Biomedical subjects

A L Weaver

Publications and source records attributed to A L Weaver.

131 records · Page 8Linked to original sources

PubMedDate not supplied

Cine phase-contrast MR flow measurements: improved precision using an automated method of vessel detection.

OBJECTIVE: The purpose of this study was to construct a method of vessel edge detection that correctly identifies vessel pixels and to compare the interuser variability of cine phase contrast MR volumetric flow rates obtained with the conventional manual method and an automated method. MATERIALS AND METHODS: The automated method was developed based on a magnitude image threshold value and compared with the manual method in a flow phantom (three users) and in velocity images of the portal vein (five users). The threshold value determined from the magnitude image was applied to a region of interest surrounding the vessel of interest on the magnitude image to construct a vessel edge detection mask m(x,y). The velocity images were then multiplied by the mask m(x,y) and volumetric flow rates determined using the identified vessel pixels. RESULTS: In the flow phantom, flow measurements with the magnitude threshold method had significantly less interuser variability compared with the manual method (p < 0.01) and were within 10% (mean 6.0%) of the actual flow versus 35% (mean 18.6%) with the manual method. Regarding flow measurements in the portal vein of six volunteers, the magnitude threshold method was significantly more precise (p < 0.01) than the manual method with a mean standard deviation between the five users of 40.4 +/- 12.9 ml/min (range 22-60 ml/min) and 110.4 +/- 32.7 ml/min (range 70-155 ml/min), respectively. CONCLUSION: The magnitude threshold method of vessel edge detection developed in this study yields flow measurements that are accurate in the model system and have significantly less interuser variability than the manual method. This method shows promise for improving the precision of cine phase contrast flow measurements.

Adult↗

PubMedDate not supplied

Diabetes mellitus and operated peptic ulcer disease.

There is some evidence of an antagonism between peptic ulcer and diabetes mellitus. This antagonism is possibly related to anomalous insulin metabolism in duodenal ulcer patients. To evaluate this issue, 471 Rochester, Minnesota residents who had surgery for peptic ulcer were examined and then followed for up to 34 years. Their experience of diabetes mellitus was compared with that of Rochester residents generally, for whom data on diabetes incidence and prevalence were available. At surgery, the prevalence of diabetes was somewhat increased for gastric and slightly diminished for duodenal ulcer patients. Of the 445 patients who were free of diabetes at surgery, 27 developed it. By 20 years, the cumulative incidence of diabetes (9.1%) was less than expected (10.3%), but over the 20 years the difference was not significant for either gastric or duodenal ulcer patients. The risk of diabetes was not influenced by age, gender, or smoking status but analysis for relative weight at surgery indicated that obese patients had a 2.6-fold increase in risk of subsequent diabetes, whereas those with less than 1.2 relative weight had reduced risk. Relative weight was the only significant predictor of the time to subsequent diabetes in a proportional hazards regression analysis. The proposition of an antagonism between peptic ulcer and diabetes is not supported by the data.

Cohort Studies↗

PubMedDate not supplied

Early experience with Wide-Platform Mk II implants. Part I: Implant survival. Part II: Evaluation of risk factors involving implant survival.

Part I of this study describes the survival of a wide-platform, wide-diameter implant (Wide-Platform Mk II). Beginning in January 1997, 85 Wide-Platform Mk II implants were placed in the jaws of 63 patients (35 males and 28 females). Male patients experienced 10 implant failures, and female patients lost 9 implants. The mean time of implant follow-up was 286 days (median, 280), with a maximum of 734 days and a minimum of 0 days. Implant loss was 19% in the mandible and 29% in the maxilla. Kaplan-Meier analysis showed a probability of implant failure after 1 year of 0.649 (confidence interval, 0.455 to 0.926) in the maxilla and of 0.751 (confidence interval, 0.616 to 0.915) in the mandible. No apparent relationship was noted between implant survival and implant length. Part II of this study evaluated the association between the survival of a new implant design and a number of potential risk factors. A retrospective chart review was conducted for all patients who received Wide-Platform Mk II implants and who agreed to allow a medical records review for research purposes. Kaplan-Meier survival curves were used to assess the probability of implant survival relative to time. The relationships between implant survival and implant location, history of tobacco use, current tobacco use, sinus grafting, bruxism, and root canal therapy were assessed by Cox proportional hazards modeling. Although the hazard ratio showed an increased risk of implant failure with some factors, particularly a history of root canal therapy in the site of implant placement (hazard ratio 3.2, P = .10), none of the factors were statistically significant. The Wide-Platform Mk II implant used in this population group was associated with a high failure rate, but the failure rate was not related to any specific risk factors reviewed.

Adult↗

PubMedDate not supplied

Antrochoanal polyps in children.

Although relatively rare, antrochoanal polyps represent one of the most common types of polyp diagnosed in children without cystic fibrosis. In an attempt to better define this entity and discuss treatment options, the histories and operative reports of all 25 children (aged 17 years and younger) diagnosed with an antrochoanal polyp between 1970 and 1997 at our institution were reviewed. All 25 children complained of nasal obstruction on presentation; other presenting symptoms included rhinorrhea (48%), snoring (36%), and mouth breathing (32%). All 25 patients were noted to have a mass in the nose on examination, and 16 (64%) also had a mass noted in the nasopharynx. All but 1 patient underwent surgical removal of the polyp: intranasal avulsion only, 2 patients; Caldwell-Luc procedures, 10 patients; intranasal procedures, 8 patients; and endoscopic procedures, 4 patients. Mean time to first recurrence was 44.5 months. Seven patients (29%) who underwent excision at our institution experienced recurrence, 3 after endoscopic procedures and 4 after intranasal procedures (with or without Caldwell-Luc; 1 of these patients had a second recurrence). Complications were unusual and included bleeding after pack removal (8.3%) and facial paresthesias (10%). Follow-up ranged from 2 days to almost 27 years and was aided by telephone interviews. We conclude that surgical treatment of these lesions is safe and effective. Endoscopic removal may result in a higher recurrence rate.

Adolescent↗

PubMedDate not supplied

Pituitary adenoma: a DNA flow cytometric study of 192 clinicopathologically characterized tumors.

A clinically, immunohistochemically and ultrastructurally characterized series of 192 pituitary adenomas was analyzed for DNA content by flow cytometry. Results were assessed not only relative to tumor immunotype, size, and invasiveness, but also with frequency of recurrence. Case selection was non-random; males predominated (1.8:1) and the ratio of macro-to-microadenomas was 4.2:1. Female patients were slightly younger and, in all adenoma categories, less often had invasive tumors: PRL (15%/30%), ACTH (17%/44%), LH/FSH (8%/27%) and null cell adenomas (0%/27%). With the exception of prolactin cell adenomas, similar proportions of macroadenomas and invasive tumors in all tumor subtypes were diploid and non-diploid. Prolactin adenomas differed in that tumors of males showed a high rate of non-diploidy (65%); such tumors were predominantly macroadenomas, but only 28% were invasive. Among GH-containing tumors 78% were macroadenomas, 40% were nondiploid, and the frequency of invasive macroadenomas was higher (49%) than in PRL tumors (21%). ACTH adenomas were mainly microadenomas (81%), their rate invasion (29%) and of non-diploidy being low (14%). Among "non-functioning" (LH/FSH, null cell adenomas), LH/FSH-producing tumors were all macroadenomas, but with low rates of invasion (23%) and non-diploidy (9%). Null cell adenomas, nearly all macroadenomas, had similar low invasion rate (21%), but were more often non-diploid (39%). In all adenoma subgroups S-phase fractions were higher in non-diploid adenomas by an overall ratio of 2.1:1. Prolactin adenomas showed the highest (15.2%) and LH/FSH adenomas the lowest (5.6%) mean S-phase fraction. When compared to long-term follow-up, neither this parameter nor ploidy correlated with tumor size or invasiveness. Lastly, long-term follow-up showed ploidy to be an unreliable predictor of tumor persistence or recurrence.

Adenoma↗