Methods and systems for signal processing in particle detection systems
First Claim
1. A method of using laser-induced fluorescence to distinguish (a) a presence of threat particles interspersed with background particles from (b) an absence of threat particles, the threat particles representing fluorescent biological substances, comprising:
- using a multiple-wavelength detection-band laser-induced fluorescence sensor to acquire a measurement set of particles for laser-induced fluorescence analysis, the sensor providing threat-present and threat-absent particle signals in response to the acquired measurement set of particles;
defining a grey-scale weighting function formulated on competing sensitivity and false positive rate factors, the sensitivity factor representing sensitivity of detecting threat particles against non-threat particles and the false positive rate factor representing a probability of falsely concluding that the acquired measurement set of particles contains threat particles;
using the weighting function to assign weights to particles in the measurement set, based on a numerical characterization of a particle and a weight associated with that characterization;
assigning weights to each particle in the measurement set, based on the weighting function; and
processing the weights assigned to the particles and producing an indication whenever a result obtained from the processing of the weights represents a likelihood of concluding correctly that the measurement set of particles contains threat particles.
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Abstract
A method for statistically distinguishing between two or more populations, such as between samples containing background and threat particles, is disclosed. According to one embodiment, the method for statistically distinguishing is a method for processing a signal in a particle detection system. The method may include characterizing each particle detected by a signal vector. The method may further include calculating a weight of each particle detected using a weighting function of the signal vectors. The weighting function may be a functional of a threat particle probability distribution and a background particle probability distribution. The method may also include summing a total weight of all particles tested and generating an alarm signal if the total weight exceeds an alarm level.
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Citations
21 Claims
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1. A method of using laser-induced fluorescence to distinguish (a) a presence of threat particles interspersed with background particles from (b) an absence of threat particles, the threat particles representing fluorescent biological substances, comprising:
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using a multiple-wavelength detection-band laser-induced fluorescence sensor to acquire a measurement set of particles for laser-induced fluorescence analysis, the sensor providing threat-present and threat-absent particle signals in response to the acquired measurement set of particles; defining a grey-scale weighting function formulated on competing sensitivity and false positive rate factors, the sensitivity factor representing sensitivity of detecting threat particles against non-threat particles and the false positive rate factor representing a probability of falsely concluding that the acquired measurement set of particles contains threat particles; using the weighting function to assign weights to particles in the measurement set, based on a numerical characterization of a particle and a weight associated with that characterization; assigning weights to each particle in the measurement set, based on the weighting function; and processing the weights assigned to the particles and producing an indication whenever a result obtained from the processing of the weights represents a likelihood of concluding correctly that the measurement set of particles contains threat particles. - View Dependent Claims (2, 3, 4, 5)
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6. A method of deciding whether a particle-containing sample of an air stream, which air stream may contain particles of interest and background particles, is a sample of interest, comprising:
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detecting a measurement set of particles in the air stream; defining a numerical characterization scheme for characterizing particles in the measurement set; individually assigning a numerical characterization to each detected particle in the measurement set; defining a grey-scale weighting function, with a range of more than two weights, capable of associating a weight with a numerical characterization; using the weighting function in assigning weights to particles in the measurement set, based on the numerical characterization of a particle and the weight associated with that characterization; processing the assigned weights for detected particles in a sample; and producing an indication, based on the processing of the assigned weights, whether the measurement set contains some particles of interest or background particles. - View Dependent Claims (7, 8, 9, 10, 11, 12, 13)
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14. A device for analyzing samples of an air stream containing particles, comprising:
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an excitation wavelength; an emission wavelength that is different from the excitation wavelength; an illumination area through which the air stream passes; a light source, comprising light at the excitation wavelength, that illuminates, in the illumination area, the particles contained in the air stream; an excitation light detector that detects light from the particles at the excitation wavelength; a fluorescence detector that detects light at the emission wavelength; a memory that accumulates particle information, including (a) data representing a count of a number of particles that has passed through the illumination area and (b) data representing light detected by the fluorescence detector; a sample-size criterion comprising data representing a maximum number of particles to be included in a complete sample, the complete sample comprising a plurality of particles; and a sample-completion testing module that applies the sample-size criterion to determine when the memory has accumulated particle data from a complete sample. - View Dependent Claims (15, 16, 17)
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18. A system for reducing the false positives in a particle detection system, comprising:
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a laser that irradiates a particle-containing airstream containing unknown particles which may be particles of interest or background particles; a fluorescence detector that detects fluorescence emitted by the particles in the airstream in response to irradiation by the laser; a non-fluorescence detector that detects particles in the airstream regardless of fluorescence; a computer-readable medium for storing; a sample size, expressible or convertible into in time, to determine a size of a sample of detected particles a sample volume rate expressible in liters per second; a sensitivity expressible by a number of Bacillus globigii particles amid a number of total particles per volume; a mean time between false positives; and a true positive confidence level; where a common log of the mean time in seconds between false positives is greater than 4 for a true positive confidence level of 90% and a sample time, sensitivity, and true positive confidence level for conditions with ratios of;
(a) 10 seconds, to (b) a ratio of 42 Bacillus globigii particles per 2500 total particles per liter. - View Dependent Claims (19, 20, 21)
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Specification