A new temperature measurement procedure using phase mapping was developed that makes use of the temperature dependence of the water proton chemical shift. Highly accurate and fast measurements were obtained during phantom and in vivo experiments. In the pure water phantom experiments, an accuracy of more than +/- 0.5 degrees C was obtained within a few seconds/slice using a field echo pulse sequence (TR/TE = 115/13 ms, matrix = 128 x 128, number of slices = 5). The temperature dependence of the water proton chemical shift was found to be almost the same for different materials with a chemical composition similar to living tissues (water, glucide, protein). Using this method, the temperature change inside a cat's brain was obtained with an accuracy of more than +/- 1 degree C and an in-plane resolution of 0.6 x 0.6 mm. The temperature measurement error was affected by several factors in the living system (B0 shifts caused by position shifts of the sample, blood flow, etc.), the position shift effect being the most serious.

Purpose: To assess the clinical feasibility of magnetic resonance (MR) imaging with a mechanical loading system for evaluation of load-bearing function in knee joints using cartilage T2 as a surrogate of cartilage matrix changes. Materials and Methods:Sagittal T2 maps of the medial and lateral femorotibial joints of 22 healthy volunteers were obtained using 3.0T MR imaging. After preloading for 6 -9 minutes, MR images under static loading conditions were obtained by applying axial compression force of 50% of body weight during imaging. T2 values of the femoral and tibial cartilage at the weight-bearing area were compared between unloading and loading conditions. Results:Under loading conditions, mean cartilage T2 decreased, depending on location of the knee cartilage. For the femoral side a significant decrease in T2 with loading was observed only at the region in direct contact with the opposing tibial cartilage, in the medial femoral cartilage (5.4%, P Ͻ 0.0005). For the tibial side a significant decrease in T2 with loading was widely observed in the medial and lateral joint, at regions both covered and not covered by the meniscus (4.3%-7.6%, P Ͻ 0.005). Conclusion:MR imaging with mechanical loading is feasible to detect site-specific changes in cartilage T2 during static loading.

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.

This article discusses the applicability to a living animal of the temperature mapping method using the water proton chemical shift obtained with three-dimensional magnetic resonance spectroscopic imaging (3D-MRSI). There are several sources of error in obtaining the spectra with 3D-MRSI: signal noise, limitation in the frequency resolution due to the finite signal length, intravoxel inhomogeneity in the static magnetic field, and variation in the magnetic field due to the eddy current magnetic field. A spectral estimation method called phase deduction complex Lorentzian fitting (PD-CLF) was proposed. Numerical simulations demonstrated that this method reduces the error in the chemical shift to one third of that obtained with the simple frequency subtraction method that uses zero-padded first Fourier transformation (FFT). The temperature images obtained using 3D-MRSI with PD-CLF clearly visualized the changes and distribution of temperature in an anesthetized rat.

A proton-chemical-shift-based temperature imaging method, called chemical shift selective phase mapping, is proposed. The technique uses frequency-selective suppression to provide frequency selectivity to the phase mapping method. Separate imaging of the phase distributions of the water and nonwater signals reduced the error due to the presence of a nonwater signal in measuring the water proton chemical shift change in two-component samples. Imaging of the phase difference between water and oil yielded an internally referenced water proton chemical shift measurement to visualize the temperature change distribution, which was unaffected by motion-induced susceptibility changes.

Object. New approaches for understanding CSF motion in healthy individuals and patients with hydrocephalus and Chiari malformation are presented. The velocity and the pressure gradient of CSF motion were determined using phase contrast (PC) MRI.Methods. The authors examined 11 healthy control subjects and 2 patients (1 with hydrocephalus and 1 with Chiari malformation), using 4-dimensional PC (4D-PC) MRI and a newly developed computer analysis method that includes calculation of the pressure gradient from the velocity field. Sagittal slices including the center of the skull and coronal slices of the foramen of Monro and the third ventricle were used.Results. In the ventricular system, mixing and swirling of the CSF was observed in the third ventricle. The velocity images showed that the CSF was pushed up and back down to the adjacent ventricle and then returned again to the third ventricle. The CSF traveled bidirectionally in the foramen of Monro and sylvian aqueduct. Around the choroid plexus in the lateral ventricle, the CSF motion was stagnant and the CSF pressure gradient was lower than at the other locations. An elevated pressure gradient was observed in the basal cistern of the subarachnoid space. Sagittal imaging showed that the more prominent pressure gradients originated around the cisterna magna and were transmitted in an upward direction. The coronal image showed a pressure gradient traveling from the central to the peripheral subarachnoid spaces that diminished markedly in the convexity of the cerebrum. The 2 patients, 1 with secondary hydrocephalus and 1 with Chiari malformation, were also examined.Conclusions. The observed velocity and pressure gradient fields delineated the characteristics of the CSF motion and its similarities and differences among the healthy individuals and between them and the 2 patients. Although the present results did not provide general knowledge of CSF motion, the authors' method more comprehensively described the physiological properties of the CSF in the skull than conventional approaches that do not include measurements of pressure gradient fields.

An echo-planar spectroscopic imaging method of temperature mapping is proposed. This method is sufficiently faster than the so-called 3D magnetic resonance spectroscopic imaging (3D-MRSI) method and does not require image subtractions, unlike the conventional phase mapping method when an internal reference signal is detectable. The water proton chemical shift measured by using the tissue lipid as an internal reference clearly visualized the temperature change in a porcine liver sample in vitro. It was also demonstrated that the internally referenced echo-planar spectroscopic imaging method could markedly reduce a temperature error caused by a simple, translational motion between scans compared with the phase-mapping method. Magn Reson Med 43:220 -225, 2000.

Background: A classification of cardiac-and respiratory-driven components of cerebrospinal fluid (CSF) motion has been demonstrated using echo planar imaging and time-spatial labeling inversion pulse techniques of magnetic resonance imaging (MRI). However, quantitative characterization of the two motion components has not been performed to date. Thus, in this study, the velocities and displacements of the waveforms of the two motions were quantitatively evaluated based on an asynchronous two-dimensional (2D) phase-contrast (PC) method followed by frequency component analysis. Methods:The effects of respiration and cardiac pulsation on CSF motion were investigated in 7 healthy subjects under guided respiration using asynchronous 2D-PC 3-T MRI. The respiratory and cardiac components in the foramen magnum and aqueduct were separated, and their respective fractions of velocity and amount of displacement were compared.Results: For velocity in the Sylvian aqueduct and foramen magnum, the fraction attributable to the cardiac component was significantly greater than that of the respiratory component throughout the respiratory cycle. As for displacement, the fraction of the respiratory component was significantly greater than that of the cardiac component in the aqueduct regardless of the respiratory cycle and in the foramen magnum in the 6-and 10-s respiratory cycles. There was no significant difference between the fractions in the 16-s respiratory cycle in the foramen magnum. Conclusions:To separate cardiac-and respiratory-driven CSF motions, asynchronous 2D-PC MRI was performed under respiratory guidance. For velocity, the cardiac component was greater than the respiratory component. In contrast, for the amount of displacement, the respiratory component was greater.