Biomedical subjects

Roop L Mahajan

Publications and source records attributed to Roop L Mahajan.

6 recordsLinked to original sources

PubMed2007

A uniaxial bioMEMS device for quantitative force-displacement measurements.

There is a need for experimental techniques that allow the simultaneous imaging of cellular cystoskeletal components with quantitative force measurements on single cells. A bioMEMS device has been developed for the application of strain to a single cell while simultaneously quantifying its force response. The prototype device presented here allows the mechanical study of a single, adherent cell in vitro. The device works in a fashion similar to a displacement-controlled uniaxial tensile machine. The device is calibrated using an AFM cantilever and shows excellent agreement with the calculated spring constant. The device is demonstrated on a single fibroblast. The force response of the cell is seen to be linear until the onset of de-adhesion with the de-adhesion from the cell platform occurring at a force of approximately 1500 nN.

Animals↗

PubMed2006

Toward a self-deploying shape memory polymer neuronal electrode.

The widespread application of neuronal probes for chronic recording of brain activity and functional stimulation has been slow to develop partially due to long-term biocompatibility problems with existing metallic and ceramic probes and the tissue damage caused during probe insertion. Stiff probes are easily inserted into soft brain tissue but cause astrocytic scars that become insulating sheaths between electrodes and neurons. In this communication, we explore the feasibility of a new approach to the composition and implantation of chronic electrode arrays. We demonstrate that softer polymer-based probes can be inserted into the olfactory bulb of a mouse and that slow insertion of the probes reduces astrocytic scarring. We further present the development of a micromachined shape memory polymer probe, which provides a vehicle to self-deploy an electrode at suitably slow rates and which can provide sufficient force to penetrate the brain. The deployment rate and composition of shape memory polymer probes can be tailored by polymer chemistry and actuator design. We conclude that it is feasible to fabricate shape memory polymer-based electrodes that would slowly self-implant compliant conductors into the brain, and both decrease initial trauma resulting from implantation and enhance long-term biocompatibility for long-term neuronal measurement and stimulation.

Algorithms↗

PubMed2006

Characterization of the RF ablation-induced 'oven effect': the importance of background tissue thermal conductivity on tissue heating.

PURPOSE: To determine the effect of background tissue thermal conductivity on RF ablation heating using ex vivo agar phantoms and computer modelling. METHOD: Two-compartment cylindrical agar phantom models (5% agar, 5% NaCl, 3% sucrose) were constructed. These included a standardized inner compartment (2 cm diameter, 4 cm length, 0.25% agar) representing a tumour, surrounded by an outer compartment representing background tissue. The thermal conductivity of the outer compartment was varied from 0.48 W m-1 degrees Celsius (normal liver) to 0.23 W m-1 degrees Celsius (fat) by adding a fat-saturated oil-based solute (10-90%) to the agar. RF ablation was applied at 2000 mA current for 2 min. Temperatures were recorded up to 4 cm from the electrode tip at 1 cm intervals. Subsequently, a 2-D finite element computer model was used to simulate RF ablation of 2-24 min duration for tumours measuring 2-4 cm in diameter surrounded by tissues of different thermal conductivity with the presence or absence of perfusion (0-5 kg m-3 s-1) (n = 44). A comparison of results was performed. RESULTS: In agar phantoms, the amount of fat in the background tissue correlated with thermal conductivity as a negative exponential function (r2 = 0.98). Significantly increased temperatures were observed at the edge of the inner compartment (1 cm from the electrode tip) as the fat content of the outer compartment increased (p < 0.01). Thus, temperatures at 2 min measured 31.5 +/- 2.2 degrees Celsius vs 45.1 +/- 3.1 degrees Celsius for thermal conductivities of 0.46 W m-1 degrees Celsius (10% fat) and 0.23 W m-1 degrees Celsius (90% fat), respectively. On the other hand, higher levels of fat led to lower temperature increases in the background compartment (0.2 +/- 0.3 degrees Celsius for 90% fat vs. 1.1 +/- 0.05 degrees Celsius for 10% fat, p < 0.05). Phantom thermal heating patterns correlated extremely well with computer modelling (r2 = 0.93), demonstrating that background tissues with low thermal conductivity increase heating within the central tumour, particularly for longer durations of RF ablation and in smaller tumours. Furthermore, computer modelling demonstrated that increases in temperature at the tumour margin for background tissues of lower thermal conductivity persisted in the presence of perfusion, with a clinically relevant 4.5 degrees Celsius difference between background thermal conductivities of fat and soft tissue for a 3 cm tumour with perfusion of 2 kg m-3 s-1, treated for 12 min. CONCLUSION: Lower thermal conductivity of background tissues significantly increases temperatures within a defined ablation target. These findings provide insight into the 'oven effect' (i.e. increased heating efficacy for tumours surrounded by cirrhotic liver or fat) and highlight the importance of both the tumour and the surrounding tissue characteristics when contemplating RF ablation efficacy.

Agar↗

PubMed2005

A classifier based on the artificial neural network approach for cardiologic auscultation in pediatrics.

OBJECTIVE: This research work was aimed at developing a reliable screening device for diagnosis of heart murmurs in pediatrics. This is a significant problem in pediatric cardiology because of the high rate of incidence of heart murmurs in this population (reportedly 77-95%), of which only a small fraction arises from congenital heart disease. The screening devices currently available (e.g. chest X-ray, electrocardiogram, etc.) suffer from poor sensitivity and specificity in detecting congenital heart disease. Thus, patients with heart murmurs today are frequently assessed by consultation as well with advanced imaging techniques. The most prominent among these is echocardiography. However, echocardiography is expensive and is usually only available in healthcare centers in major cities. Thus, for patients being evaluated with a heart murmur, developing a more accurate screening device is vital to efforts in reducing health care costs. METHODS AND MATERIAL: The data set was collected from incoming pediatrics at the cardiology clinic of The Children's Hospital (Denver, Colorado), on whom echocardiography had been performed to identify congenital heart disease. Recordings of approximately 10-15s duration were made at 44,100Hz and the average record length was approximately 60,000 points. The best three cycles with respect to signal quality sounds were extracted from the original recording. The resulting data comprised 241 examples, of which 88 were examples of innocent murmurs and 153 were examples of pathological murmurs. The selected phonocardiograms were subject to the digital signal processing (DSP) technique of fast Fourier transform (FFT) to extract the energy spectrum in frequency domain. The spectral range was 0-300Hz at a resolution of 1Hz. The processed signals were used to develop statistical classifiers and a classifier based on our in-house artificial neural network (ANN) software. For the latter, we also tried enhancements to the basic ANN scheme. These included a method for setting the decision-threshold and a scheme for consensus-based decision by a committee of experts. RESULTS: Of the different classifiers tested, the ANN-based classifier performed the best. With this classifier, we were able to achieve classification accuracy of 83% sensitivity and 90% specificity in discriminating between innocent and pathological heart murmurs. For the problem of discrimination between innocent murmurs and murmurs of the ventricular septal defect (VSD), the accuracy was higher, with sensitivity of 90% and specificity of 93%. CONCLUSIONS: An ANN-based approach for detection and identification of congenital heart disease in pediatrics from heart murmurs can result in an accurate screening device. Considering that only a simple feature set was used for classification, the results are very encouraging and point out the need for further development using improved feature set with more potent diagnostic variables.

Child↗

PubMed2004

Fast response temperature measurement and highly reproducible heating methods for 96-well plates.

Hyperthermia, the procedure of exposing cells to a temperature between 42 degrees and 49 degrees C, has been shown to be a promising approach for cancer treatment. To understand the underlying mechanisms of hyperthermic killing of cancer cells, it is critical to have an accurate temperature measurement technique and a heating method with high reproducibility. To this end, we have developed a method using fine thermocouples with fast response time to measure the temperatures in multiple wells of a 96-well plate. The accuracy of temperature measurement was +/- 0.2 degree C. Such a capability allows a complete record of the time and temperature of the treatment procedure and helps define an accurate thermal dose. We have also compared several methods for heating 96-well plates and found that use of copper blocks in contact with the lower surface of the 96-well plate in an incubator provides a highly reproducible heating method. The common method of using water bath to heat cells in vitro resulted in a decrease of cell viability even at the control temperature of 37 degrees C and a decrease in the reproducibility of certain biological assays. In summary, using these improved techniques, proposed thermal dose can be defined more precisely, and highly reproducible heating in vitro can be achieved.

Cell Culture Techniques↗

PubMed2002

A novel paradigm for telemedicine using the personal bio-monitor.

The foray of solid-state technology in the medical field has yielded an arsenal of sophisticated healthcare tools. Personal, portable computing power coupled with the information superhighway open up the possibility of sophisticated healthcare management that will impact the medical field just as much. The full synergistic potential of three interwoven technologies: (1) compact electronics, (2) World Wide Web, and (3) Artificial Intelligence is yet to be realized. The system presented in this paper integrates these technologies synergistically, providing a new paradigm for healthcare. Our idea is to deploy internet-enabled, intelligent, handheld personal computers for medical diagnosis. The salient features of the 'Personal Bio-Monitor' we envisage are: (1) Utilization of the peripheral signals of the body which may be acquired non-invasively and with ease, for diagnosis of medical conditions; (2) An Artificial Neural Network (ANN) based approach for diagnosis; (3) Configuration of the diagnostic device as a handheld for personal use; (4) Internet connectivity, following the emerging bluetooth protocol, for prompt conveyance of information to a patient's health care provider via the World Wide Web. The proposal is substantiated with an intelligent handheld device developed by the investigators for pediatric cardiac auscultation. This device performed accurate diagnoses of cardiac abnormalities in pediatrics using an artificial neural network to process heart sounds acquired by a low-frequency microphone and transmitted its diagnosis to a desktop PC via infrared. The idea of the personal biomonitor presented here has the potential to streamline healthcare by optimizing two valuable resources: physicians' time and sophisticated equipment time. We show that the elements of such a system are in place, with our prototype. Our novel contribution is the synergistic integration of compact electronics' technology, artificial neural network methodology and the wireless web resulting in a revolutionary new paradigm for healthcare management.

Adolescent↗