Karthikeyan Kuppusamy

In vivo measurement of blood oxygen saturation using magnetic resonance imaging: A direct validation of the blood oxygen level-dependent concept in functional brain imaging

A novel noninvasive magnetic resonance imaging (MRI) method was developed to determine in vivo blood oxygen saturation and its changes during motor cortex activation in small cerebral veins. Specifically, based on susceptibility measurements in the resting states, pial veins were found to have a mean oxygen saturation of Yrest = 0.544 ± 0.029 averaged over 14 vessels in 5 volunteers. During activation, susceptibility measurements revealed an oxygen saturation change of ΔYsusc = 0.14 ± 0.02. Independent evaluation from blood flow velocity measurements yielded a value of ΔYflow = 0.14 ± 0.04 for this change. These results validate the blood oxygenation level‐dependent (BOLD) model in functional MRI (fMRI). Hum. Brain Mapping 5:341–346, 1997.

HEMISPHERIC LANGUAGE DOMINANCE IN CHILDREN DEMONSTRATED BY FUNCTIONAL MAGNETIC RESONANCE IMAGING

The objective of this study was to demonstrate hemispheric language dominance in normal children. Fifteen normal children were evaluated with functional magnetic resonance imaging (MRI) using an age-related silent word spelling paradigm. The data were analyzed with the cross-correlation method, and lateralization indices were calculated in language regions as determined by Talairach coordinates. Activation foci were detected in the left inferior frontal area and were strongly lateralized, with language lateralization indices of 0.74 ± 0.21 (age 7-12 years, nine subjects), and 0.79 ± 0.18 (13-18 years, six subjects). The indices were similar to those for adults (0.83 ± 0.21, four subjects). Our study established that language is strongly lateralized to the left hemisphere in children as young as 7 years of age. (J Child Neurol 1999;14:78-82).

Functional Magnetic Resonance Imaging of the Basal Ganglia and Cerebellum Using a Simple Motor Paradigm

Activation of cortical and subcortical motor areas of the brain, including primary motor cortex, supplementary motor area, basal ganglia and cerebellum, were successfully investigated in seven right-handed, normal volunteers during a simple, rapid, thumb flexion-extension task using functional magnetic resonance imaging. A multi-slice echo-planar imaging sequence was used to cover the entire brain. A signal increase varying from 2% to 6% was observed for the different regions involved in the motor task. Moving the non-dominant thumb was associated with a more bilateral activation pattern in both putamen and cerebellar regions. This study demonstrates the capability of functional magnetic resonance imaging to delineate simultaneously many activated brain areas that are commonly thought to be involved in the performance of motor tasks.

Statistical assessment of crosscorrelation and variance methods and the importance of electrocardiogram gating in functional magnetic resonance imaging

Processing of functional magnetic resonance imaging (fMRI) data is a critical step in evaluating experimental results. We address the question of choosing between a Student t-test method, crosscorrelation method, or a weighted z-score method in analyzing functional MR images. We present an analytic analysis that makes it possible to make a statistical decision in setting the threshold for the crosscorrelation coefficient. Specifically, the theory for an receiver operating characteristic (ROC) analysis (description of type I and type II error) has been applied to the crosscorrelation method. Both theoretical predictions as well as model simulations are presented to prove that the crosscorrelation and weighted z-score method have the same statistical power. We introduce the concept of a variance image and use it to not only choose between the correlation image and a simple t-test image but also to obtain a final image that combines the efficient aspects of both the correlation and the simple t-test images. The variance image itself is shown to be an indicator of both patient motion and/or internal physiological motion in the brain. Furthermore, we delineate the importance of electrocardiogram (ECG) gating in reducing the variance in fMRI of human motor cortex.

In Vivo Verification of the Intravascular BOLD Effect

There has been much controversy over the brain/vein debate in functional magnetic resonance imaging (fMRI). Low resolution studies create a broad pattern of signal enhancement upon brain activation which could be from brain or blurred vessels. Our goal is to validate the blood oxygenation level dependent (BOLD) model and its mechanisms in relation to blood flow and susceptibility changes. We investigate the visibility of small vessels in the brain using high spatial resolution. Flow-compensated sequences are used to obtain susceptibility information and velocity-encoded sequences to measure velocities.