Detection of subclinical synovial inflammation by microwave radiometry

Review of the Capacity to Accurately Detect the Temperature of Human Skin Tissue Using the Microwave Radiation Method

Microwave radiometry (MWR) is instrumental in detecting thermal variations in skin tissue before anatomical changes occur, proving particularly beneficial in the early diagnosis of cancer and inflammation. This study concisely traces the evolution of microwave radiometers within the medical sector. By analyzing a plethora of pertinent studies and contrasting their strengths, weaknesses, and performance metrics, this research identifies the primary factors limiting temperature measurement accuracy. The review establishes the critical technologies necessary to overcome these limitations, examines the current state and prospective advancements of each technology, and proposes comprehensive implementation strategies. The discussion elucidates that the precise measurement of human surface and subcutaneous tissue temperatures using an MWR system is a complex challenge, necessitating an integration of antenna directionality for temperature measurement, radiometer error correction, hardware configuration, and the calibration and precision of a multilayer tissue forward and inversion method. This study delves into the pivotal technologies for non-invasive human tissue temperature monitoring in the microwave frequency range, offering an effective approach for the precise assessment of human epidermal and subcutaneous temperatures, and develops a non-contact microwave protocol for gauging subcutaneous tissue temperature distribution. It is anticipated that mass-produced measurement systems will deliver substantial economic and societal benefits.

Microwave Radiometry for the Diagnosis and Monitoring of Inflammatory Arthritis

The ability of microwave radiometry (MWR) to detect with high accuracy in-depth temperature changes in human tissues is under investigation in various medical fields. The need for non-invasive, easily accessible imaging biomarkers for the diagnosis and monitoring of inflammatory arthritis provides the background for this application in order to detect the local temperature increase due to the inflammatory process by placing the appropriate MWR sensor on the skin over the joint. Indeed, a number of studies reviewed herein have reported interesting results, suggesting that MWR is useful for the differential diagnosis of arthritis as well as for the assessment of clinical and subclinical inflammation at the individual large or small joint level and the patient level. MWR showed higher agreement with musculoskeletal ultrasound, used as a reference, than with clinical examination in rheumatoid arthritis (RA), while it also appeared useful for the assessment of back pain and sacroiliitis. Further studies with a larger number of patients are warranted to confirm these findings, taking into account the current limitations of the available MWR devices. This may lead to the production of easily accessible and inexpensive MWR devices that will provide a powerful impetus for personalized medicine.

Hot and cold knees: exploring differences in patella skin temperature in patients with patellofemoral pain

OBJECTIVES

To investigate the distribution of patella skin temperature (Tsk) measurements and to explore the presence of temperature subgroups in patellofemoral pain (PFP) patients.

DESIGN

Cross-sectional observational study design.

PARTICIPANTS

One dataset of 58 healthy participants and 232 PFP patients from three different datasets.

MAIN OUTCOME MEASURES

Patella skin temperature, measured by physiotherapists using a low cost hand held digital thermometer. The distribution of patella skin temperature was assessed and compared across datasets. To objectively determine the clinically meaningful number of subgroups, we used the average silhouette method. Finite mixture models were then used to examine the presence of PFP temperature subgroups. Receiver operating characteristic curves were used to estimate optimal patella Tsk thresholds for allocation of participants into the identified subgroups.

RESULTS

In contrast to healthy participants, the patella skin temperature had an obvious bimodal distribution with wide dispersion present across all three PFP datasets. The fitted finite mixture model suggested three temperature subgroups (cold, normal and hot) that had been recommended by the average silhouette method with discrimination cut-off thresholds for subgroup membership based on receiver operating curve analysis of Cold=<30.0°C; Normal 30.0-35.2°C; Hot ≥35.2°C.

CONCLUSION

A low cost hand held digital thermometer appears to be a useful clinical tool to identify three PFP temperature subgroups. Further research is recommended to deepen understanding of these clinical findings and to explore the implications to different treatments.

Imaging-based internal body temperature measurements: The journal Temperature toolbox

Noninvasive imaging methods of internal body temperature are in high demand in both clinical medicine and physiological research. Thermography and thermometry can be used to assess tissue temperature during thermal therapies: ablative and hyperthermia treatments to ensure adequate temperature rise in target tissues but also to avoid collateral damage by heating healthy tissues. In research use, measurement of internal body temperature enables us the production of thermal maps on muscles, internal organs, and other tissues of interest. The most used methods for noninvasive imaging of internal body temperature are based on different parameters acquired with magnetic resonance imaging, ultrasound, computed tomography, microwave radiometry, photoacoustic imaging, and near-infrared spectroscopy. In the current review, we examine the aforementioned imaging methods, their use in estimating internal body temperature in vivo with their advantages and disadvantages, and the physical phenomena the thermography or thermometry modalities are based on.

Joint microwave radiometry for inflammatory arthritis assessment

OBJECTIVES

Increased in-depth joint temperature measured by the rapid, easy-to-perform microwave radiometry (MWR) method may reflect inflammation, even in the absence of clinical signs. We hypothesized that MWR is useful for RA and spondyloarthritis patients' assessment.

METHODS

Clinical examination, joint ultrasound and/or MRI and MWR were performed in two independent patient-control cohorts (n = 243).

RESULTS

Among single RA joints MWR performed best in the knee using ultrasound as reference, with 75% sensitivity-73% specificity for grey-scale synovitis score ⩾2, and 80% sensitivity-82% specificity for power Doppler positivity. A stronger agreement was evident between increased knee relative temperature (Δt) and power Doppler positivity (82%) than with clinical examination (76%). In a different patient cohort with painful knees, a knee Δt ⩽0.2 predicted power Doppler positivity with 100% positive and negative predictive values. A thermo-score summing 10 Δt values of three large and seven small RA joints (elbow, knee, ankle, wrist, four hand and two foot joints of the clinically dominant arm or hand and leg or foot) correlated with ultrasound scores of synovitis/tenosynovitis (all P < 0.001) and the 28-joint Disease Activity Score (DAS28) (P = 0.004). The agreement of the thermo-score with ultrasound-defined joint inflammation (82%) was stronger than with DAS28 (64%). The thermo-score improved significantly after 90 days of treatment in patients with active RA at baseline (P = 0.004). Using MRI as reference, Δt of sacroiliac joints could discriminate between spondyloarthritis patients with or without sacroiliitis with 78% sensitivity-74% specificity.

CONCLUSION

In-depth increased MWR-derived joint temperature reflects both subclinical and clinically overt inflammation and may serve as a biomarker in arthritis.

Passive microwave radiometry in biomedical studies

Passive microwave radiometry (MWR) measures natural emissions in the range 1-10GHz from proteins, cells, organs and the whole human body. The intensity of intrinsic emission is determined by biochemical and biophysical processes. The nature of this process is still not very well known. Infrared thermography (IRT) can detect emission several microns deep (skin temperature), whereas MWR allows detection of thermal abnormalities down to several centimeters (internal or deep temperature). MWR is noninvasive and inexpensive. It requires neither fluorescent nor radioactive labels, nor ionizing or other radiation. MWR can be used in early drug discovery as well as preclinical and clinical studies.

Microwave Radiometry-Derived Thermal Changes of Small Joints as Additional Potential Biomarker in Rheumatoid Arthritis: A Prospective Pilot Study

OBJECTIVE

A prospective pilot study was performed using microwave radiometry (MR), a noninvasive method detecting in-depth tissue temperature, to evaluate whether temperature-of-small-joint-derived scores correlate to parameters commonly used to assess disease activity in rheumatoid arthritis (RA).

METHODS

Ten patients with active, untreated RA underwent clinical and laboratory assessments and joint ultrasound and MR of hand and foot small joints at baseline and at 15, 30, and 90 days after treatment onset. Mixed-model analysis for repeated measures was used to compare patient characteristics in sequential visits. Twenty age- and sex-matched healthy individuals served as control subjects.

RESULTS

Using 1248 MR-derived separate recordings from patients' joints, several thermoscores involving different joint combinations were created. When compared with clinical and ultrasound data, the best performing thermoscore involved temperatures of 16 joints (second to fifth metacarpal and proximal interphalangeal joints, bilaterally). This thermoscore correlated to the 28-joint Disease Activity Score-C-reactive protein, tender and swollen joint counts, patient's visual analog scale (all P ≤ 0.02), and the standard 7-joint ultrasound score (P < 0.03) and could also discriminate patients in high (mean, 9.2 [SD, 5.6]) or moderate (7.1 [SD, 3.5]) versus low disease activity/remission (4.2 [SD, 1.8]) (P ≤ 0.01) or healthy subjects (5.0 [SD, 1.7]) (P = 0.002).

CONCLUSIONS

Microwave radiometry-derived increased in-depth temperature indicative of local inflammation of small joints may serve as an additional biomarker in RA. Optimization of MR-based methods may result in objective assessments of RA disease activity in clinical practice.

Pre-Clinical Testing of Microwave Radiometer and a Pilot Study on the Screening Inflammation of Knee Joints

This article presents the pre-clinical evaluation of our custom-built, single-band microwave radiometer centered at 1.3 GHz for deep tissue thermometry, and a pilot study on volunteers for passive detection of inflammation in knee joints. The electromagnetic (EM) compatibility of the battery-operated radiometer for clinical use was assessed as per International Special Committee on Radio Interference (CISPR) 22 standard. The ability to detect inflammation in knee joints was assessed using a substrate integrated waveguide antenna connected to the radiometer. EM compatibility tests carried out in the laboratory indicated device immunity to intentional radiated interference up to -20 dBm injected power in the global system for mobile communication frequency band, and pre-compliance to CISPR 22 standard. Radiometer temperature measurements recorded at the lateral and medial aspects of both knees of 41 volunteers indicated mean temperature greater than 33°C for the diseased sites compared with the mean temperature of 28°C measured for the healthy sites. One-way analysis of variance statistics indicated significantly (P < 0.005) higher radiometer temperature at the diseased sites unlike the healthy sites. Thus, the EM pre-compliance of the device and the potential to measure deep tissue inflammation were demonstrated. Bioelectromagnetics. 2019;40:402-411. © 2019 Bioelectromagnetics Society.

Noninvasive detection of increased carotid artery temperature in patients with coronary artery disease predicts major cardiovascular events at one year: Results from a prospective multicenter study

BACKGROUND AND AIMS

Limited prospective data have been reported regarding the impact of carotid inflammation on cardiovascular events in patients with coronary artery disease (CAD). Microwave radiometry (MWR) is a noninvasive, simple method that has been used for evaluation of carotid artery temperature which, when increased, predicts 'inflamed' plaques with vulnerable characteristics. We prospectively tested the hypothesis that increased carotid artery temperature predicts future cerebro- and cardiovascular events in patients with CAD.

METHODS

Consecutive patients from 3 centers, with documented CAD by coronary angiography, were studied. In both carotid arteries, common carotid intima-media thickness and plaque thickness were evaluated by ultrasound. Temperature difference (ΔT), measured by MWR, was considered as the maximal temperature along the carotid artery minus the minimum; ΔT ≥0.90 °C was assigned as high. Major cardiovascular events (MACE, death, stroke, myocardial infarction or revascularization) were recorded during the following year.

RESULTS

In total, 250 patients were studied; of them 40 patients (16%) had high ΔT values in both carotid arteries. MACEs occurred in 30% of patients having bilateral high ΔT versus 3.8% in the remaining patients (p<0.001). Bilateral high ΔT was independently associated with increased one-year MACE rate (HR = 6.32, 95% CI 2.42-16.53, p<0.001, by multivariate cox regression hazard model). The addition of ΔT information on a baseline model based on cardiovascular risk factors and extent of CAD significantly increased the prognostic value of the model (c-statistic increase 0.744 to 0.845, p_dif = 0.05) CONCLUSIONS: Carotid inflammation, detected by MWR, has an incremental prognostic value in patients with documented CAD.