thermal imaging

see also:

• dermatology
• Wood's lamp - UV light for dermatologic assessment

• thermal imaging technology has rapidly developed and has now become very affordable
• they are used in many industries to detect hot spots such as in electrical or electronic circuit components
• during Covid-19 pandemic they were used at airports to detect travellers with possible fevers as they walk past
• this page related to their potential clinical utility in the ED as more sensitive tools than clinician's hands and eyes for detecting various conditions such as “subclinical” inflammation or cutaneous ischaemia such as in Raynaud's disease, peripheral vascular disease (PVD or PAD) and perhaps differentiating chilblains on dorsum of finger joints from acute arthritis

• faces are unrecognizable
• it cannot see through clothing and even glass windows or clear plastic sheets become opaque mirrors and are not able to be seen through

• unlike a Wood's lamp - UV light for dermatologic assessment or Xrays, it does not emit any potentially harmful radiation
• it does not touch the patient and thus no risk of infection control issues or electricity harm
• it has similar EMF radiation as a smartphone
• for the clinician, it is safer than a smartphone as it does not emit high power RF as there is no transmissions from the device
• it does not make any clinical decisions, there is no AI built in - clinical decisions are made by the clinician - this is just a tool like a torch or basic stethoscope

• unlike most other temperature reading devices for clinical use, these do not touch the patient's skin and most images can be taken from 0.5-1m away
• can be used when touch with clinician's bare hands is not possible or is an issue (eg. high infectious risk patients, patients with open wounds, immunocompromised patients)
  • wearing gloves substantially reduces the clinician's ability to detect subtle temperature differences

• prices for suitable devices are now under $AU200
• you do not need state of the art high resolution ultra-sensitive devices such as used by hunters for night vision

• these will fit in a scrub top pocket and are easy to carry around by clinicians
• even smaller versions are available which attach to the port of a smartphone
• most are rechargeable or use the smartphone as a battery (if they attach to the smartphone)

• these are far easier to use than ophthalmoscopes, slit lamps, stethoscopes, etc
• does not need a well-lit room - indeed it can work just as well on night shift in a darkened environment so other patients do not get woken from sleep
• many have a “manual focus” setting - however, this is not usually critical for clinical use as long as it is set to about 0.5-1m
• clinician will need to develop an understanding of how to interpret the images in the clinical context but this is really the same as applying their own vision and touch interpretation only far more sensitive and easier to acquire

• this is particularly so for subtle pathology or when clinicians must wear gloves

• by providing a visual representation of the patient's skin temperatures:
  • it allows rapid real time comparison between affected and unaffected limbs or digits
  • allows much better visual assessment of extent of inflammation or ischaemia

• the images can be saved as jpgs and then uploaded into EMR either via:
  • smartphone taking a photo of the screen image
  • removing the micro SD memory card and using a memory card reader attached to a smartphone
  • using a thermal imaging device which directly attaches to the port of a smartphone

• patients are generally curious to see what it displays and the display can help explain to them the pathology which can otherwise be hard for them to understand

• these should not be used for ascertaining a patient's core temperature
• although these are reasonably accurate if set to skin thermal emissivity of around 0.95, the actual temperature is not really needed by clinicians - it is the relative temperatures of different parts of the skin that has most utility

• it only measures infrared emissions from an object which can be used to estimate skin temperature (emissivity must be set to ~0.95 for this to be reasonably accurate)
  • it CANNOT distinguish between infection vs non-infection inflammation
  • cannot detect skin temperature if it has a wound dressing or there is clothing over it
  • measured skin temperature may not be accurate but the relative skin temperatures is what is important and this works very well
  • for measuring temperature of other objects, you may need to change the emissivity setting
• cold ambient temperatures may result in normal physiologic peripheral coldness and not be Raynaud's or PVD - hence need to allow time for skin to warm up to normal office temperatures
• limited utility
  • for most of these conditions where it is potentially useful, a good clinician can detect the problem with careful examination although this requires touch with bare hands and time which may not always be possible
  • the benefit is for the more subtle cases, and, where touch with bare hands is not possible or is an issue (eg. high infectious risk patients, patients with open wounds, immunocompromised patients)
  • thermal cameras must not be relied on for early breast cancer screening or as a standalone replacement for mammograms

• if they are used to measure body temperature then that use does apparently require TGA approval - probably as a Class IIa medical device ¹⁾²⁾
• if the device is being used on human skin within a strictly non-therapeutic context — such as testing the heat dissipation of wearable consumer electronics, checking if industrial protective clothing prevents burns, or conducting basic non-clinical academic research without diagnosing subjects — it remains an industrial tool and does not require TGA listing

• Raynaud's disease and chilblains
  • in normal people at office temperatures, the finger nails tend to be warmer than the rest of the fingers, this is lost in Raynaud's, ischaemia or very cold fingers
  • fingertips or toes will be much colder than proximal areas and much so compared with normal people's hands in that ambient temperature
  • chilblains over joints will tend to be cooler than acute arthritic joints
• peripheral vascular disease (PVD or PAD)
  • could detect differences between legs in a much more sensitive manner than clinician touch or vision
  • may help to more readily identify PVD
  • may help to better delineate claudication pain caused by PVD vs spinal stenosis
• subclinical cellulitis
  • can detect the extent of the inflammatory response far better than a clinician could do
  • this can be important in those with poor circulation and immunocompromise such as diabetics with hand or foot ulcers
  • it may allow earlier antibiotic Rx and potentially reduce untreated cold sepsis in diabetics

• unfortunately it seems there are no TGA-approved compact portable devices so it seems these types of devices could only be used for academic research at present
  • it would seem such devices would probably fit the TGA checklist for approval but a manufacturer would need to submit a product to gain the TGA approval³⁾
  • ideally, a product like the FNIRSI® TDM-120P Thermal Imaging Multimeter could be manufactured to the requirements of TGA very easily (obviously in this case removing the multimeter functionality and improving water resistance to better enable infection control cleaning)
• current TGA approved devices are not suitable for clinical use within the ED:
  • they are too big and expensive and not fit for purpose
    • eg. mass fever screening thermography machines
    • eg. skin diagnostics thermography machines