Thermography is the measurement of temperature variations at the body surface. The scientific evidence suggests that thermography may only confirm the presence of a temperature difference, and that other procedures are needed to reach a specific diagnosis. Thermography may add little to what doctors already know based on history, physical examination, and other studies.
Thermography studies are non-invasive imaging techniques that are intended to measure the skin surface temperature distribution of various organs and tissues. The infrared radiation from the tissues reveals temperature variations by producing brightly colored patterns on a liquid crystal display. Interpretation of the color pattern is thought to contribute to the diagnosis of many disorders including breast cancer, Raynaud's phenomenon, digital artery vasospasm, impaired spermatogenesis in infertile men, deep vein thrombosis, reflex sympathetic dystrophy/complex regional pain syndrome, vertebral subluxation, and others.
In contrast to the skin surface thermography techniques used by some chiropractors and other providers, a newer invasive test called a temperature gradient study involves an intravenous catheter. The catheter is threaded into the coronary arteries to directly measure temperature differences on the inner artery walls. Researchers believe this information may be related to the presence of unstable coronary artery plaques and could be useful in diagnosing vulnerable patients. Madjid et al (2006) have shown that inflamed atherosclerotic plaques are hot and their surface temperature correlates with an increased number of macrophages and decreased fibrous-cap thickness. Multiple animal and human experiments have shown that temperature heterogeneity correlates with arterial inflammation in vivo. Several coronary temperature mapping catheters are currently being developed and studied. These thermography methods can be used in the future to detect vulnerable plaques, potentially to determine patients' prognosis, and to study the plaque-stabilizing effects of different medications.
A number of medical authorities have concluded that thermography has no proven medical value, including the American Medical Association, the Office of Health Technology Assessment (OHTA), and the American Academy of Neurology. Based on a study by the OHTA, the Health Care Financing Administration (now the Center for Medicare and Medicaid Services) withdrew Medicare coverage of thermography.
Devices that have been used for thermography skin temperature differential analysis include the Nervoscope, the Temp-O-Scope, and the Neurocalometer.
There is insufficient evidence for the use of thermography for detection of breast cancer. A structured evidence review of thermography for breast cancer (Kerr, 2004) reached the following conclusions: "The evidence that is currently available does not provide enough support for the role of infrared thermography for either population screening or adjuvant diagnostic testing of breast cancer. The major gaps in knowledge at this time can only be addressed by large-scale, prospective randomised trials. More robust research on the effectiveness and costs of technologically advanced infrared thermography devices for population screening and diagnostic testing of breast cancer is needed, and the conclusions of this review should be revisited in the face of additional reliable evidence".
Other reviews have also found a need for additional research on thermography. Kennedy et al (2009) noted that thermography was first introduced as a screening tool for breast cancer in mid-1950s. However, after a 1977 study found thermography to lag behind other screening tools, the medical community lost interest in this diagnostic approach. These researchers discussed each screening tool with a focus brought to thermography. They stated that no single diagnostic tool provides excellent predictability; however, a combination that incorporates thermography may boost both sensitivity as well as specificity. The authors concluded that in light of technological advances and maturation of the thermographical industry, more research is needed to confirm the potential of thermography in providing an effective non-invasive, low-risk adjunctive tool for the early detection of breast cancer.
Mammography is currently the gold standard for breast cancer screening. Thus, sensitivities, specificities, as well as positive and negative predictive values of thermography need to be compared with those of mammography in order to ascertain if thermography is equivalent or superior to mammography. Presently, there is a lack of scientific data comparing the 2 screening techniques. In addition, there are no published evidence-based practice guidelines and/or position statements that recommend thermography as the appropriate method of screening for early detection of breast cancer.
Arora et al (2008) examined the effectiveness of a non-invasive digital infrared thermal imaging (DITI) system in the detection of breast cancer. A total of 92 patients for whom a breast biopsy was recommended based on prior mammogram or ultrasound underwent DITI. Three scores were generated: (i) an overall risk score in the screening mode, (ii) a clinical score based on patient information, and (iii) assessment by artificial neural network. Sixty of 94 biopsies were malignant and 34 were benign. Digital infrared thermal imaging identified 58 of 60 malignancies, with 97 % sensitivity, 44 % specificity, and 82 % negative predictive value depending on the mode used. Compared to an overall risk score of 0, a score of 3 or greater was significantly more likely to be associated with malignancy (30 % versus 90 %, p < 0.03). The author concluded that DITI is a valuable adjunct to mammography and ultrasound, especially in women with dense breast parenchyma. Moreover, the authors reported a high negative predictive value for thermography where "the location of the lesion under question based on prior imaging was assessed to generate a positive or negative clinical assessment", i.e., where they were unblinded to the results of the prior mammography or ultrasound. The specificity was only 11 % and the negative predictive value of thermography was only 66 % in the blinded screening mode. Furthermore, the authors stated that DITI is not currently recommended or approved as a substitute for screening mammography, and correlation of findings on DITI should be made with alternative imaging techniques. They stated that further studies are needed using a representative screening population of persons who have not been selected for biopsy based upon prior imaging results.
An American Cancer Society report Mammograms and Other Breast Imaging Procedures (2010) stated that "[t]hermography is a way to measure and map the heat on the surface of the breast using a special heat-sensing camera. It is based on the idea that the temperature rises in areas with increased blood flow and metabolism, which could be a sign of a tumor. Thermography has been around for many years, and some scientists are still trying to improve the technology to use it in breast imaging. But no study has ever shown that it is an effective screening tool for finding breast cancer early. It should not be used as a substitute for mammograms. Newer versions of this test are better able to find very small temperature differences. They may prove to be more accurate than older versions, and are now being studied to find out if they might be useful in finding cancer". Thermography is listed under "newer and experimental breast imaging methods" in this report.
Additionally, the United Kingdom's NHS Cancer Screening Programmes (2010) stated that "thermography is not a replacement for mammography. It is a relatively new test and isn't reliable enough to use either to diagnose or screen for cancer. Mammography is still the best test and is used as a world wide standard for breast screening in women over 50".
The Food and Drug Administration (FDA, 2011) stated that breast thermography should not be used instead of mammography, noting that thermography has not been approved as a stand-alone tool for breast cancer screening or diagnosis. Telethermographic devices produce infrared images and do not require exposure to radiation or breast compression, which some healthcare providers claim make them superior to mammographic devices. However, the FDA stated that "there is simply no evidence" that breast thermography can take the place of mammography. The agency has sent warning letters to manufacturers and practitioners who have made misleading claims about breast thermography use.
Currently, there is insufficient evidence to support the use of thermography for the diagnosis of complex regional pain syndrome (CRPS). The use of thermography in the diagnosis of CRPS type 1 (CRPS1) is based on the presence of temperature asymmetries between the involved area of the extremity and the corresponding area of the uninvolved extremity. However, the interpretation of thermographical images is subjective and not validated for routine use. Huygen et al (2004) developed a sensitive, specific and reproducible arithmetical model as the result of computer-assisted infra-red thermography in patients with early stage CRPS1 in one hand. Eighteen patients with CRPS1 on one hand and 13 healthy volunteers were included in the study. The severity of the disease was determined by means of pain questionnaires [visual analogue scale (VAS) pain and McGill Pain Questionnaire], measurements of mobility (active range of motion) and edema volume. Asymmetry between the involved and the uninvolved extremities was calculated by means of the asymmetry factor, the ratio and the average temperature differences. The discrimination power of the 3 methods was determined by the receiver-operating curve (ROC). The regression between the determined temperature distributions of both extremities was plotted. Subsequently the correlation of the data was calculated. In normal healthy individuals the asymmetry factor was 0.91 (0.01) (SD), whereas in CRPS1 patients this factor was 0.45 (0.07) (SD). The performance of the arithmetic model based on the ROC curve was excellent. The area under the curve was 0.97 (p < 0.001), the sensitivity and specificity was 9 2% and 94 %, respectively. Furthermore, the temperature asymmetry factor was correlated with the duration of the disease and VAS pain.
Gradl and colleagues (2003) stated that CRPS1 represents a frequent complication following distal radial fractures. These investigators studied the value of clinical evaluation, radiography and thermography in the early diagnosis of CRPS1. A total of 158 patients with distal radial fractures were followed-up for 16 weeks after trauma. Apart from a detailed clinical examination 8 and 16 weeks after trauma, thermography and bilateral radiographs of both hands were carried out. At the end of the observation period 18 patients (11 %) were clinically identified as CRPS1. The severity of the preceding trauma and the chosen therapy did not influence the process of the disease. Sixteen weeks after trauma easy differentiation between normal fracture patients and CRPS1 patients was possible. Eight weeks after distal radial fracture clinical evaluation showed a sensitivity of 78 % and a specificity of 94 %. On the other hand, thermography (58 %) and bilateral radiography (33 %) revealed poor sensitivities. The specificity was high for radiography (91 %) and again poor for thermography (66 %). These authors concluded that the results of the study support the importance of clinical evaluation in the early diagnosis of CRPS1. Plain radiographs facilitate the diagnosis as soon as bony changes develop.
Arterial wall thermography has also been used to identify rupture-prone vulnerable coronary plaque. However, the clinical value of arterial thermography in interventional cardiology has not been established.
Schaar and colleagues (2007) noted that rupture of vulnerable plaques is the principal cause of acute coronary syndrome and myocardial infarction. Identification of vulnerable plaques is therefore essential to enable the development of treatment modalities to stabilize such plaques. Thermography is one of the several novel methods being examined for detecting vulnerable plaques. It evaluates the temperature heterogeneity as an indicator of the metabolic state of the plaque. The authors concluded that while several invasive and non-invasive techniques are currently under development to assess vulnerable plaques, none has proven its value in an extensive in-vivo validation and all have a lack of prospective data.
García-García and colleagues (2008) stated that thin-capped fibroatheroma is the morphology that most resembles plaque rupture. Detection of these vulnerable plaques in-vivo is essential to being able to study their natural history and evaluate potential treatment modalities and, therefore, may ultimately have an important impact on the prevention of acute myocardial infarction and death. The investigators reported that, currently, conventional grayscale intra-vascular ultrasound, virtual histology and palpography data are being collected with the same catheter during the same pullback. A combination of this catheter with either thermography capability or additional imaging, such as optical coherence tomography or spectroscopy, would be an exciting development. Intra-vascular magnetic resonance imaging also holds much promise. The investigators stated that, to date, none of the techniques described above has been sufficiently validated and, most importantly, their predictive value for adverse cardiac events remains elusive. The investigators concluded that very rigorous and well-designed studies are needed for defining the role of each diagnostic modality. Until researchers are able to detect in-vivo vulnerable plaques accurately, no specific treatment is warranted.
Madjid and colleagues (2006) stated that up to 2/3 of acute myocardial infarctions develop at sites of culprit lesions without a significant stenosis. New imaging techniques are needed to identify those lesions with an increased risk of developing an acute complication in the near future. Inflammation is a hallmark feature of these vulnerable/high-risk plaques. These investigators have demonstrated that inflamed atherosclerotic plaques are hot and their surface temperature correlates with an increased number of macrophages and reduced fibrous-cap thickness. They noted that animal and human studies have reported that temperature heterogeneity correlates with arterial inflammation in-vivo. Several coronary temperature mapping catheters are currently being developed. These thermographic methods can be used in the future to detect vulnerable plaques, potentially to ascertain patients' prognosis, and to examine the plaque-stabilizing effects of various pharmacotherapies.
Sharif and Murphy (2010) noted that critical coronary stenoses have been shown to contribute to only a minority of acute coronary syndromes and sudden cardiac death. Autopsy studies have identified a subgroup of high-risk patients with disrupted vulnerable plaque and modest stenosis. Consequently, a clinical need exists to develop methods to identify these plaques prospectively before disruption and clinical expression of disease. Recent advances in invasive as well as non-invasive imaging techniques have shown the potential to identify these high-risk plaques. The anatomical characteristics of the vulnerable plaque such as thin cap fibro-atheroma and lipid pool can be identified with angioscopy, high frequency intra-vascular ultrasound, intra-vascular magnetic resonance imaging (MRI), and optical coherence tomography. Efforts have also been made to recognize active inflammation in high-risk plaques using intra-vascular thermography. Plaque chemical composition by measuring electro-magnetic radiation using spectroscopy is also an emerging technology to detect vulnerable plaques. Non-invasive imaging with MRI, computed tomography, and positron emission tomography also holds the potential to differentiate between low-risk and high-risk plaques. However, at present none of these imaging modalities is able to detect vulnerable plaque nor have they been shown to definitively predict outcome. Nevertheless in contrast, there has been a parallel development in the physiological assessment of advanced athero-sclerotic coronary artery disease. Thus, recent trials using fractional flow reserve in patients with modest non flow-limiting stenoses have shown that deferral of percutaneous coronary intervention with optimal medical therapy in these patients is superior to coronary intervention. The authors concluded that further trials are needed to provide more information regarding the natural history of high-risk but non flow-limiting plaque to establish patient-specific targeted therapy and to refine plaque stabilizing strategies in the future.
There is insufficient evidence to support the use of thermography in post-herpetic neuralgia. Han and associates (2010) examined the usefulness of infrared thermography as a predictor of post-herpetic neuralgia (PHN). Infrared thermography was performed on the affected body regions of 110 patients who had been diagnosed with acute herpes zoster (HZ). Demographical data collected included age, gender, time of skin lesions onset, development of PHN, and co-morbidities. The temperature differences between the unaffected and affected dermatome were calculated. Differences greater than 0.6 degrees C for the mean temperature across the face and trunk were considered abnormal. The affected side was warmer in 35 patients and cooler in 33 patients than the contralateral side. A patient's age and disease duration affected treatment outcomes. However, the temperature differences were not correlated with pain severity, disease duration, allodynia, development of PHN, and use of anti-viral agents (p > 0.05). The authors concluded that a patient's age and disease duration are the most important factors predicting PHN progression, irrespective of thermal findings, and PHN can not be predicted by infrared thermal imaging.
An Agency for Healthcare Research and Quality's report on non-invasive diagnostic techniques for the detection of skin cancers (Parsons et al, 2011) listed thermography as one of the investigational diagnostic techniques for the detection of skin cancers.
Kontos et al (2011) determined the sensitivity and specificity of DITI in a series of women who underwent surgical excision or core biopsy of benign and malignant breast lesions presenting through the symptomatic clinic. Digital infrared thermal imaging was evaluated in 63 symptomatic patients attending a 1-stop diagnostic breast clinic. Thermography had 90 true-negative, 16 false-positive, 15 false-negative and 5 true-positive results. The sensitivity was 25 %, specificity 85 %, positive-predictive value 24 %, and negative-predictive value 86 %. The authors concluded that despite being non-invasive and painless, because of the low sensitivity for breast cancer, DITI is not indicated for the primary evaluation of symptomatic patients nor should it be used on a routine basis as a screening test for breast cancer.
The Canadian Agency for Drugs and Technologies in Health’s technology assessment on Infrared thermography for population screening and diagnostic testing for breast cancer” (Morrison, 2012) states that “No randomized controlled trials have been conducted that compare the effectiveness of thermography with mammography for screening in well women, and there is no evidence regarding the cost-effectiveness of thermography used for screening. Prospective cohort studies of symptomatic patients or patients with abnormal mammograms or ultrasounds do not provide the type of evidence needed to justify the use of thermography for breast screening. Results indicate that thermography performance is worse than mammography in terms of sensitivity, specificity, and predictive values; however, some of the studies’ authors have suggested there may be a role for thermography as an adjunct diagnostic test in some cases”.
Dynamic Infrared Blood Perfusion Imaging
Dynamic infrared blood perfusion imaging (DIRI) is a new infrared imaging technique that is intended to detect changes in blood flow in tissue and organs by sensing passively emitted infrared radiation from tissues. Potential clinical applications of DIRI include: use as an adjunctive screening tool for breast cancer and other cancers; evaluation of response to cancer chemotherapy; monitoring response to therapy in diabetic peripheral vascular disease; identifying perforator vessels during pre-surgical planning; assessing post-operative perfusion of pedicle flaps following reconstructive surgery (i.e., of the breast); mapping of functional cortex in patients undergoing tumor surgery; and determining cardiac bypass graft patency and perfusion of the myocardium in cardiac surgery. Agostini and colleagues (2009) stated that dynamic infrared imaging is a promising technique in breast oncology. Currently available evidence, however, is limited to evaluations of DIRI's technical feasibility. There is an absence of evidence of the impact of DIRI on health outcomes. The BioScanIR System (OmniCorder Technologies, Inc., Bohemia, NY) is an example of a DIRI device that is commercially available.