A hand-held beta imaging probe for FDG.

OBJECTIVES: Advances in radiopharmaceuticals and clinical understanding have escalated the use of intraoperative gamma probes in surgery. However, most probes on the market are non-imaging gamma probes that suffer from the lack of ancillary information of the surveyed tissue area. We have developed a novel, hand-held digital Imaging Beta Probe™ (IBP™) to be used in surgery in conjunction with beta-emitting radiopharmaceuticals such as (18)FDG, (131)I and (32)P for real-time imaging of a surveyed area with higher spatial resolution and sensitivity and greater convenience than existing instruments. METHODS: We describe the design and validation of a hand-held beta probe intended to be used as a visual mapping device to locate and confirm excision of (18)FDG-avid primary tumors and metastases in an animal model. RESULTS: We have demonstrated a device which can generate beta images from (18)FDG avid lesions in an animal model. CONCLUSIONS: It is feasible to image beta irradiation in animal models of cancer given (18)FDG. This technology may be applied to clinical mapping of tumors and/or their metastases in the operating room. Visual image depiction of malignancy may aid the surgeon in localization and excision of lesions of interest.

Full-cycle steam sterilization in ophthalmic surgery-the effect of wrapping instruments.

PURPOSE: To determine if wrapping instruments in conjunction with full-cycle steam sterilization affects the incidence of postoperative infection in patients undergoing ophthalmic surgery in a dedicated eye center. DESIGN: Retrospective, consecutive-case, comparative study. METHODS: Two consecutive groups, each of approximately 19 000 ophthalmic surgical patients, were reviewed for postoperative infection. For both groups, the surgical instruments were sterilized using full-cycle, steam sterilization, with a single major difference. The instruments for the first group were sterilized with equipment located adjacent to the operating room and no wrapping of the instruments was used, whereas for the second group, the sterilization equipment was located at a central facility and the instruments were wrapped before being transported to the operating rooms. RESULTS: In the unwrapped sterilization group 17 presumed postoperative infections were identified, compared to 9 presumed infections in the wrapped sterilization group. Because the observed infection rates for each group were so low, this apparent difference is not statistically significant (P = .16). Similarly, differences found in the incidence of culture-positive cases of endophthalmitis (5 for unwrapped vs 3 for wrapped) were not statistically significant (P = .47). CONCLUSIONS: In a dedicated, high-volume eye facility, the incidence of presumed postoperative infection associated with unwrapped and wrapped full-cycle steam sterilization were shown to be identical within statistical error. This provides strong evidence that if eye surgical facilities carefully clean surgical instruments and follow the industry and manufacturer guidelines, they can, with confidence, use either of these 2 methods of sterilization. This study presents the first concrete data that corroborate the current position of The Joint Commission, American Academy of Ophthalmology (AAO) and American Society of Cataract and Refractive Surgery (ASCRS).

Enhanced red and near infrared detection in flow cytometry using avalanche photodiodes.

Polychromatic flow cytometry enables detailed identification of cell phenotype using multiple fluorescent parameters. The photomultiplier tubes (PMTs) used to detect fluorescence in current instruments limit the sensitivity in the long wavelength spectral range. We demonstrate the flow cytometric applications of silicon avalanche photodiodes (APDs), which have improved red sensitivity and a working fluorescence detection range beyond 1,000 nm. A comparison of the wavelength-dependent performance of the APD and PMT was carried out using pulsed light-emitting diode sources, calibrated test beads, and biological samples. A breadboard flow cytometer test bench was constructed to compare the performance of PMTs and APD detectors. The APD used an additional amplifier stage to match the internal gain of the PMT. The resolution of the APD and PMT was compared for flow cytometry applications using a pulsed light-emitting diode source over the 500-1060 nm spectral range. These measurements showed the relative changes in the signal-to-noise performance of the APD and PMT over a broad spectral range. Both the APD and PMTs were used to measure the signal-to-noise response for a set of six peak calibration beads over the 530-800 nm wavelength range. CD4-positive cells labeled with antibody-conjugated phycoerythrin or 800 nm quantum dots were identified by simultaneous detection using the APD and the PMT. The ratios of the intensities of the CD4- and CD4+ populations were found to be similar for both detectors in the visible wavelengths, but only the APD was able to separate these populations at wavelengths above 800 nm. These measurements illustrate the differences in APD and PMT performance at different wavelengths and signal intensity levels. While the APD and PMT show similar signal-to-noise performance in the visible spectral range, the dark noise of the APD detector reduces the sensitivity at low signal levels. At wavelengths longer than 650 nm, the high quantum efficiency of the APD contributes to better signal-to-noise performance. The APD detector provides enhanced performance in the long wavelength region and may be used to extend the working range of the flow cytometer beyond 1,000 nm.

Depth of interaction resolution measurements for a high resolution PET detector using position sensitive avalanche photodiodes.

We explore dual-ended read out of LSO arrays with two position sensitive avalanche photodiodes (PSAPDs) as a high resolution, high efficiency depth-encoding detector for PET applications. Flood histograms, energy resolution and depth of interaction (DOI) resolution were measured for unpolished LSO arrays with individual crystal sizes of 1.0, 1.3 and 1.5 mm, and for a polished LSO array with 1.3 mm pixels. The thickness of the crystal arrays was 20 mm. Good flood histograms were obtained for all four arrays, and crystals in all four arrays can be clearly resolved. Although the amplitude of each PSAPD signal decreases as the interaction depth moves further from the PSAPD, the sum of the two PSAPD signals is essentially constant with irradiation depth for all four arrays. The energy resolutions were similar for all four arrays, ranging from 14.7% to 15.4%. A DOI resolution of 3-4 mm (including the width of the irradiation band which is approximately 2 mm) was obtained for all the unpolished arrays. The best DOI resolution was achieved with the unpolished 1 mm array (average 3.5 mm). The DOI resolution for the 1.3 mm and 1.5 mm unpolished arrays was 3.7 and 4.0 mm respectively. For the polished array, the DOI resolution was only 16.5 mm. Summing the DOI profiles across all crystals for the 1 mm array only degraded the DOI resolution from 3.5 mm to 3.9 mm, indicating that it may not be necessary to calibrate the DOI response separately for each crystal within an array. The DOI response of individual crystals in the array confirms this finding. These results provide a detailed characterization of the DOI response of these PSAPD-based PET detectors which will be important in the design and calibration of a PET scanner making use of this detector approach.