Methods to determine response factors for infrared gas imagers used as quantitative measurement devices.

Response factors (RF) can be used to characterize relative sensitivity of one compound vs. another compound for the same measurement instrument. Use of RF allows the analysts/operators to calibrate the instrument with one compound and make measurement for a large number of compounds. This method is adopted for Flame Ionization Detector (FID) based survey instruments used in the Leak Detection and Repair (LDAR) practice for control of fugitive emissions of volatile organic compounds. Gas detecting Infrared (IR) cameras have been used for leak detection. However, the RF for IR cameras has not been well established despite some attempt to develop a method for IR camera RF. In addition to a method proposed earlier (Method 1), two new methods for IR camera RF are proposed in this paper: Method 2 based on theoretical approach and Method 3 based on experimental approach. All three methods are examined and compared. Both Methods 2 and 3 have shown the ability to characterize the behavior of RF for various compounds and substantially higher accuracy than Method 1. Method 2 provides a mechanism to generate RF for a large number of compounds without conducting experiments, and is recommended for implementation. The RF derived from this method can be used both in the emerging field of Quantitative Optical Gas Imaging (QOGI) and to answer the most common question that IR camera users ask-whether a particular compound can be imaged by a particular IR camera. IMPLICATIONS: Infrared imager is an efficient tool for detecting gas leaks from process equipment and has been used in leak detection and repair (LDAR) programs for control of fugitive emissions. However, the information regarding which chemical compounds can be imaged and how sensitive a given infrared imager is for various compounds is limited. A theoretical method is presented in this paper that can answer these questions without conducting resource-intensive experiment. The results of this theoretical method has good agreement with experimental data. The method has been used to predict relative sensitivity for 398 compounds.

Selective anterior fusion of thoracolumbar/lumbar curves in adolescents: when can the associated thoracic curve be left unfused?

STUDY DESIGN: A retrospective multicenter study was conducted to investigate patients with a major thoracolumbar/lumbar adolescent idiopathic scoliosis and an associated minor thoracic curve treated with an anterior instrumentation and fusion of the lower curve. OBJECTIVE: To establish criteria for determining when such curves can be successfully treated by an anterior only procedure of the lower curve with acceptable spinal balance and residual thoracic curve. SUMMARY OF BACKGROUND DATA: Anterior spinal instrumentation techniques have been proved effective for the management of isolated thoracolumbar/lumbar scoliosis with small compensatory thoracic curves. The success of a selective anterior fusion when the associated thoracic curve had some structural changes in a small preliminary study was variable and was the stimulus for this study. METHODS: A multicenter study involved 49 adolescent patients with a major thoracolumbar/lumbar curve in which the associated minor thoracic curve measured between 30 degrees and 55 degrees. In all the patients, the apical vertebra of the lower curve lay outside the midsacral line, and the thoracic apical vertebra fell outside a line dropped from the center of C7. Multiple radiographic parameters were evaluated. The Risser sign, height, weight, onset of menses, and closure of the triradiate cartilages were studied to access the patients' maturity. All the patients were observed at least 2 years. Patients were considered to have a satisfactory result if the thoracic curve at the final follow-up assessment measured 40 degrees or less, if balance and sagittal alignment were reasonable, and if additional procedures were not required. RESULTS: At final follow-up assessment, two groups emerged. Group 1 (n = 43) had satisfactory results. The preoperative thoracic curve in this group averaged 40 degrees and 26 degrees after surgery. The lumbar curve averaged 56 degrees before surgery and 22 degrees after surgery. Group 2 (n = 6) had unsatisfactory results. The average thoracic curve was 49 degrees before surgery 54 degrees after surgery, whereas the lumbar curve averaged 59 degrees before surgery and 27 degrees after surgery. Three of these patients underwent posterior thoracic instrumentation and fusion. CONCLUSIONS: Statistical analysis showed that a successful surgical outcome was dependent on both the structural changes in the thoracic curve and the patient's maturity. The thoracolumbar/lumbar-thoracic (TL/L:T) Cobb ratio in combination with the degree of the thoracic curve on lateral bending was the best predictor among the structural indexes. Of 44 patients with a TL/L:T Cobb ratio of 1.25 or greater and/or a thoracic curve, which bent out to 20 degrees or less, 42 had a satisfactory result. The best predictor among the maturity indexes was closure of the triradiate cartilages. Of 43 patients in whom the triradiate cartilages were closed, 42 had satisfactory results. When this data is combined, the outcome for the thoracic curve can be reasonably predicted.