title: Experimental investigation and histopathological identification of acute thermal damage in skeletal porcine muscle in relation to whole-body SAR, maximum temperature, and CEM43 °C due to RF irradiation in an MR body coil of birdcage type at 123 MHz.
abstract: OBJECTIVE
  This study is an investigation of the relationship between several characteristic parameters and acute thermal damage in porcine skeletal muscle.
  
  
  METHODS
  Fourteen pigs under injection anaesthesia were placed into a magnetic resonance body coil and exposed for different time durations to different specific energy absorption rate (SAR) levels at 123 MHz. Local temperatures were measured using four temperature sensors. Sensors 1-3 were placed in skeletal muscle and one sensor was placed in the rectum. Sensors 1 and 2 were placed in hot-spot areas and sensor 3 was placed at the periphery of the animals. The pigs were exposed to whole-body SAR (SAR-wb) between 2.5 W/kg and 5.2 W/kg for 30 or 60 min. Three animals received no SAR. After each experiment, muscle samples adjacent to the positions of sensors 1-3 were taken for frozen section analysis. Three characteristic parameters were chosen for investigation: SAR-wb, maximum sensor temperature (T-max), and cumulative equivalent minutes at 43 °C (CEM43 °C).
  
  
  RESULTS
  Histopathological criteria were established to detect acute thermal tissue damage in frozen sections such as widening of intercellular space between the muscle fibres and loss of glycogen. Clear tissue damage thresholds were found for T-max and CEM43 °C, though not for SAR-wb. For all animals with high thermal exposure, damage was also found for muscle samples adjacent to the peripheral sensor 3.
  
  
  CONCLUSIONS
  Both T-max and CEM43, are able to predict thermal damage in porcine muscle. However, CEM43 is the less ambiguous parameter. The reasons for the occurrence of the aforementioned damage at low local temperatures at the animals' periphery remain unclear and further investigations are needed.
authors.affiliation: Department of Radiation Oncology and Radiotherapy, Charité, Universitätsmedizin Berlin, Germany .
authors.forename: Jacek
authors.initials: J
authors.lastname: Nadobny
authors.forename: Robert
authors.initials: R
authors.lastname: Klopfleisch
authors.forename: Gerhard
authors.initials: G
authors.lastname: Brinker
authors.forename: Gisela
authors.initials: G
authors.lastname: Stoltenburg-Didinger
mesh_terms: D000208:Acute Disease; D000818:Animals; D001831:Body Temperature / Q000528:radiation effects*; D001833:Body Temperature Regulation; D006979:Hyperthermia, Induced / Q000009:adverse effects*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D018482:Muscle, Skeletal / Q000473:pathology / Q000528:radiation effects*; D011833:Radiation Injuries, Experimental / Q000175:diagnosis*; D011846:Radio Waves / Q000009:adverse effects*; D013552:Swine; D014916:Whole-Body Irradiation
keywords: Acute thermal damage; CEM43°C; MR body coil; frozen muscle sections; thermal damage thresholds