Capture threshold of bipolar and unipolar pacing of left ventricle via coronary sinus branch: longitudinal study.

Introduction: The aim of this paper is to first monitor the changes in the capture threshold of endovascularly placed leads for left ventricle pacing, second to compare the pacing configurations, and third to verify the effect of Steroid elution for endovascular leads. Sample and Method: The study included 202 consecutive single centre patients implanted with the Quartet™ lead (St. Jude Medical). The capture threshold and related lead parameters were tested during implantation, on the day of the patient's discharge, and 3, 9, and 15 months after implantation. The electrical energy corresponding to the threshold values for inducing ventricular contraction was recorded for subgroups of patients with bipolar and pseudo-unipolar pacing vectors and electrodes equipped with and without a slow-eluting steroids. The best setting for the resynchronization effect was generally chosen. Capture threshold was taken as a selection criterion only if there were multiple options with (expected) similar resynchronization effect. Results and Discussion: The measurements showed that the ratio of threshold energies of UNI vs. BI was 5× higher (p < 0.001) at implantation. At the end of the follow-up, it dropped to 2.6 (p = 0.012). The steroid effect in BI vectors was caused by a double capture threshold in the NSE group compared to the SE group (p < 0.001), increased by approximately 2.5 times (p < 0.001). The study concludes that after a larger initial increase in the capture threshold, the leads showed a gradual increase in the entire set. As a result, the bipolar threshold energies increase, and the pseudo-unipolar energies decrease. Since bipolar vectors require a significantly lower pacing energy, battery life of the implanted device would improve. When evaluating the steroid elution of bipolar vectors, we observe a significant positive effect of a gradual increase of the threshold energy.

Near-infrared observations of active asteroid (3200) Phaethon reveal no evidence for hydration.

Asteroid (3200) Phaethon is an active near-Earth asteroid and the parent body of the Geminid Meteor Shower. Because of its small perihelion distance, Phaethon's surface reaches temperatures sufficient to destabilize hydrated materials. We conducted rotationally resolved spectroscopic observations of this asteroid, mostly covering the northern hemisphere and the equatorial region, beyond 2.5-µm to search for evidence of hydration on its surface. Here we show that the observed part of Phaethon does not exhibit the 3-µm hydrated mineral absorption (within 2σ). These observations suggest that Phaethon's modern activity is not due to volatile sublimation or devolatilization of phyllosilicates on its surface. It is possible that the observed part of Phaethon was originally hydrated and has since lost volatiles from its surface via dehydration, supporting its connection to the Pallas family, or it was formed from anhydrous material.

Thermomechanical properties of nickel-titanium closed-coil springs and their implications for clinical practice.

INTRODUCTION: The aim was to study nickel-titanium closed-coil springs in a clinically relevant test setting with respect to the accuracy of the "preactivation" for nickel-titanium closed-coil springs application and whether it is possible to keep activation forces constant during the whole time of treatment. METHODS: We tested 10 types of springs from 5 manufacturers under clinically relevant conditions, allowing us to study the interactions between load and temperature over time. Hystereses were compared using t tests. RESULTS: Springs with a large mechanical hysteresis also showed a large thermal hysteresis. After heating shock, these springs showed intensive force spikes and persistent high loads. Some springs showed negligible thermal and mechanical hysteresis. Such springs never showed any clinically significant persistent high loads. CONCLUSIONS: Springs with a large hysteresis were unable to keep activation forces constant during the whole time of treatment even after any preactivation, and they might cause persistently high loads and possibly overloading. Only springs with minor hysteresis, low temperature dependence of force, and a clinically useful plateau have the following clinical advantages: reduced chair time, optimal rates of tooth movement, reproducible clinical results, and conservation of anchorage.

Systemic AL amyloidosis with unusual cutaneous presentation unmasked by carotenoderma.

We present a case study of an elderly woman with systemic lambda-type AL amyloidosis that featured unusually extensive cutaneous involvement. The case initially presented with a sudden hyper ß-carotenemia with carotenoderma that instigated the clinical examination including skin biopsy. A diagnosis of systemic amyloidosis was made. Immunohistochemistry and Western-blot analysis indicated the presence of lambda light chain proteins in skin amyloid deposits. However, notable co-deposition of wild-type apoA-I and transthyretin was observed which caused initial diagnostic confusion. Proteomic analysis of microdissected skin amyloid deposits by mass spectrometry confirmed lambda light chain proteins in amyloid deposits and co-deposition of apolipoprotein A-IV and serum amyloid P-component. The patient died from renal failure caused by amyloid nephropathy combined with analgesic nephropathy. The autopsy disclosed vascular, cardiac, renal and pulmonary amyloid deposition. While all amyloid deposits were positive for lambda light chain proteins, the immunodetection of apoA-I and transthyretin varied significantly among the visceral amyloid deposits. Although the patient exhibited a 1000-fold increase in serum ß-carotene levels, only a mild increase in retinol and lutein concentrations was observed. Increased ß-carotene values were also found in the liver and the skin. The mechanisms underlying this hyper ß-carotenemia remain undetermined.

Thermo-mechanical properties of NiTi closed coil springs--force degradation and force regeneration over time, viscous properties.

INTRODUCTION: The aim of this study was to find out the impact of degradation and regeneration of force over time at NiTi springs on the value and course of the final acting force and to verify the possibility of using these phenomena for a directed transition to the reverse plateau and its maintaining. METHODS: Static and cyclic mechanical loadings were performed. At first unused springs were tested. Afterwards the springs were mechanically stabilized by stress cycling and finally tested again. The difference in shape of the working curves was assessed. For simulation and description of the force degradation the modified Voight model was used. RESULTS: New springs, mainly those with large hysteresis, showed a significant stress-strain curve movement and shape changes during the cycling. The effect of the stress-strain curve course change disappeared fully in the stabilized springs. Multiple loading led to an overall decrease of force value during the measurement. The effect of force degradation and regeneration over time by simple static loading varies in the range of percentage of the nominal force in the plateau area. The transition between stress-strain curve phases caused by the degradation or regeneration of the force wasn't observed in case of mechanically stabilized springs. CONCLUSIONS: Springs should be mechanically stabilized before their application. The degree of force degradation over time is insignificant for mechanically stabilized springs. Degradation or regeneration of force over time, mechanical stabilization or micromovements in the mouth don't cause any transition between individual stress-strain curve phases.

Utilization of cone beam CT for reconstruction of dose distribution delivered in image-guided radiotherapy of prostate carcinoma - bony landmark setup compared to fiducial markers setup.

The purpose of this study was to compare two different styles of prostate IGRT: bony landmark (BL) setup vs. fiducial markers (FM) setup. Twenty-nine prostate patients were treated with daily BL setup and 30 patients with daily FM setup. Delivered dose distribution was reconstructed on cone-beam CT (CBCT) acquired once a week immediately after the alignment. Target dose coverage was evaluated by the proportion of the CTV encompassed by the 95% isodose. Original plans employed 1 cm safety margin. Alternative plans assuming smaller 7 mm margin between CTV and PTV were evaluated in the same way. Rectal and bladder volumes were compared with initial ones. While the margin reduction in case of BL setup makes the prostate coverage significantly worse (p = 0.0003, McNemar's test), in case of FM setup with the reduced 7 mm margin, the prostate coverage is even better compared to BL setup with 10 mm margin (p = 0.049, Fisher's exact test). Moreover, partial volumes of organs at risk irradiated with a specific dose can be significantly lowered (p < 0.0001, unpaired t-test). Reducing of safety margin is not acceptable in case of BL setup, while the margin can be lowered from 10 mm to 7 mm in case of FM setup.

On-line integration of computer controlled diagnostic devices and medical information systems in undergraduate medical physics education for physicians.

We designed and evaluated an innovative computer-aided-learning environment based on the on-line integration of computer controlled medical diagnostic devices and a medical information system for use in the preclinical medical physics education of medical students. Our learning system simulates the actual clinical environment in a hospital or primary care unit. It uses a commercial medical information system for on-line storage and processing of clinical type data acquired during physics laboratory classes. Every student adopts two roles, the role of 'patient' and the role of 'physician'. As a 'physician' the student operates the medical devices to clinically assess 'patient' colleagues and records all results in an electronic 'patient' record. We also introduced an innovative approach to the use of supportive education materials, based on the methods of adaptive e-learning. A survey of student feedback is included and statistically evaluated. The results from the student feedback confirm the positive response of the latter to this novel implementation of medical physics and informatics in preclinical education. This approach not only significantly improves learning of medical physics and informatics skills but has the added advantage that it facilitates students' transition from preclinical to clinical subjects.

Utilization of cone-beam CT for offline evaluation of target volume coverage during prostate image-guided radiotherapy based on bony anatomy alignment.

AIM: To assess target volume coverage during prostate image-guided radiotherapy based on bony anatomy alignment and to assess possibility of safety margin reduction. BACKGROUND: Implementation of IGRT should influence safety margins. Utilization of cone-beam CT provides current 3D anatomic information directly in irradiation position. Such information enables reconstruction of the actual dose distribution. MATERIALS AND METHODS: Seventeen prostate patients were treated with daily bony anatomy image-guidance. Cone-beam CT (CBCT) scans were acquired once a week immediately after bony anatomy alignment. After the prostate, seminal vesicles, rectum and bladder were contoured, the delivered dose distribution was reconstructed. Target dose coverage was evaluated by the proportion of the CTV encompassed by the 95% isodose. Original plans employed a 1 cm safety margin. Alternative plans assuming a smaller 7 mm margin between CTV and PTV were evaluated in the same way. Rectal and bladder volumes were compared with the initial ones. Rectal and bladder volumes irradiated with doses higher than 75 Gy, 70 Gy, 60 Gy, 50 Gy and 40 Gy were analyzed. RESULTS: In 12% of reconstructed plans the prostate coverage was not sufficient. The prostate underdosage was observed in 5 patients. Coverage of seminal vesicles was not satisfactory in 3% of plans. Most of the target underdosage corresponded to excessive rectal or bladder filling. Evaluation of alternative plans assuming a smaller 7 mm margin revealed 22% and 11% of plans where prostate and seminal vesicles coverage, respectively, was compromised. These were distributed over 8 and 7 patients, respectively. CONCLUSION: Sufficient dose coverage of target volumes was not achieved for all patients. Reducing of safety margin is not acceptable. Initial rectal and bladder volumes cannot be considered representative for subsequent treatment.

Mechanical properties of selfexpandable stents.

The stents or stentgrafts (covered stents) are the medical instruments used in invasive radiology for miniinvasive treatment of stenosis and aneurisms especially in the blood circulation system. We measured and compared the mechanical parameters of different selfexpandable Nitinol stents, which differed in the geometry (radius and length), in the type of construction (number of branches and rising of winding) and in the diameter of the used wire. The results of measurements confirmed the theoretical assumptions that just the diameter of the Nitinol wire significantly influences the rigidity and the level of compressibility of the stent as well. The compromise must be found between the required rigidity of the stent and the minimal size of the delivery system. The exact description of the relation between the mechanical properties and geometry and construction of the stents enables us to design the stent to fit the patient's needs. The results of measurement are also necessary for the design and identification of the parameters of the models of the stents.