Analysis of near-infrared spectroscopy and indocyanine green dye dilution with Monte Carlo simulation of light propagation in the adult brain.

Near-infrared spectroscopy (NIRS) combined with indocyanine green (ICG) dilution is applied externally on the head to determine the cerebral hemodynamics of neurointensive care patients. We applied Monte Carlo simulation for the analysis of a number of problems associated with this method. First, the contamination of the optical density (OD) signal due to the extracerebral tissue was assessed. Second, the measured OD signal depends essentially on the relative blood content (with respect to its absorption) in the various transilluminated tissues. To take this into account, we weighted the calculated densities of the photon distribution under baseline conditions within the different tissues with the changes and aberration of the relative blood volumes that are typically observed under healthy and pathologic conditions. Third, in case of NIRS ICG dye dilution, an ICG bolus replaces part of the blood such that a transient change of absorption in the brain tissues occurs that can be recorded in the OD signal. Our results indicate that for an exchange fraction of Delta=30% of the relative blood volume within the intracerebral tissue, the OD signal is determined from 64 to 74% by the gray matter and between 8 to 16% by the white matter maximally for a distance of d=4.5 cm.

A new subdural probe for combined intracranial pressure (ICP) and cerebral blood flow (CBF) monitoring.

We report the development of a new subdural probe for combined intracranial pressure (ICP) and cerebral blood flow (CBF) monitoring with near infrared spectroscopy (NIRS) and indocyanine green (ICG) dye dilution. For NIRS a conventional subdural ICP monitoring probe was supplied with two fiber bundles and 90-degree prisms. Injections of 25 mg ICG were performed. Regional values for the mean transit time of ICG (rmtt(ICG)), cerebral blood flow (rCBF) and cerebral blood volume (rCBV) were calculated. With prototypes of the probe in two patients with intracerebral haemorrhage 18 comparative measurements obtained simultaneously with conventional NIRS (optodes placed on the skin) and the subdural NIRS probe were performed. The new subdural NIRS probe allows combined monitoring of ICP and cerebral hemodynamics in the brain directly, without the influence of extracerebral tissue.

Perfusion and molecular diffusion-weighted MR imaging of the brain: in vivo assessment of tissue alteration in cerebral ischemia.

The combined use of perfusion imaging (PI) and diffusion-weighted imaging (DWI) is opening a new window into the processes that occur during the first hours of ischemia. DWI detects changes in molecular diffusion associated with cytotoxic edema. PI characterizes the degree of regional hypoperfusion. Regions showing mismatches between DWI and PI, i.e. hypoperfused areas with normal diffusion behavior are considered potentially salvageable. We present results of 11 patients with an occlusion of the middle cerebral artery stem and spontaneous stroke evolution. Whereas the infarct was clearly visible on initial DWI and PI, surrounding tissue at risk of infarction was marked in all patients by an increased blood volume and transit time, but only in a subgroup (n = 3) where alteration were more pronounced this tissue at risk was progressively infarcted. These human DWI and PI data show alterations in the area of tissue at risk which correlates with infarct progression.

Ultra-fast three-dimensional MR perfusion imaging of the entire brain in acute stroke assessment.

We sought to evaluate a three-dimensional (3D) whole-brain perfusion technique based on echo-shifting (PRESTO) for its performance in evaluation of acute stroke. Twenty-six patients were scanned within 6 hours after onset of hemispheric symptoms, and the results were compared with results of diffusion-weighted imaging (DWI) and digital subtraction angiography (DSA). The signal-to-noise ratio of the images was 61 +/- 3 pre-contrast and 47 +/- 3 at the bolus peak. Brain coverage on perfusion parameter maps was 95% +/- 2% compared with that displayed on T2-weighted images, with only minor artifacts related to susceptibility at the skull base. Measured regional cerebral blood volume (rCBV) reduction closely correlated to lesion size on initial DWI and to final clinical outcome (P = 0.006), consistent with results previously reported for 2D perfusion methods. Mismatches between DWI and perfusion imaging characterized the total extent of tissue at risk, and the contrast timing correlated with the amount of collateral circulation as shown on DSA. In conclusion, 3D imaging using the PRESTO technique permits high-quality perfusion imaging of the entire brain.

An assessment of the use and impact of ancillary prenatal care services to Medicaid women in managed care.

OBJECTIVES: Managed care plans under Medicaid are becoming a usual source of care for low-income pregnant women. This study describes an ancillary prenatal care service intervention developed by one managed care organization (MCO) for Medicaid-enrolled women, assesses the extent to which the intervention services were used, and appraises the influence of the intervention on prenatal care participation. METHOD: There were 226 intervention and 258 control women with a single live birth delivered between 28 and 44 weeks gestation who (1) were enrolled in the MCO's Medicaid program, (2) were high-risk based on a prenatal risk assessment, and (3) started prenatal care prior to 26 weeks gestation. Less than adequate and intensive prenatal care utilization were chosen as intervention outcomes measures. RESULTS: Family planning, a 2-month postpartum baby visit, a maternal postpartum visit, and a WIC (Special Supplemental Nutrition Program for Women, Infants, and Children) referral were among the most self-selected intervention services for this population; home health aide and breast-feeding support were the least requested services. Over 90% of those needing family planning or breast-feeding services received the services, while over 20% of the intervention group refused child care, food assistance and family violence referrals, and home health aide and smoking cessation services. The intervention group had a significantly lower risk of less than adequate utilization of prenatal care (OR = .32; 95% CI: 0.17-0.60) and was more likely to have an intensive number of prenatal care visits (OR = 1.61; 95% CI: 1.05-2.48). CONCLUSIONS: The ability of managed care organizations to provide ongoing prenatal care to Medicaid populations in a cost-effective manner depends partly on their development of packages of prenatal services that foster positive preventive health care utilization behaviors and good pregnancy outcomes. The results of this project suggest that the intervention was beneficial in the area of improving utilization of prenatal care.

Development policy and the evaluation of community self-help: the Harambee school movement in Kenya.

PIP: This attempt to objectively assess the costs and benefits of involvement in the harambee education movement for individuals and families is directed at policymakers and is an exercise in policy analysis. Evaluative studies of this nature are essential to the improvement of the of the overall quality of policymaking. Despite general agreement that harambee education projects involving secondary schools differ in many ways from types of self-help projects, few attempts have been made to assess the long-term social impact of the harambee education movement. For nearly 2 decades Kenya's harambee movement has flourished and has been largely viewed as a positive contribution to national development. Between 1969-79, the total value of contributions to self-help projects rose from around $6 million to almost $27 million, demostrating the substantial inputs of local communities to the economic growth of the country as a whole. Policymakers, after initial reservations about independent self-help, in recent years have come to rely on such activities as complementary to the government's efforts. Self-help activities aimed at expanding educational opportunity are the most significant in terms of both monetary resources expended and the scope of human involvement. Benefits are difficult to extimate. The growing number of students in harambee schools does not necessarly indicate that the majority of these students are acquiring marketable skills or that their consequent levels of academic training will prepare them to complete successfully in the job market with the average student educated in government-sponsored schools. The evidence, in fact, clearly points in the opposite direction. Yet, politicians, policymakers, and citizens continue to regard harambee activities for expanding educational opportunities atall levels as necessary contributions to Kenya's development program and to individual achievement. The direct cost to government for harambee education can be compared with the direct private expenditure on this type of ecucation. The 1976 annual private investment in harambee education was $45 million. The most direct benefits from harambee efforts are reaped by wealthier regions and communities in Kenya. The greaes social benefits derived from the government's policy toward the harambee school movement are political benefits. By symbolically drawing linkages between its national development strategy and independent self-help activities, the government can elicit the tacit support of rural communities. Direct social costs of such a policy are minimal. The indirect, long-term costs may result in disastrous, unintended consequences as the pool of educated and unemployed youths expands and as resulting ethnic and class inequalities sharpen and crystallize.^ieng

Primer on certain elements of medical decision making.

The value of a diagnostic test lies in its ability to detect patients with disease (its sensitivity) and to exclude patients without disease (its specificity). For tests with binary outcomes, these measures are fixed. For tests with a continuous scale of values, various cutoff points can be selected to adjust the sensitivity and specificity of the test to conform with the physician's goals. Principles of statistical decision theory and information theory suggest technics for objectively determining these cutoff points, depending upon whether the physician is concerned with health costs, with financial costs, or with the information content of the test.