Practical application of fMRI for surgical planning

We report our experience evaluating tasks designed to visualize regions of motor and language brain activation using functional magnetic resonant imaging (fMRI). Our goal was to identify a battery of tasks which would provide a range of brain imaging studies which could be used clinically for surgical planning, with the requirement that they could be performed and analyzed rapidly, thus, cost effectively. These tasks were chosen to assess (1) motor control of the hands, fingers, and feet, and (2) language processing using both auditory and visual task presentations. From January through April 2001, five patients and eight normal subjects were studied. A selection of three or four tasks acquired with an EPI sequence coupled with a high resolution 3D MR sequence were completed in 45- 60 min of scanner time. Identification of the location of eloquent cortex serving aspects of motor and language functions was successful in four of the five patients and all of the eight normal subjects.

Comparison of the coulometric and polarographic measurement of a high-Dk hydrogel

BACKGROUND

International Organization for Standardization (ISO) document ISO 9913-1 details procedures for oxygen permeability coefficient (Dk) measurement of hydrogel contact lens materials up to 100 barrer. A draft ISO document 9913-2 describing the coulometric technique states that the recommended procedures are suitable for nonhydrogel materials. New generation hydrogel lens materials exceed 100 barrer, which is outside the scope of both documents.

METHODS

A range of rigid gas-permeable materials from Dr. W. Benjamin's standard repository was used as a baseline to assess the accuracy of the polarographic and the coulometric methods. We also measured the permeability of a new generation hydrogel, lotrafilcon A, to explore the suitability of the polarographic and coulometric techniques for high-Dk hydrogel lenses. We modified equipment for both methods that incorporate several improvements including front surface masking to eliminate "edge effect."

RESULTS

The coulometric technique provided results similar to those previously reported for the standard rigid gas-permeable materials and yielded relative standard errors typically <10%. The polarographic technique provided results similar to the accepted values for the standard rigid gas-permeable materials Dk <70 barrer only after the edge effect correction algorithm was applied. The polarographic results showed poor precision and significant, systematic differences from accepted values for the rigid gas-permeables with Dk > 70 barrer.

CONCLUSIONS

The coulometric method is preferable for the measurement of contact lens materials with permeability >70 barrer. The coulometric method was successfully modified to include hydrogels.

Oxygen permeability of a new type of high Dk soft contact lens material

Lotrafilcon A is a biphasic block-copolymer, comprising a highly permeable siloxane-based polymeric phase, coupled with a water phase (hydrogel phase). The high oxygen permeability of this material, and the fact that it is a hydrogel, places it outside the applicability of both the polarographic ISO standard and coulometric ISO draft standards for contact lens Dk determination. The oxygen permeability (Dk) and transmissibility (Dk/t) of lotrafilcon A lenses were determined by an adaptation of the standard coulometric method. Lenses with a thickness (t) range from 30 microns to over 300 microns were measured in a liquid-to-gas and a gas-to-gas configuration in an effort to combine features of the ISO (draft) standards to yield a valid measurement of the intrinsic material's oxygen transmission characteristics. The following results, for lotrafilcon A, are the mean values and SE for the oxygen permeability coefficient (Dk) determined at 34 degrees C: 140 +/- 2 barrer with water overlay (liquid-to-gas) at 2100 rpm stirring speed, 150 +/- 5 barrer with water overlay (liquid-to-gas) at "infinite" stirring speed, and 170 +/- 2 barrer without water overlay (gas-to-gas), where barrer = 10(-11) (mlO2.cm)/(sec.cm2.mm Hg). Clinical lenses produced from this material are expected to be in the 60 to 90 microns thickness range, with an average center thickness of 80 microns. Given that the Dkmaterial is greater than or equal to 140 barrers, for this material, a parallel sided lens of 80 microns central thickness would exhibit a lens transmissibility (Dk/t) of at least 170 x 10(-9) mlO2/(sec.cm2.mm Hg) at 34 degrees C. This transmissibility is well in excess of the 87 x 10(-9) mlO2/(sec.cm2.mm Hg) value postulated to be sufficient to prevent overnight lens-induced corneal swelling and places it in the hyper-permeable material category.

Immediate electronystagmography in the diagnosis of the dizzy patient

STUDY OBJECTIVES

To determine whether the results of electronystagmography (ENG) testing improve an emergency physician's diagnosis of dizziness.

DESIGN

Prospective, one-year.

SETTING

University and three community hospital emergency departments.

TYPE OF PARTICIPANTS

Ninety-three consecutive patients presenting with dizziness.

INTERVENTIONS

ED impression was recorded after complete ED evaluation. An ENG was performed within one hour by an audiologist, who gave a reading of "central," "peripheral," or "normal." The result was given to the emergency physician, who was invited to revise his or her impression (the "ED impression after ENG result"). Final diagnosis was based on the ED impression and by contact with the patient's physician(s) as well as the patient by telephone after one and four weeks. Accuracy of ENG was assessed by comparing ENG reading with the final diagnosis using the chi(2) test. In addition, the contribution of ENG to ED diagnosis was assessed by comparing the accuracy of the ED impression after ENG reading with the ED impression alone using McNemar's test (hit versus no-hit).

MEASUREMENTS AND MAIN RESULTS

Both ED impression and the ENG significantly correlated with the final diagnostic category (chi(2) = 104.9, P < .001; chi(2) = 70.79, P < .001, respectively). ENG correctly diagnosed nine of 11 patients with central dizziness. Of 23 patients with undetermined cause after ED evaluation, ENG correctly identified seven patients with peripheral dizziness and three with central dizziness. ED impression after ENG reading was more accurate than ED impression alone (chi(2) = 6.13, P < .05).

CONCLUSION

Emergency physicians correctly categorized most dizzy patients, but audiologist performance and interpretation of an ENG significantly improved this categorization. ENG may have the potential to identify clinically unsuspected central dizziness and to categorize dizziness of "unknown" cause. Further study is needed to determine whether ENG could be performed by modifying certain types of heart monitors available in the ED.