Validation of non-invasive brain temperature estimation models during swine therapeutic hypothermia

Measurement of Healthy Adult Brain Temperature Using 1H Magnetic Resonance Spectroscopy Thermometry

PURPOSE

The purpose of this study is to measure the brain temperature (Tbr) by using 1H magnetic resonance spectroscopy (1H MRS) thermometry and investigate its age and gender differences in healthy adults. The brain temperature was further compared with the body temperature (Tbo) to investigate the possible existence of brain-body temperature gradient (∆T).

METHODS

A total of 80 subjects were included in this study. 1H MRS data were collected on a 3.0T MR scanner using Point Resolved Selective Spectroscopy (PRESS) sequence. Voxels were positioned in the right frontal (RF) lobe and left frontal (LF) lobe, respectively. The temperature of each voxel was calculated by chemical shift difference (∆δ) between H2O and NAA which was obtained by LCModel software. The average temperature of bilateral frontal lobe voxels was defined as Tbr for each subject. The average forehead temperature was acquired before MR scanning, defined as Tbo, in this study. The difference between Tbr and Tbo, denoted as the brain-body temperature gradient (∆T), was calculated. Age and gender characteristics of Tbr, ∆T and Tbo were analyzed.

RESULTS

Tbr (38.51 ± 0.59℃) was higher than Tbo (36.47 ± 0.26℃) (P < 0.05). Negative correlations were observed between Tbr and age (r = -0.49, P < 0.05) and between ∆T and age (r = -0.44, P < 0.05), whereas no correlation existed between Tbo and age (r = -0.03, P = 0.79).

CONCLUSION

Our observation demonstrated that the brain temperature, derived from 1H MRS thermometry, is significantly higher than the body temperature, indicating the existence of a brain-body temperature gradient, and the brain temperature gradually decreases with age.

A Novel Non-Invasive Thermometer for Continuous Core Body Temperature: Comparison with Tympanic Temperature in an Acute Stroke Clinical Setting

There is a growing research interest in wireless non-invasive solutions for core temperature estimation and their application in clinical settings. This study aimed to investigate the use of a novel wireless non-invasive heat flux-based thermometer in acute stroke patients admitted to a stroke unit and compare the measurements with the currently used infrared (IR) tympanic temperature readings. The study encompassed 30 acute ischemic stroke patients who underwent continuous measurement (Tcore) with the novel wearable non-invasive CORE device. Paired measurements of Tcore and tympanic temperature (Ttym) by using a standard IR-device were performed 3−5 times/day, yielding a total of 305 measurements. The predicted core temperatures (Tcore) were significantly correlated with Ttym (r = 0.89, p < 0.001). The comparison of the Tcore and Ttym measurements by Bland−Altman analysis showed a good agreement between them, with a low mean difference of 0.11 ± 0.34 °C, and no proportional bias was observed (B = −0.003, p = 0.923). The Tcore measurements correctly predicted the presence or absence of Ttym hyperthermia or fever in 94.1% and 97.4% of cases, respectively. Temperature monitoring with a novel wireless non-invasive heat flux-based thermometer could be a reliable alternative to the Ttym method for assessing core temperature in acute ischemic stroke patients.

Noninvasive Versus Invasive Brain Temperature Measurement During Targeted Temperature Management: A Preclinical Study in a Swine Cardiac Arrest Model

We aimed to evaluate correlation and agreement between noninvasive brain temperature (T_BN) and invasive brain temperature (T_BI) measurement during targeted temperature management (TTM) in a swine cardiac arrest model. Defibrillation attempts were provided after 5 minutes of ventricular fibrillation and 12 minutes of cardiopulmonary resuscitation in five pigs. After return of spontaneous circulation, TTM was provided with induction and maintenance phases with a target temperature of 33°C for 6 hours and a rewarming phase with a rewarming rate of 1°C/h for 4 hours. T_BN and T_BI were measured using a double sensor method and an intracranial catheter, respectively. Pulmonary artery temperature (T_P), esophageal temperature (T_E), and rectal temperature (T_R) were measured. Primary outcomes were correlation and agreement between T_BN and T_BI and secondary outcomes were correlation and agreement among T_BN and other temperatures. The Pearson correlation coefficient (PCC) between T_BN and T_BI was 0.95 (p < 0.001) during the whole TTM phases. PCCs between T_BN and T_BI during the induction, maintenance, and rewarming phases were 0.91 (p < 0.001), 0.88 (p < 0.001), and 0.94 (p < 0.001) and 95% limits of agreement (LoAs) between T_BN and T_BI were (-0.27°C to 0.78°C), (-0.18°C to 0.54°C), and (-0.93°C to 0.88°C), respectively. Correlation between T_BN and T_BI during the maintenance phase was higher than correlation between T_BN and T_E (PCC = 0.74, p < 0.001) or T_P (PCC = 0.81, p < 0.001). The 95% LoAs were narrowest between T_BN and T_P in the induction phase (-0.58 to 0.11), between T_BN and T_BI in the maintenance phase (-0.54 to 0.18), and between T_BN and T_R in the rewarming phase (-0.96 to 0.84). Noninvasive brain temperature showed good correlation with invasive brain temperature during TTM in a swine cardiac arrest model. Correlation was highest during the rewarming phase and lowest during the maintenance phase. Agreement between the two measurements was not clinically acceptable.