Gerald C. Huth

Fluorescence bronchoscopy for localization of carcinoma in situ.

A fluorescence bronchoscope system has been developed for imaging lung tumors by fluorescence of a previously injected, tumor-specific agent hematoporphyrin derivative. Carcinoma in situ has been localized, but there are too many false positives and negatives. A new system has been implemented which allows rapid switching between viewing of fluorescence, and viewing of the same area under white light illumination as in conventional bronchoscopy. The excitation source is a violet krypton ion laser coupled to a fused quartz fiber light conductor, with a diverging microlens to spread the light uniformly. A third-generation, microchannel plate image intensifier amplifies the weak fluorescence for viewing and video display, recording, and analysis. A movable mirror and periscope bypasses the intensifier for normal color viewing and video display and recording, with the laser shutter closed and the white light shutter open. This facilitates accurate localization, comparison of the color and fluorescence images, and precise sampling during biopsy. The improved system should reduce the false positive rate due to biopsy sampling error, and together with the video analyzer should reduce indeterminate results.

Mercuric iodide (HgI2) platelets for x-ray spectroscopy produced by polymer controlled growth

Abstract The low temperature red form of mercuric iodide has been grown by a new chemical transport method which introduces organic monomers or polymers during the crystal growth process. Resulting crystals are in the form of platelets which are more directly useful in radiation detector device application. Platelets near one centimeter in width and 200 μm in thickness have been grown in periods of a few days using only 99.9% (unpurified) starting material. Measurements of X-ray and gamma ray energy resolution from detectors fabricated from platelets have yielded a 1.15 keV (FWHM) value for the 59.5 keV Am-241 line and 400 ev (FWHM) for the 5.9 keV Fe-55 line. These are again among the highest resolution values ever measured for HgI2. Electrical carrier transport property values of HgI2 so grown equal the best values previously measured from vapor grown material.

Reconstruction of Images from Neuromagnetic Fields

In response to specific stimuli, the human brain emits a measurable magnetic field from regions actively involved in processing the stimulus. We have implemented an iterative algorithm to reconstruct images from the neuromagnetic field. Computer simulation studies performed to develop the algorithm are reported. Experimental measurements of a human visually-evoked field and images reconstructed therefrom are also reported. The results demonstrate, for the first time, the feasibility of imaging multiple sources within the brain that produce a magnetic field.

Toward the Energy Resolution Limit of Mercuric Iodide in Room Temperature Low Energy X-Ray Spectrometry

Development of mercuric iodide nuclear detectors fabricated from vapor grown single crystals continues with emphasis in our work on their capabilities as room temperature operable low-energy X-ray spectrometers. The influence of trapping in the detector crystal, electronic noise and statistical fluctuations on energy resolution of the detectors are discussed. A room temperature energy resolution value of 490 eV (FWHM) has been measured for Fe-55 (with a corresponding 420 eV value of electronic noise) using a 2mm2 HgI2 detector. The K¿ and Kß lines of Fe-55 at 5.9 keV and 6.5 keV have been separated, to our knowledge, for the first time at room temperature. A new Fano-factor value of 0.46 has been established for mercuric iodide. In the room temperature HgI2 detector - FET preamplifier combination the latter is the largest contributor to the width of the spectral line in the low energy region. Our efforts are therefore directed toward reducing room temperature preamplifier noise. A room temperature preamplifier noise level of 360 eV (HgI2) has been attained. We are currently investigating use of low noise, low capacitance FET devices in a more optimized preamplifier configuration which should further reduce the noise value (H.E. Kern, IEEE Trans. Nucl. Sci. NS-17). Also under investigation is the effect of Peltier cooling of the input stage of the FET preamplifier.

Scintillation spectrometry with HgI2 as the photodetector

Abstract A mercuric iodide (HgI2) photodetector has been used to detect light pulses from gamma-ray and alpha-particle interactions in scintillators. The photocurrent response of an HgI2 photodetector to light has been measured and found to be favorable for detecting light from most scintillators, which have their maximum emission between 400 and 560 nm. Energy spectra for alpha particles or gamma-rays from combinations of an HgI2 photodetector with various scintillators are presented. The energy resolution of the photopeak from annihilation gamma-rays is 19% with a CsI(Tl) crystal and 24% with a BGO crystal. Fabrication of HgI2 photodetectors and their optical coupling to a scintillator crystal will be described. The advantages of this new solid-state radiation detector compared to the combination of scintillator and PMT, and some proposed applications, are discussed.

Fluorescence Bronchoscopy for Localizing Early Bronchial Cancer and Carcinoma in Situ

The detection, diagnosis, and aggressive treatment of lung cancer in its intrabronchial or preinvasive phase has been shown to result in 5-year survival rates of over 70%–80% [16, 19, 29]. In the case of carcinoma in situ, resection may result in prolonged survival and possibly cure [4]. In contrast, stage I lung cancer is of the invasive type and includes lesions that have already extended to the ipsilateral hilar lymph nodes; the 5-year survival at this stage is at best about 40%–50%. In small peripheral lung cancers (less than 3.0 cm in diameter), visible on chest X-ray but without hilar lymph node involvement, 5-year survival can be up to 60% [18]. The goal of physicians, therefore, must be the diagnosis of preinvasive lung cancer in patients at high risk. High risk patients include heavy cigarette smokers who have smoked one package per day or more for 20 years or longer, particularly those over age 45 years. Patients at particularly high risk are heavy smokers who also have symptoms or signs related to lung cancer and especially include smokers who have also been occupationally exposed to asbestos, uranium mining, coke oven emissions, nickel, and chromates, which are known industrial carcinogens.

A Study of Low-Noise Preamplifier Systems for Use with Room Temperature Mercuric Iodide (Hgi2) X-Ray Detectors

An analysis of different preamplification systems for use with room temperature mercuric iodide x-ray detectors has been performed. Resistor-, drain-, and light-feedback preamplifiers have been studied. Energy resolution values of 295 eV (FWHM) for an Fe-55 source (5.9 keV) and 225 eV (FWHM) for a pulser have been obtained with both the detector and the input FET at room temperature using a pulsed-light feedback preamplifier. Improvement in energy resolution by cooling the input FET using a small Peltier element has been discussed.

Characteristic x-ray spectra of sodium and magnesium measured at room temperature using mercuric iodide detectors

Mercuric iodide detectors, operating at room temperature with the FET of the first stage of amplification cooled with a two‐stage Peltier element, have been used to detect low‐energy x rays from light elements excited by 2.0‐ and 6.1‐MeV α particles. X‐ray lines from Na (1.04 keV) and Mg (1.25 keV) have been seen for the first time with room‐temperature energy‐dispersive detectors. A resolution of 390 eV at 1.25 keV was obtained. Further improvement of the resolution is believed to be achievable. However, even the present characteristics are adequate for many applications in x‐ray fluorescence and elemental analysis. Several such possible applications are suggested.

Room-temperature mercuric iodide spectrometry for low-energy x-rays

Abstract A discussion of the limits of energy resolution in different energy ranges is given. The energy resolution of a spectrometer is analyzed in terms of the parameters characterizing the crystal, the detector, and the amplification electronics. A high-resolution room-temperature HgI 2 spectrometry system was used to measure low-energy X-ray fluorescence spectra. For the Mg K α X-ray line the measured resolution was 245 eV (fwhm); the electronic noise linewidth of the system was 225 eV. Alpha-particles were used to excite X-ray fluorescence from low- Z elements separately or in combination. The shape of the photopeaks in the spectra is discussed.

Low Energy X-Ray Spectra Measured with a Mercuric Iodide Energy Dispersive Spectrometer in a Scanning Electron Microscope

A mercuric iodide energy dispersive x-ray spectrometer, with Peltier cooling provided for the detector and input field effect transistor, has been developed and tested in a scanning electron microscope. X-ray spectra were obtained with the 15 keV electron beam. An energy resolution of 225 eV (FWHM) for Mn-K¿ at 5.9 keV and 195 eV (FWHM) for Mg-K line at 1.25 keV has been measured. Overall system noise level was 175 eV (FWHM). The detector system characterization with a carbon target demonstrated good energy sensitivity at low energies and lack of significant spectral artifacts at higher energies.