S Chervu | PubMed Health

PubMed1984

Quantitative evaluation of cerebrospinal fluid shunt flow.

We describe a rigorous method for measuring the flow of cerebrospinal fluid (CSF) in shunt circuits implanted for the relief of obstructive hydrocephalus. Clearance of radioactivity for several calibrated flow rates was determined with a Harvard infusion pump by injecting the Rickham reservoir of a Rickham -Holter valve system with 100 microCi of Tc-99m as pertechnetate. The elliptical and the cylindrical Holter valves used as adjunct valves with the Rickham reservoir yielded two different regression lines when the clearances were plotted against flow rates. The experimental regression lines were used to determine the in vivo flow rates from clearances calculated after injecting the Rickham reservoirs of the patients. The unique clearance characteristics of the individual shunt systems available requires that calibration curves be derived for an entire system identical to one implanted in the patient being evaluated, rather than just the injected chamber. Excellent correlation between flow rates and the clinical findings supports the reliability of this method of quantification of CSF shunt flow, and the results are fully accepted by our neurosurgeons.

Adult↗

PubMed1982

Thyroid uptake measurements with I-123: problems and pitfalls: concise communication.

The measurement of radioiodine uptake is generally considered to be straight-forward and accurate. However, during the past two decades, discrepancies in "normal" thyroid uptake values have been noticed between Montefiore Hospital and Medical Center and the Hospital of Albert Einstein College of Medicine. These differences were attributed to differences in patient population. Further investigation revealed that the persisting uptake discrepancies arose from neck-phantom differences and variations in procedure. Differences in presumably standardized neck-phantom attenuation characteristics have been shown to cause large variations in count rates from I-123 and I-131 standard capsules. The effect of high-voltage fluctuation on phantom count rates is more pronounced with I-123 than with I-131. In constant levels of high-energy contaminants in I-123 also affect the uptake measurements. large errors in the measurements of thyroid uptake values may result from seemingly unimportant variations in technique. A stable high-voltage power supply, precise high-voltage adjustment, careful selection of energy window, and the use of a standardized neck phantom with generally accepted attenuation characteristics are absolutely essential if RAIU values are to be compared and appropriate therapeutic doses are to be administered based on these measurements.

Humans↗