Patent ductus arteriosus and coarctation of the aorta in association with PRDM6 variants.

Patent ductus arteriosus (PDA) and coarctation of the aorta (CoA) are relatively common congenital heart defects. Pathogenic variants in PRDM6, which encodes a smooth-muscle-cell-specific transcription factor, have now been etiologically associated with non-syndromic PDA. We present three patients with PDA and CoA found to harbor PRDM6 variants, including a novel, likely-pathogenic variant.

Cardiac magnetic resonance predictors for successful primary biventricular repair of unbalanced complete common atrioventricular canal.

BACKGROUND: Patients with unbalanced common atrioventricular canal can be difficult to manage. Surgical planning often depends on pre-operative echocardiographic measurements. We aimed to determine the added utility of cardiac MRI in predicting successful biventricular repair in common atrioventricular canal. METHODS: We conducted a retrospective cohort study of children with common atrioventricular canal who underwent MRI prior to repair. Associations between MRI and echocardiographic measures and surgical outcome were tested using logistic regression, and models were compared using area under the receiver operator characteristic curve. RESULTS: We included 28 patients (median age at MRI: 5.2 months). The optimal MRI model included the novel end-diastolic volume index (using the ratio of left ventricular end-diastolic volume to total end-diastolic volume) and the left ventricle-right ventricle angle in diastole (area under the curve 0.83, p = 0.041). End-diastolic volume index ≤ 0.18 and left ventricle-right ventricle angle in diastole ≤ 72° yield a sensitivity of 83% and specificity of 81% for successful biventricular repair. The optimal multimodality model included the end-diastolic volume index and the echocardiographic atrioventricular valve index with an area under the curve of 0.87 (p = 0.026). CONCLUSIONS: Cardiac MRI can successfully predict successful biventricular repair in patients with unbalanced common atrioventricular canal utilising the end-diastolic volume index alone or in combination with the MRI left ventricle-right ventricle angle in diastole or the echocardiographic atrioventricular valve index. A prospective cardiac MRI study is warranted to better define the multimodality characteristic predictive of successful biventricular surgery.

Effects of circulatory arrest and cardiopulmonary bypass on cerebral autoregulation in neonatal swine.

BACKGROUND: Cerebral autoregulation mechanisms help maintain adequate cerebral blood flow (CBF) despite changes in cerebral perfusion pressure. Impairment of cerebral autoregulation, during and after cardiopulmonary bypass (CPB), may increase risk of neurologic injury in neonates undergoing surgery. In this study, alterations of cerebral autoregulation were assessed in a neonatal swine model probing four perfusion strategies. METHODS: Neonatal swine (n = 25) were randomized to continuous deep hypothermic cardiopulmonary bypass (DH-CPB, n = 7), deep hypothermic circulatory arrest (DHCA, n = 7), selective cerebral perfusion (SCP, n = 7) at deep hypothermia, or normothermic cardiopulmonary bypass (control, n = 4). The correlation coefficient (LDx) between laser Doppler measurements of CBF and mean arterial blood pressure was computed at initiation and conclusion of CPB. Alterations in cerebral autoregulation were assessed by the change between initial and final LDx measurements. RESULTS: Cerebral autoregulation became more impaired (LDx increased) in piglets that underwent DH-CPB (initial LDx: median 0.15, IQR [0.03, 0.26]; final: 0.45, [0.27, 0.74]; p = 0.02). LDx was not altered in those undergoing DHCA (p > 0.99) or SCP (p = 0.13). These differences were not explained by other risk factors. CONCLUSIONS: In a validated swine model of cardiac surgery, DH-CPB had a significant effect on cerebral autoregulation, whereas DHCA and SCP did not. IMPACT: Approximately half of the patients who survive neonatal heart surgery with cardiopulmonary bypass (CPB) experience neurodevelopmental delays. This preclinical investigation takes steps to elucidate and isolate potential perioperative risk factors of neurologic injury, such as impairment of cerebral autoregulation, associated with cardiac surgical procedures involving CPB. We demonstrate a method to characterize cerebral autoregulation during CPB pump flow changes in a neonatal swine model of cardiac surgery. Cerebral autoregulation was not altered in piglets that underwent deep hypothermic circulatory arrest (DHCA) or selective cerebral perfusion (SCP), but it was altered in piglets that underwent deep hypothermic CBP.

Sustained improvement in fellows' echocardiographic completeness through the coronavirus pandemic with a standardised imaging protocol.

First-year cardiology fellows must quickly learn basic competency in echocardiography during fellowship orientation. This educational process was disrupted in 2020 due to the coronavirus pandemic, as our hands-on echocardiography teaching transitioned from practice on paediatric volunteers to simulation-based training. We previously described an improvement in echocardiographic completeness after implementation of a standardised imaging protocol for the performance of acute assessments of ventricular function. Herein, we assessed whether this improvement could be sustained over the two subsequent years, including the fellowship year affected by the pandemic. Echocardiograms performed by first-year paediatric cardiology fellows to assess ventricular function were reviewed for completeness. The frequency with which each requested component was included was measured. A total demographic score (out of 7) and total imaging score (out of 23) were calculated. The pre-protocol years (2015-2017) were compared to the post-protocol years (2018-2020), and the pre-COVID years (2018-2019) were compared to the year affected by COVID (2020). There was a sustained improvement in completeness after protocol implementation with improvement in the demographic score (median increasing from 6 to 7, p < 0.001) and imaging score (median increasing from 13 to 16, p < 0.001). More individual components showed a statistically significant increase in frequency compared to our prior publication. The COVID pandemic resulted in very few differences in completeness. Demographic reporting improved modestly (p = 0.04); the imaging score was unchanged (p = 0.59). The only view obtained less frequently was the apical two-chamber view. A standardised imaging protocol allowed sustained improvements in echocardiographic completeness despite the disruption of fellowship orientation by COVID-19.

Optical Detection of Intracranial Pressure and Perfusion Changes in Neonates With Hydrocephalus.

OBJECTIVE: To demonstrate that a novel noninvasive index of intracranial pressure (ICP) derived from diffuse optics-based techniques is associated with intracranial hypertension. STUDY DESIGN: We compared noninvasive and invasive ICP measurements in infants with hydrocephalus. Infants born term and preterm were eligible for inclusion if clinically determined to require cerebrospinal fluid (CSF) diversion. Ventricular size was assessed preoperatively via ultrasound measurement of the fronto-occipital (FOR) and frontotemporal (FTHR) horn ratios. Invasive ICP was obtained at the time of surgical intervention with a manometer. Intracranial hypertension was defined as invasive ICP ≥15 mmHg. Diffuse optical measurements of cerebral perfusion, oxygen extraction, and noninvasive ICP were performed preoperatively, intraoperatively, and postoperatively. Optical and ultrasound measures were compared with invasive ICP measurements, and their change in values after CSF diversion were obtained. RESULTS: We included 39 infants, 23 with intracranial hypertension. No group difference in ventricular size was found by FOR (P = .93) or FTHR (P = .76). Infants with intracranial hypertension had significantly higher noninvasive ICP (P = .02) and oxygen extraction fraction (OEF) (P = .01) compared with infants without intracranial hypertension. Increased cerebral blood flow (P = .005) and improved OEF (P < .001) after CSF diversion were observed only in infants with intracranial hypertension. CONCLUSIONS: Noninvasive diffuse optical measures (including a noninvasive ICP index) were associated with intracranial hypertension. The findings suggest that impaired perfusion from intracranial hypertension was independent of ventricular size. Hemodynamic evidence of the benefits of CSF diversion was seen in infants with intracranial hypertension. Noninvasive optical techniques hold promise for aiding the assessment of CSF diversion timing.

Variability in atlas registration of optical intrinsic signal imaging and its effect on functional connectivity analysis.

To compare neuroimaging data between subjects, images from individual sessions need to be aligned to a common reference or "atlas." Atlas registration of optical intrinsic signal imaging of mice, for example, is commonly performed using affine transforms with parameters determined by manual selection of canonical skull landmarks. Errors introduced by such procedures have not previously been investigated. We quantify the variability that arises from this process and consequent errors from misalignment that affect interpretation of functional neuroimaging data. We propose an improved method, using separately acquired high-resolution images and demonstrate improvements in variability and alignment using this method.

Recent advances in our understanding of neurodevelopmental outcomes in congenital heart disease.

PURPOSE OF REVIEW: Patients with congenital heart disease (CHD) suffer from a pattern of neurodevelopmental abnormalities including deficits in language and executive function. In this review, we summarize recent studies that examine these outcomes, their risk factors, possible biomarkers, and attempts to develop therapeutic interventions. RECENT FINDINGS: The latest literature has highlighted the role of genetics in determining neurologic prognosis, as we have increased our understanding of potentially modifiable perioperative risk factors. The role of potentially neurotoxic medical therapies has become more salient. One recent focus has been how neurodevelopment affects quality of life and leads to a high prevalence of mental illness. Neuroimaging advances have provided new insights into the pathogenesis of deficits. SUMMARY: Although many risk factors in CHD are not modifiable, there is promise for interventions to improve neurodevelopmental outcomes in patients with CHD. Biomarkers are needed to better understand the timing and prognosis of injury and to direct therapy. Research into psychosocial interventions is urgently needed to benefit the many survivors with CHD.

A standardized imaging protocol improves quality and reduces practice variability in echocardiographic assessment of ventricular function by first-year pediatric cardiology fellows.

BACKGROUND: Echocardiography education for pediatric cardiology fellows has been a recent focus leading to the implementation of "boot camps." Less is described about continuing education through fellowship and improving image quality. We noticed practice variation in echocardiograms assessing ventricular function performed on nights and weekends. Thus, we implemented a standardized protocol and assessed its impact on imaging and reporting completeness. METHODS: We created an imaging protocol for the assessment of ventricular function in the acute setting. The protocol included demographic information, a list of images to be obtained, and the methods to quantify ventricular function. The protocol was explained to first-year fellows and distributed on an electronic quick reference card. Echocardiograms independently performed by first-year fellows during their first 4 months of on-call time were assessed pre- and postintervention using a standard rubric. RESULTS: Compliance with demographic reporting was high pre- and postintervention, but significantly improved after the standardized protocol (P < 0.001). Use of the protocol increased the median number of unique images obtained per echocardiogram from 13 to 17 (out of 23 required views, P < 0.001). Particularly improved was the performance of quantitative evaluations of function, including Simpson's method for left ventricular ejection fraction (four chamber: 40% vs 67%, P < 0.001; two chamber: 33% vs 67%, P < 0.001) and tricuspid annular plane systolic excursion (45% vs 80%, P < 0.001). CONCLUSIONS: The introduction of a standardized imaging protocol and its distribution to first-year fellows resulted in improvements in echocardiographic reporting completeness and increased the quality of information obtained by providing more quantitative assessments of ventricular function.

Echocardiographic Assessment of Diastolic Function in Children with Incident Systemic Lupus Erythematosus.

The timing and etiology of diastolic impairment in pediatric-onset systemic lupus erythematosus (SLE) are poorly understood. We compared echocardiographic metrics of left ventricular diastolic function in children at SLE diagnosis to controls and identified factors associated with diastolic indices. Echocardiograms of children aged 5-18 years within 1 year of SLE diagnosis and age-/sex-matched controls were retrospectively read by blinded cardiologists. Clinical characteristics were abstracted separately. Z-scores for diastolic indices (E/A, e', E/e', and isovolumetric relaxation time (IVRT)) were calculated using published normative data and study controls, and compared using linear mixed-effects models adjusted for blood pressure. Pericardial effusions and valvular disease were also evaluated. Linear regression was used to identify factors associated with diastolic measures. 85 children with incident SLE had echocardiograms performed a median of 6 days after diagnosis (interquartile range (IQR) 1-70). Prior cumulative prednisone exposure was minimal (median 60 mg, IQR 0-1652). SLE cases had lower E/A, lower e', higher E/e', and longer IVRT compared to controls. Though none met criteria for Grade I diastolic dysfunction, Z-scores for e', E/e', and IVRT were abnormal in 30%, 25%, and 6% of SLE cases, respectively. Greater disease activity was associated with lower septal e' (p < 0.01), higher E/e' (p = 0.02), and longer IVRT (p < 0.01). Children with incident SLE have worse diastolic indices at diagnosis compared to peers without SLE, independent of blood pressure and prior to significant prednisone exposure. Longitudinal studies will determine whether diastolic dysfunction develops in this population over time.

Postoperative Obstruction of the Pulmonary Veins in Mixed Total Anomalous Pulmonary Venous Connection.

Total anomalous pulmonary venous connection (TAPVC) is a rare form of congenital heart disease in which the pulmonary veins drain by various pathways to the right atrium instead of the left atrium. Postoperative obstruction of the pulmonary veins is a known complication. Identifying risk factors for morbidity and mortality is important for counseling and monitoring. We describe a pattern of postoperative obstruction in a specific arrangement of mixed TAPVC. Five patients with a type of mixed TAPVC, namely, three pulmonary veins connecting to the coronary sinus and the left upper pulmonary vein (LUPV) connecting to the innominate vein, were identified over an 11-year period at our institution. Two additional patients with this TAPVC arrangement were cared for at our institution after having surgery at other institutions. Of these, one patient received only comfort care at birth due to other clinical issues. The six other patients underwent surgical unroofing of the coronary sinus. The anomalous LUPV was not addressed during the initial surgery in any of these cases. Following repair, one patient died from non-cardiac reasons. The remaining five patients all developed obstruction of the repaired pulmonary veins with decompression through the unrepaired LUPV, requiring surgical revision. Three patients underwent a second reoperation as well. Three of the six repaired patients also developed refractory atrial arrhythmias. This cohort suggests that this mixed TAPVC pattern predisposes patients to obstruction after surgical repair. Further investigation may aid pediatric cardiologists in risk-stratifying and counseling these patients. Alternative surgical approaches may need to be considered.

Statistical analysis of high density diffuse optical tomography.

High density diffuse optical tomography (HD-DOT) is a noninvasive neuroimaging modality with moderate spatial resolution and localization accuracy. Due to portability and wear-ability advantages, HD-DOT has the potential to be used in populations that are not amenable to functional magnetic resonance imaging (fMRI), such as hospitalized patients and young children. However, whereas the use of event-related stimuli designs, general linear model (GLM) analysis, and imaging statistics are standardized and routine with fMRI, such tools are not yet common practice in HD-DOT. In this paper we adapt and optimize fundamental elements of fMRI analysis for application to HD-DOT. We show the use of event-related protocols and GLM de-convolution analysis in un-mixing multi-stimuli event-related HD-DOT data. Statistical parametric mapping (SPM) in the framework of a general linear model is developed considering the temporal and spatial characteristics of HD-DOT data. The statistical analysis utilizes a random field noise model that incorporates estimates of the local temporal and spatial correlations of the GLM residuals. The multiple-comparison problem is addressed using a cluster analysis based on non-stationary Gaussian random field theory. These analysis tools provide access to a wide range of experimental designs necessary for the study of the complex brain functions. In addition, they provide a foundation for understanding and interpreting HD-DOT results with quantitative estimates for the statistical significance of detected activation foci.

Spatial nonstationarity of image noise in widefield optical imaging and its effects on cluster-based inference for resting-state functional connectivity.

BACKGROUND: Resting-state functional connectivity (RSFC) analysis with widefield optical imaging (WOI) is a potentially powerful tool to develop imaging biomarkers in mouse models of disease before translating them to human neuroimaging with functional magnetic resonance imaging (fMRI). The delineation of such biomarkers depends on rigorous statistical analysis. However, statistical understanding of WOI data is limited. In particular, cluster-based analysis of neuroimaging data depends on assumptions of spatial stationarity (i.e., that the distribution of cluster sizes under the null is equal at all brain locations). Whether actual data deviate from this assumption has not previously been examined in WOI. NEW METHOD: In this manuscript, we characterize the effects of spatial nonstationarity in WOI RSFC data and adapt a "two-pass" technique from fMRI to correct cluster sizes and mitigate spatial bias, both parametrically and nonparametrically. These methods are tested on multi-institutional data. RESULTS AND COMPARISON WITH EXISTING METHODS: We find that spatial nonstationarity has a substantial effect on inference in WOI RSFC data with false positives much more likely at some brain regions than others. This pattern of bias varies between imaging systems, contrasts, and mouse ages, all of which could affect experimental reproducibility if not accounted for. CONCLUSIONS: Both parametric and nonparametric corrections for nonstationarity result in significant improvements in spatial bias. The proposed methods are simple to implement and will improve the robustness of inference in optical neuroimaging data.

Bidirectional relationship between functional connectivity and amyloid-ß deposition in mouse brain.

Brain region-specific deposition of extracellular amyloid plaques principally composed of aggregated amyloid-ß (Aß) peptide is a pathological signature of Alzheimer's disease (AD). Recent human neuroimaging data suggest that resting-state functional connectivity strength is reduced in patients with AD, cognitively normal elderly harboring elevated amyloid burden, and in advanced aging. Interestingly, there exists a striking spatial correlation between functional connectivity strength in cognitively normal adults and the location of Aß plaque deposition in AD. However, technical limitations have heretofore precluded examination of the relationship between functional connectivity, Aß deposition, and normal aging in mouse models. Using a novel functional connectivity optical intrinsic signal (fcOIS) imaging technique, we demonstrate that Aß deposition is associated with significantly reduced bilateral functional connectivity in multiple brain regions of older APP/PS1 transgenic mice. The amount of Aß deposition in each brain region was associated with the degree of local, age-related bilateral functional connectivity decline. Normal aging was associated with reduced bilateral functional connectivity specifically in retrosplenial cortex. Furthermore, we found that the magnitude of regional bilateral functional correlation in young APP/PS1 mice before Aß plaque formation was proportional to the amount of region-specific plaque deposition seen later in older APP/PS1 mice. Together, these findings suggest that Aß deposition and normal aging are associated with region-specific disruption of functional connectivity and that the magnitude of local bilateral functional connectivity predicts regional vulnerability to subsequent Aß deposition in mouse brain.

Controlling the familywise error rate in widefield optical neuroimaging of functional connectivity in mice.

Significance: Statistical inference in functional neuroimaging is complicated by the multiple testing problem and spatial autocorrelation. Common methods in functional magnetic resonance imaging to control the familywise error rate (FWER) include random field theory (RFT) and permutation testing. The ability of these methods to control the FWER in optical neuroimaging has not been evaluated. Aim: We attempt to control the FWER in optical intrinsic signal imaging resting-state functional connectivity using both RFT and permutation inference at a nominal value of 0.05. The FWER was derived using a mass empirical analysis of real data in which the null is known to be true. Approach: Data from normal mice were repeatedly divided into two groups, and differences between functional connectivity maps were calculated with pixel-wise t -tests. As the null hypothesis was always true, all positives were false positives. Results: Gaussian RFT resulted in a higher than expected FWER with either cluster-based (0.15) or pixel-based (0.62) methods. t -distribution RFT could achieve FWERs of 0.05 (cluster-based or pixel-based). Permutation inference always controlled the FWER. Conclusions: RFT can lead to highly inflated FWERs. Although t -distribution RFT can be accurate, it is sensitive to statistical assumptions. Permutation inference is robust to statistical errors and accurately controls the FWER.

Cerebral microhemorrhages in children with congenital heart disease: Prevalence, risk factors, and impact on neurodevelopmental outcomes.

Background: Infants with complex congenital heart disease (CHD) require life-saving corrective/palliative heart surgery in the first weeks of life. These infants are at risk for brain injury and poor neurodevelopmental outcomes. Cerebral microhemorrhages (CMH) are frequently seen after neonatal bypass heart surgery, but it remains unknown if CMH are a benign finding or constitute injury. Herein, we investigate the risk factors for developing CMH and their clinical significance. Methods: 192 infants with CHD undergoing corrective cardiac surgery with cardiopulmonary bypass (CPB) at a single institution were prospectively evaluated with pre-(n = 183) and/or postoperative (n = 162) brain magnetic resonance imaging (MRI). CMH severity was scored based on total number of microhemorrhages. Antenatal, perioperative, and postoperative candidate risk factors for CMH and neurodevelopmental (ND) outcomes were analyzed. Eighteen-month neurodevelopmental outcomes were assessed using the Bayley-III Scales of Infants and Toddler Development in a subset of patients (n = 82). Linear regression was used to analyze associations between risk factors or ND outcomes and presence/number of CMH. Results: The most common CHD subtypes were hypoplastic left heart syndrome (HLHS) (37%) and transposition of the great arteries (TGA) (33%). Forty-two infants (23%) had CMH present on MRI before surgery and 137 infants (85%) post-surgery. No parameters evaluated were significant risk factors for preoperative CMH. In multivariate analysis, cardiopulmonary bypass (CPB) duration (p < 0.0001), use of extracorporeal membrane oxygenation (ECMO) support (p < 0.0005), postoperative seizure(s) (p < 0.03), and lower birth weight (p < 0.03) were associated with new or worsened CMH postoperatively. Higher CMH number was associated with lower scores on motor (p < 0.03) testing at 18 months. Conclusion: CMH is a common imaging finding in infants with CHD with increased prevalence and severity after CPB and adverse impact on neurodevelopmental outcomes starting at a young age. Longer duration of CPB and need for postoperative ECMO were the most significant risk factors for developing CMH. However, presence of CMH on preoperative scans indicates non-surgical risk factors that are yet to be identified. Neuroprotective strategies to mitigate risk factors for CMH may improve neurodevelopmental outcomes in this vulnerable population.

Non-invasive diffuse optical monitoring of cerebral physiology in an adult swine-model of impact traumatic brain injury.

In this study, we used diffuse optics to address the need for non-invasive, continuous monitoring of cerebral physiology following traumatic brain injury (TBI). We combined frequency-domain and broadband diffuse optical spectroscopy with diffuse correlation spectroscopy to monitor cerebral oxygen metabolism, cerebral blood volume, and cerebral water content in an established adult swine-model of impact TBI. Cerebral physiology was monitored before and after TBI (up to 14 days post injury). Overall, our results suggest that non-invasive optical monitoring can assess cerebral physiologic impairments post-TBI, including an initial reduction in oxygen metabolism, development of cerebral hemorrhage/hematoma, and brain swelling.

Diffuse Optical Monitoring of Cerebral Hemodynamics and Oxygen Metabolism during and after Cardiopulmonary Bypass: Hematocrit Correction and Neurological Vulnerability.

Cardiopulmonary bypass (CPB) provides cerebral oxygenation and blood flow (CBF) during neonatal congenital heart surgery, but the impacts of CPB on brain oxygen supply and metabolic demands are generally unknown. To elucidate this physiology, we used diffuse correlation spectroscopy and frequency-domain diffuse optical spectroscopy to continuously measure CBF, oxygen extraction fraction (OEF), and oxygen metabolism (CMRO2) in 27 neonatal swine before, during, and up to 24 h after CPB. Concurrently, we sampled cerebral microdialysis biomarkers of metabolic distress (lactate-pyruvate ratio) and injury (glycerol). We applied a novel theoretical approach to correct for hematocrit variation during optical quantification of CBF in vivo. Without correction, a mean (95% CI) +53% (42, 63) increase in hematocrit resulted in a physiologically improbable +58% (27, 90) increase in CMRO2 relative to baseline at CPB initiation; following correction, CMRO2 did not differ from baseline at this timepoint. After CPB initiation, OEF increased but CBF and CMRO2 decreased with CPB time; these temporal trends persisted for 0-8 h following CPB and coincided with a 48% (7, 90) elevation of glycerol. The temporal trends and glycerol elevation resolved by 8-24 h. The hematocrit correction improved quantification of cerebral physiologic trends that precede and coincide with neurological injury following CPB.

Bedside optical imaging of occipital resting-state functional connectivity in neonates.

Resting-state networks derived from temporal correlations of spontaneous hemodynamic fluctuations have been extensively used to elucidate the functional organization of the brain in adults and infants. We have previously developed functional connectivity diffuse optical tomography methods in adults, and we now apply these techniques to study functional connectivity in newborn infants at the bedside. We present functional connectivity maps in the occipital cortices obtained from healthy term-born infants and premature infants, including one infant with an occipital stroke. Our results suggest that functional connectivity diffuse optical tomography has potential as a valuable clinical tool for the early detection of functional deficits and for providing prognostic information on future development.

A quantitative spatial comparison of high-density diffuse optical tomography and fMRI cortical mapping.

Functional neuroimaging commands a dominant role in current neuroscience research. However its use in bedside clinical and certain neuro-scientific studies has been limited because the current tools lack the combination of being non-invasive, non-ionizing and portable while maintaining moderate resolution and localization accuracy. Optical neuroimaging satisfies many of these requirements, but, until recent advances in high-density diffuse optical tomography (HD-DOT), has been hampered by limited resolution. While early results of HD-DOT have been promising, a quantitative voxel-wise comparison and validation of HD-DOT against the gold standard of functional magnetic resonance imaging (fMRI) has been lacking. Herein, we provide such an analysis within the visual cortex using matched visual stimulation protocols in a single group of subjects (n=5) during separate HD-DOT and fMRI scanning sessions. To attain the needed voxel-to-voxel co-registration between HD-DOT and fMRI image spaces, we implemented subject-specific head modeling that incorporated MRI anatomy, detailed segmentation, and alignment of source and detector positions. Comparisons of the visual responses found an average localization error between HD-DOT and fMRI of 4.4+/-1mm, significantly less than the average distance between cortical gyri. This specificity demonstrates that HD-DOT has sufficient image quality to be useful as a surrogate for fMRI.

Protein interface remodeling in a chemically induced protein dimer.

Although the development of chemically induced, self-assembled protein-based materials is rapidly expanding, methods for directing their assembly in solution are sparse, and problems of population heterogeneity remain. By exerting control over the assembly of advanced protein structures, new classes of ordered protein nanomaterials become feasible, affecting numerous applications ranging from therapeutics to nanostructural engineering. Focusing on a protein-based method for modulating the stability of a chemically induced dihydrofolate reductase (DHFR) dimer, we demonstrate the sensitivity of a methotrexate competition assay in determining the change in DHFR-DHFR binding cooperativity via interfacial mutations over a 1.3 kcal/mol range. This represents a change of more than 40% of the dimer complex binding energy conferred from protein-protein cooperativity (~3.1 kcal/mol). With the development of this investigative system and refinement of protein-based techniques for complex stability modulation, the directed assembly of protein nanomaterials into heterocomplexes and a concomitant decrease in population heterogeneity becomes a realizable goal.