Upper Pennsylvanian section on the north wnll of Dry Canyon III the Sacramento Mountains.6 km northeast of Alamogordo. New Mexico. The bot 10m of the creek is about the base of Missourian beds. The base of Virgilan strata is about the base of the pronounced biohermallevel. The well-marked dark thin bed below the main bioherm is composed of peloidal grainstone. foresclbedded to Ihc left (west into the Oro GrandI! basin). The bioherms are algal plate mud mounds and aredevcloped at a very gl!ntJe shelf margin and on the west nank of a Pennsylvanian anticline whose axis lay to the right edge of the photo. The axis is cut transversely by the canyon. The t .... o mounds at the wcst end are micritic cores wnh abundant algal phlles. The main mound is composed chieny offoreset•bcdded, detrita\. bioclastic nanking strata derived from organisms growing 011 mounds exposed on the soulh side of the clmyon from where the picture was taken. The ledges above the main mound level are principally limestones capping sedimentary

Functional magnetic resonance imaging (fMRI) has become a popular tool for investigations into the neural correlates of cognitive activity. One limitation of fMRI, however, is that it has difficulty imaging regions near tissue interfaces due to distortions from macroscopic susceptibility effects which become more severe at higher magnetic field strengths. This difficulty can be particularly problematic for language tasks that engage regions of the temporal lobes near the air-filled sinuses. This paper investigates susceptibility-induced signal loss in the temporal lobes and proposes that by defining a priori regions of interest and using the small-volume statistical correction of K. J. Worsley, S. Marrett, P. Neelin, A. C. Vandal, K. J. Friston, and A. C. Evans (1996, Hum. Brain Mapp. 4: 58 -83), activations in these areas can sometimes be detected by increasing the statistical power of the analysis. We conducted two experiments, one with PET and the other with fMRI, using almost identical semantic categorization paradigms and comparable methods of analysis. There were areas of overlap as well as differences between the PET and fMRI results. One anticipated difference was a lack of activation in two regions in the temporal lobe on initial analyses in the fMRI data set. With a specific region of interest, however, activation in one of the regions was detected. These experiments demonstrate three points: first, even for almost identical cognitive tasks such as those in this study, PET and fMRI may not produce identical results; second, differences between the two methods due to macroscopic susceptibility artifacts in fMRI can be overcome with appropriate statistical corrections, but only partially; and third, new data acquisition paradigms are necessary to fully deal with susceptibility-induced signal loss if the sensitivity of the fMRI experiment to temporal lobe activations is to be enhanced.

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Inhomogeneous magnetic fields produce artifacts in MR images including signal dropout and spatial distortion. A novel perturbative method for calculating the magnetic field to first order (error is second order) within and around nonconducting objects is presented. The perturbation parameter is the susceptibility difference between the object and its surroundings (for example, ϳ10 ppm in the case of brain tissue and air). This method is advantageous as it is sufficiently accurate for most purposes, can be implemented as a simple convolution with a voxel-based object model, and is linear. Furthermore, the method is simple to use and can quickly calculate the field for any orientation of an object using a set of precalculated basis images. Key words: susceptibility; distortion; simulation; field calculation Theoretical calculation of the magnetic B field, given a distribution of tissue, allows modeling of various phenomena, such as MRI signal dropout, geometric distortion, interaction of B field and motion effects, manipulation of the B field using active and weakly magnetic passive shims, and respiration effects. Existing methods for calculating the B field use full finite element calculations (1,2) or approximate solutions to Maxwell's equations given either surface models of matter interfaces (3-5), voxelbased elements (6), spherical elements (7,8), or Fourier representations (9). By using a perturbation approach to solving Maxwell's equations (10), a linear first-order solution can be found which is fast and appropriate for most MR imaging applications. In addition, the perturbation method allows the magnitude of the errors to be calculated, and hence the accuracy and appropriateness of the method to be estimated for various applications.

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These preliminary studies demonstrate that static field inhomogeneity in the human inferior frontal cortex (IFC) is significantly diminished through placement of a small amount of strongly diamagnetic material in the roof of the mouth. As a result, susceptibility-related image artifacts in this region, as observed in blood oxygen level dependent (BOLD) functional MRI (fMRI), are considerably decreased without compromising the spatial or temporal resolution of the study. Simulations of the static field utilizing perturbation theory are shown, which support the experimental results. The limitations and possible future developments of the technique are described. The application of diamagnetic passive shimming on other regions of the brain is also discussed. Routine use of the proposed method within fMRI studies is practicable through subject-specific optimization of the technique utilizing the simulation algorithm. With the use of ever higher static magnetic field (B 0 ) strengths, image artifacts arising from intrinsic magnetic susceptibility differences will continue to place restrictions on many MRI studies of the inferior frontal cortex (IFC) and inferior temporal cortices (ITCs) of the human brain (1-7). The differing magnetic susceptibilities of tissue, air, and bone within the human head bring about a distorted B 0 within the brain. The largest and most spatially complex B 0 inhomogeneities occur in the IFC, superior to the sphenoid and ethmoid sinuses, and in the ITCs, superior to the external auditory canal and mastoid air cells (8,9). The B 0 offset experienced by a spin will cause misrepresentation of its spatial location. A voxel containing spins with a range of B 0 offsets will experience intravoxel dephasing for a gradient-echo sequence. These effects lead to image artifacts of geometric distortion and signal loss that we collectively term "susceptibility artifacts."Rapid gradient-echo imaging methods, such as echo planar imaging (EPI) (10) and spiral imaging (11,12), used in blood oxygen level dependent (BOLD) functional MRI (fMRI), are particularly sensitive to these artifacts (1-5), which makes it difficult to obtain reliable fMRI studies of the IFC (3,4) and ITCs (5). There exists a strong motivation, therefore, to develop techniques that decrease susceptibility artifacts in these regions but retain BOLD contrast along with high spatial and temporal resolution.Techniques that have been used to reduce susceptibility artifacts include sequence parameter optimization (2,13,14), gradient compensation (14 -16), tailored RF pulses (17), and image unwarping (18). As we describe below, these techniques suffer from limitations (see Discussion section). However, improvement in both forms of susceptibility artifacts can be achieved, without adverse consequences for spatial or temporal resolution, by increasing the B 0 homogeneity directly. The reduced in-plane B 0 gradients that result also lead to improved sensitivity to BOLD contrast (19). This is routinely accomplished within the empty scanner bore throu...

Progressive bone disease in multiple myeloma frequently leads to osteolysis, bone resorption, pathologic fractures, vertebral compression, and hypercalcemia. We conducted a double-blind study in 173 newly diagnosed multiple myeloma patients of etidronate disodium (EHDP), a diphosphonate compound that reduces bone resorption by inhibiting osteoclastic activity. The patients were randomly assigned to receive oral EHDP 5 mg/kg/d or placebo until death or discontinuation due to intolerance or refusal. The extent of vertebral deformity was measured by a vertebral index as well as height. The frequency of pathologic fractures, hypercalcemia, and bone pain was regularly assessed, as well as size and number of osteolytic lesions. All patients received melphalan and prednisone daily for 4 days every 4 weeks as the primary chemotherapy for their disease. Although the repeated measures analysis showed a significant height loss, there was no difference between treatment arms (P = .98). There was no significant difference in bone pain, episodes of hypercalcemia, or development of pathologic fractures. Patients on EHDP showed less deterioration in their vertebral index, but this difference only approached statistical significance (P = .07). We conclude that EHDP therapy used in this dosage schedule does not have a clinically significant impact in multiple myeloma.

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