Biomedical subjects

David Levin

Publications and source records attributed to David Levin.

7 recordsLinked to original sources

PubMed2005

Techniques for efficient, real-time, 3D visualization of multi-modality cardiac data using consumer graphics hardware.

We exploit consumer graphics hardware to perform real-time processing and visualization of high-resolution, 4D cardiac data. We have implemented real-time, realistic volume rendering, interactive 4D motion segmentation of cardiac data, visualization of multi-modality cardiac data and 3D display of multiple series cardiac MRI. We show that an ATI Radeon 9700 Pro can render a 512x512x128 cardiac Computed Tomography (CT) study at 0.9 to 60 frames per second (fps) depending on rendering parameters and that 4D motion based segmentation can be performed in real-time. We conclude that real-time rendering and processing of cardiac data can be implemented on consumer graphics cards.

Algorithms↗

PubMed2004

Automated image registration of gated cardiac single-photon emission computed tomography and magnetic resonance imaging.

PURPOSE: To develop an automatic registration method for electrocardiogram-gated myocardial perfusion single-photon emission computed tomography (SPECT) and cardiac cine-magnetic resonance imaging (MRI). MATERIALS AND METHODS: Paired myocardial perfusion SPECT (MPS) and MRI from 20 patients were considered. MR images were presegmented by heart localization based on detection of cardiac motion and optimal thresholding. A registration algorithm based on mutual information was subsequently applied to all time frames or a selected subset from both modalities. RESULTS: A preprocessing step significantly improved the accuracy of the registration when compared to automatic registration performed without preprocessing. Errors in translation parameters (T(x), T(y), T(z)) averaged (1.0 +/- 1.5, 1.1 +/- 1.3, 0.9 +/- 0.9) pixels with MRI segmentation and (4.6 +/- 3.2, 3.4 +/- 2.6, 3.0 +/- 3.4) pixels without MRI segmentation. Errors in rotation parameters (R(x), R(y), R(z)) averaged (5.4 +/- 2.9, 3.4 +/- 2.7, 4.5 +/- 3.6) degrees with MRI segmentation and (9.3 +/- 6.1, 4.8 +/- 4.3, 14.6 +/- 12.6) degrees without MRI segmentation. Error was calculated as the absolute difference between the expert manual and the automatic registration transformation. CONCLUSION: Automatic registration of gated MPS and cine MRI is possible with the use of a mutual information-based technique when MR images are presegmented. Cardiac motion can be used to isolate the left ventricle (LV) on the MR images automatically, and subsequently the segmented MR images can be coregistered with gated MPS.

Algorithms↗

PubMed2004

Acceleration of 3D, nonlinear warping using standard video graphics hardware: implementation and initial validation.

Thin Plate Spline (TPS) transformations are used in many medical imaging algorithms, but are time-prohibitive for iterative or interactive use. We have utilized current generation consumer 3D graphics cards to accelerate the application of the TPS nonlinear transformation by combining hardware accelerated 3D textures, vertex shaders and trilinear interpolation. Our hardware accelerated algorithm warped a 512x512x173 Computed Tomography (CT) dataset in 2.3 s, and the same study, scaled to 256x256x173, in 0.5 s, using a set of 92 landmarks. An accelerated software implementation of the TPS transformation warped the 512x512x173 study in 32.9 s and the 256x256x173 study in 9.5 s. Subtracted images were used for qualitative analysis of the warp and the Mutual Information (MI) and Sum of Absolute Difference (SAD) similarity metrics were used to quantitatively compare the output of the hardware accelerated algorithm to that of the software algorithm. The hardware accelerated algorithm provided a 7-65 times performance increase when compared to the software algorithm, and produced output of comparable quality (MI > 300 and SAD < 1.75%).

Algorithms↗

PubMed2004

Condom use by women recently diagnosed with a sexually transmitted infection: effects of study methodology on the apparent influence of hormonal/surgical contraception.

OBJECTIVE/GOAL: The objective of this study was to investigate potential predictors of consistent condom use (CCU), including the influence of hormonal contraception/surgical sterilization (HC/SS). STUDY: Regression methods were used to predict CCU and other measures of CU among 214 sexually active, 18- to 45-year-old women previously diagnosed with a sexually transmitted infection. RESULTS: CCU was significantly associated with younger age, African American ethnicity, having casual partners, recent HIV testing, condom use self-efficacy, and concern about partner relationship. HC/SS was not significantly associated with the likelihood of CCU, before (HC/SS, 21.3%, non-HC/SS, 25.3%; odds ratio [OR], 0.798; P=0.4914) or after (OR, 1.209; P=0.5995) controlling for confounders (age, ethnicity, casual partners). Controlling for age and ethnicity eliminated initial significant or near-significant inverse associations between HC/SS and 3 alternative measures of interval condom use ("any use," "number of unprotected acts," "proportion condom-protected contacts") and substantially diminished the association between HC/SS and "condom use at last sex." CONCLUSIONS: Choice of condom use measure and control of confounding variables can substantially affect results when studying potential predictors of condom use such as HC/SS.

Adolescent↗

PubMed2002

Healthcare utilization by women in a comprehensive managed care population subsequent to diagnosis of a sexually transmitted disease.

BACKGROUND: Healthcare utilization (HCU) following a sexually transmitted disease (STD) diagnosis is poorly characterized. GOAL: The goal was to quantify HCU for new/recurrent STDs and other relevant Ob-Gyn and mental health problems in the 18 months subsequent to an STD diagnosis. STUDY DESIGN: We compared HCU between a group of females aged 18 to 45 years who were Kaiser Permanente Medical Program members with a diagnosed STD (n = 1,205) and a medical center- and age group-matched sample of women seen for a non-STD diagnosis in the same time period (n = 4820), with controlling where appropriate for age, medical center, and chronic disease status. RESULTS: An STD diagnosis was associated with significantly greater likelihood of subsequent visits for STDs (relative risk [RR] = 3.8), pelvic inflammatory disease/endometritis (RR = 2.9), candidiasis (RR = 2.0), vaginitis (RR = 2.4), cervical dysplasia (RR = 1.7), menstrual disorders/abnormal bleeding (RR = 1.3), high risk/complicated/ectopic pregnancy (RR = 1.5), and behavioral/mental health problems (RR = 1.3) than for women seen for a non-STD diagnosis. CONCLUSION: Detrimental sequelae of STDs are reflected in substantially elevated near-term HCU following an STD diagnosis.

Adult↗

PubMedDate not supplied

Characterization of small nodules by automatic segmentation of X-ray computed tomography images.

OBJECTIVE: To characterize the ability of an automatic lung nodule segmentation algorithm to measure small nodule dimensions and growth rates. METHODS: A phantom of 20 sets of 6 balls each (11 different nylon balls and 9 acrylic balls) of 1 to 9.5 mm in diameter, in foam, was imaged using x-ray computed tomography with slice thicknesses of 5, 2.5, and 1.25 mm, pitches of 3 and 6, and standard and lung resolution. Measurements consisted of volume and maximum in-plane cross-sectional areas and their derived maximum and effective diameters. Growth rates were simulated using pairs of groups of balls. RESULTS: Volume measurements overestimate volume, more so for thicker slices. For the largest balls, the error is 60% for 5-mm slices and 20% for 1.25-mm slices. Effective diameter calculated from volume better approximates actual diameter. For area measurements, errors are 0% to 5% for the largest balls, and the effective and actual diameters are closely matched. CONCLUSIONS: Below 5 mm in diameter, changes in volume should reach 100% for reliable indication of growth. Above 6 mm, the threshold for detecting change is on the order of 25% growth. Even under ideal conditions, results indicate the need for caution when making a diagnosis of malignancy on the basis of volume change.

Algorithms↗

PubMedDate not supplied

Liquid chromatographic analysis of vitamin B6 in reconstituted infant formula: collaborative study.

A liquid chromatographic (LC) method was validated for the determination of total vitamin B6 in infant formula. Total vitamin B6 was quantified by converting the phosphorylated and free vitamers into pyridoxine. Pyridoxine was determined by ion pair reversed-phase LC with fluorescence detection. The method was subjected to an AOAC collaborative study involving a factory-manufactured, milk- and soy-based infant formula. Each was spiked at 3 concentrations in the range of 0-1 microg/g and sent as blind duplicate to participant laboratories. Nine laboratories returned valid data which were statistically analyzed for outliers and precision parameters. The repeatability relative standard deviation (RSD(r)) ranges were 2.0-4.0 and 3.5-5.9% for fortified milk- and soy-based formulas, respectively. The reproducibility relative standard deviation (RSD(R)) ranges were 8.2-8.4 and 6.7-11.2% for fortified milk- and soy-based formulas, respectively. HORRAT values ranged from 0.42 to 0.53, indicating that the precision of the method is acceptable. The mean RSD(r):RSD(R) values were 0.60 and 0.55 for milk- and soy-based formulas, respectively. As expected, RSDs for the unfortified samples were higher, but their HORRAT values (0.81 and 2.06) helped define a realistic limit of quantitation as 0.05 microg/g. Recovery data were quantitative and varied between 81.4 and 98.0% (mean = 89.8%) for each of 6 spiked materials.

Animals↗