Lead and zinc removal from aqueous solutions by aminotriphosphonate-modified converted natural phosphates.

Apatite particles prepared from natural phosphate rock and grafted with nitrilotris(methylene)triphosphonate (NTP) were evaluated for Pb2+ and Zn2+ sorption from aqueous solutions. Sorption capacities as high as 640 mg.g-1 and 300 mg.g-1 could be obtained for the highest organic content (10 wt%). Analysis of the sorption isotherms using Langmuir, Freundlich and Dubinin-Kaganer-Radushkevich models revealed that Pb2+ ions have a larger affinity for apatite (sorption energy ≈ 8 kJ.mol-1) than for NTP so that organo-modified surfaces led to a heterogenous adsorption process. In contrast, Zn2+ interacts weakly (sorption energy ≈ 1 kJ.mol-1) and similarly with the mineral surface and the organic moieties following a homogenous sorption process. Such an association of organic metal ligands with reactive apatite surfaces within porous materials appears as a promising strategy to obtain efficient adsorbents at low cost and limited environmental impact.

Age related changes in the bone microstructure in patients with femoral neck fractures.

BACKGROUND: The risk of femoral neck fracture progressively increases with age. However, the reasons behind this consistent increase in the fracture risk can't be completely justified by the decrease in the bone mineral density. The objective of this study was to analyze the correlation between various bone structural features and age. STUDY DESIGN & METHODS: A total of 29 consecutive patients who suffered an intracapsular hip fracture and underwent joint replacement surgery between May 2012 and March 2013 were included in this study. A 2 cm × 1 cm Ø cylindrical trabecular bone sample was collected from the femoral heads and preserved in formaldehyde. Bone mineral density (BMD), microarchitecture, organic content and crystallography were analyzed using a Dual-energy X-ray absorptiometry scan, micro-CT scan, and high resolution magic-angle-spinning-nuclear magnetic resonance (MAS-NMR), respectively. Statistical correlations were made using Spearman´s or Pearson´s correlation tests depending on the distribution of the continuous variables. RESULTS: The mean patient age was 79.83 ± 9.31 years. A moderate negative correlation was observed between age and the hydrogen content in bone (1H), which is an indirect estimate to quantify the organic matrix (r = -0.512, p = 0.005). No correlations were observed between BMD, trabecular number, trabecular thickness, phosphorous content, apatite crystal size, and age (r = 0.06, p = 0.755; r = -0.008, p = 0.967; r = -0.046, p = 0.812; r = -0.152, p = 0.430, respectively). A weak positive correlation was observed between Charlson´s comorbidity index (CCI) and c-axis of the hydroxiapatite (HA) crystals (r = -0.400, p = 0.035). CONCLUSION: The femoral head relative protein content progressively decreases with age. BMD was not correlated with other structural bone parameters and age. Patients with higher comorbidity scores had larger HA crystals. The present results suggest that the progressive increase in the hip fracture risk in elderly patients could be partially explained by the lower bone protein content in this age group.

A unique protonated phosphate group in bone mineral not present in synthetic calcium phosphates. Identification by phosphorus-31 solid state NMR spectroscopy.

The detailed chemical composition and microstructure of freshly deposited bone mineral, and how these properties change with maturation of the mineral, have been studied intensively and still remain controversial. For example, current analytical technology is inadequate for the unambiguous characterization of the monohydrogen phosphate ions in bone mineral. Using a differential cross polarization/magic angle spinning solid state nuclear magnetic resonance spectroscopy technique, we suppress the dominant orthophosphate (PO4-3) signal to reveal the spectra of the minor phosphate constituents. This method depends upon differences in the cross polarization time constants for phosphorus-31 nuclei in protonated and non-protonated phosphate ions. It is now possible for the first time to directly measure both the proportion of acid phosphate (HPO4-2) as well as the parameters which characterize its isotropic and anisotropic chemical shift. In bone from three species at several developmental stages, we have found a single type of acid phosphate species, identical in all of the specimens examined. The phosphorus-31 isotropic chemical shift of this acid phosphate group in bone mineral corresponds precisely with that of acid phosphate in octacalcium phosphate, and not with that of brushite. In contrast, the bone acid phosphate anisotropic chemical shift parameters are close to those of brushite, and differ significantly from those of octacalcium phosphate. The orthophosphate resonances of bone mineral, synthetic hydroxyapatite and synthetic octacalcium phosphate share identical chemical isotropic shifts, and similar chemical shift anisotropies. The implication of these results is that the intimate structure of the acid phosphate group in bone mineral is unique, and that none of the common synthetic calcium phosphates accounts well for all of the observed solid state phosphorus-31 NMR properties of bone mineral.

Continuous MR bone density measurement using water- and fat-suppressed projection imaging (WASPI) for PET attenuation correction in PET-MR.

Due to the lack of signal from solid bone in normal MR sequences for the purpose of MR-based attenuation correction, investigators have proposed using the ultrashort echo time (UTE) pulse sequence, which yields signal from bone. However, the UTE-based segmentation approach might not fully capture the intra- and inter-subject bone density variation, which will inevitably lead to bias in reconstructed PET images. In this work, we investigated using the water- and fat-suppressed proton projection imaging (WASPI) sequence to obtain accurate and continuous attenuation for bones. This approach is capable of accounting for intra- and inter-subject bone attenuation variations. Using data acquired from a phantom, we have found that that attenuation correction based on the WASPI sequence is more accurate and precise when compared to either conventional MR attenuation correction or UTE-based segmentation approaches.

Influence of pulse sequence parameters at 1.5 T and 3.0 T on MRI artefacts produced by metal-ceramic restorations.

OBJECTIVES: Susceptibility artefacts from dental materials may compromise MRI diagnosis. However, little is known regarding MRI artefacts of dental material samples with the clinical shapes used in dentistry. The present phantom study aims to clarify how pulse sequences and sequence parameters affect MRI artefacts caused by metal-ceramic restorations. METHODS: A phantom consisting of nickel-chromium metal-ceramic restorations (i.e. dental crowns and fixed bridges) and cylindrical reference specimens immersed in agar gel was imaged in 1.5 and 3.0 T MRI scanners. Gradient echo (GRE), spin echo (SE) and ultrashort echo time (UTE) pulse sequences were used. The artefact area in each image was automatically calculated from the pixel values within a region of interest. Mean values for similar pulse sequences differing in one parameter at a time were compared. A comparison between mean artefact area at 1.5 and 3.0 T, and from GRE and SE was also carried out. In addition, a parametric correlation between echo time (TE) and artefact area was performed. RESULTS: A significant correlation was found between TE and artefact area in GRE images. Higher receiver bandwidth significantly reduced artefact area in SE images. UTE images yielded the smallest artefact area at 1.5 T. In addition, a significant difference in mean artefact area was found between images at 1.5 and 3.0 T field strengths (p = 0.028) and between images from GRE and SE pulse sequences (p = 0.005). CONCLUSIONS: It is possible to compensate the effect of higher field strength on MRI artefacts by setting optimized pulse sequences for scanning patients with metal-ceramic restorations.

Structure, composition, and maturation of newly deposited calcium-phosphate crystals in chicken osteoblast cell cultures.

Characterization of the very early calcium phosphate (CaP) crystals deposited in bone or in osteoblast cell cultures has been hampered by the overwhelming presence of organic matrix components and cells that obscure spectral analyses. We have overcome this problem using isolated protein-free crystals and have obtained new data including 31P nuclear magnetic resonance (NMR) spectra for the first time from mineral crystals deposited during osteoblast calcification in culture. Crystals were isolated from cultures at two time points: (a) at first calcium accumulation (day 8-10) and (b) after 60 days of culture, to assess maturational changes. The analyses show that the chemical composition overall and short range order of the early and mature crystals are characteristic of the apatite crystals found in young embryonic chick bone in vivo. No mineral phase other than apatite was detected by any of the methods used. 31P NMR spectroscopy identified the HPO4 groups as those present in bone apatite. Similar to bone apatites, no OH groups were detected by Fourier transform infrared (FTIR) spectroscopy. The temporal maturational changes in composition and structure of the mineral phase were difficult to assess because of the continuous deposition of crystals throughout culturing. The pathway of the maturational changes observed were similar to those occurring in chick bone in vivo and synthetic apatite crystals in vitro although to a much smaller extent.

Biodegradation of polysiloxanes in lymph nodes of rats measured with 29Si NMR.

Linear and cyclic polysiloxanes and extracts (free polymer) from a silicone gel-filled implant are used to investigate the reactivity of silicones in vivo. Aqueous emulsions of polysiloxanes and controls (without polysiloxanes) are injected once (day 0, approximately 10% w/v) or six times (starting at day 0, every 14 days, approximately 3% w/v) in the right thigh of rats and the popliteal and lumbar lymph nodes are harvested (3 rats per time point and compound investigated) at 2, 16, 30, 44, 58 and 72 days after the injection. 29Si NMR spectroscopy is used to detect and evaluate the presence of polysiloxanes and their metabolites in the lymph nodes. In addition to the resonance associated with the polysiloxane injected (approximately -20 ppm), the NMR spectra of lymph nodes show new resonances that are attributed to partially hydrolyzed polysiloxanes (-5 to -15 ppm) and silica (-90 to - 120 ppm). These resonances are not present in polysiloxanes emulsions before injection or in the lymph nodes of controls. Our results demonstrate that all polysiloxanes and extracts from silicone gel-filled implants are biotransformed in the lymph nodes, but high molecular weight polymer degrades at a slower rate than oligomers.

ADRF differential cross polarization spectroscopy of synthetic calcium phosphates and bone mineral.

An adiabatic demagnetization in the rotating frame (ADRF) differential cross polarization (DCP), or inversion recovery cross polarization (IRCP), technique has been developed to study synthetic calcium phosphates and bone mineral. ADRF of the protons followed by a remagnetization of the phosphorus-31 spins results in an equalization of the dipolar and phosphorus Zeeman nuclear spin temperatures. By shifting the phase of the phosphorus RF by 180 degrees during the forward cross polarization it is possible to invert the temperature of this reservoir and initiate reverse cross polarization. Transient Strombotne-Hahn oscillations were observed on inverting the temperature. The presence of these oscillations complicates the determination of a null point on the basis of cross polarization times. It is necessary to shift the phase of the RF only after a Zeeman spin temperature can be defined, and to use an RF field strength that is slightly smaller than the equivalent S-spin local dipolar field in order to produce a zero crossing after the transient oscillations have decayed.

Deconvolution techniques for removing the effects of chemical shift in 19F nuclear magnetic resonance imaging of perfluorocarbon compounds.

Nuclear magnetic resonance (NMR) imaging of perfluorocarbon (PFC) emulsions and neat liquids has shown potential for in vivo oxygen imaging in blood and organ tissue. PFC compounds exhibit complicated NMR spectra caused by chemical shifts and spin-spin couplings which can lead to artifacts and degraded spatial resolution of resulting NMR images. To correct for the chemical shift artifacts, the technique of spectral deconvolution has been applied to NMR imaging of PFC compounds. The temporal filter for this process can be directly applied to raw free induction decay data in projection reconstruction or to spin-echo data in two-dimensional Fourier transform imaging techniques. The effect of chemical shift artifacts was demonstrated through the NMR imaging of two PFC compounds (F-tributylamine and F-decalin) in phantoms. Methods are presented and demonstrated which allow the chemical shift artifacts to be removed and true images of the spatial distribution of the PFC's to be recovered.

Practical aspects involved in the design and set up of a 0.15 T, 6-coil resistive magnet, whole body NMR imaging facility.

Many technical and logistical questions must be addressed when planning the installation of an NMR imaging system. These considerations become particularly significant when the facility is being established within an existing medical center complex. This paper presents a report on the practical aspects and experience obtained in siting a 6-coil 0.15 T resistive magnet system. The topics discussed include: floor loading; ferromagnetic environment; the effect of iron on the magnet field strength and homogeneity characteristics; shimming procedures; temperature stability requirements; rf shielding; and effects of the magnetic field on common medical instrumentation and magnetic media. It was found that the field shift as a function of the distance of a steel mass from the center of the magnet exhibited an (1/r)5.2 +/- 0.5 to (1/r) 4.2 +/- 0.3 dependence for axial and radial positions respectively which, as expected, is somewhat weaker than the (1/r)6 dependence expected by point dipole approximations. Field distortions caused by the presence of ferromagnetic material in radial positions may be essentially fully compensated with first order transverse shim coils (most conveniently, the x and y imaging gradient coils could be used). Axially distributed material requires, in addition to first order z-gradient correction, higher order axial shim compensation. The temperature stability of the magnet system over the scan period must be better than 0.2 degrees C to insure that temperature-induced field fluctuations are less than the intrinsic static inhomogeneity: and, ideally, below 0.01 degrees C to reduce these fluctuations to less than those caused by power supply instability.

Nuclear magnetic resonance imaging techniques as developed modestly within a university medical center environment: what can the small system contribute at this point?

This paper describes a geometrically small NMR imaging system which has been developed and assembled within a university medical center environment. Consideration is given to the technical specifications and basic economics for the magnet system, NMR spectrometer, and computer configuration. Initial research objectives for the system are outlined which include (1) the signal-to-noise improvement potential of rotational gradient imaging, and (2) 19F tracer imaging considerations with a detailed discussion concerning the feasibility of in vivo NMR imaging of 19F-fluorodeoxyglucose (2-FDG and 3-FDG). Finally, potentially significant areas for research within the constraints of a small NMR imaging system are described.

Perfluorinated organic liquids and emulsions as biocompatible NMR imaging agents for 19F and dissolved oxygen.

Emulsions of fluorocarbons are finding considerable use in physiology for intravascular oxygen transport. Their wide clinical application as blood substitutes, anti-shock, and anti-ischemic agents seems imminent. Whole body NMR imaging is rapidly gaining clinical application and may one day almost completely supplant X-ray imaging. All of the 19F compounds used in biocompatible fluorocarbon emulsions give 19F signals identical to those in the corresponding neat liquid. In concentrations of 10% w/v they are readily imaged. The paramagnetic oxygen molecule reduces T1 in such a way as to make possible whole body imaging of oxygen. T1 typically decreases from 1-4 to 0.3-0.5 seconds and is an inverse linear function of oxygen tension. Spin-lattice relaxation times versus oxygen tensions from 0 to 600 torr have been obtained for F-decalin, F-tributylamine, and F-44E. The usefulness of these 19F effects in clinical NMR imaging depends upon the sensitivity of the method and the tolerable dose. The 19F signal may find use in monitoring 19F compounds as vapors or gases dissolved in plasma or in perfluorocarbons in neat liquid or particle form.

Nuclear magnetic resonance microscopy of atheroma in human coronary arteries.

The purpose of this study was to use direct nuclear magnetic resonance (NMR) microscopy to quantitate and image accumulations of atheroma lipids in human coronary arteries and to validate the results by comparison with histologic preparations. NMR microscopy was performed on a superconducting experimental NMR imaging system operating at 2 Tesla with a probe designed for short echo time (TE), strong B1 field strength, and small samples. Data acquisition used multiple-offset chemical encoding with offsets based on the thermotropic spectral signature of atheroma lipids within the human arterial vessel wall. Three separate channels of image data yielded color axis display of atheroma within the vessel walls. Atheroma location by histology was identified by rarefaction of stroma, as the lipids are extracted in the process of embedding in paraffin. Perimeters, areas, and a shape index (perimeter2:4 pi area) of lumen, atheroma, and outer wall were determined and compared for NMR vs histology. There was no significant difference in the measurements with the exception of luminal shape indices, which were uniformly larger by histology, attributable to flattening of the vessels during histologic preparation. NMR measurement of atheroma content of coronary artery walls agreed well with histology (r = 0.996). NMR microscopy with color axis display proved able to quantitate and image atheroma in coronary arteries, obviating the distortions and lipid removal associated with fixation, embedding, and sectioning for histology.

Communication in orthodontic treatment planning: bioethical and informed consent issues.

Orthodontic treatment planning is an interactive process in which the patient or parent and the orthodontist serve as co-decision makers. As in most partnerships, there is a natural tension between the orthodontist and the patient because of differences in their frames of reference. The orthodontist generally is influenced more by the objective findings (the problem list), whereas patients are guided more by subjective issues related to their perceived needs, desires, and values. The art of careful probing and listening to the patient as part of the treatment planning process is an essential skill. One of the most difficult situations in contemporary orthodontics is presented by the patient with a jaw discrepancy for which the alternative treatments are orthodontic camouflage through dental compensation or surgical-orthodontic correction. Computer imaging to simulate the probable treatment outcomes can facilitate communication about these alternatives by eliminating misconceptions. Full disclosure and the consideration of all viable treatment alternatives have great benefits from a risk management standpoint, in addition to their bioethical merits.

Porous block hydroxyapatite in orthognathic surgery.

Seventy-six nonconsecutive patients undergoing orthognathic surgery, in whom blocks of porous hydroxyapatite were implanted into osteotomy gaps in lieu of autogenous bone grafts, are the subjects of this report. Surgical procedures include inferior maxillary repositioning (10 patients), maxillary advancement (24 patients), transverse maxillary expansions (17 patients) and inferior repositioning of the chin (25 patients). A total of 140 anatomic sites were implanted. Eleven patients later consented to open biopsy of the implant material at a mean 10.2 months following implantation. At the time of follow-up, mean 16.3 months, excellent osseous stability was observed. Three patients developed complications relative to the presence of the implant. Twenty-one of 24 biopsy specimens demonstrated an osseous union of implant to bone with osseous deposition within the implant pores. Radiographic follow-up revealed implant blocks to maintain their volume with no change in density or discreteness. The biological behavior and biomechanical properties of porous block hydroxyapatite are discussed. These implant characteristics make it a feasible bone graft substitute in orthognathic surgery and justify its continued use in this context.

Soft tissue limitations in orthodontics: treatment planning guidelines.

Orthodontists have traditionally viewed structural discrepancies as the major limitation of treatment. In reality, it is the soft tissues that more closely determine therapeutic modifiability. The boundaries of dental compensation for an underlying jaw discrepancy are established by pressures exerted on the teeth by the lips, cheeks, and tongue; limitations of the periodontal attachment; neuromuscular influences on mandibular position; and the contours of the soft tissue facial mask. The ability of the soft tissues to adapt to changes in tooth-jaw relationships are far narrower than the anatomic limits in correcting occlusal relationships. The tolerances for soft tissue adaptation from equilibrium, periodontal, and facial balance standpoints are in the range of 2 to 3 mm for expansion of the mandibular arch and even less for changes in condylar position. Thus, analysis of the soft tissues is the critical step in orthodontic decision making, and this can only be accomplished through physical examination of the patient. Although quantitative measurements cannot be rigorously applied, guidelines for soft tissue assessment, with particular emphasis on facial esthetics, are proposed. From this perspective, a contemporary philosophy of orthodontic practice is offered, with general indications and contraindications for nonextraction, extraction, and surgical treatment.