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Biomedical subjects

Robert C McKinstry

Publications and source records attributed to Robert C McKinstry.

At least 19 recordsLinked to original sources
PubMed2006

Etiology of strokes in children with sickle cell anemia.

The most devastating complication of sickle cell anemia is cerebral infarction, affecting approximately 30% of all individuals with sickle cell anemia. Despite being one of the most common causes of stroke in infants and children, the mechanism of cerebral infarction in this population has not been extensively studied and is poorly understood. Multiple, synergistic factors are important in the pathogenesis of stroke including the hemodynamic effects of cerebral arterial occlusive disease, viscosity, chronic and acute anemia and acute medical events. This review focuses on the relationship between these factors in order to provide a foundation for further study of the etiology of strokes in this high-risk population.

Anemia, Sickle Cell↗
PubMed2006

Diffusion tensor imaging and tractography of human brain development.

Over the past decade, diffusion tensor imaging (DTI) has offered researchers and clinicians a new noninvasive window into the developing human brain, from preterm infants through adolescents and young adults. DTI improves on conventional MR imaging, such as T1-weighted and T2-weighted sequences, through its sensitivity to many microstructural features of neural organization. This has enabled visualization of the early cerebral laminar architecture in premature infants, of developing white matter before myelination, and of the microarchitecture of the cerebral cortex during preterm maturation. DTI provides reproducible quantitative measures, such as mean diffusivity and fractional anisotropy, that reflect the underlying tissue properties of gray matter and white matter and may therefore become useful as developmental milestones for the improved assessment of abnormal brain maturation. Furthermore, three-dimensional fiber tractography based on DTI can reveal the developing axonal connectivity of the human brain as well as aberrant connectivity in structural brain malformations. In this article, applications of DTI and fiber tractography to the study of human brain development are reviewed. The new insights into brain maturation afforded by DTI promise to improve the diagnostic evaluation of an array of congenital, metabolic, and neurodevelopmental disorders.

Adolescent↗
PubMed2006

Cognitive screening for silent cerebral infarction in children with sickle cell disease.

Silent cerebral infarctions have been shown to cause major morbidity in children with sickle cell disease, suggesting that silent infarctions are not as "silent" as once thought. The current definition of silent infarction includes signal changes on magnetic resonance imaging, the absence of overt abnormalities on neurologic examination, and no history of focal neurologic event. Using a decision tree algorithm, we identified a cognitive profile distinguishing children with (n=16) and without (n=49) silent infarctions. The best model combined learning slope from the California Verbal Learning Test-Children's Version and Block Design from the Wechsler Abbreviated Scale of Intelligence. Accuracy was 75%, with 75% sensitivity and 76% specificity. Administration of a brief cognitive battery may be the most feasible approach to screen for silent infarctions in children with sickle cell disease.

Adolescent↗
PubMed2005

Use of rapid-sequence magnetic resonance imaging for evaluation of hydrocephalus in children.

OBJECT: The authors examine the use of rapid-sequence magnetic resonance (rsMR) imaging to make the diagnosis of malfunctioning and/or infected shunts in patients with hydrocephalus. Computerized tomography (CT) scanning is usually used in this context because it rapidly acquires high-quality images, yet it exposes pediatric patients to particularly high levels of radiation. Standard MR imaging requires longer image acquisition time, is associated with movement artifact, and, in children, usually requires sedation. Standard MR imaging provides greater structural resolution, yet visualization of ventricular catheters is relatively poor. METHODS: The authors analyzed a series of 67 rsMR imaging examinations performed without sedation in pediatric patients with hydrocephalus whose mean age was 4 years at the time of the examination. The mean study duration was 22 minutes. Catheter visualization was good or excellent in more than 75% of studies reviewed, and image quality was good or excellent in more than 60% of studies reviewed. The authors analyzed cancer risk with a model used for atomic bomb survivors. Fifty percent of their patients with hydrocephalus had undergone more than four brain imaging studies (CT or MR imaging) in their lifetimes. For the many patients who had undergone more than 15 studies, the total estimated lifetime attributable cancer mortality risk was calculated to be at least 0.35%. CONCLUSIONS: Rapid-sequence MR imaging yields reliable visualization of the ventricular catheter and offers superior anatomical detail while limiting radiation exposure. The authors' protocol is rapid and each image is acquired separately; therefore, motion artifact is reduced and the need for sedation is eliminated. They recommend the use of rsMR imaging for nonemergent evaluation of pediatric hydrocephalus.

Adolescent↗
PubMed2004

Hand somatosensory cortex activity following selective dorsal rhizotomy: report of three cases with fMRI.

INTRODUCTION: Selective dorsal rhizotomy (SDR) is an effective treatment for lower extremity spasticity in cerebral palsy. Cortical organization in sensory cortex may be abnormal in cerebral palsy, and deafferentation is known to lead to cortical reorganization in many situations. METHODS: We used functional magnetic resonance imaging (fMRI) of hand sensory stimulation to determine if the partial deafferentation of the lower extremity sensory system, associated with SDR, led to any alterations in the cortical somatosensory representation for the upper limbs. Three patients with spastic diplegia were studied with blood oxygen level-dependent (BOLD)-fMRI before and after SDR. fMRI during tactile stimulation of the digits of the right hand was used to map hand somatosensory cortex. Comparison of the cortical maps devoted to the hand before and after SDR assessed for cortical reorganization following partial deafferentation of the lower extremity. RESULTS: In the one patient with upper extremity involvement, the hand sensory representation was markedly enhanced following SDR. In the other two patients, a normal pattern, but with diminished activity, was seen compared with preoperative findings. SDR for lower limb spastic diplegia does not lead to extensive reorganization of cortex dedicated to the representation of the upper limb. An essentially normal pattern of activation was seen both before and after SDR. CONCLUSION: The relief of attention demands associated with spasticity may explain the modulation in intensity seen after SDR in the patients who exhibited no upper extremity involvement despite lower limb spasticity.

Adolescent↗
PubMed2003

Intracranial hemorrhage progressing to porencephaly as a result of congenitally acquired cytomegalovirus infection--an illustrative report.

OBJECTIVE: To report ultrasound and magnetic resonance imaging (MRI) findings in a fetus with intracranial hemorrhage and porencephaly, presumed secondary to intrauterine cytomegalovirus (CMV) infection. METHODS: A 20-year-old, G2, P1 woman presented at 28.6 weeks' gestation after ultrasound examination demonstrated apparently isolated fetal ascites. Evaluation included maternal serology, amniocentesis, and repeated ultrasound examinations. Fetal MRI evaluation was also performed. The infant was born at 35 weeks' gestational age. RESULTS: Maternal serology was positive for CMV IgG. Intrauterine CMV infection was confirmed using polymerase chain reaction (PCR). At 31.6 weeks' gestation, ultrasound demonstrated borderline lateral cerebral ventriculomegaly. MRI of the fetal brain on the same day demonstrated parenchymal hemorrhage in the right posterior temporal and parietal regions along with mild ventricular enlargement. Sonography one day before delivery revealed brain parenchymal cystic change consistent with porencephaly of the right posterior temporal and parietal region. Postnatal ultrasound, computed tomography (CT), and MRI confirmed the diagnosis of a porencephalic cyst communicating with the posterior body of the right lateral ventricle. Placental pathology was consistent with CMV infection. CONCLUSION: This case report illustrates that fetal MRI is a useful adjunct in the evaluation of intrauterine infection with CMV.

Adult↗
PubMed2003

Brain neoplasms: epidemiology, diagnosis, and prospects for cost-effective imaging.

Currently, the literature lacks a solid body of research on decision and cost-effectiveness analysis of imaging strategies for adults and children suspected of having a brain neoplasm. This article describes the epidemiology and clinical presentation of brain neoplasms, reviews current diagnostic strategies, highlights gaps in the literature on decision and cost-effectiveness analysis, and suggests directions for future research.

Adult↗
PubMed2003

Measurement of cerebral blood flow in chronic carotid occlusive disease: comparison of dynamic susceptibility contrast perfusion MR imaging with positron emission tomography.

BACKGROUND AND PURPOSE: Our purpose was to evaluate the accuracy of cerebral blood flow (CBF) measurements obtained by using dynamic susceptibility contrast-enhanced MR imaging, including the influence of arterial input function (AIF) selection, compared with those obtained by using [(15)O]-H(2)O positron emission tomography (PET) for patients with chronic carotid occlusion. METHODS: MR images and PET scans were obtained of seven patients with unilateral carotid occlusion and were co-registered for region of interest analysis. PET CBF maps were generated by using the autoradiographic method. MR imaging CBF maps were calculated by deconvolution of the susceptibility time curve with a proximal middle cerebral artery AIF and were converted to absolute flow rates either by assuming a constant contralateral white matter CBF value of 22 mL/100 mL/min or by using individually determined PET white matter CBF values. RESULTS: Although CBF values measured by PET and MR imaging were positively correlated for every patient, the slopes and y intercepts of the regression lines varied widely among patients. The correlation was better when individual white matter CBF values measured by PET were used to scale the white matter CBF values measured by MR imaging (r = 0.84, P <.0001) than when constant contralateral CBF values were assumed (r = 0.54, P <.0001). The choice of AIF ipsilateral or contralateral to the occluded carotid artery made no statistically significant difference (P >.05) to the correlation coefficient, slope, or y intercept of the MR imaging versus PET CBF regressions for six of the seven patients. CONCLUSION: Although linearly correlated with CBF values measured by PET, dynamic susceptibility contrast-enhanced MR imaging was not accurate for measuring absolute CBF values. AIF selection relative to the side of carotid occlusion did not significantly affect calculated MR imaging CBF values for six of the seven patients.

Aged↗
PubMed2002

Reversible posterior leukoencephalopathy syndrome and silent cerebral infarcts are associated with severe acute chest syndrome in children with sickle cell disease.

Patients with severe acute chest syndrome (ACS) requiring endotracheal intubation and erythrocytopheresis are at increased risk for neurologic morbidity. This study examines patients with sickle cell disease who developed severe episodes of ACS, leading to endotracheal intubation, ventilatory support for respiratory failure, and erythrocytapheresis. Magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA) studies, a neurologic examination by a pediatric neurologist, and cognitive testing were done in all patients. Five consecutive patients, aged 3 to 9 years, were identified with severe ACS. All patients developed neurologic complications resulting from ACS episodes, including seizures (n = 2), silent cerebral infarcts (n = 3), cerebral hemorrhage (n = 2), and reversible posterior leukoencephalopathy syndrome (n = 3). Children with severe ACS should have a magnetic resonance image of the brain, neurologic examination by a neurologist, and cognitive testing to detect the presence of neurologic morbidity.

Acute Disease↗
PubMed2002

Investigation of mechanisms underlying transient T2 normalization in longitudinal studies of ischemic stroke.

PURPOSE: To determine if the phenomenon of transient normalization of T2 relaxation in the subacute stage of ischemic stroke is associated with either magnetic susceptibility effects secondary to hemorrhage or changes in tissue water content. MATERIALS AND METHODS: We utilized a rat model of transient, focal, cerebral ischemia. The possibility of hemorrhage was evaluated with T2*-weighted (T2*W) imaging and histology. Changes in water content were assessed by brain wet-to-dry weight. RESULTS: Susceptibility effects were not evident in T2*W images, and neither red blood cells nor unchelated Fe(III) was found in hematoxylin and eosin (H-E)- or Prussian Blue-stained sections, respectively. However, between the peak of T2 contrast and the point of transient T2 normalization, water content consistently decreased by an average of 3%. CONCLUSION: Transient T2 normalization is associated with normalization of water content and can occur without evidence of hemorrhage.

Analysis of Variance↗
PubMed2002

Radial organization of developing preterm human cerebral cortex revealed by non-invasive water diffusion anisotropy MRI.

Cerebral cortical development involves a complex cascade of events which are difficult to visualize in intact, living subjects. In this study, we apply diffusion tensor imaging (DTI) to the evaluation of cortical development in human infants ranging from 26 to 41 weeks gestational age (GA). Apparent diffusion of water in cortex is maximally anisotropic at 26 weeks GA and anisotropy values approach zero by 36 weeks GA. During this period, the major eigenvector of the diffusion tensor in cerebral cortex is oriented radially across the cortical plate, in accord with a predominately radial deployment of its neuronal constituents. Values for the rotationally averaged water diffusion coefficient increase between 26 and 32 weeks GA, then decrease thereafter. These changes in DTI parameters are specific to cerebral cortex and reflect changes in underlying cortical architecture and formation of neuronal connections. Because of its correlation with tissue microstructure and non-invasive nature, DTI offers unique insight into cortical development in preterm human newborns and, potentially, detection of derangements of its basic cytoarchiteture.

Anisotropy↗