TmDOTP5-: a substance for NMR temperature measurements in vivo

Autonomous animal heating and cooling system for temperature-regulated magnetic resonance experiments

Temperature is a hallmark parameter influencing almost all magnetic resonance properties (e.g., T1 , T2 , proton density, and diffusion). In the preclinical setting, temperature has a large influence on animal physiology (e.g., respiration rate, heart rate, metabolism, and oxidative stress) and needs to be carefully regulated, especially when the animal is under anesthesia and thermoregulation is disrupted. We present an open-source heating and cooling system capable of regulating the temperature of the animal. The system was designed using Peltier modules capable of heating or cooling a circulating water bath with active temperature feedback. Feedback was obtained using a commercial thermistor, placed in the animal rectum, and a proportional-integral-derivative controller was used to modulate the temperature. Its operation was demonstrated in a phantom as well as in mouse and rat animal models, where the standard deviation of the temperature of the animal upon convergence was less than a 10th of a degree. An application where brain temperature of a mouse was modulated was demonstrated using an invasive optical probe and noninvasive magnetic resonance spectroscopic thermometry measurements.

19 F VT NMR: Novel Tm3+ and Ce3+ Complexes Provide New Insight into Temperature Measurement Using Molecular Sensors

In the past few decades, magnetic resonance spectroscopy (MRS) and MR imaging (MRI) have developed into a powerful non-invasive tool for medical diagnostic and therapy. Especially 19 F MR shows promising potential because of the properties of the fluorine atom and the negligible background signals in the MR spectra. The detection of temperature in a living organism is quite difficult, and usually external thermometers or fibers are used. Temperature determination via MRS needs temperature-sensitive contrast agents. This article reports first results of solvent and structural influences on the temperature sensitivity of 19 F NMR signals of chosen molecules. By using this chemical shift sensitivity, a local temperature can be determined with a high precision. Based on this preliminary study, we synthesized five metal complexes and compared the results of all variable temperature measurements. It is shown that the highest 19 F MR signal temperature dependence is detectable for a fluorine nucleus in a Tm3+ -complex.

Lanthanide complexes with polyaminopolycarboxylates as prospective NMR/MRI diagnostic probes: peculiarities of molecular structure, dynamics and paramagnetic properties

The paramagnetic lanthanide complexes with polyaminopolycarboxylate (PAPC) ligands attract considerable attention from the standpoint of potential applications thereof as relaxation agents used in medical magnetic resonance imaging (MRI) and in luminescent materials, as well as owing to promising use thereof as paramagnetic labels for studying the properties of biopolymers since they exhibit thermodynamic stability, good solubility in aqueous media and moderate toxicity. For the last decades, the NMR methods have been used to determine the physical and chemical properties of paramagnetic Ln compounds. The studies concerning paramagnetic NMR lanthanide-induced shifts (LISs) in dissolved Ln complexes, as well as the analysis of band shape as a function of temperature make it possible to obtain valuable information on the structure, intra- and intermolecular dynamics and paramagnetic properties thereof. This review is devoted solely to the following features: firstly, the processes of intramolecular dynamics of lanthanide complexes with polyamino-polycarboxylate ligands such as DOTA, EDTA and DTPA and their derivatives studied by NMR; secondly, the LISs of lanthanide complexes with EDTA, DOTA, DTPA and some of their derivatives depending on temperature and pH. Moreover, in this review, for the first time, the dependence of the activation energy of molecular dynamics in complexes with polydentate ligands on the atomic number of the lanthanide cation is analyzed and a monotonic change in energy is detected, which is due to the effect of lanthanide contraction. It should be noted that this phenomenon is quite general and may also appear in the future in many other series of lanthanide complexes with both other multidentate ligands and with bidentate and monodentate ligands. In the future, it is possible to predict the dependence of the properties of certain lanthanide complexes on the ionic radius of the lanthanide cation based on the approaches presented in the review. In this review, we have also presented the dynamic NMR as the main research method widely used to analyze the processes of molecular dynamics, and the structural studies based on the NMR relaxation spectroscopy and LIS analysis.

Ligand Control of 59Co Nuclear Spin Relaxation Thermometry

Studying the correlation between temperature-driven molecular structure and nuclear spin dynamics is essential to understanding fundamental design principles for thermometric nuclear magnetic resonance spin-based probes. Herein, we study the impact of progressively encapsulating ligands on temperature-dependent ⁵⁹Co T ₁ (spin-lattice) and T ₂ (spin-spin) relaxation times in a set of Co(III) complexes: K₃[Co(CN)₆] (1); [Co(NH₃)₆]Cl₃ (2); [Co(en)₃]Cl₃ (3), en = ethylenediamine); [Co(tn)₃]Cl₃ (4), tn = trimethylenediamine); [Co(tame)₂]Cl₃ (5), tame = triaminomethylethane); and [Co(dinosar)]Cl₃ (6), dinosar = dinitrosarcophagine). Measurements indicate that ⁵⁹Co T ₁ and T ₂ increase with temperature for 1-6 between 10 and 60 °C, with the greatest ΔT ₁/ΔT and ΔT ₂/ΔT temperature sensitivities found for 4 and 3, 5.3(3)%T ₁/°C and 6(1)%T ₂/°C, respectively. Temperature-dependent T ₂* (dephasing time) analyses were also made, revealing the highest ΔT ₂*/ΔT sensitivities in structures of greatest encapsulation, as high as 4.64%T ₂*/°C for 6. Calculations of the temperature-dependent quadrupolar coupling parameter, Δe ² qQ/ΔT, enable insight into the origins of the relative ΔT ₁/ΔT values. These results suggest tunable quadrupolar coupling interactions as novel design principles for enhancing temperature sensitivity in nuclear spin-based probes.

Towards Photoswitchable Contrast Agents for Absolute 3D Temperature MR Imaging

Temperature can be used as clinical marker for tissue metabolism and the detection of inflammations or tumors. The use of magnetic resonance imaging (MRI) for monitoring physiological parameters like the temperature noninvasively is steadily increasing. In this study, we present a proof-of-principle study of MRI contrast agents (CA) for absolute and concentration independent temperature imaging. These CAs are based on azoimidazole substituted NiII porphyrins, which can undergo Light-Driven Coordination-Induced Spin State Switching (LD-CISSS) in solution. Monitoring the fast first order kinetic of back isomerisation (cis to trans) with standard clinical MR imaging sequences allows the determination of half-lives, that can be directly translated into absolute temperatures. Different temperature responsive CAs were successfully tested as prototypes in methanol-based gels and created temperature maps of gradient phantoms with high spatial resolution (0.13×0.13×1.1 mm) and low temperature errors (<0.22 °C). The method is sufficiently fast to record the temperature flow from a heat source as a film.

Paramagnetic Organocobalt Capsule Revealing Xenon Host-Guest Chemistry

We investigated Xe binding in a previously reported paramagnetic metal-organic tetrahedral capsule, [Co4L6]4-, where L2- = 4,4'-bis[(2-pyridinylmethylene)amino][1,1'-biphenyl]-2,2'-disulfonate. The Xe-inclusion complex, [XeCo4L6]4-, was confirmed by 1H NMR spectroscopy to be the dominant species in aqueous solution saturated with Xe gas. The measured Xe dissociation rate in [XeCo4L6]4-, koff = 4.45(5) × 102 s-1, was at least 40 times greater than that in the analogous [XeFe4L6]4- complex, highlighting the capability of metal-ligand interactions to tune the capsule size and guest permeability. The rapid exchange of 129Xe nuclei in [XeCo4L6]4- produced significant hyperpolarized 129Xe chemical exchange saturation transfer (hyper-CEST) NMR signal at 298 K, detected at a concentration of [XeCo4L6]4- as low as 100 pM, with presaturation at -89 ppm, which was referenced to solvated 129Xe in H2O. The saturation offset was highly temperature-dependent with a slope of -0.41(3) ppm/K, which is attributed to hyperfine interactions between the encapsulated 129Xe nucleus and electron spins on the four CoII centers. As such, [XeCo4L6]4- represents the first example of a paramagnetic hyper-CEST (paraHYPERCEST) sensor. Remarkably, the hyper-CEST 129Xe NMR resonance for [XeCo4L6]4- (δ = -89 ppm) was shifted 105 ppm upfield from the diamagnetic analogue [XeFe4L6]4- (δ = +16 ppm). The Xe inclusion complex was further characterized in the crystal structure of (C(NH2)3)4[Xe0.7Co4L6]·75 H2O (1). Hydrogen bonding between capsule-linker sulfonate groups and exogenous guanidinium cations, (C(NH2)3)+, stabilized capsule-capsule interactions in the solid state and also assisted in trapping a Xe atom (∼42 Å3) in the large (135 Å3) cavity of 1. Magnetic susceptibility measurements confirmed the presence of four noninteracting, magnetically anisotropic high-spin CoII centers in 1. Furthermore, [Co4L6]4- was found to be stable toward aggregation and oxidation, and the CEST performance of [XeCo4L6]4- was unaffected by biological macromolecules in H2O. These results recommend metal-organic capsules for fundamental investigations of Xe host-guest chemistry as well as applications with highly sensitive 129Xe-based sensors.

TmDOTP: An NMR-based thermometer for magic angle spinning NMR experiments

Solid state NMR is a powerful tool to probe membrane protein structure and dynamics in native lipid membranes. Sample heating during solid state NMR experiments can be caused by magic angle spinning and radio frequency irradiation such heating produces uncertainties in the sample temperature and temperature distribution, which can in turn lead to line broadening and sample deterioration. To measure sample temperatures in real time and to quantify thermal gradients and their dependence on radio frequency irradiation or spinning frequency, we use the chemical shift thermometer TmDOTP, a lanthanide complex. The H₆ TmDOTP proton NMR peak has a large chemical shift (-176.3 ppm at 275 K) and it is well resolved from the protein and lipid proton spectrum. Compared to other NMR thermometers (e.g., the proton NMR signal of water), the proton spectrum of TmDOTP, particularly the H₆ proton line, exhibits very high thermal sensitivity and resolution. In MAS studies of proteoliposomes we identify two populations of TmDOTP with differing temperatures and dependency on the radio frequency irradiation power. We interpret these populations as arising from the supernatant and the pellet, which is sedimented during sample spinning. In this study, we demonstrate that TmDOTP is an excellent internal standard for monitoring real-time temperatures of biopolymers without changing their properties or obscuring their spectra. Real time temperature calibration is expected to be important for the interpretation of dynamics and other properties of biopolymers.

Magnetic resonance thermometry and its biological applications - Physical principles and practical considerations

Most parameters that influence the magnetic resonance imaging (MRI) signal experience a temperature dependence. The fact that MRI can be used for non-invasive measurements of temperature and temperature change deep inside the human body has been known for over 30 years. Today, MR temperature imaging is widely used to monitor and evaluate thermal therapies such as radio frequency, microwave, laser, and focused ultrasound therapy. In this paper we cover the physical principles underlying the biological applications of MR temperature imaging and discuss practical considerations and remaining challenges. For biological tissue, the MR signal of interest comes mostly from hydrogen protons of water molecules but also from protons in, e.g., adipose tissue and various metabolites. Most of the discussed methods, such as those using the proton resonance frequency (PRF) shift, T₁, T₂, and diffusion only measure temperature change, but measurements of absolute temperatures are also possible using spectroscopic imaging methods (taking advantage of various metabolite signals as internal references) or various types of contrast agents. Currently, the PRF method is the most used clinically due to good sensitivity, excellent linearity with temperature, and because it is largely independent of tissue type. Because the PRF method does not work in adipose tissues, T₁- and T₂-based methods have recently gained interest for monitoring temperature change in areas with high fat content such as the breast and abdomen. Absolute temperature measurement methods using spectroscopic imaging and contrast agents often offer too low spatial and temporal resolution for accurate monitoring of ablative thermal procedures, but have shown great promise in monitoring the slower and usually less spatially localized temperature change observed during hyperthermia procedures. Much of the current research effort for ablative procedures is aimed at providing faster measurements, larger field-of-view coverage, simultaneous monitoring in aqueous and adipose tissues, and more motion-insensitive acquisitions for better precision measurements in organs such as the heart, liver, and kidneys. For hyperthermia applications, larger coverage, motion insensitivity, and simultaneous aqueous and adipose monitoring are also important, but great effort is also aimed at solving the problem of long-term field drift which gets interpreted as temperature change when using the PRF method.

Fe(ii) and Co(ii) N-methylated CYCLEN complexes as paraSHIFT agents with large temperature dependent shifts

Several complexes of Co(ii) or Fe(ii) with 1,4,7,10-tetraazacyclododecane (CYCLEN) appended with 1,7-(6-methyl)2-picolyl groups are studied as ¹H NMR paraSHIFT agents (paramagnetic shift agents) for the registration of temperature. Two of the complexes, [Co(BMPC)]²⁺ and [Fe(BMPC)]²⁺, contain methyl groups only on the methyl picolyl pendents. Two other complexes, [Co(2MPC)]²⁺ and [Fe(2MPC)]²⁺, contain picolyl groups and also methyl groups on the macrocyclic amines. All macrocyclic complexes are in high spin form as shown by solution magnetic moments in the range of 5.0-5.9μ_BM and 5.3-5.8μ_BM for Co(ii) and Fe(ii) complexes, respectively. The ¹H NMR spectra of both of the Fe(ii) complexes and one of the Co(ii) complexes are consistent with a predominant diastereomeric form in deuterium oxide solutions. The highly shifted methyl proton resonances for [Co(2MPC)]²⁺ appear at 164 and -113 ppm for macrocycle and pendent picolyl methyls and show temperature coefficients of -0.58 ppm °C^-1 and 0.49 ppm °C^-1, respectively. Fe(ii) complexes have less shifted methyl proton resonances and smaller temperature coefficients. The ¹H resonances of [Fe(2MPC)]²⁺ appear at 105 ppm and -46 ppm with corresponding temperature coefficients (CT) of -0.29 ppm °C^-1 and 0.22 ppm °C^-1, respectively. The relatively narrow linewidths of [Fe(2MPC)]²⁺, however, produce superior CT/FWHM values of 0.44 and 0.31 °C^-1 for the N-methyl and picolyl proton resonances where FWHM is the full width at half maximum of the ¹H resonance. The crystal structure of [Co(BMPC)]Cl₂ shows a six-coordinate Co(ii) bound to the macrocyclic amines and two pendent picolyl groups. The distorted trigonal prismatic geometry of the complex resembles that of an analogous complex containing four 6-methyl-2-picolyl groups, in which only two picolyl pendents are coordinated.

Brain Tumor Diagnostics and Therapeutics with Superparamagnetic Ferrite Nanoparticles

Ferrite nanoparticles (F-NPs) can transform both cancer diagnostics and therapeutics. Superparamagnetic F-NPs exhibit high magnetic moment and susceptibility such that in presence of a static magnetic field transverse relaxation rate of water protons for MRI contrast is augmented to locate F-NPs (i.e., diagnostics) and exposed to an alternating magnetic field local temperature is increased to induce tissue necrosis (i.e., thermotherapy). F-NPs are modified by chemical synthesis of mixed spinel ferrites as well as their size, shape, and coating. Purposely designed drug-containing nanoparticles (D-NPs) can slowly deliver drugs (i.e., chemotherapy). Convection-enhanced delivery (CED) of D-NPs with MRI guidance improves glioblastoma multiforme (GBM) treatment. MRI monitors the location of chemotherapy when D-NPs and F-NPs are coadministered with CED. However superparamagnetic field gradients produced by F-NPs complicate MRI readouts (spatial distortions) and MRS (extensive line broadening). Since extracellular pH (pHe) is a cancer hallmark, pHe imaging is needed to screen cancer treatments. Biosensor imaging of redundant deviation in shifts (BIRDS) extrapolates pHe from paramagnetically shifted signals and the pHe accuracy remains unaffected by F-NPs. Hence effect of both chemotherapy and thermotherapy can be monitored (by BIRDS), whereas location of F-NPs is revealed (by MRI). Smarter tethering of nanoparticles and agents will impact GBM theranostics.

Image-guided thermal ablation with MR-based thermometry

Thermal ablation techniques such as radiofrequency, microwave, high intensity focused ultrasound (HIFU) and laser have been used as minimally invasive strategies for the treatment of variety of cancers. MR thermometry methods are readily available for monitoring thermal distribution and deposition in real time, leading to decrease of incidents of normal tissue damage around targeted lesion. HIFU and laser-induced thermal therapy (LITT) are the two widely accepted tumor ablation techniques because of their compatibility with MR systems. MRI provides multiple temperature dependent parameters for thermal imaging, such as signal intensity, T1, T2, diffusion coefficient, magnetization transfer, proton resonance frequency shift (PRFS, including phase imaging and spectroscopy) as well as frequency shift of temperature sensitive contrast agents. Absolute temperature mapping techniques, including both spectroscopic imaging using metabolites as a reference and phase imaging using fat as a reference, are immune to susceptibility effects and are not dependent on phase differences. These techniques are intrinsically more reliable than relative temperature measurement by phase mapping methods. If the limitation of low temporal and spatial resolution could be overcome, these methods may be preferred for MR-guided thermal ablation systems. As of today, the most popular MR thermal imaging method applied in tumor thermal ablation surgery is, however, still PRFS based phase mapping technique, which only provides relative temperature change and is prone to motion artifacts.

Spin-crossover and high-spin iron(ii) complexes as chemical shift 19F magnetic resonance thermometers

The potential utility of paramagnetic transition metal complexes as chemical shift 19F magnetic resonance (MR) thermometers is demonstrated. Further, spin-crossover FeII complexes are shown to provide much higher temperature sensitivity than do the high-spin analogues, owing to the variation of spin state with temperature in the former complexes. This approach is illustrated through a series of FeII complexes supported by symmetrically and asymmetrically substituted 1,4,7-triazacyclononane ligand scaffolds bearing 3-fluoro-2-picolyl derivatives as pendent groups (L x ). Variable-temperature magnetic susceptibility measurements, in conjunction with UV-vis and NMR data, show thermally-induced spin-crossover for [Fe(L1)]2+ in H2O, with T1/2 = 52(1) °C. Conversely, [Fe(L2)]2+ remains high-spin in the temperature range 4-61 °C. Variable-temperature 19F NMR spectra reveal the chemical shifts of the complexes to exhibit a linear temperature dependence, with the two peaks of the spin-crossover complex providing temperature sensitivities of +0.52(1) and +0.45(1) ppm per °C in H2O. These values represent more than two-fold higher sensitivity than that afforded by the high-spin analogue, and ca. 40-fold higher sensitivity than diamagnetic perfluorocarbon-based thermometers. Finally, these complexes exhibit excellent stability in a physiological environment, as evidenced by 19F NMR spectra collected in fetal bovine serum.

Heating and temperature gradients of lipid bilayer samples induced by RF irradiation in MAS solid-state NMR experiments

The MAS solid-state NMR has been a powerful technique for studying membrane proteins within the native-like lipid bilayer environment. In general, RF irradiation in MAS NMR experiments can heat and potentially destroy expensive membrane protein samples. However, under practical MAS NMR experimental conditions, detailed characterization of RF heating effect of lipid bilayer samples is still lacking. Herein, using ¹ H chemical shift of water for temperature calibration, we systematically study the dependence of RF heating on hydration levels and salt concentrations of three lipids in MAS NMR experiments. Under practical ¹ H decoupling conditions used in biological MAS NMR experiments, three lipids show different dependence of RF heating on hydration levels as well as salt concentrations, which are closely associated with the properties of lipids. The maximum temperature elevation of about 10 °C is similar for the three lipids containing 200% hydration, which is much lower than that in static solid-state NMR experiments. The RF heating due to salt is observed to be less than that due to hydration, with a maximum temperature elevation of less than 4 °C in the hydrated samples containing 120 mmol l^-1 of salt. Upon RF irradiation, the temperature gradient across the sample is observed to be greatly increased up to 20 °C, as demonstrated by the remarkable broadening of ¹ H signal of water. Based on detailed characterization of RF heating effect, we demonstrate that RF heating and temperature gradient can be significantly reduced by decreasing the hydration levels of lipid bilayer samples from 200% to 30%. Copyright © 2016 John Wiley & Sons, Ltd.

(13) C-TmDOTA as versatile thermometer compound for solid-state NMR of hydrated lipid bilayer membranes

Recent advances in solid-state nuclear magnetic resonance (NMR) techniques, such as magic angle spinning and high-power decoupling, have dramatically increased the sensitivity and resolution of NMR. However, these NMR techniques generate extra heat, causing a temperature difference between the sample in the rotor and the variable temperature gas. This extra heating is a particularly crucial problem for hydrated lipid membrane samples. Thus, to develop an NMR thermometer that is suitable for hydrated lipid samples, thulium-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate (TmDOTA) was synthesized and labeled with (13) C (i.e., (13) C-TmDOTA) to increase the NMR sensitivity. The complex was mixed with a hydrated lipid membrane, and the system was subjected to solid-state NMR and differential scanning calorimetric analyses. The physical properties of the lipid bilayer and the quality of the NMR spectra of the membrane were negligibly affected by the presence of (13) C-TmDOTA, and the (13) C chemical shift of the complex exhibited a large-temperature dependence. The results demonstrated that (13) C-TmDOTA could be successfully used as a thermometer to accurately monitor temperature changes induced by (1) H decoupling pulses and/or by magic angle spinning and the temperature distribution of the sample inside the rotor. Thus, (13) C-TmDOTA was shown to be a versatile thermometer for hydrated lipid assemblies. Copyright © 2015 John Wiley & Sons, Ltd.

A new paramagnetically shifted imaging probe for MRI

PURPOSE

To develop and characterize a new paramagnetic contrast agent for molecular imaging by MRI.

METHODS

A contrast agent was developed for direct MRI detection through the paramagnetically shifted proton magnetic resonances of two chemically equivalent tert-butyl reporter groups within a dysprosium(III) complex. The complex was characterized in phantoms and imaged in physiologically intact mice at 7 Tesla (T) using three-dimensional (3D) gradient echo and spectroscopic imaging (MRSI) sequences to measure spatial distribution and signal frequency.

RESULTS

The reporter protons reside ∼6.5 Å from the paramagnetic center, resulting in fast T₁ relaxation (T₁  = 8 ms) and a large paramagnetic frequency shift exceeding 60 ppm. Fast relaxation allowed short scan repetition times with high excitation flip angle, resulting in high sensitivity. The large dipolar shift allowed direct frequency selective excitation and acquisition of the dysprosium(III) complex, independent of the tissue water signal. The biokinetics of the complex were followed in vivo with a temporal resolution of 62 s following a single, low-dose intravenous injection. The lower concentration limit for detection was ∼23 μM. Through MRSI, the temperature dependence of the paramagnetic shift (0.28 ppm.K^-1 ) was exploited to examine tissue temperature variation.

CONCLUSIONS

These data demonstrate a new MRI agent with the potential for physiological monitoring by MRI. Magn Reson Med 77:1307-1317, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Six-coordinate Iron(II) and Cobalt(II) paraSHIFT Agents for Measuring Temperature by Magnetic Resonance Spectroscopy

Paramagnetic Fe(II) and Co(II) complexes are utilized as the first transition metal examples of (1)H NMR shift agents (paraSHIFT) for thermometry applications using Magnetic Resonance Spectroscopy (MRS). The coordinating ligands consist of TACN (1,4,7-triazacyclononane) and CYCLEN (1,4,7,10-tetraazacyclododecane) azamacrocycles appended with 6-methyl-2-picolyl groups, denoted as MPT and TMPC, respectively. (1)H NMR spectra of the MPT- and TMPC-based Fe(II) and Co(II) complexes demonstrate narrow and highly shifted resonances that are dispersed as broadly as 440 ppm. The six-coordinate complex cations, [M(MPT)](2+) and [M(TMPC)](2+), vary from distorted octahedral to distorted trigonal prismatic geometries, respectively, and also demonstrate that 6-methyl-2-picolyl pendents control the rigidity of these complexes. Analyses of the (1)H NMR chemical shifts, integrated intensities, line widths, the distances obtained from X-ray diffraction measurements, and longitudinal relaxation time (T1) values allow for the partial assignment of proton resonances of the [M(MPT)](2+) complexes. Nine and six equivalent methyl protons of [M(MPT)](2+) and [M(TMPC)](2+), respectively, produce 3-fold higher (1)H NMR intensities compared to other paramagnetically shifted proton resonances. Among all four complexes, the methyl proton resonances of [Fe(TMPC)](2+) and [Co(TMPC)](2+) at -49.3 ppm and -113.7 ppm (37 °C) demonstrate the greatest temperature dependent coefficients (CT) of 0.23 ppm/°C and 0.52 ppm/°C, respectively. The methyl groups of these two complexes both produce normalized values of |CT|/fwhm = 0.30 °C(-1), where fwhm is full width at half-maximum (Hz) of proton resonances. The T1 values of the highly shifted methyl protons are in the range of 0.37-2.4 ms, allowing rapid acquisition of spectroscopic data. These complexes are kinetically inert over a wide range of pH values (5.6-8.6), as well as in the presence of serum albumin and biologically relevant cations and anions. The combination of large hyperfine shifts, large temperature sensitivity, increased signal-to-noise ratio, and short T1 values suggests that these complexes, in particular the TMPC-based complexes, show promise as paraSHIFT agents for thermometry.

Heat management strategies for solid-state NMR of functional proteins

Modern solid-state NMR methods can acquire high-resolution protein spectra for structure determination. However, these methods use rapid sample spinning and intense decoupling fields that can heat and denature the protein being studied. Here we present a strategy to avoid destroying valuable samples. We advocate first creating a sacrificial sample, which contains unlabeled protein (or no protein) in buffer conditions similar to the intended sample. This sample is then doped with the chemical shift thermometer Sm2Sn2O7. We introduce a pulse scheme called TCUP (for Temperature Calibration Under Pulseload) that can characterize the heating of this sacrificial sample rapidly, under a variety of experimental conditions, and with high temporal resolution. Sample heating is discussed with respect to different instrumental variables such as spinning speed, decoupling strength and duration, and cooling gas flow rate. The effects of different sample preparation variables are also discussed, including ionic strength, the inclusion of cryoprotectants, and the physical state of the sample (i.e. liquid, solid, or slurry). Lastly, we discuss probe detuning as a measure of sample thawing that does not require retuning the probe or using chemical shift thermometer compounds. Use of detuning tests and chemical shift thermometers with representative sample conditions makes it possible to maximize the efficiency of the NMR experiment while retaining a functional sample.

A lanthanide complex with dual biosensing properties: CEST (chemical exchange saturation transfer) and BIRDS (biosensor imaging of redundant deviation in shifts) with europium DOTA-tetraglycinate

Responsive contrast agents (RCAs) composed of lanthanide(III) ion (Ln3R) complexes with a variety of1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate (DOTA4S) derivatives have shown great potential as molecular imaging agents for MR. A variety of LnDOTA–tetraamide complexes have been demonstrated as RCAs for molecular imaging using chemical exchange saturation transfer (CEST). The CEST method detects proton exchange between bulk water and any exchangeable sites on the ligand itself or an inner sphere of bound water that is shifted by a paramagnetic Ln3R ion bound in the core of the macrocycle. It has also been shown that molecular imaging is possible when the RCA itself is observed (i.e. not its effect on bulk water) using a method called biosensor imaging of redundant deviation in shifts (BIRDS). The BIRDS method utilizes redundant information stored in the nonexchangeable proton resonances emanating from the paramagnetic RCA for ambient factors such as temperature and/or pH.Thus, CEST and BIRDS rely on exchangeable and nonexchangeable protons, respectively, for biosensing. We posited that it would be feasible to combine these two biosensing features into the same RCA (i.e. dual CEST and BIRDS properties). A complex between europium(III) ion (Eu3R) and DOTA–tetraglycinate [DOTA–(gly)S4] was used to demonstrate that its CEST characteristics are preserved, while its BIRDS properties are also detectable. The in vitro temperature sensitivity of EuDOTA–(gly)S4 was used to show that qualitative MR contrast with CEST can be calibrated using quantitative MR mapping with BIRDS, thereby enabling quantitative molecular imaging at high spatial resolution.

Brain temperature by Biosensor Imaging of Redundant Deviation in Shifts (BIRDS): comparison between TmDOTP5- and TmDOTMA-

Chemical shifts of complexes between paramagnetic lanthanide ions and macrocyclic chelates are sensitive to physiological variations (of temperature and/or pH). Here we demonstrate utility of a complex between thulium ion (Tm(3+)) and the macrocyclic chelate 1,4,7,10-tetramethyl 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate (or DOTMA(4-)) for absolute temperature mapping in rat brain. The feasibility of TmDOTMA(-) is compared with that of another Tm(3+)-containing biosensor which is based on the macrocyclic chelate 1,4,7,10-tetraazacyclododecane- 1,4,7,10-tetrakis(methylene phosphonate) (or DOTP(8-)). In general, the in vitro and in vivo results suggest that Biosensor Imaging of Redundant Deviation in Shifts (BIRDS) which originate from these agents (but exclude water) can provide temperature maps with good accuracy. While TmDOTP(5-) emanates three major distinct proton resonances which are differentially sensitive to temperature and pH, TmDOTMA(-) has a dominant pH-insensitive proton resonance from a -CH(3) group to allow higher signal-to-noise ratio (SNR) temperature assessment. Temperature (and pH) sensitivities of these resonances are practically identical at low (4.0T) and high (11.7T) magnetic fields and at nominal repetition times only marginal SNR loss is expected at the lower field. Since these resonances have extremely short relaxation times, high-speed chemical shift imaging (CSI) is needed to detect them. Repeated in vivo CSI scans with BIRDS demonstrate excellent measurement stability. Overall, results with TmDOTP(5-) and TmDOTMA(-) suggest that BIRDS can be reliably applied, either at low or high magnetic fields, for functional studies in rodents.

Absolute temperature MR imaging with thulium 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetramethyl-1,4,7,10-tetraacetic acid (TmDOTMA-)

MR thermometry based on the water (1)H signal provides high temporal and spatial resolution, but it has low temperature sensitivity (approximately 0.01 ppm/degrees C) and requires monitoring of another weaker signal for absolute temperature measurements. The use of the paramagnetic lanthanide complex, thulium 1,4,7,10- tetraazacyclododecane-1,4,7,10-tetramethyl-1,4,7,10-tetraacetate (TmDOTMA(-)), which is approximately 60 times more sensitive to temperature than the water (1)H signal, is advanced to image absolute temperatures in vivo using water signal as a reference. The temperature imaging technique was developed using gradient echo and asymmetric spin echo imaging sequences on 9.4 Tesla (T) horizontal and vertical MR scanners. A comparison of regional temperatures measured with TmDOTMA(-) and fiber-optic probes showed that the accuracy of imaging temperature is <0.3 degrees C. The temperature imaging technique was found to be insensitive to inhomogeneities in the main magnetic field. The feasibility of imaging temperature of intact rats at approximately 1.4 mmol/kg dose with approximately 1-mm spatial resolution in only 3 min is demonstrated. TmDOTMA(-) should prove useful for imaging absolute temperatures in deep-seated organs in numerous biomedical applications.

Non-invasive MR thermography using the water proton chemical shift

Among various proton magnetic resonance (MR) parameters, such as longitudinal relaxation time, transverse relaxation time, diffusion coefficient and chemical shift, the chemical shift of water protons is recognized as the most reliable indicator of temperature. The chemical shift is the only frequency-based parameter and is independent of the other parameters, which are measured based on the intensity of the MR signal. In this paper, the basic principle and the recent progress in imaging temperature by spectroscopic techniques using the water proton chemical shift are discussed. The advantages of spectroscopic imaging over phase mapping for measuring temperature are that the former can distinguish water resonance from other resonances, and that another resonance can be used as an internal reference to reduce the effects of external magnetic field instability, tissue susceptibility and inter-scan tissue movement or deformation. Methods utilizing various magnetic resonance spectroscopy (MRS) techniques, such as single voxel spectroscopy, conventional magnetic resonance spectroscopic imaging (MRSI), echo planar spectroscopic imaging (EPSI) and line scan echo planar spectroscopic imaging (LSEPSI) are discussed.

Improved calibration technique for in vivo proton MRS thermometry for brain temperature measurement

The most common MR-based approach to noninvasively measure brain temperature relies on the linear relationship between the (1)H MR resonance frequency of tissue water and the tissue's temperature. Herein we provide the most accurate in vivo assessment existing thus far of such a relationship. It was derived by acquiring in vivo MR spectra from a rat brain using a high field (11.74 Tesla [T]) MRI scanner and a single-voxel MR spectroscopy technique based on a LASER pulse sequence. Data were analyzed using three different methods to estimate the (1)H resonance frequencies of water and the metabolites NAA, Cho, and Cr, which are used as temperature-independent internal (frequency) references. Standard modeling of frequency-domain data as composed of resonances characterized by Lorentzian line shapes gave the tightest resonance-frequency versus temperature correlation. An analysis of the uncertainty in temperature estimation has shown that the major limiting factor is an error in estimating the metabolite frequency. For example, for a metabolite resonance linewidth of 8 Hz, signal sampling rate of 2 Hz and SNR of 5, an accuracy of approximately 0.5 degrees C can be achieved at a magnetic field of 3T. For comparison, in the current study conducted at 11.74T, the temperature estimation error was approximately 0.1 degrees C.

Brain temperature and pH measured by (1)H chemical shift imaging of a thulium agent

Temperature and pH are two of the most important physiological parameters and are believed to be tightly regulated because they are intricately related to energy metabolism in living organisms. Temperature and/or pH data in mammalian brain are scarce, however, mainly because of lack of precise and non-invasive methods. At 11.7 T, we demonstrate that a thulium-based macrocyclic complex infused through the bloodstream can be used to obtain temperature and pH maps of rat brain in vivo by (1)H chemical shift imaging (CSI) of the sensor itself in conjunction with a multi-parametric model that depends on several proton resonances of the sensor. Accuracies of temperature and pH determination with the thulium sensor - which has a predominantly extracellular presence - depend on stable signals during the course of the CSI experiment as well as redundancy for temperature and pH sensitivities contained within the observed signals. The thulium-based method compared well with other methods for temperature ((1)H MRS of N-acetylaspartate and water; copper-constantan thermocouple wire) and pH ((31)P MRS of inorganic phosphate and phosphocreatine) assessment, as established by in vitro and in vivo studies. In vitro studies in phantoms with two compartments of different pH value observed under different ambient temperature conditions generated precise temperature and pH distribution maps. In vivo studies in alpha-chloralose-anesthetized and renal-ligated rats revealed temperature (33-34 degrees C) and pH (7.3-7.4) distributions in the cerebral cortex that are in agreement with observations by other methods. These results show that the thulium sensor can be used to measure temperature and pH distributions in rat brain in vivo simultaneously and accurately using Biosensor Imaging of Redundant Deviation in Shifts (BIRDS).

An efficient (1)H/(31)P double-resonance solid-state NMR probe that utilizes a scroll coil

The construction and performance of a scroll coil double-resonance probe for solid-state NMR on stationary samples is described. The advantages of the scroll coil at the high resonance frequencies of (1)H and (31)P include: high efficiency, minimal perturbations of tuning by a wide range of samples, minimal RF sample heating of high dielectric samples of biopolymers in aqueous solution, and excellent RF homogeneity. The incorporation of a cable tie cinch for mechanical stability of the scroll coil is described. Experimental results obtained on a Hunter Killer Peptide 1 (HKP1) interacting with phospholipid bilayers of varying lipid composition demonstrate the capabilities of this probe on lossy aqueous samples.

Magnetic resonance temperature imaging for focused ultrasound surgery: a review

Magnetic resonance temperature imaging (MRTI) is an enabling technology that has recently demonstrated the potential to bring the emerging minimally invasive image-guided thermal therapy procedures, such as radiofrequency, microwave, laser, ultrasound, and cryosurgery, into the clinical setting with a level of safety and efficacy not previously possible. By coupling the wealth of soft tissue contrast mechanisms available with magnetic resonance imaging with its intrinsic temperature sensitivity, magnetic resonance imaging is in a unique position to provide image-guided treatment planning and verification and quantitative or qualitative feedback during treatment delivery, heightening of the control the physician has over the method, and enhancement of the ability to deliver conformal treatments. The basic principles behind MRTI technology and its application to minimally invasive thermal therapy during ultrasound thermal therapy delivery are reviewed in this study.

Non-invasive temperature imaging with thulium 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetramethyl-1,4,7,10-tetraacetic acid (TmDOTMA-)

Non-invasive thermometry using hyperfine-shifted MR signals from paramagnetic lanthanide complexes has attracted attention recently because the chemical shifts of these complexes are many times more sensitive to temperature than the water 1H signal. Among all the lanthanide complexes examined thus far, thulium tetramethyl-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate (TmDOTMA-) appears to be the most suitable for MR thermometry. In this paper, the feasibility of imaging the methyl 1H signal from TmDOTMA- using a frequency-selective radiofrequency excitation pulse and chemical shift-selective (CHESS) water suppression is demonstrated. A temperature imaging method using a phase-sensitive spin-echo imaging sequence was validated in phantom experiments. A comparison of regional temperature changes measured with fiber-optic probes and the temperatures calculated from the phase shift near each probe showed that the accuracy of imaging the temperature with TmDOTMA- is at least 0.1-0.2 degrees C. The feasibility of imaging temperature changes in an intact rat at 0.5-0.6 mmol/kg dose in only a few minutes is demonstrated. Similar to commonly used MRI contrast agents, the lanthanide complex does not cross the blood-brain barrier. TmDOTMA- may prove useful for temperature imaging in many biomedical applications but further studies relating to acceptable dose and signal-to-noise ratio are necessary before clinical applications.

Noninvasive thermometry using hyperfine-shifted MR signals from paramagnetic lanthanide complexes

MR thermometry techniques based on the strong water 1H signal provide high spatial and temporal resolution and have shown promise for applications such as laser surgery and RF ablation. However, these techniques have low temperature sensitivity for hyperthermia applications and are greatly influenced by local motion and susceptibility variations. 1H NMR signals from paramagnetic lanthanide complexes of Pr3+, Yb3+ and Tm3+ show up to 300-fold stronger temperature dependence compared to the water 1H signal. In addition, 1H chemical shifts of many of these complexes are insensitive to other factors such as the concentration of the paramagnetic complex, pH, [Ca2+], and the presence of plasma macro-molecules and ions. Applications of lanthanide complexes for temperature measurement in intact animals and the feasibility of mapping temperatures in phantoms have been demonstrated. Among all the lanthanide complexes examined so far, thulium 1, 4, 7, 10-tetramethyl-1, 4, 7, 10-tetraazacyclododecane-1, 4, 7, 10-tetraacetate (TmDOTMA-) appears to be the most attractive for in vivo MR thermometry. The 1H signal from the methyl groups on this complex is relatively intense because of 12 equivalent protons and provides high temperature sensitivity because of the large paramagnetic shifts induced by thulium. The possibility of imaging TmDOTMA2--in intact animals at physiologically safe concentrations has recently been demonstrated. Overall, MR thermometry methods based on hyperfine-shifted MR signals from paramagnetic lanthanide complexes appear promising for animal applications, but further studies relating to acceptable dose and signal-to-noise ratio are necessary before clinical use.

Noninvasive MR thermometry using paramagnetic lanthanide complexes of 1,4,7,10-tetraazacyclodoecane-?,??,??,??-tetramethyl-1,4,7,10-tetraacetic acid (DOTMA4-)

Noninvasive techniques to monitor temperature have numerous useful biomedical applications. However, MR thermometry techniques based on the chemical shift, relaxation rates, and molecular diffusion rate of the water 1H signal suffer from poor thermal resolution. The feasibility of MR thermometry based on the strong temperature dependence of the hyperfine-shifted 1H signal from the paramagnetic lanthanide complex thulium-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate (TmDOTA-) was recently demonstrated. The use of paramagnetic lanthanide complexes for MR thermometry can be further enhanced by improving the signal-to-noise ratio (SNR) of the observed signal. In this study, the use of lanthanide complexes of a methyl-substituted analog of DOTA4-, 1,4,7,10-tetramethyl 1,4,7,10-tetra azacyclodoecane-1,4,7,10-tetraacetic acetate (DOTMA4-) was evaluated. DOTMA4- complexes have 12 magnetically equivalent methyl protons, which provide an intense and sharper resonance compared to the corresponding DOTA- complexes. Experiments with paramagnetic Pr3+, Yb3+, Tb3+, Dy3+, and Tm3+ complexes of DOTMA4- showed that the Tm3+ complex is most favorable for MR thermometery because of the high temperature dependence of its chemical shift and its relatively narrow linewidth. The chemical shift of the methyl 1H signal from TmDOTMA- was approximately 60 times more sensitive to temperature than the water 1H shift and was insensitive to changes in concentration, pH, [Ca2+], or the presence of other ions and macromolecules. The application of TmDOTMA- for measuring temperature in a subcutaneously implanted tumor model was demonstrated. Lastly, the feasibility of obtaining 3D images from the methyl 1H resonance of TmDOTMA- was demonstrated in phantom and live animal experiments. Overall, TmDOTMA- appears to be a promising probe for MR thermometry in vivo.

Brain temperature measured by 1H-NMR in conjunction with a lanthanide complex

In vivo data on temperature distributions in the intact brain are scarce, partly due to lack of noninvasive methods for the region of interest. NMR has been exploited for probing a variety of brain activities in vivo noninvasively within the region of interest. Here we report the use of a thulium-based thermometric sensor, infused through the blood, for monitoring absolute temperature in rat brain in vivo by (1)H-NMR and validated by direct temperature measurements with thermocouple wires. Because the (1)H chemical shifts also demonstrate pH sensitivity, detection of multiple resonances was used to measure both temperature and pH simultaneously with high sensitivity. Examination of blood plasma and cerebral spinal fluid samples removed from rats infused with the thermometric sensor suggests that the complex, despite its negative charge, crosses the blood-brain barrier to enter the extracellular milieu. In the future, the thulium-based thermometric sensor may be used for monitoring temperature (and pH) distributions throughout the entire brain, examining response to therapy and evaluating changes induced by alterations in neuronal activity.

Temperature accuracy and temperature gradients in solution-state NMR spectrometers

In solution-state NMR spectrometers, there is a systematic deviation between the temperature of the sample and the temperature reported by the spectrometer. In addition, temperature gradients are often present in the sample. The size of both the temperature deviations and the temperature gradients depends on several factors, including the temperature, the flow rate of the heating/cooling gas, and the amount of radiofrequency heating.

TmDOTA-: a sensitive probe for MR thermometry in vivo

The lanthanide complex, thulium 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (TmDOTA-), has been investigated as an agent for MR thermometry in vivo. The chemical shifts of the TmDOTA- protons were highly sensitive to temperature at a clinically relevant field strength, yet insensitive to pH and the presence of Ca2+. Given the excellent stability of lanthanide-DOTA complexes and high thermal sensitivity, TmDOTA- is expected to be a good candidate for MR thermometry in vivo.

[DOTA-bis(amide)]lanthanide complexes: NMR evidence for differences in water-molecule exchange rates for coordination isomers

Two derivatives of 1,4,7,10-tetraazacyclododecane with trans-acetate and trans-amide side-chain ligating groups have been prepared and their complexes with lanthanide cations examined by multinuclear NMR spectroscopy. These lanthanide complexes exist in aqueous solution as a mixture of slowly interconverting coordination isomers with 1H chemical shifts similar to those reported previously for the major (M) and minor (m) forms of the tetraacetate ([Ln(dota)]-) and tetraamide ([Ln(dtma)]3+) complexes. As in the [Ln(dota)]- and [Ln(dtma)]3+ complexes, the m/M ratio proved to be a sensitive function of lanthanide size and temperature. An analysis of 1H hyperfine shifts in spectra of the Yb3+ complexes revealed significant differences between the axial (D1) and non-axial (D2) components of the magnetic susceptibility tensor anisotropy in the m and M coordination isomers and the energetics of ring inversion and m <==> M isomerization as determined by two-dimensional exchange spectroscopy (EXSY). (17)O shift data for the Dy3+ complexes showed that both have one inner-sphere water molecule. A temperature-dependent (17)O NMR study of bulk water linewidths for solutions of the Gd3+ complexes provided direct evidence for differences in water exchange rates for the two coordination isomers. The bound-water lifetimes (tauM298) in the M and m isomers of the Gd3+ complexes ranged from 1.4-2.4 micros and 3-14 ns, respectively. This indicates that 1) the inner-sphere water lifetimes for the complexes with a single positive charge reported here are considerably shorter for both coordination isomers than the corresponding values for the [Gd(dtma)]3+ complex with three positive charges, and 2) the difference in water lifetimes for M and m isomers in these two series is magnified in the [Gd[dota-bis(amide)]] complexes. This feature highlights the remarkable role of both charge and molecular geometry in determining the exchange rate of the coordinated water.

Simultaneous measurements of temperature and pH in vivo using NMR in conjunction with TmDOTP5-

NMR techniques for temperature and pH measurements have attracted increasing interest in recent years, motivated in part by the growing importance of medical hyperthermia for the treatment of cancer. The chemical shifts of thulium 1, 4, 7, 10-tetraazacyclododecane-1, 4, 7, 10-tetrakis(methylene phosphonate) (TmDOTP5-) have been studied as a function of temperature and pH. The results demonstrate that TmDOTP5- resonance shifts are highly sensitive to temperature (approximately 1.0 ppm/degrees C) and pH (approximately 3.2 ppm/pH unit) at clinically relevant field strengths. A new method is presented which utilizes two magnetically non-equivalent protons in TmDOTP5- for simultaneous NMR measurements of both temperature and pH. The difference in the chemical shift values of pairs of 1H resonances provides a temperature sensitivity of about 1.6 ppm/ degrees C. The technique is demonstrated in live rats undergoing ultrasound-induced hyperthermia therapy.

MR imaging of RF heating using a paramagnetic doped agarose phantom

In this paper, we present the first description of a technique to visualize and quantitate radiofrequency (RF) heating of a tissue phantom during a magnetic resonance imaging (MRI) procedure. We evaluated the heating patterns of four 10 cm diameter transmit/receive surface coils with differing degrees of distributed capacitance. The tissue phantom was a 6% agarose gel doped with 40 mM Na(4)HTm[DOTP], and possesses a conductivity intermediate to human muscle and fat. Heating was discerned via phase difference mapping using the large temperature dependent chemical shift coefficient for 23Na in Na(4)HTm[DOTP]. This coefficient is -0.5 ppm/ degrees C. Heating was highest where the phantom was closest to the surface coils, dropping off towards the center of the coil. No significant difference was observed in the heating patterns between the different surface coils. For the experimental setups used in this study, electric field 'hot spots' at the areas corresponding to the placement of the capacitor gaps were not observed.

Temperature-dependent chemical shift and relaxation times of (23)Na in Na(4)HTm[DOTP]

We describe the characterization of a (23)Na temperature-dependent chemical shift and relaxation rates in the complex, Na(4)HTm[DOTP]. This is the first characterization of a (23)Na temperature-dependent chemical shift in a nonmetallic sample. The (23)Na temperature-dependent chemical shift coefficient is approximately -0. 5 PPM/ degrees C for both an aqueous solution and a 6% agarose gel of this compound. This is 50 times the magnitude of the temperature-dependent chemical shift coefficient of water protons. The relaxation times, T(1), T(2f), and T(2s) increased by 0.1, 0.01, and 0.05 ms/ degrees C, respectively. Applications of these unique properties for designing an MRI technique for monitoring heat deposition in tissue and tissue phantoms are discussed.

Bis(methylphosphonic Acid) Derivatives of 1,4,8,11-Tetraazacyclotetradecane (Cyclam). Synthesis, Crystal and Molecular Structures, and Solution Properties

Cyclam derivatives with methylphosphonic acid arms in position 1,8 and substituent R = H, Me, CH2Ph in positions 4 and 11 are synthesised by Mannich reaction of an appropriate cyclam derivative, formaldehyde and phosphonic acid/diethyl phosphite followed by removal of protecting benzyl groups from nitrogen atoms. Mono(methylphosphonic acid) derivative of cyclam can be obtained by a similar route. Crystal structures of four phosphonic acid derivatives show the same ring conformation and orientation pendants due to strong intramolecular hydrogen bonds between phosphonate oxygen atoms and protonated nitrogen atoms adjacent over ethylene chains. The hydrogen bonds are stable even in aqueous solution. Activation parameters for destabilisation of the conformation are estimated from temperature-dependent NMR measurement. The protonation constants determined confirm the expected high basicity of the compounds and its dependence on the nitrogen atom substituents. The enhanced basicity of the nitrogen atoms non-bonded to methylenephosphonic acid moiety, is explained by the presence of the strong hydrogen bonds.

Fast spectroscopic imaging for non-invasive thermometry using the Pr[MOE-DO3A] complex

The praseodymium complex of 10-(2-methoxyethyl)-1,4,7,10-tetraaza-cyclododecane-1,4,7-tr iacetate) was evaluated as a temperature-sensitive contrast agent using the temperature dependence (approximately 0.12 ppm degrees C(-1)) of the chemical shift of its methoxy side group signal. Pr[MOE-DO3A] was employed in combination with spectroscopic imaging (SI) methods for the determination of spatially resolved 2D and 3D temperature distributions in phantoms. Conventional SI and fast echo planar SI sequences (EPSI) were implemented on a 4.7 T MR imaging system fulfilling the demands for non-invasive thermometry (NIT) with respect to thermal and temporal resolution, being <1 degree C and <20 s total measuring time, respectively. The sequences are based on a fast spin echo SI method taking into account the very short relaxation times of the Pr complex methoxy group (T1 = 28 ms, T2 = 13 ms) and its chemical shift difference (-24 ppm) from water. Calibration curves were measured in a uniformly heated water phantom and 2D SI methods were applied to dynamic heating experiments. The average differences between the temperatures measured via fibreoptic thermometer and those derived from the spectroscopic methods were < or =0.2 degrees C. Furthermore, 3D EPSI experiments with a 16 x 16 x 16 matrix size yielded temperature measurements within 17 s from voxels of size 3 x 3 x 3 mm3.

Quantitation of intracellular [Na+] in vivo by using TmDOTP5- as an NMR shift reagent and extracellular marker

A method is presented to measure the absolute concentration of intracellular Na+ ([Na+]i) in vivo by using interleaved 23Na- and 31P-nuclear magnetic resonance (NMR) spectroscopy and TmDOTP5- as shift reagent and chemical marker of tissue extracellular space (ECS). The technique was used to determine [Na+]i and relative ECS in livers of control rats (21 +/- 3 and 0.11 +/- 0.02 mM, respectively) and in rats exposed to carbon tetrachloride (103 +/- 29 and 0.23 +/- 0.03 mM, respectively). The NMR measurements were confirmed independently on excised tissue samples by using atomic absorption spectroscopy. The results confirm that TmDOTP5- can be used as a combined cation shift reagent and ECS marker, thereby allowing quantitation of [Na+]i in vivo by NMR.

Non-invasive MR thermometry by 2D spectroscopic imaging of the Pr[MOE-DO3A] complex

Future progress in regional hyperthermia requires a practical method for non-invasive thermometry. In magnetic resonance tomography, spin density, T1 relaxation time, diffusion coefficient and proton resonance frequency are candidates to measure temperature distributions. When used clinically in the pelvic region, all these methods are compromized by artifacts arising from different tissues, tissue alterations under hyperthermia, physiological and random movements, inhomogeneities, drift phenomena, and field instabilities. In this study a paramagnetic complex was evaluated, Pr[MOE-DO3A], with praseodymium as central atom, similar to common gadolinium containing MRI contrast media. The temperature dependence of its methoxy side group approximately -24 ppm downfield from the water resonance at 25 degrees C was employed to determine 2-D temperature distributions in a cylindrical agar phantom containing 9.5 mM of Pr[MOE-DO3A]. The phantom was heated externally through a water jacket creating a stationary temperature distribution throughout the phantom. At first, the correlation between temperature and the chemical shift of the methyl group of the lanthanide complex Pr[MOE-DO3A] was determined. Calibration curves obtained exhibited a linear relationship of 0.12 +/- 0.01 ppm/degree C, nearly independent from the surrounding medium. Local temperature distributions were determined employing the spatially resolved method of spectroscopic imaging (SI). 2-D spectroscopic images for three orthogonal slices were obtained by narrow-band excitation and 16 phase encoding steps in two dimensions. The FOV was 180 mm and the slice thickness in all cases was 20 mm for maximal spatial temperature resolution (11.2 x 11.2 mm2). The results indicate a measurement time of about 5s per acquisition under the following conditions: An estimated concentration of 1 mmol/l, a reduced matrix size of 8 x 8, and a reduced repetition time of 3 x T1 (TR approximately 85 ms). Those SI measurements produced a SNR of approximately 4 per acquisition, a measurements duration of 10-20 s, equivalent to two to four acquisitions per spectrum, seem sufficient for online temperature monitoring during hyperthermia. The in vitro data suggest the spectroscopic temperature measurement utilizing a temperature-sensitive Pr[MOE-DO3A] complex with a therapeutically realistic concentration of 1 mmol/l to be suitable for clinical use. Compared to the methods tested so far (rho, T1, diffusion, proton resonance), the method presented has the unique advantage of being less susceptible to artifacts. The competing methods of non-invasive thermometry employing magnetic resonance imaging are currently being investigated using the same experimental setup.

NMR temperature measurements using a paramagnetic lanthanide complex

NMR thermometry has previously suffered from poor thermal resolution owing to the relatively weak dependence of chemical shift on temperature in diamagnetic molecules. In contrast, the shifts of nuclear spins near a paramagnetic center exhibit strong temperature dependencies. The chemical shifts of the thulium 1,4,7, 10-tetraazacyclododecane-1,4,7,10-tetrakis(methylene phosphonate) complex (TmDOTP5-) have been studied as a function of temperature, pH, and Ca2+ concentration over ranges which may be encountered in vivo. The results demonstrate that the 1H and 31P shifts in TmDOTP5- are highly sensitive to temperature and may be used for NMR thermometry with excellent accuracy and resolution. A new technique is also described which permits simultaneous measurements of temperature and pH changes from the shifts of multiple TmDOTP5- spectral lines.

Non-invasive temperature mapping using MRI: comparison of two methods based on chemical shift and T1-relaxation

PURPOSE

To implement and evaluate the accuracy of non-invasive temperature mapping using MRI methods based on the chemical shift (CS) and T1 relaxation in media of various heterogeneity during focal (laser) and external thermal energy deposition.

MATERIALS AND METHODS

All measurements were performed on a 1.5 T superconducting clinical scanner using the temperature dependence of the water proton chemical shift and the T1 relaxation time. Homogeneous gel and heterogeneous muscle phantoms were heated focally with a fiberoptic laser probe and externally of varying degree ex vivo by water circulating in a temperature range of 20-50 degrees C. Magnetic resonance imaging data were compared to simultaneously recorded fiberoptic temperature readings.

RESULTS

Both methods provided accurate results in homogeneous media (turkey) with better accuracy for the chemical shift method (CS:+/-1.5 degrees C, T1:+/-2.0 degrees C). In gel, the accuracy with the CS method was +/-0.6 degrees C. The accuracy decreased in heterogeneous media containing fat (T1:+/-3.5 degrees C, CS: +5 degrees C). In focal heating of turkey muscle, the accuracy was within 1.5 degrees C with the T1 method.

CONCLUSION

Temperature monitoring with the chemical shift provides better results in homogeneous media containing no fat. In fat tissue, the temperature calculation proved to be difficult.

Synthesis, Potentiometry, and NMR Studies of Two New 1,7-Disubstituted Tetraazacyclododecanes and Their Complexes Formed with Lanthanide, Alkaline Earth Metal, Mn(2+), and Zn(2+) Ions

Two new 1,7-disubstituted-1,4,7,10-tetraazacyclododecane ligands, DO2P and DO2PME, and their complexes with Mg(2+), Ca(2+), Sr(2+), Mn(2+), Zn(2+) and Ln(3+) were prepared and characterized by pH potentiometry. The pH titration data showed that DO2P and DO2PME both form 1:1 M:L complexes with all divalent and trivalent metal ions. Protonated complexes did not appear to form with the bis(phosphonate ester) ligand, DO2PME, but were evident for all of the metal ion-DO2P complexes. The alkaline earth metal ion-DO2P complexes formed both ML and MHL complexes while the lanthanide ion (Ln(3+)), Zn(2+), and Mn(2+) complexes of DO2P formed ML, MHL, and MH(2)L species. Zn(2+) formed the most stable complex with both ligands. The stability (beta(101)) of the LnDO2PME(+) complexes increased by about 2 orders of magnitude along the lanthanide series (La(3+) to Lu(3+)) while the stability of the LnDO2P(-) complexes over this same series increased by over 3 orders of magnitude. The bis(phosphonate) ligand, DO2P, and some of its complexes formed with Ln(3+) ions were further examined by NMR spectroscopy. (1)H and (31)P spectra of DO2P collected as a function of pH provided evidence that the first two protonations on the ligand take place largely at the tertiary nitrogens. The similarity of the (31)P chemical shifts of EuDO2P(-) and EuDOTP(5)(-) indicate that DO2P forms an "in-cage" complex with Eu(3+) using all four macrocyclic ring nitrogens and the two phosphonate sidearms as ligands. (17)O NMR shifts of the water signal indicated that the DyDO2P(-) complex has two inner-sphere coordinated water molecules. In the presence of excess of DO2P, a 1:2 metal:ligand, LnDO2P(HDO2P)(4)(-), complex forms with the second ligand interacting only weakly with the coordination sites left vacant by the first DO2P. Both water proton relaxivity data for GdDO2P(-) and (31)P NMR spectra of EuDO2P(-) provide evidence for formation of an "out-of-cage" LnH(2)DO2P(+) complex at low pH values (<6.5) in which the two phosphonate groups of DO2P are only involved in bonding with the lanthanide cation.