Crystal structure of a berenil-d(CGCAAATTTGCG) complex. An example of drug-DNA recognition based on sequence-dependent structural features

The AT-selective drug berenil has been co-crystallized with the dodecanucleotide sequence d(CGCAAATTTGCG)2. The crystal structure has been solved to a resolution of 2.0 A and an R factor of 18.3%, with the location of 65 water molecules. The drug is symmetrically bound in the 5'-AATT region of the minor groove, with its amidinium groups hydrogen-bonding to O-2 atoms of the thymine base at each end of the binding site. This arrangement is distinct from that previously found for berenil with the sequence d(CGCGAATTCGCG)2, which has the drug bound to the sequencing 5'-ATT via hydrogen bonds to adenine N-3 atoms with the involvement of a bridging water molecule at one end of the binding site. The reasons for these differences are discussed in terms of changes in helical parameters; in particular propeller twist and base-pair roll are considered to be important. The conformational and base-pair geometry of the dodecanucleotide in the structure reported here, is closely similar to that for the native structure, suggesting that the 5'-AAATTT sequence does not significantly alter during drug binding, either because of its inflexibility or because its geometry is nearly ideal for berenil binding.

Contrast-to-noise ratios in maximum intensity projection images

We present a statistical analysis of the maximum intensity projection (MIP) algorithm, which is commonly used for MR angiography (MRA). The analysis explains why MIP projection images display as much as a twofold increase in signal- and contrast-to-noise ratios over those of the source image set. This behavior is demonstrated with simulations and in phantom and MRA image sets.

Evaluation of a formulation of Bacillus thuringiensis against waxmoths in stored honeycombs

Waxmoths cause significant damage to stored honeycombs of the Western honeybee Apis mellifera in Australia. A field experiment was designed to evaluate the effectiveness of a commercial formulation (Certan) of the biological control agent Bacillus thuringiensis in preventing this damage.Treatment applied at the manufacturer's recommended rate of 855 units per cm2 of honeycomb almost completely prevented damage, while untreated combs showed an average of 76% damage. The cost and practicality of applying the formulation of B. thuringiensis are discussed, together with the recommendation that new control methods for waxmoths should be researched.

Crystal and solution structures of the oligonucleotide d(ATGCGCAT)2: a combined X-ray and NMR study

A combined crystal-structure determination and NMR analysis of the octanucleotide d(ATGCGCAT)2 is reported. The X-ray analysis shows that the structure is A-form duplex in crystal state. The NMR study shows that in solution this sequence is B-type. The conformational results from each technique are presented in detail. The implications of these findings in terms of conformational flexibility and ligand binding are discussed.

Health care rationing

The following two-part article sets the scene for an ongoing dialogue in future Updates on rationing and its impact on our health care delivery system and on society at large. Part one establishes the framework for future discussions, while Part two zeros in on the efforts of one state to confront the issue head-on.

High-speed line scan MR angiography

We describe a system which forms MR angiographic images at high speed. Multiple axial sections are imaged sequentially using a 2DFT GRASS sequence with TR/TE 50/15 ms, 64 phase encodings per image. Reconstruction and projection of each image are performed immediately (within 220 ms) after data for that image are acquired. The projection angiogram is constructed line by line as the scan progresses, thereby totally eliminating any additional time required for reconstruction and projection.

Phenotypic stability and metastatic behaviour of serially xenografted rat mesotheliomas

Mesotheliomas induced in rats by intrapleural injection of the fibrous zeolite, erionite, were serially transplanted in nude mice for up to ten generations. The cell phenotypes (epithelial or sarcomatous) were well maintained during passaging, as determined morphologically and by the expression of the cytokeratin markers demonstrated in normal mesothelial cells. Some of the tumours occasionally produced metastasis in nude mice. In contrast, a cloned epithelial cell mesothelioma and sarcomatous cell mesothelioma, the original cells of which were isolated in tissue culture, both produced regular multiple metastases when passaged in nude mice. These metastases were frequently found on the visceral pleura, rather than in the lung parenchyma, in nude mice. The high metastatic rate of the xenograph mesotheliomas derived by in vitro isolation of cells from mesotheliomas is atypical of the usual behaviour of xenografts of mesotheliomas.

MR angiography with oblique gradient-recalled echo technique

Magnetic resonance (MR) angiography with use of an oblique gradient-recalled echo sequence is discussed. The technique was developed for the efficient acquisition of angiographic data when the desired projection direction is already known. The raw data set is acquired directly at the projection angle; thus, a high-resolution projection is created, despite a decrease in the number of phase-encoding views acquired per axial image. Excessive reduction in the number of views acquired causes a loss of contrast in the projection images rather than a loss of resolution. High-resolution, high-contrast MR projection angiograms can be obtained in 2 1/2 minutes, with 50 3-mm sections and 48 phase encodings per section, a repetition time of 50 msec, an echo time of 15 msec, and a flip angle of 45 degrees. This represents one-fifth the time required for a conventional angiographic image. Venous blood is successfully saturated when the saturation band is placed at a fixed distance from the current imaging section. The method is demonstrated in the imaging of the carotid bifurcation in healthy volunteers and of a patient who had undergone carotid endarterectomy.

Crystal structure of a berenil-dodecanucleotide complex: the role of water in sequence-specific ligand binding

The three-dimensional structure of a complex between the dodecanucleotide d(CGCGAATTCGCG) and the anti-trypanocidal drug berenil, has been determined to a resolution of 2.5 A. The structure has been solved by molecular replacement and refined to an R factor of 0.177. A total of 49 water molecules have been located. The drug is bound at the 5'-AAT-3' region of the oligonucleotide. At one end of the drug the amidinium group is in hydrogen-bonded contact with N3 of the adenine base complementary to the thymine of the AAT. The other amidinium group does not make direct interactions with the DNA. Instead, a water molecule mediates between them. This is in hydrogen-bonded contact with an amidinium nitrogen atom, N3 of the 5' end adenine base and the ring oxygen atom of an adjacent deoxyribose. Molecular mechanics calculations have been performed on this complex, with the drug at various positions along the sequence. These show that the observed position is only 0.8 kcal/mol higher in energy than the best position. It is suggested that there is a broad energy well in the AATT region for this drug, and that water molecules as well as the neighbouring sequence, will determine precise positioning. More general aspects of minor groove binding are discussed.

CNR enhancement in the presence of multiple interfering processes using linear filters

Given several images of the same slice, a linear filter can produce an image in which the contrast-to-noise ratio (CNR) between pathological and normal tissues is greater than in any of the initial images. To distinguish the pathology from more than one tissue, the filter should optimize the set of CNRs between the pathology and each of the interfering tissues. We define the optimal filter as the one which provides the largest value for the minimum CNR in the set and show how it is selected from a field of only four possibilities. The filter is demonstrated with both experimental phantom studies and clinical cases. Filter performance is compared with that of other techniques for distinguishing a desired feature from more than one interfering process.

Magnetic resonance imaging in patients with inflammatory arthritis of the knee

Magnetic resonance imaging (MRI) permits visualization of anatomic structures not appreciated by conventional radiographic imaging and may quantify inflammatory disease and its progression with greater sensitivity than available techniques. We therefore compared MRI with clinical evaluation and with radiographic examination of 17 patients with inflammatory arthritis of the knee. We sought to determine anatomic integrity of bone, cartilage, menisci, and ligaments, and to quantify joint effusion and synovial proliferation. Patients studied had rheumatoid arthritis (10 patients), juvenile rheumatoid arthritis (4 patients), ankylosing spondylitis (1 patient), and monoarticular arthritis (2 patients). In all patients MRI revealed clinically important abnormalities not detected by physical or conventional radiographic exams. These included proliferative synovitis (13 patients), cartilage thinning (2 patients), cartilage erosion (8 patients), bone infarction (1 patient), meniscal injury (1 patient), and synovial invagination into bone (1 patient). Also MRI indicated inflammatory disease to be quantitatively greater than had been appreciated on clinical examination or routine X-ray studies--proliferative synovitis (12 patients), erosion (7 patients), effusion (8 patients), cartilage thinning (11 patients), and ligamentous/meniscal damage (1 patient). These findings led to reassessment of anatomic staging and influenced therapeutic decision for these patients. Thus MRI provides clinically important information about joint integrity and inflammatory disease, with a sensitivity and resolution considerably beyond conventional techniques.

Describing small-scale structure in random media using pulse-echo ultrasound

A method for estimating structural properties of random media is described. The size, number density, and scattering strength of particles are estimated from an analysis of the radio frequency (rf) echo signal power spectrum. Simple correlation functions and the accurate scattering theory of Faran [J.J. Faran, J. Acoust. Soc. Am. 23, 405-418 (1951)], which includes the effects of shear waves, were used separately to model backscatter from spherical particles and thereby describe the structures of the medium. These methods were tested using both glass sphere-in-agar and polystyrene sphere-in-agar scattering media. With the appropriate correlation function, it was possible to measure glass sphere diameters with an accuracy of 20%. It was not possible to accurately estimate the size of polystyrene spheres with the simple spherical and Gaussian correlation models examined because of a significant shear wave contribution. Using the Faran scattering theory for spheres, however, the accuracy for estimating diameters was improved to 10% for both glass and polystyrene scattering media. It was possible to estimate the product of the average scattering particle number density and the average scattering strength per particle, but with lower accuracy than the size estimates. The dependence of the measurement accuracy on the inclusion of shear waves, the wavelength of sound, and medium attenuation are considered, and the implications for describing the structure of biological soft tissues are discussed.

Physics and statistics of medical imaging

Extraordinary progress has been made over the last two decades in the development and dissemination of new medical imaging technologies. The development of computed tomography, positron emission tomography, and magnetic resonance imaging, as well as major innovations to the conventional imaging modalities, have revolutionized medical diagnostic imaging. Despite their many differences, all of these modalities can be viewed from a common perspective: being described in terms of the underlying physical properties imaged, the type of radiation/detection system used to produce the images, and the imaging performance that the modality achieves, both in absolute terms and relative to that of a conceptual ideal observer. This is a US government work. There are no restrictions on its use.

Cardiovascular risk factors among black schoolchildren: comparisons among four Know Your Body studies

Baseline cardiovascular risk factor variables were obtained from 1,041 black District of Columbia children in Grades 4-6 as part of a Know Your Body evaluation project. Screening included height, weight, triceps skinfold measurements, systolic and diastolic blood pressures, step-test for fitness, serum cholesterol, high-density lipoprotein cholesterol and thiocyanate. Results were compared with those in three other Know Your Body studies, Bronx, New York, Westchester, New York, and Los Angeles, and indicated that District of Columbia black children are more likely to have high cholesterol levels and to fail the fitness test than black children in the other studies. In the District of Columbia, obese children had significantly higher total serum cholesterol, systolic, diastolic, and high-density lipoprotein levels, and were less fit than other District of Columbia children; almost three-fourths of all of the children had one or more risk factors. Socioeconomic status was negatively correlated with diastolic blood pressure, skinfold thickness, and cholesterol levels and was positively correlated with high-density lipoprotein cholesterol. Rates of obesity and diastolic blood pressure were consistent with Bronx and Westchester comparisons suggesting that socioeconomic status interacts with ethnicity to determine risk factor levels. The existence of children with multiple risk factors in all of the Know Your Body studies supports the need for early intervention.

Statistical properties of radio-frequency and envelope-detected signals with applications to medical ultrasound

Both radio-frequency (rf) and envelope-detected signal analyses have lead to successful tissue discrimination in medical ultrasound. The extrapolation from tissue discrimination to a description of the tissue structure requires an analysis of the statistics of complex signals. To that end, first- and second-order statistics of complex random signals are reviewed, and an example is taken from rf signal analysis of the backscattered echoes from diffuse scatterers. In this case the scattering form factor of small scatterers can be easily separated from long-range structure and corrected for the transducer characteristics, thereby yielding an instrument-independent tissue signature. The statistics of the more economical envelope- and square-law-detected signals are derived next and found to be almost identical when normalized autocorrelation functions are used. Of the two nonlinear methods of detection, the square-law or intensity scheme gives rise to statistics that are more transparent to physical insight. Moreover, an analysis of the intensity-correlation structure indicates that the contributions to the total echo signal from the diffuse scatter and from the steady and variable components of coherent scatter can still be separated and used for tissue characterization. However, this analysis is not system independent. Finally, the statistical methods of this paper may be applied directly to envelope signals in nuclear-magnetic-resonance imaging because of the approximate equivalence of second-order statistics for magnitude and intensity.

Exercise and arthritis

Recreational exercise has achieved great popularity. Possible benefits to participants are increased longevity, decreased risk of cardiovascular disease, improved psychological well-being, and greater fitness. A very important but as yet unanswered concern is whether regular exercise will lead to degenerative joint disease or osteoarthritis. Many factors (e.g. physical characteristics of participants, biomechanical and physical features, nature of the playing surface and sport, manner of participation, preventive measures, and certain medical considerations) might influence the risk of developing osteoarthritis from sports participation. However, none of these have been evaluated. Although studies with animals have identified situations in which articular cartilage degeneration may be accelerated, experimental observations have not found normal joint motion in exercising animals to be harmful to joints. Anecdotal observations in man have suggested relationships between recreational activities and degenerative joint disease. However, those few controlled studies reported indicate that exercise need not be deleterious to joints. We interpret available data as suggesting that reasonable recreational exercise, carried out within limits of comfort, putting joints through normal motions, without underlying joint abnormality, even over many years, need not inevitably lead to joint injury.

Potential exposure to metal fumes, particulates, and organic vapors during radiotherapy shielding block fabrication

The shielding-block fabrication areas of three hospitals were surveyed to assess inhalation exposure to lead (Pb), cadmium (Cd), bismuth (Bi), and tin (Sn) fumes, as well as styrene and methyl chloride vapors. Area and personal breathing zone samples were collected for various steps in the block fabrication process. Only 3 of 16 air samples for metals resulted in detectable levels of Pb and/or Cd. The levels were well below the Occupational Safety and Health Administration (OSHA) Permissible Exposure Limits, excluding a sample which contained a visible metal fragment. Bi and Sn were not detected in any samples. Methyl chloride and styrene vapors were not detected in any air samples during foam cutting procedures. Total particulates (TP) were measurable in 11 of 17 air samples (ranging from 0.01 to 2.1 mg/m3). TP values were below the OSHA federal standard for nuisance particulates, which is 15 mg/m3. The data suggest that the materials and procedures sampled do not present an inhalation hazard to employees who construct shielding blocks. Precautions should, however, be exercised to prevent exposure under extreme procedural conditions such as soldering or overheating of alloy, and by other means such as ingestion. Care should also be taken during cleanup or housekeeping to prevent re-entrainment into the work atmosphere of mechanically generated metal particles or materials condensed within melting pots (which may be high in metal content).

Unified Approach to the Detection and Classification of Speckle Texture in Diagnostic Ultrasound

Second order statistics have been derived for the speckle in diagnostic ultrasound that arises from diffuse (incoherent) scattering in the presence of distributed and organized specular (coherent) scattering. They serve as the basis for a three-dimensional feature space in which tissue textures can be classified. The covariance matrix of the measurements in this space is a generalization of the speckle spot number or sampling concept that arises in the study of signal or lesion detectability.

Unified snr analysis of medical imaging systems

The ideal observer signal to noise ratio (snr) has been derived from statistical decision theory for all of the major medical imaging modalities. This snr provides an absolute scale for image system performance assessment and leads to instrumentation design goals and constraints for imaging system optimisation since no observer can surpass the performance of the ideal observer. The dependence of detectable detail size on exposure or imaging time follows immediately from the analysis. A framework emerges for comparing data acquisition techniques, e.g. reconstruction from projections versus Fourier methods in nmr imaging, and time of flight positron emission tomography (tofpet) versus conventional pet. The approach of studying the ideal observer is motivated by measurements on human observers which show that they can come close to the performance of the idea) observer, except when the image noise has negative correlations-as in images reconstructed from projections-where they suffer a small but significant penalty.

Anesthetic gas exposure. Protecting the OR environment

A trace gas study was conducted at The University of Michigan Hospitals to assess levels of anesthetic gas in the OR environment. Samples were collected at various sites associated with anesthesia equipment in 18 operating rooms and three treatment rooms where general anesthesia was used routinely. Waste anesthetic gas levels were found to vary widely and, depending upon anesthesiologists' work practices and equipment design, significant personnel exposures were documented. Although standard turbulent air flow, nonrecirculating systems are used in most ORs, areas of high gas concentration were identified. Such locations included the area between the gas machine and adjacent wall, and along the perimeter of the patient drapes. Gas concentrations were influenced by such variables as the distance from the anesthesia equipment to the exhaust grilles, and personnel movement. Anesthetizing techniques and work practices are the major contributors to waste anesthesia levels in the OR environment.

More Unified Analysis of Medical Imaging System SNR Characteristics

The ideal observer signal-to-noise ratio has been derived from statistical decision theory for all of the major medical imaging modalities. This yields an absolute scale for image performance assessment and instrumentation design and optimization. Applications include: the functional dependence of detectable detail size on exposure or imaging time; a framework for comparing data acquisition techniques, e.g., Fourier methods vs reconstruction from projections in NMR imaging; calculations of realizable limits, e.g., the limiting gain of time-of-flight PET scanning. Measurements on human observers show that they can come close to ideal performance, except when the noise has negative correlations as in images reconstructed from projections. In this latter case they suffer a small but significant penalty.