Development of ex vivo brain hemorrhage phantom for photoacoustic imaging.

Brain hemorrhage, specifically intraventricular hemorrhage (IVH), is considered one of the primary and leading causes of cerebral anomalies in neonates. Several imaging modalities including the most popular, cranial ultrasound, are not capable of detecting early stage IVHs. Photoacoustic imaging (PAI) exhibited great potential for detecting cerebral hemorrhage in studies limited to small animal models, but these models are not comparable to neonatal brain morphology. However, hemorrhage detection in large animal models using PAI is rare due to the complexity and cost of inducing hemorrhage in vivo. Moreover, in vitro studies are unable to represent the physiology and environment of the hemorrhagic lesion. Here, we proposed a pseudo hemorrhage implementation method in the sheep brain that allows us to mimic different hemorrhagic lesions ex vivo without compromising the complexity of cerebral imaging. This approach enables a true evaluation of PAI performance for detecting hemorrhages and can be utilized as a reference to optimize the PAI system for in vivo imaging.

Transfontanelle photoacoustic imaging of intraventricular brain hemorrhages in live sheep.

Intraventricular (IVH) and periventricular (PVH) hemorrhages in preterm neonates are common because the periventricular blood vessels are still developing up to 36 weeks and are fragile. Currently, transfontanelle ultrasound (US) imaging is utilized for screening for IVH and PVH, largely through the anterior fontanelle. However for mild hemorrhages, inconclusive diagnoses are common, leading to failure to detect IVH/PVH or, when other clinical symptoms are present, use of second stage neuroimaging modalities requiring transport of vulnerable patients. Yet even mild IVH/PVH increases the risk of moderate-severe neurodevelopmental impairment. Here, we demonstrate the capability of transfontanelle photoacoustic imaging (TFPAI) to detect IVH and PVH in-vivo in a large animal model. TFPAI was able to detect IVH/PVH as small as 0.3 mL in volume in the brain (p < 0.05). By contrast, US was able to detect hemorrhages as small as 0.5 mL. These preliminary results suggest TFPAI could be translated into a portable bedside imaging probe for improved diagnosis of clinically relevant brain hemorrhages in neonates.

Transfontanelle photoacoustic imaging for in-vivo cerebral oxygenation measurement.

The capability of photoacoustic (PA) imaging to measure oxygen saturation through a fontanelle has been demonstrated in large animals in-vivo. We called this method, transfontanelle photoacoustic imaging (TFPAI). A surgically induced 2.5 cm diameter cranial window was created in an adult sheep skull to model the human anterior fontanelle. The performance of the TFPAI has been evaluated by comparing the PA-based predicted results against the gold standard of blood gas analyzer measurements.

Primary care spatial density and nonurgent emergency department utilization: a new methodology for evaluating access to care.

OBJECTIVE: To determine the spatial and demographic characteristics of pediatric patients who make nonurgent visits (NUVs) to an urban pediatric emergency department (ED). We hypothesized that the rate of NUVs would be inversely associated with the spatial density of primary care providers (PCPs). METHODS: A retrospective, cross-sectional analysis was conducted for all visits to Washington, DC's principal pediatric ED between 2003 and 2006. NUVs were defined by a unique algorithm combining resource allocation, ambulatory-sensitive diagnoses, and billing data. Multivariate linear regression analysis was used to determine the association of PCP density and demographic variables on the spatial rate of NUVs. RESULTS: Over the 4-year period, 35.1% (52,110) of the 148,314 ED visits by Washington, DC, residents were nonurgent. NUVs were most associated with neighborhood median household income <$40,000 and low spatial density of PCPs. For every 1-unit increase in PCP density, the spatial rate of NUVs decreased by 9%. The odds of a visit being nonurgent were significantly higher for African Americans and Hispanics than for whites (odds ratio [OR] 2.4, 95% confidence interval [CI] 2.19-2.64; and OR 2.6, 95% CI 2.36-2.86, respectively), for patients using public insurance versus private (OR 1.46, 95% CI 1.42-1.50), and for patients age <5 years (OR 2.66, 95% CI 2.60-2.72). CONCLUSIONS: Low spatial density of primary care is strongly associated with nonurgent ED utilization. Improving spatial distribution of primary care may decrease ED misuse and improve access to the medical home.