Biomedical subjects

Rohit Bhargava

Publications and source records attributed to Rohit Bhargava.

17 recordsLinked to original sources

PubMed2007

Mammaglobin vs GCDFP-15: an immunohistologic validation survey for sensitivity and specificity.

There are limited data that compare the usefulness of mammaglobin with gross cystic disease fluid protein-15 (GCDFP-15) in the identification of breast carcinomas. Whole tissue sections of 29 breast carcinomas with matched lymph node metastases and 63 breast carcinomas on tissue microarray were stained with mammaglobin cocktail and GCDFP-15 antibodies. In addition, tissue microarrays (US Biomax, Rockville, MD) containing 544 different human tumors were also stained with the mammaglobin antibody cocktail. Positive staining was seen in 67 (55.4%) of 121 breast carcinomas with mammaglobin and in 28 cases (23.1%) with GCDFP-15. In the majority of cases, the staining intensity and number of cells staining were higher with mammaglobin than with GCDFP-15. Positive mammaglobin staining was also seen in 44 (8.1%) of 544 nonbreast tumors. Mammaglobin is a more sensitive marker than GCDFP-15 for breast carcinoma; however, it lacks the specificity of GCDFP-15.

Biomarkers, Tumor↗

PubMed2006

Basal phenotype of ductal carcinoma in situ: recognition and immunohistologic profile.

The basal phenotype of breast carcinoma was demonstrated from a study of gene expression profiles, which demonstrated five carcinoma phenotypes with differing immunohistologic profiles and outcomes. The basal phenotype, so-named because of an immunohistologic profile that is similar to myoepithelial cells of the breast, has poor outcomes. While the invasive basal phenotype has been described, there is a paucity of literature regarding the existence or recognition of a precursor lesion. We searched our CoPath database for breast carcinomas in the age group of 37 years or less, and this yielded 98 cases from the years 2001 to April 2006. Pathology reports were screened for those cases that were negative for estrogen and progesterone receptors and HER-2/neu (triple negative). A total of 16 cases (16/98, 16%) fulfilled these criteria. Histology was reviewed and immunostains were performed for Cytokeratins 14, 17, and 5/6, vimentin, EGFR, c-kit, smooth muscle actin and p63. All 16 cases had a high-grade invasive ductal carcinoma, Nottingham score 9/9, with geographic necrosis, good circumscription and lymphoid infiltrates. Of the 16 cases, 13 exhibited at least one area of ductal carcinoma in situ (DCIS). The DCIS types were solid, flat or micropapillary, high nuclear grade, with comedonecrosis and invariably associated with intense lymphoid inflammatory cell infiltration. Of 16 invasive cases, 14 (88%) were positive for CK14, CK17, CK5/6 and EGFR; 94% were vimentin positive, while half or less of cases were positive for smooth muscle actin, c-kit or p63. All of the DCIS components demonstrated the same immunohistologic profile as the invasive component. A DCIS component of solid, flat or micropapillary type exists in the basal phenotype of breast carcinoma, and it demonstrates the same immunophenotype as the invasive carcinoma, typically positive for CK5/6, CK14, CK17, vimentin and EGFR, but negative for ER/PR and HER-2/neu.

Actins↗

PubMed2006

High throughput assessment of cells and tissues: Bayesian classification of spectral metrics from infrared vibrational spectroscopic imaging data.

Vibrational spectroscopy allows a visualization of tissue constituents based on intrinsic chemical composition and provides a potential route to obtaining diagnostic markers of diseases. Characterizations utilizing infrared vibrational spectroscopy, in particular, are conventionally low throughput in data acquisition, generally lacking in spatial resolution with the resulting data requiring intensive numerical computations to extract information. These factors impair the ability of infrared spectroscopic measurements to represent accurately the spatial heterogeneity in tissue, to incorporate robustly the diversity introduced by patient cohorts or preparative artifacts and to validate developed protocols in large population studies. In this manuscript, we demonstrate a combination of Fourier transform infrared (FTIR) spectroscopic imaging, tissue microarrays (TMAs) and fast numerical analysis as a paradigm for the rapid analysis, development and validation of high throughput spectroscopic characterization protocols. We provide an extended description of the data treatment algorithm and a discussion of various factors that may influence decision-making using this approach. Finally, a number of prostate tissue biopsies, arranged in an array modality, are employed to examine the efficacy of this approach in histologic recognition of epithelial cell polarization in patients displaying a variety of normal, malignant and hyperplastic conditions. An index of epithelial cell polarization, derived from a combined spectral and morphological analysis, is determined to be a potentially useful diagnostic marker.

Bayes Theorem↗

PubMed2006

Comparison of two antibodies for immunohistochemical evaluation of epidermal growth factor receptor expression in colorectal carcinomas, adenomas, and normal mucosa.

BACKGROUND: Immunohistochemical staining for epidermal growth factor receptor (EGFR) has been used as a criterion for the selection of patients with colon cancer for anti-EGFR therapy. Two antibodies, the PharmDx kit and the 31G7 clone, are used commonly for immunohistochemistry by various laboratories. No comparative studies on the performance of these 2 antibodies are available. METHODS: EGFR status was evaluated in 744 tissue microarray core samples from primary and metastatic colorectal carcinomas, colorectal adenomas, and normal colorectal mucosa with both the PharmDx kit and the clone 31G7 monoclonal antibodies. The stains were compared for staining intensity by using an automated image-analysis system. The intensity of positive staining (brown color) was measured on a scale from 0 to 255. The staining intensity also was scored manually as 0, 1 +, 2 +, and 3 +. RESULTS: Statistically, the median staining intensities scored by the automated system between the 2 antibodies did not differ significantly, although, within each category of samples (normal, adenoma, carcinoma, and metastases), the PharmDx antibody staining was slightly more intense than the clone 31G7 antibody staining. There was a linear correlation between automated image-analysis and manual scoring categories. The median automated image-analysis intensity scores for the 4 manual scoring categories with the PharmDx kit were as follows: 0 staining, 67.5; 1 + staining, 75.5; 2 + staining, 89.6; and 3 + staining, 106.0. The median automated image-analysis intensity scores for the 4 manual scoring categories with the clone 31G7 antibody were as follows: 0 staining, 71.3; 1 + staining, 73.6; 2 + staining, 84.6; and 3 + staining, 99.1. The classification of tumors as EGFR-negative (0 staining) or positive (1 +, 2 +, or 3 + staining) was concordant in 151 of 160 carcinomas (94.4%) with 2 antibodies using manual scoring. Five samples (3%) that scored 1 + with the PharmDx kit antibody scored 0 with the clone 31G7 antibody; whereas 4 samples (2.5%) that scored 1 + with the clone 31G7 antibody scored 0 with the PharmDx kit antibody. CONCLUSIONS: The EGFR expression results obtained by immunohistochemistry using both the EGFR PharmaDx kit and the 31G7 clone were comparable. Either antibody may be used for immunohistochemical detection of EGFR in colorectal carcinomas. In addition, manual scoring had an excellent correlation with automated scoring.

Adenocarcinoma↗

PubMed2005

Infrared spectroscopic imaging for histopathologic recognition.

The process of histopathology, comprising tissue staining and morphological pattern recognition, has remained largely unchanged for over 140 years. Although it is integral to clinical and research activities, histopathologic recognition remains a time-consuming, subjective process to which only limited statistical confidence can be assigned because of inherent operator variability. Although immunohistochemical approaches allow limited molecular detection, significant challenges remain in using them for quantitative, automated pathology. Vibrational spectroscopic approaches, by contrast, directly provide nonperturbing molecular descriptors, but a practical spectroscopic protocol for histopathology is lacking. Here we couple high-throughput Fourier transform infrared (FTIR) spectroscopic imaging of tissue microarrays with statistical pattern recognition of spectra indicative of endogenous molecular composition and demonstrate histopathologic characterization of prostatic tissue. This automated histologic segmentation is applied to routine archival tissue samples, incorporates well-defined tests of statistical significance and eliminates any requirement for dyes or molecular probes. Finally, we differentiate benign from malignant prostatic epithelium by spectroscopic analyses.

Diagnosis, Differential↗

PubMed2005

Distinction of endometrial stromal sarcomas from 'hemangiopericytomatous' tumors using a panel of immunohistochemical stains.

Endometrial stromal sarcomas are low-grade malignant tumors that may pose a diagnostic challenge, especially when they are present in an extrauterine site. Owing to the presence of an arborizing vasculature and cells with an undifferentiated appearance, endometrial stromal sarcomas can be confused with several soft-tissue neoplasms. We studied 17 endometrial stromal sarcomas, eight hemangiopericytomas, 14 solitary fibrous tumors, and 16 synovial sarcomas immunohistochemically, detecting the following antigens: CD10, estrogen receptor, progesterone receptor, bcl-2, CD34, smooth muscle antigen, epithelial membrane antigen and cytokeratin (AE1/AE3). Most endometrial stromal sarcomas stained positively for CD10 (16/17), estrogen receptor (17/17), progesterone receptor (15/17), and bcl-2 (17/17). Staining with antismooth muscle antigen was seen in 11 of 17 cases of endometrial stromal sarcoma, with more intense staining seen in areas showing smooth muscle differentiation. Staining with AE1/3 was seen in four of 17 endometrial stromal sarcomas, with two of the positive cases containing epithelioid cells. None of the endometrial stromal sarcomas expressed epithelial membrane antigen or CD34. More than half of the hemangiopericytomas (4/8) and solitary fibrous tumors (9/14) cases demonstrated CD10 expression either focally or in a patchy cytoplasmic and membranous pattern. Hemangiopericytomas, solitary fibrous tumors, and synovial sarcomas did not express estrogen receptor. Four of eight hemangiopericytomas and seven of 14 solitary fibrous tumors also showed patchy progesterone receptor expression. CD34 expression was identified in six of eight hemangiopericytomas and 13 of 14 solitary fibrous tumors, but we did not find expression of CD34 in synovial sarcoma. Differences between endometrial stromal sarcoma and other soft-tissue tumors were detected for all of the immunohistochemical markers (P<0.05), except anti-bcl-2 and AE1/3. Antibodies against CD10 mark a substantial number of hemangiopericytomas and solitary fibrous tumors (albeit not diffusely) and should always be combined with antiestrogen receptor and CD34 when the differential diagnosis includes endometrial stromal sarcoma. Unlike estrogen receptor antibodies, progesterone receptor antibodies show at least focal nuclear staining in most hemangiopericytomas, solitary fibrous tumors and rare synovial sarcomas, and are not useful for this differential diagnosis. All endometrial stromal sarcomas expressed bcl-2, mostly in a diffuse pattern, but this did not distinguish between endometrial stromal sarcoma and mimics. We therefore recommend the use of a small antibody panel comprising anti-CD10, anti-estrogen receptor, and anti-CD34 to distinguish endometrial stromal sarcomas from tumors with a predominant hemangiopericytomatous growth pattern.

Adolescent↗

PubMed2005

EGFR gene amplification in breast cancer: correlation with epidermal growth factor receptor mRNA and protein expression and HER-2 status and absence of EGFR-activating mutations.

The human epidermal growth factor receptor (HER) family of receptor tyrosine kinase has been extensively studied in breast cancer; however, systematic studies of EGFR gene amplification and protein overexpression in breast carcinoma are lacking. We studied EGFR gene amplification by chromogenic in situ hybridization (CISH) and protein expression by immunohistochemistry in 175 breast carcinomas, using tissue microarrays. Tumors with >5 EGFR gene copies per nucleus were interpreted as positive for gene amplification. Protein overexpression was scored according to standardized criteria originally developed for HER-2. EGFR mRNA levels, as measured by Affymetrix U133 Gene Chip microarray hybridization, were available in 63 of these tumors. HER-2 gene amplification by fluorescence in situ hybridization (FISH) and protein overexpression by immunohistochemistry were also studied. EGFR gene amplification (copy number range: 7-18; median: 12) was detected in 11/175 (6%) tumors, and protein overexpression was found in 13/175 (7%) tumors. Of the 11 tumors, 10 (91%) with gene amplification also showed EGFR protein overexpression (2+ or 3+ by immunohistochemistry). The EGFR mRNA level, based on Affymetrix U133 chip hybridization data, was increased relative to other breast cancer samples in three of the five tumors showing gene amplification. Exons 19 and 21 of EGFR, the sites of hotspot mutations in lung adenocarcinomas, were screened in the 11 EGFR-amplified tumors but no mutations were found. Three of these 11 tumors also showed HER-2 overexpression and gene amplification. Approximately 6% of breast carcinomas show EGFR amplification with EGFR protein overexpression and may be candidates for trials of EGFR-targeted antibodies or small inhibitory molecules.

Adenocarcinoma↗

PubMed2005

Identification of MYCN gene amplification in neuroblastoma using chromogenic in situ hybridization (CISH): an alternative and practical method.

Chromogenic in situ hybridization (CISH) is a recently developed technique, which utilizes the general principles of in situ hybridization and a detection system similar to immunohistochemistry. To assess the utility of CISH for analysis of MYCN gene amplification, we compared this assay with established diagnostic assays such as Southern blot analysis (SB) and fluorescent in situ hybridization (FISH). CISH was performed on 67 cases of neuroblastoma using tissue microarray (65 cases) and whole tissue sections (2 cases). Unequivocal, high-level amplification (> or =10 gene copies per tumor nucleus) was identified in 19 of 67 (28.4%) tumors. Two (3%) tumors showed low-level amplification (6-9 gene copies per tumor nucleus). No amplification was seen in 46 of 67 (68.6%) tumors. SB data were available in 44 tumors. Forty-one of the 44 tumors (93%) showed concordant results between CISH and SB. Three tumors showed MYCN amplification by CISH but no amplification by SB, most likely due to dilution effect of nonneoplastic tissue in the test samples. Two of these three tumors also showed MYCN amplification by FISH, and the third tumor was not analyzed by FISH. FISH data were available in total of 30 tumors. All 30 tumors showed concordant results between CISH and FISH for classifying a tumor as MYCN amplified or not amplified. We conclude that CISH is an accurate method for determining MYCN gene amplification, with added advantages that make it a more practically useful method.

Child, Preschool↗

PubMed2005

Fourier transform infrared vibrational spectroscopic imaging: integrating microscopy and molecular recognition.

The recent development of Fourier transform infrared (FTIR) spectroscopic imaging has enhanced our capability to examine, on a microscopic scale, the spatial distribution of vibrational spectroscopic signatures of materials spanning the physical and biomedical disciplines. Recent activity in this emerging area has concentrated on instrumentation development, theoretical analyses to provide guidelines for imaging practice, novel data processing algorithms, and the introduction of the technique to new fields. To illustrate the impact and promise of this spectroscopic imaging methodology, we present fundamental principles of the technique in the context of FTIR spectroscopy and review new applications in various venues ranging from the physical chemistry of macromolecular systems to the detection of human disease.

Algorithms↗

PubMed2005

HER-2/neu and topoisomerase IIa gene amplification and protein expression in invasive breast carcinomas: chromogenic in situ hybridization and immunohistochemical analyses.

We studied HER-2/neu (HER-2) and topoisomerase IIa (topo2a) amplification (using chromogenic in situ hybridization) and overexpression (immunohistochemical analysis) in 113 invasive breast carcinomas. A gene copy number/chromosome 17 copy number ratio of 2.0 or higher indicated amplification. A topo2a/chromosome 17 ratio of less than 0.8 indicated gene deletion. HER-2 overexpression was scored according to standard HercepTest guidelines (DAKO, Carpinteria, CA). Overexpression of topo2a was identified when nuclear staining was found in more than 5% of tumor cells. Of 113 tumors, 104 were analyzed successfully for HER-2 and topo2a amplification. Of the 104, 64 showed HER-2 amplification; 25 of these (39%) also showed topo2a amplification. No amplification was found in 40 tumors. Deletion of topo2a was seen in 7 (11%) of 64 HER-2-amplified tumors and 2 (5%) of 40 nonamplified tumors. Of 25 tumors with topo2a amplification, 18 (72%) overexpressed topo2a. Only 3 (4%) of 79 tumors without topo2a amplification overexpressed topo2a. Amplification of topo2a is associated with HER-2 amplification but not vice versa. Amplification of topo2a resulted in protein overexpression in 72% of tumors, but topo2a overexpression rarely occurred without gene amplification. Identification of topo2a and HER-2 status might have therapeutic and prognostic implications.

Antigens, Neoplasm↗

PubMed2005

Chromogenic in situ hybridization for the detection of HER-2/neu gene amplification in breast cancer with an emphasis on tumors with borderline and low-level amplification: does it measure up to fluorescence in situ hybridization?

We compared chromogenic in situ hybridization (CISH) with fluorescence in situ hybridization (FISH) for assessing HER-2/neu gene amplification using tissue microarrays (TMAs) made from formalin-fixed, paraffin-embedded tissue blocks from 113 cases of invasive breast carcinoma. TMAs were created using 0.6-mm tissue cores with 4 sampled cores per tumor. For both assays, a HER-2/chromosome 17 signal ratio of 2.0 or more was considered positive for gene amplification. The average ratio of cores from the same tumor was used for determination of gene amplification status of that particular tumor Of 113 cases, 102 were tested successfully by both assays. The results were concordant in 100.0% of cases (63 amplified; 39 nonamplified). All 22 cases of borderline (ratio, 2.0-2.5) or low-level (ratio, 2.6-3.9) amplification by FISH also showed HER-2 gene amplification by CISH. CISH is as sensitive as FISH in detecting borderline and low-level HER-2 amplification. Reliable recognition of the invasive carcinoma area by light microscopy and preservation of the test slides are added advantages of CISH. CISH performs as well as FISH in the analysis of HER-2 gene amplification in breast cancer and might have advantages in certain situations.

Breast Neoplasms↗

PubMed2004

Epstein-Barr virus positive large B-cell lymphoma arising in a patient previously treated with Cladribine for hairy cell leukemia.

We describe the case of a patient treated with 2-chloro-2'-deoxyadenosine, CdA or Cladribine for hairy cell leukemia who subsequently developed an Epstein Barr virus (EBV)-positive polymorphous large B-cell lymphoma (p-LBCL). The time interval between Cladribine therapy and development of p-BCL was 11 months and morphologically resembled an EBV-positive post transplant lymphoproliferative disorder (PTLD). Molecular genetic studies for EBV-clonality by Southern blot hybridization showed a clonal population of infected cells, implying that this was an EBV induced lesion. The chronology of events suggest that Cladribine, a purine analog which has been previously described to induce long-lasting immunodeficiency, can, in some cases, weaken the host defense mechanism to a level at which an innocuous EBV infection may transform the normal lymphoid cells into an aggressive neoplasm. Unlike most methotrexate-related lymphoproliferative disorders (LPDs), which undergo spontaneous remission after discontinuation of therapy, LPDs secondary to purine analogs often fails to resolve after discontinuation of therapy and requires additional therapy. Our patient was treated with rituximab following the diagnosis of p-LBCL, with the goal of improving the pancytopenia to permit chemotherapy. However, the patient failed to show any dramatic improvements in counts, developed systemic symptoms and progressive ascites. He expired 3 weeks after a second dose of rituximab. Cladribine is a potent immunosuppressive agent and should be included with the list of immunosuppressive agents that may be associated with EBV-related B-cell lymphoproliferative disorders.

Aged↗

PubMed2004

Serous endometrial cancers that mimic endometrioid adenocarcinomas: a clinicopathologic and immunohistochemical study of a group of problematic cases.

BACKGROUND: Uterine serous carcinomas (USCs) can exhibit an architecturally well-differentiated tubuloglandular morphology with or without an accompanying papillary growth pattern. These features make it difficult to distinguish USCs from endometrial endometrioid carcinomas (EECs). Given the aggressive behavior of USC, compared with EEC, and differences in management, it is important to correctly classify endometrial carcinomas that exhibit a tubuloglandular architecture with high nuclear grade. We sought an immunohistochemical panel to minimize subjectivity in the distinction of USC from EEC. MATERIALS AND METHODS: We identified 8 problematic endometrial cancers, exhibiting a tubuloglandular growth pattern and high nuclear grade, whose classification as EEC or USC was debated or resulted in disagreement. We selected 13 cases of International Federation of Gynecology and Obstetrics (FIGO) grade 2 EEC and 16 cases of USC as controls. An immunohistochemical panel, including p53, beta-catenin, cyclin D1, estrogen receptor (ER), progesterone receptor (PR), and PTEN, was evaluated. RESULTS: As a group, the clinical features and immunoprofile of the study cases resembled those of the serous controls. The study cases expressed p53, beta-catenin, cyclin D1, and ER and PR, and showed loss of PTEN in 75%, 12.5%, 0%, 37.5%, 37.5%, and 12.5% of cases, respectively. p53, beta-catenin, cyclin D1, ER and PR expression, and PTEN loss were seen in 87.5%, 0%, 19%, 31%, 12%, and 0% of the serous controls and in 7%, 70%, 54%, 92%, 92%, and 61.5% of the endometrioid controls, respectively. The combination of lack of p53 expression, positive PR expression, and loss of PTEN best distinguished between EEC and USC using discriminant analysis (multivariate P = 0.008, <0.001, and 0.05, respectively). CONCLUSION: In endometrial carcinomas exhibiting high nuclear grade and low architectural grade, using a panel of immunohistochemical stains may facilitate the distinction of USC from EEC. Our clinical and immunohistochemical data also support the concept that there is a group of endometrial adenocarcinomas composed of tubular glands that are indeed serous carcinomas.

Aged↗

PubMed2004

Feasibility of using tissue microarrays for the assessment of HER-2 gene amplification by fluorescence in situ hybridization in breast carcinoma.

Tissue microarrays (TMAs) have been commonly used to study protein expression by immunohistochemistry (IHC). However, limited data exist on the validity of using TMAs to study gene amplification. In this study, we evaluated the feasibility of using breast carcinoma TMAs to study HER-2 gene amplification by fluorescence in situ hybridization (FISH). In addition, hormonal receptor status (ER and PR) and HER-2 protein overexpression by IHC were also studied, and results were compared with whole tissue sections. FISH for HER-2 was performed on formalin-fixed paraffin-embedded tissue from 114 invasive breast carcinomas both on whole tissue sections and on TMAs containing the same tumors. The TMA was created using 0.6-mm tissue cores with four sampled cores per tumor from the same tissue block used for whole section FISH. The PathVysion HER-2 probe kit was used for the FISH analysis. A ratio of HER-2:Chromosome17 > or =2.0 was interpreted as positive for gene amplification. The ER or PR was interpreted as positive when nuclear staining was detected in more than 10% of tumor cells. The HER-2 IHC (HercepTest; DAKO Corp, Carpinteria, CA) results were interpreted as 0, 1+, 2+, and 3+ according to standard criteria. The FISH results in the TMA and whole sections were concordant in 99 out of 101 successfully analyzed cases (99%). The FISH scores were consistent among the two to four cores in the majority of the cases. ER and PR results were concordant between whole sections and TMA cores in 97% (107/110) and 89% (97/109) cases, respectively. The overall concordance for HER-2 status by IHC between whole sections and TMA cores was 86% (94 out of 109 cases). TMAs are a reliable approach to study HER-2 gene amplification in a high throughput manner.

Adenocarcinoma↗

PubMed2004

Gram-Schmidt orthogonalization for rapid reconstructions of Fourier transform infrared spectroscopic imaging data.

Increasingly voluminous Fourier transform infrared (FT-IR) spectroscopic imaging data sets are being generated with the advent of both faster array detectors and the implementation of time-resolved imaging techniques, resulting in data processing becoming the limiting step in visualizing sample heterogeneity and temporal profile evolution. We report the application of a Gram-Schmidt vector orthogonalization procedure in interferogram space to provide a significant time saving advantage in processing of one to two orders of magnitude in comparison to conventional spectral processing. Illustrative data from human skin biopsies and from dynamic molecular reorganizations within liquid crystalline microdomains is employed to discuss the capabilities and limitations of this information-extraction approach.

Biopsy↗

PubMed2003

Time-resolved Fourier transform infrared spectroscopic imaging.

Fourier transform infrared (FT-IR) imaging allows simultaneous spectral characterization of large spatial areas due to its multichannel detection advantage. The acquisition of large amounts of data in the multichannel configuration results, however, in a poor temporal resolution of sequentially acquired data sets, which limits the examination of dynamic processes to processes that have characteristic time scales of the order of minutes. Here, we introduce the concept and instrumental details of a time-resolved infrared spectroscopic imaging modality that permits the examination of repetitive dynamic processes whose half-lives are of the order of milli-seconds. As an illustration of this implementation of step-scan FT-IR imaging, we examine the molecular responses to external electric-field perturbations of a microscopically heterogeneous polymer-liquid crystal composite. Analysis of the spectroscopic data using conventional univariate and generalized two-dimensional (2D) correlation methods emphasizes an additional capability for accessing of simultaneous spatial and temporal chemical measurements of molecular dynamic processes.

Crystallization↗

PubMed2002

Effective time averaging of multiplexed measurements: a critical analysis.

Multiplexing and time averaging of signal are effective noise reduction protocols applied in many analytical measurement systems. The efficacy of these protocols may be reduced by random occurrences of high-magnitude noise that do not conform to the statistical distribution of noise for all other measurements in the data set. This high-magnitude noise, which may have an insignificant probability of occurrence for a single measurement, almost certainly affects data collected in a multichannel, multiplexed modality, such as Fourier transform infrared (FT-IR) spectroscopic imaging employing focal plane array detectors. To recover time-averaging advantages in these cases, we present a general coaddition method that uses two statistical measures, the mean and median of the ensemble of measurements of a signal, to obtain a better estimate of the true signal than that estimated by time averaging alone. This method, termed median filtered time averaging, is shown to be an effective noise removal procedure for FT-IR imaging data. The effects of noise removal on time averaging and multiplexing are examined theoretically and are demonstrated for hyperspectral infrared microspectroscopic imaging data obtained from human skin biopsies by using a rapid data acquisition procedure.

Spectroscopy, Fourier Transform Infrared↗