title: Thermometry of red blood cell concentrate: magnetic resonance decoding warm up process.
abstract: OBJECTIVE
  Temperature is a key measure in human red blood cell concentrate (RBC) quality control. A precise description of transient temperature distributions in RBC units removed from steady storage exposed to ambient temperature is at present unknown. Magnetic resonance thermometry was employed to visualize and analyse RBC warm up processes, to describe time courses of RBC mean, surface and core temperatures by an analytical model, and to determine and investigate corresponding model parameters.
  
  
  METHODS
  Warm-up processes of 47 RBC units stored at 1-6°C and exposed to 21.25°C ambient temperature were investigated by proton resonance frequency thermometry. Temperature distributions were visualized and analysed with dedicated software allowing derivation of RBC mean, surface and core temperature-time courses during warm up. Time-dependence of mean temperature was assumed to fulfil a lumped capacitive model of heat transfer. Time courses of relative surface and core temperature changes to ambient temperature were similarly assumed to follow shifted exponential decays characterized by a time constant and a relative time shift, respectively.
  
  
  RESULTS
  The lumped capacitive model of heat transfer and shifted exponential decays described time-dependence of mean, surface and core temperatures close to perfect (mean R(2) were 0.999±0.001, 0.996±0.004 and 0.998±0.002, respectively). Mean time constants were τmean = 55.3±3.7 min, τsurface = 41.4±2.9 min and τcore = 76.8±7.1 min, mean relative time shifts were Δsurface = 0.07±0.02 and Δcore = 0.04±0.01. None of the constants correlated significantly with temperature differences between ambient and storage temperature.
  
  
  CONCLUSIONS
  Lumped capacitive model of heat transfer and shifted exponential decays represent simple analytical formulas to describe transient mean, surface and core temperatures of RBC during warm up, which might be a helpful tool in RBC temperature monitoring and quality control. Independence of constants on differences between ambient and storage temperature suggests validity of models for arbitrary storage and ambient temperatures.
authors.affiliation: Healthcare Sector, Siemens AG, Graz, Austria. gert.reiter@siemens.com
authors.forename: Gert
authors.initials: G
authors.lastname: Reiter
authors.forename: Ursula
authors.initials: U
authors.lastname: Reiter
authors.forename: Thomas
authors.initials: T
authors.lastname: Wagner
authors.forename: Noemi
authors.initials: N
authors.lastname: Kozma
authors.forename: Jörg
authors.initials: J
authors.lastname: Roland
authors.forename: Helmut
authors.initials: H
authors.lastname: Schöllnast
authors.forename: Franz
authors.initials: F
authors.lastname: Ebner
authors.forename: Gerhard
authors.initials: G
authors.lastname: Lanzer
mesh_terms: D004912:Erythrocytes; D006801:Humans; D011522:Protons; D013048:Specimen Handling; D013696:Temperature; D062125:Thermometry / Q000379:methods*; D013997:Time Factors
chemical_list: D011522:Protons