Evaluating blood supply changes in the osteonecrosis of the femoral head using gadobutrol-based steady-state MR angiography

OBJECTIVES

Assess the feasibility of using gadobutrol-based steady-state (SS) MR angiography (MRA) to evaluate the blood supply changes of osteonecrosis of the femoral head (ONFH).

MATERIALS AND METHODS

Participants were recruited in this prospective study from December 2021 to May 2022 in a single center. The number of superior retinacular arteries (SRAs), inferior retinacular arteries (IRAs), anterior retinacular arteries (ARAs), and overall retinacular arteries (ORAs), as well as the affected rates of SRA and IRA, were determined and compared between healthy and ONFH hips and between hips across the Association Research Circulation Osseous (ARCO) staging I-IV.

RESULTS

Twenty healthy and 64 ONFH hips were evaluated in 54 participants. There were significant differences between ARCO I-IV for the number of ORAs (mean of 3.5, 2.3, 1.7, and 0.8 for ARCO I-IV, respectively; p < .001), SRAs (median of 2.5, 1, 0.5, and 0 for ARCO I-IV, respectively; p < .001), and the affected rate of SRAs (20.00%, 65.22%, 77.78%, 92.31% for ARCO I-IV, respectively, p = 0.002). There were significant differences between ONFH and healthy hips for the number of ORAs (median of 5 vs. 2; p < .001), SRAs (median of 3 vs. 1; p < .001), IRAs (median of 1 vs. 1; p < .001), ARAs (median of 0 vs. 0; p = 0.04), and also the affected rate of SRAs (5.00% vs. 67.20%, p < .001) and IRAs (30% vs. 84.4%, p < .001).

CONCLUSION

Gadobutrol-enhanced SS MRA is a feasible method for evaluation of hemodynamics in ONFH.

CLINICAL RELEVANCE STATEMENT

Gadobutrol-enhanced magnetic resonance angiography can evaluate blood supply changes of ONFH and therefore helps to aid in the diagnosis and guide treatment of ONFH.

KEY POINTS

• Gadobutrol-enhanced magnetic resonance angiography showed changes in the retinacular artery related to the severity of femoral osteonecrosis. • Gadobutrol-enhanced magnetic resonance angiography revealed a reduced blood supply to the ischemic necrotic femoral head compared to the healthy counterparts.

Comparison and Optimization of Cardiovascular Risk Scores in Predicting the 4-Year Outcome of Patients with Obstructive Coronary Arteries Disease

Objective

How well cardiovascular risk models perform in selected atherosclerosis patients for predicting outcomes is unknown. We sought to compare the performance of cardiovascular risk models (Framingham, Globorisk, SCORE2 & SCORE2-OP, and an updated new model) in predicting the 4-year outcome of patients with obstructive coronary artery disease (CAD).

Methods

Patients with suspected CAD who underwent coronary computed tomography angiography (CCTA) were recruited. Obstructive CAD was defined from CCTA as ≥ 50% stenosis. Computed tomography images, the scores of the cardiovascular risk models, and 4-year composite endpoints were assessed. Whether the patients underwent revascularization within 60 days after CCTA was also recorded. Multivariate regression analysis and receiver operating characteristics (ROC) curve analysis were performed.

Results

A total of 95 patients (mean age: 69.5 ± 10.33 years; 69 males) with obstructive CAD were included in this study. After the ROC analysis, the Framingham, Globorisk, SCORE2 & SCORE2-OP risk score showed prediction values with AUC 0.628 (95% CI: 0.532-0.725), 0.647 (95% CI: 0.542-0.742), 0.684 (95% CI: 0.581-0.776), respectively. Multivariate regression analysis showed that, among the three risk models, only SCORE2 & SCORE2-OP risk score was associated with composite endpoints (hazard ratio: 1.050; 95% CI: 1.021-1.079; p = 0.001) after adjusting for confounding factors. The AUC of the new risk model by combing SCORE2 & SCORE2-OP risk score with revascularization and the number of obstructive vessels in predicting composite endpoints reached 0.898 (95% CI: 0.819-0.951).

Conclusion

The SCORE2 & SCORE2-OP risk score combined with the number of obstructive vessels and revascularization is predictive for adverse outcomes in patients with obstructive CAD.

20-hydroxyeiscosatetraenoic acid may be as a predictor of malignant middle cerebral artery infarction in patients with massive middle cerebral artery infarction

Background

Early identification of massive middle cerebral artery infarction (MCAI) at risk for malignant MCAI (m-MCAI) may be useful in selecting patients for aggressive therapies. The aim of this study was to determine whether CYP metabolites may help to predict impending m-MCAI.

Methods

This is a prospective, two-center observational study in 256 patients with acute massive MCAI. Plasma levels of 20-hydroxyeicosatetraenoic acid (20-HETE), epoxyeicosatrienoic acids, and dihydroxyeicosatrienoic acids were measured at admission. Brain computed tomography (CT) was performed at admission and repeated between day 3 and 7, or earlier if there was neurological deterioration. The primary outcome was m-MCAI. The m-MCAI was diagnosed when follow-up brain CT detected a more than two-thirds space-occupying MCAI with midline shift, compression of the basal cisterns, and neurological worsening.

Results

In total of 256 enrolled patients, 77 (30.1%) patients developed m-MCAI. Among the 77 patients with m-MCAI, 60 (77.9%) patients died during 3 months of stroke onset. 20-HETE level on admission was significantly higher in patients with m-MCAI than those without m-MCAI. There was an increase in the risk of m-MCAI with increase of 20-HETE levels. The third and fourth quartiles of 20-HETE levels were independent predictors of m-MCAI (OR: 2.86; 95% CI: 1.16 – 6.68; P = 0.025, and OR: 4.23; 95% CI: 1.35 – 8.26; P = 0.002, respectively).

Conclusions

Incidence of m-MCAI was high in patients with massive MCAI and the prognosis of m-MCAI is very poor. Elevated plasma 20-HETE may be as a predictor for m-MCAI in acute massive MCAI, and it might useful in clinical practice in therapeutic decision making.

Radiomics Model Based on MR Images to Discriminate Pancreatic Ductal Adenocarcinoma and Mass-Forming Chronic Pancreatitis Lesions

Background

It is difficult to identify pancreatic ductal adenocarcinoma (PDAC) and mass-forming chronic pancreatitis (MFCP) lesions through conventional CT or MR examination. As an innovative image analysis method, radiomics may possess potential clinical value in identifying PDAC and MFCP. To develop and validate radiomics models derived from multiparametric MRI to distinguish pancreatic ductal adenocarcinoma (PDAC) and mass-forming chronic pancreatitis (MFCP) lesions.

Methods

This retrospective study included 119 patients from two independent institutions. Patients from one institution were used as the training cohort (51 patients with PDAC and 13 patients with MFCP), and patients from the other institution were used as the testing cohort (45 patients with PDAC and 10 patients with MFCP). All the patients had pathologically confirmed results, and preoperative MRI was performed. Four feature sets were extracted from T1-weighted imaging (T1WI), T2-weighted imaging (T2WI), and the artery (A) and portal (P) phases of dynamic contrast-enhanced MRI, and the corresponding radiomics models were established. Several clinical characteristics were used to discriminate PDAC and MFCP lesions, and clinical model was established. The results of radiologists’ evaluation were compared with pathology and radiomics models. Univariate analysis and the least absolute shrinkage and selection operator algorithm were performed for feature selection, and a support vector machine was used for classification. The receiver operating characteristic (ROC) curve was applied to assess the model discrimination.

Results

The areas under the ROC curves (AUCs) for the T1WI, T2WI, A and, P and clinical models were 0.893, 0.911, 0.958, 0.997 and 0.516 in the primary cohort, and 0.882, 0.902, 0.920, 0.962 and 0.649 in the validation cohort, respectively. All radiomics models performed better than clinical model and radiologists’ evaluation both in the training and testing cohorts by comparing the AUC of various models, all P<0.050. Good calibration was achieved.

Conclusions

The radiomics models based on multiparametric MRI have the potential ability to classify PDAC and MFCP lesions.

Improving the accuracy of pre-operative evaluation of neurovascular conflict in trigeminal neuralgia using magnetic resonance subtraction

PURPOSE

To investigate the ability of magnetic resonance (MR) subtraction to evaluate neurovascular conflict (NVC) and to compare it with conventional MR protocols.

METHODS

This prospective study included 82 patients with trigeminal neuralgia who underwent microvascular decompression for NVC. All patients had a pre-operative examination using 3T MRI. The MRI protocols used comprised 3D balanced (B)-fast field echo (FFE), 3D steady-state magnetic resonance angiography (MRA), and 3D T1-FFE sequences. MR subtraction images were obtained by subtracting native images from B-FFE and steady-state MRA. NVC evaluation was performed using subtraction images (MR subtraction) and combination images (conventional MR protocols using B-FFE and T1-FFE in combination). Clinical assessment of the degree of compression, the type of compressing vessel, and the location of conflict were undertaken by two independent observers. The two methods were then compared using surgical criteria.

RESULTS

MR subtraction exhibited greater accuracy than the conventional method in terms of the estimated severity of conflict (87.80% vs. 57.32%, p < 0.05), and demonstrated better consistency with surgical findings (k = 0.794 vs. k = 0.365, p < 0.05). For the type of compressing vessel and the location of conflict, both methods were highly accurate and agreed to a similar extent with surgical findings (p = 0.987, compressing vessel; p = 0.665, location of conflict).

CONCLUSION

MR subtraction proved reliable in NVC pre-operative evaluation, with increased accuracy when estimating severity. This result strongly supports the wider use of MR subtraction as the preferred choice in clinical application.

AB0131 RESPIRATORY TRACT POLY(I:C) STIMULATION ACCELERATES SALIVARY GLAND IMMUNE DYSFUNCTION IN SPONTANEOUS SJOGREN’S SYNDROME ANIMAL MODEL

Background:

Sjogren’s syndrome is one of the most common autoimmune diseases, with a prevalence of 0.33% to 0.77% in Chinese people, characterized by focal infiltration of lymphocytes in glands and the production of multiple autoantibodies. Studies have shown that virus infection may play a crucial role in the occurrence and development of this disease.

Objectives:

It has been shown that airway stimulation with poly(I:C) can mimic respiratory tract viral infection to some extent. Thus, this study was aimed to investigate the dynamic immune responses in salivary gland after respiratory tract poly(I:C) stimulation in NOD mice.

Methods:

The 5-week-old NOD mice were given respiratory tract poly(I:C) stimulation to mimic the respiratory virus infection once every other day for a total of 5 times (the total dose is 100μg), and the control group were given the same dose of sterile PBS. After 8 weeks, the mice were sacrificed to obtain and analyze the salivary gland tissues.

Results:

We found that the salivary gland flow rate was decreased and the blood glucose was influenced by the Viroid stimulation during the early stage in poly(I:C) stimulated group compared with that in PBS group. Accordingly, the pathological injury of salivary gland tissues in poly(I:C) stimulated group was more serious, including decreased volumes of the salivary glands, increased number of pathological focus score and the increased area of lymphocyte infiltration. Furthermore, we found that the expression of IL-33 in salivary glands of poly(I:C) stimulated NOD mice was increased, especially the expression of IL-33 in the acini and ducts. Moreover, the expression of IFN-I and IFN-II is up-regulated in salivary glands.

Conclusion:

The results of this study suggest that respiratory tract poly(I:C) stimulation accelerates salivary gland immune dysfunction in spontaneous sjogren’s syndrome NOD mice, which mechanisms need to be further investigated.

References:

[1] Pathogenetic mechanisms in the initiation and perpetuation of Sjogren’s syndrome. Nat Rev Rheumatol 2010; 6: 529-537.

[2]Primary Sjögren’s Syndrome. N Engl J Med.2018 378(10):931-939.

[3]Epidemiology of primary Sjögren’s syndrome: a systematic review and meta-analysis. Ann Rheum Dis 2015; 74: 1983-9.

[4]Vitamin D insufficiency in a large MCTD population. Autoimmun Rev 10:317–324.

[5]Epstein-Barr virus persistence and infection of autoreactive plasma cells in synovial lymphoid structures in rheumatoid arthritis. Ann Rheum Dis 72:1559–1568

[6]Liew, F., Girard, J. & Turnquist, H. Interleukin-33 in health and disease. Nat Rev Immunol 16, 676–689 (2016) doi:10.1038/nri.2016.95

[7]Interleukin-33 and the function of innate lymphoid cells. Trends in Immunology, August 2012, Vol. 33, No. 8

[8]Increased Levels of Interleukin 33 in Sera and Synovial Fluid from Patients with Active Rheumatoid Arthritis YASUSHI MATSUYAMA et al The Journal of Rheumatology January 2010, 37 (1) 18-25

[9]Potential involvement of the IL-33-ST2 axis in the pathogenesis of primary Sjogren’s syndrome, Ann Rheum Dis, 2014, 73(6): 1259-1263.

[10]The Interleukin 33/ST2 axis in patients with primary Sjogren syndrome: expression in serum and salivary glands, and the clinical association, J Rheumatol, 2015, 42(2): 264-271.

[11]Kok MR, Baum BJ, Tak PP, et al Use of localised gene transfer to develop new treatment strategies for the salivary component of Sjögren’s syndrome Annals of the Rheumatic Diseases 2003;62:1038-1046.

Acknowledgments:

NO

Disclosure of Interests:

None declared

SAT0294 IL33 ACTIVATES FIBROBLASTS AND INDUCES SKIN FIBROSIS IN SYSTEMIC SCLEROSIS

Background:

Systemic sclerosis (SSc) is a chronic immune-mediated autoimmune disease that is characterized by fibrotic changes of the skin and internal organs, which in turn leads to distortion of tissue structure and gradual loss of organ function. So far, there is still no treatment allows full recovery from this severe disorder. Therefore, it is of great social significance to study the pathogenesis of this disease and find new targets for treatment. Interleukin 33 (IL-33), which is a potent inducer of type 2 immune response, has been confirmed to be involved in the development and progression of multiple fibrotic diseases. However, the role and mechanism of IL-33 in SSc-related fibrosis remains unclear.

Objectives:

To clarify the role of interleukin 33 (IL-33) and its receptor Suppression of tumorigenicity 2 (ST2) in the skin fibrosis of SSc, so to provides a new target for the treatment of fibrosis in patients with SSc.

Methods:

The levels of IL-33 and ST2 was analysed in human samples, murine models of SSc and in cultured fibroblasts by immunohistochemistry and immunofluorescence. The functional role of IL-33 was evaluated by detecting changes in proliferation, migration, and activation of fibroblasts stimulated with recombinant IL-33 protein. MAPK and NF-κB signallings of fibroblasts were assessed by western blotting and analyses of target genes. The role of IL-33 in skin fibrosis was analysed in IL-33 deficient mice (il33−/−) and wild-type controls injected with bleomycin or NaCl.

Results:

The expression of IL-33 and its receptor ST2 were up-regulated in skin lesions of SSc patients (Fig 1 A-C) and bleomycin-treated mice(Fig1 D-F). Compared to the healthy skin, the skin from SSc patients expressed more ST2 on fibroblasts membrane(Fig 1 B-C). IL33 induces MAPK and IκBα activation in human dermal fibroblast(Fig 2 A), and promote proliferation, migration and production of collagen of human dermal fibroblasts, but not the release of inflammatory factors(IL-6, MCP-1)(Fig2 B-G). Mice deficient for IL33 are protected from bleomycin-induced dermal fibrosis (Fig3).

Fig 1.

Increased expression of IL33, ST2 in SSc patients and bleomycin-treated mice.

Fig 2.

IL33 induces MAPK and IκBα activation in human dermal fibroblast, and and promote proliferation, migration and production of collagen of human dermal fibroblasts.

Fig 3.

Mice deficient for IL33 are protected from bleomycin-induced dermal fibrosis.

Conclusion:

IL33 promotes skin fibrosis by activating fibroblasts, and IL33/ST2 may be an important target for the treatment of fibrosis in patients with SSc.

References:

[1]Ingegnoli F, Ughi N, Mihai C. Update on the epidemiology, risk factors, and disease outcomes of systemic sclerosis. Best practice & research. Clinical rheumatology. 2018;32(2):223-240.

[2]Schmitz J, Owyang A, Oldham E, et al. IL-33, an interleukin-1-like cytokine that signals via the IL-1 receptor-related protein ST2 and induces T helper type 2-associated cytokines. Immunity. 2005;23(5):479-490.

[3]Molofsky AB, Savage AK, Locksley RM. Interleukin-33 in Tissue Homeostasis, Injury, and Inflammation.Immunity.2015;42(6):1005-1019.

Disclosure of Interests:

None declared

Magnetic resonance imaging for preoperative staging of pancreatic cancer based on the 8th edition of AJCC guidelines

Background

Preoperative staging of pancreatic cancer determines the choice of treatment. Magnetic resonance imaging (MRI) plays an important role in preoperative staging of pancreatic cancer. The American Joint Committee on Cancer (AJCC) TNM staging system was revised to its 8^th version in 2016, there has been no report correlating the 8^th edition of the AJCC TNM staging with preoperative MRI examinations and pathological findings. The purpose of our study is to determine the staging accuracy and evaluate the resectability by using MRI about pancreatic cancer compared with intraoperative or pathological findings according to the 8^th edition of the AJCC TNM staging system.

Methods

One hundred thirty-two patients with a pathological diagnosis of pancreatic cancer who underwent preoperative MRI were identified. The clinical data, MRI findings and pathological findings were analyzed. Preoperative MRI staging and resectability evaluation were compared with pathological findings. The accuracy of MRI for preoperative T and N staging was evaluated, and the sensitivity, specificity and accuracy of MRI in evaluating the resectability were assessed. All the staging and resectability assessments were according to the 8^th edition of the AJCC TNM staging system.

Results

Analysis showed that the accuracy of MRI for evaluation of the T and N stages was 82.6% (109/132) and 74.2% (98/132), respectively. The sensitivity and specificity of MRI in assessing the resectability were 94.2% and 71.4%, respectively. Integrating the 8^th edition of the AJCC TNM stage, no significant differences were identified between the preoperative MRI and pathological results for the staging of pancreatic cancer (P=0.805).

Conclusions

MRI is highly accurate for T staging and moderately accurate for N staging. MRI provides important preoperative evaluation of the stage and resectability of pancreatic cancer based on the 8^th edition of the AJCC TNM staging system.

Detection of vascularity of femoral head using sub-millimeter resolution steady-state magnetic resonance angiography-initial experience

OBJECTIVE

The purpose of this study was to use the steady-state (SS) magnetic resonance angiography (MRA) with a sub-millimeter resolution to detect the arteries supplying to the femoral head (FH).

MATERIALS AND METHOD

SS MRA scanning of hips was performed bilaterally in 15 healthy volunteers. A blood pool contrast agent was used. The scanning protocol included a 0.8-mm³ isotropic T1-fast field echo sequence with spectral fat suppression technique. Two highly qualified radiologists independently evaluated the medial circumflex femoral artery (MCFA), the lateral circumflex femoral artery (LCFA), and the three retinacular arteries including superior retinacular artery (SRA), inferior retinacular artery (IRA), and anterior retinacular artery (ARA). The intraosseous branches of the three retinacular arteries were also evaluated. An orthopaedic surgeon was consulted in case of disagreement. Observation by the two radiologists and support from the orthopaedic surgeon served as the end result. Agreement between the two observer radiologists was evaluated.

RESULTS

Interobserver agreement between the two radiologists was found to be substantial to perfect. Of the 30 hips, the LCFA and MCFA were detected in all hips; the SRA and IRA were detected in most hips (100%, 90%), and the ARA was detected in 13 hips (43%). The intraosseous branches of SRA and IRA were detected in 30 and 22 hips (100%, 73%), respectively, while the intraosseous branches of ARA were detected in 11 hips (37%).

CONCLUSION

The main arteries supplying the FH can be detected by the SS MRA, making it a novel method to detect the vascularity of FH.

Regulatory T-cell levels in systemic lupus erythematosus patients: a meta-analysis

Background

The contribution of regulatory T-cells (Tregs) to systemic lupus erythematosus (SLE) pathogenesis remains a matter of debate. The objective of this study was to quantify the association between peripheral blood Tregs and disease status in SLE patients.

Method

EMBASE and PubMed databases were searched using ‘systemic lupus erythematosus’ and ‘regulatory T-cells’ as relevant key terms. A meta-analysis of studies that examined the proportion of Tregs among peripheral blood mononuclear cells (PBMCs) and CD4+T-cells was performed using Stata software. Subgroup analysis was performed based on ethnic groups and Treg definition markers.

Results

The Treg/PBMC and Treg/CD4+T-cell ratios were significantly lower in SLE patients than in healthy controls (HCs), whereas patients with active and inactive SLE showed no difference in these indicators. A subgroup analysis indicated that Asian SLE patients had a substantially lower proportion of Tregs/PBMCs than HCs, but this difference was not seen for white and Latin American SLE patients. Patients defined by CD4+CD25+Foxp3+, CD4+CD25+ and CD4+Foxp3+ had a much lower Treg/PBMC ratio compared with HCs. Ethnic groups and choice of Treg definition markers had no influence on the proportion of Tregs/CD4+T-cells.

Conclusion

The proportion of Tregs among both PBMCs and CD4+T-cells was significantly decreased in SLE patients. Ethnic group and Treg definition markers may influence the proportion of Tregs among PBMCs. Further study of the correlation between SLE disease activity and the proportion of Tregs in peripheral blood is needed to determine the physiological role of this association.

Scanning electron microscope measurement of width and shape of 10nm patterned lines using a JMONSEL-modeled library

The width and shape of 10nm to 12 nm wide lithographically patterned SiO2 lines were measured in the scanning electron microscope by fitting the measured intensity vs. position to a physics-based model in which the lines' widths and shapes are parameters. The approximately 32 nm pitch sample was patterned at Intel using a state-of-the-art pitch quartering process. Their narrow widths and asymmetrical shapes are representative of near-future generation transistor gates. These pose a challenge: the narrowness because electrons landing near one edge may scatter out of the other, so that the intensity profile at each edge becomes width-dependent, and the asymmetry because the shape requires more parameters to describe and measure. Modeling was performed by JMONSEL (Java Monte Carlo Simulation of Secondary Electrons), which produces a predicted yield vs. position for a given sample shape and composition. The simulator produces a library of predicted profiles for varying sample geometry. Shape parameter values are adjusted until interpolation of the library with those values best matches the measured image. Profiles thereby determined agreed with those determined by transmission electron microscopy and critical dimension small-angle x-ray scattering to better than 1 nm.

Scanning electron microscope measurement of width and shape of 10nm patterned lines using a JMONSEL-modeled library

The width and shape of 10nm to 12 nm wide lithographically patterned SiO2 lines were measured in the scanning electron microscope by fitting the measured intensity vs. position to a physics-based model in which the lines' widths and shapes are parameters. The approximately 32 nm pitch sample was patterned at Intel using a state-of-the-art pitch quartering process. Their narrow widths and asymmetrical shapes are representative of near-future generation transistor gates. These pose a challenge: the narrowness because electrons landing near one edge may scatter out of the other, so that the intensity profile at each edge becomes width-dependent, and the asymmetry because the shape requires more parameters to describe and measure. Modeling was performed by JMONSEL (Java Monte Carlo Simulation of Secondary Electrons), which produces a predicted yield vs. position for a given sample shape and composition. The simulator produces a library of predicted profiles for varying sample geometry. Shape parameter values are adjusted until interpolation of the library with those values best matches the measured image. Profiles thereby determined agreed with those determined by transmission electron microscopy and critical dimension small-angle x-ray scattering to better than 1 nm.

HMGB1 is involved in chronic rejection of cardiac allograft via promoting inflammatory-like mDCs

Chronic rejection that leads to diffuse narrowing and occlusion of graft vessels is the most important cause of morbidity and mortality following cardiac transplantation. The role and underlying mechanism of high-mobility group box 1 (HMGB1), as an established inflammatory mediator in acute rejection, remains poorly understood in chronic rejection. Here, we assessed the effects and mechanisms of HMGB1 on the chronic rejection using single MHC Class II-mismatched mouse cardiac transplantation model. It was found that HMGB1 was increased accompanying with the development of chronic rejection, while blockade of HMGB1 with specific neutralizing mAb substantially ameliorated chronic rejection-mediated vasculopathy and fibrosis of allograft, as well as markedly decreased T cell infiltration and production of IL-17A and interferon-gamma in allograft and recipient's spleen. Further, anti-HMGB1 antibody treatment significantly declined the number and frequency of mature dendritic cells (DCs) in allograft and recipient's spleen, especially CD11b(+) Ly6C(high) matured DCs that share the phenotypes with inflammatory-DCs. These findings indicate that HMGB1 contributes to chronic rejection, and HMGB1 blockade may be a novel mean to disrupt the proinflammatory loop after heart transplantation.

Simulated SEM images for resolution measurement

Resolution is a key performance metric, which often defines the quality of a scanning electron microscope (SEM). Traditionally, there is the subjective measurement of the distance between two points on special "resolution" samples and there are several computer-based resolution-calculation methods. These computer-based resolution-calculation methods are much more precise than direct measurement, but none of them can currently be considered an objective way of measuring the resolution. The methods are still under development; therefore, objective testing is necessary. One approach to algorithm testing is to use simulated images. Simulated images are very useful for this purpose because they can be well-defined in all parameters unlike the real SEM images. Simulated images can be generated that closely mimic the gold-on-carbon SEM test sample images that usually consist of bright grains on a dark background. Simulation can account for edge effect, roughness of the substrate, different focusing, drift and vibration, and noise. Shapes, positions, and sizes of the grain structures are random. The simulated images can be then used for testing the resolution-calculation methods, especially for finding how the particular properties of SEM images affect the resultant instrument performance and image resolution. To support this testing, NIST has developed and made available a reference set of simulated SEM images generated using the methods described in this article.

The nature of the RNA products synthesized in vitro with a cell-free extract from TMV-infected tobacco leaves

A cell-free extract containing TMV-RNA replicase was prepared from TMV-infected tobacco leaves. It could synthesize double-stranded RNAs in the presence of four nucleoside triphosphates (among them, UTP was tritium-labelled), magnesium ion and actinomycin D. It was confirmed by polyacrylamide-agarose gel electrophoresis, RNase treatment, thermal denaturation and self annealing that 3H-ds RNAs, obtained from phenol-SDS extraction and Serva cellulose column chromatography, consisted of replicative form (RF) and replicative intermediate (RI) of TMV-RNA, with molecular weights of 40 X 10(6) and 5.0 X 10(6), respectively. Molecular hybridization competition experiment showed that 60-70% of the nascent RNAs in the 3H-ds RNA were plus strand of tMV-RNA.