Neural Spike Sorting Under Nearly 0 dB Signal-to-Noise Ratio Using Nonlinear Energy Operator and Artificial Neural-Network Classifier

We report a result on neural spike sorting under conditions where the signal-to-noise ratio is very low. The use of nonlinear energy operator enables the detection of an action potential, even when the SNR is so poor that a typical amplitude thresholding method cannot be applied. The superior detection ability facilitates the collection of a training set under lower SNR than that of the methods which employ simple amplitude thresholding. Thus, the statistical characteristics of the input vectors can be better represented in the neural-network classifier. The trained neural-network classifiers yield the correct classification ratio higher than 90% when the SNR is as low as 1.2 (0.8 dB) when applied to data obtained from extracellular recording from Aplysia abdominal ganglia using a semiconductor microelectrode array.This work was supported by the Ministry of Health and Welfare, Korea, under Grant HMP-98- E-1-0006

A Wavelet-Based Method for Action Potential Detection from Extracellular Neural Signal Recording with Low Signal-to-Noise Ratio

We present a method for the detection of action potentials, an essential first step in the analysis of extracellular neural signals. The low signal-to-noise ratio (SNR) and similarity of spectral characteristic between the target signal and background noise are obstacles to solving this problem and, thus, in previous studies on experimental neurophysiology, only action potentials with sufficiently large amplitude have been detected and analyzed. In order to lower the level of SNR required for successful detection, we propose an action potential detector based on a prudent combination of wavelet coefficients of multiple scales and demonstrate its performance for neural signal recording with varying degrees of similarity between signal and noise. The experimental data include recordings from the rat somatosensory cortex, the giant medial nerve of crayfish, and the cutaneous nerve of bullfrog. The proposed method was tested for various SNR values and degrees of spectral similarity. The method was superior to the Teager energy operator and even comparable to or better than the optimal linear detector. A detection ratio higher than 80% at a false alarm ratio lower than 10% was achieved, under an SNR of 2.35 for the rat cortex data where the spectral similarity was very high.This work was supported by the Korea Science and Engineering Foundation (KOSEF) through the Nano Bioelectronics and Systems Research Center

Noise Performance Design of CMOS Preamplifier for the Active Semiconductor Neural Probe

A systematic design guideline is presented for the noise performance of preamplifier for semiconductor neural probe which contains on-chip electronic circuitry. The overall signal-to-noise ratio (SNR) is calculated considering the spectral characteristics of the measured extracellular action potential and the low-frequency noise spectrum of the CMOS device from typical fabrication processes. An analytical expression of the output noise power is derived, and utilized to tailor the frequency response and device parameters which are controllable by the circuit designer. An analysis of the output SNR of a two-stage CMOS differential amplifier is given and the major factors which have significant effects on the SNR are determined. We showed that a little deviation of the input device sizes and transconductance ratio from the optimal values can significantly deteriorate the SNR. Quantitative information of the preamplifier circuit parameters for satisfactory noise performance is provided.The work was supported in part by the Korea Science and Engineering Foundation through the Nano Bio-electronics and System Center, by the Ministry of Health and Welfare, Korea under Grant HMP-98-E-1-0006, 1998-1999, by the Basic Research program of Korea Electronic Technology Institute (KETI)-MEMS under Grant 2000-X-5119, 1999-2000, and by the Brain Korea 21 project

Reconstructive challenge of dermatofibrosarcoma protuberans in the female breast

Dermatofibrosarcoma protuberans is an uncommon locally aggressive malignant neoplasm that most frequently appears in the trunk, followed by the extremities, head, and neck. But occurrence in the breast is extremely rare. We present a case of a 28-year-old woman, who had a history of trauma 5 years previously and excision 1 year before presentation at our clinic. We performed wide excision, together with microscopic and immunohistochemical analysis. No postoperative oncologic treatment was used and she remains disease-free 1 year after the surgery without any tumor recurrence. Here, we report a case of dermatofibrosarcoma protuberans in the female breast and present a detailed discussion of the diagnosis and treatment with reference to available literatures

Coagulase-Positive Staphylococcal Necrotizing Fasciitis Subsequent to Shoulder Sprain in a Healthy Woman

Necrotizing fasciitis (NF) is a deep infection of the subcutaneous tissue that progressively destroys fascia and fat; it is associated with systemic toxicity, a fulminant course, and high mortality. NF most frequently develops from trauma that compromises skin integrity, and is more common in patients with predisposing medical conditions such as diabetes mellitus, atherosclerosis, alcoholism, renal disease, liver disease, immunosuppression, malignancy, or corticosteroid use. Most often, NF is caused by polymicrobial pathogens including aerobic and anaerobic bacteria. NF caused by Staphylococcus aureus as a single pathogen, however, is rare. Here we report a case of NF that developed in a healthy woman after an isolated shoulder sprain that occurred without breaking a skin barrier, and was caused by Staphylococcus aureus as a single pathogen

Dieulafoy's Lesion of Jejunum: Presenting Small Bowel Mass and Stricture

Dieulafoy's lesion is an uncommon cause of gastrointestinal bleeding. Hemorrhage occurs through mucosal erosion from an abnormally dilated submucosal artery. Although Dieulafoy's lesion is usually located in the stomach, it may occur anywhere in the gastrointestinal tract. We report here on a case of jejunal Dieulafoy's lesion presenting as a mass and short segment stricture on CT and enteroclysis