dehiscence, clicks evoked a high-magnitude, low-threshold, 9-millisecond-latency vestibulo-ocular reflex that aligns with the superior canal, suggesting superior canal receptor hypersensitivity to sound.

Effectiveness of interventions designed to reduce the use of imaging for low-back pain: a systematic review

Background: Rates of imaging for low-back pain are high and are associated with increased health care costs and radiation exposure as well as potentially poorer patient outcomes. We conducted a systematic review to investigate the effectiveness of interventions aimed at reducing the use of imaging for low-back pain. Methods: We searched MEDLINE, Embase, CINAHL and the Cochrane Central Register of Controlled Trials from the earliest records to June 23, 2014. We included randomized controlled trials, controlled clinical trials and interrupted time series studies that assessed interventions designed to reduce the use of imaging in any clinical setting, including primary, emergency and specialist care. Two independent reviewers extracted data and assessed risk of bias. We used raw data on imaging rates to calculate summary statistics. Study heterogeneity prevented meta-analysis. Results: A total of 8500 records were identified through the literature search. Of the 54 potentially eligible studies reviewed in full, 7 were included in our review. Clinical decision support involving a modified referral form in a hospital setting reduced imaging by 36.8% (95% confidence interval [CI] 33.2% to 40.5%). Targeted reminders to primary care physicians of appropriate indications for imaging reduced referrals for imaging by 22.5% (95% CI 8.4% to 36.8%). Interventions that used practitioner audits and feedback, practitioner education or guideline dissemination did not significantly reduce imaging rates. Lack of power within some of the included studies resulted in lack of statistical significance despite potentially clinically important effects. Interpretation: Clinical decision support in a hospital setting and targeted reminders to primary care doctors were effective interventions in reducing the use of imaging for low-back pain. These are potentially low-cost interventions that would substantially decrease medical expenditures associated with the management of low-back pain.

Risk factors for a recurrence of low back pain

BACKGROUND CONTEXTnThe clinical importance of lumbar pathology identified on magnetic resonance imaging (MRI) remains unclear. It is plausible that pathology seen on MRI is a risk factor for a recurrence of low back pain (LBP); however, to our knowledge, this has not been investigated by previous studies.nnnPURPOSEnThe aim was to investigate whether lumbar pathology, identifiable on MRI, increases the risk of a recurrence of LBP.nnnSTUDY DESIGNnThis was a prospective inception cohort study with 1-year follow-up.nnnPATIENT SAMPLEnSeventy-six people who had recovered from an episode of LBP within the previous 3 months were included.nnnOUTCOME MEASURESnThe primary outcome was time to recurrence of LBP, which was determined by contacting participants at 2-month intervals for 12 months.nnnMETHODSnAll participants underwent a baseline assessment including MRI scan and completion of a questionnaire, which assessed a range of potential risk factors for recurrence. Magnetic resonance imaging scans were reported for the presence of a range of MRI findings. The primary analysis investigated the predictive value of two clinical features (age and number of previous episodes) and six MRI findings (disc degeneration, high intensity zone, Modic changes, disc herniation, facet joint arthrosis, and spondylolisthesis) in a multivariate Cox regression model. We decided a priori that dichotomous predictors with hazard ratios (HRs) of greater than 1.5 or less than 0.67 would be considered potentially clinically important and justify further investigation.nnnRESULTSnOf the eight predictors entered into the primary multivariate model, three (disc degeneration, high intensity zone, and number of previous episodes) met our a priori threshold for potential importance. Participants with disc degeneration score greater than or equal to 3 (Pfirrmann scale) had a HR of 1.89 (95% confidence interval [CI] 0.42-8.53) compared with those without. Patients with high intensity zone had an HR of 1.84 (95% CI 0.94-3.59) compared with those without. For every additional previous episode, participants had an HR of 1.04 (95% CI 1.02-1.07).nnnCONCLUSIONSnWe identified promising risk factors for a recurrence of LBP, which should be further investigated in larger trials. The findings suggest that pathology seen on MRI plays a potentially important role in recurrence of LBP.

Liposuction for Advanced Lymphedema: A Multidisciplinary Approach for Complete Reduction of Arm and Leg Swelling

PurposeThis research describes and evaluates a liposuction surgery and multidisciplinary rehabilitation approach for advanced lymphedema of the upper and lower extremities.MethodsA prospective clinical study was conducted at an Advanced Lymphedema Assessment Clinic (ALAC) comprised of specialists in plastic surgery, rehabilitation, imaging, oncology, and allied health, at Macquarie University, Australia. Between May 2012 and 31 May 2014, a total of 104 patients attended the ALAC. Eligibility criteria for liposuction included (i) unilateral, non-pitting, International Society of Lymphology stage II/III lymphedema; (ii) limb volume difference greater than 25xa0%; and (iii) previously ineffective conservative therapies. Of 55 eligible patients, 21 underwent liposuction (15xa0arm, 6xa0leg) and had at least 3xa0months postsurgical follow-up (85.7xa0% cancer-related lymphedema). Liposuction was performed under general anesthesia using a published technique, and compression garments were applied intraoperatively and advised to be worn continuously thereafter. Limb volume differences, bioimpedance spectroscopy (L-Dex), and symptom and functional measurements (using the Patient-Specific Functional Scale) were taken presurgery and 4xa0weeks postsurgery, and then at 3, 6, 9, and 12xa0months postsurgery.ResultsMean presurgical limb volume difference was 45.1xa0% (arm 44.2xa0%; leg 47.3xa0%). This difference reduced to 3.8xa0% (arm 3.6xa0%; leg 4.3xa0%) by 6xa0months postsurgery, a mean percentage volume reduction of 89.6xa0% (arm 90.2xa0%; leg 88.2xa0%) [pxa0<xa00.001]. All patients had improved symptoms and function. Bioimpedance spectroscopy showed reduced but ongoing extracellular fluid, consistent with the underlying lymphatic pathology.ConclusionsLiposuction is a safe and effective option for carefully selected patients with advanced lymphedema. Assessment, treatment, and follow-up by a multidisciplinary team is essential.

Dual-energy computed tomography - How accurate is gemstone spectrum imaging metal artefact reduction: its application to orthopedic metal implants

Objective To assess the accuracy and suitability of dual-energy computed tomography (DECT) in scanning metals used in orthopedic implants. Materials and Methods Four metal phantoms (Cobalt Chrome, Titanium Grade 5, Stainless Steel 316, and Stainless Steel 630), commonly used materials in orthopedic implants, were scanned by conventional, polychromatic CT as well as Gemstone Spectrum Imaging (GSI) DECT, with and without metal artefact reduction software (MARS). Scans were assessed for artefact based on Hounsfield unit values; and surfaces generated, based on a Canny edge detection algorithm. Two separate metal implants were also scanned and assessed for dimensional accuracy. Results Conventional, polychromatic CT, and GSI DECT (without MARS) scans displayed major beam hardening in the presence of all four metals. The GSI DECT with MARS showed very clear and reproducible boundaries with minimal noise surrounding the metal phantoms. However, geometric analysis found overestimation of the dimensions, volume, and surface area for most of the metal phantoms. Titanium displayed the least artefact, compared to the other metals, in all scan scenarios. Conclusions Although metal artefact reduction using GSI DECT looks superior to conventional CT, when measured objectively, it was shown to overestimate geometries and skew dimensions. The GSI DECT with MARS should be used with caution, especially when assessing questions of implant shape or wear.

Intraosseous hibernoma: characterization of five cases and literature review

ObjectiveTo describe the imaging and histopathological findings and provide an overview of a recently described and rare cause of bone sclerosis.Materials and methodsFive cases of intra-osseous hibernoma of bone that presented over the last year. The imaging and histopathology is reviewed.ResultsAll cases were identified in asymptomatic middle-aged to elderly adults as incidental findings with bone sclerosis in the axial skeleton. MRI showed lesions that were T1 hypointense to subcutaneous fat and hyperintense to skeletal muscle and one showed contrast enhancement. Glucose avidity was demonstrated on FDGPET in both cases tested and isotope bone scan performed in three cases showed strong positivity in two, but uptake was inconspicuous in one case.ConclusionsIntra-osseous hibernoma is a rare cause of sclerotic bone lesions, predominating in the axial skeleton of middle-aged and elderly adults. They have a non-aggressive appearance on CT and on MRI are T1 hypointense to subcutaneous fat and hyperintense to skeletal muscle. They are usually T2 hyperintense and may show peripheral contrast enhancement. They may show increased glucose avidity on FDGPET and may or may not be positive on isotope bone scans. We suspect that with ever-increasing use of a variety of imaging techniques, particularly in a setting of staging for malignant disease, more such cases will come to light. This diagnosis should be added to the differential diagnosis of sclerotic bone lesions.

Preoperative progressive pneumoperitoneum complementing chemical component relaxation in complex ventral hernia repair

BackgroundA rarely used technique for enabling closure of large ventral hernias with loss of domain is preoperative progressive pneumoperitoneum (PPP), which uses intermittent insufflation to gradually stretch the contracted abdominal wall muscles, increasing the capacity of the abdominal cavity. This allows the re-introduction of herniated viscera into the abdominal cavity and assists in closure of giant hernias which may otherwise be considered inoperable.MethodsThis was a prospective study assessing 16 patients between 2013 and 2015 with multi-recurrent ventral hernia. All patients were treated preoperatively with both Botulinum Toxin A (BTA) injections to the lateral abdominal wall muscles to confer flaccid paralysis, and short-term PPP to passively expand the abdominal cavity. All patients underwent serial abdominal CT imaging, with pre- and post-treatment circumference measurements of the peritoneal cavity and hernia sac, prior to undergoing operative mesh repair of their hernia.ResultsThe mean hernia defect size was 236xa0cm2, with mean 28xa0% loss of domain. The mean overall duration of PPP was 6.2xa0days. The mean gain in abdominal circumference was 4.9xa0cm (5.6xa0%) (p 0.002) after BTA and PPP. Fascial closure and mesh hernia repair were performed in all 16 patients, with no patients suffering from postoperative abdominal hypertension, ventilatory impairment, or wound dehiscence. There are no hernia recurrences to date. Eight patients (50xa0%) experienced PPP-related complications, consisting of subcutaneous emphysema, pneumothorax, pneumomediastinum, pneumocardium, and metabolic acidosis. No complication required intervention.ConclusionsPPP is a useful adjunct in the repair of complex ventral hernia. It passively expands the abdominal cavity, allowing viscera to re-establish right of domain. At the same time, it helps to minimize the risks of postoperative abdominal compartment syndrome and the sequelae of fascial closure under tension. However, its benefits must be carefully weighed with the risk of serious complications, such as infection, perforation, pneumothorax, and pneumomediastinum.