Spinal cord magnetic resonance imaging for investigation of nonneurogenic lower urinary tract dysfunction--can the yield be improved?

PURPOSE: Magnetic resonance imaging has been used to detect occult neuropathy in patients with nonneurogenic lower urinary tract dysfunction. There is substantial controversy surrounding the role of this test for lower urinary tract dysfunction. We identified factors associated with positive magnetic resonance imaging to improve patient selection. MATERIALS AND METHODS: A case-control study was done in all pediatric patients referred to our radiology department for spinal magnetic resonance imaging primarily because of lower urinary tract symptoms between 1995 and 2004. Patients with known neurological disorders or anomalies associated with neurogenic bladder (overt spinal dysraphism, imperforate anus, etc) were excluded. A total of 80 patients with a median age of 6.5 years (range 4 to 17) were identified, of whom 47 (59%) were female. Bivariate analysis was used to evaluate the association of certain variables with positive magnetic resonance imaging findings, including patient age, gender, type of urinary symptoms, fecal soiling, abnormal neuro-orthopedic examination, lumbar cutaneous findings, resistance to medical management and urodynamic findings. RESULTS: Magnetic resonance imaging revealed spinal abnormalities in 6 cases (7.5%), including intradural arachnoid cyst in 1, sacral dysgenesis in 3, syrinx/hydromyelia in 1 and tethered cord in 1. An abnormal lumbar cutaneous finding was the only variable associated with positive magnetic resonance imaging (Fisher's exact test p = 0.002). CONCLUSIONS: Spinal magnetic resonance imaging has a low impact in the management of lower urinary tract dysfunction. With proper patient selection the pretest probability of positive magnetic resonance imaging may be increased and, therefore, many unnecessary studies may be avoided. Abnormal cutaneous findings are associated with abnormal magnetic resonance imaging.

Characterisation and optimisation of AC conductimetric biosensors.

Urease, immobilised on interdigitated gold electrodes, is employed as a model enzyme for characterisation and optimisation of a.c. conductimetric sensors. The sensors' response is measured over a frequency range of 20 Hz to 300 kHz and an optimum operating frequency established. The activity of the urease, both in solution and immobilised states, is investigated and Km values obtained. The effect of method of immobilisation and enzyme loading on the sensors' performance are studied and urease electrodes are characterised as a function of temperature, pH and electrolyte concentration. An important finding, particularly for conductimetric sensors designed for clinical use, is that proper consideration of the effects of electrode polarisation must be taken into account in order to maintain high sensor sensitivity at physiological electrolyte concentrations. Measurements of urea concentration in untreated serum are described.

Novel hexacyanoferrate (III)-modified carbon electrodes: application in miniaturized biosensors with potential for in vivo glucose sensing.

We adapted a new technology for the modification of carbon base electrodes for use as probe-type, potentially implantable glucose sensors. Carbon rods (diameter 0.3 mm) were modified by repeated potential cycling in 0.1 M potassium hexacyanoferrate (III). The modified-carbon electrodes were sealed in plastic pipette tips with an exposed reaction area where glucose oxidase was immobilized using glutaraldehyde. An outer membrane of Nafion, followed by 15% (w/v) polyurethane, was applied over the enzyme layer. The miniature modified-carbon glucose sensors displayed a sensitivity to glucose in phosphate-buffered saline of 91.4 +/- 19 nA/mM (mean +/- SEM) and a linear range up to 5.3 +/- 1 mM glucose when operated at 750 mV versus a silver/silver chloride reference. Corresponding, unmodified-carbon based glucose sensors displayed a lower sensitivity of 20.7 +/- 3 nA/mM with a linear range up to 3.8 +/- 0.5 mM. The modified-carbon glucose sensors responded to glucose when operated in plasma but with a reduced sensitivity compared with that in buffered saline. Glucose sensors displayed good stability for up to 6.5 days during continuous operation in 5 mM buffered glucose solution. Interference from ascorbate and 4-acetamidophenol at both physiological and pharmacological ranges was significantly lower at the modified-carbon base electrodes than that at the unmodified-carbon base electrodes. Also, the relatively large effect of ascorbate and 4-acetamidophenol at the unmodified-carbon base electrode was reduced considerably when the base electrode was coated with glucose oxidase, Nafion and polyurethane membranes.

Recent advances in amperometric glucose biosensors for in vivo monitoring.

Electrochemical biosensors for glucose, based on the specific glucose oxidizing enzyme glucose oxidase, have generated considerable interest. Several commercial devices based on this principle have been developed and are widely used for in vitro monitoring of glucose e.g. in hospitals, doctors surgeries and for home monitoring by patients themselves. A significant advance in the application of biosensor technology would be the development of portable, implantable sensors which could continuously indicate the blood glucose concentration, enabling swift corrective action to be taken by the patient. This review highlights recent developments in amperometric glucose biosensors for in vivo monitoring and also considers the remaining barrier which need to be overcome to enable successful introduction of an implantable sensor.