A fast Bayesian reconstruction algorithm for emission tomography with entropy prior converging to feasible images

The development and tests of an iterative reconstruction algorithm for emission tomography based on Bayesian statistical concepts are described. The algorithm uses the entropy of the generated image as a prior distribution, can be accelerated by the choice of an exponent, and converges uniformly to feasible images by the choice of one adjustable parameter. A feasible image has been defined as one that is consistent with the initial data (i.e. it is an image that, if truly a source of radiation in a patient, could have generated the initial data by the Poisson process that governs radioactive disintegration). The fundamental ideas of Bayesian reconstruction are discussed, along with the use of an entropy prior with an adjustable contrast parameter, the use of likelihood with data increment parameters as conditional probability, and the development of the new fast maximum a posteriori with entropy (FMAPE) Algorithm by the successive substitution method. It is shown that in the maximum likelihood estimator (MLE) and FMAPE algorithms, the only correct choice of initial image for the iterative procedure in the absence of a priori knowledge about the image configuration is a uniform field.

Climatic and biotic upheavals following the end-Permian mass extinction

Recovery from the end-Permian mass extinction is frequently described as delayed(1-3), with complex ecological communities typically not found in the fossil record until the Middle Triassic epoch. However, the taxonomic diversity of a number of marine groups, ranging from ammonoids to benthic foraminifera, peaked rapidly in the Early Triassic(4-10). These variations in biodiversity occur amidst pronounced excursions in the carbon isotope record, which are compatible with episodes of massive CO2 outgassing from the Siberian Large Igneous Province(4,11-13). Here we present a high-resolution Early Triassic temperature record based on the oxygen isotope composition of pristine apatite from fossil conodonts. Our reconstruction shows that the beginning of the Smithian substage of the Early Triassic was marked by a cooler climate, followed by an interval of warmth lasting until the Spathian substage boundary. Cooler conditions resumed in the Spathian. We find the greatest increases in taxonomic diversity during the cooler phases of the early Smithian and early Spathian. In contrast, a period of extreme warmth in the middle and late Smithian was associated with floral ecological change and high faunal taxonomic turnover in the ocean. We suggest that climate upheaval and carbon-cycle perturbations due to volcanic outgassing were important drivers of Early Triassic biotic recovery.

Effect of tibial tray inclination on the femoro-tibial contact pattern of a mobile total knee arthroplasty

Introduction: The posterior inclination of the tibial component is an important factor that can affect the success of total knee arthroplasty. It can reduce the posterior impingement and thus increase the range of flexion, but it may also induce instability in flexion, anterior impingement between the polyethylene of postero-stabilizing knee prosthesis, and anterior conflict with the cortical bone and the stem. Although the problem is identified, there is still a debate on the ideal inclination angle and the surgical technique to avoid an excessive posterior inclination. The aim of this study was to predict the effect of a posterior inclination of the tibial component on the contact pattern on the tibial insert, using a numerical musculoskeletal model of the knee joint. Methods: A 3D finite element model of the knee joint was developed to simulate an active and loaded squat movement after total knee arthroplasty. Flexion was actively controlled by the quadriceps muscle and muscle activations were estimated from EMG data and were synchronized by a feedback algorithm. Two inclinations of the tibial tray were considered: a posterior inclination of 0° or 10°. During the entire range of flexion, the following quantities were calculated: the tibiofemoral and patello-femoral contact force, and the contact pattern on polyethylene insert. The antero-posterior displacement of the contact pattern was also measured. Abaqus 6.7 was used for all analyses. Results: The tibio-femoral and patello-femoral contact forces increased during flexion and reached respectively 4 and 7 BW (bodyweight) at 90° of flexion. They were slightly affected by the inclination of the tibial tray. Without posterior inclination, the contact pattern on the tibial insert remained centered. The contact pressure was lower than 5 MPa below 60° of flexion, but exceeded 20 MPa at 90° of flexion. The posterior inclination displaced the contact point posteriorly by 2 to 4 mm. Conclusion: The inclination of the tibial tray displaced the contactpattern towards the posterior border of the tibial insert. However, even for 10° of inclination, the contact center remained far from the posterior border (12 mm). There was no instability predicted for this movement.

Production of calves following nonsurgical transfer of fresh and refrigerated bovine demi-embryos

Selostus: Vasikoiden tuottaminen tuoreilla ja kylmäsäilytetyillä halkaistuilla alkioilla

Prophylactic use of bevacizumab to avoid anterior segment neovascularization following proton therapy for uveal melanoma.

PURPOSE: To investigate whether the prophylactic use of bevacizumab reduces the rate of rubeosis after proton therapy for uveal melanoma and improves the possibility to treat ischemic, reapplicated retina with laser photocoagulation. DESIGN: Comparative retrospective case series. METHODS: Uveal melanoma patients with ischemic retinal detachment and treated with proton therapy were included in this institutional study. Twenty-four eyes received prophylactic intravitreal bevacizumab injections and were compared with a control group of 44 eyes without bevacizumab treatment. Bevacizumab injections were performed at the time of tantalum clip insertion and were repeated every 2 months during 6 months, and every 3 months thereafter. Ultra-widefield angiography allowed determination of the extent of retinal ischemia, which was treated with laser photocoagulation after retinal reapplication. Main outcome measures were the time to rubeosis, the time to retinal reattachment, and the time to laser photocoagulation of ischemic retina. RESULTS: Baseline characteristics were balanced between the groups, except for thicker tumors and larger retinal detachments in the bevacizumab group, potentially to the disadvantage of the study group. Nevertheless, bevacizumab prophylaxis significantly reduced the rate of iris rubeosis from 36% to 4% (log-rank test P = .02) and tended to shorten the time to retinal reapplication until laser photocoagulation of the nonperfusion areas could be performed. CONCLUSIONS: Prophylactic intravitreal bevacizumab in patients treated with proton therapy for uveal melanoma with ischemic retinal detachment prevented anterior segment neovascularization, until laser photocoagulation to the reapplied retina could be performed.

Early stage disc degeneration does not have an appreciable affect on stiffness and load transfer following vertebroplasty and kyphoplasty.

Vertebroplasty and kyphoplasty have been reported to alter the mechanical behavior of the treated and adjacent-level segments, and have been suggested to increase the risk for adjacent-level fractures. The intervertebral disc (IVD) plays an important role in the mechanical behavior of vertebral motion segments. Comparisons between normal and degenerative IVD motion segments following cement augmentation have yet to be reported. A microstructural finite element model of a degenerative IVD motion segment was constructed from micro-CT images. Microdamage within the vertebral body trabecular structure was used to simulate a slightly (I = 83.5% of intact stiffness), moderately (II = 57.8% of intact stiffness), and severely (III = 16.0% of intact stiffness) damaged motion segment. Six variable geometry single-segment cement repair strategies (models A-F) were studied at each damage level (I-III). IVD and bone stresses, and motion segment stiffness, were compared with the intact and baseline damage models (untreated), as well as, previous findings using normal IVD models with the same repair strategies. Overall, small differences were observed in motion segment stiffness and average stresses between the degenerative and normal disc repair models. We did however observe a reduction in endplate bulge and a redistribution in the microstructural tissue level stresses across both endplates and in the treated segment following early stage IVD degeneration. The cement augmentation strategy placing bone cement along the periphery of the vertebra (model E) proved to be the most advantageous in treating the degenerative IVD models by showing larger reductions in the average bone stresses (vertebral and endplate) as compared to the normal IVD models. Furthermore, only this repair strategy, and the complete cement fill strategy (model F), were able to restore the slightly damaged (I) motion segment stiffness above pre-damaged (intact) levels. Early stage IVD degeneration does not have an appreciable effect in motion segment stiffness and average stresses in the treated and adjacent-level segments following vertebroplasty and kyphoplasty. Placing bone cement in the periphery of the damaged vertebra in a degenerative IVD motion segment, minimizes load transfer, and may reduce the likelihood of adjacent-level fractures.

Reproducibility of 3D free-breathing magnetic resonance coronary vessel wall imaging.

AIMS: Although the coronary artery vessel wall can be imaged non-invasively using magnetic resonance imaging (MRI), the in vivo reproducibility of wall thickness measures has not been previously investigated. Using a refined magnetization preparation scheme, we sought to assess the reproducibility of three-dimensional (3D) free-breathing black-blood coronary MRI in vivo. METHODS AND RESULTS: MRI vessel wall scans parallel to the right coronary artery (RCA) were obtained in 18 healthy individuals (age range 25-43, six women), with no known history of coronary artery disease, using a 3D dual-inversion navigator-gated black-blood spiral imaging sequence. Vessel wall scans were repeated 1 month later in eight subjects. The visible vessel wall segment and the wall thickness were quantitatively assessed using a semi-automatic tool and the intra-observer, inter-observer, and inter-scan reproducibilities were determined. The average imaged length of the RCA vessel wall was 44.5+/-7 mm. The average wall thickness was 1.6+/-0.2 mm. There was a highly significant intra-observer (r=0.97), inter-observer (r=0.94), and inter-scan (r=0.90) correlation for wall thickness (all P<0.001). There was also a significant agreement for intra-observer, inter-observer, and inter-scan measurements on Bland-Altman analysis. The intra-class correlation coefficients for intra-observer (r=0.97), inter-observer (r=0.92), and inter-scan (r=0.86) analyses were also excellent. CONCLUSION: The use of black-blood free-breathing 3D MRI in conjunction with semi-automated analysis software allows for reproducible measurements of right coronary arterial vessel-wall thickness. This technique may be well-suited for non-invasive longitudinal studies of coronary atherosclerosis.

Fonction ventriculaire gauche après revascularisation pour occlusion d'une coronaire d'une durée de 1-2 heures [Left ventricular function following revascularization for occlusion of a coronary artery lasting 1 to 2 hours].

The time-lag between coronary occlusion and irreversible damage to the myocardium is ill-defined in man. In 10 patients the changes in left ventricular function have been studied after coronary occlusion during diagnostic or therapeutic cardiac catheterization of 1-2 hours' duration. Revascularization was achieved either surgically or through intracoronary streptokinase infusion. The interval between occlusion and onset of extracorporal circulation or reopening was 61 to 119 minutes. Despite enzyme elevation (CPK, CK-MB, SGOT) and appearance of Q-waves in 5 patients, no significant alteration of left ventricular function was noted on repeat cardiac catheterization 10 to 230 days after the accident. These observations, suggest that coronary occlusion of 1-2 hours' duration fails to produce significant irreversible damage to the myocardium despite electrocardiographic and enzymatic signs of myocardial infarction.

Gene loss and evolutionary rates following whole-genome duplication in teleost fishes.

Teleost fishes provide the first unambiguous support for ancient whole-genome duplication in an animal lineage. Studies in yeast or plants have shown that the effects of such duplications can be mediated by a complex pattern of gene retention and changes in evolutionary pressure. To explore such patterns in fishes, we have determined by phylogenetic analysis the evolutionary origin of 675 Tetraodon duplicated genes assigned to chromosomes, using additional data from other species of actinopterygian fishes. The subset of genes, which was retained in double after the genome duplication, is enriched in development, signaling, behavior, and regulation functional categories. The evolutionary rate of duplicate fish genes appears to be determined by 3 forces: 1) fish proteins evolve faster than mammalian orthologs; 2) the genes kept in double after genome duplication represent the subset under strongest purifying selection; and 3) following duplication, there is an asymmetric acceleration of evolutionary rate in one of the paralogs. These results show that similar mechanisms are at work in fishes as in yeast or plants and provide a framework for future investigation of the consequences of duplication in fishes and other animals.

Aortic vessel wall magnetic resonance imaging at 3.0 Tesla: a reproducibility study of respiratory navigator gated free-breathing 3D black blood magnetic resonance imaging.

The purpose of this study was to evaluate a free-breathing three-dimensional (3D) dual inversion-recovery (DIR) segmented k-space gradient-echo (turbo field echo [TFE]) imaging sequence at 3T for the quantification of aortic vessel wall dimensions. The effect of respiratory motion suppression on image quality was tested. Furthermore, the reproducibility of the aortic vessel wall measurements was investigated. Seven healthy subjects underwent 3D DIR TFE imaging of the aortic vessel wall with and without respiratory navigator. Subsequently, this sequence with respiratory navigator was performed twice in 10 healthy subjects to test its reproducibility. The signal-to-noise (SNR), contrast-to-noise ratio (CNR), vessel wall sharpness, and vessel wall volume (VWV) were assessed. Data were compared using the paired t-test, and the reproducibility of VWV measurements was evaluated using intraclass correlation coefficients (ICCs). SNR, CNR, and vessel wall sharpness were superior in scans performed with respiratory navigator compared to scans performed without. The ICCs concerning intraobserver, interobserver, and interscan reproducibility were excellent (0.99, 0.94, and 0.95, respectively). In conclusion, respiratory motion suppression substantially improves image quality of 3D DIR TFE imaging of the aortic vessel wall at 3T. Furthermore, this optimized technique with respiratory motion suppression enables assessment of aortic vessel wall dimensions with high reproducibility.

Iliac wing fracture following graft harvesting from the anterior iliac crest: literature review based on a case report.

The morbidity of bone graft harvesting from the iliac crest has been widely discussed in the literature. For some authors, it is considered to be low and for others relatively high. We report on a case of a fracture of the iliac wing after graft harvesting from the anterior iliac crest despite good surgical technique. This complication is well known and most of these fractures heal uneventfully if treated conservatively. However, if anatomical and technical considerations are respected, the patient could be spared this inconvenience. Based on a literature review, we discuss the procedure's potential complications and how to avoid them in an update.

Traumatic hernia of the abdominal wall after pelvic and acetabular fracture: a case report.

Traumatic hernia of the abdominal wall is a rare and easily missed injury in the presence of major pelvic and abdominal lesions. We present a radiographically documented case of combined pelvic and acetabular fracture with a major contralateral traumatic hernia with avulsion of the internal oblique, the external oblique and the transverse abdominal muscles diagnosed four months after the initial trauma. To our knowledge no similar case has been described in the current literature.

Atypical headache following dural puncture in obstetrics.

BACKGROUND: In obstetrics, post-dural puncture headache is a well-recognised complication. Typical symptoms include fronto-temporal or occipital headache, worsening with ambulation and improving in the decubitus position. Occasionally, patients present with non-postural headache, although relatively little is known about this atypical presentation. The purpose of this study was to determine the incidence, associated signs and risk factors for this atypical manifestation of post-dural puncture headache. METHODS: We analysed a series of 27 064 parturients having a neuraxial procedure between January 2001 and December 2010. Using data from electronic anaesthesia patient records, medical charts and a postpartum quality audit, we identified all parturients with atypical post-dural puncture headache. We assessed the incidence and used uni- and multivariate analysis to identify associated risk factors. RESULTS: Amongst 142 parturients with post-dural puncture headache, eight (5.6%, 95% CI 1.7-9.4%) had atypical non-postural headache. Associated symptoms were stiffness and pain in the cervical, thoracic or lumbar vertebral area, visual disturbances and vertigo. Significant risk factors for developing atypical signs were previous migraine, odds ratio 6.1 (95% CI 1.2-28.7), a more cephalad level of needle insertion, odds ratio 17.2 (95% CI 1.4-210.1) and identification of dural puncture by aspiration of cerebrospinal fluid from the epidural catheter, odds ratio 5.5 (95% CI 1.2-24.4). Following multivariate analysis, recognition of dural puncture by aspiration of cerebrospinal fluid from the epidural catheter was the most significant predictor of non-orthostatic postdural puncture headache. CONCLUSION: Anaesthetists should be aware of this atypical clinical presentation, particularly if there is a past history of migraine, a more cephalad level of needle insertion or identification of dural puncture by aspiration of cerebrospinal fluid from the epidural catheter.

Large cystic tumour at the chest wall mimicking an echinococcosis: a case report.

The authors report an atypical late onset of a big axillary lymphatic malformation in a 41-year-old male. Considering the patient's history and clinical findings at first presentation, the swelling was highly suspicious for malignancy or cystic echinococcosis. A consequent CT showed non infiltrative growth with inhomogeneous density but remained non conclusive regarding diagnosis. Subsequently incision biopsy revealed lymphatic tissue and raised suspicion for lymphatic malformation. The tumour was excised completely and showed no recurrence in a 1-year follow up. Late onset lymphatic malformations can mimic malignant tumours or other rare conditions such as echinococcosis which has to be taken into consideration as differential diagnosis especially in known areas of hydatid diseases.