Theoretical evaluation of peripheral nerve stimulation during MRI with an implanted spinal fusion stimulator

This study examines the requirements for nerve excitation near a spinal fusion implant during magnetic resonance imaging. The implant is the Spinal Fusion SpF device manufactured by Electro Biology Inc. The electric field induced within the biological medium was calculated using a three-dimensional finite difference model (described in a separate paper by Beuchler et al. from the University of Utah). Magnetic thresholds were obtained for excitation of myelinated nerve fibers that are near the implant. Minimum (rheobase) thresholds were determined for long duration dB/dt pulses, as well as strength-duration time constants (from which thresholds at other durations could be determined) for various geometries between the implant and a myelinated nerve fiber. The lowest thresholds occur when a large (20-microm diameter) fiber is situated near the bare tip of a wire from the implant, and a long duration (2 ms) stimulus is provided for which dB/dt is constant and monophasic. Magnetic thresholds for shorter durations of dB/dt are higher in accordance with a strength-duration law. In a magnetic field having a time derivative of 10 T/s that is uniform over the torso, nerve excitation is possible under worst-case conditions only for nerve fibers that are within 0.14 mm of the bare wire tip of the implant. With 20 T/s, excitation is possible only within 1 mm of the wire tip.

Fingerprint matching of E. coli strains with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry of whole cells using a modified correlation approach

We have developed a mathematical algorithm to compare and distinguish matrix-assisted laser desorption/ionization (MALDI) mass spectra of whole bacteria cells. This fingerprint matching technique eliminates the subjectivity involved in visually comparing two spectra to determine whether they match and it provides a quantitative measure of spectral similarity. Using it, we have distinguished twenty five different strains of a single bacteria species, E. coli. Cells are grown in culture, samples are prepared, and MALDI-TOF mass spectra are recorded for each strain. Pairs of spectra are compared by a modified cross-correlation procedure. This modified approach increases the sensitivity of correlation analysis to small spectral differences. The technique can be fine-tuned by varying the number of intervals into which spectra are divided.

Maximum pulsed electromagnetic field limits based on peripheral nerve stimulation: application to IEEE/ANSI C95.1 electromagnetic field standards

This communication proposes a rationale for maximum pulsed magnetic field limits in the electromagnetic-field standards of IEEE/ANSI C95.1. The peak limits, intended to protect against peripheral nerve excitation by pulsed fields, are adapted from existing standards for patient exposure in magnetic resonance imaging (MRI) examinations.

Detection of the bacteriological sex factor in E. coli by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry is employed to detect the presence of the bacteriological sex factor, a trait that allows some bacteria to transfer genetic information to others by means of conjugation. The principal advantage of the method is its speed. Twenty different strains of E. coli were analyzed and the results were consistent with previously known genetic information. The sex factor could be transferred from one strain to another and the outcome verified by mass spectrometry.

Chronic low back pain rehabilitation programs: a study of the optimum duration of treatment and a comparison of group and individual therapy

STUDY DESIGN

Eighty-four patients with chronic low back pain were treated using cognitive behavioral principles on a pain management program. Outcome data were collected at four points: 10 weeks before treatment, immediately before and immediately after treatment, and 6 months after treatment. In part 1 of the study, patients were assigned randomly to group or individual treatment contexts. In part 2 of the study, patients were assigned randomly to programs of 15, 30, or 60 hours duration.

OBJECTIVES

To identify the differences in outcome between programs that treated patients as part of a group and those that treated patients individually and the effects of duration of treatment on outcome.

SUMMARY OF BACKGROUND DATA

Cognitive behavioral programs have been shown to be an effective means of managing chronic low back pain. The literature is concerned with group programs, however, the duration of which vary widely.

METHOD

Psychological and functional variables were measured before and after treatment and at the 6-month follow-up visit. Changes in these variables were measured, and comparisons were made between group and individual programs and between 15-, 30-, and 60-hour programs.

RESULTS

Data analysis showed a significant, beneficial effect of intervention in terms of the majority of variables; however, these changes were generally independent of whether patients were treated as part of a group or individually and whether patients completed a 15-, 30-, or 60-hour program.

CONCLUSIONS

Cognitive behavioral rehabilitation programs have been demonstrated to be an effective means of reducing psychological distress, of changing cognition, and of improving the function of patients with chronic low back pain; however, the length of program and whether patients were treated individually or as part of a group did not affect outcome. This finding has clinical and economic implications.

Rapid analysis of hemoglobin from whole human blood by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Matrix-assisted laser desorption time-of-flight mass spectrometry (MALDI-TOFMS) is applied to the analysis of whole human blood. No separation or purification steps are required to observe individual globins and the sensitivity of the method is excellent. Mass accuracy and precision are 0.01% using a linear TOF system with pulsed ion extraction. Sickle-cell hemoglobin is easily distinguishable from normal hemoglobin. The speed and simplicity of the method make it potentially attractive for large-scale population screening.

Chloramphenicol for the treatment of vancomycin-resistant enterococcal infections

A retrospective study of patients who received chloramphenicol for the treatment of serious vancomycin-resistant enterococcal infections between 1 January 1993 and 31 August 1993 was conducted at the University of Pennsylvania Medical Center (Philadelphia). Antimicrobial susceptibilities as well as the clinical course of infection, adverse events, and response to therapy of 16 patients were reviewed. Forty-seven percent of enterococcal isolates were susceptible only to chloramphenicol, tetracycline, and nitrofurantoin. Types of infection included bacteremias (n = 7), abscesses (n = 7), and others (n = 5). Of 14 patients for whom a clinical response could be ascertained, eight (57%) showed improvement after treatment. Of 11 patients for whom a microbiological response could be ascertained, eight (73%) had sterile cultures after treatment. No lasting adverse effect related to the drug occurred. In-hospital mortality was 56%, but only one death could be directly attributed to vancomycin-resistant enterococcal infection. Chloramphenicol appears to be a useful and well-tolerated agent for the treatment of serious vancomycin-resistant enterococcal infections.

The prediction of chronicity in patients with an acute attack of low back pain in a general practice setting

STUDY DESIGN

Three hundred patients, attending their general practitioners with attacks of acute low back pain, formed the subject population for a study of fear avoidance and other variables in the prediction of chronicity. Follow-up was at 2 and 12 months.

OBJECTIVE

The hypothesis to be tested was that evidence of psychological morbidity, particularly fear-avoidance behavior, would be manifest from the outset of the presenting attack in susceptible subjects.

SUMMARY OF BACKGROUND DATA

While back pain is an almost universal human experience, only about 5% of sufferers seek medical advice. Most of these respond to conservative treatment. However, approximately 10% of those who experience an acute attack of low back pain go on to become chronic sufferers.

METHODS

Psychosocial and physiological data (including fear-avoidance measures) were collected from a sample of 300 acute low back pain patients within 1 week of presentation and at 2 months, to try to predict 12 month outcome.

RESULTS

Data analysis showed that subjects who had not recovered by 2 months were those who went on to become chronic low back pain patients (7.3%). Using multiple regression analyses, fear-avoidance variables were the most successful in predicting outcome. Using multiple discriminant function analyses, the results suggest that the outcome in terms of the future course of low back pain can be correctly classified in 66% from fear-avoidance variables alone and in 88% of patients from all variables.

CONCLUSIONS

The results suggest that, at the earliest stage of low back pain, fear of pain should be identified by clinicians and, where this is severe, pain confrontation should arguably form part of the approach to treatment.

High resolution matrix-assisted laser desorption/ionization time-of-flight analysis of single-stranded DNA of 27 to 68 nucleotides in length

Mass spectra of single-stranded DNA oligonucleotides were acquired using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). Resolution enhancement using space-velocity correlation focusing allows for facile observation of different oligomers, the direct observation of individual DNA-metal adducts, and investigation of counter ion structure.