Preoperative N stage evaluation in advanced gastric cancer patients using multidetector CT: can the sum of the diameters of metastatic LNs be used for N stage evaluation?

AIM: To compare the diagnostic performance of total counts of metastatic lymph nodes (LN-sum) and conventional multidetector (MD) computed tomography (CT) staging in the nodal evaluation of advanced gastric cancer (AGC) patients. MATERIALS AND METHODS: In total, 127 consecutive patients who underwent preoperative MDCT and gastrectomy for AGC were identified. Metastatic LNs on MDCT were defined as LNs with a short axis ≥8 mm, marked or heterogeneous enhancement, and morphological features (central necrosis, round shape, clustering). The sensitivity, specificity, accuracy, positive predictive value (PPV), and negative predictive value (NPV) of the N-stage using LN-sum and conventional MDCT staging were generated and compared. In addition, metastatic LN counts between the MDCT and the histopathological examinations and correlation between LN-sum and histopathological nodal status were analysed. RESULTS: The total counts of metastatic LNs on MDCT was significantly smaller than those detected in histopathological assessments (p<0.0001). LN-sum showed significant correlation with the pathological N stage and the number of metastatic LNs (rho=0.69, 0.73, p<0.0001). The areas under the receiver operating characteristic curve were 0.896, and 0.835, for N stage ≥N2 and N3, with cut-off values of 12.5 and 23.5 mm, respectively. LN-sum provided better diagnostic performance than conventional MDCT staging for discriminating N0-2 versus N3; sensitivity, accuracy, PPV and NPV of LN-sum were significantly higher (80.4 versus 52.2%, 81.1 versus 68.5%, 71.2 versus 57.1%, and 88 versus 74.1%). CONCLUSION: LN-sum may be sufficiently useful in assessing the N3 stage of AGC and may help to plan appropriate therapy for AGC patients.

False-positive cytopathology results for papillary thyroid carcinoma: A trap for thyroid surgeons.

OBJECTIVES: Current preoperative diagnosis of thyroid nodules remains imperfect despite recent advances in cytopathology and molecular diagnostics. False positivity in preoperative fine-needle aspiration cytology (FNAC) may lead to overtreatment of patients, including total thyroidectomy, and sometimes to lawsuits for misdiagnosis and malpractice. In this study, we analysed clinical characteristics and pathologic findings in patients with false positivity for papillary thyroid carcinoma (PTC) in FNAC. METHODS: We retrospectively reviewed permanent pathology results from 3788 patients who underwent thyroid surgery. Among them, 48 patients had lesions that were deemed suspicious or positive (Bethesda class V or VI) for PTC in preoperative FNAC. We reviewed clinic-pathologic data, radiologic findings and surgical planning in these patients. RESULTS: The prevalence of pathologic thyroiditis was significantly higher among patients with false-positive FNAC results than in those with confirmed PTC (54.2% vs 9.2%, P<.001). The analysis of the permanent pathology reports showed that 26 patients had chronic lymphocytic thyroiditis and 22 patients had no evidence of thyroiditis. Among the patients without pathologic thyroiditis, 19 patients (86.4%) had nodular hyperplasia and three (13.6%) had follicular adenoma, while among the patients with pathologic thyroiditis, seven (26.9%) had no nodule, 14 (53.8%) had nodular hyperplasia, two (7.7%) had hyalinized nodules, two (7.7%) had follicular adenoma and one (3.8%) had a hyalinizing trabecular tumour. In 42 patients, the extent of surgery (total thyroidectomy or hemithyroidectomy) was to be determined according to the intra-operative frozen section biopsy results. Among them, four (10.5%) had inconclusive frozen section results, and 38 (90.5%) had benign results on frozen section. CONCLUSIONS: Patient counselling about the possibility of false positivity is still important. And the presence of thyroiditis might create confusion in the interpretation of cytopathologic results.

Association between the prevalence of dental caries in children and factors related to their mothers.

OBJECTIVES: We assessed the association between the socio-economic, behavioural, psychological and oral health status factors of Korean mothers with the status of dental caries in their children using nationwide representative data from the Fourth Korean National Health and Nutrition Examination Survey. METHODS: Children were categorized into child (CG, 6-11 years) and adolescent (AG, 12-18 years) groups. Responses from both the child and his/her mother were included in the analysis. The data for mother-child pairs were analysed using the chi-square test and multiple logistic regression of complex samples along with other covariates, including frequency of daily tooth brushing, tooth brushing before going to bed, regular dental check-up and unmet dental care needs. RESULTS: The prevalence of dental caries in the CG was 2.4 times higher in children with mothers having ≥1 permanent tooth caries than in those with mothers having no caries (P < 0.001). In the AG, the risk of permanent tooth caries was higher in children with mothers who received less education and experienced stress (P < 0.05), and the risk was also higher (2.4 times) in children with mothers with ≥1 active permanent tooth caries than in those whose mothers did not have caries (P < 0.001). CONCLUSIONS: The mothers' oral health status was significantly associated with the existence of dental caries in their children, even after adjusting for child-related variables. Strategies for promoting oral health in children and adolescents by including individual and family factors based on the sociocultural background of the country will be necessary.

Comparison of calcium alginate and carboxymethyl cellulose for nasal packing after endoscopic sinus surgery: a prospective, randomised, controlled single-blinded trial.

OBJECTIVES: Calcium alginate is a biodegradable gel-transforming agent widely used for nasal packing. It can reduce pain and improve comfort. However, few randomised controlled trials have compared the efficacy of calcium alginate nasal packing with that of other biodegradable gel-transforming materials. DESIGN: Prospective, randomised, single-blinded controlled study. SETTING: Yonsei University Severance Hospital, a tertiary academic medical centre. PARTICIPANTS: Twenty-seven patients (54 nostrils) with chronic rhinosinusitis who were scheduled for bilateral endoscopic sinus surgery were enrolled. After surgery, one nostril was packed with calcium alginate and the other with carboxymethyl cellulose. Only patients with an intersinus chronic rhinosinusitis severity score difference of ≤1 were included. MAIN OUTCOME MEASURES: Visual analogue scale (VAS) scores for postoperative pain, discomfort from nasal discharge and pain during packing removal were analysed. Two independent rhinologists who were blinded to the assessments separately scored adhesions, oedema and infection by endoscopic digital photography at 1, 4 and 8 weeks postoperatively. RESULTS: There were no significant differences in VAS scores for postoperative pain, discomfort from nasal discharge or pain during packing removal between calcium alginate packings and carboxymethyl cellulose packings. Inter-rater variability of adhesion, oedema and infection scores was acceptable. Adhesion severity and oedema scores at 4 weeks were significantly lower with calcium alginate packing than with carboxymethyl cellulose. Infection severity scores also tended to be lower with calcium alginate than with carboxymethyl cellulose, but the difference was not significant. CONCLUSIONS: Calcium alginate nasal packing is associated with reduced severity of oedema and adhesions after endoscopic sinus surgery.

Experimental study of the potential hazards of surgical smoke from powered instruments.

BACKGROUND: Many surgical instruments have been replaced with powered devices in open gastrointestinal and laparoscopic surgery. The production of smoke as a result of vaporization of surgical tissue is inevitable, and exposure to surgical smoke is a long-standing concern. These vapours are potentially hazardous to patients and surgical teams. The present research was designed to compare various surgical devices to determine whether viable cells exist in their surgical smoke. METHODS: The search for viable cells in surgical smoke was conducted using both in vitro and in vivo experiments. Various cancers were cauterized with electrocautery, radiofrequency ablation and ultrasonic scalpels, and the resulting surgical smoke was aspirated with Transwell(®) membrane; viable cells were sought in the surgical smoke. In an in vivo experiment, samples of SCC7 were cauterized with an ultrasonic scalpel and the sediment from the rinsed Transwell(®) membrane liquid after centrifugation was injected subcutaneously into the lower back of mice. RESULTS: Viable cells were found only in the smoke from ultrasonic scalpels (in all 25 samples taken 5 cm from the cautery; 2 of 25 samples at 10 cm). Viable cells in the surgical smoke from ultrasonic scalpels implanted in mice grew in 16 of 40 injection sites. Histological and biochemical analyses revealed that these cancer cells were identical to the cancer cells cauterized by the ultrasonic scalpel. CONCLUSION: Viable tumour cells are produced in the surgical smoke from tumour dissection by ultrasonic scalpel. Surgical relevance Surgical smoke is a byproduct of dissection using a number of powered devices. Hazards to operating room personnel and patients are unclear. This study has shown that use of an ultrasonic dissection device can produce smoke that contains viable tumour cells. Although the model is somewhat artificial, a theoretical risk exists, and measures to evacuate surgical smoke efficiently are important.

Serpin peptidase inhibitor clade A member 1 is a biomarker of poor prognosis in gastric cancer.

BACKGROUND: In a previous study, we reported that serpin peptidase inhibitor clade A member 1 (serpinA1) is upregulated in Snail-overexpressing gastric cancer. Although serpinA1 has been studied in several types of cancer, little is known about its roles and mechanisms of action. In this study, we examined the role of serpinA1 in the migration and invasion of gastric cancers and determined its underlying mechanism. METHODS: Expression levels were assessed by western blot analyses and real-time PCR. Snail binding to serpinA1 promoter was analysed by chromatin immunoprecipitation (ChIP) assays. The roles of serpinA1 were studied using cell invasion and migration assays. In addition, the clinicopathologic and prognostic significance of serpinA1 expression were validated in 400 gastric cancer patients using immunohistochemical analysis. RESULTS: Overexpression of Snail resulted in upregulation of serpinA1 in gastric cancer cell lines, AGS and MKN45, whereas knockdown of Snail inhibited serpinA1 expression. Chromatin immunoprecipitation analysis showed that overexpression of Snail increased Snail recruitment to the serpinA1 promoter. Overexpression of serpinA1 increased the migration and invasion of gastric cancer cells, whereas knockdown of serpinA1 decreased invasion and migration. Moreover, serpinA1 increased mRNA levels and release of metalloproteinase-8 in gastric cancer cells. Serpin peptidase inhibitor clade A member 1 was observed in the cytoplasm of tumour cells and the stroma by immunohistochemistry. Enhanced serpinA1 expression was significantly associated with increased tumour size, advanced T stage, perineural invasion, lymphovascular invasion, lymph node metastases, and shorter overall survival. CONCLUSIONS: Serpin peptidase inhibitor clade A member 1 induces the invasion and migration of gastric cancer cells and its expression is associated with the progression of gastric cancer. These results may provide a potential target to prevent invasion and metastasis in gastric cancer.

Relationship between prosthodontic status and nutritional intake in the elderly in Korea: National Health and Nutrition Examination Survey (NHANES IV).

OBJECTIVES: Many health issues have been reported to be associated with poor nutritional status. We sought to examine the association between nutritional intake and oral health status in elderly people. METHODS: The association between perceived disability in mastication and prosthodontic status was analysed using multiple logistic regression. Multiple linear regression was used to analyse the association between prosthodontic status and nutritional intake. RESULTS: The elderly subjects with partial or full dentures reported chewing difficulties 1.62-fold more frequently (95% CI: 1.06-2.49) than those with natural teeth or a fixed prosthesis after adjusting for gender, TMD (temporomandibular disorder), household income and education level. Additionally, daily nutritional intakes of energy, protein, fat, ash, calcium, phosphorus and thiamine were decreased significantly in elderly with partial or full dentures compared with those with no prosthesis or with a fixed prosthesis (P < 0.05). CONCLUSIONS: Our findings underline oral health status and perceived disability in mastication are associated with dietary imbalances in the elderly. We suggest that the evaluation of patients' nutritional status should be considered as a part of an overall plan for dental hygiene care.

Polyethylene wear particles play a role in development of osteoarthritis via detrimental effects on cartilage, meniscus, and synovium.

OBJECTIVE: While ultra-high molecular weight polyethylene (UHMWPE) wear particles are known to cause periprosthetic osteolysis, its interaction with other intra-articular tissues in the case of partial joint arthroplasties is not well understood. We hypothesized that UHMWPE particles per se would interact with intra-articular tissue, which by acting as inflammatory reservoirs, would subsequently induce osteoarthritic (OA) changes. Our goal was to assess the inflammatory response, phagocytic activity, as well as apoptosis of intra-articular cells in the presence of UHMWPE particles in vitro, and the in vivo response of those tissues after intra-articular injection of particles in a murine model. DESIGN: Three cell types were used for the in vitro study; chondrocytes, meniscal fibrochondrocytes, and synoviocytes. Each cell type was cultured with two different concentrations of UHMWPE particles. Pro-inflammatory cytokine production, phagocytosis, and apoptosis were analyzed. In vivo experiments were done by injecting two concentrations of UHMWPE particles into normal and murine OA model knee joints. RESULTS: In vitro experiments showed that UHMWPE particles increase pro-inflammatory cytokine and mediator (IL-1ß, IL-6, TNF-α, Nitric Oxide, and Prostaglandin E2) production, phagocytosis of particles, and apoptosis in all cell types. In vivo experiment showed degeneration of cartilage and meniscus, as well as synovitis after particle injection. CONCLUSIONS: UHMWPE wear particles per se exert detrimental effects in cartilage, synovium, and meniscus of the knee joint resulting in pro-inflammatory cytokine release, phagocytosis of particles and apoptosis. Particles induced and exacerbated OA changes in a murine model.

Establishment of a reliable and reproducible murine osteoarthritis model.

OBJECTIVE: Many osteoarthritis (OA) models have been developed in mice to understand OA progression and evaluate new OA therapies. However, the individual variation of the joint lesions remains a critical problem in most of the current OA models. We established an OA model in C57BL/6 mice that is more reproducible and amenable to therapeutic intervention by controlling their movement. DESIGN: OA was induced in 9-week-old C57BL/6 mice by destabilizing the medial meniscus. The mice were then raised in the standard cage for free movement or in a confined cage customized to restrict movement. Mice in the confined cage were subjected to no exercise or exercise of 400, 800, and 1200 m/day. RESULTS: OA lesions of mice in the confined cage were more severe in the exercise group and showed much less variation. However, the patterns of OA lesions over time were quite different depending on the amount of daily exercise; the patterns increased linearly until 8 weeks in 400 m/day exercise group, but showed plateauing after 4 weeks in 800 m/day and 1200 m/day groups. The validity of our novel OA model with movement control was proven by successfully discriminating the therapeutic effect of hyaluronic acid (HA) in histological scores, while the OA model using standard caging showed a statistically insignificant difference. CONCLUSION: The mouse OA model using the confine cage and enforced periodic exercise of mice is more reproducible and reliable than standard caging methods.

Management of gastric epithelial neoplasia in patients requiring esophagectomy for esophageal cancer.

Esophageal squamous cell carcinoma is occasionally associated with malignancies located in other regions of the alimentary tract, as well as in the head, neck, and upper respiratory tract. The stomach is most commonly used for reconstruction of the alimentary tract after esophagectomy for esophageal cancer. When synchronous tumors are located in the stomach, it is often unsuitable for use in esophageal reconstruction. In such cases, an invasive procedure involving anastomosis between the esophagus and the colon must be performed. However, this procedure is associated with a high incidence of mortality and morbidity. Seven patients with synchronous esophageal cancer and gastric epithelial neoplasia were encountered. First, endoscopic submucosal dissection (ESD) was performed for the gastric epithelial neoplasia. Then, following successful ESD, Ivor-Lewis esophagectomy for esophageal cancer was planned 1 to 2 weeks later. A total of 11 gastric epithelial lesions were found in seven patients. En bloc resection by ESD was possible in all 11 lesions and histologically complete resection was achieved in all 11 lesions. Follow-up endoscopy was done 1-2 weeks after ESD; six patients with well-healing ulcers underwent esophagectomy the next day (8 or 15 days after ESD). In one patient with a poorly healed ulcer, a second follow-up endoscopy was done 1 week later and then esophagectomy was performed the next day (22 days after ESD). Post-surgical complications related to ESD, such as bleeding or mediastinal leak, were not seen in any of the seven patients. In patients with synchronous esophageal cancer and gastric epithelial neoplasia, ESD for gastric epithelial neoplasia followed by Ivor-Lewis esophagectomy 1 to 2 weeks later is an effective choice of treatment.

Endoscopic submucosal resection of esophageal subepithelial lesions using band ligation.

Subepithelial lesions (SELs) are occasionally found in the esophagus during upper endoscopy. Sometimes endoscopic resection is needed for accurate diagnosis or in the rare cases of malignant transformation of SELs. In this case series, we evaluated the usefulness of endoscopic submucosal resection with a ligation device (ESMR-L) in esophageal SELs. Twenty-three patients with 25 esophageal SELs that were no larger than 13 mm and were localized within the muscularis mucosae or submucosa were enrolled. ESMR-L was successfully performed in all 25 SELs. The en bloc resection rate was 100% (25/25), and histologically complete resection was achieved in 24 lesions (24/25, 96%). After resection of the lesion by snare, minor immediate bleeding occurred in four cases, but there was no delayed bleeding or perforation.

Magnetic Properties of Electrodeposited Cobalt-Platinum (CoPt) and Cobalt-Platinum-Phosphide (CoPtP) Thin Films.

CoPt and CoPtP thin films were synthesized using direct current (DC) aqueous electrodeposition from weak alkaline solutions. The basic plating solutions of binary CoPt thin films consisted of cobalt pyrophosphate [Co2P2O7] and chloroplatinic acid [H2PtCl6]. Various amounts of sodium hypophosphite [NaH2PO2] was added to deposit ternary CoPtP thin films. The film composition was adjusted by varying the several electrodeposition parameters including electrolyte composition, solution pH, and current density and correlated to their microstructure and magnetic property (i.e. coercivity and squareness). For the binary CoPt thin films, the maximum coercivities [in-plane coercivity (Hc,//) = ∼1,600 Oe, and perpendicular coercivity (Hc,⊥) = ∼2,500 Oe] were obtained from electrolytes containing 0.01 M H2PtCl6 + 0.04 M Co2P2O7 at current density (CD) of 7.5 mA cm-2. In the case of ternary CoPtP electrodeposits, the maximum coercivities (Hc,// = ∼2,600 Oe, and Hc,⊥ = ∼3,800 Oe) were achieved from baths containing 0.015 M H2PtCl6, 0.07 M Co2P2O7, 0.8 M NaH2PO2 at CD of 7.5 mA cm- 2 and solution pH 9. It was suggested that microstructure and magnetic properties are affected not only by the type of substrate but also by chemical compositions and electrodeposition conditions.

Use of the subcutaneous lumbar spine (SLS) index as a predictor for surgical complications in lumbar spine surgery.

BACKGROUND CONTEXT: Lumbar spine surgeries require adequate exposure to visualize key structures and limited exposure can make surgery more technically difficult, thus increasing the potential for complications. Body mass index and body mass distribution have been shown to be associated with worse surgical outcomes. PURPOSE: This study aims to further previous investigations in elucidating the predictive nature of body mass distribution with peri- and postoperative complications in lumbar surgery. STUDY DESIGN/SETTING: This is a retrospective study conducted at a single institution. PATIENT SAMPLE: Two hundred eighty-five patients who underwent lumbar laminectomy, laminotomy, or posterior lumbar interbody fusion or transforaminal lumbar interbody fusion procedures between 2013 and 2016. OUTCOME MEASURES: Magnetic resonance imaging (MRI) results and electronic medical records were reviewed for measurements and relevant complications. METHODS: Previously known risk factors were identified and MRI measurements of subcutaneous adipose depth (SAD) relative to spinous process height (SPH) were measured at the surgical site to generate the subcutaneous lumbar spine (SLS) index. This measurement was then analyzed in association with recorded surgical complications. RESULTS: The SLS index was found to be a significant risk factor for total complications (0.292, p=.041), perioperative complications (0.202, p=.015), and need for revision surgery (0.285, p<.001). The SAD alone proved to be negatively associated with perioperative complications (-0.075, p=.034) and need for revision surgery (-0.104, p=.001), with no predictive association seen for total or postoperative complications. Linear regression revealed an SLS index of 3.43 as a threshold value associated with a higher risk of total complications, 5.8 for perioperative complications, and 3.81 for the need for revision surgeries. CONCLUSION: Body mass distribution of the surgical site as indicated by SAD to SPH (SLS index) is significantly associated with increasing risk of postoperative and perioperative complications as well as increased likelihood for necessary revision surgery. This relationship was shown to be a more accurate indication of perioperative risk than previous standards of body mass index and SAD alone, and may allow spine surgeons to assess surgical risk when considering lumbar spine surgery using simple calculations from standard preoperative MRI results.

CUT-PCR: CRISPR-mediated, ultrasensitive detection of target DNA using PCR.

Circulating tumor DNA (ctDNA) has emerged as a tumor-specific biomarker for the early detection of various cancers. To date, several techniques have been devised to enrich the extremely small amounts of ctDNA present in plasma, but they are still insufficient for cancer diagnosis, especially at the early stage. Here, we developed a novel method, CUT (CRISPR-mediated, Ultrasensitive detection of Target DNA)-PCR, which uses CRISPR endonucleases to enrich and detect the extremely small amounts of tumor DNA fragments among the much more abundant wild-type DNA fragments by specifically eliminating the wild-type sequences. We computed that by using various orthologonal CRISPR endonucleases such as SpCas9 and FnCpf1, the CUT-PCR method would be applicable to 80% of known cancer-linked substitution mutations registered in the COSMIC database. We further verified that CUT-PCR together with targeted deep sequencing enables detection of a broad range of oncogenes with high sensitivity (<0.01%) and accuracy, which is superior to conventional targeted deep sequencing. In the end, we successfully applied CUT-PCR to detect sequences with oncogenic mutations in the ctDNA of colorectal cancer patients' blood, suggesting that our technique could be adopted for diagnosing various types of cancer at early stages.

Smad4 expression in gastric adenoma and adenocarcinoma: frequent loss of expression in diffuse type of gastric adenocarcinoma.

Smads are signal transducers for the members of the TGF-beta superfamily. Of these Smads, Smad4 is essential for TGF-beta signaling. The purpose of this study was to elucidate Smad4 expression and localization in 65 gastric adenomas, 49 intestinal-type and 39 diffuse type of gastric adenocarcinomas (including 12 cases of fresh frozen tissue) using Real-time RT-PCR and immunohistochemistry. Real-time RT-PCR showed that intestinal type gastric adenocarcinomas have higher Smad4 mRNA expression than diffuse type gastric adenocarcinomas. Immunohistochemical stain for Smad4 revealed that expression of Smad4 was significantly lower in diffuse-type gastric adenocarcinoma than intestinal-type gastric adenocarcinomas. Also, higher Smad4 protein expression in intestinal type gastric adenocarcinomas than overall gastric adenoma was noted. The rate of reduced Smad4 expression was higher in advanced gastric cancer than early gastric cancer. These results suggest that Smad4 might play different roles in human gastric carcinogenesis, especially between intestinal type and diffuse type of gastric adenocarcinoma.

Results of single and double autografts for high-risk neuroblastoma patients.

Although intensive therapy with autologous bone marrow transplantation (ABMT) has improved the outcome of advanced neuroblastoma, nearly half the patients with this disease still relapse after a single ABMT. In our previous study, 10 of 22 patients relapsed within 16 months post-transplantation. Predictive risk-factors for relapse were the presence of bone lesions at diagnosis, and a minor response or progressive disease at transplantation. In order to improve the outcome of these high-risk patients, we tested the feasibility of double autografts. To date, eight patients have been treated, and no treatment-related deaths were observed. Six remain in CR or with stable disease for 6 to 29 months. Although more cases and longer observation are needed to draw conclusions, these results are encouraging.

Chronic graft-versus-host disease in children and adolescents after bone marrow transplantation from HLA-matched donors.

We analyzed 98 pediatric patients who underwent bone marrow transplantation (BMT) from serologically HLA-matched related donors (RD) or unrelated donors (UD) at our institute to clarify the actual status of chronic graft-versus-host disease (cGVHD). There were 36 evaluable cases of RD-BMT and 35 of UD-BMT. cGVHD was observed in 8 RD-BMT cases (22.2%) and in 23 UD-BMT cases (65.7%). In the RD-BMT cases, the limited and extensive types of cGVHD were observed in 4 cases each, whereas in the UD-BMT cases, the limited type was seen in 11 cases and the extensive type in 12. Prior acute GVHD was observed in 6 RD-BMT cases and in 18 UD-BMT cases. Two RD-BMT patients with extensive type cGVHD died of relapse and cytomegalovirus infection, and 4 UD-BMT patients died because of bronchiolitis obliterans, fungal infection, liver failure, and multiple organ failure, respectively. The incidence of cGVHD in these pediatric patients was as high as that in adult patients when UD-BMT was performed. Some UD-BMT patients required long-term immunosuppressive therapy after BMT. These findings suggest that cGVHD is a serious problem in pediatric UD-BMT. Therefore, intensive prophylaxis and treatment of GVHD must always be performed after UD-BMT.

Evaluation of virtual source beam configurations for rapid tomographic reconstruction of gas and vapor concentrations in workplaces.

Beam path average data from an Open Path Fourier Transform Infrared (OP-FTIR) spectrometer can be used to reconstruct two-dimensional concentration maps of the gas and vapor contaminants in workplaces and the environment using computed tomographic (CT) techniques. However, a practical limitation arises because in the past, multiple-source and detector units were required to produce a sufficient number of intersecting beam paths in order to reconstruct concentration maps. Such a system can be applied to actual field monitoring situations only with great expense and difficulty. A single monostatic OP-FTIR system capable of rapid beam movement can eliminate this deficiency. Instead of many source and detector units, a virtual source arrangement has been proposed using a number of flat mirrors and retroreflectors to obtain intersecting folded beam paths. Three virtual source beam configurations generated for a single-beam steerable FTIR system were tested using 54 flat mirrors and four retroreflectors or 54 flat mirrors and 56 retroreflectors mounted along the perimeter walls of a typical 24- x 21-ft test room. The virtual source CT configurations were numerically evaluated using concentration maps created from tracer gas concentration distributions measured experimentally in a test chamber. Synthetic beam path integral data were calculated from the test maps and beam configurations. Computer simulations of different beam configurations were used to determine the effects of beam geometry. The effects of noise and peak reducing artifacts were evaluated. The performance of the tomographic reconstruction strategy was tested as a function of concentration and concentration gradients.

Tomographic reconstruction of tracer gas concentration profiles in a room with the use of a single OP-FTIR and two iterative algorithms: ART and PWLS.

Computed tomographic (CT) reconstructions of air contaminant concentration fields were conducted in a room-sized chamber employing a single open-path Fourier transform infrared (OP-FTIR) instrument and a combination of 52 flat mirrors and 4 retroreflectors. A total of 56 beam path data were repeatedly collected for around 1 hr while maintaining a stable concentration gradient. The plane of the room was divided into 195 pixels (13 x 15) for reconstruction. The algebraic reconstruction technique (ART) failed to reconstruct the original concentration gradient patterns for most cases. These poor results were caused by the "highly underdetermined condition" in which the number of unknown values (156 pixels) exceeds that of known data (56 path integral concentrations) in the experimental setting. A new CT algorithm, called the penalized weighted least-squares (PWLS), was applied to remedy this condition. The peak locations were correctly positioned in the PWLS-CT reconstructions. A notable feature of the PWLS-CT reconstructions was a significant reduction of highly irregular noise peaks found in the ART-CT reconstructions. However, the peak heights were slightly reduced in the PWLS-CT reconstructions due to the nature of the PWLS algorithm. PWLS could converge on the original concentration gradient even when a fairly high error was embedded into some experimentally measured path integral concentrations. It was also found in the simulation tests that the PWLS algorithm was very robust with respect to random errors in the path integral concentrations. This beam geometry and the use of a single OP-FTIR scanning system, in combination with the PWLS algorithm, is a system applicable to both environmental and industrial settings.