J. Helpern - Academia.edu (original) (raw)

Papers by J. Helpern

Biochemical Society Transactions, 2000

Magnetic Resonance in Medicine, 1995

A method of correcting motional artifacts in diffusionweighted images is described. Motion causes... more A method of correcting motional artifacts in diffusionweighted images is described. Motion causes changes in the phase of the k-space NMR signal and thereby introduces positional shifts (or ghosts) in the spatial domain. By correcting the phase of the NMR signal before Fourier transformation, the image sharpness is greatly enhanced. The new method measures the phases of the NMR signal once and stores this phase information in a phase map. Subsequent images with motional artifacts are corrected during postprocessing using this reference phase map.

Brain and Behavior

This is an open access article under the terms of the Creative Commons Attribution License, which... more This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

PURPOSE Although medial temporal lobe epilepsy (MTLE) is a common neurological disorder, there re... more PURPOSE Although medial temporal lobe epilepsy (MTLE) is a common neurological disorder, there remains a lack of reliable biomarkers for monitoring its clinical course and treatment response. Diffusion MRI (dMRI) tractography is a unique and powerful tool for characterization of white matter (WM) connectivity and may provide entirely new insights into network abnormalities associated with MTLE. The goals of this study were to investigate WM connectivity changes in MTLE, and to evaluate the association between these alterations and disease severity (seizure frequency) in patients. METHOD AND MATERIALS Nineteen patients with MTLE and 28 age- and sex-matched healthy control subjects underwent dMRI scans. Patients were divided into a well-controlled (≤ 4 seizures a year) and a poorly controlled subgroup based on their response to antiepileptic drug therapy. The two subgroups did not significantly differ in terms of age, age of seizure onset, or duration of disease. Streamline tractograp...

Radiology, 1992

The authors investigated early human focal ischemia with phosphorus-31 nuclear magnetic resonance... more The authors investigated early human focal ischemia with phosphorus-31 nuclear magnetic resonance spectroscopy at 1.89 T to characterize the temporal evolution and relationship of brain pH and phosphate energy metabolism. Data from 65 symptomatic patients were prospectively studied; none of the patients had had ischemic stroke in the internal carotid artery territory before. Twenty-eight neurologically normal individuals served as control subjects. Serial ischemic brain pH levels indicated a progression from early acidosis to subacute alkalosis. When acidosis was present there was a significant elevation in the relative signal intensity of inorganic phosphate (Pi) and significant reductions in signal intensities of alpha-adenosine triphosphate (ATP) and gamma-ATP compared with those of control subjects. Ischemic brain pH values directly correlated with the relative signal intensity of phosphocreatine (PCr) and the PCr index and inversely correlated with the signal intensity of Pi. There was a general lack of correlation between either ischemic brain pH or phosphate energy metabolism and the initial clinical stroke severity. The data suggest a link between high-energy phosphate metabolism and brain pH, especially during the period of ischemic brain acidosis, and the authors propose that effective acute stroke therapy should be instituted during this period.

Proceedings of the National Academy of Sciences, 2014

NMR in Biomedicine, 1989

Dysprosium(III) triethylenetraamine-N,N,N',N",N"',N"&a... more Dysprosium(III) triethylenetraamine-N,N,N',N",N"',N"'-hexaacetic acid (DyTTHA3-) was used as an aqueous chemical shift reagent in conjunction with high-resolution nuclear magnetic resonance (NMR) spectroscopy to monitor 87-rubidium (87Rb+) transport in human erythrocyte suspensions. NMR spectra demonstrated two resonances which were assigned to the intra- and extracellular compartments of the erythrocyte suspension. Uptake of 87Rb+ was shown to proceed via the [Na,K]-ATPase dependent pump as evidenced by the inhibition of uptake in the presence of ouabain. The steady state intra- to extracellular concentration ratio of 87Rb was 3.00 and 1.13 in the absence and presence of ouabain, respectively. The rate of uptake of 87Rb+ in the absence and presence of ouabain was found to be 1.3 and 0.5 mmol Rb+/L erythrocytes/h at 18 mM Rb+, respectively. Data are also presented which indicate that the intracellular component of 87Rb is less than 100% NMR visible.

NMR in Biomedicine, 2012

We present high-resolution anatomical imaging of the cervical spinal cord in healthy volunteers a... more We present high-resolution anatomical imaging of the cervical spinal cord in healthy volunteers at the ultrahigh field of 7 T with a prototype four-channel radiofrequency coil array, in comparison with 3-T imaging of the same subjects. Signal-to-noise ratios at both field strengths were estimated using the rigorous Kellman method. Spinal cord cross-sectional area measurements were performed, including whole-cord measurements at both fields and gray matter segmentation at 7 T. The 7-T array coil showed reduced sagittal coverage, comparable axial coverage and the expected significantly higher signal-to-noise ratio compared with equivalent 3-T protocols. In the cervical spinal cord, the signal-to-noise ratio was found by the Kellman method to be higher by a factor of 3.5 with the 7-T coil than with standard 3-T coils. Cervical spine imaging in healthy volunteers at 7 T revealed not only detailed white/gray matter differentiation, but also structures not visualized at lower fields, such as denticulate ligaments, nerve roots and rostral-caudal blood vessels. Whole-cord cross-sectional area measurements showed good agreement at both field strengths. The measurable gray/white matter cross-sectional areas at 7 T were found to be comparable with reports from histology. These pilot data demonstrate the use of higher signal-to-noise ratios at the ultrahigh field of 7 T for significant improvement in anatomical resolution of the cervical spinal cord, allowing the visualization of structures not seen at lower field strength, particularly for axial imaging.

Neurosurgery, 1991

1H Magnetic resonance imaging (MRI) was used to study the effects of photodynamic therapy (PDT) o... more 1H Magnetic resonance imaging (MRI) was used to study the effects of photodynamic therapy (PDT) on normal rat brain (n = 5) using T1-, T2-, diffusion-, and proton density (rho)-weighted images. Rats received intraperitoneal injections of 12.5 mg/kg of Photofrin II, and 48 hours later the dural area over the frontal cortex was treated with 35 J/cm2 of light (632 +/- 1 nm). The T1-, T2-, and diffusion-weighted images revealed an evolving high contrast region of brain that corresponded to the PDT-treated area. Lesioned brain exhibited significant increases in T1 and T2 relaxation times at 1 day (P less than 0.01) and 3 days (T1, P = 0.018; T2, P less than 0.01) after treatment, compared with the contralateral equivalent volume of nonlesioned brain. Water proton diffusion coefficient (DW) in the lesioned area decreased at 1 day (P = 0.026) and increased at 3 days (P = 0.012) compared with nonlesioned brain. An increase in the proton density ratio (rho D/rho O) from PDT (rho D) versus nonlesioned side (rho O) was found 3 days after PDT treatment (P = 0.03). The data indicate that the biophysical parameters obtained from magnetic resonance imaging scans, T1, T2, DW, and proton density, can be used to monitor changes in an evolving photochemically induced lesion.

Neurology, 2013

Objectives: The objective of this study was to evaluate whether patients with surgically refracto... more Objectives: The objective of this study was to evaluate whether patients with surgically refractory medial temporal lobe epilepsy (MTLE) exhibit a distinct pattern of structural network organization involving the temporal lobes and extratemporal regions. Methods: We retrospectively studied 18 healthy controls and 20 patients with medication refractory unilateral MTLE who underwent anterior temporal lobectomy for treatment of seizures. Patients were classified as seizure-free or not seizure-free at least 1 year after surgery. The presurgical brain connectome was calculated through probabilistic connectivity from MRI-diffusion tensor imaging from 83 anatomically defined regions of interest encompassing the whole brain. The connectivity patterns were analyzed regarding group differences in regional connectivity and network graph properties. Results: Compared with controls, patients exhibited a decrease in connectivity involving ipsilateral thalamocortical regions, with a pathologic increase in ipsilateral medial temporal lobe, insular, and frontal connectivity. Among patients, those not seizure-free exhibited a higher connectivity between structures in 1) the ipsilateral medial and lateral temporal lobe, 2) the ipsilateral medial temporal and parietal lobe, and 3) the contralateral temporal pole and parietal lobe. Patients not seizure-free also exhibited lower small-worldness in the subnetwork within the ipsilateral temporal lobe, with higher subnetwork integration at the expense of segregation. Conclusions: MTLE is associated with network rearrangement within, but not restricted to, the temporal lobe ipsilateral to the onset of seizures. Networks involving key components of the medial temporal lobe and structures traditionally not removed during surgery may be associated with seizure control after surgical treatment of MTLE. Neurology ® 2013;81:1704-1710 GLOSSARY DWI 5 diffusion-weighted image; FDT 5 FMRIB's Diffusion Toolbox; MTLE 5 medial temporal lobe epilepsy; MUSC 5 Medical University of South Carolina; ROI 5 region of interest.

Neurology, 1989

We used in vivo phosphorus 31 nuclear magnetic resonance (31P NMR) spectroscopy to study regional... more We used in vivo phosphorus 31 nuclear magnetic resonance (31P NMR) spectroscopy to study regional high-energy phosphate and phospholipid metabolism in brains of patients with dementia associated with probable Alzheimer&amp;#39;s disease (AD) and multiple subcortical cerebral infarctions (MSID). The MSID patients demonstrated elevations of the phosphocreatine (PCr)/inorganic orthophosphate (Pi) ratio in both the temporoparietal and frontal regions. Phosphomonoesters (PME) and the ratio of PME to phosphodiesters were elevated in the temporoparietal region of AD. Pi was also elevated in the frontal and temporoparietal regions of AD. Findings from 31P NMR were accurate in distinguishing MSID from AD. Values of PCr/Pi accurately classified 100% of the MSID patients and 92% of AD. Pi and PME, considered jointly, also accurately classified all MSID and all but 1 AD. Findings from in vivo 31P NMR spectroscopy appear to yield metabolic profiles useful in distinguishing AD from MSID.

Magnetic Resonance in Medicine, 2005

Quantitative determination of cerebral blood volume (CBV) is important for understanding brain ph... more Quantitative determination of cerebral blood volume (CBV) is important for understanding brain physiology and pathophysiology. In this work, a novel approach is presented for accurate measurement of absolute CBV (aCBV) using vascular-space-occupancy (VASO) MRI, a blood-nulling pulse sequence, in combination with the T(1) shortening property of Gd-DTPA. Two VASO images with identical imaging parameters are acquired before and after contrast agent injection, resulting in a subtracted image that reflects the amount of blood present in the brain, i.e., CBV. With an additional normalizing factor, aCBV in units of milliliters of blood per 100 mL of brain can be estimated. Experimental results at 1.5 and 3 T systems showed that aCBV maps with high spatial resolution can be obtained with high reproducibility. The averaged aCBV values in gray and white matter were 5.5 +/- 0.2 and 1.4 +/- 0.1 mL of blood/100 mL of brain, respectively. Compared to dynamic susceptibility contrast techniques, VASO MRI is based upon a relatively straightforward theory and the calculation of CBV does not require measurement of an arterial input function. In comparison with previous pre/postcontrast difference approaches, VASO MRI provides maximal signal difference between pre- and postcontrast situation and does not require the use of whole blood for signal normalization.

Magnetic Resonance in Medicine, 1994

Magnetic Resonance in Medicine, 1989

3'P NMR spectroscopy was used to monitor the metabolic response ofthe tibialis anterior muscle gr... more 3'P NMR spectroscopy was used to monitor the metabolic response ofthe tibialis anterior muscle group to transcutaneous nerve stimulation of the peroneal nerve at a rate of 4 Hz for 5 min in human volunteers (n = 8). It is demonstrated that this technique can be used as a method of investigating effort-free and compensation-independent skeletal mUSCk exercise.

Magnetic Resonance in Medicine, 2009

The magnetic field correlation (MFC) at an applied field level of 3 T was estimated by means of M... more The magnetic field correlation (MFC) at an applied field level of 3 T was estimated by means of MRI in several brain regions for 21 healthy human adults and one subject with aceruloplasminemia. For healthy subjects, highly elevated MFC values compared to surrounding tissues were found within the basal ganglia. These are argued as being primarily the result of microscopic magnetic field inhomogeneities generated by non-heme brain iron. The MFC in the aceruloplasminemia subject was significantly higher than for healthy adults in the globus pallidus, thalamus and frontal white matter, consistent with the known increased brain iron concentration associated with this disease.

Magnetic Resonance Imaging, 1991

Magnetic Resonance Imaging, 2001

Magnetic Resonance Imaging, 1984

Cephalalgia, 1988

The intracellular pH (pHi) of cerebral cortex was measured in migraine patients by use of in vivo... more The intracellular pH (pHi) of cerebral cortex was measured in migraine patients by use of in vivo phosphorus-31 NMR spectroscopy. No changes in pHi were measured during a migraine attack. The long-standing concept that the headache of migraine is due to cerebral vaso-dilatation induced by prodromal vasospasm-induced ischemic acidosis is not substantiated.