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Thermometry of red blood cell concentrate: magnetic resonance decoding warm up process.

Reiter G, Reiter U, Wagner T, Kozma N, Roland J, Schöllnast H, Ebner F, Lanzer G - PLoS ONE (2013)

Bottom Line: 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.Independence of constants on differences between ambient and storage temperature suggests validity of models for arbitrary storage and ambient temperatures.

View Article: PubMed Central - PubMed

Affiliation: Healthcare Sector, Siemens AG, Graz, Austria. gert.reiter@siemens.com

ABSTRACT

Purpose: 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.

Conclusion: 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.

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Related in: MedlinePlus

PRF image evaluation flow chart. TSE images were used to segment RBC volume, SAGM and reference phantoms RP. Sample height h and width w and center cRBC = h/2 were determined from the central slice. RBC volume was calculated as sum of segmented RBC areas in the 7 slices multiplied by slice distance. After phase drift correction via medians of reference phantom phases, corrected RBC difference phases φ were recalculated to temperatures, which can be visualized color encoded. Thermal RBC core (RBCcore) was defined as region with minimum temperature in the central slice throughout warm up. It should be noticed, that slices 1 and 7 are slightly noisier than the more central slices because of their close vicinity to the irregular borders of the pouch and the large echo time of 20 ms choosen to increase overall precision of temperature measurements.
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pone-0057931-g002: PRF image evaluation flow chart. TSE images were used to segment RBC volume, SAGM and reference phantoms RP. Sample height h and width w and center cRBC = h/2 were determined from the central slice. RBC volume was calculated as sum of segmented RBC areas in the 7 slices multiplied by slice distance. After phase drift correction via medians of reference phantom phases, corrected RBC difference phases φ were recalculated to temperatures, which can be visualized color encoded. Thermal RBC core (RBCcore) was defined as region with minimum temperature in the central slice throughout warm up. It should be noticed, that slices 1 and 7 are slightly noisier than the more central slices because of their close vicinity to the irregular borders of the pouch and the large echo time of 20 ms choosen to increase overall precision of temperature measurements.

Mentions: Phase difference images were transformed to RBC temperature maps by dedicated software developed in Matlab (R2010b. The MathWorks Inc., Natick, Massachusetts). Evaluation flow chart, including RBC, SAGM and reference phantom segmentation, determination of non-temperature-related phase differences in the reference phantoms and correction of phase differences in RBC by the median of the phase differences in the reference phantoms is shown in Fig. 2. From corrected phase differences φ in RBC, corresponding temperatures T were calculated according to T = Tstorage+(φ/2π⋅αRBC⋅γ⋅B0⋅TE) where αRBC is the mean PRF thermal coefficient of RBC derived from calibration measurements and Tstorage the temperature of RBC at onset of measurements [19]. RBC volume (as RBC area times slice distance), RBC pouch’s volume (as pouch’s area including RBC and SAGM times slice distance) height and width as well as its center position were derived from segmentation. Thermal RBC core position was defined as the position in the sample, where time-averaged temperature was minimal.


Thermometry of red blood cell concentrate: magnetic resonance decoding warm up process.

Reiter G, Reiter U, Wagner T, Kozma N, Roland J, Schöllnast H, Ebner F, Lanzer G - PLoS ONE (2013)

PRF image evaluation flow chart. TSE images were used to segment RBC volume, SAGM and reference phantoms RP. Sample height h and width w and center cRBC = h/2 were determined from the central slice. RBC volume was calculated as sum of segmented RBC areas in the 7 slices multiplied by slice distance. After phase drift correction via medians of reference phantom phases, corrected RBC difference phases φ were recalculated to temperatures, which can be visualized color encoded. Thermal RBC core (RBCcore) was defined as region with minimum temperature in the central slice throughout warm up. It should be noticed, that slices 1 and 7 are slightly noisier than the more central slices because of their close vicinity to the irregular borders of the pouch and the large echo time of 20 ms choosen to increase overall precision of temperature measurements.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3585280&req=5

pone-0057931-g002: PRF image evaluation flow chart. TSE images were used to segment RBC volume, SAGM and reference phantoms RP. Sample height h and width w and center cRBC = h/2 were determined from the central slice. RBC volume was calculated as sum of segmented RBC areas in the 7 slices multiplied by slice distance. After phase drift correction via medians of reference phantom phases, corrected RBC difference phases φ were recalculated to temperatures, which can be visualized color encoded. Thermal RBC core (RBCcore) was defined as region with minimum temperature in the central slice throughout warm up. It should be noticed, that slices 1 and 7 are slightly noisier than the more central slices because of their close vicinity to the irregular borders of the pouch and the large echo time of 20 ms choosen to increase overall precision of temperature measurements.
Mentions: Phase difference images were transformed to RBC temperature maps by dedicated software developed in Matlab (R2010b. The MathWorks Inc., Natick, Massachusetts). Evaluation flow chart, including RBC, SAGM and reference phantom segmentation, determination of non-temperature-related phase differences in the reference phantoms and correction of phase differences in RBC by the median of the phase differences in the reference phantoms is shown in Fig. 2. From corrected phase differences φ in RBC, corresponding temperatures T were calculated according to T = Tstorage+(φ/2π⋅αRBC⋅γ⋅B0⋅TE) where αRBC is the mean PRF thermal coefficient of RBC derived from calibration measurements and Tstorage the temperature of RBC at onset of measurements [19]. RBC volume (as RBC area times slice distance), RBC pouch’s volume (as pouch’s area including RBC and SAGM times slice distance) height and width as well as its center position were derived from segmentation. Thermal RBC core position was defined as the position in the sample, where time-averaged temperature was minimal.

Bottom Line: 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.Independence of constants on differences between ambient and storage temperature suggests validity of models for arbitrary storage and ambient temperatures.

View Article: PubMed Central - PubMed

Affiliation: Healthcare Sector, Siemens AG, Graz, Austria. gert.reiter@siemens.com

ABSTRACT

Purpose: 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.

Conclusion: 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.

Show MeSH
Related in: MedlinePlus