Stereoscopic depth discrimination in the visual cortex: neurons ideally suited as disparity detectors.

The possibility has been explored that a subset of physiologically identifiable cells in the visual cortex is especially suited for the processing of stereoscopic depth information. First, characteristics of a disparity detector that would be useful for such processing were outlined. Then, a method was devised by which detailed binocular response data were obtained from cortical cells. In addition, a model of the disparity detector was developed that includes a plausible hierarchical arrangement of cortical cells. Data from the cells compare well with the requirements for the archetypal disparity detector and are in excellent agreement with the predictions of the model. These results demonstrate that a specific type of cortical neuron exhibits the desired characteristics of a disparity detector.

Receptive-field dynamics in the central visual pathways.

Neurons in the central visual pathways process visual images within a localized region of space, and a restricted epoch of time. Although the receptive field (RF) of a visually responsive neuron is inherently a spatiotemporal entity, most studies have focused exclusively on spatial aspects of RF structure. Recently, however, the application of sophisticated RF-mapping techniques has enabled neurophysiologists to characterize RFs in the joint domain of space and time. Studies that use these techniques have revealed that neurons in the geniculostriate pathway exhibit striking RF dynamics. For a majority of cells, the spatial structure of the RF changes as a function of time; thus, these RFs can be characterized adequately only in the space-time domain. In this review, the spatiotemporal RF structure of neurons in the lateral geniculate nucleus and primary visual cortex is discussed.

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.

Comparison of contrast detail curves of full field digital with screen film breast phantom images.

In this investigation, we imaged a standard breast phantom and compared the contrast detail curves from a prototype full breast digital mammography system with the corresponding curves for a conventional, analog screen-film system. The full breast digital system exhibited superior contrast detail detectability. The results from this study will be used to plan future clinical evaluations comparing full breast digital and screen film mammography.

Ultrasonic detection of osteomyelitis. Pathologic correlation in an animal model.

The authors correlated sonographic findings with histologic findings in a rabbit model of osteomyelitis. Staphylococcus aureus osteomyelitis was induced in the femora of 11 New Zealand white rabbits. The opposite leg was used as a control. Sonographic findings showed fluid adjacent to the bone in 11 cases. The fluid was believed to be an inflammatory exudate, and its presence suggested osteomyelitis. Pathologic analysis showed extraperiosteal purulent fluid adjacent to the cortex as well as histopathologic changes of osteomyelitis in the 11 rabbits. There was one false-positive sonographic diagnosis of osteomyelitis in a rabbit that had a soft tissue abscess adjacent to the cortex.

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.

The impact of methadone and drug-free treatment on criminal behavior.

The present study was initiated to evaluate the effect of methadone versus drug-free treatment on a series of criminal involvement measures. A 50% random sample of the 776 clients who had registered with the Central Intake Unit over a one year period was selected for intensive study. Data were collected through examination of intake and treatment files for pre- and post-admission time periods. Arrest, conviction and incarceration rates as well as correctional status were measured and compared across pre-treatment, intake and three month post-intake periods. The arrest rate for the total sample decreased radically from 92.8% upon entering treatment to 8% after three months in treatment. The subsequent rates at 6, 9 and 12 months decreased in a fairly consistent manner. This trend was similar in the methadone, drug-free, and methadone/drug-free groups for either arrests, convictions or incarceration rates with time in treatment. The relationship between arrests and employment and drug use was also examined. No association was found between use of opiates as measured by urinalysis results and frequency of arrest. Similarly, arrest rates showed no significant association with employment rates during the first nine months of treatment, although the comparison at twelve months was significant with only 16.7% of those employed clients being arrested.

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.

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.

Color flow mapping.

Color flow mapping systems have become widely used in the short time since their development. These systems overlay a pseudo-color velocity map upon the gray-scale two-dimensional image. Between 4 and 16 pulses are directed to each line-of-sight, and this requirement reduces the frame rate in comparison with the gray-scale image. Other limitations of color flow mapping include its ability to estimate only the velocity toward or away from the transducer and an increase in the variance in comparison with spectral Doppler. Potential artifacts include aliased velocities and the detection of flow in hypoechoic or hyperechoic nonvascular structures. Clinical applications include cardiology, studies of the abdominal and peripheral vasculature, evaluation of organ perfusion and the differentiation of tumors. Most current systems use narrowband estimators that examine a fixed sample volume and detect a change in phase between two pulses. Wideband estimators that can track red blood cells in two or three dimensions are under evaluation. Narrowband estimators, including the autocorrelator, the short Fourier transform and second order autoregressive filters, are compared with wideband estimators including cross-correlation, sum-absolute-difference and the wideband maximum likelihood estimator. Because the intensity of blood echoes is far smaller than echoes from surrounding tissue, high pass filters have been developed that can reject the larger signal from tissue using the return from a small number of pulses. Other areas of research include strategies for flow estimation with contrast agents, three-dimensional color flow mapping and power Doppler flow mapping.

Standardized evaluation of techniques for measuring the spectral compression of the myoelectric signal.

A digital algorithm was designed to produce band-limited noise with adjustable median frequency and amplitude. This algorithm produces test signals with spectral characteristics typical of those of the surface myoelectric signals encountered in muscle fatigue studies. These synthesized signals provide the basis for standardized evaluation of the performance of various techniques which monitor the spectral compression of the myoelectric signal during muscle fatigue.

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.

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.

Diagnostic efficacy of compressed digitized real-time sonography of uterine fibroids.

RATIONALE AND OBJECTIVES: The authors investigated the diagnostic efficacy of compression of real-time ultrasound (US) examinations. METHODS: Low- and high-compression recordings (9:1 and 15:1, respectively) of examinations were generated by using Joint Photographic Experts Group algorithms. Seven radiologists used a five-level response scale to answer questions about the presence, number, and location of focal fibroid tumors in 67 randomly sorted uterine examinations. The images were viewed after no, low, and high compression. Results were evaluated by using multipatient, multireader receiver operating characteristic jack-knife analysis. RESULTS: Given the reduction in the US digital video rates from 74 Mbit/sec for uncompressed images to 8 Mbit/sec for low compression and 4.7 Mbit/sec for high compression, there were no statistically significant differences in accuracy between the compression schemes. Confidence intervals suggested that the sample size was adequate. CONCLUSION: Compressed images with compression ratios of 9:1 and 15:1 were diagnostically equivalent to uncompressed images of uterine fibroid tumors.

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.

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.

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.

Theoretical and clinical approaches to the treatment of adolescent drug addiction.

Psychologists, social workers, addiction specialists, and occupational therapists often find themselves faced with clients who not only are addicted but also have personal, family, and social problems. These combined problems make the drug-abusing client an extremely difficult one to work with. Occupational therapists have a particular challenge in that they must not only understand and analyze their clients' occupational behavior but also their needs as addicts. This paper describes an approach to adolescent addiction that presents a clinical and theoretical consideration that could be helpful to professionals who work with addicted or drug-abusing clients. In the approach a fusion must be made between the client and the therapist or treatment program. The fusion is temporary but long enough to provide opportunities for clients to work through their feelings of anger, aggression, and sadism, as well as their ego and superego problems. To understand all aspects of their use of drugs, an easily memorized two-dimensional scheme is drawn by the client and therapist together and is used to formulate a treatment plan. Separation from the therapist or program is an essential part of treatment. At this time the client is given the kind of emotional support required to establish new relationships.

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.