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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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Experimental setup.(a) PRF calibration measurements were performed with RBC stored in a plastic cup. RBC temperature was derived from the calibration thermometer T (tip diameter = 5 mm) positioned at the center of RBC using a thermometer holder TH. A reference phantom RP was positioned in a plastic grid. To avoid thermal cooling of RP by RBC, the wall of the grid next to RBC was isolated by air cushion plastic. (b) RBC units were mounted in upright position in a two-layer plastic frame F (Lego®) with minimum distance of 1–2 mm. For investigation, RBC units were plugged to an adjustment unit AU (Lego®) fixed in a 12 channel head coil adapted with 2 reference phantoms RP kept at MR investigation room temperature Tambient throughout experiments.
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pone-0057931-g001: Experimental setup.(a) PRF calibration measurements were performed with RBC stored in a plastic cup. RBC temperature was derived from the calibration thermometer T (tip diameter = 5 mm) positioned at the center of RBC using a thermometer holder TH. A reference phantom RP was positioned in a plastic grid. To avoid thermal cooling of RP by RBC, the wall of the grid next to RBC was isolated by air cushion plastic. (b) RBC units were mounted in upright position in a two-layer plastic frame F (Lego®) with minimum distance of 1–2 mm. For investigation, RBC units were plugged to an adjustment unit AU (Lego®) fixed in a 12 channel head coil adapted with 2 reference phantoms RP kept at MR investigation room temperature Tambient throughout experiments.

Mentions: To derive PRF thermal coefficient of RBC, a series of 12 calibration measurements was performed [25], [26]. A calibration unit (Fig. 1a) build-up of refrigerated RBC, a reference bulb thermometer (Ludwig Schneider Messtechnik, Wertheim, Germany, overall accuracy ±0.2°C) and a reference phantom (5 g agar solved in 500 ml water) kept at ambient temperature to measure non-temperature related phase drifts was positioned in a 1.5 T MR system (Siemens Magnetom Espree, Erlangen, Germany), centered in a 12 channel head coil. After acquisition of reference images, difference phase images covering the thermometer tip with 7 gapless transversal slices and thermometer reference temperatures were measured with 3 min pause time for RBC temperatures between 1 and 18°C. Parameters of the 2D multislice gradient echo (GRE) sequence were repetition time = 33.15 ms, echo time TE = 20 ms, flip angle = 14°, voxel size = 1.1×1.1×7.5 mm3, field of view = 170×170 mm2, bandwidth = 65 Hz/Pix and data acquisition time = 38 s. (Due to this protocol no radio frequency induced heating was noticed in bulb thermometer equipped phantoms at ambient temperature.).


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)

Experimental setup.(a) PRF calibration measurements were performed with RBC stored in a plastic cup. RBC temperature was derived from the calibration thermometer T (tip diameter = 5 mm) positioned at the center of RBC using a thermometer holder TH. A reference phantom RP was positioned in a plastic grid. To avoid thermal cooling of RP by RBC, the wall of the grid next to RBC was isolated by air cushion plastic. (b) RBC units were mounted in upright position in a two-layer plastic frame F (Lego®) with minimum distance of 1–2 mm. For investigation, RBC units were plugged to an adjustment unit AU (Lego®) fixed in a 12 channel head coil adapted with 2 reference phantoms RP kept at MR investigation room temperature Tambient throughout experiments.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3585280&req=5

pone-0057931-g001: Experimental setup.(a) PRF calibration measurements were performed with RBC stored in a plastic cup. RBC temperature was derived from the calibration thermometer T (tip diameter = 5 mm) positioned at the center of RBC using a thermometer holder TH. A reference phantom RP was positioned in a plastic grid. To avoid thermal cooling of RP by RBC, the wall of the grid next to RBC was isolated by air cushion plastic. (b) RBC units were mounted in upright position in a two-layer plastic frame F (Lego®) with minimum distance of 1–2 mm. For investigation, RBC units were plugged to an adjustment unit AU (Lego®) fixed in a 12 channel head coil adapted with 2 reference phantoms RP kept at MR investigation room temperature Tambient throughout experiments.
Mentions: To derive PRF thermal coefficient of RBC, a series of 12 calibration measurements was performed [25], [26]. A calibration unit (Fig. 1a) build-up of refrigerated RBC, a reference bulb thermometer (Ludwig Schneider Messtechnik, Wertheim, Germany, overall accuracy ±0.2°C) and a reference phantom (5 g agar solved in 500 ml water) kept at ambient temperature to measure non-temperature related phase drifts was positioned in a 1.5 T MR system (Siemens Magnetom Espree, Erlangen, Germany), centered in a 12 channel head coil. After acquisition of reference images, difference phase images covering the thermometer tip with 7 gapless transversal slices and thermometer reference temperatures were measured with 3 min pause time for RBC temperatures between 1 and 18°C. Parameters of the 2D multislice gradient echo (GRE) sequence were repetition time = 33.15 ms, echo time TE = 20 ms, flip angle = 14°, voxel size = 1.1×1.1×7.5 mm3, field of view = 170×170 mm2, bandwidth = 65 Hz/Pix and data acquisition time = 38 s. (Due to this protocol no radio frequency induced heating was noticed in bulb thermometer equipped phantoms at ambient temperature.).

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