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Biomedical subjects

L W Grossman

Publications and source records attributed to L W Grossman.

At least 19 recordsLinked to original sources
PubMed1998

Determining the imaging quality of intraocular lenses.

PURPOSE: To validate the proposed optical requirements of a draft international standard for intraocular lenses (IOLs). SETTING: Eight optical testing laboratories in the United States, Germany, Japan, and The Netherlands. METHODS: The testing laboratories performed modulation transfer function (MTF) tests on various IOLs using a model eye and visual resolution tests in air. Each laboratory performed duplicate measurements on a set of 43 lenses that was circulated among the testing laboratories. RESULTS: The interlaboratory tests showed that the MTF measurements using a model eye had better repeatability and reproducibility than the more common industry practice of resolution testing in air with parallel light and the United States Air Force three-bar target. However, the two methods correlated well. The commonly applied criterion that an IOL resolve in air at least 60% of the Rayleigh cutoff spatial frequency corresponded to a minimum requirement of 0.43 MTF units at 100 mm-1 in a model eye. CONCLUSIONS: Either criterion may be applied in accordance with a proposed international standard for IOLs. The model eye method can be applied over a broader range of dioptric powers and is relevant for materials that interact with aqueous. Both tests appear to have a greater ability to detect unwanted surface aberrations than resolution testing of IOLs in a water cell using parallel light, a method described in the current American National Standards Institute standard.

Diagnostic Techniques, Ophthalmological↗
PubMed1997

Constrained reconstruction applied to 2-D chemical shift imaging.

The method of constrained reconstruction, previously applied to magnetic resonance imaging (MRI), is extended to magnetic resonance spectroscopy. This method assumes a model for the MR signal. The model parameters are estimated directly from the phase encoded data. This process obviates the need for the fast Fourier transform (FFT) (which often exhibits limited resolution and ringing artifact). The technique is tested on simulated data, phantom data, and data acquired from human liver in vivo. In each case, constrained reconstruction offers spatial resolution superior to that obtained with the FFT.

Artifacts↗
PubMed1996

Accuracy in determining intraocular lens dioptric power assessed by interlaboratory tests.

PURPOSE: To describe a testing program conducted by a standards group as a guide for setting international tolerances for intraocular lens (IOL) dioptric power. SETTING: Multicenter study. METHODS: Seven biconvex, poly(methyl methacrylate) IOLs ranging in power from 10.00 through 30.00 diopter (D) were circulated among nine participating laboratories experienced in IOL optical measurements. Each laboratory performed repeated optical tests to determine dioptric power. These results were analyzed for repeatability and reproducibility in accordance with methods specified by the International Organization for Standardization. RESULTS: Intralaboratory repeatability was less than 0.5% of the dioptric power, and interlaboratory reproducibility, when following a normalized procedure for correction and conversion, was less than 1.0% of the dioptric power. CONCLUSION: Tolerance limits of +/0 0.30 D in the range 0 to 15.00 D, +/- 0.40 D for 15.50 to 25.00 D, and +/- 0.50 D for 25.50 to 30.00 D have been proposed as an international standard for IOLs. The contribution of IOL power error within the limits of the standard are estimated to contribute less than 1.0% to the total error in postoperative refractive prediction.

Lenses, Intraocular↗
PubMed1996

Induction of lambda prophage by 213 nm laser radiation: a quantitative comparison with 193 nm excimer radiation using image analysis.

We compared the DNA damage produced by radiation from two UV laser wavelengths, 213 nm and 193 nm, with that produced by noncoherent 254 nm radiation. Following irradiation of Escherichia coli BR339, a bacteriophage lambda lysogen containing the lacZ gene, pro-phage induction was measured by assaying for beta-galactosidase. Because of the limited penetration by UV laser wavelengths an agar overlay of the lysogen was used as the irradiation target. Irradiation of 254 nm was performed in buffer suspension followed by transfer of 5 microL spots onto assay plants. Computer image analysis was used to monitor the rate of product formation, observed as an increase in optical density of the irradiated zones on assay plates. We found that the rate of product formation was a more reproducible unit of comparison than the optical density present at the end of the reaction. Although the rate of product formation was not linearly related to enzyme concentration, the data could be fit to a simple logarithmic function. Using this method, we concluded that the DNA damaging ability of 213 nm radiation was 10 times more efficient than 193 nm radiation and about 100 times less efficient than 254 nm noncoherent radiation.

Bacteriophage lambda↗
PubMed1992

Optical performance of decentered monofocal intraocular lenses.

A model eye water cell was used to evaluate the optical performance of biconvex, meniscus, and plano-convex (spheric and aspheric) monofocal poly(methyl methacrylate) intraocular lenses when the lenses were centered and when they were decentered 1 mm and 2 mm. Resolution, induced astigmatism, and modulation transfer function measurements were performed for all lenses with the more convex surface of the lens oriented toward the incident light. The same measurements were performed for the plano-convex and meniscus lenses in the reverse orientation. The lens shapes least affected by decentration were the biconvex and spheric plano-convex with the convex surface oriented toward the incident light. When centered, the aspheric plano-convex lenses had the best overall contrast performance based on the modulation transfer function measurements. However, once decentered the performance of the aspheric lenses approached that of the meniscus lenses in the reverse orientation, the lens shape which had the worst performance.

Lenses, Intraocular↗
PubMed1991

Survey of the optical quality of intraocular lens implants.

Intraocular lenses (IOLs) from 15 U.S. firms were tested for conformance to the requirements of the American National Standards Institute Z80.7 standard for IOLs. A total of 162 IOLs were tested for resolution, astigmatism, and accuracy of labeled power. Average resolving power was 78% of the diffraction limit, much better than the ANSI minimum requirement which is typically equivalent to 30% of the diffraction limit. This suggests that the ANSI Z80.7 requirement could be significantly tightened with little effect on current production practices. Only one IOL exhibited astigmatism in excess of 0.25 diopter. Differences between measured and labeled power in excess of 0.50 diopter were found in 22 lenses, indicating that accuracy of refractive power may be the most commonly missed optical requirement of the standard.

Equipment Design↗
PubMed1991

Optical quality testing of monofocal intraocular lens implants with a 3 mm and a 4 mm aperture.

The optical quality of 81 monofocal poly(methyl methacrylate) intraocular lenses (IOLs) from eight U.S. firms was tested using a 3 mm aperture, as recommended by the American National Standards Institute Z80.7 standard for IOLs, and a 4 mm aperture. The use of the larger aperture had no effect on the measurements of refractive power and astigmatism. When examined with the 3 mm aperture, the average resolving power of the IOLs was 81% of the diffraction limit; when examined with the 4 mm aperture, the average resolving power was 67% of the diffraction limit. Use of the larger aperture would ensure that a larger area of the IOL had been examined. Incorporating the larger aperture into the ANSI minimum resolution requirement would not appreciably affect the rejection rate for currently manufactured monofocal lenses.

Lenses, Intraocular↗
PubMed1991

Resolution testing of intraocular lenses.

A basic goal associated with the manufacture of intraocular lenses (IOLs) is that they not be vision limiting. Manufacturers must therefore test IOL resolution against some minimum requirement. Currently, American National Standards Institute voluntary standard Z80.7-1984 addresses IOL optical requirements. One criterion of this standard is a minimum resolving power of 100 line-pairs-per-millimeter. This report presents some results of lens testing that suggest this standard is inadequate because it may not control the performance of a large enough fraction of the optic aperture.

Humans↗
PubMed1986

Noise analysis of scintillation camera images: stochastic and non-stochastic effects.

An analysis of noise was performed on scintillation camera images. The analysis was performed on sets of field floods, uniform exposures over the field of view, in such a way that stochastic and non-stochastic effects were separable. Stochastic noise for the digitally acquired images was found to approach the limit of Poisson count statistics. The non-stochastic component of the calculations dominated the results at the lower spatial frequencies. These results hold true even after standard methods of uniformity correction are applied, primarily due to the effects of Compton scatter events. The noise power spectrum calculations carry information about the patterns of the noise in flood images. Examples of digitisation, photomultiplier tube mottle and edge-packing artefacts are presented.

Photography↗
PubMed1985

Accidental Cs-137 contamination.

Widespread use of radionuclides in medicine and industry poses the possibility of radiation accidents. We describe such an occurrence involving three industrial workers. The accident resulted from careless handling of a Cs-137 source. Evaluation of the Cs-137 whole body burden was carried out using stationary and scanning whole body counters. In addition, regional and whole body activity from contamination was assessed using an uncollimated gamma camera. This report emphasizes the value of the gamma camera for detection of radionuclide contamination in radiation accidents.

Accidents, Occupational↗
PubMed1985

Gallium-67 lung uptake: conjugate-view technique.

A conjugate-view technique is derived for calculation of absolute gallium-67 (Ga-67) uptake from scintillation-camera images. The technique combines counts of posterior and anterior images of the lung with an attenuation correction obtained from cobalt-57 (Co-57) transmission imaging. The formulation is such that the effects of Compton scatter build-up are accounted for. Studies utilizing a canine model indicated that, normally, more activity is located in the chest wall than in the lungs. The quantitative technique must therefore accurately account for a variety of Ga-67 distributions, including that in the chest wall. Calculations were performed using a three-component model comparing results obtained with the conjugate-view approach to the actual uptake. These calculations suggest that an assumption of uniform activity distribution allows an accuracy of approximately +/- 10% over a broad range of body-part thicknesses and uptake by the lungs. It was concluded that the conjugate-view technique is necessarily approximate but can provide clinically useful results.

Animals↗
PubMed1983

Myocardial perfusion imaging with 99mTc-DMPE in man.

Technetium-99m DMPE (99mTc-DMPE) is a newly synthesized myocardial perfusion imaging agent that shows intense myocardial accumulation in the dog. In the present study, dosimetry and potential clinical usefulness of this agent were assessed in four human subjects. Absorbed radiation doses were low, with the highest doses consisting of 200 mrad/mCi (54 microGy/MBq) to the gallbladder and 160 mrad/mCi (43 microGy/MBq) to the liver. No evidence of clinical toxicity was found. Technetium-99m DMPE did image the myocardium, but the ratio of target to nontarget activity was less favorable than that observed in the dog. Intense hepatic 99mTc-DMPE activity interfered with clinical imaging of the cardiac apex in two of the four subjects. We conclude that the prototype radiopharmaceutical, 99mTc-DMPE, is capable of myocardial perfusion imaging in man but the planar myocardial images produced are of inferior quality compared with 201Tl myocardial images. Further work is justified to develop related compounds to overcome the clinical limitations described.

Adult↗
PubMed1983

Thallium-201 imaging artifacts not detected by technetium-99m or cobalt-57 quality-control testing.

Early stages of hydration in a sodium iodide crystal may cause artifactual "hot" spots on thallium-201 heart images. This phenomenon was observed when a mobile gamma camera was used even though the daily quality-control flood-field views revealed no apparent abnormalities. Nevertheless, hot spots were visible on thallium-201 and xenon-133 flood-field images. With asymmetric photopeak positioning using a technetium-99m source, hot spots were noted in addition to phototube nonuniformities. Subsequently, the camera head was disassembled, the crystal was inspected visually, and the crystal seal was found to be broken. Hydration of the crystal was confirmed by the camera manufacturer. Quality-control procedures should test for hydration-induced artifacts on a regular basis.

Animals↗
PubMed1982

Basal kinetic studies of Tc-99m DMPE as a myocardial imaging agent in the dog.

Newly synthesized Tc-99m dichlorobis(1,2-dimethylphosphino)ethane (DMPE) was investigated as a myocardial imaging agent with respect to its kinetics (dependent on both time and regional coronary blood flow), its percent organ uptake, and its imaging characteristics in the anesthetized dog. Most of these data are compared with those of Tl-201. Blood clearance of the two agents is essentially the same. Compared with Tl-201, Tc-99m DMPE shows faster overall kinetics, higher heart-to-lung ratio, equally good correlation with a wide range of regional blood flows, and higher liver uptake. At the time of peak myocardial uptake, the mean heart uptake of Tl-201 is 4.3%, compared with 2.9% for Tc-99m DMPE, yet only 0.9% uptake of Tc-99m DMPE is found in the lung as compared with 3.3% for Tl-201. These differences result in a heart-to-lung ratio of 2:1 for Tc-99m DMPE and 1:1 for Tl-201, based on the data obtained from the time-activity curve. The quantitative findings are supported by the superior quality of Tc-99m DMPE images of both normal and infarcted dog heart. The high hepatic uptake of Tc-99m DMPE is not a serious problem if images are obtained within 5-60 min after dose. These basic kinetic studies suggest that Tc-99m DMPE is a promising myocardial imaging agent.

Animals↗
PubMed1981

The accuracy of 99Molybdenum assays in 99mTechnetium solutions.

A study was performed to determine the accuracy of 99Mo measurements using three commercial dose calibrators with their 99Mo assay shields. One 99Mo assay shield allowed excessive penetration by the lower energy 99mtc photons, resulting in the calibrator's falsely high interpretation of the activity of 99Mo present in the high-activity 99mTc eluates. All three calibrators performed adequately with a National Bureau of Standards 99Mo standard in equilibrum with 99mTc. By using low-activity aliquots of 99Mo and 99mTc, a low-level linearity test was performed. Two of the calibrators were found to have a threshold of approximately 10 microCi (370 kBq) for a nonzero 99Mo response, although one of these occasionally produced variable nonzero responses below its threshold. Only one of the calibrators was found to reflect accurately the activity of 99Mo present under all conditions tested.

Calibration↗
PubMed1981

Film reciprocity law failure in scintillation camera imaging.

Sensitometric measurements of scintillation camera images show that substantial changes in film response occur with variations in imaging time or dot focus. Both the speed and the slope of the film characteristic curve are affected. The phenomenon responsible for the variation in response is referred to as "film reciprocity law failure" and is inherent in the image-forming process.

Photography↗