title: Detection of subclinical synovial inflammation by microwave radiometry.
abstract: OBJECTIVE
  Microwave Radiometry is a non-invasive method which determines within seconds the in vivo temperature of internal tissues at a depth of 3-7 cm with an accuracy of ±0.2°C. In this proof-of-concept study, we tested the hypothesis that, in absence of relevant clinical signs, increased local temperature detected by microwave radiometry reflects subclinical synovial inflammation, using ultrasound as reference method.
  
  
  METHODS
  Knees of healthy controls, subjects with recent knee trauma and symptom-free patients with rheumatoid arthritis (RA) or osteoarthritis were examined by placing the microwave radiometry sensor, a) at the upper one third of the anterior surface of the thigh (control-point), and b) over the suprapatellar recess. Ultrasound was performed immediately after and the possible presence of fluid and/or synovitis was correlated with microwave radiometry findings.
  
  
  RESULTS
  In 30 healthy and 10 injured knees the temperature was always lower than thigh (32.3±1.1 and 31.8±1.4 versus 34.1±0.9 and 33.6±1.2°C with a difference (ΔΤ) of -1.8±0.2 and -1.9±0.4°C respectively). Of 40 RA and 20 osteoarthritis knees examined, ultrasound findings indicative of subclinical inflammation (fluid effusion and/or Doppler signal) were found in 24 and 12, respectively, in which the temperature was higher than healthy knees and ΔΤ was lower (-0.9±0.7 in RA and -1.0±0.5 in osteoarthritis versus -1.8±0.2°C, p<0.001). The 5 RA knees with power Doppler findings indicative of grade 2 inflammation had a ΔΤ 3 times lower compared to healthy (-0.6±0.6, p = 0.007), whereas the 9 RA and the 7 osteoarthritis knees with additionally fluid effusion, had even lower ΔΤ (-0.4±0.7, p<0.001).
  
  
  CONCLUSIONS
  Using a safe, rapid and easy-to-perform method, such as microwave radiometry, thermal changes within the knee joint may reflect non-clinically apparent joint inflammation. Refinement of this method, including production of sensors for small joints, could result to the development of the ideal objective tool to detect subclinical synovitis in clinical practice.
authors.affiliation: First Department of Propedeutic and Internal Medicine, Athens University Medical School, Athens, Greece.
authors.forename: Evangelia
authors.initials: E
authors.lastname: Zampeli
authors.forename: Ioannis
authors.initials: I
authors.lastname: Raftakis
authors.forename: Archontoula
authors.initials: A
authors.lastname: Michelongona
authors.forename: Chara
authors.initials: C
authors.lastname: Nikolaou
authors.forename: Antonia
authors.initials: A
authors.lastname: Elezoglou
authors.forename: Konstantinos
authors.initials: K
authors.lastname: Toutouzas
authors.forename: Elias
authors.initials: E
authors.lastname: Siores
authors.forename: Petros P
authors.initials: PP
authors.lastname: Sfikakis
mesh_terms: D000328:Adult; D000368:Aged; D001172:Arthritis, Rheumatoid / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000473:pathology; D042241:Early Diagnosis; D005122:Exudates and Transudates; D005260:Female; D006801:Humans; D007718:Knee Injuries / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000473:pathology; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000473:pathology*; D008297:Male; D008872:Microwaves; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000473:pathology; D011874:Radiometry / Q000379:methods; D013585:Synovitis / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000473:pathology; D013696:Temperature; D014463:Ultrasonography