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Biomedical subjects

T J Mosher

Publications and source records attributed to T J Mosher.

At least 19 recordsLinked to original sources
PubMed2003

1H magnetic resonance spectroscopy of nanomelic chicken cartilage: effect of aggrecan depletion on cartilage T2.

OBJECTIVE: To determine the effect of proteoglycan depletion on cartilage proton magnetic resonance (MR) spectroscopy T2 using nanomelic chicken cartilage, a genetic mutant that completely lacks aggrecan. DESIGN: Proton MR spectroscopic T2 measurements of normal embryonic and nanomelic femoral epiphyseal cartilage were obtained using a 96-echo pulse sequence with inter-echo delay times increased logarithmically over the TE period of 60 micros to 1.7 s. The relative intensity and distribution of cartilage T2 components were determined by fitting signal decay curves to a multi-exponential function. The number of T2 components in the signal decay curves was determined by the degree of freedom limited r2 of the fit. RESULTS: For normal fetal chicken cartilage, 97.6 +/- 0.2% (mean +/- 95% confidence interval) of the total signal comprises a long T2 component (179.1 +/- 1.3 ms) with a relatively small short T2 component (0.5 +/- 0.4 ms). The T2 distribution for nanomelic cartilage is more heterogeneous with four components identified: two short T2 components (0.5 +/- 0.02 and 7.3 +/- 0.6 ms), a large intermediate component (56.4 +/- 5.6 ms), and a broadly distributed long component (137.5 +/- 16.6 ms). In nanomelic cartilage there is greater heterogeneity of cartilage T2 indicating greater variation in water proton mobility and exchange of water with the extracellular matrix. CONCLUSION: Absence of aggrecan in the extracellular cartilage matrix produces greater heterogeneity in cartilage T2, but will not increase T2 as has been previously reported with degenerative change of the collagen matrix.

Aggrecans↗
PubMed2001

Lumbar spine mechanical response to axial compression load in vivo.

STUDY DESIGN: Lumbar spine kinematic response to a 1.0 body weight compressive load was measured in vivo by comparison of relaxed and loaded magnetic resonance image sets in the sagittal plane. OBJECTIVES: To identify and measure acute response mechanisms of the lumbar spine during compression loading. SUMMARY OF BACKGROUND DATA: The isolated ligamentous spine buckles under small loads (88 N); yet, the spine supports >10 times that load in daily activities. Mechanical function of the lumbar spine in vivo is not well understood, and only a few studies examined the spine during in vivo loading. METHODS: Magnetic resonance imaging scans of subjects were taken while subjects were relaxed and while supporting a 1.0 body weight compressive load. Vertebral bodies and disc perimeters were digitized, and relative centroid positions were measured and compared between conditions. Lumbar rotation, bending, compression, and disc translation were determined. Two parameter ensembles were analyzed to describe mechanisms of "spine shrinkage" (decrease of projected spine length) and lumbosacral response. RESULTS: All subjects underwent spine shrinkage (-3.9 +/- 1.2 mm) dominated by cumulative bending, except in three subjects where the rotation component dominated. Levels L2-L4 extended, while L5 flexed, and dL2 through dL4 translated anterior, while dL5 translated posterior. Significant segmental deformations were as follows: L3 extension (-3.3 +/- 3.1 degrees ), dL5 disc translation (-1.4 +/- 1.4 mm), and posterior sacral rotation (3.2 +/- 4.7 degrees ). CONCLUSIONS: Spine shrinkage occurred mainly from spine bending and rotation, with only small contribution from spine compression (shortening along the spine curvature). Response pattern groupings indicated at least two unique subgroups, but the cause remains to be determined.

Adult↗
PubMed2001

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.

Adult↗
PubMed2001

MR imaging and T2 mapping of femoral cartilage: in vivo determination of the magic angle effect.

OBJECTIVE: The purpose of this study was to perform a quantitative evaluation of the effect of static magnetic field orientation on cartilage transverse (T2) relaxation time in the intact living joint and to determine the magnitude of the magic angle effect on in vivo femoral cartilage. MATERIALS AND METHODS: Quantitative T2 maps of the femoral-tibial joint were obtained in eight asymptomatic male volunteers using a 3-T magnet. Cartilage T2 profiles (T2 vs normalized distance from subchondral bone) were evaluated as a function of orientation of the radial zone of cartilage with the applied static magnetic field (B(0)). RESULTS: At a normalized distance of 0.3 from bone, cartilage T2 is 8.6% longer in cartilage oriented 55 degrees to B(0) compared with cartilage oriented parallel with B(0). Greater orientation variation is observed in more superficial cartilage. At a normalized distance of 0.6, cartilage T2 is 18.3% longer. The greatest orientation effect is observed near the articular surface where T2 is 29.1% longer at 55 degrees. CONCLUSION: The effect of orientation on cartilage T2 is substantially less than that predicted from prior ex vivo studies. The greatest variation in cartilage T2 is observed in the superficial 20% of cartilage. Given the small orientation effect, it is unlikely that the "magic angle effect" accounts for regional differences in cartilage signal intensity observed in clinical imaging. We hypothesize that regional differences in the degree of cartilage compression are primarily responsible for the observed regional differences in cartilage T2.

Adult↗
PubMed2000

Human articular cartilage: influence of aging and early symptomatic degeneration on the spatial variation of T2--preliminary findings at 3 T.

PURPOSE: To determine if age and early symptomatic degeneration alter the spatial dependency of cartilage T2. MATERIALS AND METHODS: In 25 asymptomatic volunteers and six volunteers with symptoms of patellar chondromalacia, quantitative T2 maps of patellar cartilage were obtained with a multiecho, spin-echo magnetic resonance imaging sequence at 3.0 T. Spatial variation in T2 was evaluated as a function of participant age and symptoms. RESULTS: All asymptomatic volunteers demonstrated a continuous increase in T2 from the radial zone to the articular surface. In the population aged 46-60 years compared with younger volunteers, there was a statistically significant (P < .05) increase in T2 of the transitional zone. In symptomatic volunteers, the increase in T2 was larger in magnitude and focal in distribution. In five of the six symptomatic volunteers, the increase in T2 was greater than the 95% prediction interval determined from data in the corresponding age-matched asymptomatic population. CONCLUSION: Aging is associated with an asymptomatic increase in T2 of the transitional zone of articular cartilage. Preliminary results indicate this diffuse increase in T2 in senescent cartilage is different in appearance than the focally increased T2 observed in damaged articular cartilage.

Adult↗
PubMed1999

Magnetic resonance imaging of superficial cartilage lesions: role of contrast in lesion detection.

Excised patellar cartilage phantoms with artificial surface lesions were imaged in a 2 g/dl albumin solution to determine the effect of cartilage/fluid contrast on detection of early degenerative change. Surface lesions consisted of full-thickness holes, superficial grooves, and coarse abrasion. Phantoms were imaged with a T1-weighted fast low-angle shot (FLASH) and T2*-weighted dual-echo in the steady state (DESS) sequence. Although both sequences were able to identify full-thickness holes, they underestimated the presence of superficial grooves and extent of fibrillation. Despite greater bulk tissue contrast between cartilage and fluid for the FLASH sequence, detection of fibrillation was poorer compared with the DESS images. The results of this study suggest that surface properties of fibrillated cartilage contribute significantly to the insensitivity of magnetic resonance imaging in detecting superficial lesions. In contrast to previous papers suggesting that T1-weighted spoiled gradient-echo imaging provides the greatest accuracy for lesion detection, our results indicate that, in the presence of joint fluid, T2*-weighted imaging increases detection of superficial lesions. J. Magn. Reson. Imaging 1999;10:178-182.

Animals↗
PubMed1999

Iron and manganese homeostasis in chronic liver disease: relationship to pallidal T1-weighted magnetic resonance signal hyperintensity.

The hyperintense signal in the globus pallidus of cirrhotic patients on T1-weighted magnetic resonance (MR) imaging has been postulated to arise from deposition of paramagnetic manganese2+ (Mn). Intestinal absorption of both iron and Mn are increased in iron deficiency; iron deficiency may therefore increase susceptibility to Mn neurotoxicity. To investigate the relationships between MR signal abnormalities and Mn and Fe status, 21 patients with chronic liver disease were enrolled (alcoholic liver disease, 5; primary biliary cirrhosis, 9; primary sclerosing cholangitis, 3; hepatitis B virus, 2; hepatitis C virus, 1; alpha1-antitrypsin deficiency, 1). Signal hyperintensity in the pallidum on axial T1 weighted images (repetition time/evolution time: 500 ms/15 ms) was observed in 13 of 21 subjects: four patients had mild hyperintensity, three moderate, and six exhibited marked hyperintensity. Erythrocyte Mn concentrations were positively correlated with the degree of the MR hyperintensity (Kendall's tau-b=0.52, P<0.005). The log of erythrocyte Mn concentration was also inversely correlated with all measures of iron status: hemoglobin (Pearson's R=-0.73, P<0.0005); hematocrit (R=-0.62, P<0.005); serum Fe concentrations (R=-0.65, P<0.005); and TIBC saturation (R=-0.62, P<0.005). These findings confirm the association of Mn with the development of pallidal hyperintensity in patients with liver disease. We further found that iron deficiency is an exacerbating factor, probably because of increased intestinal absorption of Mn. We therefore recommend that patients with chronic liver disease avoid Mn supplements without concurrent iron supplementation.

Adult↗
PubMed1998

Removal of local field gradient artifacts in T2*-weighted images at high fields by gradient-echo slice excitation profile imaging.

Development of high magnetic field MRI techniques is hampered by the significant artifacts produced by B0 field inhomogeneities in the excited slices. A technique, gradient-echo slice excitation profile imaging (GESEPI), is presented for recovering the signal lost caused by intravoxel phase dispersion in T2*-weighted images. This technique superimposes an incremental gradient offset on the slice refocusing gradient to sample k-space over the full range of spatial frequencies of the excitation profile. A third Fourier transform of the initial two-dimensional image set generates an image set in which the artifacts produced by the low-order B0 inhomogeneity field gradients in the sample are separated and removed from the high-order microscopic field gradients responsible for T2* contrast. Application to high field brain imaging, at 3.0 T for human and at 9.4 T for immature rat imaging demonstrates the significant improvement in quality of the T2*-weighted contrast images.

Algorithms↗
PubMed1997

Thoracic spiral CT: delivery of contrast material pushed with injectable saline solution in a power injector.

A method of power injection of contrast material pushed with injectable saline solution during thoracic computed tomography (CT) was evaluated in 75 patients to help decrease the amount of contrast material necessary. Patients received 50-125 mL of 60% nonionic contrast material alone or pushed with 50 mL of saline. A volume of 75 mL of contrast material pushed with saline provided enhancement of the thoracic vasculature equal to that provided by a 125-mL volume of contrast material administered alone (P < .001) and caused significantly less beam-hardening artifact (P < .01).

Aorta, Thoracic↗
PubMed1997

Spatial variation of T2 in human articular cartilage.

PURPOSE: To determine the spatial variation of in vivo cartilage T2 in young asymptomatic adults. MATERIALS AND METHODS: Quantitative T2 maps of seven asymptomatic young male adults and one male volunteer with a history of previous intraarticular chondroid fragments were calculated by using a multiecho, spin-echo magnetic resonance imaging sequence at 3.0 T. The T2 maps were bilinearly interpolated to generate T2 profiles across the thickness of cartilage. RESULTS: All seven asymptomatic volunteers demonstrated a monotonic increase in T2, which increased from 32 msec +/- 1 in the deep radial zone and 48 msec +/- 1 in the deep transitional zone to 67 msec +/- 2 in the outer transitional superficial zone. The T2 profile of the volunteer with superficial fibrillation observed at arthroscopy demonstrated marked spatial heterogeneity and a statistically significant increase in cartilage T2. CONCLUSION: There is a reproducible pattern of increasing T2 that is proportional to the known spatial variation in cartilage water and is inversely proportional to the distribution of proteoglycans. The authors postulate that these regional T2 differences are secondary to the restricted mobility of cartilage water within an anisotropic solid matrix.

Adult↗
PubMed1995

Other renal tumors.

Explore the source record for details and available documents.

Adenoma, Oxyphilic↗
PubMed1993

Simultaneous determination of intracellular magnesium and pH from the three 31P NMR Chemical shifts of ATP.

The simultaneous determination of intracellular [MgT]/[ATPT] and pH from the three 31P NMR chemical shifts of ATP has been demonstrated using two-dimensional calibrations. The resulting pH will more accurately represent that of healthy tissue than by using the standard NMR technique. As a result of other possible complexes of MgATP and uncertainties in intracellular pH, errors in the values of KMgATPD (pH), the MgATP NMR shift limits, and thus intracellular magnesium levels are reduced by using this self-consistent analytical method. Direct determination of free magnesium from the (gamma-beta) shifts of ATP may be more sensitive in the alkaline pH range than with the commonly used (alpha-beta) shifts. In addition, the calibration data sets allow for a graphical representation of the uncertainty in magnesium due to the uncertainty in the measured chemical shifts and pH. Our results indicate that KMgATPD is consistent with the literature and favors a value near 50 microM at pH 7.2, but that free magnesium levels will be lower than most prior estimates.

Adenosine Triphosphate↗
PubMed1992

Error in the calibration of the MgATP chemical-shift limit: effects on the determination of free magnesium by 31P NMR spectroscopy.

The measurement of free intracellular magnesium (Mg2+) using the 31P chemical shifts of ATP requires the use of appropriate calibration solutions to determine the chemical-shift limits delta ATP alpha beta and delta MgATP alpha beta. Solutions containing excess Mg2+ contain significant amounts of Mg2ATP and yield positive errors in the value of delta MgATP alpha beta. For physiological applications this may overestimate free intracellular Mg2+ by as much as 300%. This error may be minimized if appropriate mole ratios of Mg2+/ATP are used to calibrate delta MgATP alpha beta.

Adenosine Triphosphate↗
PubMed1992

Hydrogen ion concentration is not the sole determinant of muscle metaboreceptor responses in humans.

We examined the effects of exercise conditioning on muscle sympathetic nerve activity (MSNA) during handgrip and posthandgrip circulatory arrest (PHG-CA). Two conditioning stimuli were studied: forearm dominance and bodybuilding. Static handgrip at 30% maximal voluntary contraction followed by PHG-CA led to a rise in MSNA smaller in dominant than in nondominant forearms (99% vs. 222%; P less than 0.02) and in body builders than in normal volunteers (28% vs. 244%; P less than 0.01). Separate 31P NMR experiments showed no effect of dominance on forearm pH but a pH in bodybuilders higher (6.88) than in normal volunteers (6.79; P less than 0.02) during PHG-CA. Our second goal was to determine if factors besides attenuated [H+] contribute to this conditioning effect. If differences in MSNA during exercise were noted at the same pH, then other mechanisms must contribute to the training effect. We measured MSNA during ischemic fatiguing handgrip. No dominance or bodybuilding effect on pH was noted. However, we noted increases in MSNA smaller in dominant than nondominant forearms (212% vs. 322%; P less than 0.02) and in bodybuilders than in normal volunteers (161% vs. 334%; P less than 0.01). In summary, MSNA responses were less during exercise of conditioned limbs. Factors aside from a lessening of muscle acidosis contribute to this effect.

Adult↗
PubMed1991

Magnetic susceptibility measurement using a double-DANTE tagging (DDT) sequence.

Preliminary results are presented for the nuclear magnetic resonance (NMR) measurement of field gradients generated by differences in magnetic susceptibility. The DDT technique maps the resonant frequency throughout the sample in a single image. Regions of paramagnetic and diamagnetic susceptibility are differentiated with a single magnitude-calculated image.

Humans↗
PubMed1991

Skeletal muscle metaboreceptor exercise responses are attenuated in heart failure.

BACKGROUND: Resting sympathetic nervous system activity is increased in heart failure. Whether sympathetic nervous system responses during exercise are increased is controversial. Furthermore, the role of muscle metaboreceptors and central command in regulating sympathetic outflow has been largely unexplored. METHODS AND RESULTS: Muscle sympathetic nerve activity (MSNA, peroneal nerve) was measured in nine heart failure subjects and eight age-matched control subjects during static exercise (30% maximal voluntary contraction) for 2 minutes and during a period of posthandgrip regional circulatory arrest. This maneuver isolates the metaboreceptor contribution to sympathetic nervous system responses. MSNA responses were similar during static exercise in the two groups. During posthandgrip regional circulatory arrest we observed a marked attenuation in MSNA responses in the heart failure subjects (15% increase in heart failure versus 57% increase in control subjects). A cold pressor test demonstrated a normal MSNA response to a potent nonspecific stimulus in the heart failure subjects (heart failure subjects, 141% increase; control subjects, 215% increase; NS). Nuclear magnetic resonance spectroscopy studies in five separate heart failure subjects and five control subjects suggested that the attenuated metaboreceptor response in heart failure was not due to reduced H+ production. CONCLUSIONS: Skeletal muscle metaboreceptor responses are impaired in heart failure. Because MSNA responses during static exercise are similar in the two groups, mechanisms aside from metaboreceptor stimulation must be important in increasing sympathetic nervous system activity.

Exercise↗
PubMed1990

A DANTE tagging sequence for the evaluation of translational sample motion.

A magnetic resonance imaging sequence that is sensitive to translational motion such as that seen with cardiac contraction is presented. The sequence employs DANTE radio-frequency excitation with a continuous magnetic field gradient to generate a grid pattern of lines. There is improved line resolution and reduced eddy-current formation over current techniques.

Heart↗