Combined volumetric T1, T2 and secular-T2 quantitative MRI of the brain: age-related global changes (preliminary results)

The combined T1, T2 and secular-T2 pixel frequency distributions of 24 adult human brains were studied in vivo using a technique based on the mixed-TSE pulse sequence, dual-space clustering segmentation and histogram gaussian decomposition. Pixel frequency histograms of whole brains and the four principal brain compartments were studied comparatively and as function of age. For white matter, the position of the T1 peak correlates with age (R2 =.7868) when data are fitted to a quadratic polynomial. For gray matter, a weaker age correlation is found (R2 =.3687). T2 and secular-T2 results are indicative of a weaker correlation with age. The technique and preliminary results presented herein may be useful for characterizing normal as well as abnormal aging of the brain, and also for comparison with the results obtained with alternative quantitative MRI methodologies.     

Development of T2-relaxation values in regional brain sites during adolescence

Brain tissue changes accompany multiple neurodegenerative and developmental conditions in adolescents. Complex processes that occur in the developing brain with disease can be evaluated accurately only against normal aging processes. Normal developmental changes in different brain areas alter tissue water content, which can be assessed by magnetic resonance (MR) T2 relaxometry. We acquired proton-density (PD) and T2-weighted images from 31 subjects (mean age±S.D., 17.4±4.9 years; 18 male), using a 3.0-T MR imaging scanner. Voxel-by-voxel T2-relaxation values were calculated, and whole-brain T2-relaxation maps constructed and normalized to a common space template. We created a set of regions of interest (ROIs) over cortical gray and white matter, basal ganglia, amygdala, thalamic, hypothalamic, pontine and cerebellar sites, with sizes of ROIs varying from 12 to 243 mm³; regional T2-relaxation values were determined from these ROIs and normalized T2-relaxation maps. Correlations between R2 (1/T2) values in these sites and age were assessed with Pearson's correlation procedures, and gender differences in regional T2-relaxation values were evaluated with independent-samples t tests. Several brain regions, but not all, showed principally positive correlations between R2 values and age; negative correlations emerged in the cerebellar peduncles. No significant differences in T2-relaxation values emerged between males and females for those areas, except for the mid pons and left occipital white matter; males showed higher T2-relaxation values over females. The findings indicate that T2-relaxation values vary with development between brain structures, and emphasize the need to correct for such age-related effects during any determination of potential changes from control values.     

In vivo determination of multiexponential T2 relaxation in the brain of patients with multiple sclerosis

In vivo measurement of T2 relaxation times in multiple sclerosis (MS) lesions by magnetic resonance imaging (MRI) is potentially useful for the evaluation of the disease activity. Seven patients with definite MS were investigated over a period of three years (19 examinations), using a whole-body MRI scanner operating at 0.15 T with a specially designed high-power radio-frequency head coil. A modified CPMG sequence with a 180 degree pulse interval of TE = 6 msec and 128 echoes was used for the T2 relaxation measurement of the areas of increased signal (AIS) and white matter (WM). A biexponential T2 analysis of each pixel of the spin-echo images was computed. The T2 relaxation processes were found to be a monoexponential function in WM. The T2 relaxation times of apparently normal white matter in MS patients was significantly longer than in control subjects. The T2 relaxation curves of the AIS were found in most cases to fit a biexponential function characterized by a short and a long T2. T2 long relaxation times of AIS were spread out over a wide range (150-560 msec). The study of T2 long histograms shows that some AIS can be divided into two or three parts depending on the T2 long values. Each of these parts may correspond to a pathological process such as edema, demyelination and gliosis. Evolution of T2 relaxation times over a period of time cannot as yet be correlated with modifications in the clinical state.     

Principal component and linear discriminant analysis of T1 histograms of white and grey matter in multiple sclerosis

Twenty-three relapsing remitting multiple sclerosis (RRMS) patients and 14 controls were imaged to produce normal-appearing white and grey matter T1 histograms. These were used to assess whether histogram measures from principal component analysis (PCA) and linear discriminant analysis (LDA) out-perform traditional histogram metrics in classification of T1 histograms into control and RRMS subject groups and in correlation with the expanded disability status score (EDSS). The histograms were classified into one of two groups using a leave-one-out analysis. In addition, the patients were scanned serially, and the calculated parameters correlated with the EDSS. The classification results showed that the more complex techniques were at least as good at classifying the subjects as histogram mean, peak height and peak location, with PCA/LDA having success rates of 76% for white matter and 68%/65% for grey matter. No significant correlations were found with EDSS for any histogram parameter. These results indicate that there is much information contained within the grey matter as well as the white matter histograms. Although in these histograms PCA and LDA did not add greatly to the discriminatory power of traditional histogram parameters, they provide marginally better performance, while relying only on data-driven feature selection.     

Primary Matter Creation in a Weyl–Dirac Cosmological Model

In the framework of an integrable Weyl–Dirac (W–D) theory a cosmological model is proposed. It describes a universe that began its expansion from a primary pre-Planckian geometric entity containing no matter. During the pre-Planckian period, from R ₀ =5.58×10 ^–36 cm to R_I=5.58×10 ^–34 cm, this embryonic universe has undergone a very rapid expansion and cosmic matter was created by geometry. At R_I the universe was already filled with matter having the Planckian density _P and being in the state of prematter (P=–), while the Weylian geometric elements were insignificant. This state is the Planckian egg that has served as the initial state of the singularity-free cosmological model ⁽¹⁾ considered in the framework of Einstein's general theory of relativity. The W–D character of the geometry and the cosmological constant are significant in the pre-Planckian period during the matter creation. In the dust-dominated period a relic of the W–D geometry causes a global dark matter effect. In between the pre-Planckian and dust period one has Einstein's framework and is negligible.     

The hidden mass of the universe

It is generally accepted that the hidden mass of the Universe consists of massive neutrinos or other hypothetical particles (axions, photinos, etc. We assert that there is no basis for such hypotheses. Even if the neutrino possesses a mass, it would be too small, and despite the great efforts to observe the other particles, the results have been negative. If the mass distribution law f(M) M^–2 established for meteors meteorites and asteroids in the range between 10^–12 and 10²⁰ g is extended to the Universe as a whole, one obtains values for the density of the luminous matter, transparency of the galaxies and of the Universe which agree with those observed. It is assumed that the primordial deuterium was burnt up during continuous star formation, and the deuterium observed at present is of a secondary origin. It is shown that very probably the metallicity of stars of the solar type may in reality be tens of times greater than that observed in the photosphere which reflects only the metallicity of a convection layer with a thickness of less than 0.2 of the radius. The difficulties that arise if it is assumed that the dark matter consists of hypothetical noninteracting particles are mentioned: at t 10¹³ sec there cannot be any perturbations of the density of particles with mc²<20 eV at a level of 10^–4 (absence of fluctuations of the microwave background radiation); particles with mc²>10³ eV should decay during a period of 10⁸–10⁹ years and thus distort significantly the t(T) dependence; particles with mc²>10⁵ eV strongly reduce the thermonuclear synthesis time and consequently (D/H)>10^–3 and (⁴HeH)<0.2.I. V. Kurchatov Institute of Atomic Energy, Moscow. Translated from Izvestiya Vysshikh Uchebnikh Zavedenii, Fizika, No. 1, pp. 13–22, January, 1993.     

Negative luminescence in semiconductors: a retrospective view

Twenty-five years ago, we introduced the phenomenon of negative luminescence (NL) into semiconductor physics. This paper provides an overview of work conducted to develop this fundamental concept. Initially, we consider the first-principle approach to radiation interaction with basic matter and the major properties of NL. Then we describe the problems of NL direct measurements in homogeneous materials and structures. Finally, we emphasize the use of NL approach in applications involving devices for infrared (IR) wavelength (3–12 μm) high-temperature (300–400 K) optoelectronics. Our subjects will include NL IR emitting diodes, radiative coolers, IR dynamic scene simulators, light up-conversion devices, and the Stealth effect in IR.     

The measurement of R2, and R2′ in HIV-infected patients using the prime sequence as a measure of brain iron deposition

Brain iron deposition was assessed at 1.5 T in the caudate nucleus, globus pallidus and frontal and parietooccipital white matter in 28 human immunodeficiency virus (HIV)-infected patients and 15 control subjects with a new Partially Refocussed Interleaved Multi-Echo sequence by measuring 1/T₂, 1/T₂^* and 1/T2′ (i.e., R₂, and R₂′). There were significant differences in the R₂ and of the caudate nucleus (p < 0.0001 and p < 0.05) and the R₂, and R₂′ of the globus pallidus (p < 0.001, p < 0.005 and p < 0.05) in HIV-infected patients compared to control subjects. There was a trend for higher values of R₂, and R₂′ in the globus pallidus and caudate nucleus in HIV-infected patients with later stage HIV disease. These results suggest that there is greater iron deposition in the basal ganglia of HIV-infected patients compared with control subjects, with a predilection for the globus pallidus. The relationship between iron deposition in the brain and various parameters of severity of HIV infection remains uncertain.     

Brain metabolite alterations demonstrated by proton magnetic resonance spectroscopy in diabetic patients with retinopathy

Due to the homology between retinal and cerebral microvasculatures, retinopathy is a putative indicator of cerebrovascular dysfunction. This study aimed to detect metabolite changes of brain tissue in type 2 diabetes mellitus (T2DM) patients with diabetic retinopathy (DR) using proton magnetic resonance spectroscopy (¹H-MRS). Twenty-nine T2DM patients with DR (DR group), thirty T2DM patients without DR (DM group) and thirty normal controls (NC group) were involved in this study. Single-voxel ¹H-MRS (TR: 2000 ms, TE: 30 ms) was performed at 3.0 T MRI/MRS imager in cerebral left frontal white matter, left lenticular nucleus, and left optic radiation. Our data showed that NAA/Cr ratios of the DR group were significantly lower than those of the DM group in the frontal white matter and optic radiation. In the lenticular nucleus, MI/Cr ratios were significantly higher in the DM group than those in the NC group, while MI/Cr ratios were significantly lower in the DR group than those in the DM group. In the frontal white matter, NAA/Cho ratios were found to be decreased in the DR group as compared to the NC group. Additionally, our finding indicated that NAA/Cr ratios were negatively associated with DR severity in both the frontal white matter and optic radiation. A decrease in NAA indicated neuronal loss and the likely explanation for a decrease in MI was glial loss. In conclusion, we inferred that cerebral neurons and glia cells were damaged in patients with DR. Our data support that DR is associated with brain tissue damage.     

Bi-phase age-related brain gray matter magnetic resonance T1ρ relaxation time change in adults

ObjectivesTo investigate normative value and age-related change of brain magnetic resonance T1ρ relaxation at 1.5 T.MethodsThis study was approved by the local ethical committee with participants' written consent obtained. There were 42 adults healthy volunteers, including 20 males (age: 41 ± 16 (mean ± standard deviation) years, range: 22–68 years,) and 22 females (age: 39 ± 15 years, range: 21–62 years). MRI was performed at 1.5 T using 3D fluid suppressed turbo spin echo sequence. Regions-of-interests (ROIs) were obtained by atlas-based tissue segmentation and T1ρ was calculated by fitting the mean value to mono-exponential model. Correlation between T1ρ relaxation of brain gray matter regions and age was investigated.ResultsA regional difference among individual gray matter areas was noted; the highest values were observed in the hippocampus (98.37 ± 5.37 ms, median: 97.88 ms) and amygdala (94.95 ± 4.34 ms, median: 94.73 ms), while the lowest values were observed in the pallidum (83.81 ± 5.49 ms, median: 83.77 ms) and putamen (83.93 ± 4.76 ms, median: 83.99 ms). Gray matter T1ρ values decreased slowly (mean slope: − 0.256) and significantly (p < 0.05) with age in gray matter for subjects younger than 40 years old, while for subjects older than 40 years old there was no apparent correlation between T1ρ relaxation and age. Global white matter measured T1ρ value of 88.65 ± 3.47 ms (median: 87.86 ms), and the correlation with age was not significant (p = 0.18).ConclusionGray matter T1ρ relaxation demonstrates a bi-phase change with age in adults of 22–68 years.     

Temperature dependences of the flow and critical shear stresses of dispersion-hardening alloys

A study was made of the temperature dependences of the flow stress _0.1 (T) and of the critical shear stress _cr(T) of Cu-15% A1-(1–2)% Co, Cu-8% A1-(2–2.8)% Co, and Cu-4% A1–2% Co alloys containing noncoherent intermetallic particles. In the case of single crystals at temperatures 77–673° K there was a good agreement between the theoretically calculated values of the Orowan hardening and those found experimentally, so that the dependence _cr(T) was governed by the temperature dependence of the shear modulus G(T). For polycrystalline samples the usual dependence of the mechanical propertiesties on the grain size was not observed. At temperatures from 77 to 473–573°K the dependence _0.1 (T) was similar to the dependence G(T) and a good agreement was observed between the theoretically calculated dispersion hardening effects with those found experimentally. At temperatures T > 473–573°K the deformation was influenced greatly by grain-boundary glide, which enhanced the dependence _0.1 (T) compared with that expected theoretically.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 85–91, June, 1980.     

MR assessment of the brain maturation during the perinatal period: quantitative T2 MR study in premature newborns

The purpose of our study is to trace in vivo and during the perinatal period, the brain maturation process with exhaustive measures of the T2 relaxation time values. We also compared regional myelination progress with variations of the relaxation time values and of brain signal. T2 relaxation times were measured in 7 healthy premature newborns at the post-conceptional age of 37 weeks, using a Carr-Purcell-Meiboom-Gill sequence (echo time 60 to 150 ms), on a 2.35 Tesla Spectro-Imaging MR system. A total of 62 measures were defined for each subject within the brain stem, the basal ganglia and the hemispheric gray and white matter. The mean and standard deviation of the T2 values were calculated for each location. Regional T2 values changes and brain signal variations were studied. In comparison to the adult ones, the T2 relaxation time values of both gray and white matter were highly prolonged and a reversed ratio between gray and white matter was found. The maturational phenomena might be regionally correlated with a T2 value shortening. Significant T2 variations in the brainstem (p < 0.02), the mesencephalon (p < 0.05), the thalami (p < 0.01), the lentiform nuclei (p < 0.01) and the caudate nuclei (p < 0.02) were observed at an earlier time than they were visible on T2-weighted images. In the cerebral hemispheres, T2 values increased from the occipital white matter to parietal, temporal and frontal white matter (p < 0.05) and in the frontal and occipital areas from periventricular to subcortical white matter (p < 0.01). Maturational progress was earlier and better displayed with T2 measurements and T2 mapping. During the perinatal period, the measurements and analysis of T2 values revealed brain regional differences not discernible with T2-weighted images. It might be a more sensitive indicator for assessment of brain maturation.     

MR quantification of muscle fatty replacement in McArdle''s disease

McArdle's disease is an energy-dependant disorder of skeletal muscle caused by the inability to break down glycogen. The aim of this study was to quantify fatty replacement in patients with McArdle's disease. Calf and thigh axial spin echo T₁-weighted magnetic resonance (MR) images (repetition time 500 ms, echo time 25 ms) were obtained at 0.5 T in nine patients with McArdle's disease (age 51 ± 16 years, range 26–74) and nine sex- and age-matched healthy subjects (age 52 ± 16 years, range 29–78) to quantify intramuscular fat. Regions of interest were drawn manually, encompassing the largest cross section of muscle. A fatty replacement index (IF) was determined from histograms of signal in the regions of interest in calf and thigh muscles. In normal subjects, IF = 3.6 ± 2.8% in calf and 4.9 ± 2.3% in thigh. In patients, IF = 11 ± 9.3% in calf and 13.5 ± 10.4% in thigh, significantly different from IF values in normal subjects (p = .03). IF correlated well with age in patients (p = .03). In older patients, up to 25% of the muscle volume was replaced by fat. Patients with McArdle's disease, usually weakly disabled, exhibit significant muscle fatty replacement on MR images. These findings suggest a progressive muscle loss over time related to the disease process.     

Prediction of total cerebral tissue volumes in normal appearing brain from sub-sampled segmentation volumes

The need for anatomical coverage and multi-spectral information must be balanced against examination and processing time to ensure high-quality, feasible imaging protocols for clinical research of cerebral development in normal-appearing brains. The focus of this study was to create and assess models to estimate total cerebral volumes of gray matter, white matter, and cerebrospinal fluid (CSF) from anatomically defined sub-samples of full clinical examinations. Pediatric patients (18F, 11M; aged 1.7 to 18.7, median 5.2 years) underwent a clinical imaging protocol consisting of 3 mm contiguous T1-, T2-, PD-, and FLAIR-weighted images after obtaining informed consent. Magnetic resonance imaging (MRI) sets were registered, RF-corrected, and then analyzed with a hybrid neural network segmentation and classification algorithm to identify normal brain parenchyma. The correlation between the image subsets and the total cerebral volumes of gray matter, white matter and CSF were examined through linear regression analyses. Five sub-sampled sets were defined and assessed in each patient to produce estimation models which were all significantly correlated (p < 0.001) with the total cerebral volumes of gray matter, white matter, and CSF. Volumes were estimated from as little as a single representative slice requiring minimal processing time, 27 min, but with an average estimation error of approximately 6%. Larger sub-samples of approximately three-quarters of the full cerebral volume required much more processing time, 2 h and 4 min, but produced estimates with an average error less than 2%. This study demonstrated that investigators can choose the amount of cerebrum sampled to optimize the acquisition and processing time against the degree of accuracy needed in the total cerebral volume estimates.     

Temperature anomalies in the dispersion and absorption of sound near phase transition points at low temperatures

We examined the attenuation and dispersion of sound during phase transitions with an overdamped soft mode at low temperatures. The obtained temperature and frequency dependences differ from results known at the high-temperature asymptote. The temperature anomalies are sharper. At low frequencies, the attenuation behaves like (T – T_c)^–5/2 for a critical phonon spectrum isotropic in k, and like (T–T_c)^–2 for uniaxial ferroelectrics. The presence of a temperature anomaly is characteristic also for high-frequency attenuation, behaving like (T–T_c)^–1/2 and ln(T–T_c)., respectively. We discuss briefly the results obtained from an experimental test.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 70–74, January, 1989.     

Activation of Visuomotor Systems during Visually Guided Movements: A Functional MRI Study

The dorsal stream is a dominant visuomotor pathway that connects the striate and extrastriate cortices to posterior parietal areas. In turn, the posterior parietal areas send projections to the frontal primary motor and premotor areas. This cortical pathway is hypothesized to be involved in the transformation of a visual input into the appropriate motor output. In this study we used functional magnetic resonance imaging (fMRI) of the entire brain to determine the patterns of activation that occurred while subjects performed a visually guided motor task. In nine human subjects, fMRI data were acquired on a 4-T whole-body MR system equipped with a head gradient coil and a birdcage RF coil using aT^*₂-weighted EPI sequence. Functional activation was determined for three different tasks: (1) a visuomotor task consisting of moving a cursor on a screen with a joystick in relation to various targets, (2) a hand movement task consisting of moving the joystick without visual input, and (3) a eye movement task consisting of moving the eyes alone without visual input. Blood oxygenation level-dependent (BOLD) contrast-based activation maps of each subject were generated using period cross-correlation statistics. Subsequently, each subject's brain was normalized to Talairach coordinates, and the individual maps were compared on a pixel by pixel basis. Significantly activated pixels common to at least four out of six subjects were retained to construct the final functional image. The pattern of activation during visually guided movements was consistent with the flow of information from striate and extrastriate visual areas, to the posterior parietal complex, and then to frontal motor areas. The extensive activation of this network and the reproducibility among subjects is consistent with a role for the dorsal stream in transforming visual information into motor behavior. Also extensively activated were the medial and lateral cerebellar structures, implicating the cortico–ponto–cerebellar pathway in visually guided movements. Thalamic activation, particularly of the pulvinar, suggests that this nucleus is an important subcortical target of the dorsal stream.     

A pulsar inside the Sun?

The Crimean observation of solar oscillations in 1974–1982 showed that the basic period of pulsation of the Sun hidden in its deep interior was equal to P ₀=160.0101±0.0001min. More recently, the period was changed to the new value P ₁=159.9662±0.0006min, which almost coincided with the annual sidelobe of the former period P ₀. The amplitude of the P₁ oscillation has increased considerably over 1994–1995. We substantiate the hypothesis that a) the change in the period was caused by the interaction of the P₀ oscillation with the rapid rotation of the solar core and that b) the latter has the form of a compact, highly magnetized object like a neutron star rotating with sidereal period P₁.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 10, pp. 1210–1214, October, 1996.The author expresses his gratitude to the referee for his honest and useful comments to this paper. The author is also thankful to V. I. Haneychuk and T. T. Tsap for their active participation in the solar observations at the CrAO which were used in the present paper. This work was supported in part by the International Science Foundation under Grants No. UCU000 and UCU200.     

One- and two-dimensional C–H/N–H dipolar correlation experiments under fast magic-angle spinning for determining the peptide dihedral angle φ

A recently proposed ¹³C–¹H recoupling sequence operative under fast magic-angle spinning (MAS) [K. Takegoshi, T. Terao, Solid State Nucl. Magn. Reson. 13 (1999) 203–212.] is applied to observe ¹³C–¹H and ¹⁵N–¹H dipolar powder patterns in the ¹H–¹⁵N–¹³C–¹H system of a peptide bond. Both patterns are correlated by ¹⁵N-to-¹³C cross polarization to observe one- or two-dimensional (1D or 2D) correlation spectra, which can be simulated by using a simple analytical expression to determine the H–N–C–H dihedral angle. The 1D and 2D experiments were applied to N-acetyl[1,2-¹³C,¹⁵N] -valine, and the peptide φ angle was determined with high precision by the 2D experiment to be ±155.0°±1.2°. The positive one is in good agreement with the X-ray value of 154°±5°. The 1D experiment provided the value of φ=±156.0°±0.8°.     

Topology and Fragility in Cosmology

We introduce the notion of topological fragility and briefly discuss some examples from the literature. An important example of this type of fragility is the way globally anisotropic Bianchi V generalisations of the FLRW k = –1 model result in a radical restriction on the allowed topology of spatial sections, thereby excluding compact cosmological models with negatively curved three-sections with anisotropy. An outcome of this is to exclude chaotic mixing in such models, which may be relevant, given the many recent attempts at employing compact FLRW k = –1 models to produce chaotic mixing in the cosmic microwave background radiation, if the Universe turns out to be globally anisotropic.     

Nonstationary diffusion in a multiphase medium

The process of nonstationary diffusion of matter in a multiphase medium with sharp steps of the diffusion coefficient and an arbitrary number of phases is considered. The boundary conditions at the points of phase separation are determined. An exact solution is obtained, and the nonstationary concentration of matter is shown to be described by an infinite superposition of time-dependent Gaussian curves. Some examples are proposed and the results obtained are interpreted physically.State University, Nizhny Novgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, Nos. 1–2, pp. 56–68, January–February, 1995.