A computer algorithm for the simulation of any nuclear magnetic resonance (NMR) imaging method

More than a dozen Nuclear Magnetic Resonance (NMR) imaging methods have been described using different radio-frequency pulse sequences, magnetic field gradient variations, and data processing. In order to have a theoretical understanding in the most general case, we have conceived a computer program for the simulation of NMR imaging techniques. The algorithm uses the solution of the Bloch equations at each point of a simulated object. The direction of every elementary magnetic moment is computed at each instant, and stored in an array giving the global signal to be processed, whatever the pulse and gradient sequence. To test the validity of this program, we have simulated some well-known experimental results. Some applications are presented which contribute to the understanding of image distortions and to techniques such as selective radio-frequency pulse or oscillating gradients. This program can be used to unravel physical and technological causes of image distortions, to have a "microscopic" look at any parameter of an experiment, and to study the contrast given by various NMR imaging techniques as a function of the three NMR parameters, i.e., the hydrogen nuclei density rho and the relaxation times T1 and T2.     

Research and progress in magnetic resonance imaging of triple-negative breast cancer

Triple-negative breast cancer (TNBC), which characterized by distinct biological and clinical pathological features, has a worse prognosis because the lack of effective therapeutic targets. Breast MR is the most accurate imaging modality for diagnosis of breast cancer currently. MR imaging recognition could assist in diagnosis, pretreatment planning and prognosis evaluation of TNBC. MR findings of a larger solitary lesion, mass with smooth mass margin, high signal intensity on T₂-weighted images and rim enhancement are typical MRI features associated with TNBC. Further work is necessary about the clinical application of dynamic contrast-enhanced MR imaging (DCE-MRI), DWI and MRS.     

The change in the character of phase transition with nickel in the Ho(Co,Ni)2 compounds

The series Ho(Co_1-cN_c)₂ has been investigated in the composition range c?0.15 by spin-echo NMR of ¹⁶⁵Ho and by magnetic measurements. From NMR data a value of (9.5±0.1)μ_B is estimated for holmium in HoCo₂. Magnetisation measurements on the same compound give (7.9±0.1)μ_B/fu. An assumption of 0.8μ_B for the cobalt moment aligned antiparallel to that of holmium leads to a value of 9.5μ_B for holmium in agreement with the value estimated from NMR. The substitution of nickel for cobalt causes a rapid fall in both the hyperfine field, and the ordering temperatures, while the molecular moment shows a simultaneous rise. These are attributed to a rapid fall in the cobalt moment which leads to a bootstrap process involving the strength of the exchange field and the magnitude of the cobalt moment. Nickel substitution also leads to a change in the character of the magnetic phase transition. Initially first order, this transition becomes second order on exceeding ≈ 9 at% Ni.     

Study of temperature variations of NMR spectra in monohydrates FeSO4. 1 H2O and MgSO4. 1 H2O

The paper deals with a study of the proton nuclear magnetic resonance (NMR) of crystallization water in isomorphous monohydrates MgSO₄. 1 H₂O and FeSO₄. 1 H₂O in the temperature range 123–313 K. The NMR second moment for diamagnetic MgSO₄. 1 H₂O shows only a weak dependence on temperature but the one for paramagnetic FeSO₄. 1 H₂O is rather strong. Results obtained for FeSO₄. 1 H₂O are in a good agreement with the Kroon's theory of NMR in paramagnetics. The Curie-Weiss constant and the effective magnetic moment of Fe²⁺ ions in FeSO₄. 1 H₂O are derived from the temperature dependence of NMR second moment. The motion of molecules of crystallization water in these hydrates is discussed on the basis of temperature dependences of the width and second moment of NMR spectra.     

Potential industrial applications of inhomogeneous broadening imaging.

Variations in magnetic susceptibility at air-water interfaces can result in inhomogeneous broadening of the NMR line. By special asymmetrical imaging techniques, originally developed for lung imaging, images can be formed of only those molecules that experience this inhomogeneous broadening. The basic concepts and latest developments in inhomogeneous-broadening-imaging techniques are described. Potential industrial applications are also discussed.     

Helimagnetism in gallium substituted LuMn<Subscript>6</Subscript>Ge<Subscript>6</Subscript> studied by nuclear magnetic resonance

Zero-field nuclear magnetic resonance (NMR) of all NMR isotopes (¹⁷⁵Lu, ⁵⁵Mn, ⁷³Ge, ^69,71Ga) in LuMn₆Ge_6-xGa_x, 0 ≤ x ≤ 1, is used to monitor the variation of the hyperfine interaction with the sequence of antiferromagnetic - helimagnetic - ferromagnetic arrangement of the manganese moments of subsequent Kagomé net planes achieved by variation of the gallium content x. According to the ⁵⁵Mn-NMR results, the local Mn moment varies by less than ±5% in this series. ¹⁷⁵Lu-NMR proves canting of the antiferromagnetic sublattices in LuMn₆Ge₆. The anisotropy of the Ge magnetic hyperfine interaction decreases with increasing separation from the hexagonal Lu plane, whereas the absolute value of its isotropic part is only qualitatively correlated with the average separation of the six nearest Mn neighbours. Due to the anisotropic magnetic and electric hyperfine interaction at Ge and Ga sites, the non-collinear magnetic structures are clearly reflected by the NMR spectra, which are described quantitatively in this contribution. The preferred Mn moment direction rotates away from the c direction with x. The conduction or bonding electron spin polarization at the Ga nuclei is increased by 35–80% compared to the Ge nuclei. We argue that this is related with the variation of the magnetic order with the Ga content.     

Labeling of macrophages using bacterial magnetosomes and their characterization by magnetic resonance imaging

This work investigated macrophages labeled with magnetosomes for the possible detection of inflammations by MR molecular imaging. Pure magnetosomes and macrophages containing magnetosomes were analyzed using a clinical 1.5 T MR-scanner. Relaxivities of magnetosomes and relaxation rates of cells containing magnetosomes were determined. Peritonitis was induced in two mice. T₁, T₂ and T₂* weighted images were acquired following injection of the probes. Pure magnetosomes and labeled cells showed slight effects on T₁, but strong effects on T₂ and T₂* images. Labeled macrophages were located with magnetic resonance imaging (MRI) in the colon area, thus demonstrating the feasibility of the proposed approach.     

新一代永磁型磁共振成像系统及其医学应用

简述了世界磁共振成像技术的发展趋势,分析了永磁型共振成像系统的常见不足及其产生的物理原因,据此,提出了解决这些问题的方法,同时,介绍了解决这些问题之后开发出的新一代永磁型磁振成像系统Ｏｐｅｎ Ｍａｒｋ２０００的特点及其在医学上的应用。     

Simulating magnetic nanoparticle behavior in low-field MRI under transverse rotating fields and imposed fluid flow

In the presence of alternating-sinusoidal or rotating magnetic fields, magnetic nanoparticles will act to realign their magnetic moment with the applied magnetic field. The realignment is characterized by the nanoparticle's time constant, τ. As the magnetic field frequency is increased, the nanoparticle's magnetic moment lags the applied magnetic field at a constant angle for a given frequency, Ω, in rad s⁻¹. Associated with this misalignment is a power dissipation that increases the bulk magnetic fluid's temperature which has been utilized as a method of magnetic nanoparticle hyperthermia, particularly suited for cancer in low-perfusion tissue (e.g., breast) where temperature increases of between 4 and 7 °C above the ambient in vivo temperature cause tumor hyperthermia. This work examines the rise in the magnetic fluid's temperature in the MRI environment which is characterized by a large DC field, B₀. Theoretical analysis and simulation is used to predict the effect of both alternating-sinusoidal and rotating magnetic fields transverse to B₀. Results are presented for the expected temperature increase in small tumors ( radius) over an appropriate range of magnetic fluid concentrations (0.002-0.01 solid volume fraction) and nanoparticle radii (1-10 nm). The results indicate that significant heating can take place, even in low-field MRI systems where magnetic fluid saturation is not significant, with careful the goal of this work is to examine, by means of analysis and simulation, the concept of interactive fluid magnetization using the dynamic behavior of superparamagnetic iron oxide nanoparticle suspensions in the MRI environment. In addition to the usual magnetic fields associated with MRI, a rotating magnetic field is applied transverse to the main B₀ field of the MRI. Additional or modified magnetic fields have been previously proposed for hyperthermia and targeted drug delivery within MRI. Analytical predictions and numerical simulations of the transverse rotating magnetic field in the presence of B₀ are investigated to demonstrate the effect of Ω, the rotating field frequency, and the magnetic field amplitude on the fluid suspension magnetization. The transverse magnetization due to the rotating transverse field shows strong dependence on the characteristic time constant of the fluid suspension, τ. The analysis shows that as the rotating field frequency increases so that Ωτ approaches unity, the transverse fluid magnetization vector is significantly non-aligned with the applied rotating field and the magnetization's magnitude is a strong function of the field frequency. In this frequency range, the fluid's transverse magnetization is controlled by the applied field which is determined by the operator. The phenomenon, which is due to the physical rotation of the magnetic nanoparticles in the suspension, is demonstrated analytically when the nanoparticles are present in high concentrations (1-3% solid volume fractions) more typical of hyperthermia rather than in clinical imaging applications, and in low MRI field strengths (such as open MRI systems), where the magnetic nanoparticles are not magnetically saturated. The effect of imposed Poiseuille flow in a planar channel geometry and changing nanoparticle concentration is examined. The work represents the first known attempt to analyze the dynamic behavior of magnetic nanoparticles in the MRI environment including the effects of the magnetic nanoparticle spin-velocity. It is shown that the magnitude of the transverse magnetization is a strong function of the rotating transverse field frequency. Interactive fluid magnetization effects are predicted due to non-uniform fluid magnetization in planar Poiseuille flow with high nanoparticle concentrations.     

Nuclear magnetic resonance imaging techniques as developed modestly within a university medical center environment: What can the small system contribute at this point?

This paper describes a geometrically small NMR imaging system which has been developed and assembled within a university medical center environment. Consideration is given to the technical specifications and basic economics for the magnet system, NMR spectrometer, and computer configuration. Initial research objectives for the system are outlined which include (1) the signal-to-noise improvement potential of rotational gradient imaging, and (2) ¹⁹F tracer imaging considerations with a detailed discussion concerning the feasibility of in vivo NMR imaging of ¹⁹F-fluorodeoxyglucose (2-FDG and 3-FDG). Finally, potentially significant areas for research within the constraints of a small NMR imaging system are described.     

Single-sided mobile NMR apparatus using the transverse flux of a single permanent magnet

This study presents a simple design for a mobile, single-sided nuclear magnetic resonance (NMR) apparatus which uses the magnetic flux parallel to the magnetization direction of a single, disc-shaped permanent magnet polarized in radial direction. The stray magnetic field above the magnet is approximately parallel to the magnetization direction of the magnet and is utilized as the B₀ magnetic field of the apparatus. The apparatus weighs 1.8 kg, has a compact structure and can be held in one's palm. The apparatus generates a B₀ field strength of about 0.279 T at the center of apparatus surface and can acquire a clear Hahn echo signal of a pencil eraser block lying on the RF coil in one shot. Moreover, a strong static magnetic field gradient exists in the direction perpendicular to the apparatus surface. The strength of the static magnetic field gradient near the center of the apparatus surface is about 10.2 T/m; one-dimensional imaging of thin objects and liquid self-diffusion coefficient measurements can be performed therein. The available spatial resolution of the one-dimensional imaging experiments using a 5×5 mm horizontal sample area is about 200 μm. Several nondestructive inspection applications of the apparatus, including distinguishing between polyethylene grains of different densities, characterizing epoxy putties of distinct set times and evaluating the fat content percentages of milk powders, are also demonstrated. Compared with many previously published designs, the proposed design bears a simple structure and generates a B₀ magnetic field parallel to the apparatus surface, simplifying apparatus construction and simultaneously rendering the selection of the radiofrequency coil relatively flexible.     

On the interpretation of NMR experiments in CoGa alloys

We show that in Co_xGa_1?x alloys NMR data reported by Grover et al. in combination with existing magnetization data can be interpreted as follows. The group of atoms consisting of a Co antistructure atom and its eight nearest neighbours behaves as a magnetic entity. The (saturation) magnetic moment of the anti-structure atom (?1.6μ_B) is much larger than the corresponding moment on a neighbouring Co atom (?0.16 μ_B).     

Body Temperature Mapping by Magnetic Resonance Imaging

Abstract

There are numerous clinical situations, such as hyperthermia cancer therapy, under which body temperature has to be accurately evaluated. Magnetic Resonance Imaging presently offers the best set of non-invasive methods for body temperature mapping, including diffusion imaging, relaxation time measurement, magnetization transfer contrast and chemical shift spectroscopic imaging. The basic NMR parameters involved in each are first analyzed. The role of temperature in their physical variation is then presented and finally the different practical MRI methods are briefly discussed. In the present slate of available technology and for basic physical reasons, the T 1 method appears the best compromise at low and medium magnetic field in a limited temperature range. Chemical shift could be theoretically more promising but strictly depends from the homogeneity and stability of the magnet and will be available only at high or very high field.

     

基于AD607芯片的核磁共振模拟接收机

核磁共振波谱和核磁共振成像技术（MRI）已经成为一种广泛应用于物理、化学、材料、生物医学等领域的重要研究工具和医疗诊断手段,但是仪器复杂、价格昂贵. 本文提出了一种改进的基于AD607芯片的模拟接收机设计. 相对于传统的模拟接收机,此设计可以减少接收机使用的外围器件的数量,从而简化设备. 而相对于全数字接收机,本文提出的设计结构简单,并且可以工作在较高的频率. 文章最后给出了核磁共振成像实验的结果.     

Magnetic order in the structurally disordered helicoidal magnet Cr<Subscript>1/3</Subscript>NbS<Subscript>2</Subscript>: NMR at <Superscript>53</Superscript>Cr nuclei

The Cr_1/3NbS₂ magnet is studied by nuclear magnetic resonance (NMR) at ⁵³Cr nuclei in a zero applied magnetic field. The following two frequency ranges are distinguished in the ⁵³Cr NMR spectrum at T = 4.2 K: ν ₁ = 64–68 MHz and ν ₂ = 49–51 MHz. They can be related to two valence states of chromium ions, namely, Cr⁴⁺ and Cr³⁺. The components of the electric field gradient, the hyperfine fields, and the magnetic moment at chromium atoms are determined. The NMR data demonstrate that the magnetic moments of chromium lie in plane ab and form a magnetic structure consisting of regions with a helicoidal magnetic order and regions where this order is broken.     

Gd complexes of diethylenetriaminepentaacetic acid conjugates of low-molecular-weight chitosan oligosaccharide as a new liver-specific MRI contrast agent

This study was to describe the synthesis of complexes of gadolinium diethylenetriaminepentaacetic acid conjugates of low-molecular-weight chitosan oligosaccharide Gd-DTPA-CSn (n = 6, 8, 11) as a new class of contrast agent as well as its magnetic property in a pilot magnetic resonance imaging. The efficacy of the contrast agent was assessed by measuring the longitudinal relaxivity (r₁), FLASH imaging in phantoms in vitro and signal intensity in vivo of the rat abdominal axial imaging. The r₁ of Gd-DTPA-CS₁₁ was up to 11.65 mM^− 1·s^− 1, which was 3 times higher than that of the analogous MRI contrast agent Gd-DTPA in commercial use. In vivo MR images of rat obtained with Gd-DTPA-CS₁₁ showed strong signal enhancement in liver and the vessels of the liver parenchyma during the extended period of time. The present study suggests that the new synthesized gadolinium complexes can be used as a new class of practical liver-specific MRI contrast agent because of its superior performance compared with Gd-DTPA.     

NMR imaging in human pregnancy: A preliminary study

In an effort to demonstrate the potential of nuclear magnetic resonance imaging (NMR) in the management of pregnancy, 15 patients in the first trimester and one in the third trimester of pregnancy have been investigated in the Aberdeen University NMR imager. Simple measurements of biparietal diameter and crown-rump length were made from both the NMR images and the ultrasound images on the same day, with good correlation between the two. The NMR data was displayed as inversion recovery, calculated T₁, proton density and S₁–S₂ images. The proton density and S₁–S₂ images were found to be the most useful for the demonstration of the fetus and for discriminating between placenta and uterus. The calculated T₁ data provided accurate quantification of the proton-spin lattice relaxation times of the different tissues, indicating that this measurement may be of use in the study of fetal brain development and placental function. The inversion recovery images showed poor tissue discrimination and were found to be of limited value. The unique information available using NMR and the non-invasive nature of the technique indicated that it should provide a useful method for the investigation of both fetal development and placental function in addition to making basic measurements of fetal size.     

Nuclear magnetic resonance diagnosis of an anaplastic astrocytoma

A patient presented with an 8-month history of a progressive left homonymous visual field deficit, left hemiparesis, and a left thalamocortical sensory deficit that was not detectable by repeated conventional neurodiagnostic evaluations. Proton nuclear magnetic resonance (NMR) imaging revealed a right parietal lesion characterized by a prolonged T₂ (spin-spin relaxation time). At surgery, the mass proved to be an anaplastic astrocytoma. NMR appears to be more sensitive than x-ray computerized tomography scanning in some patients with malignant gliomas and offers the clinician an additional probe with which to evaluate these patients.     

The Nd–Mn exchange interaction,low temperature specific heat and magnetism of Nd2/3Ca1/3MnO3

The low temperature specific heat and magnetic characteristics of Nd_2/3Ca_1/3MnO₃ perovskite are studied in a wide range of magnetic fields (up to 9 T). Temperature dependent specific heat data show a broadened Schottky-like anomaly below 20 K caused by splitting of the Nd³⁺ ions ground-state doublet in the effective molecular field H_ex, determined by exchange interaction between Nd and Mn spin systems supplemented by an applied external magnetic field. Existence of the splitting at zero magnetic field and expressed field dependence is the evidence of a strong exchange coupling between Nd and Mn magnetic subsystems. The Nd-ions magnetic ordering leads to an additional contribution to the magnetic moment of the system below 30 K, producing anomalies of the magnetic loss and field-cooled and zero-field-cooled magnetizations. The observed broadened Schottky-like anomalies are fitted for each applied magnetic field by the sum of three Schottky functions. Applied magnetic field extends the anomaly region and shifts it to higher temperatures. Splitting of the higher crystal field Kramers doublets gives an additional contribution to the heat capacity in magnetic fields. The ground state doublet g-factors g_|| and g_⊥ were estimated to be 3.4 and 2.2, respectively, and H_ex was estimated to be 9 T. The Nd³⁺ ions magnetic moment estimated from the magnetization data agrees with the value obtained from the specific heat data.     

Nonempirical and quasi-classical approaches to the calculation of the electronic transition dipole moments

The dependence of the electronic transition dipole moment on the internuclear separation is calculated nonempirically for the Meinel band of the N ₂ ⁺ molecular ion using the Gaussian 98 software package with different basis sets. The results are compared with the dependences obtainedby the semiempirical methods. The basic relationships of the R-centroid method are derived, and the quasi-classical nature of this method is demonstrated. It is confirmed that the dependence of the electronic transition dipole moment on the internuclear separation is described most reliably by using the semiempirical methods. The vibronic transition dipole moment is shown to be an oscillating function of the vibrational quantum number v1 (with v2=const) or v2 (with v1=const).