Rest or redistribution thallium myocardial imaging for resting myocardial perfusion: a detailed comparison with regional wall motion

Redistribution thallium-201 (201T1) imaging is the most common method of assessing resting myocardial perfusion. However, the equivalence of a redistribution image and a separate rest injection is unclear. Although the presence of a defect on rest imaging has normally been equated with the presence of a myocardial infarction, it has recently been shown that a significant proportion of fixed defects on exercise-redistribution 201T1 actually represent areas of viable myocardium. This study was a detailed comparison of rest and redistribution imaging in 30 patients undergoing routine exercise 201T1 scanning for the assessment of coronary artery disease. A small dose (15 MBq) of 201T1 was administered at rest following the imaging in three standard planar views. Similar stress images were acquired using a further 50-55 MBq of 201T1 administered at peak effort. Redistribution images were acquired 3-4 h later and equilibrium blood pool ventriculography performed using in vivo labelling with 600 MBq 99Tcm-pertechnetate. Of 150 abnormal segments on the exercise scans, 74 (49%) were identified as being reversible on the redistribution scans and 58 (39%) on the rest images. Only 39 (53%) of these reversible defects were identified on both the redistribution and rest scans. Only 41% of the fixed defects on the redistribution images (32% of fixed defects on the rest images) had abnormal wall motion. Therefore, rest and redistribution images are not equivalent. Both rest and redistribution images significantly overestimate myocardial infarction. This may have significant effects on patient selection for revascularization procedures and therefore all patients having perfusion scintigraphy should also have additional assessment of regional wall motion to allow accurate classification of the functional status of myocardial segments.     

Serum and plasma markers of nutritional status in children infected with the human immunodeficiency virus

OBJECTIVE: To determine whether reduced serum or plasma protein and micronutrient levels are common in children infected with the human immunodeficiency virus (HIV) and whether these levels are different in children with growth retardation compared to those with normal growth. SUBJECTS: Children were separated into three groups: (a) HIV-infected with growth retardation (HIV + Gr); (b) HIV-infected with normal growth (HIV+); (c) HIV-uninfected with normal growth (HIV-). All children were afebrile and free of acute infection at the time of study. During a 24-hour stay in the Pediatric Clinical Research Unit, blood was drawn for analysis of total protein, albumin, zinc, selenium, and vitamin A levels; growth measurements were obtained; and dietary intake was assessed by 24-hour weighed food intake and 24-hour dietary recall. STATISTICAL ANALYSIS: Mean differences between groups were assessed by analysis of variance, and differences in the frequency of nutrient deficiency were determined by chi 2 analysis. RESULTS: Thirty-eight children between 2 and 11 years of age were studied: 10 HIV + Gr, 18 HIV+, and 10 HIV-. No statistically significantly differences were noted in mean levels of albumin, prealbumin, zinc, and selenium. Mean serum level of vitamin A was significantly higher in the HIV + Gr group than in the other two groups. There were no significant differences between groups in the frequency of deficiency for any nutrient studied. Mean energy and nutrient intake was similar among groups. APPLICATIONS/CONCLUSIONS: Abnormal serum or plasma protein or micronutrient levels were uncommon in this cohort of HIV-infected children, even in children with growth retardation. Routine monitoring of the level of proteins and micronutrients studied is unnecessary in the absence of specific clinical indicators of deficiency.     

Electron spin resonance linewidths of Fe3+ in magnesium oxide

Electron spin resonance linewidths of Fe³⁺ in single crystal MgO at 9 GHz were examined experimentally and theoretically for a range of Fe³⁺ concentration. In contrast to the behaviour expected from dipolar broadening the experimental derivative peak-to-peak linewidth for the 1/2 ↔ −1/2 transition, about 0.6 mT at 77 K and a polar angle of 0°, was independent of concentration from 140 to 8500 ppm. The calculated dipolar linewidths greatly exceeded those observed and values of the ratio of moments M ₄ ^1/4 /M ₂ ^1/2 derived from the experimental data lay between 1.33 and 1.48. Optical examination, coupled with heat-treatment experiments, confirmed that the predominant valency state present was Fe³⁺. The data suggested that Fe³⁺ entered the lattice substitutionally, occupying magnesium sites, and that the linewidths were determined by exchange narrowing over the whole concentration range examined.     

Detection and validation of the body edge in low count emission tomography images

Segmentation of the body edge in tomographic images with low count, noisy edges is needed for both PET and SPECT respiratory motion correction and brain SPECT attenuation correction. To reduce noise we re-projected tomographic images and searched for edges in the projection count profiles or their spatial derivatives. Edge location versus projection angle was fitted with cosine basis functions after rejecting outliers and including information about edges of previous sections. We processed 10 s duration FDG PET of the thorax, HMPAO brain, DAT brain and lung perfusion SPECT. Stable edges for all four types of scan were achieved but with different profiles. Edges were validated against edges of coregistered CT or MRI. The best root mean square (rms) accuracy was 8.2 mm (PET) and 5.2 mm (brain SPECT). Inter-scan variability (standard deviation) in the estimated-to-control edge distance for 17 PET scans was 0.4 mm, for 25 ordered subset expectation maximisation (OSEM) reconstructed brain SPECT 1.0 mm and for 18 filtered back-projection (FBP) reconstructed brain SPECT 1.4 mm.     

Reversing the inhibitory effect of nicotine on spinal fusion using an osteoinductive protein extract

STUDY DESIGN: The effect on spinal fusion of an osteoinductive bone protein extract in the presence of a known inhibitor of spinal fusion (systemic nicotine) was studied prospectively in an animal model of posterolateral lumbar fusion. OBJECTIVES: To evaluate the ability of a bovine-derived osteoinductive bone protein extract to overcome the inhibitory effect of nicotine in a rabbit spine fusion model. SUMMARY OF BACKGROUND DATA: Multiple studies have demonstrated the ability of a variety of osteoinductive growth factors to serve as a bone graft substitute for lumbar spinal fusion under "normal" healing conditions. METHODS: Forty-eight adult female New Zealand white rabbits underwent spine arthrodesis at L5-L6 while receiving systemic nicotine through a subcutaneous miniosmotic pump. Arthrodesis was performed using one of the following three graft materials: 1) autogenous iliac crest, 2) osteoinductive bone protein delivered in an allogeneic demineralized bone matrix/ collagen carrier, or 3) osteoinductive bone protein delivered with autogenous iliac crest. Fusions were assessed by blinded manual palpation, radiography, and biomechanical testing. RESULTS: Of the 44 rabbits manually tested by blinded observers, all 14 in the osteoinductive bone protein plus autogenous iliac crest bone group had solid fusions (14 of 14), whereas the fusion rate was less in the osteoinductive bone protein plus demineralized bone matrix group (nine of 14, 64%; P = 0.02), and there were no fusions in the autogenous iliac crest only group (0 of 16, 0%; P = 0.000001). The use of osteoinductive bone protein with autogenous bone produced stronger and stiffer fusions compared with those using autogenous bone alone or osteoinductive bone protein with allograft bone. CONCLUSIONS: Cigarette smoking and nicotine are inhibitory factors in the healing of fractures and spine fusions. This study shows that the inhibitory effect of nicotine can be overcome with an osteoinductive bone growth factor in an animal model.     

Cocurrent gas—liquid flow in packed columns

A model is proposed for cocurrent gas liquid flow through a packed bed. For a given packing, gas and liquid flow rates, we proposed that (i) liquid holdup is a function only of pressure gradient and liquid flow rate and (ii) pressure gradient is only a function of liquid holdup and gas flow rate. Equations are presented which permit the prediction of pressure gradient and liquid holdup for cocurrent upflow and cocurrent downflow in a packed bed. Predictions from the model are shown to be in reasonable agreement with the experimental observations of Turpin and Huntington.     

Model to predict friction transitions for mixed lubrication in the three-pin-on-disc machine

A simple model of the division of load between asperity contacts and hydrodynamic support in a three-pin-on-disc machine was constructed. The predictions of the model show fair agreement with experimental measurements of the coefficient of friction in temperature scan experiments with phosphor bronze pins sliding on a hard steel disc lubricated by mineral oils containing a zinc dithiophosphate additive. The correlation with the wear results is poor.     

On the closed form mechanistic modeling of milling: Specific cutting energy,torque, and power

Specific energy in metal cutting, defined as the energy expended in removing a unit volume of workpiece material, is formulated and determined using a previously developed closed form mechanistic force model for milling operations. Cutting power is computed from the cutting torque, cutting force, kinematics of the cutter, and the volumetric material removal rate. Closed form expressions for specific cutting energy were formulated and found to be functions of the process parameters: pressure and friction for both rake and flank surfaces and chip flow angle at the rake face of the tool. Friction is found to play a very important role in cutting torque and power. Experiments were carried out to determine the effects of feedrate, cutting speed, workpiece material, and flank wear land width on specific cutting energy. It was found that the specific cutting energy increases with a decrease in the chip thickness and with an increase in flank wear land.     

Immediate consolidation behaviour of aqueous pigment coatings applied to porous substrates

A high-speed, laboratory-scale, film-press coater was used to study the surface structure characteristics of aqueous-based pigment coatings when applied to a paper substrate. The film-press coating trials were monitored on-line with a high-resolution digital camera. The resulting images were quantified using a four-segmentation method, developed specifically to investigate the ‘degree of dryness’ experienced by the coating layer at different times from the initial application of coating. This method was based on an assessment of the grey level (GL) intensity described by the on-line images. Coating consolidation times were found to be quite rapid, with the first critical concentration (FCC) occurring at 0.020 s from application and the second critical concentration (SCC) occurring at 0.041 s. These results differ greatly from many consolidation studies in the literature, which typically report much longer consolidation times. This is primarily because they have used model substrates (usually non-porous), simplified coating formulations and often applied coat weights that are significantly higher than would commonly be used with film-press coating technology. This study has therefore highlighted the importance of developing laboratory equipment that accurately mimics film-press technology on porous substrates, and also the significant contributions of porous substrates and coating thickness (among others) on consolidation processes. It has subsequently shown that if these factors are removed from model systems, the influences on FCC and SCC are considerable. Other results were that higher nip pressures influenced the initial dewatering characteristics of the coating, but at longer times, the nip pressure had little effect on the resulting structure. Lower coat weights resulted in faster consolidation times as expected, and coating speed had little effect on the resultant images or coating structure.