Qing X. Yang

Spatial variation in cartilage T2 of the knee

Technical limitations imposed by resolution and B1 homogeneity have thus far limited quantitative in vivo T2 mapping of cartilage to the patella. The purpose of this study is to develop T2 mapping of the femoral/tibial joint and assess regional variability of cartilage T2 in the knee. Quantitative in vivo T2 mapping of the knee was performed on 15 asymptomatic adults (age, 22–44) using a 3T MR scanner. There is a consistent pattern of spatial variation in cartilage T2 with longer values near the articular surface. The greatest variation occurs in the patella, where T2 increases from 45.3 ± 2.5 msec at a normalized distance of 0.33–67 ± 5.5 msec at a distance of 1.0. These results demonstrate feasibility of performing in vivo T2 mapping of femoral tibial cartilage. Except for the superficial 15% where T2 values are lower, the spatial variation in T2 of femoral and tibial cartilage is similar to patellar cartilage. J. Magn. Reson. Imaging 2001;14:50–55.

Analysis of wave behavior in lossy dielectric samples at high field

Radiofrequency (RF) field wave behavior and associated nonuniform image intensity at high magnetic field strengths are examined experimentally and numerically. The RF field produced by a 10‐cm‐diameter surface coil at 300 MHz is evaluated in a 16‐cm‐diameter spherical phantom with variable salinity, and in the human head. Temporal progression of the RF field indicates that the standing wave and associated dielectric resonance occurring in a pure water phantom near 300 MHz is greatly dampened in the human head due to the strong decay of the electromagnetic wave. The characteristic image intensity distribution in the human head is the result of spatial phase distribution and amplitude modulation by the interference of the RF traveling waves determined by a given sample‐coil configuration. The numerical calculation method is validated with experimental results. The general behavior of the RF field with respect to the average brain electrical properties in a frequency range of 42–350 MHz is also analyzed. Magn Reson Med 47:982–989, 2002.

Central brightening due to constructive interference with, without, and despite dielectric resonance

To aid in discussion about the mechanism for central brightening in high field magnetic resonance imaging (MRI), especially regarding the appropriateness of using the term dielectric resonance to describe the central brightening seen in images of the human head.

Different excitation and reception distributions with a single‐loop transmit‐receive surface coil near a head‐sized spherical phantom at 300 MHz

Calculations and experiments were used to examine the B1 field behavior and signal intensity distribution in a 16‐cm diameter spherical phantom excited by a 10‐cm diameter surface coil at 300 MHz. In this simple system at this high frequency very complex RF field behavior exists, resulting in different excitation and reception distributions. Included in this work is a straightforward demonstration that coil receptivity is proportional to the magnitude of the circularly polarized component of the B1 field that rotates in the direction opposite to that of nuclear precession. It is clearly apparent that even in very simple systems in head‐sized samples at this frequency it is important to consider the separate excitation and reception distributions in order to understand the signal intensity distribution. Magn Reson Med 47:1026–1028, 2002.

Combined R2* and Diffusion Tensor Imaging Changes in the Substantia Nigra in Parkinson's Disease†‡

Recent magnetic resonance imaging studies suggest an increased transverse relaxation rate and reduced diffusion tensor imaging fractional anisotropy values in the substantia nigra in Parkinsons disease. The transverse relaxation rate and fractional anisotropy changes may reflect different aspects of Parkinsons disease‐related pathological processes (ie, tissue iron deposition and microstructure disorganization). This study investigated the combined changes of transverse relaxation rate and fractional anisotropy in the substantia nigra in Parkinsons disease. High‐resolution magnetic resonance imaging (T2‐weighted, T2*, and diffusion tensor imaging) were obtained from 16 Parkinsons disease patients and 16 controls. Bilateral substantia nigras were delineated manually on T2‐weighted images and coregistered to transverse relaxation rate and fractional anisotropy maps. The mean transverse relaxation rate and fractional anisotropy values in each substantia nigra were then calculated and compared between Parkinsons disease subjects and controls. Logistic regression, followed by receiver operating characteristic curve analysis, was employed to investigate the sensitivity and specificity of the combined measures for differentiating Parkinsons disease subjects from controls. Compared with controls, Parkinsons disease subjects demonstrated increased transverse relaxation rate (P < .0001) and reduced fractional anisotropy (P = .0365) in the substantia nigra. There was no significant correlation between transverse relaxation rate and fractional anisotropy values. Logistic regression analyses indicated that the combined use of transverse relaxation rate and fractional anisotropy values provides excellent discrimination between Parkinsons disease subjects and controls (c‐statistic = 0.996) compared with transverse relaxation rate (c‐statistic = 0.930) or fractional anisotropy (c‐statistic = 0.742) alone. This study shows that the combined use of transverse relaxation rate and fractional anisotropy measures in the substantia nigra of Parkinsons disease enhances sensitivity and specificity in differentiating Parkinsons disease from controls. Further studies are warranted to evaluate the pathophysiological correlations of these magnetic resonance imaging measurements and their effectiveness in assisting in diagnosing Parkinsons disease and following its progression.

MRI and Histological Analysis of Beta-Amyloid Plaques in Both Human Alzheimer's Disease and APP/PS1 Transgenic Mice

To investigate the relationship between MR image contrast associated with beta‐amyloid (Aβ) plaques and their histology and compare the histopathological basis of image contrast and the relaxation mechanism associated with Aβ plaques in human Alzheimers disease (AD) and transgenic APP/PS1 mouse tissues.

Measurement and correction of transmitter and receiver induced nonuniformities in vivo

Signal intensity nonuniformities in high field MR imaging limit the ability of MRI to provide quantitative information and can negatively impact diagnostic scan quality. In this paper, a simple method is described for correcting these effects based on in vivo measurement of the transmission field B1+ and reception sensitivity maps. These maps can be obtained in vivo with either gradient echo (GE) or spin echo (SE) imaging sequences, but the SE approach exhibits an advantage over the GE approach for correcting images over a range of flip angles. In a uniform phantom, this approach reduced the ratio of the signal SD to its mean from around 30% before correction to approximately 6% for the SE approach and 9% for the GE approach after correction. The application of the SE approach for correcting intensity nonuniformities is demonstrated in vivo with human brain images obtained using a conventional spin echo sequence at 3.0 T. Furthermore, it is also shown that this in vivo B1+ and reception sensitivity mapping can be performed using segmented echo planar imaging sequences providing acquisition times of less than 2 min. Although the correction presented here is demonstrated with a simultaneous transmit and receive volume coil, it can be extended to the case of separate transmission and reception coils, including surface and phase array coils. Magn Reson Med 53:408–417, 2005.

Olfactory Deficit Detected by fMRI in Early Alzheimer’s Disease

Alzheimers disease (AD) is accompanied by smell dysfunction, as measured by psychophysical tests. Currently, it is unknown whether AD-related alterations in central olfactory system neural activity, as measured by functional magnetic resonance imaging (fMRI), are detectable beyond those observed in healthy elderly. Moreover, it is not known whether such changes are correlated with indices of odor perception and dementia. To investigate these issues, 12 early stage AD patients and 13 nondemented controls underwent fMRI while being exposed to each of three concentrations of lavender oil odorant. All participants were administered the University of Pennsylvania Smell Identification Test (UPSIT), the Mini-Mental State Examination (MMSE), the Mattis Dementia Rating Scale-2 (DRS-2), and the Clinical Dementia Rating Scale (CDR). The blood oxygen level-dependent (BOLD) signal at primary olfactory cortex (POC) was weaker in AD than in HC subjects. At the lowest odorant concentration, the BOLD signals within POC, hippocampus, and insula were significantly correlated with UPSIT, MMSE, DRS-2, and CDR scores. The BOLD signal intensity and activation volume within the POC increased significantly as a function of odorant concentration in the AD group, but not in the control group. These findings demonstrate that olfactory fMRI is sensitive to the AD-related olfactory and cognitive functional decline.

17β-Estradiol inhibits iron hormone hepcidin through an estrogen responsive element half-site.

Interaction of estrogen with iron at the systemic level is long suspected, but direct evidence linking the two is limited. In the present study, we examined the effects of 17β-estradiol (E2) on hepcidin, a key negative regulator of iron absorption from the liver. We found that transcription of hepcidin was suppressed by E2 treatment in human liver HuH7 and HepG2 cells, and this down-regulation was blocked by E2 antagonist ICI 182780. Chromatin immunoprecipitation, deletion, and EMSA detected a functional estrogen responsive element half-site that is located between -2474 and -2462 upstream from the start of transcription of the hepcidin gene. After cloning the human hepcidin promoter into the pGL3Luc-Reporter vector, luciferase activity was also down-regulated by E2 treatment in HepG2 cells. E2 reduced hepcidin mRNA in wild-type mice as well as in hemochromatosis Fe gene knockout mice. In summary, our data suggest that hepcidin inhibition by E2 is to increase iron uptake, a mechanism to compensate iron loss during menstruation. This mechanism may also contribute to increased iron stores in oral contraceptive users.

Manipulation of image intensity distribution at 7.0 T: Passive RF shimming and focusing with dielectric materials

To investigate the effects of high dielectric material padding on RF field distribution in the human head at 7.0 T, and demonstrate the feasibility and effectiveness of RF passive shimming and focusing with such an approach.