Quantitative assessment of bone marrow hematopoiesis using parametric magnetic resonance imaging

Spatial maps of the percentage cellularity in pelvic bone marrow were calculated at a resolution of 15.6 mm3 from six volunteers and 10 patients treated for documented hematologic disease using a three-point Dixon MRI pulse sequence. The percentage cellularity calculation was aided by analyzing a two-dimensional feature space consisting of the apparent water fraction (Wa), and the T2 relaxation time of water (T2w). An extracellular water fraction was assigned to each voxel on the basis of a two-component T2w algorithm. In six cases, the method was compared to results obtained from core biopsies or aspirates of the posterior iliac crest. The results indicate that segmentation schemes that combine high-quality phase-contrast imaging with nuclear relaxation time measurements can potentially identify the true fractional marrow volume occupied by hematopoietic elements in a variety of clinical situations.     

Finding parametric representations of the cortical sulci using an active contour model

The cortical sulci are brain structures resembling thin convoluted ribbons embedded in three dimensions. The importance of the sulci lies primarily in their relation to the cytoarchitectonic and functional organization of the underlying cortex and in their utilization as features in non-rigid registration methods. This paper presents a methodology for extracting parametric representations of the cerebral sulcus from magnetic resonance images. The proposed methodology is based on deformable models utilizing characteristics of the cortical shape. Specifically, a parametric representation of a sulcus is determined by the motion of an active contour along the medial surface of the corresponding cortical fold. The active contour is initialized along the outer boundary of the brain and deforms toward the deep root of a sulcus under the influence of an external force field, restricting it to lie along the medial surface of the particular cortical fold. A parametric representation of the medial surface of the sulcus is obtained as the active contour traverses the sulcus. Based on the first fundamental form of this representation, the location and degree of an interruption of a sulcus can be readily quantified; based on its second fundamental form, shape properties of the sulcus can be determined. This methodology is tested on magnetic resonance images and it is applied to three medical imaging problems: quantitative morphological analysis of the central sulcus; mapping of functional activation along the primary motor cortex and non-rigid registration of brain images.     

Dynamic properties of Lednev's parametric resonance mechanism

This paper presents a further development of the mechanism for the detection of weak magnetic fields proposed by [Lednev (1991): Bioelectromagnetics 12:71-75]. The fraction of excited oscillator states of an unhydrated ion is studied in a dynamic model driven by the predicted (time-varying) transition probability in the presence of thermal noise and an unspecified excitation mechanism. The main results of Lednev are confirmed. In addition, I conclude that ultraharmonic and ultrasubharmonic resonances may also be observed, provided that the response time of the dynamic system is similar to the period of the oscillating magnetic field. I discuss the time scales involved in the mechanism and present theoretical constraints on these parameters. The crucial requirement for the theory's applicability is that the lifetime of the excited states of the affected ion oscillator exceeds the period of the applied magnetic field. Numerical solutions of the dynamic system are given and are shown to correspond well to theoretical expectations. The main discrepancy between the theories of Lednev and of Blanchard and Blackman [Blanchard and Blackman (1994): Bioelectromagnetics 15:217-238] appears to be due to an inconsistency in the latter paper. The general problem of robust analysis of experimental data is discussed, and I suggest a test of compliance with the Lednev model that is independent of all parameters except for the ratio of oscillating and static field strength (B1/B0) for many resonance conditions and experimental models.     

Differentiation of healthy from cirrhotic livers. Evaluation of parametric images after contrast administration in magnetic resonance imaging

RATIONALE AND OBJECTIVES: The authors describe a method to differentiate healthy from cirrhotic livers by the analysis of their behavior after paramagnetic contrast administration on magnetic resonance imaging. METHODS: A dynamic single-slice spoiled-gradient recalled echo magnetic resonance imaging after contrast administration was performed on 67 patients (36 healthy livers and 31 cirrhotic livers). Three parametric images (averaged-enhancement, maximum-enhancement, and maximum-velocity) were reconstructed from the temporal dynamic images. Liver values were quantified by means of a region-of-interest procedure. RESULTS: Relative averaged-enhancement and maximum-enhancement values were significantly different ( P < 0.05) between cirrhotic and normal livers. There was a significant correlation between the parametric values and the Child-Turcotte index of hepatic chronic insufficiency (P < 0.05). CONCLUSIONS: Parametric images allow characterization of the signal-versus-time pixel-by-pixel variations in dynamic magnetic resonance imaging. The averaged-enhancement and maximum-enhancement values can be used to differentiate healthy from cirrhotic livers with accuracy. The higher values found in cirrhotic patients may reflect an overall increase in the amount of extracellular contrast present with respect to healthy livers. The degree of liver brightness in cirrhotic patients probably is related to an increased amount of interstitial space, an indirect measurement of hepatic necrosis.     

Evaluation of hilar pulmonary vessels using magnetic resonance angiography (MRA)

OBJECTIVE: To assess the relationship between ethnicity and decision-makers expressing healthcare wishes in a group of frail older persons enrolled in the Program of All-inclusive Care for the Elderly (PACE). DESIGN: A retrospective chart review of 1193 participants in the PACE program. SETTING: Program of All-inclusive Care for the Elderly, a comprehensive managed care demonstration program serving frail older participants at 10 sites across the nation. PARTICIPANTS: A total of 1193 older adults, all of whom met state criteria for nursing home level of care. Three hundred were non-Hispanic whites, 364 were black, 156 were Hispanic, and 288 were Asian. MEASUREMENTS: Demographic characteristics of the patients and the presence or absence of an alternative decision-maker; the characteristics of alternative decision-makers included the relationship to the participant as recorded in the patient's medical record. RESULTS: Ninety-one percent of white patients expressed their own healthcare wishes in contrast to only 85% of Hispanic, 83% of Asian, and 67% of black patients. An alternative decision-maker was identified for about 15% of Asians and Hispanics and for one-third of blacks, but only about 8% of whites had an alternative decision-maker. Black and Hispanic patients were most likely to have a daughter as an alternative decision-maker, Asians were most likely to have a son, and whites patients were most likely to have a spouse as an alternative decision-maker. Blacks, particularly black men, were the most likely to have a relative other than a spouse or child as an alternative decision-maker. CONCLUSIONS: In this population, we found significant ethnic variation in the person identified to be the decision-maker in a group of frail older people. Ethnic variation reflected sociodemographic as well as cultural differences. However, there are important limitations to this study, and caution should be used in extrapolating the results to other populations or in attributing the results to ethnicity alone. An awareness of cross-cultural patterns in identified or de facto decision-makers can be significant for healthcare workers when they approach patients and their families about issues surrounding end of life decisions.     

Indirect pharmacodynamic response models do not require any parametric pharmacokinetic model to be fitted to effect-time data

Indirect response models (IRM) represent one of the possible ways to explain and quantitatively describe a delayed pharmacodynamic effect at non-steady-state conditions. The standard way to get estimates of pharmacodynamic (PD) parameters of IRM consists of two steps. First, an appropriate parametric pharmacokinetic (PK) model (compartmental, polyexponential, etc.) is to be fitted to plasma concentration-time data, and then IRM is fitted to PD data having PD model as an input. In the present work it is demonstrated that a simple piecewise function which consists in interpolation lines connecting concentration-time points can be used as a universal nonparametric PK model thereby allowing to skip the first step. MS Excel spreadsheets implementing this PK model and four known versions of IRM are presented. The usefulness of the approach is demonstrated by fitting IRMs to simulated data as well as to real PK/PD data of warfarin and terbutaline. Estimates of IRM parameters obtained with the nonparametric PK model were close to that published in the literature.     

Positron emission tomography metabolic data corrected for cortical atrophy using magnetic resonance imaging

The correct interpretation of clinical positron emission tomography (PET) data depends largely on the physical limits of the PET scanner. The partial volume effect (PVE) is related to the size of the studied object compared to the spatial resolution. It represents one of the most important limiting factors in quantitative data analysis. This effect is increased in the case of atrophy, as in patients with Alzheimer disease (AD), and it influences measurement of the metabolic reduction generally seen in cerebral degeneration. In this case, interpretation can be biased, because cortical activity will be underestimated due to the atrophy. In general, anatomical images of AD patients have shown diffuse atrophy, while PET studies have found widespread hypometabolism affecting the parietal and temporal lobes. Although hypometabolic areas usually correspond to atrophic regions, they also occur without such changes. Thus, the aim is to differentiate authentic hypometabolism (decrease of glucose consumption per unit volume of gray matter) from that due to PVE from atrophy (cell loss). Consequently, we are using a method for three-dimensional (3D) correction of human PET data with 3D magnetic resonance imaging (MRI). We measured atrophy and metabolism by using both T1-weighted MR images and high and medium resolution PET scans. We injected 12 patients and controls with [18F]fluorodeoxyglucose for glucose consumption measurements. Atrophy was estimated in the following way. We isolated the cerebral structures, using a segmentation technique on the MRI scans, into gray matter (GM), white matter, and cerebrospinal fluid. We superimposed the PET images onto the MR images to obtain anatomo-functional correlations. We degraded the segmented MR images to the resolution of the PET images by a convolution process to create a PET image correction map. We corrected the metabolic PET data for the PVE. We studied the cerebral metabolic rate of glucose in the GM where metabolic variation is the most relevant to AD. By dealing with problems relating to the sensitivity to the segmentation and to the PET-MRI coregistration, computation of MRI convolution processes provided the degree of PVE on a pixel-by-pixel basis, allowing correction of hypometabolisms contained in GM PET values. Global cortical metabolism increased after correction for PVE by, on average, 29 and 24% for tomographs acquired with medium (TTV03 LETI) and high (ECAT 953B CTI/Siemens) resolution, respectively, whereas the cortical metabolism increased by 75 and 65% for the respective tomographs in AD patients. The difference of metabolism between scans after correction for PVE was less than before correction, decreasing from 31 to 17%. This difference was most marked in the frontal and temporal lobes. Fusion imaging allowed correction for PVE in metabolic data using 3D MRI and determination of whether a change in the apparent radiotracer concentration in PET data reflected an alteration in GM volume, a change in radiotracer concentration per unit volume of GM, or both.     

Assessing enzyme substrate specificity using combinatorial libraries and electrospray ionization-Fourier transform ion cyclotron resonance mass spectrometry

A model experiment for the 'on-line' screening of substrate libraries by enzymes using combinatorial libraries in combination with electrospray ionization-Fourier transform ion cyclotron resonance (ESI-FTICR) mass spectrometry has been performed. The reaction between the electrophilic substrate 1-chloro-2,4-dinitrobenzene and component of a H-gamma-Glu-Cys-Xxx-OH library, catalyzed by glutathione-S-transferase, has been monitored. It shows the feasibility of 'two-dimensional' screening of substrate libraries by ESI-FTICR mass spectrometry.     

Phase correction for collision model analysis and enhanced resolving power of fourier transform ion cyclotron resonance mass spectra

Phase correction of FT-ICR data yields an absorption spectrum that offers a gain by up to a factor of 2 in mass resolving power (at half-maximum peak height), compared to conventional magnitude-mode display. That improvement is equivalent to doubling the applied magnetic field strength, without loss in signal-to-noise (S/N) ratio, provided that the time-domain data are padded with an equal number of zeroes before FFT. Our simple, visual, user-interactive algorithm quickly corrects for zero-order and first-order variation of phase with frequency. We find that the theoretical mass resolving power enhancement for pressure-limited absorption-mode over magnitude-mode line shape depends on the collision mechanism: factor of 1.40 for hard sphere vs 3(1/2) for Langevin (ion: induced dipole). Thus, the experimental enhancement in mass resolving power (factor of 1.43 +/- 0.09) for isotopically resolved peaks in the FT-ICR mass spectra of electrosprayed bovine carbonic anhydrase (approximately 29 kDa) directly supports the hard-sphere collision model. Optimal implementation of phasing requires the following: (a) a delay between excitation and detection of less than half of one sampling interval to avoid baseline "roll" and Gibb's oscillations; (b) accurate analog-to-digital conversion; (c) a sufficiently long acquisition period to yield several data points per absorption-mode peak width at half-maximum peak height; and (d) avoidance of FT-ICR apodization functions (e.g., Hamming and Hanning) that suppress the initial time-domain data. Pulsed single-frequency excitation (duration much less than the reciprocal of the Nyquist bandwidth) can eliminate higher than first-order variation of phase with frequency. Phased FT-ICR spectra should prove especially desirable for analysis of complex mixtures, for resolving isotopic distributions in electrosprayed multiply charged macromolecules and for characterizing ion collisions (and thus ion size and shape).     

A comparison of parametric and non-parametric analyses of opinion data.

Questionnaire item responses were analyzed by testing the significance of the differences of percents in response categories, using a non-parametric test, and by testing the group differences in mean item scores, based on weights assigned the responses, using a critical ratio test. The two approaches gave equivalent results in almost all cases. Item mean scores correlated with percent-in-category generally .90 or higher. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A parametric model of utility for two-person distributions.

Describes the development and outcomes of a parametric model of utility for 2-person distributions. Implications of the model led to 2 experiments in which precise predictions could be made about Ss' preferences for choices between 2-person outcomes; most Ss behaved in accordance with predictions. (34 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Breast implants. Evaluation of breast implants using magnetic resonance imaging (MRI)

Ureteral injury is a potential complication of any abdominal or pelvic surgery. Gynecological surgery has traditionally accounted for most injuries. In the last decade, there have been major advances in endoscopic surgery including ureteroscopy and laparoscopy, both of which may cause ureteral injury. Increased use of these procedures change the nature of ureteral injuries. From 1988 to 1997, 22 patients with 24 ureteral injuries were identified. The causes, diagnostic methods and treatments were reviewed. Ureteral injury was defined as any laceration, transection or ligation of the ureter that required an unexpected procedure for repair, stent or drainage. In 24 ureteral injuries, there were 20 unilateral cases and 2 bilateral cases eight men (33%) were 15 to 43 years old (mean age 30), and 14 women including 2 case of bilateral lesion (67%) were 30 to 75 years old (mean age of 46). The injuries were on the right side in 11 cases (46%), left side 13 cases (54%), and in the upper, and lower third of the ureter in 7 (29%) and 17 cases (71%), respectively. Bilateral injuries were all in the lower ureter and another 2 cases of lower ureteral injuries were combined with bladder injuries. In the cases of ureteral injuries, iatrogenic injuries accounted for 19 cases (79%). Of these, urological surgery, laparoscopic surgery, ureteroscopic procedures and gynecological surgery accounted for 1 (4%), 2(8%), 5(21%) and 11 cases (46%) respectively. Between 1988 and 1992, there were 7 cases, and after 1993, there were 17 cases of ureteral injuries. The injuries caused by trauma and gynecological surgery remained stable in the 2 period. The recent increases were caused by endoscopic procedures including ureteroscopy and laparoscopy. Of the 24 cases, 13 cases (54%) were managed by ureteroneocystostomy, 5 cases (21%) by nephrectomy, 4 cases (17%) by ureteroureterotomy, 1 case by PCN and 1 case by double-J catheter stenting only. The early recognition and repair at injury allow for better results with fewer complications. Delayed finding or commitant infection may lead to failure of reconstructive procedure and lead to nephrectomy.     

Estimation of excess risk from case-control data using Aalen's linear regression model

We introduce methods for statistical inference in Aalen's non-parametric linear regression model of disease incidence (Aalen, 1989, Statistics in Medicine 8, 907-925) from nested case-control data. These methods provide the basis for estimation of excess risk as a linear function of dose and absolute risk for a given exposure history. The methods are illustrated by estimating excess and absolute risks associated with radon exposure and smoking from nested case-control samples from the Colorado Plateau uranium miners cohort.