Characterization of the reciprocity law failure in three mammography screen-film systems.

The purpose of this project was to quantify reciprocity law failure (RLF) for mammography screen-film systems. Three widely used screen-film systems were evaluated: the Kodak MinR 2000 system. Fuji UM Mammo Fine screen and Fuji UM MA HC film, and Agfa MR Detail screen and Agfa Mammoray MR5 film. The logit algorithm that linearizes logistic curve shapes was utilized to characterize film sensitometric response. Different values of mammographic phantom thickness, tube current, and kVp were used to vary screen-film exposure rates. RLF was quantified by examining the dependence of logit parameters (maximum and minimum film density, curve shift, and slope) on exposure rate. The shift of the logit curve was found to be a good indicator of the screen-film system speed, while the slope of the logit curve is affected by the RLF. RLF leads to changes in film contrast as well as speed. For the range of exposure rates measured (50-fold), screen-film contrast and speed varied by factors of 2 and 3.5, respectively. Film contrast decreased as exposure rate increased. The greatest changes were observed with the Kodak MinR 2000 screen-film system.

Cerebrospinal fluid fistula: detection with MR cisternography.

PURPOSE: Our goal was to assess the role of MR cisternography in the examination of patients with suspected CSF rhinorrhea. METHODS: MR cisternography was performed as a heavily T2-weighted fast spin-echo study with fat suppression and video reversal of the images in 37 patients over a 3-year interval. Twenty-four of the patients subsequently had exploratory surgery for fistula. Statistical analysis of the surgical results was compared with the findings at MR cisternography. RESULTS: MR cisternography showed significant correlation with surgical findings, with sensitivity, specificity, and accuracy of 0.87, 0.57, and 0.78, respectively. CONCLUSION: MR cisternography proved to be an accurate diagnostic imaging technique in the evaluation of suspected CSF rhinorrhea.

Parametrization of mammography normalized average glandular dose tables.

Data from existing tables of normalized glandular doses in mammography were parametrized to determine analytical expressions that match tabulated results within known uncertainties. The parametrization was performed for three different target/filter combinations (molybdenum target-molybdenum filter, molybdenum target-rhodium filter, and rhodium target-rhodium filter) and three different breast compositions (100% adipose, 50% adipose-50% glandular, and 100% glandular). The analytical expressions provide the normalized glandular dose for any breast composition within stated ranges of tabulated input parameters (kVp, half-value layer, and breast thickness). The maximum difference between tabulated and parametrized data is 1.29%, which is smaller than the stated 2% uncertainty in tabulated dose data due to uncertainties in the x-ray spectra models used to generate the tables. Analytical expressions are easily coded to create custom functions that return the normalized glandular dose for the set of input parameters. Examples of implementation are presented in Microsoft Visual Basic for Applications (VBA).

Computed model of gadolinium enhanced MRI of breast disease.

OBJECTIVE: Investigation has shown that the most useful MRI finding for the detection of breast cancer is enhancement following in travenous contrast. However, many widely different imaging protocols have been used. The purpose of this study is to explicate factors that affect the signal intensity of breast lesions after intravenous gadolinium. METHODS AND MATERIALS: A computer model was developed using equations based on published data. The effect of gadolinium on breast tissues was calculated using the model with appropriate values for baseline tissue relaxation times, relaxivity of gadolinium at the given field strength and concentration of gadolinium based on published data, for the TR, TE, flip angle and field strength of several published sequences used for enhanced breast MRI. RESULTS: The computer model allows comparison of the performance of different sequences, which can be displayed graphically. These vary in their performance, largely dependent on T1 weighting. Enhancement is also affected by the baseline of the T1 of the lesion and sensitivity of the sequence to gadolinium. Malignant lesions demonstrate greater observed enhancement than predicted when assuming symmetric distribution of contrast, indicating there is greater accumulation of gadolinium, accounting for the differential enhancement between benign and malignant lesions. CONCLUSIONS: MRI sequences vary greatly in their demonstration of enhancement after intravenous gadolinium contrast. Numerical diagnostic criteria such as % signal intensity change must be interpreted with care when using a different sequence than that on which the criterion was developed. There is preferentially greater accumulation of contrast in malignant lesions, whether due to angiogenesis or altered permeability.

On the stationary states in gradient echo imaging.

A formalism is presented that concisely describes the magnetization of a sample subjected to a periodic series of RF pulses. In this formalism, the steady state of the magnetization is shown to be a sum of magnetic substates, each with unique contrast characteristics. When more than one substate contributes to a given image, the substates interfere with each other, producing ghosts and other artifacts. Properly designed gradient protocols can image single substates, producing ghost-free images. The contrast of the image depends largely on the choice of the imaged substate. Analytic solutions for unspoiled, RF spoiled, and gradient spoiled magnetizations are presented.

Retinal arteriolar macroaneurysms: long-term visual outcome.

Visual outcome was analysed in 16 consecutive eyes with symptomatic retinal arteriolar macroaneurysms treated by direct laser photocoagulation and 26 consecutive symptomatic eyes followed with no treatment. No difference existed between groups in presenting visual acuity, macular involvement, presence of macular subretinal fluid, or presence or location of associated haemorrhage. The mean follow up was 41 months. In the 26 untreated eyes, visual acuity was improved by 2 or more lines in 13 (50%), was unchanged in nine (35%), and decreased in four cases (15%). In the 16 treated cases, three improved (19%), seven were unchanged (43%), and six had decreased visual acuity (38%). The average minimum angle of resolution improved 0.53 log units in untreated cases and decreased 0.14 log units in treated cases (p = 0.02). Multivariable logistic regression modelling analysis revealed that laser treatment remained a significant risk factor for final visual acuity of less than 20/80 even when controlling for the effects of subretinal haemorrhage and foveal subretinal fluid (odds ratio 8.4, p = 0.01). Laser photocoagulation directly to the macroaneurysm did not improve the visual outcome in this series.

Magnetic resonance contrast agents. Physical basis of relaxation.

Only through a combined understanding of contrast agent properties and fundamental contrast mechanisms, optimal administration and imaging techniques can be applied to contrast-enhanced MR imaging. It is impossible to cover all aspects of the physics of paramagnetic contrast agents in a short review. The basic theories of paramagnetic relaxation enhancement and susceptibility effects, presented in this article, are intended to help readers understand the behavior of existing contrast agents in clinical studies. Additional information about these phenomena can be found in other published reviews, and for a more in-depth coverage, the reader should turn to monographs and scientific papers that discuss the particular topics of interest.

Laboratory information system for nuclear magnetic resonance relaxometry in biomedical materials (NMR LIS). I. Data acquisition and experiment control.

A large and comprehensive Laboratory Information System (LIS) was developed for a laboratory that specializes in the studies of nuclear magnetic resonance (NMR) relaxation behavior in biomedical materials. Several programs have been developed (data acquisition and hardware control, data analysis, theoretical modeling, utilities like plotting, FFT, and peak fitting), and several other are under development (data postprocessing, database management, linkage to other systems). This paper describes a software module that was developed to control the hardware (to communicate with the NMR spectrometer pulse programmer, magnet power supply, temperature controller), to achieve efficient data acquisition through a parallel interface to the ADC devices, and to provide a user friendly interface to a complex laboratory system.

Laboratory information system for nuclear magnetic resonance relaxometry in biomedical materials (NMR LIS). II. Data analysis.

Data analysis modules for Nuclear Magnetic Resonance Relaxometry LIS are described. Since the experimental NMR results from biomedical samples often exhibit complex structure that arises from complexity of tissue, the analysis methods focus on search, investigation, and evaluation of complex multiexponential relaxation features. Two algorithms have been implemented: an enhanced spin grouping method that is based on a multiexponential curve stripping algorithm, and an eigenvalue decomposition method, implemented as modified DISCRETE program.

Analysis of variance for 'component stripping' decomposition of multiexponential curves.

An extended analysis of variance is presented for a multiexponential curve fitting procedure, known as 'curve stripping', 'curve peeling', or 'successive subtraction'. In addition to the standard, single variable curves, this analysis includes the two dimensional multiexponential surface analysis. The calculations take into account features required by the graphical user interface that was specifically designed to facilitate the fitting process. The evaluation of the goodness of fit includes an F test (to evaluate the number of components needed to fit the data), and correlation coefficients (to evaluate individual parameters).

Surgical management of a long-standing subfoveal neovascular membrane secondary to ocular histoplasmosis.

Subretinal neovascular membranes located under the fovea typically lead to significant visual loss. Laser treatment has been limited due to the anatomic location of the neovascular process, but surgical removal has been reported with promising results. We surgically removed a long-standing, presumed ocular histoplasmosis syndrome (POHS) subfoveal neovascular membrane that had been present for 10 months in a patient's only functional eye, with unexpected good results. This case suggests that the good visual outcomes achieved by surgically excising smaller subfoveal neovascular membranes early in their natural history also can be achieved in selected patients with more chronic and severe subfoveal neovascular processes.

Retinal periphlebitis in patients with acquired immunodeficiency syndrome with cytomegalovirus retinitis mimics acute frosted retinal periphlebitis.

Acute frosted retinal periphlebitis is an inflammatory condition of unknown origin characterized by marked perivenular infiltration in otherwise healthy patients. We encountered seven patients with acquired immunodeficiency syndrome who exhibited visual loss associated with an unusual diffuse retinal periphlebitis very similar in appearance to acute frosted retinal periphlebitis. Each patient developed a thick inflammatory infiltrate surrounding the retinal venules, creating a frosted appearance. Two cases were bilateral. All patients had areas of more typical cytomegalovirus retinitis in their involved eye(s). Five of six patients treated with ganciclovir sodium showed improvement not only of the cytomegalovirus retinitis but also of the periphlebitis. Although we do not have histopathologic evidence that cytomegalovirus was the cause of these cases of periphlebitis, we believe that periphlebitis may be a previously unrecognized finding of cytomegalovirus retinitis in patients with acquired immunodeficiency syndrome. So far, there is no evidence implicating cytomegalovirus as the cause of acute frosted retinal periphlebitis in healthy patients.

A comparison of total body water measurements using whole-body magnetic resonance imaging versus tritium dilution in primates.

Standard techniques conventionally used to assess body composition have various drawbacks which include a requirement for specialized equipment and expertise not widely available, radiation exposure, extensive study time periods, and limited clinical utility. Anthropometric methods, which are more clinically feasible, also involve substantially greater calculation error. This study was designed to compare a newly developed whole-body magnetic resonance (MR) imaging technique with standard tritium dilution (THO) to measure total body water (TBW) in eight primates (Macaca fascicularis). Sedated primates underwent whole-body MR imaging (10-12 contiguous 50-mm slices) and TBW was computed using a previously validated program. After 5 days to allow for primate recovery and stabilization, TBW measurements were repeated using THO methodology. Linear regression analysis of TBWMRI (72.1 +/- 5.7% body wt) compared with TBWTHO (73.8 +/- 3.2% body wt) yielded a Pearson correlation of r = 0.8145, P = 0.02 with a mean squared error of 2.14. Whole-body MR imaging determination of TBW correlates well with THO, requires less time (20 min versus 24 hr), and does not expose the subject to radiation. This study suggests that whole-body MR imaging is an accurate technique for in vivo body composition analysis. As demonstrated by the body size of this investigational primate model, the technique maybe particularly applicable to the study of human infants.

Broad line quantitative chemical shift spectroscopy.

Proton NMR spectroscopy was applied to quantitate the measurement of total body water/fat distributions in vivo. A special MR protocol was developed to excite a thick slab of tissue and display the magnitude NMR spectrum of the collected response signal. Very short echo time TE (8 ms) and long repetition time TR (4000 ms) were used to minimize relaxation damping of the signal intensities. The spectrum was then decomposed into individual lines and proton densities of different species were calculated. Proton density information was converted into weight percentage data using stoichiometrical and physiological information. The technique was validated using phantoms that contained different mixtures of water/maize oil. A high-resolution NMR spectrum of maize oil samples was used to determine the stoichiometric information. The test results showed good agreement with the known composition of the phantom within the whole range of water content (0-100%). This method is very fast since no phase encoding of data is required. Preliminary results for monkeys show promising potential in clinical applications.

Long-term visual outcome in Terson syndrome.

The presentation and long-term visual outcome in 30 eyes with Terson syndrome is evaluated. In 25 of 30 eyes (83%), visual acuity of 20/50 or better was attained. This occurred in 12 of 16 eyes (75%) managed by observation alone and 12 of 14 eyes (86%) treated by pars plana vitrectomy. The most common long-term sequelae in all eyes studied was the formation of an epiretinal membrane. These occurred in 14 of 18 eyes (78%) followed for 3 or more years but accounted for significant visual loss in only 2 eyes. There was no difference in final visual outcome between those patients undergoing vitrectomy and those managed conservatively. However, visual recovery was more rapid in eyes undergoing vitrectomy despite the fact that vitrectomy was reserved for eyes with more dense vitreous hemorrhage.

A complete solution to the model describing Carr-Purcell and Carr-Purcell-Meiboom-Gill experiments in a two-site exchange system.

A general solution for the relaxation decay function observed in both CP and CPMG spin-echo experiments, performed on systems governed by a two-site chemical exchange mechanism, is presented. This solution not only provides the relaxation time constants, but also supplies complete information about relative component sizes. Solutions are analytical, but results are complex enough to warrant computer-assisted calculations. Programming suggestions, based on the extensive tests performed, are provided.

Evaluation of a new magnetic resonance imaging method for quantitating adipose tissue areas.

We have developed a new magnetic resonance imaging (MRI) protocol to quantitate intraabdominal and subcutaneous fat and have validated it by comparing measurements of fat areas by MRI with those obtained by computed tomography (CT) in 11 asymptomatic volunteers who all had a single CT and MRI image taken at the level of the umbilicus. The new MRI protocol was based on a water-fat separation method by which the slice selection routines excite water and fat protons in different positions along the slice select direction. This method performed more reliably than earlier methods based on phase differences between water and fat signals. Fat areas measured by MRI exceeded those measured by CT by 8-22 percent, and fat areas and ratios obtained by MRI correlated well with CT (r = 0.98 for areas and, for ratios, r = 0.81). The ratio of intraabdominal/subcutaneous fat measured by MRI in seven males was significantly greater than that in four females. We also compared the new method with a previously published inversion recovery (IR) method in seven additional volunteers. Agreement between the two methods was excellent, and the major differences were technical: the IR protocol produced images that may require custom image processing programs when obtained on some scanners. Comparability of the two methods provides further reassurance of the validity of both. MRI presents an attractive opportunity for directly measuring intraabdominal fat in order to correlate this with metabolic parameters and to visualize changes during weight loss.