Hye Young Heo

Detecting activity-evoked pH changes in human brain

Localized pH changes have been suggested to occur in the brain during normal function. However, the existence of such pH changes has also been questioned. Lack of methods for noninvasively measuring pH with high spatial and temporal resolution has limited insight into this issue. Here we report that a magnetic resonance imaging (MRI) strategy, T1 relaxation in the rotating frame (T1ρ), is sufficiently sensitive to detect widespread pH changes in the mouse and human brain evoked by systemically manipulating carbon dioxide or bicarbonate. Moreover, T1ρ detected a localized acidosis in the human visual cortex induced by a flashing checkerboard. Lactate measurements and pH-sensitive 31P spectroscopy at the same site also identified a localized acidosis. Consistent with the established role for pH in blood flow recruitment, T1ρ correlated with blood oxygenation level-dependent contrast commonly used in functional MRI. However, T1ρ was not directly sensitive to blood oxygen content. These observations indicate that localized pH fluctuations occur in the human brain during normal function. Furthermore, they suggest a unique functional imaging strategy based on pH that is independent of traditional functional MRI contrast mechanisms.

Quantitative assessment of amide proton transfer (APT) and nuclear overhauser enhancement (NOE) imaging with extrapolated semi-solid magnetization transfer reference (EMR) signals: Application to a rat glioma model at 4.7 Tesla.

To quantify amide proton transfer (APT) and nuclear Overhauser enhancement (NOE) contributions to in vivo chemical exchange saturation transfer MRI signals in tumors.

Quantitative assessment of amide proton transfer (APT) and nuclear overhauser enhancement (NOE) imaging with extrapolated semisolid magnetization transfer reference (EMR) signals: II. Comparison of three EMR models and application to human brain glioma at 3 Tesla.

To evaluate the use of three extrapolated semisolid magnetization transfer reference (EMR) methods to quantify amide proton transfer (APT) and nuclear Overhauser enhancement (NOE) signals in human glioma.

Applying amide proton transfer-weighted MRI to distinguish pseudoprogression from true progression in malignant gliomas

To assess amide proton transfer‐weighted (APTW) imaging features in patients with malignant gliomas after chemoradiation and the diagnostic performance of APT imaging for distinguishing true progression from pseudoprogression.

Simultaneous detection and separation of hyperacute intracerebral hemorrhage and cerebral ischemia using amide proton transfer MRI

To explore the capability of amide proton transfer (APT) imaging in the detection of hemorrhagic and ischemic strokes using preclinical rat models.

Quantitative assessment of the effects of water proton concentration and water T1 changes on amide proton transfer (APT) and nuclear overhauser enhancement (NOE) MRI: The origin of the APT imaging signal in brain tumor

To quantify pure chemical exchange–dependent saturation transfer (CEST) related amide proton transfer (APT) and nuclear Overhauser enhancement (NOE) signals in a rat glioma model and to investigate the mixed effects of water content and water T1 on APT and NOE imaging signals.

Whole‐brain amide proton transfer (APT) and nuclear overhauser enhancement (NOE) imaging in glioma patients using low‐power steady‐state pulsed chemical exchange saturation transfer (CEST) imaging at 7T

To explore the relationship of amide proton transfer (APT) and nuclear Overhauser enhancement (NOE) signal intensities with respect to different World Health Organization (WHO) brain tumor grades (II to IV) at 7T.

Insight into the quantitative metrics of chemical exchange saturation transfer (CEST) imaging.

To evaluate the reliability of four CEST imaging metrics for brain tumors, at varied saturation power levels and magnetic field strengths (3−9.4 Tesla (T)).

Accelerating chemical exchange saturation transfer (CEST) MRI by combining compressed sensing and sensitivity encoding techniques

To evaluate the feasibility of accelerated chemical‐exchange‐saturation‐transfer (CEST) imaging using a combination of compressed sensing (CS) and sensitivity encoding (SENSE) at 3 Tesla.

Selecting the reference image for registration of CEST series.

To compare different reference images selected for registration among chemical exchange saturation transfer (CEST) series.