Interpretation of SPECT wall motion with deep learning.

OBJECTIVES: We sought to develop a novel deep learning (DL) workflow to interpret single-photon emission computed tomography (SPECT) wall motion. BACKGROUND: Wall motion assessment with SPECT is limited by image temporal and spatial resolution. Visual interpretation of wall motion can be subjective and prone to error. Artificial intelligence (AI) may improve accuracy of wall motion assessment. METHODS: A total of 1038 patients undergoing rest electrocardiogram (ECG)-gated SPECT and echocardiography were included. Using echocardiography as truth, a DL-model (DL-model 1) was trained to predict the probability of abnormal wall motion. Of the 1038 patients, 317 were used to train a DL-model (DL-model 2) to assess regional wall motion. A 10-fold cross-validation was adopted. Diagnostic performance of DL was compared with human readers and quantitative parameters. RESULTS: The area under the receiver operating characteristic curve (AUC) and accuracy (ACC) of DL model (AUC: .82 [95% CI: .79-.85]; ACC: .88) were higher than human (AUC: .77 [95% CI: .73-.81]; ACC: .82; P < .001) and quantitative parameter (AUC: .74 [95% CI: .66-.81]; ACC: .78; P < .05). The net reclassification index (NRI) was 7.7%. The AUC and accuracy of DL model for per-segment and per-vessel territory diagnosis were also higher than human reader. The DL model generated results within 30 seconds with operable guided user interface (GUI) and therefore could provide preliminary interpretation. CONCLUSIONS: DL can be used to improve interpretation of rest SPECT wall motion as compared with current human readers and quantitative parameter diagnosis.

Interpreting Wide-Complex Tachycardia With the Use of Artificial Intelligence.

BACKGROUND: Adopting artificial intelligence (AI) in medicine may improve speed and accuracy in patient diagnosis. We sought to develop an AI algorithm to interpret wide-complex tachycardia (WCT) electrocardiograms (ECGs) and compare its diagnostic accuracy with that of cardiologists. METHODS: Using 3330 WCT ECGs (2906 supraventricular tachycardia [SVT] and 424 ventricular tachycardia [VT]), we created a training/validation (3131) and a test set (199 ECGs). A convolutional neural network structure using a modification of differentiable architecture search was developed to differentiate between SVT and VT. RESULTS: The mean accuracy of electrophysiology (EP) cardiologists was 92.5% with sensitivity 91.7%, specificity 93.4%, positive predictive value 93.7%, and negative predictive value 91.7%. Non-EP cardiologists had an accuracy of 73.2 ± 14.4% with sensitivity, specificity, and positive and negative predictive values of 59.8 ± 18.2%, 93.8 ± 3.7%, 93.6 ± 2.3%, and 73.2 ± 14.4%, respectively. AI had superior sensitivity and accuracy (91.9% and 93.0%, respectively) than non-EP cardiologists and similar performance compared with EP cardiologists. Mean time to interpret each ECG varied from 10.1 to 13.8 seconds for EP cardiologists and from 3.1 to 16.6 seconds for non-EP cardiologists. AI required a mean of 0.0092 ± 0.0035 seconds for each ECG interpretation. CONCLUSIONS: AI appears to diagnose WCT with accuracy superior to non-EP cardiologists and similar to EP cardiologists. Using AI to assist with ECG interpretations may improve patient care.

Normalized Subendocardial Myocardial Attenuation on Coronary Computed Tomography Angiography Predicts Postoperative Adverse Cardiovascular Events: Coronary CTA VISION Substudy.

BACKGROUND: Abnormalities in computed tomography myocardial perfusion has been associated with coronary artery disease and major adverse cardiovascular events (MACE). We sought to investigate if subendocardial attenuation using coronary computed tomography angiography predicts MACE 30 days postelective noncardiac surgery. METHODS: Using a 17-segment model, coronary computed tomography angiography images were analyzed for subendocardial and transmural attenuation and the corresponding blood pool. The segment with the lowest subendocardial attenuation and transmural attenuation were normalized to the segment with the highest subendocardial and transmural attenuation, respectively (SUBnormalized, and TRANSnormalized, respectively). We evaluated the independent and incremental value of myocardial attenuation to predict the composite of cardiovascular death or nonfatal myocardial infarction. RESULTS: Of a total of 995 coronary CTA VISION (Coronary Computed Tomographic Angiography and Vascular Events in Noncardiac Surgery Patients Cohort Evaluation Study) patients, 735 had available images and complete data for these analyses. Among these patients, 60 had MACE. Based on Revised Cardiovascular Risk Index, 257, 302, 138, and 38 patients had scores of 0, 1, 2, and ≥3, respectively. On coronary computed tomography angiography, 75 patients had normal coronary arteries, 297 patients had nonobstructive coronary artery disease, 264 patients had obstructive disease, and 99 patients had extensive obstructive coronary artery disease. SUBnormalized was an independent and incremental predictor of events in the model that included Revised Cardiovascular Risk Index and coronary artery disease severity. Compared with patients in the highest tertile of SUBnormalized, patients in the second and first tertiles had an increased hazards ratio for events (2.23 [95% CI, 1.091-4.551] and 2.36 [95% CI, 1.16-4.81], respectively). TRANSnormalized, as a continuous variable, was also found to be a predictor of MACE (P=0.027). CONCLUSIONS: Our study demonstrates that SUBnormalized and TRANSnormalized are independent and incremental predictors of MACE 30 days after elective noncardiac surgery. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT01635309.

Are Training Programs Ready for the Rapid Adoption of CCTA?: CBME in CCTA.

OBJECTIVES: This study sought to assess training volumes and its relationship to learning and identify potential new thresholds for determining expertise. BACKGROUND: Competency-based medical education (CBME) is being rapidly adopted and therefore training programs will need to adapt and identify new and novel methods of defining, measuring, and assessing clinical skills. METHODS: Consecutive cardiac computed tomography (CT) studies were interpreted independently by trainees and expert readers, and their interpretations (Agatston score, coronary artery disease severity, and Coronary Artery Disease Reporting and Data System) were collected. Kappa agreements were measured between trainees and experts for every 50 consecutive cases. Agreements between trainees and experts were tracked and compared with the agreement between expert readers. RESULTS: A total of 36 trainees interpreted 14,432 cardiac CT studies. Agreement between trainees and experts increased with CT case volumes, but trainees learned at different rates. Using a threshold for expertise, skill of measuring coronary calcification was achieved within 50 cases, but expertise for coronary CT angiography appeared to require a mean case volume of 750, comprising 400 abnormal cases. CONCLUSIONS: Current volume-based training guidelines may be insufficient and higher case volumes may be required. We demonstrate that tracking cardiac CT learners is feasible and that CBME could be incorporated into CT training programs.

A Systematic Review of the Effect of N-Acetylcysteine on Serum Creatinine and Cystatin C Measurements.

INTRODUCTION: N-acetylcysteine (NAC) is an antioxidant that can regenerate glutathione and is primarily used for acetaminophen overdose. NAC has been tested and used for preventing iatrogenic acute kidney injury or slowing the progression of chronic kidney disease, with mixed results. There are conflicting reports that NAC may artificially lower measured serum creatinine without improving kidney function, potentially by assay interference. Given these mixed results, we conducted a systematic review of the literature to determine whether there is an effect of NAC on kidney function as measured with serum creatinine and cystatin C. METHODS: A literature search was conducted to identify all study types reporting a change in serum creatinine after NAC administration. The primary outcome was change in serum creatinine after NAC administration. The secondary outcome was a change in cystatin C after NAC administration. Subgroup analyses were conducted to assess effect of creatinine assay (Jaffe vs. non-Jaffe and intravenous vs. oral). RESULTS: Six studies with a total of 199 participants were eligible for the systematic review and meta-analysis. There was a small but significant decrease in serum creatinine after NAC administration overall (weighted mean difference [WMD], -2.80 µmol/L [95% confidence interval {CI} -5.6 to 0.0]; P = 0.05). This was greater with non-Jaffe methods (WMD, -3.24 µmol/L [95% CI -6.29 to -0.28]; P = 0.04) than Jaffe (WMD, -0.51 µmol/L [95% CI -7.56 to 6.53]; P = 0.89) and in particular with intravenous (WMD, -31.10 µmol/L [95% CI -58.37 to -3.83]; P = 0.03) compared with oral NAC (WMD, -2.5 µmol/L [95% CI -5.32 to 0.32]; P = 0.08). There was no change in cystatin C after NAC administration. DISCUSSION: NAC causes a decrease in serum creatinine but not in cystatin C, suggesting analytic interference rather than an effect on kidney function. Supporting this, the effect was greater with non-Jaffe methods of creatinine estimation. Future studies of NAC should use the Jaffe method of creatinine estimation when kidney outcomes are being reported. Even in clinical settings, the use of an enzymatic assay when high doses of intravenous NAC are being used may result in underdiagnosis or delayed diagnosis of acute kidney injury.

Effect of proton pump inhibitors on Rubidium-82 gastric uptake using positron emission tomography myocardial perfusion imaging.

BACKGROUND: Rb-82 positron emission tomography (PET) myocardial perfusion imaging (MPI) is a robust tool for the evaluation of coronary artery disease (CAD). However, gastric uptake and spillover can be seen in 10% of Rb-82 PET MPI studies, commonly affecting the inferior wall, and can preclude the accurate identification of myocardial ischemia. We sought to understand the relationship between Rb-82 gastric uptake and the use of proton pump inhibitors (PPI). METHODS: 600 consecutive patients who presented for a clinically indicated Rb-82 PET MPI study were prospectively enrolled. In addition to the clinical history, PPI use was ascertained (medication, dose, frequency and duration of use, and time of last dose). Patients were categorized as PPI and non-PPI users. Rb-82 uptake in the gastrium, myocardium, and liver were measured at rest. Absolute uptake values and gastric:hepatic ratios were compared in PPI and non-PPI users. RESULT: Of 600 enrolled patients, 181 (30.2%) patients were using PPI. The gastric Rb-82 uptake in PPI users was 23% higher than non-PPI users (146 ± 52 kBq/cc vs 119 ± 40 kBq/cc, respectively; P < 0.001). The resting gastric:hepatic Rb-82 uptake ratio was also 23% higher in PPI vs non-PPI users (2.7 ± 1.0 vs 2.2 ± 0.8, respectively; P < 0.001). CONCLUSION: The gastric uptake of Rb-82 appears to be greater in patients actively using PPI and may identify a group who might be at greater risk of non-diagnostic Rb-82 PET MPI.

Competency-Based Medical Education: Do the Cardiac Imaging Training Guidelines Have it Right?

OBJECTIVES: This study sought to: 1) determine if the current training volume guidelines are reasonable for attaining competence for interpreting myocardial perfusion imaging (MPI); and if not, 2) identify potential thresholds for training volumes and competence. BACKGROUND: There is a growing desire to adopt competency-based medical education (CBME). As such, the implementation of CBME will require new and novel methods of defining, measuring, and assessing clinical competence. The potential use of CBME in cardiac imaging has not been well studied. METHODS: Consecutive MPI studies were interpreted independently by trainees, and expert readers reviewed the same studies. Studies were quantified using summed scores and % left ventricular (LV) ischemia and the kappa agreement between trainee and expert were measured every 50 cases. Agreement for all MPI and abnormal MPI cases was calculated. RESULTS: A total of 24 trainees interpreted 9,668 MPI studies over 37 months. Agreement between trainees and expert readers increased with MPI case volumes but at different rates. The threshold for competence was set at 2 SDs below expert interobserver agreement. The average trainee surpassed this threshold for both summed stress score and %LV ischemia after 800 studies and after 400 abnormal MPI studies. Trainees learned at different rates and surpassed the competence threshold after different case volumes. CONCLUSIONS: The use of CBME within nuclear cardiology appears to be feasible. Our results suggest that current guidelines may be insufficient to ensure competence and would support the need to increase the MPI case volumes. The use of CBME principles would suggest that trainees may achieve competence at different rates and our results suggest a shift in focus from volume-based learning toward target agreement thresholds.

Novel injectable gallium-based self-setting glass-alginate hydrogel composite for cardiovascular tissue engineering.

Composite biomaterials offer a new approach for engineering novel, minimally-invasive scaffolds with properties that can be modified for a range of soft tissue applications. In this study, a new way of controlling the gelation of alginate hydrogels using Ga-based glass particles is presented. Through a comprehensive analysis, it was shown that the setting time, mechanical strength, stiffness and degradation properties of this composite can all be tailored for various applications. Specifically, the hydrogel generated through using a glass particle, wherein toxic aluminium is replaced with biocompatible gallium, exhibited enhanced properties. The material's stiffness matches that of soft tissues, while it displays a slow and tuneable gelation rate, making it a suitable candidate for minimally-invasive intra-vascular injection. In addition, it was also found that this composite can be tailored to deliver ions into the local cellular environment without affecting platelet adhesion or compromising viability of vascular cells in vitro.

The effect of tantalum incorporation on the physical and chemical properties of ternary silicon-calcium-phosphorous mesoporous bioactive glasses.

Synthesis and characterization of the first mesoporous bioactive glasses (MBGs) containing tantalum are reported here, along with their potential application as hemostats. Silica MBGs were synthesized using with the molar composition of (80-x)% Si, 15% Ca, 5% P, and x% Ta. It was found that incorporation of >1 mol % Ta into the MBGs changes their physical and chemical properties. Increasing Ta content from 0 to 10 mol % causes a decrease in the surface area and pore volume of ~20 and ~35%, respectively. This is due to the increase in nonbridging oxygens and mismatch of thermal expansion coefficient which created discontinuities in the ordered channel structure. However, the effect is not significant on the amount of ions (Si, Ca, P, and Ta) released, from the sample into deionized water, for short durations (<60 min). In a mouse tail-cut model, a significant decrease in bleeding time (≥50% of average bleeding time) was found for Ta-MBGs compared to having no treatment, Arista, and MBG without Ta. Further studies are proposed to determine the mechanism of Ta involvement with the hemostatic process. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 2229-2237, 2019.

The Effect of N-Acetylcysteine on Creatinine Measurement: Protocol for a Systematic Review.

BACKGROUND: N-acetylcysteine (NAC) is an antioxidant which can regenerate glutathione and is primarily used for acetaminophen overdose. It is also a potential therapy to prevent iatrogenic acute kidney injury or slow the progression of chronic kidney disease. It has been considered in this context by many studies with mixed results. Notably, a biological-mechanism rationale for a protective effect of NAC has never been adequately reported. Among conflicting reports, there appears to be evidence that NAC may artificially lower measured serum creatinine without improving kidney function, potentially by assay interference. Given these mixed results, a systematic review of the literature will be conducted to determine whether there is an effect of NAC on kidney function measured with serum creatinine. OBJECTIVE: To determine the effect of NAC on kidney function. DESIGN: A systematic review and meta-analysis. SETTINGS: Prospective studies, with administration of NAC, in the absence of any other change in kidney function (such as contrast administration or surgery). PATIENTS: Adult humans aged 18 years old or more, either healthy volunteers or with chronic kidney disease, were administered with NAC. Populations having little to no kidney function such as in end-stage kidney disease will be excluded. MEASUREMENTS: Serum creatinine and/or cystatin C measurements before and after NAC administration. METHODS: An information specialist will assist in searching MEDLINE, EMBASE, and the Cochrane CENTRAL databases to identify all study types including randomized controlled trials, and prospective cohort studies reporting change in serum creatinine after NAC administration. Two reviewers will independently screen the titles and abstracts of the studies obtained from the search using predefined inclusion criteria and will then extract data from the full texts of selected studies. The weighted mean difference will be calculated for change in creatinine with NAC, using random-effects analysis. Quality assessment will be done with the Cochrane Risk of Bias tool for randomized trials and the Newcastle-Ottawa Scale for observational studies. RESULTS: The outcome of interest is kidney function as reported by either change in serum creatinine and/or serum cystatin C measurement for randomized trials or comparing baseline (pre-NAC dose) values and those following the NAC dose. LIMITATIONS: Possible heterogeneity and publication bias and lack of mechanistic data. CONCLUSIONS: This systematic review will provide a synthesis of current evidence on the effect of NAC on serum creatinine measurement. These findings will provide clinicians with guidelines and serve as a strong research base for future studies in this field. SYSTEMATIC REVIEW REGISTRATION: This review is registered with PROSPERO, CRD42017055984.

CONTEXTE: La N-acétylcystéine (NAC) est un antioxydant capable de régénérer le glutathion et principalement utilisé pour traiter les cas de surdose d'acétaminophène. La NAC pourrait également s'avérer efficace comme traitement préventif de l'insuffisance rénale aiguë iatrogénique ou pour ralentir la progression de l'insuffisance rénale chronique. Cette substance a fait l'objet de plusieurs études dans ce contexte, mais les résultats demeurent mitigés. Notamment, il reste toujours à rapporter adéquatement une justification de l'effet protecteur de la NAC sur la base d'un mécanisme biologique. Parmi les rapports contradictoires, certaines données montreraient que la NAC abaisse artificiellement les valeurs de créatinine sérique mesurées sans améliorer la fonction rénale, potentiellement par interférence de l'essai. À la lumière de ces résultats divergents, une revue systématique de la littérature sera effectuée pour déterminer si la NAC produit un effet sur la fonction rénale mesurée par la créatinine sérique. OBJECTIF: Mesurer l'effet de l'administration de NAC sur la fonction rénale. TYPE D'ÉTUDE: Une revue systématique de la littérature et une méta-analyse. CADRE: Les études prospectives avec administration de NAC sans autres changements dans la fonction rénale; l'administration d'un produit de contraste ou une intervention chirurgicale, par exemple. SUJETS: Des adultes, volontaires sains ou atteints de néphropathie chronique, ayant reçu de la NAC. Seront exclues les populations dont la fonction rénale est faible ou inexistante; notamment, les cas d'insuffisance rénale terminale. MESURES: Des mesures de la créatinine sérique et/ou de la cystatine C faites avant et après l'administration de NAC. MÉTHODOLOGIE: Un documentariste spécialisé assistera les recherches dans les bases de données MEDLINE, EMBASE et Cochrane CENTRAL afin de répertorier tous les types d'essais, y compris les essais contrôlés à répartition aléatoire, et toutes les études de cohorte prospectives faisant état d'une variation de la créatinine sérique à la suite de l'administration de NAC. À l'aide de critères d'inclusion prédéfinis, deux réviseurs seront indépendamment chargés de trier les titres et abrégés des études répertoriées lors de la revue de la littérature. Ils devront ensuite extraire les données des textes des études qui auront été retenues. Une analyse des effets aléatoires sera utilisée pour calculer la moyenne pondérée des écarts pour les variations observées dans les mesures de créatinine en présence de NAC. La qualité des essais aléatoires sera évaluée à l'aide de l'outil Cochrane sur le risque de biais, et celle des études observationnelles sera mesurée avec l'échelle de Newcastle-Ottawa. RÉSULTATS: Le principal résultat d'intérêt est la fonction rénale telle que rapportée soit par un changement dans les mesures de créatinine sérique et/ou de la cystatine C dans les essais à répartition aléatoire, soit en comparant les valeurs mesurées avant et après l'administration d'une dose de NAC. LIMITES: L'hétérogénéité des données, de possibles biais de publication et un manque de données mécanistiques. CONCLUSION: Cette revue systématique offrira une synthèse des données probantes actuelles sur l'effet de la NAC sur les mesures de créatinine sérique. Ces résultats fourniront des lignes directrices aux cliniciens et serviront de bases solides pour les recherches futures dans ce domaine.

Decision Support Tools, Systems, and Artificial Intelligence in Cardiac Imaging.

Noninvasive cardiac imaging is widely used for the diagnosis and management of cardiac patients. The increasing demand for cardiac imaging begins to exceed the number of available interpreting physicians, leaving less time to interpret studies. In addition, the busy clinician is facing the increasingly daunting task of keeping abreast of current medical advancements and the ongoing changes in disease diagnosis and therapy. Committing to memory and recalling such large volumes of information is challenging and is responsible for difficulties in adopting the rapid changes in imaging practice, and is likely partially responsible for errors in patient diagnosis and management. Diagnostic errors rank high in the cause of death in the United States, and are more common than any other medical error and are responsible for most malpractice claims. Most of these errors are related to cognitive errors. The use of artificial intelligence systems that can serve as complementary methods to assist humans with decision making can potentially prevent these errors. The past decades witnessed the development and integration of these tools, which can assist physicians with image interpretation. These tools work to optimize image quality for better visualization and accompany all imaging modalities, starting from patient selection for the appropriate test, patient preparation, image acquisition, processing, and finally interpretation. Current and future directions for technologies that support cardiac imaging physicians are discussed in this review.

Inter- and Intraobserver Agreement of 18F-FDG PET/CT Image Interpretation in Patients Referred for Assessment of Cardiac Sarcoidosis.

Recent studies have reported the usefulness of 18F-FDG PET in aiding with the diagnosis and management of patients with cardiac sarcoidosis (CS). However, image interpretation of 18F-FDG PET for CS is sometimes challenging. We sought to investigate the inter- and intraobserver agreement and explore factors that led to important discrepancies between readers. Methods: We studied consecutive patients with no significant coronary artery disease who were referred for assessment of CS. Two experienced readers masked to clinical information, imaging reports, independently reviewed 18F-FDG PET/CT images. 18F-FDG PET/CT images were interpreted according to a predefined standard operating procedure, with cardiac 18F-FDG uptake patterns categorized into 5 patterns: none, focal, focal on diffuse, diffuse, and isolated lateral wall or basal uptake. Overall image assessment was classified as either consistent with active CS or not. Results: One hundred scans were included from 71 patients. Of these, 46 underwent 18F-FDG PET/CT with a no-restriction diet (no-restriction group), and 54 underwent 18F-FDG PET/CT with a low-carbohydrate, high-fat and protein-permitted diet (low-carb group). There was agreement of the interpretation category in 74 of 100 scans. The κ-value of agreement among all 5 categories was 0.64, indicating moderate agreement. For overall clinical interpretation, there was agreement in 93 of 100 scans (κ = 0.85). When scans were divided into the preparation groups, there was a trend toward higher agreement in the low-carb group versus the no-restriction group (80% vs. 67%, P = 0.08). Regarding the overall clinical interpretation, there was also a trend toward greater agreement in the low-carb group versus the no-restriction group (96% vs. 89%, P = 0.08). Conclusion: The interobserver agreement of cardiac 18F-FDG uptake image patterns was moderate. However, agreement was better regarding overall interpretation of CS. Detailed prescan dietary preparation seemed to improve interobserver agreement.

Mid-diastolic left ventricular volume and mass: Normal values for coronary computed tomography angiography.

BACKGROUND: The adoption of prospectively ECG-triggered acquisition coronary computed tomography angiography (CTA) has resulted in the inability to measure left ventricle (LV) end-diastolic volume and LV ejection fraction. However other prognostic measures such as LV mass and LV mid-diastolic volume (LVMDV) can still be assessed. The objective of this study is to establish normal reference values for LVMDV and LV mass. METHODS: Left ventricular mid-diastolic volumes and LV mass were prospectively measured in 2647 consecutive 'normal' patients undergoing prospectively ECG-triggered coronary CTA. Patients with known coronary artery disease (prior myocardial infarction or prior revascularization), heart failure, congenital heart disease, heart transplant or prior cardiac surgery were excluded. Commercially available software was used to calculate the LVMDV and LV mass. RESULTS: Among the 2647 patient cohort (mean age = 58 years, 54% men), the mean LVMDV indexed for body surface area was 57.5 ± 15.3 mL/m2 and 64.5 ± 20.2 mL/m2 for women and men, respectively. The mean indexed LV mass was 52.2 ± 10.9 g/m2 for women and 63.6 ± 13.7 g/m2 for men. Indexed LVMDV decreased with increasing age. The presence of hypertension, diabetes and obstructive coronary artery disease did not have a clinically relevant impact on these values. Age and sex specific upper limits of normal were defined. CONCLUSION: We establish normal reference ranges for LVMDV and LV mass using prospectively ECG-triggered coronary CTA. These benchmarks may identify patients at increased risk of adverse events, supporting the potential for clinical reporting of these metrics.

Validation of a Multimodality Flow Phantom and Its Application for Assessment of Dynamic SPECT and PET Technologies.

Simple and robust techniques are lacking to assess performance of flow quantification using dynamic imaging. We therefore developed a method to qualify flow quantification technologies using a physical compartment exchange phantom and image analysis tool. We validate and demonstrate utility of this method using dynamic PET and SPECT. Dynamic image sequences were acquired on two PET/CT and a cardiac dedicated SPECT (with and without attenuation and scatter corrections) systems. A two-compartment exchange model was fit to image derived time-activity curves to quantify flow rates. Flowmeter measured flow rates (20-300 mL/min) were set prior to imaging and were used as reference truth to which image derived flow rates were compared. Both PET cameras had excellent agreement with truth ( [Formula: see text]). High-end PET had no significant bias (p > 0.05) while lower-end PET had minimal slope bias (wash-in and wash-out slopes were 1.02 and 1.01) but no significant reduction in precision relative to high-end PET (<15% vs. <14% limits of agreement, p > 0.3). SPECT (without scatter and attenuation corrections) slope biases were noted (0.85 and 1.32) and attributed to camera saturation in early time frames. Analysis of wash-out rates from non-saturated, late time frames resulted in excellent agreement with truth ( [Formula: see text], slope = 0.97). Attenuation and scatter corrections did not significantly impact SPECT performance. The proposed phantom, software and quality assurance paradigm can be used to qualify imaging instrumentation and protocols for quantification of kinetic rate parameters using dynamic imaging.

Silica-Based and Borate-Based, Titania-Containing Bioactive Coatings Characterization: Critical Strain Energy Release Rate, Residual Stresses, Hardness, and Thermal Expansion.

Silica-based and borate-based glass series, with increasing amounts of TiO2 incorporated, are characterized in terms of their mechanical properties relevant to their use as metallic coating materials. It is observed that borate-based glasses exhibit CTE (Coefficient of Thermal Expansion) closer to the substrate's (Ti6Al4V) CTE, translating into higher mode I critical strain energy release rates of glasses and compressive residual stresses and strains at the coating/substrate interface, outperforming the silica-based glasses counterparts. An increase in the content of TiO2 in the glasses results in an increase in the mode I critical strain energy release rate for both the bulk glass and for the coating/substrate system, proving that the addition of TiO2 to the glass structure enhances its toughness, while decreasing its bulk hardness. Borate-based glass BRT3, with 15 mol % TiO2 incorporated, exhibits superior properties overall compared to the other proposed glasses in this work, as well as 45S5 Bioglass® and Pyrex.

Kinetics of the addition of olefins to Si-centered radicals: the critical role of dispersion interactions revealed by theory and experiment.

Solution-phase rate constants for the addition of selected olefins to the triethylsilyl and tris(trimethylsilyl)silyl radicals are measured using laser-flash photolysis and competition kinetics. The results are compared with predictions from density functional theory (DFT) calculations, both with and without dispersion corrections obtained from the exchange-hole dipole moment (XDM) model. Without a dispersion correction, the rate constants are consistently underestimated; the errors increase with system size, up to 10(6) s(-1) for the largest system considered. Dispersion interactions preferentially stabilize the transition states relative to the separated reactants and bring the DFT-calculated rate constants into excellent agreement with experiment. Thus, dispersion interactions are found to play a key role in determining the kinetics for addition reactions, particularly those involving sterically bulky functional groups.

Antibacterial analysis of a zinc-based glass polyalkenoate cement.

Infection following surgery can result in significant pain and morbidity for patients undergoing vertebroplasty/kyphoplasty, and often results in revision surgery. This study focuses on the development of Al-free glass polyalkenoate cements (GPCs) based on 0.04SrO-0.12CaO-0.36ZnO-0.48SiO( 2) glass, with the intent of optimizing their antibacterial efficacy by incorporating low-molecular-weight polyacrylic acids (PAA) and trisodium citrate (TSC), and evaluating the resultant GPCs against bacteria relevant to spinal infections, P. aeruginosa and E. coli. Ion-release profiles were determined for the GPC formulation containing E6 PAA (Cement A) and E7 PAA (Cement B), and Zn, Na, and Sr release was recorded over 1, 7, and 30 days. Inhibition was found in E. coli at each time period (0-30 days) and this generally decreased with exposure time in water. The largest GPC inhibition zones were produced by Cement A (6 mm); however the control material Simplex P + tobramycin produced much higher inhibition zones (11 mm). When testing the GPC against P. aeruginosa, inhibition was only present at the 0-day time period. Simplex P + tobramycin was found to produce inhibition at each time frame. Analysis of the agar from the inhibition zone of the E. coli test revealed that there is a significant change in Zn concentration as compared to a control agar specimen, which suggests that Zn release is responsible for the antibacterial effect of the GPCs.

Evaluation of two novel aluminum-free, zinc-based glass polyalkenoate cements as alternatives to PMMA bone cement for use in vertebroplasty and balloon kyphoplasty.

Vertebroplasty (VP) and balloon kyphoplasty (BKP) are now widely used for treating patients in whom the pain due to vertebral compression fractures is severe and has proved to be refractory to conservative treatment. These procedures involve percutaneous delivery of a bolus of an injectable bone cement either directly to the fractured vertebral body, VB (VP) or to a void created in it by an inflatable bone tamp (BKP). Thus, the cement is a vital component of both procedures. In the vast majority of VPs and BKPs, a poly(methyl methacrylate) (PMMA) bone cement is used. This material has many shortcomings, notably lack of bioactivity and very limited resorbability. Thus, there is room for alternative cements. We report here on two variants of a novel, bioactive, Al-free, Zn-based glass polyalkenoate cement (Zn-GPC), and how their properties compare to those of an injectable PMMA bone cement (SIMPL) that is widely used in VP and BKP. The properties determined were injectability, radiopacity, uniaxial compressive strength, and biaxial flexural modulus. In addition, we compared the compression fatigue lives of a validated synthetic osteoporotic VB model (a polyurethane foam cube with an 8 mm-diameter through-thickness cylindrical hole), at 0-2300 N and 3 Hz, when the hole was filled with each of the three cements. A critical review of the results suggests that the performance of each of the Zn-GPCs is comparable to that of SIMPL; thus, the former cements merit further study with a view to being alternatives to an injectable PMMA cement for use in VP and BKP.

Time-resolved molecular frame dynamics of fixed-in-space CS2 molecules.

Random orientation of molecules within a sample leads to blurred observations of chemical reactions studied from the laboratory perspective. Methods developed for the dynamic imaging of molecular structures and processes struggle with this, as measurements are optimally made in the molecular frame. We used laser alignment to transiently fix carbon disulfide molecules in space long enough to elucidate, in the molecular reference frame, details of ultrafast electronic-vibrational dynamics during a photochemical reaction. These three-dimensional photoelectron imaging results, combined with ongoing efforts in molecular alignment and orientation, presage a wide range of insights obtainable from time-resolved studies in the molecular frame.