Automated rejection of contaminated surface measurements for improved surface registration in image guided neurosurgery.

Most image guided Neurosurgery employs adhesively mounted external fiducials for registration of medical images to the surgical workspace. Due to high logistical costs associated with these artificial landmarks, we strive to eliminate the need for these markers. At our institution, we developed a handheld laser stripe triangulation device to capture the surface contours of the patient's head while oriented for surgery. Anatomical surface registration algorithms rely on the assumption that the patient's anatomy bears the same geometry as the 3D model of the patient constructed from the imaging modality employed. During the time interval from which the patient is imaged and placed in the Mayfield head clamp in the operating room, the skin of the head bulges at the pinsite and the skull fixation equipment itself optically interferes with the image capture laser. We have developed software to reject points belonging to objects of known geometry while calculating the registration. During the course of development of the laser scanning unit, we have acquired surface contours of 13 patients and 2 cadavers. Initial analysis revealed that this automated rejection of points improved the registrations in all cases, but the accuracy of the fiducial method was not surpassed. Only points belonging to the offending instrument are removed. Skin bulges caused by the clamps and instruments remain in the data. We anticipate that careful removal of the points in these skin bulges will yield registrations that at least match the accuracy of the fiducial method.

Lamotrigine analysis in serum by high-performance liquid chromatography.

Lamotrigine is an anticonvulsant drug soon to be introduced to the North American market. It is chemically unrelated to any currently available antiepileptic drug. The objective of this study was to develop a quantitative high-performance liquid chromatography assay for lamotrigine in serum. Lamotrigine was extracted from serum at alkaline pH into ethyl acetate after addition of the internal standard (BW725C78). After mixing, the organic layer was evaporated to dryness before dissolving the residue in methanol for isocratic separation on a RP-8 column (5 microns) with a mobile phase of water/0.5 M phosphate buffer at pH 6.5/acetonitrile (790/10/200) with eluant monitoring at 306 nm. Calibration was performed with five serum standards (2-32 microM and recovery averaged 88% at 25 microM. Between-run precision was 4.1 and 2.5% C.V. at 13.6 and 31.6 microM, respectively. At room temperature, lamotrigine was stable for a minimum of 7 days. Interference studies were performed on serum specimens containing commonly monitored drugs. The only potentially interfering drug was carbamazepine, which elutes 2.5 times longer than lamotrigine. We conclude that this is a reliable method for quantitation of lamotrigine in serum.

Colorimetric and gas chromatographic procedures for glycolic acid in serum: the major toxic metabolite of ethylene glycol.

Monitoring of individuals poisoned with ethylene glycol involves analysis of ethylene glycol in serum. The objective of this procedure was to validate a colorimetric and gas chromatographic procedure for glycolic acid in serum. The colorimetric procedure requires no sophisticated instrumentation and has been shown to be specific for glycolic acid. A gas chromatographic procedure has also been developed involving methyl derivatization of glycolic acid and the internal standard (propionic acid). These methods have been used for the analysis of serum specimens from ethylene glycol poisoned patients. Glycolic acid has been recognized as the major toxic agent in ethylene glycol poisoning but current methods available do not allow analysis in a clinically relevant turnaround time. These two procedures allow glycolic acid quantitation by procedures readily set up in most clinical toxicology laboratories.

Toxicological analysis of a fatal baclofen (Lioresal) ingestion.

A fatality following ingestion of the drug baclofen (Lioresal) is described. Baclofen was identified in urine by gas chromatography/mass spectrometry. After derivatization with trinitrobenzene sulfonic acid, baclofen was quantitated in serum and urine by high-performance liquid chromatography. The concentration of baclofen was 17 mg/L in serum and 760 mg/L in urine collected approximately 12 h after the overdose. To our knowledge, this is only the second reported fatality involving a baclofen overdose. The previous case did not include quantitation of baclofen in any biological fluid.

Gas chromatographic analysis of methyl formate and application in methanol poisoning cases.

A modified headspace gas chromatographic method for analysis of formate in biological fluids is described. Serum or whole blood specimens were methylated in the presence of concentrated sulfuric acid and sodium propionate (internal standard) dissolved in methanol. Derivatization was performed at 35 degrees C for 30 min before injection (0.5 mL headspace) onto a Hallcomid-Carbowax packed GLC column. Using serum or aqueous standards, the method was linear from 5 to 100 mg/dL. The limit of detection was 2.5 mg/dL. Day-to-day precision was less than 5% (CV) at 54 mg/dL formate. Formate and methanol were analyzed in 3 methanol poisonings, two of which were fatal. Formate analysis is considered important in any patient with suspected methanol poisoning who presents for medical assistance with metabolic acidosis. The extent of ocular toxicity correlates better with formate concentration than with methanol concentration.