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Biomedical subjects

R A Levy

Publications and source records attributed to R A Levy.

At least 37 records · Page 2Linked to original sources
PubMed1995

Three-dimensional craniocervical helical CT: is isotropic imaging possible?

PURPOSE: To assess whether isotropic resolution is attainable in three-dimensional craniocervical helical computed tomography (CT). MATERIALS AND METHODS: Two cadaveric cervical spine and two orbital phantoms were scanned in air and water by using 180 degrees-interpolated helical CT with three-dimensional reconstruction. Scan parameters yielded nominally isotropic voxels with reconstruction of 1-mm collimated and incremental sections at 0.2-mm intervals. CT scan angle was varied with the assumption that volume-averaging artifacts should be scan angle-independent with isotropic voxels. Twelve blinded observers analyzed three-dimensional images generated from multiple CT orientations to assess changes in volume-averaging artifacts that would indicate voxel anisotropy. RESULTS: Significant observable differences in three-dimensional image representation were present in test anatomic regions in one cervical spine phantom (two-tailed P < .006) and in both orbital phantoms (P < .008 and P < .006). No statistically significant differences were present for control anatomic regions. CONCLUSION: Isotropic scanning is not possible in three-dimensional craniocervical helical CT.

Adult↗
PubMed1994

Semiautomated three-dimensional craniofacial imaging and modeling.

RATIONALE AND OBJECTIVES: The author identified clinical parameters and developed thresholding strategies that facilitate semiautomated three-dimensional craniofacial imaging and modeling. METHODS: A polyvinylchloride phantom was imaged on a computed tomography (CT) scanner using multiple scan planes, surrounding media, and two-dimensional reconstruction filters. Three-dimensional reconstructions were performed by an experienced operator on a commercial workstation. A simple mathematical thresholding algorithm derived from these trials was applied to 17 embryologic craniofacial specimens and compared with operator-selected thresholds in the generation of three-dimensional CT images. RESULTS: Utilization of the parameter alpha provides an experimental framework in which operator-selected thresholds can be used to refine simple mathematical thresholding formulae. We demonstrated significant changes in three-dimensional image accuracy based on CT scan plane. CONCLUSIONS: Experimentation with a CT phantom enables semiautomated three-dimensional craniofacial imaging and modeling. Further investigation of two-dimensional CT craniofacial datasets is justified.

Computer Simulation↗
PubMed1994

Preliminary experience with selective laser sintering models of the human temporal bone.

PURPOSE: To assess the accuracy of three-dimensional models of the human temporal bone generated from CT data. METHODS: Thin-section CT of a left human cadaveric temporal bone was performed using multiple-scan planes (axial, coronal, and sagittal) at 1.5-mm section thickness and 0.25-mm pixel size with an edge-enhancement two-dimensional algorithm. CT data were converted to toggle point format based upon a threshold value of 200 (approximately -830 HU) obtained from prior experimentation with a CT phantom. Selective laser sintering of polycarbonate powder was performed at a beam diameter of 0.060 inches (1.5 mm), 100 scan lines per inch, layer thickness of 0.010 inches (0.25 mm), and layer repeat factor of 4. The polycarbonate models were then scanned in the axial, coronal, and sagittal planes and compared with the original CT data. Anatomic dissection of the models was performed for further verification of the imaging findings. RESULTS: Models of high anatomic accuracy were generated. Shortening by a factor of 0.67 along the Z axis secondary to the layer repeat factor of 4 resulted in distortion of the models. Distortion in the XY plane ranged from 0% to 20%. Differences in model accuracy based on the initial CT scan plane were observed. A significant amount of nonsintered or partially sintered polycarbonate resulted in intermediate density on the CT images. CONCLUSIONS: Selective laser sintering can result in accurate modeling of detailed anatomic structures in the human temporal bone. Further investigation of materials and factors contributing to the accuracy of selective laser sintering in the manufacturing of high-resolution anatomic models is warranted.

Humans↗
PubMed1992

Phospholipid binding of antiphospholipid antibodies and placental anticoagulant protein.

We evaluated the interaction of antiphospholipid antibodies (aPL) with placental anticoagulant protein I (PAP I), a calcium-dependent phospholipid binding protein which may act as a natural anticoagulant. Clotting assays showed additive prolongation of clotting times with aPL and PAP I. ELISA and vesicle phospholipid binding studies showed PAP I inhibition of aPL binding to phospholipid but no inhibition of PAP I-phospholipid binding by aPL. aPL and PAP I interact additively in anticoagulant activity in in vitro clotting systems and compete for phospholipid in ELISA system. These data support the hypotheses that aPL and PAP I may recognize similar phospholipid epitopes and that in vivo interaction may occur.

Annexins↗
PubMed1992

Clinical aspects of therapeutic substitution.

A variety of problems are associated with the operation, quality, costs, and benefits of therapeutic substitution programmes. Adequate communication of procedures, events, and failures are essential features of a safe therapeutic substitution policy. However, case reports of suboptimal therapy and differences in pharmacological profiles of related agents indicate the potential for clinical nonequivalence even between similar drugs of a class. Suboptimal or failed therapy associated with such nonequivalence may offset savings in drug costs resulting from therapeutic substitution. Thus, consultation on behalf of each patient is necessary for optimal therapy and maximum cost savings. Currently, there are no data on the interchangeability of specific agents of a class and the effects of therapeutic substitution on overall treatment costs. Thus, the health and economic outcomes of therapeutic substitution policies are unknown.

Clinical Protocols↗
PubMed1992

Prescription cost sharing: economic and health impacts, and implications for health policy.

Cost sharing for prescription pharmaceuticals--in the form of copayments, coinsurance, or deductibles--is now common in healthcare systems throughout the world. Although there are no studies that directly or convincingly measure the effects of prescription cost sharing on health status or treatment outcomes, cost sharing does appear to reduce utilisation of pharmaceuticals; however, more information is required concerning the relationship between cost sharing and prescription-filling behaviour. Additionally, outcomes studies are needed to define appropriate and inappropriate cost-sharing levels for particular groups of patients, based on income, disease, employment status, and other factors. Cost sharing for pharmaceuticals and other medical services is likely to increase in the near future. As a result, consumers will have a greater role in treatment decisions and will also become more interested in knowing the value of the medicines they are asked to purchase. They are therefore likely to demand pharmaceutical products that are more cost-effective and products that improve quality of life. The increased implementation of cost-sharing programmes necessitates the adoption of appropriate cost-sharing policies, which incorporate the following general principles: 1. Consumers must be provided with the information required to make informed decisions, including the value of the medication, its importance in the treatment plan, and the consequences of not having the prescription filled. 2. Aggressive or abusive cost-sharing features that deny access to optimal pharmaceutical therapy must be avoided. 3. Inappropriate cost sharing, either fixed level or percentage of the prescription cost, may affect disease control and ultimately health or functional status. 4. Cost sharing restricted to pharmaceuticals may encourage replacement of drug therapy with more expensive forms of treatment; therefore, cost sharing should apply to the full range of medical services to prevent service substitution.

Aged↗
PubMed1991

The effect of computed tomographic scan orientation on information loss in the three-dimensional reconstruction of tripod zygomatic fractures.

Fractures modeled in the dried skull indicate that the initial plane of computed tomography (CT) section contributes to the accuracy of three-dimensional (3D) images generated from two-dimensional (2D) CT data. The authors retrospectively analyzed seven clinical cases of tripod zygomatic fractures that were imaged with both axial and coronal CT scan orientations. Ten observers evaluated paired 3D CT images, one generated from 2D CT data in the axial plane and the other generated from coronal 2D CT data, for each of the seven cases of tripod fractures. A G-E 9800 CT scanner with the 3D98 Quick processing system were used for the 3D reconstructions. The axial scan orientation resulted in 3D reconstructions that had significantly less information loss in the display of the tripod fractures than did those based on coronal CT data (P less than .025).

Humans↗
PubMed1990

Characteristics of high-titer IgG antiphospholipid antibody in systemic lupus erythematosus patients with and without fetal death.

Although high-titer IgG antiphospholipid antibody (aPL) is a predictor of mid-pregnancy fetal death in women with systemic lupus erythematosus (SLE), some SLE patients with high-titer aPL carry pregnancies normally, and to term. To determine potential antibody differences between IgG aPL-positive women with and without fetal death, we studied aPL isotype, subclass, anticoagulant activity, phospholipid specificity, and antibody avidity in selected sera from pregnant SLE patients with high-titer IgG aPL. For controls, we selected sera from pregnant SLE patients who had negative results on tests for IgG aPL (with and without fetal loss). None of the specified antibody characteristics distinguished between the aPL-positive patient groups, nor were other specificities defined in IgG aPL-negative sera from women with fetal death. Although high-titer aPL is a good predictor of fetal death, currently known characteristics, other than a high titer of aPL, do not identify which women will experience this complication.

Antibody Specificity↗
PubMed1990

Fatty acid chain is a critical epitope for antiphospholipid antibody.

To explore the role of phospholipid fatty acids in binding of antiphospholipid antibody (aPL) in ELISA, we tested aPL binding to phospholipids containing fatty acids of varying chain length and degree of saturation using direct ELISA and inhibition methods. Polyclonal IgG and IgM human aPL's bind to C18:1 phosphatidylglycerol (PG) better than to C18:0 PG or C18:2 PG. Binding is greater to C18 than to C14:0 or C16:0 PGs; aPL's do not bind to C12:0 PG. aPL binding is not inhibited by C18:1 diacylglycerol, glycerol-3-phosphate, myoinositol, or myoinositol phosphate. The fatty acid chains are critical determinants for antigen recognition and, by projection, biological activity of aPL.

Autoantibodies↗
PubMed1990

Lysophosphatidylethanolamine is the antigen to which apparent antibody to phosphatidylethanolamine binds.

Because binding of antiphospholipid antibody (aPL) to phosphatidylethanolamine (PE) is central to the definition of the antigenic epitope targeted by aPLs, we examined the binding of aPL-positive SLE sera to PE under various conditions. No serum bound to PE uncontaminated with lysophosphatidylethanolamine (1PE), but many aPL-positive sera bound to 1PE-contaminated PE and to 1PE coated onto an ELISA plate. Absorption studies indicated partial cross-reactivity between PE containing 1PE and cardiolipin. We conclude that clinical aPLs do not bind to PE. Prior reports to the contrary most likely represent binding of aPL to PE's degradation product, 1PE.

Autoantibodies↗
PubMed1990

Effects of omega-3 fish oils on plasma lipids, lipoprotein composition, and postheparin lipoprotein lipase in women with IDDM.

Because the apparent reduction in cardiovascular risk noted in nondiabetic populations that ingest diets rich in marine lipids containing omega-3 fatty acids is believed to result in part from their capacity to modify the composition and physicochemical behavior of lipoproteins, we sought to determine whether dietary supplementation with marine lipids might favorably affect lipoprotein composition in insulin-dependent diabetes mellitus (IDDM). Eight normolipidemic IDDM women (mean +/- SD age 29.8 +/- 4.7 yr) were studied before and 3 mo after receiving a marine-lipid concentrate (Super-EPA) containing 6 g omega-3 fatty acids and a total of 12 mg of cholesterol daily. Weight, insulin requirements, and glycosylated hemoglobin remained stable. After treatment, mean +/- SD plasma triglyceride (TG) levels fell (before, 81.7 +/- 22 mg/dl; after, 69.19 +/- 17; P less than 0.025). High-density lipoprotein2 (HDL2) cholesterol (before, 10.98 +/- 5.45 mg/dl; after, 18.43 +/- 7.93; P less than 0.01), its major apolipoprotein A-I (apoAI), and the major phospholipids (sphingomyelin and lecithin) all rose significantly. ApoB and plasma and low-density lipoprotein cholesterol levels and HDL3 composition were unchanged. Postheparin hepatic and lipoprotein lipase activities were unaffected by marine lipids. These data indicate that women with IDDM experience apparently beneficial effects on TG and HDL2 from dietary supplementation with omega-3 fatty acids administered in a low-cholesterol-containing oil without adversely affecting overall diabetes management. If these changes in lipoprotein concentration and composition prove to have antiatherogenic consequences and are free of long-term toxicity, these agents may have a role in the therapy of IDDM patients.

Adult↗
PubMed1990

Characteristics of IgG antiphospholipid antibodies in patients with systemic lupus erythematosus and syphilis.

To evaluate the similarities and differences of antiphospholipid antibodies (aPL) in systemic lupus erythematosus (SLE) and syphilis, we studied 20 SLE and 16 syphilis high titer IgG aPL sera for antibody isotype, avidity, phospholipid specificity, light chain and IgG subclass. Syphilis aPL had lower avidity, with kappa light chain and IgG1 and IgG3 predominance, in contrast to higher avidity, with lambda light chain and IgG2 and IgG4 predominance in SLE aPL. Phospholipid specificities were similar. SLE and syphilis aPL both recognize phospholipid epitopes but differ in important antibody characteristics.

Autoantibodies↗
PubMed1989

Clinical differences among nonsteroidal antiinflammatory drugs: implications for therapeutic substitution in ambulatory patients.

The practice of therapeutic substitution, i.e., replacing one drug with another chemically different drug from the same therapeutic class, represents an important therapeutic modification with potential clinical significance far beyond that of generic substitution. Adverse consequences following therapeutic substitution of nonsteroidal antiinflammatory drugs (NSAID) is of special concern because of substantial differences among these agents in pharmacokinetic, pharmacological, and clinical properties. Therapeutic substitution of NSAID for ambulatory patients may result in compromised clinical outcome because (1) patient response is unpredictable and selection of the optimal agent must be tailored for each patient; (2) substantial differences exist in adverse reaction profiles; (3) drug interaction studies are lacking; and (4) selection of an agent must be individualized to ensure compliance with the dosing regimen. Cost savings achieved through therapeutic substitution of NSAID may be lost by additional overall treatment costs due to adverse reactions or suboptimal therapy. The occurrence of adverse or suboptimal effects in ambulatory patients is more likely if NSAID are substituted without full knowledge of the patient's medical history and clinical status. Communication between the pharmacy and prescribing physician regarding a patient's specific needs is essential for rational substitution among NSAID.

Ambulatory Care↗