Patent Description:
The specification relates generally to spectroscopy, and, in particular, to a method and system for analyzing a sample using cavity ring-down spectroscopy.

The diagnosis of certain physiological conditions can be challenging. One such physiological condition is lung cancer that is amongst the most prevalent and deadliest forms of cancer. While the prognosis can be improved when lung cancer is discovered in its early, localized stage, most cases are diagnosed when the cancer has already started to spread. Survival rates for lung cancer significantly decline as it spreads from a localized instance to other regions. For this reason, early detection of lung cancer is critical.

Currently, low-dose computed tomography ("LDCT") is recommended to screen for lung cancer. However, this approach is linked with a high false positive rate, resulting in many patients being subjected to unnecessary follow-up evaluations. Along with the high expenses associated with the technology and the patients' exposure to radiation, its lack of sensitivity makes LDCT an unattractive solution as its low specificity can lead to a high false-positive rate.

The abundance of recent research regarding breath biomarkers for lung cancer detection shows promise for this alternate form of screening. Thousands of volatile organic compounds ("VOCs") have been identified in exhaled human breath, ranging in concentrations from parts per million by volume (ppmv) to parts per trillion by volume (pptv). While there is a belief that cancerous cells influence the production of a set of VOCs in the body that can travel through the bloodstream, into the lungs, and out of the body in exhaled breath, there is no strong agreement on what this particular set of VOCs is.

The most widely used technique for VOC detection in exhaled breath is mass spectrometry, which is commonly combined with gas chromatography ("GC-MS"). GC-MS is popular because it offers high selectivity and sensitivity in compound detection and strong accuracy in compound identification. The likelihood that two compounds would behave similarly in both the mass spectrometer and the gas chromatograph is low, making GC-MS a reliable choice when certainty is essential. In lung cancer breath analysis, the earliest use of GC-MS for analyzing lung cancer breath biomarkers was in <NUM>. Several studies have since followed, collectively identifying dozens of potential biomarkers. Despite the progress made with this technique, GC-MS is impractical for widespread clinical use because it is expensive, time-consuming, and requires complex procedures for sample collection, limiting its applications to laboratory research.

Another technology emerging in breath analysis is the electronic nose ("E-nose"), which uses an array of gas-sensitive sensors to detect different groups of VOCs. This method of VOC detection has some advantages over GC-MS, like its relatively low cost, small size, speed, and ability to be used in "online" applications. Online breath analysis has the potential to eliminate the need for sample storage and provide more immediate feedback to clinicians. However, E-noses are far from ideal. They require frequent calibration, they are sensitive to humidity and temperature changes, and they experience drifting and memory effects. They also tend to lack the features that make GC-MS attractive, like its high sensitivity, high selectivity and its ability to identify individual compounds.

Cavity ring-down spectroscopy ("CRDS") is an approach that is generally used to analyze a sample via its absorption spectra. A typical CRDS system employs a laser generating a beam that is directed into a cavity of a chamber having two highly reflective mirrors. The beam is normally within the visible light spectrum, or the near infrared ("IR") spectrum, and is tuned to a single wavelength. The beam is then reflected repeatedly between the mirrors, which allow a fraction of the light to escape the ring-down cavity.

In order to "fill" the ring-down cavity, the length of the cavity has to be in tune with the laser wavelength. This is generally done by adjusting the position of one of the two mirrors. When the laser is in resonance with a cavity mode, intensity builds up in the cavity due to constructive interference. When the light entering the cavity is extinguished, the intensity of the light in the ring-down cavity, when empty, decays at a pre-determined rate. A small fraction of the light is not reflected by the mirrors and escapes the ring-down cavity. The intensity of the escaping light is measured by a sensor component to determine the decay rate.

When a sample is placed in the ring-down cavity, analytes (e.g., volatile organic compounds) present in the sample absorb some of the light, thereby accelerating the decay of the intensity of the light in the ring-down cavity. Absorption spectra are generated by measuring the decay times of the light in the presence of the sample at specific wavelengths relative to the decay times of the light in the absence of the sample at these wavelengths. Identification and quantification of individual analytes in the sample can be achieved via a number of methods, such as, for example, the performance of a linear regression of the measured absorption spectra for the sample with the known absorption spectra of various analytes.

While individual analytes can be readily identified, the particular analytes that can be used to positively detect the presence or absence of a particular physiological condition can be unclear, such as is the case for lung cancer. Breath samples can be collected from a patient in a non-invasive manner and analyzed via CRDS, but, as there is no widely accepted agreement on the analytes that evidence the presence or absence of lung cancer in breath, and as the breath samples contain numerous confounding components that can make detection of single analytes difficult, a different approach is required.

<CIT> discloses a method and apparatus capable of detecting constituents of a gas at extremely low concentrations using cavity ring-down spectroscopy of pre-concentrated samples, which may be provided using a medium, which is absorbent of at least a first particular gas under a first environmental condition and desorbent of the particular gas under a second environmental condition, at different desorption temperatures of said medium.

<CIT> discloses a method and device for detecting explosive compounds in an air sample in which the air sample is filtered with activated carbon treated with a weakly basic solution, after which the air sample is divided into two parts, with one part being heated at lower temperatures to decompose non-explosive nitrogenous compounds and the second part being heated at higher temperatures to decompose explosive nitrogenous compounds. Nitrogen dioxide is measured in both portions of the air sample using cavity ring-down spectroscopy, and the presence or absence of explosive nitrogenous compounds in the air sample is determined.

<NPL>) discloses "Combining Preconcentration of Air Samples with Cavity Ring-Down Spectroscopy for Detection of Trace Volatile Organic Compounds in the Atmosphere".

<CIT> discloses systems and methods for analysing time-decay signals in a cavity ring-down spectroscopy system.

<CIT> discloses an apparatus and method for rapidly and accurately identifying and quantifying analytes in a complex mixture.

The present invention is defined in the independent claims <NUM> and <NUM>. Particular embodiments are defined in the dependent claims <NUM> to <NUM> and <NUM> to <NUM>.

A method for analyzing a sample using cavity ring-down spectroscopy according to the present invention comprises: desorbing a first part of a sample from a thermal desorption tube heated to a first desorption temperature to load the first part of the sample into a ring-down cavity; for each of a first set of wavelengths: generating, via at least one laser, a laser beam at the wavelength directed into the ring-down cavity; extinguishing the laser beam entering the ring-down cavity; and registering light intensity decay data for light exiting the ring-down cavity via a light intensity sensor system; loading a second part of the sample desorbed from the thermal desorption tube heated to a second desorption temperature; for each of a second set of wavelengths: generating, via the at least one laser, a laser beam at the wavelength directed into the ring-down cavity; extinguishing the laser beam entering the ring-down cavity; and registering light intensity decay data for light exiting the ring-down cavity via a light intensity sensor system; determining, via at least one processor, a probability from the light intensity decay data using a predictive model that is at least partially based on the dataset of light intensity decay data for the first set of wavelengths and the second set of wavelengths that a subject from which the sample was received has a physiological condition or a degree of a physiological condition at least indirectly using a dataset of light intensity decay data for previously analyzed samples for which the presence or absence of the physiological condition or the degree of the physiological condition has been identified.

The physiological condition can be lung cancer.

The sample and previously analyzed samples can be breath samples.

The second set of wavelengths can be equal to the first set of wavelengths.

The method can further include combining the light intensity decay data from the second part of the sample to the light intensity decay data from the first part of the sample for each of the first set of wavelengths.

The determining can be performed using a predictive model trained at least partially using the dataset of light intensity decay data for previously analyzed samples.

The generating, the extinguishing, and the registering can be performed until a control module determines that a desired level of light intensity decay data has been collected.

A system for analyzing a sample using cavity ring-down spectroscopy according to the present invention comprises: a ring-down cavity; at least one laser operable to generate a laser beam at each of a first set of wavelengths, the laser beam being directed into the ring-down cavity; a sample-loading system for loading a first part of a sample from a thermal desorption tube into the ring-down cavity for analysis, and for unloading the first part of the sample from the ring-down cavity; a light intensity sensor system positioned to register light intensity decay data for light exiting the ring-down cavity; at least one processor operably coupled to the sample-loading system, the at least one laser, and the light intensity sensor system; a storage storing computer-readable instructions that, when executed by the at least one processor, cause the at least one processor to: control the sample-loading system to desorb the first part of the sample by heating the thermal desorption tube to a first desorption temperature to load the first part of the sample into the ring-down cavity; for each of the first set of wavelengths: operate the at least one laser to generate the laser beam directed into the ring-down cavity; extinguish the laser beam entering the ring-down cavity; and register light intensity decay data for light exiting the ring-down cavity via the light intensity sensor system; control the sample-loading system to desorb a second part of the sample by heating the thermal desorption tube to a second desorption temperature to load the second part of the sample into the ring-down cavity after unloading the first part of the sample from the ring-down cavity, for each of a second set of wavelengths: operate the at least one laser to generate the laser beam directed into the ring-down cavity; extinguish the laser beam entering the ring-down cavity; and register light intensity decay data for light exiting the ring-down cavity via the light intensity sensor system; and determine a probability from the light intensity decay data for the first set of wavelengths that a subject from which the sample was received has a physiological condition or a degree of a physiological condition at least indirectly using a predictive model that is at least partially based on a dataset of light intensity decay data for previously analyzed samples for which the presence or absence of the physiological condition or the degree of the physiological condition has been identified.

The at least one processor can combine the light intensity decay data from the second part of the sample to the light intensity decay data to the first part of the sample for each of the first set of wavelengths.

The at least one processor can repeat the operating extinguishing, and registering until the at least one processor determines that a desired level of light intensity decay data has been collected.

The second desorption temperature can be greater than the first desorption temperature.

The first desorption temperature can be equal to the second desorption temperature.

Each subsequent desorption temperature in at least one of the at least two sequences of desorption temperatures can be higher than a previous desorption temperature in the at least one of the at least two sequences of desorption temperatures.

Other technical advantages may become readily apparent to one of ordinary skill in the art after review of the following figures and description.

For a better understanding of the embodiment(s) described herein and to show more clearly how the embodiment(s) may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings in which:.

Unless otherwise specifically noted, articles depicted in the drawings are not necessarily drawn to scale.

For simplicity and clarity of illustration, where considered appropriate, reference numerals may be repeated among the Figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiment or embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein may be practiced without these specific details. In other instances, well-known methods, procedures and components have not been described in detail so as not to obscure the embodiments described herein. It should be understood at the outset that, although exemplary embodiments are illustrated in the figures and described below, the principles of the present disclosure may be implemented using any number of techniques, whether currently known or not. The present disclosure should in no way be limited to the exemplary implementations and techniques illustrated in the drawings and described below.

Various terms used throughout the present description may be read and understood as follows, unless the context indicates otherwise: "or" as used throughout is inclusive, as though written "and/or"; singular articles and pronouns as used throughout include their plural forms, and vice versa; similarly, gendered pronouns include their counterpart pronouns so that pronouns should not be understood as limiting anything described herein to use, implementation, performance, etc. by a single gender; "exemplary" should be understood as "illustrative" or "exemplifying" and not necessarily as "preferred" over other embodiments. Further definitions for terms may be set out herein; these may apply to prior and subsequent instances of those terms, as will be understood from a reading of the present description.

The components of the systems and apparatuses described herein may be integrated or separated. used in this document, "each" refers to each member of a set or each member of a subset of a set.

Any module, unit, component, server, computer, terminal, engine or device exemplified herein that executes instructions may include or otherwise have access to computer readable media such as storage media, computer storage media, or data storage devices (removable and/or non-removable) such as, for example, magnetic disks, optical disks, or tape. Computer storage media may include volatile and non-volatile, removable and non-removable media implemented in any method or technology for storage of information, such as computer readable instructions, data structures, program modules, or other data. Examples of computer storage media include RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by an application, module, or both. Any such computer storage media may be part of the device or accessible or connectable thereto. Further, unless the context clearly indicates otherwise, any processor or controller set out herein may be implemented as a singular processor or as a plurality of processors. The plurality of processors may be arrayed or distributed, and any processing function referred to herein may be carried out by one or by a plurality of processors, even though a single processor may be exemplified. Any method, application or module herein described may be implemented using computer readable/executable instructions that may be stored or otherwise held by such computer readable media and executed by the one or more processors.

The following disclosure presents a novel approach to performing analysis using CRDS. Unlike in traditional approaches in which light intensity decay data is compared to light intensity decay data for single known analytes, the light intensity decay data registered for a sample is analyzed at least indirectly using a dataset of light intensity decay data for a set of previously analyzed samples that have been identified as having a physiological condition or a degree of a physiological condition. In a preferred embodiment, this is done with a predictive model generated using machine learning on a set of training data. In addition, a process of incrementally desorbing the sample from the thermal desorption tube can be used to provide additional information about the sample. Still further, a predictive model can be improved by using machine learning to determine which combinations of desorption temperatures and/or wavelengths provide light intensity decay data that has a greater correlation with the physiological condition or the degrees of the physiological condition with which the plurality of samples have been identified.

A physiological condition is any type of state that a subject can be in. Physiological conditions can include diseases, infections, functional states of one or more organs or body systems, etc. Degrees of physiological conditions can include severities, stages (such as cancer stages), growth size, glandular output, etc. Degrees of a physiological condition can be binary in some scenarios to represent the presence or absence of the physiological condition in subjects. Degrees may be discrete or may be continuous.

Various components of a CRDS system <NUM> for analyzing a sample in accordance with a particular embodiment are shown in <FIG>. A CO2 laser <NUM> and a carbon-<NUM> O2 laser <NUM> are provided. The CO2 laser <NUM> and the carbon-<NUM> O2 laser <NUM> are gas tube lasers that emit at a series of quasi-evenly-spaced, well-known frequencies that can be rapidly selected using an adjustable diffraction grating apparatus. Gas tube laser technology has a long history and is a stable and robust way of generating infrared radiation at precisely-known frequencies. Both the CO2 laser <NUM> and the carbon-<NUM> O2 laser <NUM> emit light in the mid-IR spectrum.

Each of the CO2 laser <NUM> and the carbon-<NUM> O2 laser <NUM> has an actuator and an output coupler that enable adjustment of the length of the laser cavity as well as an actuator to change the angle of grating at the back of the cavity, thereby changing its pitch to adjust which wavelengths it reflects. By both adjusting the length of the laser cavity and changing the angle of the grating, the laser can be very accurately tuned to a specific wavelength and desired mode quality.

The CO2 laser <NUM> produces a first laser beam <NUM>, and the carbon-<NUM> O2 laser <NUM> produces a second laser beam <NUM>. Depending on the light frequency desired, either the CO2 laser <NUM> is tuned and generates the first laser beam <NUM> while the carbon-<NUM> O2 laser <NUM> is detuned, or the carbon-<NUM> O2 laser <NUM> is tuned and generates the second laser beam <NUM> while the CO2 laser <NUM> is detuned. In this manner, at most only one of the CO2 laser <NUM> and the carbon-<NUM> O2 laser <NUM> outputs a beam at any particular time so that the first beam <NUM> and the second beam <NUM> are not combined simultaneously. Mid-infrared, and specifically long wavelength infrared, was chosen as the type of light as most volatile organic compounds absorb light in this range. As a result, multiple volatile organic compounds can be measured by a single system. CO2 lasers operate in this range and have sufficient power and linewidth narrowness for ring-down spectroscopy. Using two lasers adds to the range and number of available wavelengths that the CRDS system <NUM> can use to analyze samples.

The first laser beam <NUM> is redirected via a mirror <NUM> on an optic mount towards a beam splitter <NUM>. The beam splitter <NUM> is partially reflective and partially transmissive, and splits each of the first laser beam <NUM> and the second laser beam <NUM> into two beams, a sampling beam <NUM>, and a working beam <NUM> that has the same characteristics as the sampling beam <NUM> and can be of similar intensity as the sampling beam <NUM>.

The sampling beam <NUM> is received by a fast infrared detector <NUM>. The fast infrared detector <NUM> measures the amplitude and the beat frequency of the sampling beam <NUM> using an oscilloscope. The beat frequency can indicate the presence of higher order modes resulting from a less-than-optimal tuning of the CO2 laser <NUM> or the carbon-<NUM> O2 laser <NUM>. In response to the detection of an undesirable beat frequency, the corresponding laser <NUM> or <NUM> is tuned until the amplitude of the beat frequency is minimized or eliminated while maximizing the intensity. If the amplitude of the beat frequency cannot be reduced below an acceptable level, the laser can be tuned to a different wavelength.

The working beam <NUM> continues to a first optical modulator <NUM>, which then deflects the working beam <NUM> to a mirror <NUM> on an optic mount. The mirror <NUM> redirects the light towards a second optical modulator <NUM> that, in turn, deflects the working beam <NUM> to a focusing lens <NUM>. The optical modulators are used to control the intensity of the light beam generated by the laser. In the present embodiment, the first and second optical modulators <NUM>, <NUM> are acousto-optic modulators ("AOMs"), also referred to as Bragg cells. AOMs are one type of optical modulator that uses a piezoelectric transducer coupled to a material such as germanium or glass. In the described embodiment, the material is germanium. When an oscillating electric signal is applied to the piezoelectric transducer, the piezoelectric transducer vibrates, creating sound waves in the material. These sound waves expand and compress the material, thereby creating periodic variations in the refractive index and allowing for Bragg diffraction. Light entering the AOM at the first order Bragg angle relative to the plane perpendicular to the axis of propagation of the acoustic wave will be deflected by an amount equal to twice the Bragg angle at maximum efficiency. Extinguishing the electric signal removes the Bragg diffraction properties of the material and causes the light to pass through undeflected, effectively attenuating the light along the deflected optical path. A by-product of the AOM is that the frequency of the light being deflected is shifted.

In other embodiments, the optical modulators could alternatively be electro-optic modulators. An electro-optic modulator is another type of optical modulator that applies a DC or low-frequency electric field to a material to distort the position, orientation, and/or shape of the molecules of the material. As a result, the refractive index is altered to change the phase of the outgoing beam as a function of the applied field. By sending the beam through a polarizer, the phase modulation is converted to intensity modulation. In another method, a phase modulator when placed in a branch of an interferometer can act as an intensity modulator.

Further, while the CRDS system <NUM> is described as having two optical modulators, in other embodiments, the CRDS system can have fewer or a greater number of optical modulators.

The first and second optical modulators <NUM>, <NUM> act as attenuators to adjust the intensity of the working beam <NUM> and extinguish the beam at the commencement of a ring-down event. A ring-down event includes the extinguishing of the working beam <NUM> illuminating a ring-down cavity or the detuning of the laser for the ring-down chamber, and the collection of light intensity data from the ring-down chamber. As they are AOMs, the first and second optical modulators <NUM>, <NUM> use the acousto-optic effect to diffract the light using sound waves (normally at radio-frequency). In each of the first and second optical modulators, a piezoelectric transducer is coupled to a material such as germanium or glass, and an oscillating electric signal is used to cause the piezoelectric transducer to vibrate. The vibrating piezoelectric transducer creates sound waves in the material that expand and compress the material, thereby creating period variations in the refractive index and allowing for Bragg diffraction. Light entering the AOM at Bragg angle relative to the plane perpendicular to the axis of propagation of the acoustic wave will be deflected by an amount equal to twice the Bragg angle at maximum efficiency. Extinguishing the electric signal removes the Bragg diffraction properties of the material and causes the light to pass through undeflected, effectively extinguishing the light along the deflected optical path. Hence, the intensity of the sound can be used to modulate the intensity of the light in the deflected beam.

The intensity of the light deflected by each of the first and second optical modulators <NUM>, <NUM> can be between about <NUM>%, representing a maximum deflection efficiency of the optical modulators <NUM>, <NUM>, and an attenuation limit of each of the first and second optical modulators <NUM>, <NUM> of about <NUM>% of the input light intensity. When the acoustic wave applied to the germanium is turned off, the deflected beam loses about <NUM> dB, or <NUM>%, of the previous intensity. The attenuation limit means the upper limit of how much of the input light intensity can be reduced by the optical modulator.

Optic modulators are asymmetrical in that, as a side effect, they Doppler-shift the frequency of light in a first mode when the input light is received at a first end thereof, and they Doppler-shift the frequency of light in a second mode that is counter to the first mode when the input light is received at a second end thereof and the attenuation power is the same. The Doppler shift of the frequency of the light is, however, in the same direction regardless of whether the light enters at a first end or at a second end.

Conventional CRDS systems use a single optical modulator and, as a result, have a working beam that is frequency shifted. These frequency shifts are generally small in relation to the frequency of the light, and can change the manner in which the light is absorbed by matter in the cavity, but this frequency shift can be compensated for during the analysis. If diffraction is towards the acoustic wave source of an AOM, the frequency shift is downwards, and if diffraction is away from the acoustic wave source, the frequency shift is upwards. As discussed, the effect is minimal.

The working beam <NUM> deflected by the second optical modulator <NUM> is focused via a focusing lens <NUM>. As the laser beam, and thus the working beam <NUM>, travels from the CO2 laser <NUM> or the carbon-<NUM> O2 laser <NUM>, it continues to diverge. The focusing lens <NUM> focuses the working beam <NUM> back down.

A mirror <NUM> on an optic mount thereafter redirects the working beam <NUM> towards a ring-down chamber <NUM>. The two mirrors <NUM>, <NUM> extend the length of the path of the working beam <NUM>.

The ring-down chamber <NUM> is an elongated tube defining a resonant cavity referred to as a ring-down cavity <NUM> therein. A front cavity mirror 88a and a rear cavity mirror 88b (alternatively referred to herein as cavity mirrors <NUM>) are positioned at longitudinal ends of the ring-down cavity <NUM>. The cavity mirrors <NUM> are highly reflective, both to light directed to the cavity mirrors <NUM> from outside of the ring-down cavity <NUM> and directed to the cavity mirrors <NUM> within the ring-down cavity <NUM>. As a result, a fraction of the working beam <NUM> is directed at the front cavity mirror 88a, about <NUM>%, passes through the front cavity mirror 88a, and enters the ring-down cavity <NUM>, and the majority of the working beam <NUM>, about <NUM>% is reflected back towards the mirror <NUM>.

The cavity mirrors <NUM> are mounted on mirror mounts <NUM> that are actuatable to adjust the positioning and orientation of the cavity mirrors <NUM>. In particular, the front cavity mirror 88a towards the front of the ring-down cavity <NUM> is mounted on a mirror mount <NUM> that is actuatable via three mechanized micrometers 96a. The rear cavity mirror 88b towards the rear of the ring-down cavity <NUM> is mounted on a mirror mount <NUM> that is actuatable via three piezoelectric micrometers 96b that can be manually adjusted for optical alignment or with a piezo that allows them to be adjusted further with the piezo driver.

The angle of each of cavity mirror <NUM> can be changed so that they are sufficiently aligned so that when a light beam enters the ring-down cavity <NUM>, the light beam does not deviate. If one of the cavity mirrors <NUM> is askew, then some of the light gets reflected to the side of the ring-down cavity <NUM>, intensity of the light is lost, high-order modes result, amongst other things. The micrometers <NUM> can also be simultaneously tuned to change the length of the ring-down cavity <NUM> without affecting the angle alignment. This allows for the tuning of the ring-down cavity <NUM> so that the ring-down cavity <NUM> resonates at the frequency of the light that is entering the ring-down cavity <NUM>.

The focusing lens <NUM> focuses the laser light to match the optical mode of the ring-down cavity <NUM>, so that the minimum waist of the beam is positioned at the same place as the minimum beam waist of the ring-down cavity <NUM>. The position of the focusing lens <NUM> can be adjusted to match the optical mode of a range of laser wavelengths.

A light intensity sensor system in the form of a liquid nitrogen-cooled detector <NUM> is positioned behind the rear cavity mirror 88b to receive light escaping through it. The liquid nitrogen-cooled detector <NUM> measures the intensity of the light that escapes the ring-down cavity <NUM>. Other types of light intensity sensor systems for measuring the intensity of the escaping light can be used in place of the liquid nitrogen-cooled detector <NUM>.

Samples are loaded into the ring-down cavity <NUM> from a thermal desorption tube <NUM> that is used to collect the samples for testing.

Referring now to <FIG>, an exemplary thermal desorption tube <NUM> is shown. The thermal desorption tube <NUM> has a stainless-steel casing <NUM> that is tubular, defining an aperture <NUM> at each end thereof. A receiving end <NUM> of the thermal desorption tube <NUM> receives a sample. In the exemplary described embodiment, the sample is human breath collected from a human for testing. A foam separator <NUM> is positioned towards the receiving end and is configured to distribute fluid pressure more evenly across the cross-section of the stainless-steel casing <NUM>. An adsorbent material <NUM> is positioned adjacent to the foam separator <NUM> and another foam separator <NUM>. The separators may alternatively be made of a wire mesh or other suitable material. The adsorbent material <NUM> is very porous, has a relatively high surface area, and is selected for sampling specific compounds to trap and retain the compounds of interest even in the presence of other compounds. Further, the adsorbent material <NUM> allows the collected compounds to be easily desorbed or extracted for analysis. In addition, the solid adsorbent which is selected does not react with the sample. In the particular example, the solid adsorbent is Tenax or a carbon material. As a sample is received via the receiving end <NUM>, the sample is more concentrated towards the receiving end <NUM> of the thermal desorption tube <NUM>. In other embodiments, the composition and configuration of the thermal desorption tubes can vary, as will be appreciated by a person skilled in the art.

During sample collection, breath is collected via a breath collection apparatus into which the thermal desorption tube <NUM> is fit. The breath collection apparatus can be relatively small, such as a wearable mask, or can be relatively large, such as a tabletop unit into which a person breathes. The breath sample is received via the receiving end <NUM> of the thermal desorption tube <NUM>. Human breath contains a variety of small and large molecules that are then trapped by the adsorbent material <NUM> in the thermal desorption tube <NUM>. In other embodiments, other types of gaseous samples can be collected via the thermal desorption tubes.

Referring again to <FIG>, a sample-loading system <NUM> is used to load samples from thermal desorption tubes <NUM> into the ring-down cavity <NUM>, and evacuate the sample-loading system <NUM>, including the ring-down cavity <NUM>. During loading of a sample, the sample-loading system <NUM> fills the ring-down cavity <NUM> with at least part of the sample that has been collected (i.e., to desorb the sample from the thermal desorption tube <NUM>, get the sample into the ring-down cavity <NUM> without introducing contaminants), brings the pressure and temperature in the ring-down cavity to one atmosphere and <NUM> degrees Celsius, and seals the ring-down cavity <NUM>. In this embodiment, the absorption spectra for a set of samples to which the measured absorption spectra are at least indirectly compared are determined at this pressure and temperature to ensure consistency between these parameters which can affect the results. In other embodiments, however, the pressure and temperature can be fixed at other levels for the known and measured absorption spectra. During evacuation of the at least part of a sample, the sample-loading system <NUM> cleans the previously provided sample from the ring-down cavity <NUM> and the various conduits for guiding samples from the thermal desorption tube <NUM> to the ring-down cavity <NUM>.

The sample-loading system <NUM> has an intake portion that includes a nitrogen gas source <NUM>. The nitrogen gas source <NUM> is a supply of very clean nitrogen gas that is pressurized or that can pressurize the nitrogen gas to at least above one atmosphere of pressure. In the present embodiment, the nitrogen gas source <NUM> is pressurized at five psi above ambient pressure, but can be varied as long as the compression is sufficient to pressurize the ring-down cavity <NUM> to one atmosphere, or some other selected atmospheric pressure at which the analyses are run. In the illustrated embodiment, the nitrogen gas source <NUM> is the nitrogen gas that evaporates off a liquid nitrogen reservoir. The nitrogen gas source <NUM> is connected via conduit <NUM> to a gas inlet valve 124a. An auxiliary gas inlet valve 124b enables connection of other gases, but is not regularly employed. The gas inlet and auxiliary gas inlet valves 124a, 124b are in communication with a gas intake line 120a. A pressure meter <NUM> is positioned along the gas intake line 120a, as well as a gas intake line valve 124c. A filter 130a is positioned along the gas intake line 120a in front of a cavity inlet valve 124d that seals the gas intake line 120a from the ring-down cavity <NUM>. The filter 130a inhibits the entry of contaminants into the ring-down cavity <NUM> where they can deposit on the cavity mirrors <NUM> and interfere with reflection.

The gas inlet and auxiliary gas inlet valves 124a, 124b are in communication with a pathing valve 124e. The pathing valve 124e enables or disables direct access to a desorption tube line 120b and a sample outlet line 120c.

The desorption tube line 120b includes a forward valve 124f and a rearward valve <NUM>. The thermal desorption tube <NUM> is positioned between the forward valve 124f and the rearward valve <NUM>, with the receiving end <NUM> of the thermal desorption tube <NUM> being positioned towards the rearward valve <NUM>. The thermal desorption tube <NUM> is positioned within a heater <NUM> that is controllable to heat the thermal desorption tube <NUM> to a range of temperatures.

The sample outlet line 120c includes a sample outlet valve <NUM> and a mass flow controller <NUM>.

The sample-loading system <NUM> also has an outlet portion that includes a cavity outlet valve 124i in communication with the ring-down cavity <NUM>. An outlet line <NUM> is in communication with the cavity outlet valve 124i. A pressure meter <NUM> is positioned along the outlet line <NUM>. A vacuum cutoff valve 124j is positioned between the pressure meter <NUM> and a vacuum pump <NUM>. A vacuum intake valve <NUM> is in communication with the vacuum pump <NUM> and draws air through a pump intake line <NUM>. A filter 130b is positioned in the pump intake line <NUM> to inhibit entry of contaminants that can interfere with the working of the vacuum pump <NUM>.

Valves 124a to <NUM> may be alternatively referred to herein as valves <NUM>.

While the cavity inlet valve 124d and the cavity outlet valve 124i are shown for convenience coupled to the ring-down cavity <NUM> at certain locations, it will be understood that the locations at which the valves 124d, 124i are coupled to the ring-down cavity <NUM> may vary. In a preferred configuration, the cavity inlet valve 124d is in communication with the ring-down cavity <NUM> towards an end thereof adjacent the front cavity mirror 88a and the cavity outlet valve 124i is in communication with the ring-down cavity <NUM> towards an end thereof adjacent the rear cavity mirror 88b.

When a new sample is to be loaded into the ring-down cavity <NUM>, the thermal desorption tube <NUM> containing the new sample is coupled to the sample-loading system <NUM> as shown in <FIG>.

During an evacuation phase, the vacuum intake valve <NUM> is opened and the vacuum pump <NUM> is turned on. The vacuum intake valve <NUM> is then closed, and the vacuum cutoff valve 124j, the cavity outlet valve 124i, the cavity inlet valve 124d, the gas intake line valve 124c, and the pathing valve 124e are opened in succession. The contents of the lines along this path and the ring-down cavity <NUM> are evacuated from the CRDS system <NUM> by the vacuum pump <NUM>. The pressure meter <NUM> enables the determination of when the system has been evacuated sufficiently, especially when the pressure meter <NUM> is cut off from the vacuum pump <NUM>. When it is determined that the system has been evacuated sufficiently, these same open valves 124j, 124i, 124d, 124c, and 124e are then closed in the reverse order. Thereafter, during a nitrogen fill phase, valves 124a, 124c, 124d, 124i, and 124j are opened to allow nitrogen gas from the nitrogen gas source <NUM> to fill the lines 120a and <NUM>. The nitrogen gas is then purged using another evacuation phase. The nitrogen fill phase and the evacuation phase can be repeated as desired to clear out the lines. The CRDS system <NUM> is thus evacuated of the previously tested sample.

During the loading of the new sample, the thermal desorption tube <NUM> is flushed to remove carbon dioxide and water from the thermal desorption tube <NUM> so that the amount of carbon dioxide and water loaded into the ring-down cavity <NUM> is minimized. In order to flush the thermal desorption tube <NUM>, the gas intake valve 124a, the gas intake line valve 124c, and the rearward valve <NUM> are opened to give a path to the nitrogen gas to forward flush the thermal desorption tube <NUM>. The thermal desorption tube <NUM> is selected to inhibit the collection of carbon dioxide and water with the sample, but there is still typically some carbon dioxide and water in the thermal desorption tube <NUM>.

<NUM> of nitrogen gas is put through the thermal desorption tube to get out carbon dioxide and water that have remained in the thermal desorption tube <NUM> from the original sample. Then the forward valve 124f and the sample outlet valve <NUM> are opened to provide a path to the mass flow controller <NUM>. The mass flow controller <NUM> allows the nitrogen gas and borne carbon dioxide and water to be released at a specified flow rate. In the present configuration, this flow rate is <NUM> / min. All the valves <NUM> are then closed.

Once the carbon dioxide and the water have been removed from the thermal desorption tube <NUM>, the sample-loading system <NUM> is evacuated again using the same process discussed above to remove the nitrogen gas just introduced in the sample-loading system <NUM> lines. The heater <NUM> surrounding the thermal desorption tube <NUM> then heats the thermal desorption tube <NUM> to the desired temperature to thermally desorb the at least part of the new sample within the thermal desorption tube <NUM>. The gas inlet valve 124a, the pathing valve 124e, the forward valve 124f, the rearward valve <NUM>, and the cavity inlet valve 124d are then opened to provide a direct path for the nitrogen gas from the nitrogen gas source <NUM>, through the thermal desorption tube <NUM> having desorbed compounds of interest, and to the ring-down cavity <NUM>.

It is desired to achieve a pressure of one atmosphere within the ring-down cavity <NUM> as all of the reference data collected and analyzed is at this pressure level, thereby ensuring that the results are repeatable.

The gas inlet valve 124a is toggled open and closed by the system, then the system waits for the pressure reading at the pressure meter <NUM> to stabilize and reach one atmosphere. If, upon stabilization of the pressure meter <NUM>, the pressure reading is still below one atmosphere, the gas inlet valve 124a is toggled again to repeat the process until the pressure reading is one atmosphere. When the pressure meter <NUM> shows that the pressure level in the ring-down cavity <NUM> is one atmosphere, the valves are all closed.

If it is desired to desorb at multiple temperatures, the vacuum pump <NUM> is turned on, the cavity outlet valve 124i and the vacuum cutoff valve 124j are opened to evacuate the ring-down cavity <NUM>. Then the cavity outlet valve 124i is closed before the desorption process is repeated.

A full evacuation is generally not performed between multiple desorptions as there is still some of the sample between the rearward valve <NUM> and the cavity inlet valve 124d that would be otherwise lost.

By pressurizing a fixed volume ring-down cavity containing the sample to a desired pressure level in this manner, the surface area within the ring-down cavity to which compounds can adhere can be decreased in comparison to variable volume ring-down cavities that may be used to raise the pressure within the cavity to the desired level.

Further, the pressure meter <NUM> is upstream from the path of the sample from the thermal desorption tube <NUM> to the ring-down cavity <NUM>, thereby preventing its contamination by the sample.

<FIG> is a schematic diagram of an electronic control subsystem <NUM> for various components of the CRDS system <NUM> that are also illustrated. All of the lines represent electrical or electronic signals, with arrows representing unidirectional communications, setting of a voltage, etc., and lines that are not arrows representing bidirectional communications.

A control module <NUM> including one or more processors acts as a computer system that controls the function of the various components illustrated in <FIG>. The control module <NUM> has one or more processors <NUM> and storage <NUM> storing computer-executable instructions that, when executed by the processor <NUM>, cause the processor <NUM> to direct the other components of the CRDS system <NUM> as described herein. The control module <NUM> can be any type of component that includes at least one processor executing computer executable instructions to control operation of the other components of the CRDS system <NUM> as described herein.

A pair of RF drivers <NUM> send approximately <NUM> signal to power the CO2 laser <NUM> and the carbon-<NUM> O2 laser <NUM>. Each of the lasers <NUM>, <NUM> is tuned using an output coupler and a diffraction grating. A grating actuator <NUM> actuates (turns) the diffraction grating. Another actuator actuates (translates) the output coupler. Each output coupler is driven by a 1000V output coupler piezo <NUM>. A two-channel high-voltage amplifier <NUM> that powers the output coupler piezos <NUM> is adjustable between 0V and 1000V. The high-voltage amplifier <NUM> is set with an analog output signal from a data acquisition ("DAQ") card <NUM> in the control module <NUM>. The DAQ generates output between 0V and 10V, and the high-voltage amplifier <NUM> multiplies the signal by <NUM> to generate a signal of 0V to 1000V to power the output coupler piezo <NUM>. Each grating actuator <NUM> that changes the angle for the grating is driven by an actuator driver <NUM> that is given instructions by the control module <NUM> via RS-<NUM>. Each grating actuator <NUM> is moved so many millimeters, which is translated into a pitch angle of the laser <NUM>, <NUM>.

Data signals from the pressure meters <NUM>, <NUM> of the sample-loading system <NUM> are received through RS-<NUM>.

The fast infrared detector <NUM> is connected to a small amplifier <NUM> and an oscilloscope <NUM> that can be used to read the amplitude and frequency of the beat signal that is used to tune the lasers <NUM>, <NUM>.

A temperature controller <NUM> for the thermal desorption tube heater <NUM> is controlled via RS-<NUM> by the control module <NUM>. The tube heater <NUM> includes a temperature sensor and a piece of aluminum that has heating tape wrapped around it. The heating tape and the temperature sensor are both connected to the temperature controller <NUM> which is a PID (proportional integral derivative) controller. The PID controller sets and reads back the temperature via RS-<NUM> to the main control module <NUM>.

A relay board <NUM> is connected to the control module <NUM> and is used to turn on and off all of the solenoid valves <NUM> and the vacuum pump <NUM>.

A three-channel piezo driver <NUM> drives piezo actuators <NUM> that actuate the micrometers 96b to adjust the length of the ring-down cavity <NUM>. Each channel has two components: communications to the piezo driver through RS-<NUM>, and analog input from the DAQ card <NUM>. In other embodiments, two or more piezo drivers can be employed.

Each optical modulator <NUM>, <NUM> is driven with an RF driver <NUM> that sends approximately a <NUM> signal. Changing the frequency of the RF driver <NUM> changes the Bragg angle for a given optical wavelength, or changes the optical wavelength that a given or fixed Bragg angle is attuned to. If the RF driver <NUM> is tuned to a specific frequency and set to full power, most of the working beam <NUM> (about <NUM>%) gets through. If adjusted to <NUM>%, <NUM>%, then the optical modulator <NUM>, <NUM> will attenuate. If the RF driver <NUM> is set to zero, the optical modulator <NUM>, <NUM> shuts off completely. The frequency of the RF driver <NUM> is set through a component via RS232. An analog and digital component can set the amplitude and the on/off condition of the RF driver <NUM>. In particular, the DAQ card <NUM> sends a signal via a digital output ("DO") to a timing circuit <NUM> which, in turn, generates the four necessary signals needed to enable and set the amplitude of the RF drivers. The timing circuit <NUM> is also in communication with the control module <NUM> via a digitizer <NUM>, enabling the control module <NUM> to control its operation in either a steady state condition or a ring-down triggering condition in which the timing circuit <NUM> sets the four voltages to zero, and then returns to the previous voltage level after a pre-determined amount of time. The digitizer <NUM> sends a trigger pulse to the timing circuit <NUM> to cause the optical modulators <NUM>, <NUM> to extinguish the laser light provided to the ring-down cavity <NUM> during a ring down event.

A method <NUM> of analyzing a sample using the CRDS system <NUM> of <FIG> is shown in <FIG>. Traditionally, the sample to be analyzed using CRDS is desorbed at a single temperature. In the method <NUM>, a part of a sample in a thermal desorption tube is first desorbed at a first temperature, and then at least one additional part of the sample is desorbed from the thermal desorption tube at at least one additional temperature. In some scenarios, it is desirable to separate parts of the sample for analysis with the CRDS system <NUM>. For example, acetone and ammonia can be desorbed from a thermal desorption tube at a lower temperature. As acetone and ammonia can overwhelm the spectra, obfuscating other substances in the sample, it can be desirable to desorb and analyze portions of the sample at different temperatures to isolate various substances from other substances. In other embodiments, it can be desirable to desorb the sample at the same temperature two or more times, as some constituents of the sample may desorb readily at that temperature the first time and other constituents of the sample may desorb less readily at that temperature the first time, but may desorb equally readily the second time. As the other constituents may have readily desorbed, they are less present to desorb the second time and thus the other constituents are more isolated. The set of ordered desorption temperatures thus can include a single desorption temperature or an ordered set of two or more desorption temperatures.

Referring now to <FIG>, <FIG>, and <FIG>, the method <NUM> begins with the setting of the temperature of the heater <NUM> to a first of the ordered set of desorption temperatures (<NUM>). In this particular configuration, a set of one or more temperatures at which the sample is to be desorbed from the thermal desorption tube <NUM> can be ordered. In one preferred approach, the desorption temperatures are ordered from lowest to highest. In another embodiment, the ordered set of desorption temperatures can include two desorption temperatures that are the same or similar. There can be benefit to desorbing a portion of a sample at a temperature to release readily desorbed components/compounds that is then analyzed, and then desorbing another portion of the sample at the same temperature to release less-readily desorbed components/compounds that can be analyzed with a reduced amount of the more readily desorbed components/compounds.

A first of the ordered set of desorption temperatures is selected, and the heater <NUM> is operated to heat the thermal desorption tube <NUM> to the first desorption temperature. Once the thermal desorption tube <NUM> is heated to the first desorption temperature via the heater <NUM>, the part of the sample that has been desorbed at the first temperature is then loaded into the ring-down cavity <NUM>, as previously described (<NUM>). Upon loading of the part of the sample in the ring-down cavity <NUM>, a laser beam is generated by one of the lasers <NUM>, <NUM> that is tuned to one of a set of wavelengths (<NUM>). The set of wavelengths can be selected from the wavelengths at which the lasers <NUM>, <NUM> can produce a beam in any manner as desired. The generated laser beam is directed through the first optical modulator <NUM>, reflected by the mirror <NUM>, through the second optical modulator <NUM>, and reflected by the mirror <NUM> into the ring-down chamber <NUM>. The optical modulators <NUM>, <NUM> attenuate the working beam <NUM> somewhat to modulate its intensity.

When the working beam <NUM> reaches the front cavity mirror 88a, a fraction, about <NUM>%, penetrates the front cavity mirror 88a to enter the ring-down cavity <NUM>. The majority of the working beam, about <NUM>%, is initially reflected back along the same path to the working laser <NUM> or <NUM>.

Initially, the ring-down cavity <NUM> is not illuminated. Light enters the ring-down cavity <NUM> and, as the majority of the light in the ring-down cavity <NUM> is reflected between the two cavity mirrors <NUM>, the amount, or power, of light in the ring-down cavity <NUM> starts increasing as further light is introduced from outside via the working beam <NUM>. A certain fraction of the light leaks out past the cavity mirrors <NUM>. It takes a duration of time to "fill" the ring-down cavity <NUM> with light, and this can occur when the cavity length is equal to an adjacent resonance length of the ring-down cavity <NUM> for the tuned laser. At that point, there is an equilibrium between the incoming light and the leakage.

Once this equilibrium is achieved, the laser beam directed into the ring-down cavity <NUM> is extinguished (<NUM>). The laser beam entering the ring-down cavity <NUM> can be extinguished in a number of manners. In the particular embodiment, the digitizer <NUM> sends a trigger pulse to the timing circuit <NUM> to cause the optical modulators <NUM>, <NUM> to extinguish the laser light provided to the ring-down cavity <NUM>. In other embodiments, the laser can be turned off, or detuned so that it does not resonate for the configured cavity length, etc..

The timing circuit <NUM> simultaneously directs the first and second optical modulators <NUM>, <NUM> to attenuate the light beam at or close to an attenuation limits of the optical modulators <NUM>, <NUM> to reduce an intensity of the light beam from the first optical modulator <NUM>. In the CRDS system <NUM>, by directing both optical modulators <NUM>, <NUM> to shut off simultaneously, the amount of light deflected by the first optical modulator <NUM> during the short span of time is markedly reduced by the second optical modulator <NUM> as it is shutting down.

The second optical modular <NUM> greatly increases the attenuation achieved via the first optical modulator <NUM> alone. In the currently described embodiment, if the first optical modulator <NUM> can attenuate by <NUM> dB, and the second optical modulator <NUM> can attenuate by an additional <NUM> dB, with the total attenuation achieved via the optical modulators <NUM>, <NUM> being the sum of their attenuation, or <NUM> dB. During filling of the ring-down cavity <NUM> with light, the optical modulators <NUM>, <NUM> attenuate the working beam <NUM> to modulate its intensity. In the present configuration, each of the optical modulators <NUM>, <NUM> attenuate the working beam <NUM> by <NUM> dB, for a total attenuation of 10dB. As a result, each of the optical modulators <NUM>, <NUM> can still further attenuate the working beam <NUM> by <NUM> dB for a total further attenuation of <NUM> dB during the extinguishing of the working beam <NUM>. In a conventional setup, one optical modulator would have to attenuate a working beam by <NUM> dB, leaving <NUM> dB of further attenuation available for extinguishing the working beam. As will be understood, the working beam <NUM> can be extinguished much more rapidly via <NUM> dB of further attenuation via the two optical modulators <NUM>, <NUM> than with one optical modulator with <NUM> dB of further attenuation. As a result, the amount of additional light introduced into the ring-down cavity <NUM> after the optical modulators <NUM>, <NUM> have been directed to shut down is a small fraction of the light further introduced by a single optical modulator setup in a conventional CRDS system. By extinguishing the working beam <NUM> more quickly, the measured decay of light in the ring-down cavity <NUM> is less affected by the additional light during the ramp-down times of the optical modulators <NUM>, <NUM>, thus granting higher precision when matching the observed decay times against known decay times.

Extinguishing of the laser light provided to the ring-down cavity <NUM> commences a ring-down event. The resonating laser light provided to the ring-down cavity <NUM> can be extinguished in other manners in alternative embodiments, such as, for example, by detuning the laser. By initiating the triggering of a ring-down event via a threshold, the ring-down event can be timed to occur during the peak while the ring-down cavity <NUM> is in resonance with the laser light, and not on one side of the peak. Further, as the bandwidth of the resonance is about <NUM> millivolts, the resolution of the piezo driver <NUM> is insufficiently granular to properly track the peak.

During the ring-down event, the control module <NUM> registers light intensity decay data reported by the liquid nitrogen-cooled detector <NUM> exiting from the back end of the ring-down cavity <NUM> (<NUM>). The ring-down event lasts about ten microseconds in the present configuration, but can last a longer or shorter time in other embodiments. The light decay time is about two microseconds.

It is then determined if the ring-down event is to be repeated (<NUM>). In this embodiment, the CRDS system <NUM> is configured to collected light intensity decay data for <NUM> ring-down events.

About <NUM> microseconds after when the ring-down event is triggered, the timing circuit <NUM> directs the optical modulators <NUM>, <NUM> to recommence allowing the working beam <NUM> through to the ring-down cavity <NUM>. If the light intensity decay data from <NUM> ring-down events has been captured, the control module <NUM> stops operation of the piezo driver <NUM>, and then determines the decay rate from the ring-down event data, which refers to the light intensity decay data and may be used interchangeably herein. If, instead, it is determined at <NUM> that further light intensity decay data is to be collected, the control module <NUM> continues to direct the piezo driver <NUM> to actuate the rear cavity mirror 88b. As the aggregate voltage attains a maximum or minimum, it commences to proceed in an opposite direction. That is, if the aggregate voltage AV was increasing prior to achieving the maximum voltage in its range, the aggregate voltage AV then decreases back towards the voltage corresponding with the resonance length RL. Alternatively, if the aggregate voltage AV was decreasing prior to achieving the minimum voltage in its range, the aggregate voltage AV then increases back towards the voltage corresponding with the resonance length RL. In this manner, ring-down events are triggered in both directions.

The light intensity decay data is collected as quickly as possible, as various outputs can drift. For example, the piezo actuators <NUM> can have a settling time referred to as piezo creep.

In other embodiments, any number of ring-down events can be employed at each wavelength and desorption temperature. In one embodiment, the ring-down events at a wavelength and desorption temperature can be performed until a desired level of light intensity decay data has been collected. The light intensity decay data collected thus far can be quickly analyzed as it is collected to determine if it appears to be valid. After a desired number of ring-down events for which valid light intensity decay data is collected, the system can deem that sufficient data has been collected at that wavelength and desorption temperature. This can in many scenarios shorten the time required to perform the analysis.

Upon collecting the light intensity decay data for the selected wavelength, the light intensity decay data for the particular sample, desorption temperature, and wavelength may be processed by the control module <NUM>, such as by determining a decay rate for each ring-down event and averaging these values. Other approaches can be employed to process the ring-down event data.

It is then determined if there are other wavelengths in the set at which the laser is to be generated (<NUM>). If there are other wavelengths to be generated, the method <NUM> returns to <NUM>, at which the laser <NUM>, <NUM> is tuned to generate a laser beam of the newly selected wavelength.

The process is repeated for lights of other wavelengths to generate an absorption spectrum for the sample at the particular desorption temperature. The light intensity data from the liquid nitrogen-cooled detector <NUM> provides or is readily converted to, in effect, light intensity decay data that indicates how quickly the light of the particular wavelength was absorbed by the part of the sample that was loaded into the ring-down cavity <NUM>.

For example, the light generated by the CO<NUM> laser <NUM> provides absorption coefficients for a range of wavelengths. Similarly, absorption coefficients can be generated for a range of wavelengths for the light from the carbon-<NUM> O2 laser <NUM>. In this manner, an absorption spectrum can be developed for the sample.

Once an absorption spectrum across the set of wavelengths is generated for the part of the sample desorbed at the first temperature, the part of the sample is unloaded from the ring-down cavity (<NUM>). It is determined if there are other temperatures in the ordered set to which the thermal desorption tube <NUM> is to be heated to desorb other parts of the sample for analysis in the ring-down cavity <NUM> (<NUM>). If it is determined that there are other temperatures at which a part of the sample is to be desorbed, the heater is set to the next desorption temperature at <NUM>. In the present embodiment, a next desorption temperature to which the thermal desorption tube <NUM> is heated is higher than the previous desorption temperatures(s) to which the thermal desorption tube <NUM> was heated. If the ordered set of desorption temperatures includes a single desorption temperature, the method <NUM> does not return to <NUM>.

As previously noted, desorption of the sample contained in the thermal desorption tube <NUM> at another temperature that is higher than other temperatures at which the thermal desorption tube <NUM> was previously desorbed can yield a different subset of the compounds / substance in the sample.

Once the light intensity decay data has been collected for each of the desorption temperatures, the CRDS system <NUM> analyzes the light intensity decay data for the set of wavelengths and the set of desorption temperatures to determine a probability that the patient from which the sample was drawn has a particular physiological condition or a degree of a physiological condition (<NUM>). The probability is determined at least indirectly using a dataset of light intensity decay data for previously analyzed samples for which the presence or absence of the physiological condition or a degree of the physiological condition (i.e., lung cancer in the exemplary embodiment) has been identified. The determination of the probability can use a predictive model that is at least partially based on the dataset of light intensity decay data for previously analyzed samples.

The CRDS system <NUM> can determine the probability that the subject from which the analyzed sample was drawn has one of a set of discrete degrees of the physiological condition, and then present the most likely degree of the physiological condition or the entire set of probabilities. Further, the CRDS system <NUM> can also provide a confidence level for each of the results.

The light intensity decay data collected at each desorption temperature can be analyzed at least indirectly using the dataset of light intensity decay data for the previously analyzed samples that is segregated by the same or similar desorption temperatures. Preferably, the dataset of light intensity decay data for the previously analyzed samples was collected using the same or a similar sequence of temperatures for desorbing parts of the sample. In an alternative embodiment, the light intensity decay data from two or more desorption temperatures from the sample can be combined together, and analyzed using a predictive model generated at least partially based on light intensity decay data for previously analyzed samples that is treated in the same or similar manner (i.e., the light intensity decay data for corresponding desorption temperatures is aggregated). A predictive model can be generated from the dataset of light intensity decay data for the previously analyzed samples. One preferred approach is by using supervised machine learning.

The dataset of light intensity decay data for previously analyzed samples represents spectra for entire parts of the previously collected samples and not any one particular volatile organic compound. By adopting this more wholistic approach to analyzing a sample, there is less reliance on the identification of contentious volatile organic compounds to predict the probability that the sample currently being analyzed comes from a subject having the physiological condition. The subject can be a person or another animal or organism.

The predictive model is generated using machine learning techniques at least partially by using the dataset of light intensity decay data as a training set.

It can be challenging to obtain a sufficiently large sample dataset for predicting the presence or absence of certain physiological conditions. Some pre-processing steps can be beneficial in such circumstances. This can be particularly true for certain physiological conditions.

In order to manage missing values in the spectrum, interpolation techniques, such as spline interpolation, using neighboring absorbance values in the spectrum can be employed. If the available wavelengths are not evenly spaced, average values from comparable subjects identified by a k-nearest neighbor search can be used, as can a VOC regression approach to approximate missing values.

Where high variability is observed in the previously collected data, it can be attributable to natural VOC variations and other confounding variables. Baseline correction can be used to eliminate any unwanted trends, such as via the use of common spectroscopy detrending techniques (e.g., linear, quadratic, and Savitzky-Golay detrending). Spectral subtraction techniques can also be employed for highly concentrated VOCs like acetone and ammonia, which are common to all subjects and may be masking small, important details in the spectra.

Similarly, common normalization techniques can be used to improve sample consistency. In addition to those based on individual spectra (min-max, peak, standard normal variate normalization for example), methods that normalize across all spectra (such as multiplicative scatter correction) can be employed.

A comprehensive analysis of the spectra and clinical factors is used to identify unobvious relationships and confounders in the dataset of light intensity decay data for previously analyzed samples to improve data interpretation and identify subgroups that are incorporated into the predictive model. There are a number of confounding factors in breath VOC analysis that include age, sex, smoking, alcohol consumption, medication use, and other diseases. Unsupervised clustering techniques, along with supervised predictive models that classify spectra according to possible confounders, are used to assess these factors. Similarly, spectral data for different subgroups can be used to train separate models for lung cancer detection.

Features such as spectral derivative-based features, projected features, and wavelet transform-based features are being employed for feature extraction. Derivative-based features are particularly useful because they apply some inherent baseline and scale correction for inter-individual variability. Barcode features and a one-dimensional form of the local binary patterns (1D-LBP) can also be used. Further, features derived from a time-series of desorptions of samples at different temperature sequences can also be employed.

The various pre-processing and feature extraction methods can be combined, along with the information found in the confounding factor and subgroup analysis, to create the final classification system. To reduce system dimensionality and remove unhelpful, redundant features, a few feature selection techniques may be used. Statistics-based filter methods like minimum redundancy maximum relevance ("mRMR") selection can be employed, as well as classification-based wrapper methods, like sequential feature selection ("SFS") and genetic algorithm ("GA") selection. Simple support vector machine ("SVM"), discriminant analysis (LDA and QDA), and KNN classifiers can be employed to evaluate features in the wrapper selection methods and to build and validate the numerous classification models.

Various alternative approaches and methods can be employed for generating the predictive model.

<FIG> shows a method <NUM> for generating a predictive model. In this approach, a set of desorption temperature sequences are identified for exploration. A sequence of desorption temperatures is an ordered set of temperatures to which the thermal description tube is heated to desorb parts of the sample contained therein. Desorption of the sample using a particular sequence of temperatures can enable different selective parts of the sample to be desorbed and analyzed separately, which can enable different aspects of the sample to be more readily identified. Certain features of a sample may be more readily apparent from the light intensity decay data captured for certain desorption temperature sequences. For example, if a first component/compound is desorbable from the thermal desorption tube <NUM> at a certain temperature and confounds a second component/compound that is desorbable at a slightly elevated temperature, features of the light intensity decay data for a sample may become more apparent using a desorption temperature sequence that has a desorption temperature equal to that of the first component/compound, and then a subsequent desorption temperature equal to or above that of the second component/compound. These relationships between the desorption temperature sequences and the features exposed may not in some cases be readily apparent. As a result, the particular sequence which yields the best correlation to the presence or absence may not be readily apparent without exploration. In another aspect, if the light intensity decay data registered at two desorption temperature sequences yield substantially equal correlations to the subset(s) of samples drawn from subjects having the physiological condition or a degree of the physiological condition, it may be desirable to select the shorter desorption temperature sequence, for example.

While the general method will be described with reference to the CRDS system <NUM>, it will be understood that the approach may be conducted using a plurality of local or distributed CRDS systems and other computers using a common set of parameters and standard practices.

The method <NUM> commenced with the selection of sample (<NUM>). The sample is selected from a set of samples from subjects that have been identified as one of having a physiological condition and not having the physiological condition. Then a desorption temperature sequence is selected from a set of desorption temperature sequences (<NUM>). The set of desorption temperature sequences can be chosen based on scientific evidence, randomly, etc. The desorption temperature of the heater <NUM> is set to the next desorption temperature in the sequence (<NUM>). If the sequence is yet unprocessed, the first desorption temperature in the sequence is selected.

Next, a part of the sample is then desorbed and loaded (<NUM>). The heater <NUM> is heated to the selected desorption temperature from the sequence and a part of the sample is desorbed. the sample-loading system <NUM> loads the desorbed part of the sample into the ring-down cavity <NUM>.

The control module <NUM> then operates one of the lasers <NUM>, <NUM> to generate a laser beam of the selected wavelength. The laser beam is directed into the ring-down cavity <NUM> to "fill" the ring-down cavity <NUM> with light.

Once the control module <NUM> determines that there is sufficient light in the ring-down cavity <NUM>, the control module <NUM> directs the optical modulators to extinguish the laser beam that is directed into the ring-down cavity <NUM> (<NUM>).

The liquid nitrogen-cooled detector <NUM> registers the light intensity exiting the ring-down cavity <NUM> via the rear cavity mirror 88b (<NUM>). Light intensity decay data corresponds to the detected intensity of the light exiting the ring-down cavity <NUM> over time, and is transmitted to the control module <NUM>. Upon completion of the ring-down, the control module <NUM> determines whether to repeat the ring-down event (<NUM>). The ring-down event may be repeated many times to reduce the effect of abnormalities. If another ring-down event is to be performed at the selected wavelength, the method <NUM> returns to <NUM>, wherein a laser beam at the selected wavelength is generated. It is then determined if there are other wavelengths in the set to be used (<NUM>). It there are other wavelengths, the method <NUM> returns to <NUM>, at which a laser beam is generated at the next selected wavelength. If, instead, it is determined that there are no other wavelengths in the set, it is determined if there is another desorption temperature in the sequence (<NUM>). If there is at least another desorption temperature in the sequence, the next desorption temperature in the sequence is selected and the heater <NUM> is heated to that temperature to desorb another part of the sample at <NUM>.

If, instead, it is determined that there are no other desorption temperatures in the sequence at <NUM>, it is then determined whether there are other desorption temperature sequences to be explored (<NUM>). If there are other unexplored desorption temperature sequences, a next desorption temperature sequence is selected at <NUM>. When a new desorption temperature sequence is selected, a new thermal desorption tube from the same subject is used, as the sample in the previously used thermal desorption tube <NUM> has been at least partially desorbed.

Once all of the desorption temperature sequences have been explored, it is determined if there are any other samples in the set that have yet to be analyzed (<NUM>). If there still yet unanalyzed samples in the set, another sample is selected at <NUM> for analysis.

If, instead, it is determined that all of the samples have been analyzed at <NUM>, the correspondence between the light intensity decay data and the identification of the subjects from which the samples are drawn as having the physiological condition or degrees of the physiological condition for each desorption temperature sequence is then determined (<NUM>). The correspondence between the light intensity decay data and the identification of the samples as having the physiological condition or a degree of the physiological condition is stronger when there is a set of features that are significantly more prevalent in samples from subjects identified as having the physiological condition or a degree of the physiological condition. That is, if there is a particular set of features that each occurs in <NUM> percent of subjects having a physiological condition and in <NUM> percent of subjects not having the physiological condition for a particular sequence of desorption temperatures, then the light intensity decay data for the sequence of desorption temperatures may have a relatively good correlation to the presence or absence of the physiological condition in the subjects from which the samples are obtained. While this is an example, any pattern between the light intensity decay data and the presence of the physiological condition or a degree of the physiological condition can indicate the presence of a correlation between the light intensity decay data and the presence of the physiological condition or the degree of the physiological condition.

A desorption temperature sequence is then selected based on the correspondence between the light intensity decay data and the identification of the subject from which the samples were drawn as having the physiological condition or a degree of the physiological condition for each desorption temperature sequence (<NUM>). The desorption temperature sequence may be selected entirely based on the measured correlation, or on the correlation in combination with other factors. Other factors can determine the selection of the sequence of desorption temperatures, such as the number of desorption temperatures in the sequence, thereby determining the amount of time to perform the analysis.

A predictive model is then generated using the selected desorption temperature sequence at least partially selected based on the correlations (<NUM>).

Where a sequence of temperatures is used to desorb a sample from a thermal desorption tube, it can be unadvantageous to analyze parts of samples that are desorbed at certain temperatures. The desorption may be performed at certain temperatures to remove substances that are less of interest than those desorbed at other temperatures.

<FIG> shows a method <NUM> of analyzing a sample via CRDS. In the method <NUM>, a part of the sample is desorbed at a first temperature and is, in effect, discarded as it may have little correlation to the presence or absence of a physiological condition in a patient. A second part of the sample is desorbed at a second temperature. The second part of the sample is deemed to have a relatively high correlation to the presence of the physiological condition or a degree of the physiological condition and is thus analyzed via CRDS.

The method <NUM> commences with the setting of the temperature of the heater <NUM> at a first desorption temperature by the control module <NUM> (<NUM>). Heating of the heater <NUM> to the first desorption temperature causes the thermal desorption tube <NUM> to be heated and a first part of the sample to be desorbed. The sample-loading system <NUM> is then directed by the control module <NUM> to expel the first part of the sample without performing CRDS on the first part. The first part of the sample may be expelled to the surrounding atmosphere, to a collection cannister, or may be removed from the path between the thermal desorption tube <NUM> and the ring-down cavity <NUM> via any other suitable approach. In a presently preferred embodiment, the first sample is expelled through the mass flow controller <NUM> by closing valves 124b and 124d, and by opening valves 124a, 124c, <NUM>, 124f, and <NUM>, much in the same manner that carbon dioxide and water are expelled from the thermal desorption tube <NUM>.

After expelling the first part of the sample, the heater is heated to a second desorption temperature (<NUM>). The second desorption temperature is generally higher than the first temperature and, as a result, causes different substances to be desorbed from the thermal desorption tube <NUM>. In other embodiments, the second desorption temperature is the same as or lower than the first desorption temperature. While a good portion of some components/compounds may have already been desorbed at the previous desorption temperature, virtually all of other confounding substances may have been desorbed as well, thus facilitating the isolation of these components/compounds. The second part of the sample is then loaded into the ring-down cavity <NUM> for analysis, as described above (<NUM>). Next, the control module <NUM> operates one of the lasers <NUM>, <NUM> to generate a laser beam at a selected wavelength (<NUM>). The laser beam is directed into the ring-down cavity <NUM> to fill the cavity with light. Once the ring-down cavity <NUM> is filled, the laser beam is extinguished (<NUM>). The liquid nitrogen-cooled detector <NUM> then registers the intensity of the light exiting the ring-down cavity <NUM> via the rear cavity mirror 88b (<NUM>). The light exiting the ring-down cavity <NUM> represents light intensity decay data that is registered by the liquid nitrogen-cooled detector <NUM> and transmitted to the control module <NUM>.

Once the ring-down event is complete, it is determined whether to repeat the ring-down event again (<NUM>). As noted above, it can be desirable to repeat the ring-down event a number of times and then determine one or more collective metrics by determining a decay rate for the light intensity decay data for each ring-down and then averaging the decay rates to minimize the effect of aberrations. If another ring-down event is to be repeated, a laser beam is generated at the selected wavelength at <NUM>. If, instead, no more ring-down events are to be performed, it is determined whether there are other wavelengths in the set of wavelengths to be analyzed (<NUM>). If it is determined that there are other wavelengths to be analyzed, a laser beam of a next one of the wavelengths is generated at <NUM>. If, instead, there are no more wavelengths to generate a laser beam at for performing CRDS, the light intensity decay data collected at <NUM> is then analyzed (<NUM>), after which the method <NUM> ends. The collected light intensity decay data is then analyzed.

While the at least one processor that analyzes the light intensity decay data and generates a predictive model is shown and described as being fully integrated with the other elements of the CRDS system, in other embodiments, one or more of the at least one processor can be provided in a separate computer system that has storage and performs some or all of the functionality of the control module in the above-described and illustrated embodiment.

<FIG> shows a system <NUM> for analyzing a sample using CRDS in another embodiment. The system <NUM> includes a CRDS system <NUM> similar to that of <FIG>. The CRDS system <NUM> has a control module <NUM> that has at least one processor for controlling operation of the various elements of the CRDS system <NUM>. The control module <NUM> is in communication with a computer system <NUM> over a data communications network <NUM>. The computer system <NUM> can be any single computer or multiple computers coupled together locally and/or remotely to provide the described functionality. The data communications network <NUM> can be any suitable medium enabling the control module <NUM> and the computer system <NUM> to communicate at least the light intensity decay data and any associated parameters associated therewith, such as wavelengths, the temperature at which the at least part of the sample was desorbed, as well as any other subject-specific data, such as the above-noted confounding factors, a subject identifier, time and location information for when and where the sample was analyzed, etc..

<FIG> shows a number of physical and logical components of the computer system <NUM>, including a central processing unit ("CPU") <NUM>, random access memory ("RAM") <NUM>, an input/output ("I/O") interface <NUM>, a communications interface <NUM>, non-volatile storage <NUM>, and a local bus <NUM> enabling the CPU <NUM> to communicate with the other components. The CPU <NUM> can include one or more processors and executes at least an operating system, as well as a spectra evaluation application. The RAM <NUM> provides relatively responsive volatile storage to the CPU <NUM>. The I/O interface <NUM> allows for input to be received from one or more devices, such as a keyboard, a mouse, etc., and outputs information to output devices, such as a display and/or speakers. The communications interface <NUM> permits communication with other computing devices like the control module <NUM> over computer networks such as the data communications network <NUM>. The non-volatile storage <NUM> stores the operating system and programs, including computer-executable instructions for implementing the spectra evaluation application. During operation of the computer system <NUM>, the operating system, the programs and the data may be retrieved from the non-volatile storage <NUM> and placed in RAM <NUM> to facilitate execution.

While, in the above-described embodiment, the light sources are two lasers that produce light in the mid-infrared range, it will be appreciated that other light sources can be employed. For example, a laser producing light in the visible spectrum or a near-infrared laser can be employed. Further, in some scenarios, the CRDS system can include only one laser, or three or more lasers, to generate the working beam.

Electro-optic modulators can be used in place of acousto-optic modulators.

The acousto-optic modulators can be configured so that the frequency of the working beam is shifted up or down. As long as the net frequency shift effected by the acousto-optic modulators shifts the frequency of the working beam significantly away from the frequency of the working beam being generated by the laser(s) so that the reflected light is outside of the bandwidth of the laser light being generated, the amount of interference between the reflected light and the generated working beam can be minimized.

In other embodiments, more than two optical modulators can be employed in a CRDS system to provide further extinguishing capacity to more quickly extinguish the working beam at the commencement of a ring-down event. Further, in further embodiments, a single optical modulator can be employed.

One or more focusing lenses can be employed in other embodiments, and translated to enable repositioning of the lenses to allow mode-matching of each wavelength of the lasers.

Other types of events can be triggered as the cavity length is proximal to the resonance length of the cavity for the particular selected wavelength.

Analysis of the samples can be performed at pressure levels other than one atmosphere in other embodiments. The breadth of the absorption spectrum may change accordingly.

Although specific advantages have been enumerated above, various embodiments may include some, none, or all of the enumerated advantages.

Claim 1:
A method (<NUM>) for analyzing a sample using cavity ring-down spectroscopy, comprising
desorbing a first part of a sample from a thermal desorption tube (<NUM>) heated to a first desorption temperature (<NUM>) to load (<NUM>) the first part of the sample into a ring-down cavity (<NUM>);
for each of a first set of wavelengths:
generating, via at least one laser (<NUM>, <NUM>), a laser beam at the wavelength (<NUM>) directed into the ring-down cavity (<NUM>);
extinguishing the laser beam (<NUM>) entering the ring-down cavity (<NUM>); and
registering light intensity decay data (<NUM>) for light exiting the ring-down cavity (<NUM>) via a light intensity sensor system (<NUM>);
loading a second part of the sample (<NUM>) desorbed from the thermal desorption tube (<NUM>) heated to a second desorption temperature (<NUM>);
for each of a second set of wavelengths:
generating, via the at least one laser (<NUM>, <NUM>), a laser beam at the wavelength (<NUM>)
directed into the ring-down cavity (<NUM>);
extinguishing the laser beam (<NUM>) entering the ring-down cavity (<NUM>); and
registering light intensity decay data (<NUM>) for light exiting the ring-down cavity (<NUM>) via a light intensity sensor system (<NUM>). determining (<NUM>), via at least one processor (<NUM>, <NUM>), a probability from the light intensity decay data using a predictive model that is at least partially based on the dataset of light intensity decay data for the first set of wavelengths and the second set of wavelengths that a subject from which the sample was received has a physiological condition or a degree of a physiological condition at least indirectly using a dataset of light intensity decay data for previously analyzed samples for which the presence or absence of the physiological condition or the degree of the physiological condition has been identified.