Infrared Detectors in Medical Applications

VIGO System infrared detectors and detection modules at MWIR and LWIR spectral ranges can be across an extensive range of biological, biotechnological, and medical applications including human breath analysis, non-invasive blood tests, dentistry, pharmacy and protein composition analysis. Some of them are detailed below.

1. Human Breath Analysis

Breath analysis has become a key field of medical research. There are more than 3000 substances contained in exhaled breath. The concentration of many depends on an individual’s health status.

These substances are known as biomarkers and may be used to diagnose various diseases or pathological processes in human body.

Breath analysis is an excellent screening test because it is rapid, non-invasive, and painless. However, because of low concentrations of biomarkers in human breath, the use of high resolution measurement techniques and sensitive detectors is necessary.

Infrared detectors are used extensively in the development of breath analysis equipment. Compared to other techniques, those based on mid-IR laser absorption spectroscopy for trace gas sensing offer faster response times

Table 1. Breath biomarkers detected by IR detectors. Source: VIGO System

Breath biomarker Health condition Selected absorption line, µm Measurement Technique
CH3COH
acetaldehyde
• after alcohol consumption
• lung cancer
5.79 and 5.67 TDLAS
C2H6
ethane
• oxidative stress
• Alzheimer’s disease
3.33 TDLAS
C3H6O
acetone
• type 1 diabetes 8.2 QCL-based infrared spectrometer
CH4
methane
• oxidative stress
• cancer
3.3916 and 3.3920 HWG-TLAS
NO nitrogen monoxide • asthma
• chronic bronchitis
• allergic rhinitis
5.26296 ICOS
NH3
ammonia
• renal diseases
• asthma
10.341 pulsed QCL-based spectrometer
CH2O
formaldehyde
• lung and breast cancer 3.530 ICOS
HCN
hydrogen cyanide
• cystic fibrosis 1.538 ICOS
CH3SH
methanethiol
• halitosis
• hepatic cirrhosis
• encephalopathy
• coma
3.3565 WMS/TDLAS
C2H4
ethylene
• lipid peroxidation
• ultraviolet radiation damage of skin
10.309 pulsed QCL-based spectrometer
OCS
carbonyl sulfide
• hepatic failure
• cystic fibrosis
• rejected lung transplant
4.86 TDLAS

 

Note: TDLAS – Tunable Diode Laser Absorption Spectroscopy; HWG-TLAS – Hollow WaveGuide-Tunable Laser Absorption Spectroscopy; ICOS – Integrated Cavity Output Spectroscopy; WMS-TDLAS – Wavelength Modulation Spectroscopy-Tunable Diode Laser Absorption Spectroscopy

A. Project Sensormed

The Optoelectronic sensor system was developed using laser absorption spectroscopy with a VIGO detection module to identify biomarkers of certain diseases: asthma, angina, stomach diseases, and elevated bilirubin levels in the blood, including Gilbert’s syndrome, Dubin-Johnson syndrome, Rotor syndrome, Crigler-Najjar syndrome.

This sensor system is comprised of five functional blocks:

  • sampling system – breath collection
  • conditioning system – gas sample preparation
  • CEAS (Cavity Enhanced Absorption Spectroscopy) sensor – detection
  • dual spectral MUPASS (MUltiPass Absorption Spectroscopy System) sensor – detection
  • signal processing system – data analysis

Sensormed optoelectronic breath analyzer.

Figure 1. Sensormed optoelectronic breath analyzer. Image Credit: VIGO System

The patient’s exhaled breath is collected by the sampling system collects. In line with the ATS / ERS standards, it can function in ‘on-line’ or ‘off-line’ mode.

In the conditioning system preparation of the gas, a sample is conducted for additional processing: eliminating moisture, generating a negative pressure and providing appropriate airflow velocity.

CEAS sensor detects NO (nitric oxide): It uses QCL laser (λ= 5.26 μm) and VIGO highly sensitive IR detection module with detection limit of approx. 30 ppb. To identify CH4 (methane) and CO (carbon monoxide), a two-spectral MUPASS sensor with one multi-pass cell is utilized.

The limit of detection of methane (λ= 2.2536 μm) was 100 ppb, and for carbon monoxide (λ= 2.336 μm) it was 400 ppb. The signals from the sensors are recorded by the interface block and transmitted to the signal processing system (computer & software) where the results obtained are input, visualized and analyzed.

B. Liver Function Capacity Testing

The appropriate evaluation of liver function capacity is crucial for liver surgery, liver transplantation, oncology and hepatology. The methacetin breath test characterizes a safe and accurate diagnostic tool in the analysis of hepatic functional mass in chronic liver disease patients.

The dynamic liver function test is predicated on the metabolism of 13C-methacetin. Methacetin is metabolized by the liver-specific hepatic cytochrome P450 1A2 system to acetaminophen and 13C-formaldehyde, which is then transformed into a number of fast enzymatic steps to 13CO2, which are subsequently transported via the bloodstream to the lung and then exhaled.

Individual liver function can be evaluated by the continual measurement of 13CO2 / 12CO2 ratio.

Principle of <sup>13</sup>C-methacetin breath test.

Figure 2. Principle of 13C-methacetin breath test. Image Credit: VIGO System

C. The 13C Urea Breath Test in the Diagnosis of Helicobacter Pylori Infection

The urea breath test is one of the most crucial non-invasive methods for identifying Helicobacter pylori infection. It is predicated on Helicobacter pylori’s capability to convert urea to carbon dioxide and ammonia. Patients ingest urea labelled with a non-radioactive carbon-13.

Within 10 to 30 minutes, the presence of isotope-labelled carbon dioxide 13CO2 in exhaled breath determines that the urea was split. This signifies the presence of urease in the stomach – the enzyme that Helicobacter pylori use to metabolize, and hence that Helicobacter pylori bacteria are present.

Principle of <sup>13</sup>C urea breath test.

Figure 3. Principle of 13C urea breath test. Image Credit: VIGO System

2. Non-Invasive In-Vivo Glucose Sensing

A needle-free glucose-sensing device allows people with diabetes to measure their blood sugar levels non-invasively. This could considerably improve the quality of life of diabetes patients. Additionally, these devices also enable healthy people to monitor and manage their blood glucose levels to sustain a healthy and active life.

The mid-IR region features strong vibrational resonances for many molecules, including glucose. Compared to the near-IR range, glucose absorption features in mid-IR are much easier to distinguish from other competing absorbers.

The main challenge when using mid-IR radiation for in vivo glucose sensing is that the penetration depth in skin is limited due to high water absorption.

Principle of operation mid-IR non-invasive glugose measurements in skin using QCL spectroscopy.

Figure 4. Principle of operation mid-IR non-invasive glugose measurements in skin using QCL spectroscopy. Image Credit: VIGO System

Radiation from a pulsed QC laser, with a tuning range between 8 – 10 μm, is concentrated on human skin. The light is then absorbed by glucose molecules and back-scattered off the dermis layer of the human skin.

Stored in a miniaturized integrating sphere, the divergent light exiting the skin is detected by VIGO TE cooled LWIR detector.

3. Dentistry

A. Early Detection of Tooth Decay

The conventional methods for decay, A.on and radiography, are impractical for detecting early caries lesions.

If dental caries are diagnosed early, before a considerable amount of the tooth is destroyed, remineralization therapy can avoid tooth decay and stabilize or reverse carious lesions. This can eliminate the need for invasive treatment.

Infrared detector applied to early detection of tooth decay.

Figure 5. Infrared detector applied to early detection of tooth decay. Image Credit: VIGO System

The system measures the level of glow (luminescence) and heat (photothermal radiometry) the tooth releases when low power pulsed laser light is shone onto the tooth.

Laser radiation reacts differently when interacting with decayed teeth and healthy teeth. It is possible to detect lesions as small as 50 μm and up to 5 mm below the tooth surface. IR laser radiation hitting the tooth enamel and dentin is transformed into heat and increases the temperature of the tooth by about 1oC.

This minimal increase in temperature should have little effect on the health or integrity of the dental pulp or nerve of the tooth. By modifying the cycling frequency of the laser pulse, it is possible to probe varying depths inside enamel or dentin.

VIGO MWIR infrared detector facilitates the capture of the thermal radiation emitted and measures the heat travel distance to provide information relative to the deeper regions of the tooth. Another part of laser energy is transformed to visible luminescence, which can be analyzed by a simple photodetector.

B. Anesthesia-Free CO2 Laser Dental Surgery

Laser dentistry uses precisely focused laser light sources to treat a variety of dental conditions. It provides a cost-effective, more efficient, and comfortable treatment option for dental procedures involving soft or hard tissue in comparison to drills and other non-laser tools.

Soft tissue refers to the gums, hard tissue to the teeth. The hard tissue CO2 laser can pass through tooth structure as the laser radiation is absorbed by the combination of water and a specific mineral present in teeth.

It is utilized to shape teeth and prepare teeth for composite bonding, the reparation of dental fillings that are worn down, and to take away some tooth structure.

The laser facilitates cavity preparations and the removal of carious tooth structure in a high number of cases without the need for local anesthesia. Surgical lasers must meet radiation safety performance standards. VIGO LWIR detectors facilitate precise control and safe operation of dental lasers.

If you require safe and RoHS compliant infrared detection systems dedicated to specific medical applications, contact VIGO System today.

This information has been sourced, reviewed and adapted from materials provided by VIGO System.

For more information on this source, please visit VIGO System.

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