Implementation of N-Interval fourier transform analysis - Application to compound action potentials.

N-Interval Fourier Transform Analysis (N-FTA) allows for spectral separation of a periodic target signal from uncorrelated background interference. A N-FTA pseudo-code is presented. The spectral resolution is defined by the repetition rate of the near periodic signal. Acceptance criteria for spectral targets were defined such that the probability of accepting false positives is less than 1500. Simulated and recorded neural compound action potentials (CAPs) were investigated. Simulated data allowed for comparison with reference solutions demonstrating the stability of N-FTA at conditions being comparable to real world data. Background activity was assessed with small errors. Evoked target components were assessed down to power spectral density being approximately N times below the background level. Validation was completed investigating a measured CAP. In neurophysiological recordings, this approach allows for accurate separation of near periodic evoked activity from uncorrelated background activities for frequencies below 1kHz.•N-FTA allows for spectral separation of a periodic target signal from uncorrelated interference by analyzing a segment containing N target signal repetitions.•A MATLAB implementation of the algorithm is provided along with simulated and recorded data.•N-FTA was successfully validated using simulated and measured data for CAPs.

Fitting the determined impedance in the guinea pig inner ear to Randles circuit using square error minimization in the range of 100 Hz to 50 kHz.

Objective. Several lumped and distributed parameter models of the inner ear have been proposed to improve vestibular implant stimulation. The models should account for all significant physical phenomena that influence the current propagation, such as the electrical double layer (EDL) and medium polarization. The electrical properties of the medium are reflected in the electrical impedance; therefore, the study aimed to measure the impedance in the guinea pig inner ear and construct its equivalent circuit.Approach. The electrical impedance was measured from 100 Hz to 50 kHz between a pair of platinum electrodes immersed in 0.9% NaCl saline solution using sinusoidal voltage signals. The Randles circuit was fitted to the measured impedance in the saline solution in order to estimate the EDL parameters (C,W,andRct) of the electrode interface in saline. Then, the electrical impedance was measured between all combinations of the electrodes located in the semicircular canal ampullae and the vestibular nerve in the guinea pigin vitro. The extended Randles circuit considering the medium polarization (Ri,Re,Cm) together with EDL parameters (C,Rct) obtained from the saline solution was fitted to the measured impedance of the guinea pig inner ear. The Warburg element was assumed negligible and was not considered in the guinea pig model.Main results. For the set-up used, the obtained EDL parameters were:C=27.09*10-8F,Rct=18.75kΩ.The average values of intra-, extracellular resistances, and membrane capacitance wereRi=4.74kΩ,Re=45.05kΩ,Cm=9.69*10-8F,respectively.Significance. The obtained values of the model parameters can serve as a good estimation of the EDL for modelling work. The EDL, together with medium polarization, plays a significant role in the electrical impedance of the guinea pig inner ear, therefore, they should be considered in electrical conductivity models to increase the credibility of the simulations.

Evaluating selection criteria for optimized excitation coils in magnetorelaxometry imaging.

Objective.Magnetorelaxometry imaging (MRXI) is an experimental imaging technique applicable for noninvasive, qualitative and quantitative imaging of magnetic nanoparticles (MNPs). Accurate reconstructions of nanoparticle distributions are crucial for several novel treatment methods employing MNPs such as magnetic drug targeting or magnetic hyperthermia therapy. Hence, it is desirable to design MRXI setups such that the reconstruction accuracy is maximized for a given set of design parameters. Several attempts exist in literature that focus on the improvement of MRXI and other related linear inverse problems with respect to various figures of merit. However, to date it remains unclear, which approach leads to the largest benefit for the reconstruction accuracy. Thus, the aim of this study is to compare the different figures of merit, thereby determining the most reliable and effective optimization approach for magnetorelaxometry setups.Approach.In the present simulation study, we translate these figures of merit to various cost functions, allowing us to optimize the electromagnetic coil positions and radii of two distinct MRXI setups with an adapted tabu search algorithm. Multiple artificial MNP phantoms are reconstructed employing the optimized setups and the resulting imaging qualities are subsequently compared.Main results.The extensive amount of generated synthetic data unprecedented in previous MRXI studies identifies the condition number as the most reliable indicator for good imaging results. This is the case for both the qualitative as well as the quantitative reconstruction accuracies.Significance.The results of this study show that optimized coil configurations increase the reconstruction quality compared to the state-of-the-art. The insights obtained here can also be extended to other design parameters of MRXI setups, thus enabling more reliable reconstructions of MNP ensembles which will ultimately render the aforementioned treatment methods safer and more efficient.

[39-Year-Old Woman with Severe COVID-19 Pneumonia: Successful Weaning after Septic Shock and Forefoot Amputation after Microvascular Complications]. / 39-jährige Frau mit schwerer COVID-19-Pneumonie: Erfolgreiches Weaning nach septischem Schock und Vorfußamputation wegen mikrovaskulärer Komplikationen.

We present the case of a slightly obese 39-year-old patient with a severe course of COVID-19 pneumonia. The patient was referred from a hospital to regular care with suspected COVID-19 pneumonia. The initial clinical symptoms consisted of dysuria and fever. A bilateral infiltrate was seen in the chest x-ray. In the CT thorax, advanced COVID-19 typical changes were found on both sides. The COVID-19 infection was confirmed by a positive SARS-CoV-2 PCR from the nasopharynx smear. In the case of progressive ARDS with respiratory exhaustion, the patient was intubated and invasively ventilated. When a bacterial superinfection was suspected, we initiated empirical antibiotic therapy. In addition, a therapy with dexamethasone was applied. Therapy with ASA and weight-adapted semi-therapeutic low molecular weight heparin was also carried out. During the intensive care treatment the patient developed a fulminant septic shock with consecutive severe thrombocytopenia. A dilated tracheotomy was performed. The weaning progress was hampered by recurrent septic attacks. Necrosis in the area of ​​the right foot was identified as the cause of the septic relapses. As there was no alternative focus, surgical rehabilitation with partial amputation was carried out. The patient then remained infection-free and could be weaned from the respirator.

A Lead Field Two-Domain Model for Longitudinal Neural Tracts-Analytical Framework and Implications for Signal Bandwidth.

Somatosensory evoked potentials are a well-established tool for assessing volley conduction in afferent neural pathways. However, from a clinical perspective, recording of spinal signals is still a demanding task due to the low amplitudes compared to relevant noise sources. Computer modeling is a powerful tool for gaining insight into signal genesis and, thus, for promoting future innovations in signal extraction. However, due to the complex structure of neural pathways, modeling is computationally demanding. We present a theoretical framework which allows computing the electric potential generated by a single axon in a body surface lead by the convolution of the neural lead field function with a propagating action potential term. The signal generated by a large cohort of axons was obtained by convoluting a single axonal signal with the statistical distribution of temporal dispersion of individual axonal signals. For establishing the framework, analysis was based on an analytical model. Our approach was further adopted for a numerical computation of body surface neuropotentials employing the lead field theory. Double convolution allowed straightforward analysis in the frequency domain. The highest frequency components occurred at the cellular membrane. A bandpass type spectral shape and a peak frequency of 1800 Hz was observed. The volume conductor transmitting the signal to the recording lead acted as an additional bandpass reducing the axonal peak frequency from 200 Hz to 500 Hz. The superposition of temporally dispersed axonal signals acted as an additional low-pass filter further reducing the compound action potential peak frequency from 90 Hz to 170 Hz. Our results suggest that the bandwidth of spinal evoked potentials might be narrower than the bandwidth requested by current clinical guidelines. The present findings will allow the optimization of noise suppression. Furthermore, our theoretical framework allows the adaptation in numerical methods and application in anatomically realistic geometries in future studies.

Impedance and conductivity of bovine myocardium during freezing and thawing at slow rates - implications for cardiac cryo-ablation.

Increasing impedance during freezing might be a valuable marker for guiding cardiac cryo-ablation. We provide model based insights on how decreasing temperature below the freezing point of tissue relates to the percentage of frozen water. Furthermore, we provide experimental data for comparing this percentage with the increase in impedance. Measurements were performed on a bovine tissue sample at frequencies between 5 and 80 kHz. Slow cooling and heating rates were applied to minimize temperature gradients in the myocardial sample and to allow accurate assessment of the freezing point. Computer simulation was applied to link impedance with temperature dependent conductivities. The osmotic virial equation was used to estimate the percentage of frozen water. Measurements identified the freezing point at -0.6 ∘C. At -5 ∘C, impedance rose by more than a factor of ten compared to that at the freezing point and the percentage of frozen water was estimated as being 89%. At -49 ∘C impedance had increased by up to three orders of magnitude and ice formation was most pronounced in the extracellular space. Progressive ice formation in tissue is reflected by a large increase in impedance, and impedance increases monotonically with the percentage of frozen water. Its analysis allows for experimental assessment of factors relevant to cell death. Solid ice contributes to the rupture of the micro-vasculature, while phase shifts reflect concentration differences between extra- and intracellular space driving osmotic water transfer across cell membranes.

Are screening serum creatinine levels necessary prior to outpatient CT examinations?

PURPOSE: To determine the percentage of outpatients with elevated serum creatinine levels (>/=2.0 mg/dL [177 micromol/L]) and associated reported risk factors for contrast material-induced nephrotoxic reactions (eg, diabetes, renal disease, male, age >/= 60 years, chemotherapy) who undergo computed tomography (CT) and to define a true high-risk population. MATERIALS AND METHODS: The serum creatinine levels were obtained in a total of 2,034 consecutive outpatients (969 male, 1,065 female) who underwent contrast material-enhanced CT. In addition, selected patient charts were reviewed to determine the presence of risk factors for contrast material-induced nephrotoxic reactions. RESULTS: Only 66 (3.2%) had an elevated serum creatinine level. Risk factors were identified in 64 of the 66 (97%) patients with an elevated serum creatinine level. Renal disease was present in 62 of the 66 (94%) patients. Two of the 66 patients with an elevated creatinine level had no identifiable risk factors, representing 0.1% of the total number of patients. CONCLUSION: The data suggest that the majority of patients with a serum creatinine level of at least 2.0 mg/dL (177 micromol/L) will be identified by screening for risk factors. Careful patient screening, especially for renal disease, at the time of scheduling could result in considerable savings in terms of radiology man-hours expended and laboratory costs.

Outcome of examinations self-referred as a result of spiral CT of the abdomen.

RATIONALE AND OBJECTIVES: The interpretation of an abdominal computed tomographic (CT) scan is occasionally inconclusive. In many of these cases, the radiologist suggests an additional imaging test for further confirmation or clarification. The purpose of this study was to evaluate the outcome of self-referral by the radiologist after abdominal CT scanning. MATERIALS AND METHODS: Reports from 545 consecutive abdominal CT scans were reviewed to track recommendations for additional imaging. In patients who underwent the additional work-up, a determination of the effect of the study was attempted. In patients who did not, explanations were sought. Wording of the recommendations was also recorded. RESULTS: Recommendations were made for additional imaging studies in 105 (19.3%) patients. Of these, 32 (30.5%) were performed and 31 (96.9%) were helpful by confirming malignancy (n = 5), confirming a benign process (n = 24), or being therapeutic (n = 2). In one, no information was added. There were 63 (60.0%) patients who did not undergo the recommended studies. Reasons included "no clinical indication" (n = 51), alternative study performed (n = 9), or study previously performed (n = 3). In eight (7.6%) patients the chart provided insufficient information about whether the patient underwent the study, and in two (1.9%) the chart was unavailable. Wording of the recommendation had no effect on whether the study was performed (P > .05). CONCLUSION: Although interpretation of abdominal CT scans leads to recommendations for additional imaging in a minority of cases, these recommendations were infrequently followed. When followed, however, the findings from the recommended studies were usually helpful. Better clinical information is perhaps the best way to reduce self-referral by radiologists.

Imaging and radiologic management of upper urinary tract infections.

Most infections of the upper urinary tract respond promptly to antibiotic therapy and imaging is not necessary. Patients with urinary obstruction, diabetes, or immunocompromise are more likely to develop complicated infection, abscess, or have unusual organisms. Chronic granulomatous processes involving the kidney are usually related to recurrent bacterial infections. Again, stone disease or obstruction is often an underlying problem. In those patients who do not respond promptly to treatment or have a more complicated clinical picture, imaging can assess the severity and extent of disease. CT scan is the study of choice for diagnostic evaluation in these patients and directs percutaneous intervention when appropriate. Placement of drainage catheters is often curative but also may allow the patient to stabilize until surgical treatment is accomplished. One exception is the diagnosis of pyonephrosis, which may be accomplished more easily by ultrasound. In these cases, PCN placement is generally needed and is performed under fluoroscopic guidance. Ultimately, however, definitive surgical intervention often is needed to relieve the underlying obstruction.

Robotic assistance in orthopaedic surgery. A proof of principle using distal femoral arthroplasty.

The term "robot" refers to a precision mechanical device that is accurately controlled by a computer using intelligent software. The term "robotic assistance" refers to the use of such a device to aid a surgeon in the optimal conduct of a procedure, particularly one requiring specified geometrical relationships. The authors have been exploring the application of robotic assistance in situations in which accuracy and precision are required in orthopaedic surgery. The initial application concerned the planning, positioning, and orientation cuts and holes of the bone required for the femoral component of a total knee arthroplasty. A three-dimensional digitizing template allowed the surgeon to specify the desired position and orientation of the component's articular surfaces in relation to the distal femur. The robotic system used this spatial relationship, along with its knowledge of the geometry of the component selected by the surgeon, to plan the precise location of the required bone cuts and holes. Finally, the robotic assistant sequentially positioned saw and drill guides with respect to the distal femur so that the surgeon made these cuts and holes in the locations necessary for optimal component fit, position, and orientation. The robotic assistant functioned easily in the operating room environment; increased the accuracy; and decreased the time, equipment, and personnel required for the conduct of the geometrical part of this surgical procedure.

Developmental and age-related processes that influence the longevity and senescence of photosynthetic tissues in arabidopsis.

Factors that influence the longevity and senescence of photosynthetic tissues of Arabidopsis were investigated. To determine the influence of reproductive development on the timing of somatic tissue senescence, the longevity of rosette leaves of the Landsberg erecta strain and of isogenic mutant lines in which flowering is delayed (co-2) or sterile flowers are produced (ms1-1) were compared. No difference in the timing of senescence of individual leaves was observed between these lines, indicating that somatic tissue longevity is not governed by reproductive development in this species. To examine the role of differential gene expression in the process of leaf senescence, cDNA clones representing genes that are differentially expressed in senescing tissues were isolated. Sequence analysis of one such clone indicated homology to previously cloned cysteine proteinases, which is consistent with a role for the product of this gene in nitrogen salvage. RNA gel blot analysis revealed that increased expression of senescence-associated genes is preceded by declines in photosynthesis and in the expression of photosynthesis-associated genes. A model is presented in which it is postulated that leaf senescence is triggered by age-related declines in photosynthetic processes.

Evaluation of biomatrix hydroxyapatite ocular implants with technetium-99m-MDP.

Hydroxyapatite ocular implants appear to offer excellent cosmetic reconstruction with lower rates of infection and extrusion compared to other integrated implants. However, vascularization of the implant needs to be established before the artificial eye is attached to the implant. Technetium-99m-methylene diphosphonate (MDP) scintigraphy can be utilized as a noninvasive method for determining the vascularity of the hydroxyapatite ocular implants. A case is presented in which 99mTc-MDP uptake in the implant was deemed sufficient for further surgical intervention.

Hepatocellular carcinoma: CT appearance after percutaneous ethanol ablation therapy. Work in progress.

Nine patients with biopsy-proved hepatocellular carcinoma underwent percutaneous ethanol ablation therapy (PEAT) with computed tomographic (CT) guidance. Twenty-five ablation sessions were performed in nine lesions ranging in size from 1.8 to 6.5 cm. Repeat biopsy was performed in seven of those nine lesions between 1 and 2 months after completion of therapy. CT scans obtained immediately after ablation demonstrated a necrotic area equal in size to the target lesion in five patients; four of those five patients have had negative findings at biopsy and are free of known disease. None of the patients with CT evidence of limited necrosis are currently free of disease. Peripheral nodularity was demonstrated after ablation in three patients at CT; none are free of disease. All four patients in whom there was no peripheral nodularity are free of known disease. Thus, CT evidence of necrosis and lack of nodularity immediately after PEAT are suggestive of absence of disease.

Prognostic factors for gastrointestinal and bronchopulmonary carcinoid tumors.

Data collected by population-based cancer registries in Iowa and metropolitan Atlanta were evaluated to determine prognostic factors for gastrointestinal (n = 270) and bronchopulmonary (n = 151) carcinoids. The predictors considered in univariate and multivariate analyses were: age, sex, race, marital status, anatomic subsite, stage, occurrence of other malignancies, and surgery. For surgically treated gastrointestinal tumors, the cumulative percentages of survivors at five years were: appendix, 85.6%; small intestine, 66.0%; and large intestine, 37.7%. The likelihood of death from gastrointestinal carcinoids was found to be related independently to increasing age (P = 0.001), advanced stage (P less than 0.0001), location within the large intestine (P less than 0.0001), and occurrence of another malignancy (P = 0.02). The overall five-year survival rate for bronchopulmonary carcinoids was 87.6%, and lack of surgical treatment (P less than 0.0001) and advanced stage (P = 0.006) were associated independently with unfavorable prognosis.

The Hitselberger sign as a perception phenomenon.

In the Hitselberger test the patient has to estimate the magnitude of the tactile part of a compound audio-tactile stimulus. From this point of view it is doubtful, that the sign is a simple peripheral phenomenon based on the impairment of the facial nerve by tumor pressure. To investigate the process of audiotactile perception we developed a device which delivers a calibrated compound audio-tactile stimulus. In the tested 70 patients with different sensorineural lesions there was no significant difference between the percentage values of positive Hitselberger signs in the various diagnostic groups. Evaluation of the different factors influencing the Hitselberger test results in a new concept of audiotactile perception.