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Biomedical subjects

Manuel L Brown

Publications and source records attributed to Manuel L Brown.

5 recordsLinked to original sources
PubMed2003

Prevalence effect in a laboratory environment.

PURPOSE: To measure observer performance at various levels of prevalence. MATERIALS AND METHODS: A multiobserver multiabnormality receiver operating characteristic (ROC) study to assess the effect of prevalence on observer performance was conducted. Fourteen observers, including eight faculty members, two fellows, and four residents, interpreted 1,632 posteroanterior chest images with five prevalence levels by using a nested study design. Performance comparisons were accomplished by using a multireader multicase approach to assess the effect of prevalence from 28% (69 of 249) to 2% (31 of 1,577) on diagnostic accuracy. The mean times required to review and report a case were analyzed and compared for different levels of prevalence and readers' experience. RESULTS: Area under the ROC curve demonstrated that, with the study experimental conditions, no significant effect could be measured as a function of prevalence (P >.05) for any abnormality, group of cases, or readers. There were no significant differences (P >.05) in the mean times required to review and report cases at different prevalence levels and with different groups of readers. CONCLUSION: The consistency in the results and the size of this study suggest that with laboratory conditions, if a prevalence effect exists, it is quite small in magnitude; hence, it will not likely alter conclusions derived from such studies.

Laboratories↗
PubMed2002

Sentinel lymph node biopsy in head and neck squamous cell carcinoma.

OBJECTIVES/HYPOTHESIS: Sentinel lymph node biopsy is a minimally invasive method to stage the regional lymphatics that has revolutionized the management of patients with intermediate-thickness cutaneous melanoma. Head and neck surgeons have been encouraged by the accuracy of sentinel lymph node biopsy in cutaneous melanoma and have applied the technique to patients with head and neck squamous cell carcinoma (HNSCC). The objectives of the study were 1) to study the feasibility and accuracy of sentinel lymph node biopsy as a method to stage the regional lymphatics in HNSCC and 2) to determine whether there are qualitative differences between the cutaneous and mucosal lymphatics that would affect the technique used in HNSCC. STUDY DESIGN: Two methods of investigation were employed: a prospective laboratory study using a feline model for sentinel lymph node biopsy and a retrospective review of patients who received lymphoscintigraphy before neck dissection and intraoperative identification of the sentinel lymph node. METHODS: Lymphoscintigraphy and a gamma probe were used in four felines to study the kinetics of technetium-labeled sulfa colloid (Tc-SC) in the mucosal lymphatics. In the second part of the feline study, eight subjects were studied intraoperatively. Tc-SC and isosulfan blue dye were used to study the injection technique for the mucosal lymphatics and to determine the time course of the dye and Tc-SC to the sentinel lymph node. In Part II of the present study, a retrospective review of 33 patients with HNSCC was conducted. Twenty patients (stage N0) whose treatment included elective neck dissection were studied with preoperative lymphoscintigraphy and underwent intraoperative identification of the sentinel lymph node to determine the accuracy and feasibility of sentinel lymph node biopsy. Eight patients with palpable neck disease and five patients with recurrent or second primary disease whose previous treatment included neck dissection were also studied with lymphoscintigraphy before neck dissection. RESULTS: In the feline study, both Tc-SC and isosulfan blue dye traversed the lymphatics rapidly, appearing in the sentinel lymph node in less than 5 minutes. Modification of the injection technique used for cutaneous melanoma was required to depict the sentinel lymph node of the base of tongue. In the human study, the sentinel lymph node was accurately identified in 19 of 20 (95%) N0 patients. On average, 2.9 sentinel lymph nodes (range, 1-5) were identified in 2.2 (range, 1-4) levels of the neck. Sentinel lymph nodes were bilateral in 4 of 19 patients. When the sentinel lymph node was identified, it accurately predicted the pathological nodal status of the regional lymphatics. Three of 20 patients had cervical metastases, and the sentinel lymph node was identified in 2 of 3 patients with pathologic nodes (pN+). Focal areas of radiotracer uptake were identified in seven of eight patients with palpable disease. These areas corresponded to the level with palpable disease in four patients. The lymphatics delineated by lymphoscintigraphy in the five patients with previous neck dissection were outside the levels that had been dissected. Lymphoscintigraphy depicted collateral patterns of lymphatic drainage. CONCLUSIONS: Sentinel lymph node biopsy is technically feasible and is a promising, minimally invasive method for staging the regional lymphatics in patients with stage N0 HNSCC. Lymphoscintigraphy alone may determine the levels that require treatment in patients with disrupted or previously operated cervical lymphatics.

Adult↗
PubMed2002

Observer performance studies: detection of single versus multiple abnormalities of the chest.

OBJECTIVE: We used receiver operating characteristic (ROC) analysis to compare two methods of evaluating observer performance in detecting an abnormality on chest radiographs. In the first method, the abnormality in question, rib fracture, was one of five investigated, and it was the only one of interest in the second. MATERIALS AND METHODS: Eight experienced observers viewed 117 posteroanterior chest radiographs in two interpretation modes. Fifty-four of these images depicted rib fractures that had been rated as subtle for detection. The likelihood of the presence of a rib fracture was rated as one of five abnormalities in question in one mode and the sole abnormality of interest in the other mode. RESULTS: Six of the observers performed better during the single-abnormality mode, one performed equally well in both modes, and one performed better during the multiple-abnormality mode. The average area under the ROC curves (A(z)) was 0.73 +/- 0.07 for the multiple-abnormality mode and 0.80 +/- 0.04 for the single-abnormality mode. The results were significantly different (p < 0.05). CONCLUSION: Study methodology can significantly affect the results in ROC studies, particularly for abnormalities that may not be perceived as primary or important. The order in which abnormalities appear on a checklist report form may be important.

Area Under Curve↗