Magnetic resonance elastography of skeletal muscle deep tissue injury

The current state‐of‐the‐art diagnosis method for deep tissue injury in muscle, a subcategory of pressure ulcers, is palpation. It is recognized that deep tissue injury is frequently preceded by altered biomechanical properties. A quantitative understanding of the changes in biomechanical properties preceding and during deep tissue injury development is therefore highly desired. In this paper we quantified the spatial–temporal changes in mechanical properties upon damage development and recovery in a rat model of deep tissue injury. Deep tissue injury was induced in nine rats by two hours of sustained deformation of the tibialis anterior muscle. Magnetic resonance elastography (MRE), T₂‐weighted, and T₂‐mapping measurements were performed before, directly after indentation, and at several timepoints during a 14‐day follow‐up. The results revealed a local hotspot of elevated shear modulus (from 3.30 ± 0.14 kPa before to 4.22 ± 0.90 kPa after) near the center of deformation at Day 0, whereas the T₂ was elevated in a larger area. During recovery there was a clear difference in the time course of the shear modulus and T₂. Whereas T₂ showed a gradual normalization towards baseline, the shear modulus dropped below baseline from Day 3 up to Day 10 (from 3.29 ± 0.07 kPa before to 2.68 ± 0.23 kPa at Day 10, P < 0.001), followed by a normalization at Day 14. In conclusion, we found an initial increase in shear modulus directly after two hours of damage‐inducing deformation, which was followed by decreased shear modulus from Day 3 up to Day 10, and subsequent normalization. The lower shear modulus originates from the moderate to severe degeneration of the muscle. MRE stiffness values were affected in a smaller area as compared with T₂. Since T₂ elevation is related to edema, distributing along the muscle fibers proximally and distally from the injury, we suggest that MRE is more specific than T₂ for localization of the actual damaged area.     

磁共振弹性图

磁共振弹性图(magnetic resonance elastography,MRE)利用磁共振成像(MRI)技术,测量由外力引起的组织内部质点位移空间分布,以此为输入对弹性力学的逆问题进行求解,从而获得组织弹性系数的空间分布图。介绍了M RE的成像原理,综述其各种成像手段以及MRE在医学上的应用和前景。     

Non-invasive measurement of brain viscoelasticity using magnetic resonance elastography

The purpose of this work was to develop magnetic resonance elastography (MRE) for the fast and reproducible measurement of spatially averaged viscoelastic constants of living human brain. The technique was based on a phase-sensitive echo planar imaging acquisition. Motion encoding was orthogonal to the image plane and synchronized to intracranial shear vibrations at driving frequencies of 25 and 50 Hz induced by a head-rocker actuator. Ten time-resolved phase-difference wave images were recorded within 60 s and analyzed for shear stiffness and shear viscosity. Six healthy volunteers (six men; mean age 34.5 years; age range 25-44 years) underwent 23-39 follow-up MRE studies over a period of 6 months. Interindividual mean +/- SD shear moduli and shear viscosities were found to be 1.17 +/- 0.03 kPa and 3.1 +/- 0.4 Pas for 25 Hz and 1.56 +/- 0.07 kPa and 3.4 +/- 0.2 Pas for 50 Hz, respectively (P < or = 0.01). The intraindividual range of shear modulus data was 1.01-1.31 kPa (25 Hz) and 1.33-1.77 kPa (50 Hz). The observed modulus dispersion indicates a limited applicability of Voigt's model to explain viscoelastic behavior of brain parenchyma within the applied frequency range. The narrow distribution of data within small confidence intervals demonstrates excellent reproducibility of the experimental protocol. The results are necessary as reference data for future comparisons between healthy and pathological human brain viscoelastic data.     

Value of whole breast magnetic resonance elastography added to MRI for lesion characterization

The purpose of this work was to assess the diagnostic value of magnetic resonance elastography (MRE) in addition to MRI to differentiate malignant from benign breast tumors, and the feasibility of performing MRE on the whole breast. MRE quantified biomechanical properties within the entire breast (50 slices) using an 11 min acquisition protocol at an isotropic image acquisition resolution of 2 × 2 × 2 mm³. Fifty patients were included. Finally, 43 patients (median age 52) with a suspect breast lesion detected by mammography and/or ultrasound were examined by MRI and MRE at 1.5 T. The viscoelastic parameters, i.e. elasticity (G_d), viscosity (G_l), the magnitude of the complex shear modulus , and the phase angle , were measured via MRE and correlated with MRI Breast Imaging—Reporting and Data System (BI‐RADS) score, histological type, and histological grade. Stroma component and angiogenesis were also correlated with viscoelastic properties. In the 43 lesions, G_d decreased and y increased with the MRI BI‐RADS score (p_Gd = 0.02, p_y = 0.002), whereas (G_l) and y were increased in malignant lesions (p_Gl = 0.045, p_y = 0.0004). The area under the curve increased from 0.84 for MRI BI‐RADS alone to 0.92 with the MRI BI‐RADS and y (AUC increase +0.08; 95% CI (?0.003; 0.16)). Lesion characterization using the y parameter increased the diagnostic accuracy. The phase angle y was found to have a significant role (p = 0.01) in predicting malignancy independently of the MRI BI‐RADS. Interestingly, histological analysis showed no correlation between viscoelastic parameters and percentage and type of stroma, CD34 quantification of vessels, or histological grade. The combination of MRE and MRI improves the diagnostic accuracy for breast lesions in the studied cohort. In particular, the phase angle y was found to have a significant role in predicting malignancy in addition to BI‐RADS.     

In vivo brain viscoelastic properties measured by magnetic resonance elastography

Magnetic resonance elastography (MRE) is a non-invasive imaging technique used to visualise and quantify mechanical properties of tissue, providing information beyond what can be currently achieved with standard MR sequences and could, for instance, provide new insight into pathological processes in the brain. This study uses the MRE technique at 3 T to extract the complex shear modulus for in vivo brain tissue utilizing a full three-dimensional approach to reconstruction, removing contributions of the dilatational wave by application of the curl operator. A calibrated phantom is used to benchmark the MRE measurements, and in vivo results are presented for healthy volunteers. The results provide data for in vivo brain storage modulus (G'), finding grey matter (3.1 kPa) to be significantly stiffer than white matter (2.7 kPa). The first in vivo loss modulus (G') measurements show no significant difference between grey matter (2.5 kPa) and white matter (2.5 kPa).     

Magnetic resonance elastography of the lungs: A repeatability and reproducibility study

Lung diseases are one of the leading causes of death worldwide, from which four million people die annually. Lung diseases are associated with changes in the mechanical properties of the lungs. Several studies have shown the feasibility of using magnetic resonance elastography (MRE) to quantify the lungs' shear stiffness. The aim of this study is to investigate the reproducibility and repeatability of lung MRE, and its shear stiffness measurements, obtained using a modified spin echo‐echo planar imaging (SE‐EPI) MRE sequence. In this study, 21 healthy volunteers were scanned twice by repositioning the volunteers to image right lung both at residual volume (RV) and total lung capacity (TLC) to assess the reproducibility of lung shear stiffness measurements. Additionally, 19 out of the 21 volunteers were scanned immediately without moving the volunteers to test the repeatability of the modified SE‐EPI MRE sequence. A paired t‐test was performed to determine the significant difference between stiffness measurements obtained at RV and TLC. Concordance correlation and Bland–Altman's analysis were performed to determine the reproducibility and repeatability of the SE‐EPI MRE‐derived shear stiffness measurements. The SE‐EPI MRE sequence is highly repeatable with a concordance correlation coefficient (CCC) of 0.95 at RV and 0.96 at TLC. Similarly, the stiffness measurements obtained across all volunteers were highly reproducible with a CCC of 0.95 at RV and 0.92 at TLC. The mean shear stiffness of the lung at RV was 0.93 ± 0.22 kPa and at TLC was 1.41 ± 0.41 kPa. TLC showed a significantly higher mean shear stiffness (P = 0.0004) compared with RV. Lung MRE stiffness measurements obtained using the SE‐EPI sequence were reproducible and repeatable, both at RV and TLC. Lung shear stiffness changes across respiratory cycle with significantly higher stiffness at TLC than RV.     

Simultaneous multislice rapid magnetic resonance elastography of the liver

To design and validate a rapid Simultaneous Multi‐slice (SMS) Magnetic Resonance Elastography technique (MRE), which combines SMS acquisition, in‐plane undersampling and an existing rapid Magnetic Resonance Elastography (MREr) scheme to allow accelerated data acquisition in healthy volunteers and comparison against MREr. SMS‐MREr sequence was developed by incorporating SMS acquisition scheme into an existing MREr sequence that accelerates MRE acquisition by acquiring data during opposite phases of mechanical vibrations. The MREr sequence accelerated MRE acquisition by acquiring data during opposite phases of mechanical vibrations. Liver MRE was performed on 23 healthy subjects using MREr and SMS‐MREr sequences, and mean stiffness values were obtained for manually drawn regions of interest. Linear correlation and agreement between MREr‐ and SMS‐MREr‐based stiffness values were investigated. SMS‐MREr reduced the scan time by half relative to MREr, and allowed acquisition of four‐slice MRE data in a single 17‐second breath‐hold. Visual comparison suggested agreement between MREr and SMS‐MREr elastograms. A Pearson's correlation of 0.93 was observed between stiffness values derived from MREr and SMS‐MREr. Bland–Altman analysis demonstrated good agreement, with ?0.08 kPa mean bias and narrow limits of agreement (95% CI: 0.23 to ?0.39 kPa) between stiffness values obtained using MREr and SMS‐MREr. SMS can be combined with other fast MRE approaches to achieve further acceleration. This pushes the limit on the acceleration that can be achieved in MRE acquisition, and makes it possible to conduct liver MRE exams in a single breath‐hold.     

Analysis and improvement of motion encoding in magnetic resonance elastography

Magnetic resonance elastography (MRE) utilizes phase contrast magnetic resonance imaging (MRI), which is phase locked to externally generated mechanical vibrations, to measure the three‐dimensional wave displacement field. At least four measurements with linear‐independent encoding directions are necessary to correct for spurious phase contributions if effects from imaging gradients are non‐negligible. In MRE, three encoding schemes have been used: unbalanced four‐ and six‐point and balanced four‐point (‘tetrahedral’) encoding. The first two sensitize to motion with orthogonal gradients, with the four‐point method acquiring a single reference scan without motion sensitization, whereas three additional scans with inverted gradients are used with six‐point encoding, leading to two‐fold higher displacement‐to‐noise ratio (DNR) and 50% longer scan duration. Balanced four‐point (tetrahedral) encoding encodes along the four diagonals of a cube, with one direction serving as a reference for the other three encoding directions, similar to four‐point encoding. The objective of this work is to introduce a theoretical framework to compare different motion sensitization strategies with respect to their motion encoding efficiency in two fundamental encoding limits, the gradient strength limit and the dynamic range limit, which are both placed in relation to conventional gradient recalled echo (GRE)‐ and spin echo (SE)‐based MRE sequences. We apply the framework to the three aforementioned schemes and show that the motion encoding efficiency of unbalanced four‐ and six‐point encoding schemes in the gradient‐limited regime can be increased by a factor of 1.5 when using all physical gradient channels concurrently. Furthermore, it is demonstrated that reversing the direction of the reference in balanced four‐point (tetrahedral) encoding results in the Hadamard encoding scheme, which leads to increased DNR by compared with balanced four‐point encoding and 2.8 compared with unbalanced four‐point encoding. As an example, we show that optimal encoding can be utilized to reduce the acquisition time of standard liver MRE in vivo from four to two breath holds.     

Magnetic resonance elastography‐derived stiffness of the kidneys and its correlation with water perfusion

Stiffness plays an important role in diagnosing renal fibrosis. However, kidney stiffness is altered by perfusion changes in many kidney diseases. Therefore, the aim of the current study is to determine the correlation of kidney stiffness with water intake. We hypothesize that kidney stiffness will increase with 1 L of water intake due to increased water perfusion to the kidneys. Additionally, stiffness of the kidneys will correlate with apparent diffusion coefficient (ADC) and fractional anisotropy (FA) values before and after water intake. A 3 T MRI scanner was used to perform magnetic resonance elastography and diffusion tensor imaging of the kidneys on 24 healthy subjects (age range: 22‐66 years) before and after water intake of 1 L. A 3D T1‐weighted bladder scan was also performed to measure bladder volume before and after water intake. A paired t‐test was performed to evaluate the effect of water intake on the stiffness of kidneys, in addition to bladder volume. A Spearman correlation test was performed to determine the association between stiffness, bladder volume, ADC and FA values of both kidneys before and after water intake. The results show a significant increase in stiffness in different regions of the kidney (ie, percentage increase ranged from 3.6% to 7.5%) and bladder volume after water intake (all P < 0.05). A moderate significant negative correlation was observed between change in kidney stiffness and bladder volume (concordance correlation coefficient = ‐0.468, P < 0.05). No significant correlation was observed between stiffness and ADC or FA values before and after water intake in both kidneys (P > 0.05). Water intake caused a significant increase in the stiffness of the kidneys. The negative correlation between the change in kidney stiffness and bladder volume, before and after water intake, indicates higher perfusion pressure in the kidneys, leading to increased stiffness.     

Three-dimensional analysis of shear wave propagation observed by in vivo magnetic resonance elastography of the brain

Dynamic magnetic resonance elastography (MRE) is a non-invasive method for the quantitative determination of the mechanical properties of soft tissues in vivo. In MRE, shear waves are generated in the tissue and visualized using phase-sensitive MR imaging methods. The resulting two-dimensional (2-D) wave images can reveal in-plane elastic properties when possible geometrical biases of the wave patterns are taken into account. In this study, 3-D MRE experiments of in vivo human brain are analyzed to gain knowledge about the direction of wave propagation and to deduce in-plane elastic properties. The direction of wave propagation was determined using a new algorithm which identifies minimal wave velocities along rays from the surface into the brain. It was possible to quantify biases of the elastic parameters due to projections onto coronal, sagittal and transversal image planes in 2-D MRE. It was found that the in-plane shear modulus is increasingly overestimated when the image slice is displaced from narrow slabs of 2-5cm through the center of the brain. The mean shear modulus of the brain was deduced from 4-D wave data with about 3.5kPa. Using the proposed slice positions in 2-D MRE, this shear modulus can be reproduced with an acceptable error within a fraction of the full 3-D examination time.     

Magnetic resonance elastography of the lumbar back muscles: A preliminary study

Back pain is associated with increased lumbar paraspinal muscle (LPM) stiffness identified by manual palpation and strain elastography. Recently, magnetic resonance elastography (MRE) has allowed the stiffness of muscle to be characterized noninvasively in vivo, providing quantitative 3D stiffness maps (elastograms). The aim of this study was to characterize the stiffness (shear modulus, SM) of the LPM (multifidus and erector spinae) using MRE. MRE of the lumbar region was performed on seven adults in supine position. MRE was acquired in three muscular states: relaxed with outstretched legs, stretched with passive pelvis flexion, and contracted with outstretched legs and tightened trunk muscles. The mean SM was measured within a region of interest manually defined in the multifidus, erector spinae, and the entire paraspinal compartment. The intermuscular difference and the effects of stretching and contraction were assessed by ANOVA and t‐tests. At rest, the mean SM of the paraspinal compartment was 1.6 ± 0.2 kPa. It increased significantly with stretching to 1.65 ± 0.3 kPa, and with contraction to 2.0 ± 0.7 kPa. Irrespective of muscular state, the erector spinae was significantly stiffer than the multifidus. The multifidus underwent proportionally higher stiffness changes from rest to contraction and stretching. MRE can be used to measure the stiffness of the LPM in different muscular states. We hypothesize that, irrespective of posture, the erector spinae behaves as semi‐rigid beam, and ensures permanent stiffness of the spine. The multifidus behaves as an adaptable muscle that provides segmental flexibility to the spine and tunes the spine stiffness. Clin. Anat. 31:514–520, 2018. © 2018 Wiley Periodicals, Inc.     

In vivo elasticity measurements of extremity skeletal muscle with MR elastography

MR elastography (MRE) has been shown to be capable of non-invasively measuring tissue elasticity even in deep-lying regions. Although limited studies have already been published examining in vivo muscle elasticity, it is still not clear over what range the in vivo elasticity values vary. The present study intends to produce further information by examining four different skeletal muscles in a group of 12 healthy volunteers in the age range of 27-38 years. The examinations were performed in the biceps brachii, the flexor digitorum profundus, the soleus and the gastrocnemius. The average shear modulus was determined to be 17.9 (+/- 5.5), 8.7 (+/- 2.8), 12.5 (+/- 7.3) and 9.9 (+/- 6.8) kPa for each muscle, respectively. To ascertain the reproducibility of the examination, the stiffness measurements in two volunteers were repeated seven times for the biceps brachii. These examinations yielded a mean shear modulus of 11.3 +/-.7 and 13.3 +/- 4.7 kPa for the two subjects. For elasticity reconstruction, an automated reconstruction algorithm is introduced which eliminates variation due to subjective manual image analysis. This study yields new information regarding the expected variation in muscle elasticity in a healthy population, and also reveals the expected variability of the MRE technique in skeletal muscle.     

磁共振弹性成像的初步实验研究

目的：研究磁共振弹性成像（MRE）技术。方法：研制外部激发装置，设计成像脉冲序列，制作模拟人体软组织的体模。激发装置由序列控制，于体模表面产生低频率剪切波。脉冲序列采用梯度回波序列，在x、y或z轴上施加运动敏感梯度（MSG）。剪切波导致的介质内的周期性移位可使接收信号产生周期性相位位移，从测得的相位位移就能计算出每个体素的移位值，直接显示介质内剪切波的传播。通过调整相位偏置，获得一个完整周期内剪切波的动态传播图像。相位图经局部频率估算法（LFE）处理后计算出量化的弹性模景图。实验采用浓度为1．0％和1．5％不同弹性的琼脂凝胶体模，激发频率分别采用150Hz、200Hz、250Hz和300Hz。结果：MRE的相位图显示了剪切波在体模内的传播，剪切波的波长随激发频率和体模弹性变化。波长与激发频率呈反比，与体模弹性呈正比。剪切波的波长在不同激发频率和不同浓度体模之间呈严格的比例关系。计算出的弹性模量图清楚显示了两种浓度介质的弹性对比。结论：MRE的相位图可显示剪切波在介质内的传播，弹性图可量化和显示介质的弹性模量。     

2型糖尿病患者海马体脑功能连接的磁共振成像研究

目的:应用功能磁共振成像技术研究2 型糖尿病（T2D）患者静息状态下海马功能连接的变化。方法:采集27 例 T2D患者和32例正常人的脑功能磁共振成像信号,选择海马的4个分区作为种子点计算功能连接,对海马与其他脑区的 功能连接强度与临床指标进行相关性分析。结果:与正常人相比,T2D患者的右前海马与梭状回、枕中回之间的功能连接 减弱;左前海马与梭状回功能连接增强;右后海马与距状回功能连接减弱;左后海马与舌回功能连接增强。结论:T2D患 者相关脑区功能连接的改变可能与视觉相关认知功能的损伤有关,这为理解T2D患者海马体的功能提供线索。     

Overhauser‐enhanced magnetic resonance elastography

Magnetic resonance elastography (MRE) is a powerful technique to assess the mechanical properties of living tissue. However, it suffers from reduced sensitivity in regions with short T₂ and T₂* such as in tissue with high concentrations of paramagnetic iron, or in regions surrounding implanted devices. In this work, we exploit the longer T₂* attainable at ultra‐low magnetic fields in combination with Overhauser dynamic nuclear polarization (DNP) to enable rapid MRE at 0.0065 T. A 3D balanced steady‐state free precession based MRE sequence with undersampling and fractional encoding was implemented on a 0.0065 T MRI scanner. A custom‐built RF coil for DNP and a programmable vibration system for elastography were developed. Displacement fields and stiffness maps were reconstructed from data recorded in a polyvinyl alcohol gel phantom loaded with stable nitroxide radicals. A DNP enhancement of 25 was achieved during the MRE sequence, allowing the acquisition of 3D Overhauser‐enhanced MRE (OMRE) images with (1.5 × 2.7 × 9) mm³ resolution over eight temporal steps and 11 slices in 6 minutes. In conclusion, OMRE at ultra‐low magnetic field can be used to detect mechanical waves over short acquisition times. This new modality shows promise to broaden the scope of conventional MRE applications, and may extend the utility of low‐cost, portable MRI systems to detect elasticity changes in patients with implanted devices or iron overload. Copyright © 2016 John Wiley & Sons, Ltd.     

Magnetic resonance imaging performed on a hydrated mummy of medieval Korea

Previous investigations have shown that magnetic resonance imaging (MRI) can be employed as an efficient non‐invasive diagnostic tool in studies on Egyptian mummies. MRI, moreover, because it produces especially clear images of well‐hydrated tissue, could be a particularly effective diagnostic option for mummies that still retain humidity within tissues or organs. Therefore, in the present study, we tested MRI on a 17th century mummy, one of the most perfectly preserved ‘hydrated mummies’ ever found in Korea, in order to determine the quality of images that could be obtained. We found that the diagnostic value of an MRI scan of the hydrated mummy was not inferior to that of a computed tomography scan. The T1‐ and T2‐weighted magnetic resonance (MR) signals showed unique patterns not easily obtained by computed tomography, the resultant MR images revealing the organ specificities clearly. Overall, the quality of the MR images from the hydrated mummy was superb and the scientific value of MRI in the study of hydrated mummies should not be underestimated.     

核磁共振图像引导的放疗技术进展

利用磁共振成像(MRI)进行图像引导放射治疗(简称:放疗)是近年来受到广泛关注并取得一定研究进展的新技术。该技术结合了MRI成像的优点,具有在线实时追踪肿瘤和临近危及器官以及实时优化放疗计划方案的功能。为了能对该技术的研究有全方位的认识和了解,对国际上在此方面开展的研究进展和动态有所掌握,本文对相关研究进行了综述和概括,以便于让该领域的研究者和医师对此技术的近况有所了解,并展开相应研究。本文就MRI的优点、核磁加速器的研究发展、剂量学相关研究进展和在线引导、自适应优化研究进展等方面进行综述,同时也探讨了这些技术今后可能的发展方向,期望本文综述能为临床医生和相关研究人员了解领域内的研究进展提供一定的参考。     

Cerebral multifrequency MR elastography by remote excitation of intracranial shear waves

The aim of this study was to introduce remote wave excitation for high‐resolution cerebral multifrequency MR elastography (mMRE). mMRE of 25–45‐Hz drive frequencies by head rocker stimulation was compared with mMRE by remote wave excitation based on a thorax mat in 12 healthy volunteers. Maps of the magnitude |G*| and phase φ of the complex shear modulus were reconstructed using multifrequency dual elasto‐visco (MDEV) inversion. After the scan, the subjects and three operators assessed the comfort and convenience of cerebral mMRE using two methods of stimulating the brain. Images were acquired in a coronal view in order to identify anatomical regions along the spinothalamic pathway. In mMRE by remote actuation, all subjects and operators appreciated an increased comfort and simplified procedural set‐up. The resulting strain amplitudes in the brain were sufficiently large to analyze using MDEV inversion, and yielded high‐resolution viscoelasticity maps which revealed specific anatomical details of brain mechanical properties: |G*| was lowest in the pons (0.97 ± 0.08 kPa) and decreased within the corticospinal tract in the caudal–cranial direction from the crus cerebri (1.64 ± 0.26 kPa) to the capsula interna (1.29 ± 0.14 kPa). By avoiding onerous mechanical stimulation of the head, remote excitation of intracranial shear waves can be used to measure viscoelastic parameters of the brain with high spatial resolution. Therewith, the new mMRE method is suitable for neuroradiological examinations in the clinic. Copyright © 2015 John Wiley & Sons, Ltd.     

Magnetic resonance thermometry of flowing blood

Blood temperature is a key determinant of tissue temperature and can be altered under normal physiological states, such as exercise, in diseases such as stroke or iatrogenically in therapies which modulate tissue temperature, such as therapeutic hypothermia. Currently available methods for the measurement of arterial and venous temperatures are invasive and, for small animal models, are impractical. Here, we present a methodology for the measurement of intravascular and tissue temperature by magnetic resonance imaging (MRI) using the lanthanide agent TmDOTMA^? (DOTMA, tetramethyl‐1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetic acid; Tm, thulium). The approach makes use of phase‐sensitive imaging measurements, combined with spectrally selective excitation, to monitor the temperature‐dependent shift in the resonance of proton nuclei associated with water and with methyl groups of TmDOTMA^?. Measurements were first made in a flow phantom modelling diastolic blood flow in the mouse aorta or inferior vena cava (IVC) and imaged using 7‐T preclinical MRI with a custom‐built surface coil. Flowing and static fluid temperatures agreed to within 0.12°C for these experiments. Proof‐of‐concept experiments were also performed on three healthy adult mice, demonstrating temperature measurements in the aorta, IVC and kidney following a bolus injection of contrast agent. A small (0.7–1°C), but statistically significant, higher kidney temperature compared with the aorta (p  = 0.002–0.007) and IVC (p  = 0.003–0.03) was shown in all animals. These findings demonstrate the feasibility of the technique for in vivo applications and illustrate how the technique could be used to explore the relationship between blood and tissue temperature for a wide range of applications.     

Reproducibility of whole‐brain temperature mapping and metabolite quantification using proton magnetic resonance spectroscopy

Assessing brain temperature can provide important information about disease processes (e.g., stroke, trauma) and therapeutic effects (e.g., cerebral hypothermia treatment). Whole‐brain magnetic resonance spectroscopic imaging (WB‐MRSI) is increasingly used to quantify brain metabolites across the entire brain. However, its feasibility and reliability for estimating brain temperature needs further validation. Therefore, the present study evaluates the reproducibility of WB‐MRSI for temperature mapping as well as metabolite quantification across the whole brain in healthy volunteers. Ten healthy adults were scanned on three occasions 1 week apart. Brain temperature, along with four commonly assessed brain metabolites—total N‐acetyl‐aspartate (tNAA), total creatine (tCr), total choline (tCho) and myo‐inositol (mI)—were measured from WB‐MRSI data. Reproducibility was evaluated using the coefficient of variation (CV). The measured mean (range) of the intra‐subject CVs was 0.9% (0.6%‐1.6%) for brain temperature mapping, and 4.7% (2.5%‐15.7%), 6.4% (2.4%‐18.9%) and 14.2% (4.4%‐52.6%) for tNAA, tCho and mI, respectively, with reference to tCr. Consistently larger variability was found when using H₂O as the reference for metabolite quantifications: 7.8% (3.3%‐17.8%), 7.8% (3.1%‐18.0%), 9.8% (3.7%‐31.0%) and 17.0% (5.9%‐54.0%) for tNAA, tCr, tCho and mI, respectively. Further, the larger the brain region (indicated by a greater number of voxels within that region), the better the reproducibility for both temperature and metabolite estimates. Our results demonstrate good reproducibility of whole‐brain temperature and metabolite measurements using the WB‐MRSI technique.