Search for the pygmy dipole resonance in 68Ni at 600 MeV/nucleon.

The gamma decay from Coulomb excitation of 68Ni at 600 MeV/nucleon on a Au target was measured using the RISING setup at the fragment separator of GSI. The 68Ni beam was produced by a fragmentation reaction of 86Kr at 900 MeV/nucleon on a 9Be target and selected by the fragment separator. The gamma rays produced at the Au target were measured with HPGe detectors at forward angles and with BaF2 scintillators at backward angles. The measured spectra show a peak centered at approximately 11 MeV, whose intensity can be explained in terms of an enhanced strength of the dipole response function (pygmy resonance). Such pygmy structure has been predicted in this unstable neutron-rich nucleus by theory.

The physiology of stereopsis.

Binocular disparity provides the visual system with information concerning the three-dimensional layout of the environment. Recent physiological studies in the primary visual cortex provide a successful account of the mechanisms by which single neurons are able to signal disparity. This work also reveals that additional processing is required to make explicit the types of signal required for depth perception (such as the ability to match features correctly between the two monocular images). Some of these signals, such as those encoding relative disparity, are found in extrastriate cortex. Several other lines of evidence also suggest that the link between perception and neuronal activity is stronger in extrastriate cortex (especially MT) than in the primary visual cortex.

De-escalation antimicrobial chemotherapy in critically III patients: pros and cons.

In spite of advances in critical care, nosocomial infections still have a considerable impact on Intensive Care Unit (ICU) and hospital length of stay, mortality and costs. Several authors suggest that antibiotic therapy should be instituted as soon as sepsis is suspected in critically patients. Over the last two decades the rates of occurrence for pathogens have significantly changed under selective pressure from broad-spectrum antimicrobial therapy. Shifts from predominance of gram-negative to gram-positive organisms and outbreaks of resistant pathogens address the need for appropriate empirical regimens. Agents such as ceftazidime, imipenem and, more recently, meropenem and tazobactam have been used successfully as monotherapy. Two different clinical trials have reported that meropenem monotherapy is significantly more effective than ceftazidime-based therapy. Because of the outbreak of methicillin-resistant Staphylococcus aureus and Staphylococcus epidermidis, some investigators suggest adding a glycopeptide to beta-lactamase inhibitor and carbapenem as initial empirical therapy. Such a regimen should be administered before definitive proof of infections and until the results of microbial investigation are available (de-escalation antimicrobial chemotherapy). On the other hand, several authors do not recommend glycopeptide administration in an attempt to limit nosocomial outbreaks of vancomycin-resistant enterococci (VRE) and staphylococci (VRS) and to avoid secondary drawbacks, such as nephrotoxicity and ototoxicity. De-escalation antimicrobial chemotherapy should be tailored to critically ill patients according to their clinical status, severity of illness and suspicion of sepsis or nosocomial pneumonia.

MRI-guided needle localization: technique.

Magnetic resonance imaging (MRI) is being used increasingly in breast cancer diagnosis. Such indications include the search for a breast primary in women with metastatic carcinoma in the axillary lymph nodes, improving surgical planning in women with a biopsy-proven breast cancer, and in screening very high-risk women. If a suspicious lesion is found by MRI, localization with either directed additional mammographic or sonographic views or with MRI-guided needle localization or biopsy is necessary. We describe the use of a biopsy device with embedded internal fiducial markers. The coordinates for needle placement are calculated by distances between the fiducial markers and the lesion. The technique is simple to master and is aided by the use of a practice phantom.

Technique and pitfalls of ultrasound-guided core-needle biopsy of the breast.

When using ultrasound guidance to perform core-needle biopsy, the curvature of the breast can be used to advantage. By entering the breast from the periphery, chest wall injury is avoided and needle visualization is improved. Visualization of the needle is expedited by bringing the needle to the lesion by using a gentle sweeping motion while keeping the transducer relatively fixed in position. Standard techniques can be modified for difficult lesions, such as those that are mobile, deep, small, or in a large breast. Careful correlation with the mammogram will insure biopsy of the corresponding sonographic lesion. Although complications are uncommon, hematoma or infection may occur after the procedure. With practice, application of standard and modified techniques can result in efficient and accurate ultrasound-guided percutaneous core-needle biopsy of the breast.

CLEPS: how police and hospital security work together in a large city.

The authors discuss the formation of CLEPS--a partnership of police and private security, with representatives from six area hospitals--to improve communication and reduce criminal incidents in both the city and the hospitals. They provide details on why the organization was formed, its goals and objectives, its accomplishments, and future plans.

Functional micro-organization of primary visual cortex: receptive field analysis of nearby neurons.

It is well established that multiple stimulus dimensions (e.g., orientation and spatial frequency) are mapped onto the surface of striate cortex. However, the detailed organization of neurons within a local region of striate cortex remains unclear. Within a vertical column, do all neurons have the same response selectivities? And if not, how do they most commonly differ and why? To address these questions, we recorded from nearby pairs of simple cells and made detailed spatiotemporal maps of their receptive fields. From these maps, we extracted and analyzed a variety of response metrics. Our results provide new insights into the local organization of striate cortex. First, we show that nearby neurons seldom have very similar receptive fields, when these fields are characterized in space and time. Thus, there may be less redundancy within a column than previously thought. Moreover, we show that correlated discharge increases with receptive field similarity; thus, the local dissimilarity between neurons may allow for noise reduction by response pooling. Second, we show that several response variables are clustered within striate cortex, including some that have not received much attention such as response latency and temporal frequency. We also demonstrate that other parameters are not clustered, including the spatial phase (or symmetry) of the receptive field. Third, we show that spatial phase is the single parameter that accounts for most of the difference between receptive fields of nearby neurons. We consider the implications of this local diversity of spatial phase for population coding and construction of higher-order receptive fields.

Organization of disparity-selective neurons in macaque area MT.

Neurons selective for binocular disparity are found in a number of visual cortical areas in primates, but there is little evidence that any of these areas are specialized for disparity processing. We have examined the organization of disparity-selective neurons in the middle temporal visual area (MT), an area shown previously to contain an abundance of disparity-sensitive neurons. We recorded extracellularly from MT neurons at regularly spaced intervals along electrode penetrations that passed through MT either normal to the cortical surface or at a shallow oblique angle. Comparison of multiunit and single-unit recordings shows that neurons are clustered in MT according to their disparity selectivity. Across the surface of MT, disparity-selective neurons are found in discrete patches that are separated by regions of MT that exhibit poor disparity tuning. Within disparity-selective patches of MT, we typically observe a smooth progression of preferred disparities (e.g. , near to far) as our electrode travels parallel to the cortical surface. In electrode penetrations normal to the cortical surface, on the other hand, MT neurons generally have similar disparity tuning, with little variation from one recording site to the next. Thus disparity-tuned neurons are organized into cortical columns by preferred disparity, and preferred disparity is mapped systematically within larger, disparity-tuned patches of MT. Combined with other recent findings, the data suggest that MT plays an important role in stereoscopic depth perception in addition to its well known role in motion perception.

The fetal-pelvic index has minimal utility in predicting fetal-pelvic disproportion.

OBJECTIVE: Our purpose was to evaluate the fetal-pelvic index in our patient population and to determine whether it would be predictive of route of delivery. STUDY DESIGN: One hundred seventy-six patients with a previous history or clinical findings in the current pregnancy suggestive of fetal-pelvic disproportion participated in this Human Investigation Committee-approved study. All underwent fetal ultrasonographic examinations and modified digital radiography before labor. Fetal head and abdominal circumferences and maternal inlet and midpelvic circumferences were determined, and the fetal-pelvic index was calculated. RESULTS: Ninety-one patients fulfilled all aspects of the study, including rigorous criteria pertaining to labor management. Thirty of these patients underwent cesarean delivery and 61 were delivered vaginally. The fetal-pelvic index value for the vaginal delivery group was -5.4 +/- 5.3, as opposed to -2.4 +/- 5.8 in the cesarean delivery group (P <.02). Notwithstanding this difference, the fetal-pelvic index had a low overall ability to predict fetal-pelvic disproportion (0.65) and had associated sensitivity and specificity of 0.27 and 0.84, respectively. Predictive thresholds other than zero were tested, but optimal predictive ability, at a fetal-pelvic index cutoff of 2, was only 70% (sensitivity 0.20, specificity 0.95). CONCLUSION: In our patient population the fetal-pelvic index was only moderately predictive of fetal-pelvic disproportion. Factors other than those assessed by the fetal-pelvic index are probably important in determining the route of delivery. Further studies are indicated.

Cortical area MT and the perception of stereoscopic depth.

Stereopsis is the perception of depth based on small positional differences between images formed on the two retinae (known as binocular disparity). Neurons that respond selectively to binocular disparity were first described three decades ago, and have since been observed in many visual areas of the primate brain, including V1, V2, V3, MT and MST. Although disparity-selective neurons are thought to form the neural substrate for stereopsis, the mere existence of disparity-selective neurons does not guarantee that they contribute to stereoscopic depth perception. Some disparity-selective neurons may play other roles, such as guiding vergence eye movements. Thus, the roles of different visual areas in stereopsis remain poorly defined. Here we show that visual area MT is important in stereoscopic vision: electrical stimulation of clusters of disparity-selective MT neurons can bias perceptual judgements of depth, and the bias is predictable from the disparity preference of neurons at the stimulation site. These results show that behaviourally relevant signals concerning stereoscopic depth are present in MT.

Idiopathic arterial calcification of infancy: sonographic and magnetic resonance findings with pathologic correlation.

Idiopathic arterial calcification of infancy is a rare condition characterized by extensive arterial calcification and stenoses of large and medium sized arteries. We report the sonographic and magnetic resonance angiographic findings of this entity and correlate them with the findings at autopsy.

Placement of endovascular embolization microcoils to localize the site of breast lesions removed at stereotactic core biopsy.

In 13 cases, a breast abnormality was inadvertently removed during stereotactic core biopsy, and a 0.5- or 1.0-cm-long endovascular embolization microcoil was placed to mark the biopsy site. In seven patients, the microcoils allowed successful preoperative localization of the lesion site. In six patients, 6-month follow-up mammograms showed no change in microcoil position. Placement of embolization microcoils helped localize the site of breast lesions removed during stereotactic core biopsy.

Percutaneous breast biopsy for nonpalpable lesions.

Increasingly, biopsies for suspected breast abnormalities are conducted by percutaneous needle extraction of core samples rather than by standard surgical excision or fine-needle aspiration (FNA) of cellular material. Core-needle biopsies are highly accurate and have many advantages over surgical excisions, including reduction of the morbidity and cost of breast disease diagnosis. Limitations include differentiating atypical ductal hyperplasia from ductal carcinoma in situ. Equipment and technique for stereotactic and ultrasound-guided core breast biopsy are discussed. Appropriate indications for core-needle biopsy, excisional biopsy after needle localization, and FNA are provided. Appropriate management after core-needle biopsy includes the establishment of concordance of histologic results with the level of suspicion of the mammographic findings to prevent false-negative core biopsies. A recommendation for return to regular mammographic screening, short-interval (6-month) mammographic follow-up, or repeat core or surgical appearance depends on this correlation.

Sonographic features of mammary oil cysts.

Mammographic lesions that are pathognomonic for oil cysts require no further evaluation. Oil cysts, however, may first be discovered by ultrasonography. Between 1988 and 1995, we performed sonography of 26 oil cysts in 15 patients. Sonography was used to evaluate a palpable finding when an oil cyst was not initially perceived on the mammogram (47%) or as an initial evaluation of a palpable lump (33%); in addition, oil cysts were identified incidentally in 20% of cases. Retrospective review showed that the sonographic appearance of oil cysts is highly variable; only 8% mimic simple apocrine cysts. Twelve percent mimic an intracystic mass. Most have smooth walls (88%), are hypoechoic (65%), and have neither enhancement or shadowing (50%). The sonographic appearance of oil cysts can be suggestive of a pathologic lesion such as an intracystic carcinoma. Unnecessary biopsy can be avoided using directed mammography.

Evaluation of a turkey-breast phantom for teaching freehand, US-guided core-needle breast biopsy.

RATIONALE AND OBJECTIVES: Use of a turkey-breast phantom for developing freehand ultrasound (US)-guided core-needle biopsy skills was evaluated. MATERIALS AND METHODS: Thirteen diagnostic radiology trainees with varied experience in freehand US-guided breast core-needle biopsy were given instruction and allowed to practice the technique in a turkey-breast phantom. Three attempts were made before and after instruction and practice, and a questionnaire regarding experience, confidence, and anxiety was administered after these attempts. Technique, accuracy, and completion time were evaluated. RESULTS: Confidence related to procedure performance increased (P < .01), but the change in anxiety was not statistically significant. Accuracy improved, with the target being obtained in 87% of passes performed after instruction and practice versus 56% initially. Difficulty with visualizing the core needle sonographically during phantom biopsy decreased from 49% to 5% of attempts. Needle positioning perpendicular to the chest wall was observed initially in 38% of passes but was not observed after instruction and practice. There was no statistically significant change in time to complete biopsy. CONCLUSION: For teaching US-guided breast core-needle biopsy, use of a turkey-breast phantom helps improve technique, accuracy, and confidence of diagnostic radiology trainees.

Spatiotemporal receptive field organization in the lateral geniculate nucleus of cats and kittens.

We have studied the spatiotemporal receptive-field organization of 144 neurons recorded from the dorsal lateral geniculate nucleus (dLGN) of adult cats and kittens at 4 and 8 wk postnatal. Receptive-field profiles were obtained with the use of a reverse correlation technique, in which we compute the cross-correlation between the action potential train of a neuron and a randomized sequence of long bright and dark bar stimuli that are flashed throughout the receptive field. Spatiotemporal receptive-field profiles of LGN neurons generally exhibit a biphasic temporal response, as well as the classical center-surround spatial organization. For nonlagged cells, the first temporal phase of the response dominates, whereas for lagged neurons, the second temporal phase of the response is typically the largest. This temporal phase difference between lagged and nonlagged cells accounts for their divergent behavior in response to flashed stimuli. Most LGN cells exhibit some degree of space-time inseparability, which means that the receptive field cannot simply be viewed as the product of a spatial waveform and a temporal waveform. In these cases, the response of the surround is typically delayed relative to that of the center, and there is some blending of center and surround during the time course of the response. We demonstrate that a simple extension of the traditional difference-of-Gaussians (DOG) model, in which the surround response is delayed relative to that of the center, accounts nicely for these findings. With regard to development, our analysis shows that spatial and temporal aspects of receptive field structure mature with markedly different time courses. After 4 wk postnatal, there is little change in the spatial organization of LGN receptive fields, with the exception of a weak, but significant, trend for the surround to become smaller and stronger with age. In contrast, there are substantial changes in temporal receptive-field structure after 4 wk postnatal. From 4 to 8 wk postnatal, the shape of the temporal response profile changes, becoming more biphasic, but the latency and duration of the response remain unchanged. From 8 wk postnatal to adulthood, the shape of the temporal profile remains approximately constant, but there is a dramatic decline in both the latency and duration of the response. Comparison of our results with recent data from cortical (area 17) simple cells reveals that the temporal development of LGN cells accounts for a substantial portion of the temporal maturation of simple cells.

Encoding of binocular disparity by complex cells in the cat's visual cortex.

To examine the roles that complex cells play in stereopsis, we have recorded extracellularly from isolated single neurons in the striate cortex of anesthetized paralyzed cats. We measured binocular responses of complex cells using a comprehensive stimulus set that encompasses all possible combinations of positions over the receptive fields for the two eyes. For a given position combination, stimulus contrast could be the same for the two eyes (2 bright or 2 dark bars) or opposite (1 bright and 1 dark). These measurements provide a binocular receptive field (RF) profile that completely characterizes complex cell responses in a joint domain of left and right stimulus positions. Complex cells typically exhibit a strong selectivity for binocular disparity, but are only broadly selective for stimulus position. For most cells, selectivity for disparity is more than twice as narrow as that for position. These characteristics are highly desirable if we assume that a disparity sensor should exhibit position invariance while encoding small changes in stimulus depth. Complex cells have nearly identical binocular RFs for bright and dark stimuli as long as the sign of stimulus contrast is the same for the two eyes. When stimulus contrast is opposite, the binocular RF also is inverted such that excitatory subregions become suppressive. We have developed a disparity energy model that accounts for the behavior of disparity-sensitive complex cells. This is a hierarchical model that incorporates specific constraints on the selection of simple cells from which a complex cell receives input. Experimental data are used to examine quantitatively predictions of the model. Responses of complex cells generally agree well with predictions of the disparity energy model. However, various types of deviations from the predictions also are found, including a highly elongated excitatory region beyond that supported by a single energy mechanism. Complex cells in the visual cortex appear to provide a next level of abstraction in encoding information for stereopsis based on the activity of a group of simple-type subunits. In addition to exhibiting narrow disparity tuning and position invariance, these cells seem to provide a partial solution to the stereo correspondence problem that arises in complex natural scenes. Based on their binocular response properties, these cells provide a substantial reduction in the complexity of the correspondence problem.

Attitudes of radiology residents toward personal computing: results of survey.

RATIONALE AND OBJECTIVES: The authors' purpose was to evaluate radiology residents' assessment of their own computer skills for potential development of computer training in a residency curriculum. METHODS: The authors conducted a survey to evaluate the attitudes of radiology residents concerning personal computing. Surveys were completed by 136 radiology residents from six academic institutions. RESULTS: Sixty percent of residents surveyed considered themselves to be computer literate and 93% would like further computer training. Fifty-six percent had a computer at home and 9% had a laptop. Almost all residents had access to a computer at work. Word processing and medical literature searches were the most common computer tasks performed by residents. Image processing was the least common task performed. Although all hospitals surveyed were connected to the Internet, only 26% of residents used the Internet and 14% used Internet teaching files. Most residents expressed a preference for self-paced, on-line evening training sessions. CONCLUSION: Most radiology residents believed they possessed adequate computer skills. This proportion has markedly increased over that found in previous surveys. Radiology residents desire and could likely benefit from computer training included as part of the residency curriculum.

The role of stereotactic biopsy in abnormal mammograms.

Core needle biopsy using either stereotactic or ultrasonographic guidance is a reasonable and accurate alternative to surgical biopsy for diagnosis of most nonpalpable breast lesions. An important component of a stereotactic core breast biopsy procedure is the mammographic and pathologic correlation of findings to plan optimal patient management. The level of suspicion of a mammographic lesion, the accuracy of stereotactic targeting, and the confirmation of microcalcifications in specimen radiographs for calcified lesions must be considered carefully and correlated with the histopathologic findings. Meticulous operator technique is essential to provide representative samples of the mammographic abnormality. Properly performed, imaging-guided percutaneous core breast biopsy has reduced the morbidity of surgical breast biopsy and the overall cost of breast cancer diagnosis. Recent work has demonstrated that stereotactic core breast biopsy can reduce the cost of diagnosing mammographically detected breast lesions by more than 50%. At a time when health-care policy and reimbursement decisions are influenced by cost considerations, increased use of stereotactic core breast biopsy is anticipated. Meticulous attention to technique allows maximal realization of the benefits of this procedure.

The neural coding of stereoscopic depth.

Stereopsis is a process by which the visual system gauges the relative depth of objects in three-dimensional space by measuring minute positional differences between left and right images. According to the standard notion, this information is thought to be encoded in the primary visual cortex by differences in receptive field (RF) positions for the two eyes. We have developed in alternative model by which stereoscopic information is coded and transformed through a hierarchical chain of processing in the primary visual cortex. Initially, first-order neurons of the visual cortex, simple cells, encode depth information by a scheme based on differences in internal receptive field structure between left and right eyes. Further abstraction of information is achieved by a subset of second-order neurons, complex cells, that are well suited for the detection of depth information in a manner unaffected by positional variations of objects. We review physiological evidence from studies of the cat and monkey that are relevant to the proposed scheme.