Off-resonance Saturation Pulse Research Articles

Advances in diffuse glioma assessment: preoperative and postoperative applications of chemical exchange saturation transfer.

Chemical Exchange Saturation Transfer (CEST) is a technique that uses specific off-resonance saturation pulses to pre-saturate targeted substances. This process influences the signal intensity of free water, thereby indirectly providing information about the pre-saturated substance. Among the clinical applications of CEST, Amide Proton Transfer (APT) is currently the most well-established. APT can be utilized for the preoperative grading of gliomas. Tumors with higher APTw signals generally indicate a higher likelihood of malignancy. In predicting preoperative molecular typing, APTw values are typically lower in tumors with favorable molecular phenotypes, such as isocitrate dehydrogenase (IDH) mutations, compared to IDH wild-type tumors. For differential diagnosis, the average APTw values of meningiomas are significantly lower than those of high-grade gliomas. Various APTw measurement indices assist in distinguishing central nervous system lesions with similar imaging features, such as progressive multifocal leukoencephalopathy, central nervous system lymphoma, solitary brain metastases, and glioblastoma. Regarding prognosis, APT effectively differentiates between tumor recurrence and treatment effects, and also possesses predictive capabilities for overall survival (OS) and progression-free survival (PFS).

-correction of magnetization transfer saturation maps optimized for 7T postmortem MRI of the brain.

Magnetization transfer saturation ( ) is a useful marker to probe tissue macromolecular content and myelination in the brain. The increased -inhomogeneity at T and significantly larger saturation pulse flip angles which are often used for postmortem studies exceed the limits where previous correction methods are applicable. Here, we develop a calibration-based correction model and procedure, and validate and evaluate it in postmortem 7T data of whole chimpanzee brains. The dependence of was investigated by varying the off-resonance saturation pulse flip angle. For the range of saturation pulse flip angles applied in typical experiments on postmortem tissue, the dependence was close to linear. A linear model with a single calibration constant is proposed to correct bias in by mapping it to the reference value of the saturation pulse flip angle. was estimated voxel-wise in five postmortem chimpanzee brains. "Individual-based global parameters" were obtained by calculating the mean within individual specimen brains and "group-based global parameters" by calculating the means of the individual-based global parameters across the five brains. The linear calibration model described the data well, though was not entirely independent of the underlying tissue and . Individual-based correction parameters and a group-based global correction parameter ( ) led to visible, quantifiable reductions of -biases in high-resolution maps. The presented model and calibration approach effectively corrects for inhomogeneities in postmortem 7T data.

Non-invasive monitoring of in vitro gastric milk protein digestion kinetics by 1H NMR magnetization transfer

Processing of milk involves heating, which can modify the structure and digestibility of its proteins. In vitro models are useful for studying protein digestion. However, validating these models with in vivo data is challenging. Here, we non-invasively monitor in vitro gastric milk protein digestion by protein-water chemical exchange detected by 1H nuclear magnetic resonance (NMR) magnetization transfer (MT). We obtained either a fitted composite exchange rate (CER) with a relative standard error of ≤10% or the MT ratio (MTR) of the intensity without or with an off-resonance saturation pulse, from just a single spectral acquisition. Both CER and MTR, affected by the variation in the amount of semi-solid protons, decreased during in vitro gastric digestion in agreement with standard protein content analyses. The decrease was slower in heated milk, indicating slower breakdown of the coagulum. Our results open the way to future quantification of protein digestion in vivo by MRI.

Magnetization transfer ratio: a quantitative imaging biomarker for 5q spinal muscular atrophy.

We quantified peripheral nerve lesions in adults with 5q-linked spinal muscular atrophy (SMA) type 3 by analysing the magnetization transfer ratio (MTR) of the sciatic nerve, and tested its potential as a novel biomarker for macromolecular changes. Eighteen adults with SMA 3 (50% SMA 3a, 50% SMA 3b) and 18 age-/sex-matched healthy controls prospectively underwent magnetization transfer contrast imaging in a 3-Tesla magnetic resonance scanner. Two axial three-dimensional gradient echo sequences, with and without an off-resonance saturation rapid frequency pulse, were performed at the right distal thigh. Sciatic nerve regions of interest were manually traced on 10 consecutive axial slices in the images generated without off-resonance saturation, and then transferred to corresponding slices generated by the sequence with the off-resonance saturation pulse. Subsequently, MTR and cross-sectional areas (CSAs) of the sciatic nerve were analysed. In addition, detailed neurologic, physiotherapeutic and electrophysiologic examinations were conducted in all patients. Sciatic nerve MTR and CSA reliably differentiated between healthy controls and SMA 3, 3a or 3b. MTR was lower in the SMA 3 (P<0.0001), SMA 3a (P<0.0001) and SMA 3b groups (P=0.0020) than in respective controls. In patients with SMA 3, MTR correlated with all clinical scores, and arm nerve compound motor action potentials (CMAPs). CSA was lower in the SMA 3 (P<0.0001), SMA 3a (P<0.0001) and SMA 3b groups (P=0.0006) than in controls, but did not correlate with clinical scores or electrophysiologic results. Magnetization transfer ratio is a novel imaging marker that quantifies macromolecular nerve changes in SMA 3, and positively correlates with clinical scores and CMAPs.

Magnetization Transfer Ratio in Peripheral Nerve Tissue: Does It Depend on Age or Location?

Magnetization transfer contrast imaging provides indirect information on the concentration of "bound" water protons and their interactions with "free" water molecules. The purpose of this study is to analyze location- and age-dependent changes in the magnetization transfer ratio (MTR) of lower extremity nerves. Ten younger (20-32 years) and 5 older (50-63 years) healthy volunteers underwent magnetization transfer contrast imaging at 3 Tesla Two 3-dimensional gradient echo sequences with and without an off-resonance saturation pulse (repetition time: 58 milliseconds; echo time: 2.46 milliseconds; band width: 530 Hz/Px; flip angle: α = 7°) were acquired at 3 different locations covering the proximal thigh to the distal lower leg in the group of younger volunteers and at 2 different locations covering the proximal to distal thigh in the group of older volunteers. Sciatic and tibial nerve regions of interest (ROIs) were manually drawn and additional ROIs were placed in predetermined muscles. Magnetization transfer ratios were extracted from respective ROIs and calculated for each individual and location. In young volunteers, mean values of nerve and muscle MTR were not different between the proximal thigh (nerve: 20.34 ± 0.91; muscle: 31.71 ± 0.29), distal thigh (nerve: 19.90 ± 0.98; P = 0.76; muscle: 31.53 ± 0.69; P = 0.87), and lower leg (nerve: 20.82 ± 1.07; P = 0.73; muscle: 32.44 ± 1.11; P = 0.51). An age-dependent decrease of sciatic nerve MTR was observed in the group of older volunteers (16.95 ± 1.2) compared with the group of younger volunteers (20.12 ± 0.65; P = 0.019). Differences in muscle MTR were not significant between older (31.01 ± 0.49) and younger (31.62 ± 0.37; P = 0.20) volunteers. The MTR of lower extremity nerves shows no proximal-to-distal gradient in young healthy volunteers but decreases with age. For future studies using MTR in peripheral nerve disorders, these findings suggest that referencing magnetization transfer contrast values in terms of age, but not anatomical nerve location is required.

MRI gradient-echo phase contrast of the brain at ultra-short TE with off-resonance saturation

Larmor-frequency shift or image phase measured by gradient-echo sequences has provided a new source of MRI contrast. This contrast is being used to study both the structure and function of the brain. So far, phase images of the brain have been largely obtained at long echo times as maximum phase signal-to-noise ratio (SNR) is achieved at TE = T2* (∼40 ms at 3T). The structures of the brain, however, are compartmentalized and complex with a wide range of signal relaxation times. At such long TE, the short-T2 components are largely attenuated and contribute minimally to phase contrast. The purpose of this study was to determine whether proton gradient-echo images of the brain exhibit phase contrast at ultra-short TE (UTE). Our data showed that UTE images acquired at 7 T without off-resonance saturation do not contain significant phase contrast between gray and white matter. However, UTE images of the brain can attain strong phase contrast even at a nominal TE of 106 μs by using off-resonance RF saturation pulses, which provide direct saturation of ultra-short-T2 components and indirect saturation of longer-T2 components via magnetization transfer. In addition, phase contrast between gray and white matter acquired at UTE with off-resonance saturation is reversed compared to that of the long-T2 signals acquired at long TEs. This finding opens up a potential new way to manipulate image phase contrast of the brain. By accessing short and ultra-short-T2 species, MRI phase images may further improve the characterization of tissue microstructure in the brain.

PRO-QUEST: a rapid assessment method based on progressive saturation for quantifying exchange rates using saturation times in CEST.

To develop a new MRI technique to rapidly measure exchange rates in CEST MRI. A novel pulse sequence for measuring chemical exchange rates through a progressive saturation recovery process, called PRO-QUEST (progressive saturation for quantifying exchange rates using saturation times), has been developed. Using this method, the water magnetization is sampled under non-steady-state conditions, and off-resonance saturation is interleaved with the acquisition of images obtained through a Look-Locker type of acquisition. A complete theoretical framework has been set up, and simple equations to obtain the exchange rates have been derived. A reduction of scan time from 58 to 16 minutes has been obtained using PRO-QUEST versus the standard QUEST. Maps of both T1 of water and B1 can simply be obtained by repetition of the sequence without off-resonance saturation pulses. Simulations and calculated exchange rates from experimental data using amino acids such as glutamate, glutamine, taurine, and alanine were compared and found to be in good agreement. The PRO-QUEST sequence was also applied on healthy and infarcted rats after 24 hours, and revealed that imaging specificity to ischemic acidification during stroke was substantially increased relative to standard amide proton transfer-weighted imaging. Because of the reduced scan time and insensitivity to nonchemical exchange factors such as direct water saturation, PRO-QUEST can serve as an excellent alternative for researchers and clinicians interested to map pH changes in vivo.

Abstract P4-02-08: Repeatability and reproducibility of quantitative breast MRI in community imaging centers: Preliminary results

Abstract Introduction: The primary purpose of this study is to evaluate the repeatability and reproducibility of quantitative breast MRI across community imaging centers with the ultimate goal of using these techniques to predict breast cancer response early in the course of neoadjuvant therapy (NAT). Dynamic contrast-enhanced MRI (DCE-MRI), diffusion-weighted MRI (DW-MRI), and magnetization transfer MRI (MT-MRI) performed early in the course of breast NAT has the potential to predict eventual response prior to changes in tumor size. This enables tailoring of treatment plans and the opportunity to substitute ineffective therapies with alternative approaches. We present preliminary results on the reproducibility and repeatability of T1, apparent diffusion coefficient (ADC), and magnetization transfer ratio (MTR) measurements in normal breast fibroglandular tissue (FGT) in the community setting. Experimental Design: MRI was performed at two community imaging centers and one academic research facility using 3T Siemens Skyra scanners equipped with 8- or 16-channel breast coils. To assess repeatability of the imaging techniques, normal subjects (N=10, ages 22-62) were scanned twice, separated by subject repositioning. To assess reproducibility across sites, normal subjects (N=3) were scanned at three imaging centers. To assess quantitative T1 measurements, subjects were scanned using a spoiled gradient echo (SPGE) sequence and variable flip angles (2, 4, 6, …, 20) with TR/TE = 7.9/2.71 ms and corrected for B1inhomogeneity. To assess the ADC, subjects were scanned using an echo-planar monopolar spin echo sequence with the following parameters: TR/TE = 3000/52 ms and b-values = 0, 200, 800 s/mm2. MT-MRI was acquired using two gradient echo sequences with TR/TE = 48.0/6.40 ms, one with the inclusion of a 1500 Hz off-resonance saturation pulse. FGT was segmented using k-means clustering. Women undergoing NAT for breast cancer are being recruited and scanned with DCE-MRI, DW-MRI, and MT-MRI at baseline (prior to beginning therapy) and three early time points during the course of NAT to evaluate early prediction of response to therapy. Results: Reproducibility scans of normal breast FGT yielded an average difference of 8.4% in T1 measurement, 7.0% in ADC measurement, and 12.7% in MTR measurement between sites. Repeatability scans of the same subject's FGT showed an average percent difference of 6.7% in T1 measurement, 4.5% in ADC measurement, and 11.6% in MTR measurement between the two scans. A multi-site trial performing quantitative DCE-MRI, DW-MRI, and MT-MRI in patients undergoing breast NAT in the community setting (N=16 at the time of submission) has been ongoing to predict response to NAT using quantitative MRI. Conclusion: Quantitative DCE-, DW-, and MT-MRI of the breast is both repeatable and reproducible across MRI scanners in community imaging centers. A quantitative breast MRI protocol can be deployed at community imaging centers for breast cancer patients. These results and ongoing work highlight the feasibility of future clinical dissemination of quantitative MRI for predicting early response to NAT, therefore expanding these novel techniques to a widespread patient population. We acknowledge the support of CPRIT RR160005. Citation Format: Sorace AG, Virostko J, Wu C, Jarrett AM, Barnes SL, Luci J, Patt DA, Goodgame B, Avery S, Yankeelov TE. Repeatability and reproducibility of quantitative breast MRI in community imaging centers: Preliminary results [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P4-02-08.

Magnetization transfer ratio for the assessment of perianal fistula activity in Crohn's disease.

Assessment of perianal fistulas is important to guide management of Crohn's disease (CD). Our objectives were to analyze the feasibility of magnetization transfer (MT) imaging to assess fistulas and to evaluate its contribution in assessing disease activity. During 15 months, all patients referred for perianal fistulas in CD underwent 3T-MRI including diffusion, T2/T1-weighted gadolinium-enhanced sequences and MT sequences (one with an off-resonance saturation pulse of 800 and one with 1200 Hz). We collected Van Assche score, fistula activity signs by analyzing T2, diffusion and contrast enhancement. We calculated MT ratio (MTR) with a ROI in the largest fistula. Twenty-nine patients (mean 34.9 years, range 17-53) were included. Van Assche score was 11.7, range 4-21. In 22 patients, the fistula presented with a bright T2 and diffusion signal with contrast enhancement, and was characterized as active. Mean MTR was respectively 47.2 (range 12-68) and 34.3 (range 11-57) at 800 and 1200 Hz. MTR at 800 Hz was significantly lower in non-active (34, range 12-55) than in active fistulas (51, range 24-68) (p < 0.02). MTR is feasible for the assessment of fistulas in CD and in the future could be used to help identify active and non-active fistulas. • MTR is feasible for the assessment of perianal fistulas in CD. • MT allows quantitative imaging of perianal fistula activity in CD. • MTR could be used to help identify active and non-active fistulas in CD.

Short‐term exercise‐induced changes in hydration state of healthy achilles tendons can be visualized by effects of off‐resonant radiofrequency saturation in a three‐dimensional ultrashort echo time MRI sequence applied at 3 tesla

Off-resonant RF saturation influences signal intensity dependent on free and bound water fractions as well as the macromolecular content. The extent of interaction between these compartments can be evaluated by using the off-resonance saturation ratio (OSR). Combined with UTE sequences quantification of OSR even in tendinous tissues with extremely fast signal decay is possible. The aim of this prospective study was to investigate short-term exercise-induced effects of hydration state of the Achilles tendon by means of OSR and tendon volume. Measurements of OSR and tendon volume before and after ankle-straining activity were performed in seven healthy male volunteers (median age 29 years) using a 3D UTE sequence with implemented off-resonance saturation pulse at 3T (off-resonance frequency 2/3 kHz) and by an automated contour detection in isotropic T2-weighted MR images with sub-millimeter resolution, respectively. Different tendon regions were evaluated. Reproducibility of OSR was measured in subsequent imaging sets. Root-mean-square-deviation (RMSD) and coefficient of variations (CV) were determined. RMSD of OSR in resting position were between 0.006 and 0.01 for different tendon regions and off-resonance frequencies (CV 2 to 3%). A significant increase (P < 0.05) of OSR after exercise was seen in all tendon regions except at the insertion (off-resonance frequency 3 kHz). Tendon volume was decreased significantly after ankle-straining activity (P = 0.003). The observed decreased tendon volume and increased OSR directly after exercise indicates a short-term change in tendinous proton compartments, most likely a loss of free water molecules within the tendon.

Ultrashort echo time MR imaging with off‐resonance saturation for characterization of pathologically altered Achilles tendons at 3 T

Off-resonance radiofrequency saturation pulses applied prior to regular excitation in MR sequences can be used to modify signal contrast based on magnetization transfer and direct saturation effects. Clinical applicability and value of ultrashort echo time sequences combined with off-resonance saturation pulses was tested in 16 healthy and 14 tendinopathic as well as paratendinopathic Achilles tendons in vivo at 3 T. A 3D ultrashort echo time sequence in combination with a gaussian off-resonance saturation pulse (frequency offset: 1000-5000 Hz) was used to modify the detectable MR signal intensity from the Achilles tendon. Off-resonance saturation ratio was calculated as the relative reduction in signal intensity under selective off-resonance saturation in relation to a reference measurement without any saturation pulse. Off-resonance saturation ratio in tendons of healthy volunteers ranged from 0.52 ± 0.06 (1000 Hz) to 0.24 ± 0.02 (5000 Hz), whereas symptomatic tendinopathic tendons (0.35 ± 0.04 to 0.17 ± 0.02) and asymptomatic tendinopathic tendons (0.41 ± 0.06 to 0.21 ± 0.02) showed significantly lower mean off-resonance saturation ratio values. Off-resonance saturation ratio values might provide a sensitive and quantitative marker for assessment of pathological microstructure alterations of the Achilles tendon.

Flow‐enhanced off‐resonance saturation for remote detection of iron‐based contrast agents

A switchable contrast mechanism, flow enhanced off-resonance saturation, is presented. This technique combines the effects of flow and off-resonance saturation for remote detection of iron oxide contrast agents incorporated into a vessel wall. Initial results from phantom experiments are presented and show the feasibility of this method. A specific saturation contrast could be observed. This contrast mechanism is highly dependent on field homogeneity and spectral selectivity of the off-resonance saturation pulses. The contrast scales directly with the pulse offset of the used saturation pulses, the flow velocity in the vessel, and the duration of the off-resonance saturation module prior to the imaging sequence. This technique has the potential to detect iron-loaded atherosclerotic plaques in future in vivo applications.

Ultrashort TE imaging with off‐resonance saturation contrast (UTE‐OSC)

Short T(2) species such as the Achilles tendon and cortical bone cannot be imaged with conventional MR sequences. They have a much broader absorption lineshape than long T(2) species, therefore they are more sensitive to an appropriately placed off-resonance irradiation. In this work, a technique termed ultrashort TE (UTE) with off-resonance saturation contrast (UTE-OSC) is proposed to image short T(2) species. A high power saturation pulse was placed +1 to +2 kHz off the water peak to preferentially saturate signals from short T(2) species, leaving long T(2) water and fat signals largely unaffected. The subtraction of UTE images with and without an off-resonance saturation pulse effectively suppresses long T(2) water and fat signals, creating high contrast for short T(2) species. The UTE-OSC technique was validated on a phantom, and applied to bone samples and healthy volunteers on a clinical 3T scanner. High-contrast images of the Achilles tendon and cortical bone were generated with a high contrast-to-noise ratio (CNR) of the order of 12 to 20 between short T(2) and long T(2) species within a total scan time of 4 to 10 min.

Improvement in the contrast of CEST MRI via intermolecular double quantum coherences

The tremendous potential of chemical exchange saturation transfer (CEST) agents as an emerging class of magnetic resonance imaging contrast media has been demonstrated in recent years. In a CEST experiment, a high CEST contrast is always welcome. However, when the exchange rate is low, which may happen in exchangeable solute protons of low concentration, it is usually hard to obtain an excellent CEST efficiency. Recently, we noted that the intermolecular multiple quantum coherence signal is more sensitive to the changes of the magnetization magnitude than a conventional single quantum coherence signal. Consequently, it may be easier when used in obtaining a CEST contrast. In this note, a modified COSY (two-dimensional correlated spectroscopy) revamped with an asymmetric Z-gradient echo detection (CRAZED) sequence combined with an off-resonance saturation pulse followed by a standard spin-echo imaging sequence was designed to obtain a better CEST contrast image based on the intermolecular double quantum coherence method. An analytical expression was derived from a dipolar field theory. Experiments were performed on an agar–glucose phantom, and the results demonstrate the feasibility of our method.

Equivalent cross‐relaxation rate imaging of axillary lymph nodes in breast cancer

To determine whether equivalent cross-relaxation rate (ECR) imaging (ECRI) is a feasible method for optimization of axillary lymph node dissection (ALND) and thereby improve quality-of-life (QOL). A total of 50 breast cancer patients underwent ECRI, with off-resonance saturation pulse at frequency offset of 5 ppm. ECR threshold values were determined to evaluate metastases to lymph nodes in the ALND group before examining the relationship between ECR value and cellular density. Metastases to lymph nodes of the sentinel lymph node biopsy (SLNB) group were evaluated based on the results of the ALND group. In the ALND group, regions without metastases showed a higher cellular density and ECR value than those with metastases. The relationship of ECR value to cellular density formed two clusters according to the presence or absence of metastasis; cellular density was related to ECR value for both clusters. In the SLNB group, supposing a threshold ECR value of 80%, sensitivity and specificity were 88.2% and 100%, respectively. ECRI is a potentially useful method for cellular density imaging of axillary lymph nodes. ECRI provides active information that enables ALND to be avoided, thus improving QOL.

Equivalent cross-relaxation rate imaging of breast cancer.

To determine whether equivalent cross-relaxation rate (ECR) imaging is a feasible method for demonstrating breast cancer. Fifteen breast cancer patients underwent both ECR imaging, with off-resonance saturation pulses at frequency offsets of 7 and 19 ppm (ECR-7 and ECR-19, respectively) from water resonance, and gadolinium (Gd)-enhanced dynamic magnetic resonance imaging (MRI) of the breast. The mean tumor size was 26.5 mm. The tumor outlines defined by their shape and margin on ECR-7 images were compared with the subtraction images produced by the dynamic study, and the distribution of hyperintensity areas and their shapes on ECR-19 images were assessed. All patients had surgery and pathological findings were compared to ECR images. The tumor outline of 13/15 (87%) tumors on ECR-7 images was nearly identical to that on subtraction images; ECR-19 images demonstrated the location and degree of fibrosis. The tumor outline of the other two tumors was less clear on ECR-7 images, and internal hyperintensity on ECR-19 images reflected intratumoral fibrotic foci. ECR-7 and -19 imaging findings allowed identification of four distinct tumor types that reflected the tumor growth patterns and their internal structures associated with fibrosis. ECR imaging is a feasible imaging technique for demonstrating breast cancer.

Equivalent cross-relaxation rate imaging in the synthetic copolymer gels and invasive ductal carcinomas of the breast

The values of equivalent cross-relaxation rate (ECR) correlated well with [i] water conditions in various copolymer gels and [ii] nature of malignant cells with regard to nuclear dysplasia and mitotic potential in breast carcinomas. The synthetic copolymer gels composed of any two or three monomers among 2-hydroxyethyl methacrylate (HEMA), glycidyl methacrylate (GMA), N-vinyl-2-pyrrolidinone (N-VP), methyl methacrylate (MMA) and benzyl methacrylate (BMA). The ECR measurement was performed by using an off-resonance saturation pulse under conventional field-echo imaging at frequency within ± 75 ppm apart from the water resonance frequency. The ECR values were readily to determine and non-time consuming parameter for cross relaxation rate. The ECR values at the frequency offset by 7-ppm (ECR-7) were divided the sample gels two classes, which must correspond to hydrophilic or hydrophobic ones. The sensitivity in the gels was nearly equivalent to the cross-relaxation rate itself. In the breast carcinomas, the ECR-7 correlates with the nature of malignant cells with regard to nuclear dysplasia and mitotic potential. The ECR-7 is better or more accurate than the STR-7 because the SDNRs between carcinoma and glandular tissue increased by approximately 50% on the ECR-7 compared with the STR-7. Thus the ECR values could be a new parameter for malignancy and cell proliferative activity of the breast carcinomas with non-invasive modalities by magnetic resonance imaging.

Saturation Transfer Ratio in Magnetic Resonance Imaging. A Novel Physical Parameter for Evaluation of the Hydrophilicity of Synthetic Copolymer Gels

It was first found that there is good correlation between saturation transfer ratio (STR) values in magnetic resonance imaging (MRI) measurement and the hydrophilicity of various synthetic copolymer gels containing 2-hydroxyethyl methacrylate (HEMA), glycidryl methacrylate (GMA), N-vinyl-2-pyrrolidinone (N-VP), and/or methyl methacrylate (MMA). The hydrophilicity of these copolymer gels was characterized by water contents evaluated by differential scanning calorimeter (DSC) and also the solubility parameter in theoretical sense. The MRI measurement was performed by conventional field-echo imaging as well as under the irradiation of an off-resonance saturation pulse apart by 75, 19, and 4ppm from a resonance point of water. The STR values offset at the 75-ppm correlated well with the total water contents in the samples. The values offset at the 19-ppm divided the samples into two classes corresponding to hydrophilic and hydrophobic gels. In the case of 4-ppm offset, the hydrophilic gels showed significantly higher STR values than the hydrophobic ones and the values among the hydrophilic gels were reflective to the constrained water content in the gel. Moreover the values correlated linearly with the solubility parameter of the samples. Thus the STR values in measurement of MRI could be adopted as a new useful parameter for molecular or material characterization of synthetic copolymers without any invasive processes.

Ethanol in Human Brain by Magnetic Resonance Spectroscopy: Correlation With Blood and Breath Levels, Relaxation, and Magnetization Transfer

Background: Proton magnetic resonance spectroscopy (1H MRS) allows measurement of alcohol in the human brain after alcohol consumption. However, the quantity of alcohol that can be detected in the brain by 1H MRS pulse sequences has been controversial, with values ranging from about 24% to 94% of the temporally concordant blood alcohol concentrations. The quantitation of brain alcohol is critically affected by the kinetics of alcohol uptake and elimination, by the relaxation times of the protons that give rise to the brain alcohol signal, and by the specifics of both pulse sequence timing and radio frequency pulse applications. Methods: We investigated these factors in 20 light-drinking subjects after oral administration of approximately 0.85 g/kg body weight of alcohol by localized 1H MRS and measurements of blood and breath alcohol concentrations obtained at the same time. Specifically, we measured transverse and longitudinal relaxation times of brain alcohol and its signal saturation on application of on- or off-resonance radio frequency pulses. All 1H MRS measurements were performed at a time after brain and blood alcohol concentrations had equilibrated. Results: 1H MRS measures of brain alcohol were correlated highly with both breath and blood alcohol concentrations after equilibration in brain tissue. The measured 1H MRS relaxation times of brain alcohol were shorter than given in previous reports that were limited by smaller subject numbers, improper use of 1H MRS methods, and estimates rather than measurements. The brain alcohol signal decreased by about 30% on application of on- or off-resonance saturation pulses. Conclusions: 1H MRS allows direct measurement of brain alcohol, formerly only possible indirectly through inferences from breath alcohol levels. Quantitation of brain alcohol levels need to take into account measured relaxation times and alcohol signal attenuation due to presence and timing of standard radio frequency MRS pulses. Saturation experiments give evidence for the existence of more than one compartment of brain alcohol characterized by different molecular environments. They suggest that a fraction of brain alcohol is invisible to 1H MRS.

Ethanol in Human Brain by Magnetic Resonance Spectroscopy: Correlation With Blood and Breath Levels, Relaxation, and Magnetization Transfer

Proton magnetic resonance spectroscopy (1H MRS) allows measurement of alcohol in the human brain after alcohol consumption. However, the quantity of alcohol that can be detected in the brain by 1H MRS pulse sequences has been controversial, with values ranging from about 24% to 94% of the temporally concordant blood alcohol concentrations. The quantitation of brain alcohol is critically affected by the kinetics of alcohol uptake and elimination, by the relaxation times of the protons that give rise to the brain alcohol signal, and by the specifics of both pulse sequence timing and radio frequency pulse applications. We investigated these factors in 20 light-drinking subjects after oral administration of approximately 0.85 g/kg body weight of alcohol by localized 1H MRS and measurements of blood and breath alcohol concentrations obtained at the same time. Specifically, we measured transverse and longitudinal relaxation times of brain alcohol and its signal saturation on application of on- or off-resonance radio frequency pulses. All 1H MRS measurements were performed at a time after brain and blood alcohol concentrations had equilibrated. 1H MRS measures of brain alcohol were correlated highly with both breath and blood alcohol concentrations after equilibration in brain tissue. The measured 1H MRS relaxation times of brain alcohol were shorter than given in previous reports that were limited by smaller subject numbers, improper use of 1H MRS methods, and estimates rather than measurements. The brain alcohol signal decreased by about 30% on application of on- or off-resonance saturation pulses. 1H MRS allows direct measurement of brain alcohol, formerly only possible indirectly through inferences from breath alcohol levels. Quantitation of brain alcohol levels need to take into account measured relaxation times and alcohol signal attenuation due to presence and timing of standard radio frequency MRS pulses. Saturation experiments give evidence for the existence of more than one compartment of brain alcohol characterized by different molecular environments. They suggest that a fraction of brain alcohol is invisible to 1H MRS.