Dilation of subglacial sediment governs incipient surge motion in glaciers with deformable beds.

Glacier surges are quasi-periodic episodes of rapid ice flow that arise from increases in slip rate at the ice-bed interface. The mechanisms that trigger and sustain surges are not well understood. Here, we develop a new model of incipient surge motion for glaciers underlain by sediments to explore how surges may arise from slip instabilities within a thin layer of saturated, deforming subglacial till. Our model represents the evolution of internal friction, porosity and pore water pressure within the till as functions of the rate and history of shear deformation, and couples the till mechanics to a simple ice-flow model. Changes in pore water pressure govern incipient surge motion, with less permeable till facilitating surging because dilation-driven reductions in pore water pressure slow the rate at which till tends towards a new steady state, thereby allowing time for the glacier to thin dynamically. The reduction of overburden (and thus effective) pressure at the bed caused by dynamic thinning of the glacier sustains surge acceleration in our model. The need for changes in both the hydromechanical properties of the till and the thickness of the glacier creates restrictive conditions for surge motion that are consistent with the rarity of surge-type glaciers and their geographical clustering.

Breast imaging in coronal planes with simultaneous pulse echo and transmission ultrasound.

Clear delineation of breast architecture was achieved with compound pulse echo ultrasound imaging in which the images were acquired in the coronal planes used for quantitative transmission ultrasonic computed tomography. Since most connective tissue planes in the breast radiate toward the nipple, compound scans from the sides of the breast record normal interfaces more consistently and reveal greater symmetries in normal portions of relatively full breasts than do conventional scans in sagittal or transverse planes. Simultaneous acquisition of the pulse echo images and images representing the local ultrasound attenuation coefficient and speed of ultrasound suggested complementary role for reflection and through-transmission images in breast cancer detection. The high quality of pulse echo images in coronal planes provides the potential for more complete pulse echo diagnosis and the basis for spatial correlation of lesions viewed in pulse echo and ultrasonic computed tomograms. These observations may permit routine ultrasonic computed tomography of the breast in the clinical setting.

Regional mu opioid receptor regulation of sensory and affective dimensions of pain.

The endogenous opioid system is involved in stress responses, in the regulation of the experience of pain, and in the action of analgesic opiate drugs. We examined the function of the opioid system and mu-opioid receptors in the brains of healthy human subjects undergoing sustained pain. Sustained pain induced the regional release of endogenous opioids interacting with mu-opioid receptors in a number of cortical and subcortical brain regions. The activation of the mu-opioid receptor system was associated with reductions in the sensory and affective ratings of the pain experience, with distinct neuroanatomical involvements. These data demonstrate the central role of the mu-opioid receptors and their endogenous ligands in the regulation of sensory and affective components of the pain experience.

The Reference Image Database to Evaluate Response to therapy in lung cancer (RIDER) project: a resource for the development of change-analysis software.

Critical to the clinical evaluation of effective novel therapies for lung cancer is the early and accurate determination of tumor response, which requires an understanding of the sources of uncertainty in tumor measurement and subsequent attempts to minimize their effects on the assessment of the therapeutic agent. The Reference Image Database to Evaluate Response (RIDER) project seeks to develop a consensus approach to the optimization and benchmarking of software tools for the assessment of tumor response to therapy and to provide a publicly available database of serial images acquired during lung cancer drug and radiation therapy trials. Images of phantoms and patient images acquired under situations in which tumor size or biology is known to be unchanged also will be provided. The RIDER project will create standardized methods for benchmarking software tools to reduce sources of uncertainty in vital clinical assessments such as whether a specific tumor is responding to therapy.

"Anatometabolic" tumor imaging: fusion of FDG PET with CT or MRI to localize foci of increased activity.

Positron emission tomographic (PET) images of visceral cancers are commonly visualized as "hot spots" of increased activity with relatively little normal anatomy discernable, when 2-[18F]-fluoro-2-deoxy-D-glucose (FDG) is used as the tracer. We describe a method by which computed tomography or magnetic resonance anatomic images can be digitally fused in three dimensions, using a rigid rotate-translate scale model with PET "metabolic" images, to simultaneously display registered anatomic and metabolic information. Such "anatometabolic" fusion images were produced in 10 patients with a variety of visceral cancers. External fiducial markers placed during both the anatomic and the metabolic study, as well as internal anatomic fiducials defined from landmarks observed on reconstructed transmission images, were used to achieve image fusion. The mean error magnitude +/- s.e.m. of fiducial registration in the nine patients with successful realignments was 5.0 +/- 0.8 mm. The mean accuracy in realignment between known anatomic structures seen on both the anatomic study and on the emission PET scan (but not used in realignment) was 6.3 +/- 0.8 mm. Localization of foci of increased FDG uptake to specific anatomic structures was achieved by this method, which represented an enhancement over the rudimentary anatomy available from the emission images alone. Anatometabolic fusion images made using this reasonably simple method should prove useful in the management of patients with cancer and other diseases.

Automatic computer processing of digital 2-dimensional echocardiograms.

Quantitative studies of left ventricular function using 2-dimensional echocardiography have been limited because of a lack of computerized methods to automatically analyze the echocardiographic images. Previous computer efforts have been directed at digitizing the video output of the 2-D echocardiogram, but this digitizing method has significant limitations. A direct digitization method that produces improvement in signal-to-noise ratio and, subsequently, improved automatic detection of endocardial and epicardial borders, was developed. With definition of these edges, left ventricular global and regional analysis is possible frame by frame so that dynamic changes in cardiac function may be assessed throughout the cardiac cycle. Further technologic advances in 2-D echocardiographic acquisition and image processing should allow computer processing of 2-D echocardiographic data in real time.

Liver dysfunction in residents exposed to leachate from a toxic waste dump.

It has been estimated that there are some 30,000 chemical waste dumps in the United States. Many of these landfill operations were undertaken in the early 1950s and 1960s, when knowledge regarding the safe and prolonged containment of the waste buried was nonexistent or minimal at best. As a result, many of these dump sites were located in areas that were geologically unsuitable for toxic chemical wastes. The Love Canal area in Niagara Falls, NY, is probably the best known of these dump sites. While a few of these sites have attracted wide media coverage, the availability of objective scientific information regarding the health effects of such sites has been deficient. The present study of a large toxic waste dump located in Hardeman County, TN, its contamination of surface and underground aquifers and the health effects on the area residents exposed via ingestion of contaminated water, offers the first objective evidence of organ dysfunction in such a human population. During this study comprehensive evaluation of that population revealed multiple symptoms, evidence of hepatomegaly and elevated liver function tests apparently caused by ingestion of water contaminated by numerous organic chemicals, many of which are known to be hepatotoxins.

Flow effects in multislice, spin-echo magnetic resonance imaging. Model, experimental verification, and clinical examples.

Flowing blood is responsible for a number of complex effects on clinical magnetic resonance (MR) images. To help elucidate these effects, a computer model of a conventional multislice spin-echo pulse sequence was developed. Using TR, TE, and direction of slice acquisition, the model calculates and plots a profile of MR signal intensity vs. z-axis velocity. The model predicts complex profiles with multiple segments of MR signal loss depending on TR, TE, direction of flow, sequence and timing of slice excitation, and slice location relative to adjacent slices. Model predictions were verified by imaging a bulk-flow phantom, consisting of a rotating cylinder filled with a manganese chloride solution with T1 = 840 msec and characterized by a velocity-gradient resolution of 0.23 cm/sec/pixel. In conventional spin-echo MRI of medium and large vessels using body coils, in which the velocity gradients exceed 2-5 cm/sec/pixel, most of the flow artifacts are averaged and are difficult to appreciate. However, bright crescents or rings of MR signal occasionally are seen in the inferior vena cava and portal vein, which the model is invoked to explain. The bulk-flow phantom will find use as a tool for calibrating flow-sensitive pulse sequences when these become widely available.

Lesion detectability in ultrasonic computed tomography of symptomatic breast patients.

From 95 subjects imaged with both speed of sound and attenuation ultrasonic computed tomography (UCT), analyses were performed on 40 cases for which unequivocal clinical diagnoses were available for correlation. This paper describes the UCT image characteristics and addresses the hypothesis that carcinomas and other lesions can be detected and localized by means of simple visual criteria or lesion characteristics that are quantitative relative to those of other breast tissues in the same patient. The most useful within-patient criterion was selection of the solid mass with the highest speed of sound in either breast (12 of 12 carcinomas). Architectural asymmetry between breasts in the three types of images was a significant contributing factor in visual image interpretation in seven of the eight cancer patients in whom there were comparable images of both breasts. Solid masses were discriminated by attenuation coefficient and pulse echo criteria. Our results did not substantiate the hypothesis that the average speed of sound throughout the cancer containing breast would be higher than in the contralateral breast. These results are better than might be expected from pulse echo imaging alone on this population. However, clinical implementation probably should be deferred until the technique is made more convenient and less expensive, or more accurate with a greater promise for diagnosis of minimal cancers.

Liver-tumor boundary detection: human observer vs computer edge detection.

As a preliminary step in computing tumor volume, we developed a computer edge detection program to define the liver-tumor interface in computed tomography (CT) images. Computer program performance was tested using CT images from a lucite liver/tumor phantom; from normal livers containing computer-generated pseudotumors of known size, object contrast, and liver-tumor edge gradients; and from 12 abdominal livers containing 19 focal tumors, eight with well-defined and 11 with ill-defined borders. Calculated sizes of the tumor phantom and pseudo-tumors were compared with measured volumes and predetermined cross-sectional areas, respectively. In the absence of a truth standard for the size of the focal hepatic tumors, computer-calculated cross-sectional areas of the tumors were compared with the measurements made by an experienced interpreter of CT images using the trackball cursor at the CT console. The console measurements were made five times on separate days during a one-week period. The variability in the measured areas of these tumors averaged 7.1% for the well-defined tumors and 14.0% for the poorly defined tumors (P = 0.05). The edge-linking algorithm systematically overestimated the volumes of individual slices of the hemispherical tumors in the lucite phantom. Nevertheless, because of algorithm failure in the slices containing the poles of the hemispheres, errors in total tumor volumes were -2.1% for the 5.1 cm radius tumor, +1.2% for the 2.7 cm radius tumor, and +15% for the 1.8 cm radius tumor. The edge-linking algorithm was reasonably successful in calculating areas of pseudotumors with object contrast of 3.0% or greater and steep edge gradients.(ABSTRACT TRUNCATED AT 250 WORDS)

Intravascular ultrasound imaging of vascular responsiveness in isolated perfused canine arteries.

We investigated the feasibility of using intravascular ultrasound imaging to analyze vascular physiology in various arterial beds. Canine superficial femoral, external iliac, and common carotid arteries were harvested and suspended and perfused in a bath of oxygenated, heated, physiologic salt solution. A 6-Fr, 20-MHz ultrasound imaging catheter was inserted into the lumen of the arteries and serial images were acquired after bolus injections of either serotonin or normal saline into the extravascular bathing medium. Serotonin resulted in a significant time- and dose-dependent decrease in cross-sectional area in muscular femoral arteries (P less than .001): -5.2% with 10(-8) M serotonin, -15% with 10(-7) M, and -28% with 10(-6) M. Histologically transitional iliac arteries demonstrated less marked changes, while elastic carotid arteries demonstrated no significant changes. Our results indicate that intravascular ultrasound may be used to quantify and differentiate responses to vasoconstrictive agents in different vascular beds.

Pre- to postnatal reduction in ultrasound attenuation coefficient of the liver.

A recent study showed the ultrasound attenuation coefficient of fetal liver between 26 and 40 weeks of gestation to be 26% higher than after birth. To test the hypothesis that ultrasound attenuation is sensitive to fetal liver glycogen concentration, the livers of 24 fetuses were examined at 5 MHz just prior to and just after birth. The mean pre- to post-delivery reduction in attenuation coefficient was 0.08 dB cm-1 MHz-1 +/- 0.02 (SEM), or 17% of the post-delivery mean. This is consistent with the increase in attenuation measured by others in liver homogenate when glycogen was added. An increase in measurement accuracy, correlation with glycogen content, and, possibly, control for biological variability will be required to make predictions in individual cases, as opposed to these averages. A simple test of glycogen content would be of value scientifically and in prenatal and postnatal management.

Generating a normalized geometric liver model using warping.

RATIONALE AND OBJECTIVES: Automated liver surface determination in abdominal computed tomography scans, currently difficult to achieve, is of interest to determine liver location and size for various medical applications, including radiation therapy treatment planning, surgical planning, and oncologic monitoring. The authors propose to facilitate automation by the addition of a priori shape information in the form of a liver model. METHODS: The normalized geometric liver model is generated by averaging outlines from a set of normal liver studies previously registered using thin-plate spline warping. The model consists of an averaged liver surface, a set of anatomic landmarks, and a deformation function. RESULTS: A liver model is presented and its ability to represent normal liver shapes is demonstrated. CONCLUSIONS: Liver surface warping provides a means of data normalization for model construction and a means of model deformation for representation of liver organ shapes.

Sonographic identification of lung maturation in the fetal lamb.

Ultrasound evaluation of fetal lung development in utero could be a noninvasive method for frequent monitoring of the state of pulmonary maturity and predicting when parturition could occur with minimum or no risk of respiratory distress syndrome of the newborn. In cases of high-risk obstetric management in premature labor, this ability may be a particularly useful tool. To pursue this possibility, the lungs and livers of 13 living fetal lambs were successfully imaged with a modified clinical B-scanner under carefully controlled conditions; physiologic function tests on the excised lungs determined the state of pulmonary maturity. In eight cases, maturity or immaturity was correctly identified by sonographic criteria. The results wer ambiguous in four cases. One case of immature lung was incorrectly identified as mature. The trends established in these animal studies appear promising and with refinement may form the basis for sonographic assessment of fetal lung maturity in a clinical setting.

Sperm count results from 861 American chemical/agricultural workers from 14 separate studies.

This article presents data from 861 men who have participated in 14 separate occupational studies on testicular function. This population represents the largest series taken from occupational studies. The mean and median sperm counts were 107.1 and 83.0 million/ml of semen, respectively. The percentage of men with sperm counts less than 20 million/ml of semen was 8.7%. No significant differences were noted for age or race. A major issue in occupational studies requiring semen samples is how to successfully recruit the target population to participate. The number of semen samples requested can influence willingness to participate. Data from 137 men, each with three separate sperm counts, indicate that a single sample will suffice for an occupational study.

Bulk flow model for multislice magnetic resonance imaging sequences with phantom validation.

A simple conceptual model for describing the effects of one-dimensional bulk flow on image intensities is presented and validated using a multislice imaging sequence specific to one vendor. The model allows quantitative estimates of echo amplitudes versus velocity by using the equation of motion to follow the pulse history of fluid volumes influenced by the readout pulse for any slice of interest. Each affected volume is divided into equal elemental components and the state of each component is computed at discrete times in a pulse position-timing diagram until readout occurs. The final amplitude for the composite volume is determined by the signed summation of each of the elemental components. Validation of the quantitative model was performed by imaging a rotating bulk flow phantom centered at each of the slices of a multislice, partial saturation, spin-echo sequence. Effects due to rf field inhomogeneities were normalized by dividing the results of the dynamic scans by the corresponding static one. The results presented here are relatively insensitive to odd-echo dephasing (even echo rephasing).

Robust three-dimensional object definition in CT and MRI.

This work describes the application of an object definition algorithm to the medical imaging environment for the task of automated detection of anatomical boundaries in three dimensions in the presence of low spatial frequency nonstationarities. We have chosen the Liou-Jain algorithm and have modified it for use with 3D medical image datasets and extended it by including a recruitment operator that corrects for the algorithm's inherent volume underestimation. The algorithm avoids problems in both traditional statistical segmentation and 2D techniques and elegantly bridges the gap between traditional gradient-based edge finding and regression-based segmentation techniques. Results are shown for MRI datasets from the human abdomen and brain and for a CT dataset of a liver tumor, as well as an MRI scan of a glioma in a rat brain. For comparison, the human abdomen dataset was processed by a multivariate, statistical classifier. The results demonstrate the statistical technique's susceptibility to low spatial frequency nonstationarities due to rf field inhomogeneity; the Liou-Jain algorithm is shown to be immune to this effect. Further, the results show spatial consistency as a result of inherent characteristics of the algorithm. Volumes identified by the algorithm are visualized and assessed qualitatively in three dimensions. Quantitative accuracy of the algorithm's volume estimates is assessed by the use of a phantom. This work demonstrates that this technique is effective in automatically detecting anatomical organ and lesion surfaces in 3D medical datasets that are corrupted by low spatial frequency nonstationarity and in obtaining volume estimates.

Automated generation of a four-dimensional model of the liver using warping and mutual information.

The use of mutual information (MI) based alignment to map changes in liver shape and position from exhale to inhale was investigated. Inhale and exhale CT scans were obtained with intravenous contrast for six patients. MI based alignment using thin-plate spine (TPS) warping was performed between each inhale and exhale image set. An expert radiation oncologist identified corresponding vessel bifurcations on the exhale and inhale CT image and the transformation for identified points was determined. This transformation was then used to determine the accuracy of the MI based alignment. The reproducibility of the vessel bifurcation identification was measured through repeat blinded vessel bifurcation identification. Reproducibility [standard deviation (SD)] in the L/R, A/P, and I/S directions was 0.11, 0.09, and 0.14 cm, respectively. The average absolute difference between the transformation obtained using MI based alignment and the vessel bifurcation in the L/R, A/P, and I/S directions was 0.13 cm (SD=0.10 cm), 0.15 cm (SD=0.12 cm), and 0.15 cm (SD-0.14 cm), respectively. These values are comparable to the reproducibility of bifurcation identification, indicating that MI based alignment using TPS warping is accurate to within measurement error and is a reliable tool to aid in describing deformation that the liver undergoes from the exhale to inhale state.

Median and spatial low-pass filtering in ultrasonic computed tomography.

To reduce noise- and reconstruction-related artifacts in ultrasound computed tomography, the use of combined median and Hamming-weighted spatial low-pass filtering is evaluated. The evaluation of the reconstruction filters uses both computer-generated projections of a known object with the least mean-square error criterion as well as a more subjective evaluation of conventional ultrasonic attenuation and speed of sound images.

Retrospective correction of intensity inhomogeneities in MRI.

Medical imaging data sets are often corrupted by multiplicative inhomogeneities, often referred to as nonuniformities or intensity variations, that hamper the use of quantitative analyses. The authors describe an automatic technique that not only improves the worst situations, such as those encountered with magnetic resonance imaging (MRI) surface coils, but also corrects typical inhomogeneities encountered in routine volume data sets, such as MRI head scans, without generating additional artifact. Because the technique uses only the patient data set, the technique can be applied retrospectively to all data sets, and corrects both patient independent effects, such as rf coil design, and patient dependent effects, such as attenuation of overlying tissue experienced both in high field MRI and X-ray computed tomography (CT). The authors show results for several MRI imaging situations including thorax, head, and breast. Following such corrections, region of interest analyses, volume histograms, and thresholding techniques are more meaningful. The value of such correction algorithms may increase dramatically with increased use of high field strength magnets and associated patient-dependent rf attenuation in overlying tissues.