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Lisa C. Krishnamurthy

Bio: Lisa C. Krishnamurthy is an academic researcher from Georgia State University. The author has contributed to research in topics: Medicine & Psychology. The author has an hindex of 9, co-authored 26 publications receiving 241 citations. Previous affiliations of Lisa C. Krishnamurthy include United States Department of Veterans Affairs & Emory University.

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Journal ArticleDOI
TL;DR: There has not been a systematic study to examine neonatal blood T1/T2 relaxometry in neonates, so this present study aims to investigate this topic.
Abstract: Purpose Knowledge of blood T1 and T2 is of major importance in many applications of MRI in neonates. However, to date, there has not been a systematic study to examine neonatal blood T1/T2 relaxometry. This present study aims to investigate this topic. Methods Using freshly collected blood samples from human umbilical cord, we performed in vitro experiments under controlled physiological conditions to measure blood T1 and T2 at 3 Tesla (T) and their dependence on several factors, including hematocrit (Hct), oxygenation (Y) and temperature. Results The arterial T1 in neonates was 1825 ± 184 ms (Hct = 0.42 ± 0.08), longer than that of adult blood. Neonatal blood T1 was strongly dependent on Hct (P < 0.001) and Y (P = 0.005), and the dependence of T1 on Y was more prominent at higher Hct. The arterial T2 of neonatal blood was 191 ms at an Hct of 0.42, which was also longer than adult blood. Neonatal blood T2 was positively associated with blood oxygenation and negatively associated with hematocrit level, and can be characterized by an exchange model. Neonatal blood T1 was also positively associated with temperature (P < 0.001). Conclusion The values provided in this report may provide important reference and calibration information for sequence optimization and quantification of in vivo neonatal MRI studies. Magn Reson Med, 2015. © 2015 Wiley Periodicals, Inc.

61 citations

Journal ArticleDOI
TL;DR: The present study aims to develop a noninvasive, rapid, and reproducible method to measure Yv in a vessel‐specific manner.
Abstract: Purpose Measurement of venous oxygenation (Yv) is a critical step toward quantitative assessment of brain oxygen metabolism, a key index in many brain disorders. The present study aims to develop a noninvasive, rapid, and reproducible method to measure Yv in a vessel-specific manner. Theory The method, T2-Relaxation-Under-Phase-Contrast MRI, utilizes complex subtraction of phase-contrast to isolate pure blood signal, applies nonslice-selective T2-preparation to measure T2, and converts T2 to oxygenation using a calibration plot. Methods Following feasibility demonstration, several technical aspects were examined, including validation with an established global Yv technique, test–retest reproducibility, sensitivity to detect oxygenation changes due to hypoxia and caffeine challenges, applicability of echo-planar-imaging (EPI) acquisition to shorten scan duration, and ability to study veins with a caliber of 1–2 mm. Results T2-Relaxation-Under-Phase-Contrast was able to simultaneously measure Yv in all major veins in the brain, including sagittal sinus, straight sinus, great vein, and internal cerebral vein. T2-Relaxation-Under-Phase-Contrast results showed an excellent agreement with the reference technique, high sensitivity to oxygenation changes, and test–retest variability of 3.5 ± 1.0%. The use of segmented-EPI was able to reduce the scan duration to 1.5 minutes. It was also feasible to study pial veins and deep veins. Conclusion T2-Relaxation-Under-Phase-Contrast MRI is a promising technique for vessel-specific oxygenation measurement. Magn Reson Med 71:978–989, 2014. © 2013 Wiley Periodicals, Inc.

47 citations

Journal ArticleDOI
TL;DR: While knowledge is rapidly accumulating, larger trials emphasising how to select optimal paradigms for individualised aphasia treatment are needed and a model of how to incorporate the growing knowledge into clinical practice could help to focus future research.
Abstract: Given the profound impact of language impairment after stroke (aphasia), neuroplasticity research is garnering considerable attention as means for eventually improving aphasia treatments and how they are delivered. Functional and structural neuroimaging studies indicate that aphasia treatments can recruit both residual and new neural mechanisms to improve language function and that neuroimaging modalities may hold promise in predicting treatment outcome. In relatively small clinical trials, both non-invasive brain stimulation and behavioural manipulations targeting activation or suppression of specific cortices can improve aphasia treatment outcomes. Recent language interventions that employ principles consistent with inducing neuroplasticity also are showing improved performance for both trained and novel items and contexts. While knowledge is rapidly accumulating, larger trials emphasising how to select optimal paradigms for individualised aphasia treatment are needed. Finally, a model of how to incorporate the growing knowledge into clinical practice could help to focus future research.

46 citations

Journal ArticleDOI
TL;DR: A 12-week physical activity intervention can change rsFC between primary motor regions and default mode network areas, which may be associated with improved motor performance.
Abstract: Objective: We have previously demonstrated that aerobic exercise improves upper extremity motor function concurrent with changes in motor cortical activity using task-based functional magnetic resonance imaging (fMRI). However, it is currently unknown how a 12-week aerobic exercise intervention affects resting-state functional connectivity (rsFC) in motor networks. Previous work has shown that over a 6-month or 1-year exercise intervention, older individuals show increased resting state connectivity of the default mode network and the sensorimotor network (Voss et al., 2010b; Flodin et al., 2017). However, the effects of shorter-term 12-week exercise interventions on functional connectivity have received less attention. Method: Thirty-seven sedentary right-handed older adults were randomized to either a 12-week aerobic, spin cycling exercise group or a 12-week balance-toning exercise group. Resting state functional magnetic resonance images were acquired in sessions PRE/POST interventions. We applied seed-based correlation analysis to left and right primary motor cortices (L-M1 and R-M1) and anterior default mode network (aDMN) to test changes in rsFC between groups after the intervention. In addition, we performed a regression analysis predicting connectivity changes PRE/POST intervention across all participants as a function of time spent in aerobic training zone regardless of group assignment. Results: Seeding from L-M1, we found that participants in the cycling group had a greater PRE/POST change in rsFC in aDMN as compared to the balance group. When accounting for time in aerobic HR zone, we found increased heart rate workload was positively associated with increased change of rsFC between motor networks and aDMN. Interestingly, L-M1 to aDMN connectivity changes were also related to motor behavior changes in both groups. Respective of M1 laterality, comparisons of all participants from PRE to POST showed a reduction in the extent of bilateral M1 connectivity after the interventions with increased connectivity in dominant M1. Conclusion: A 12-week physical activity intervention can change rsFC between primary motor regions and default mode network areas, which may be associated with improved motor performance. The decrease in connectivity between L-M1 and R-M1 post-intervention may represent a functional consolidation to the dominant M1. Topic Areas: Neuroimaging, Aging.

33 citations

Journal ArticleDOI
TL;DR: This work aims to establish a calibration plot between blood T2, Y, and hematocrit at 7 T, and using T2‐relaxation‐under‐spin‐tagging MRI, determine human venous blood oxygenation in vivo.
Abstract: Purpose: The calibratable relationship between blood oxygenation (Y) and T2 allows quantification of cerebral venous oxygenation. We aim to establish a calibration plot between blood T2, Y, and hematocrit at 7 T, and using T2-relaxation-underspin-tagging MRI, determine human venous blood oxygenation in vivo. Methods: In vitro experiments were performed at 7 T on bovine blood samples using a Carr-Purcell-Meiboom-Gill-T2 sequence, from which we characterized the relationship among T2, Y, and hematocrit. T2-relaxation-under-spin-tagging MRI was implemented at 7 T to measure venous blood T2 in vivo, from which oxygenation was estimated using the in vitro calibration plot. Hyperoxia was performed to test the sensitivity of the method to oxygenation changes, and the 7 T results were compared with those at 3 T. Results: In vitro data showed that arterial and venous T2 at 7 T are 68 and 20 ms, respectively, at a typical hematocrit of 0.42. In vivo measurement showed a cerebral venous oxygenation of 64.7 6 5.0% and a test-retest coefficient-of-variation of 3.6 6 2.4%. Hyperoxia increased Yv by 9.0 6 1.4% (P ¼ 0.001) and the 3 and 7 T results showed a strong correlation (R ¼ 0.95) across individuals. Conclusion: We provided an in vitro calibration plot for conversion of blood T2 to oxygenation at 7 T and demonstrated its utility in vivo. Magn Reson Med 71:2035–2042, 2014.

33 citations


Cited by
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01 Jan 2016
TL;DR: This book helps people to enjoy a good book with a cup of coffee in the afternoon, instead they juggled with some malicious bugs inside their laptop.
Abstract: Thank you for downloading magnetic resonance imaging physical principles and sequence design. As you may know, people have look numerous times for their chosen books like this magnetic resonance imaging physical principles and sequence design, but end up in harmful downloads. Rather than enjoying a good book with a cup of coffee in the afternoon, instead they juggled with some malicious bugs inside their laptop.

695 citations

Journal ArticleDOI
TL;DR: The use of tDCS in schizophrenia is in the early stages of investigation for relief of symptoms in people who are not satisfied with their response to antipsychotic medication.

434 citations

Journal ArticleDOI
Trey Hedden1
TL;DR: In this article, the authors used the Scaled Subprofile Model (SSM) with MRI voxel-based morphometry (VBM) to identify regionally distributed patterns of brain changes associated with healthy aging.
Abstract: reflect the regionally distributed effects of healthy aging from MCI and AD. Methods: Applications of multivariate network analyses using the Scaled Subprofile Model (SSM; Moeller et al., 1987) with MRI voxelbased morphometry (VBM) will be presented in studies of healthy aging, amnestic MCI, and AD. As a modified form of principal component analysis, the SSM produces regional patterns and corresponding subject scores that reflect an individual’s pattern expression. Bootstrap re-sampling is performed to determine robust regional contributions to the patterns. Results: SSM analyses with MRI VBM have identified regionally distributed patterns of brain changes associated with healthy aging that show reproducible regional features across samples, with regions in the prefrontal cortex appearing most consistently reduced. Application of this MRI multivariate network analysis method in young and old non-human primates further supports the preferential reduction of prefrontal cortex, in a model of healthy aging in which the full complement of AD pathology does not occur. The identified age-related SSM VBM patterns differ from the SSM pattern reflecting the continuum of clinical severity from normal to amnestic MCI to AD, in which medial and lateral temporal reductions are prominent. In addition, greater expression of this AD-related pattern was associated with the subsequent conversion to dementia in individuals with amnestic MCI. Conclusions: Together, these findings illustrate the potential for using multivariate analyses, like SSM, as a complement to univariate analysis methods to characterize regionally distributed brain changes associated with healthy and pathological aging. The use of this analytic approach may enhance early detection and has the potential to aid in the evaluation of treatments in human and non-human animal models of aging and AD.

142 citations

Journal ArticleDOI
TL;DR: In this article, a prospective observational case control study was conducted to compare the flow and T2 of blood in the major fetal vessels and brain imaging findings using MRI, which revealed the expected circulatory redistribution in response to hypoxia.

111 citations

Journal ArticleDOI
TL;DR: Combined FDNIRS–DCS parameters improve the understanding of the underlying physiology and have the potential to serve as bedside biomarkers of treatment response and optimization.
Abstract: Pathophysiologic mechanisms involved in neonatal hypoxic ischemic encephalopathy (HIE) are associated with complex changes of blood flow and metabolism. Therapeutic hypothermia (TH) is effective in reducing the extent of brain injury, but it remains uncertain how TH affects cerebral blood flow (CBF) and metabolism. Ten neonates undergoing TH for HIE and seventeen healthy controls were recruited from the NICU and the well baby nursery, respectively. A combination of frequency domain near infrared spectroscopy (FDNIRS) and diffuse correlation spectroscopy (DCS) systems was used to non-invasively measure cerebral hemodynamic and metabolic variables at the bedside. Results showed that cerebral oxygen metabolism (CMRO2i) and CBF indices (CBFi) in neonates with HIE during TH were significantly lower than post-TH and age-matched control values. Also, cerebral blood volume (CBV) and hemoglobin oxygen saturation (SO2) were significantly higher in neonates with HIE during TH compared with age-matched control neonates. Post-TH CBV was significantly decreased compared with values during TH whereas SO2 remained unchanged after the therapy. Thus, FDNIRS–DCS can provide information complimentary to SO2 and can assess individual cerebral metabolic responses to TH. Combined FDNIRS–DCS parameters improve the understanding of the underlying physiology and have the potential to serve as bedside biomarkers of treatment response and optimization.

105 citations