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Papers by Michael Smith

Research paper thumbnail of Predicting Hiring Managers' Intentions to Use I.T. Certification in the Selection Process

International Journal of Information Technology and Management, 2005

Individuals applying for jobs differ in terms of knowledge, skills, abilities and other character... more Individuals applying for jobs differ in terms of knowledge, skills, abilities and other characteristics, which challenges managers to assess the capabilities of candidates. Certification is used in some Information Technology fields to ensure that job candidates possess certain knowledge and proficiencies. This research investigates the factors that influence a given hir- ing manager's intention to use IT certification as part

Research paper thumbnail of A framework of the use of certifications by hiring personnel in it hiring decisions

ACM SIGMIS Database, 2010

IT certification represents a common and growing practice with significant implications for manag... more IT certification represents a common and growing practice with significant implications for managing in-house IT workers and outsourcing contracts. Prior research is of limited value in understanding its use in common personnel decisions, such as hiring, and its role in the IS profession because of possible sponsor bias, conflicting findings, and inattention to the hiring process or the value of

Research paper thumbnail of Predicting the Intention of Undergraduate IS Students to Earn IT Certification

proc.isecon.org

IT/IS hiring managers have indicated that they may use certification to differentiate between job... more IT/IS hiring managers have indicated that they may use certification to differentiate between job candidates with similar levels of education and experience. Some studies and salary surveys have indicated that certified employees make more money and bonuses than noncertified workers. Despite the obvious benefits, some IS students choose not to pursue certification. This study will use the Theory of Planned Behavior to identify the factors that influence students' intentions to earn an IS-related certification. The different effects of cognitive beliefs and affect (feelings) will be explored. Results will be compared to those of a similar study of hiring managers to identify differences.

Research paper thumbnail of Neuroinflammation and Both Cytotoxic and Vasogenic Edema Are Reduced in Interleukin-1 Type 1 Receptor-Deficient Mice Conferring Neuroprotection

Stroke, 2005

Background and Purpose-Interleukin-1 (IL-1) is a proinflammatory cytokine implicated in multiple ... more Background and Purpose-Interleukin-1 (IL-1) is a proinflammatory cytokine implicated in multiple neurodegenerative diseases, including stroke. However, to date, there is no consensus regarding which receptor(s) mediates the detrimental effects of IL-1. We hypothesized that abrogating IL-1 type 1 receptor (IL-1R1) signaling would reduce edema, chemokine expression, and leukocyte infiltration; lower levels of iNOS; and, consequently, decrease free radical damage after mild hypoxia/ischemia (H/I), thus preserving brain cells. Methods-IL-1R1 null mice and wild-type mice were subjected to a mild H/I insult. MRI was used to measure the area affected at 30 minutes and 48 hours after H/I. An RNAse protection assay was used to evaluate changes in chemokine mRNA expression. RT-PCR was used to assess inducible nitric oxide synthase (iNOS) and endothelial nitric oxide synthase mRNA levels. Immunohistochemistry was used to assess leukocyte infiltration. Western blots were used to assess iNOS and glutamate aspartate transporter protein levels. Results-IL-1R1 null mice had reduced cytotoxic and vasogenic edema. The volume of hyperintense signal on T 2 -weighted images was reduced on average by 90% at 48 hours after H/I. The induction of multiple chemokine mRNAs was significantly reduced in IL-1R1 null mice compared with wild-type mice at 18 and 72 hours after H/I, which correlated with fewer infiltrating CD3ϩ leukocytes. Levels of iNOS protein and mRNA (but not glutamate aspartate transporter) were significantly reduced in the IL-1R1 mouse brain. Conclusions-These findings indicate that abrogating IL-1R1 signaling could protect brain cells subsequent to a mild stroke by reducing edema and immune cell recruitment, as well as by limiting iNOS-mediated free radical damage. (Stroke. 2005;36:2226-2231.)

Research paper thumbnail of Increased Plasma Beta-Hydroxybutyrate, Preserved Cerebral Energy Metabolism, and Amelioration of Brain Damage During Neonatal Hypoxia Ischemia with Dexamethasone Pretreatment

Pediatric Research, 2000

Dexamethasone (DEX) pretreatment has been shown to be neuroprotective in a neonatal rat model of ... more Dexamethasone (DEX) pretreatment has been shown to be neuroprotective in a neonatal rat model of hypoxia ischemia (HI). The exact mechanism of this neuroprotection is still unknown. This study used 31 P nuclear magnetic resonance spectroscopy to monitor energy metabolism during a 3-h episode of HI in 7-d-old rat pups in one of two groups. The first group was pretreated with 0.1 mL saline (i.p.) and the second group was treated with 0.1 mL of 0.1mg/kg DEX (i.p.) 22 h before HI. Animals pretreated with DEX had elevated nucleoside triphosphate and phosphocreatine levels during HI when compared with controls. Salinetreated animals had significant decreases in nucleoside triphosphate and phosphocreatine and increases in inorganic phosphate over this same period. 31 P nuclear magnetic resonance data unequivocally demonstrate preservation of energy metabolism during HI in neonatal rats pretreated with DEX. Animals pretreated with DEX had little or no brain damage following 3 h of HI when compared with matched controls, which experienced severe neuronal loss and cortical infarction. These same pretreated animals had an increase in blood beta-hydroxybutyrate levels before ischemia, suggesting an increase in ketone bodies, which is the neonate's primary energy source. Elevation of ketone bodies appears to be one of the mechanisms by which DEX pretreatment provides neuroprotection during HI in the neonatal rat. Abbreviations DEX, dexamethasone HI, hypoxia ischemia NTP, nucleoside triphosphate NMR, nuclear magnetic resonance NMRS, nuclear magnetic resonance spectroscopy BHB, beta-hydroxybutyrate D-␤-HBA, D-␤-hydroxybutyrate dehydrogenase ABSTRACT 248

Research paper thumbnail of Regional activation in the rat brain during visceral stimulation detected by c-fos expression and fMRI

Neurogastroenterology and Motility, 2005

Aim: The aim of the study was to determine and compare the areas of brain activated in response t... more Aim: The aim of the study was to determine and compare the areas of brain activated in response to colorectal distention (CRD) using functional magnetic resonance imaging (fMRI) and c-fos protein expression. Methods: For fMRI study (3.0 T magnet), anaesthetized rats underwent phasic CRD, synchronized with fMRI acquisition. Stimulation consisted of eight cycles of balloon deflation (90 s) and inflation (30 s), at 40, 60 or 80 mmHg of pressure. For c-fos study two sets of experiments were performed on anaesthetized rats: comparing (A) brain activation in rats with the inserted colorectal balloon (n ¼ 5), to the rats without the balloon (n ¼ 5); and (B) rats with inserted balloon (n ¼ 10), to the rats with inserted and distended balloon (n ¼ 10). The pressure of 80 mmHg was applied for 2 h of 30 s inflation and 90 s deflation, alternating cycles. Results: Functional MRI revealed significant activation in the amygdala, hypothalamus, thalamus, cerebellum and hippocampus. Significant increase in c-fos expression was observed in amygdala and thalamus in the first set of experiments, and hypothalamus and parabrachial nuclei in the second. Conclusion: The two methods are not interchangeable but appeared to be complementary: fMRI was more sensitive, whereas c-fos had much greater resolution.

Research paper thumbnail of Progress in high field MRI at the University of Florida

Magma: Magnetic Resonance Materials in Physics, Biology, and Medicine, 2001

In this article we report on progress in high magnetic field MRI at the University of Florida in ... more In this article we report on progress in high magnetic field MRI at the University of Florida in support of our new 750MHz wide bore and 11.7T/40cm MR instruments. The primary emphasis is on the associated rf technology required, particularly high frequency volume and phased array coils. Preliminary imaging results at 750MHz are presented. Our results imply that the pursuit of even higher fields seems warranted.

Research paper thumbnail of Three-dimensional mapping of the static magnetic field inside the human head

Magnetic Resonance in Medicine, 1996

Finite element analysis was used to calculate the static magnelic field within the three-dimensio... more Finite element analysis was used to calculate the static magnelic field within the three-dimensional head model. Localized field distributions were evaluated by using the magnetic field histogram technique. Experimental field maps and histograms of ithe human head were also obtained to validate the simulation results. Field deviations and gradients inside the human head cause NMR signal frequency shifts and line broadening, respectively. Voxels 2 x 2 x 0.5 cm may have frequency diflerences of more than 2.0 ppm. The linewidth of a single voxeel may be broadened by more than 0.5 ppm. Calculated and experimental field maps are in excellent agreement. The global field distortion in the human head is primarily due to the susceptibility difference between air and tissues and their corresponding geometrical shapes.

Research paper thumbnail of Consideration of magnetically-induced and conservative electric fields within a loaded gradient coil

Magnetic Resonance in Medicine, 2006

We present a method to calculate the electric (E)-fields within and surrounding a human body in a... more We present a method to calculate the electric (E)-fields within and surrounding a human body in a gradient coil, including E-fields induced by the changing magnetic fields and "conservative" E-fields originating with the scalar electrical potential in the coil windings. In agreement with previous numerical calculations, it is shown that magnetically-induced E-fields within the human body show no real concentration near the surface of the body, where nerve stimulation most often occurs. Both the magnetically-induced and conservative E-fields are shown to be considerably stronger just outside the human body than inside it, and under some circumstances the conservative Efields just outside the body can be much larger than the magnetically-induced E-fields there. The order of gradient winding and the presence of conductive RF shield can greatly affect the conservative E-field distribution in these cases. Though the E-fields against the outer surface of the body are not commonly considered, understanding gradient E-fields may be important for reasons other than peripheral nerve stimulation (PNS), such as potential interaction with electrical equipment. Magn Reson Med 55:1424 -1432, 2006.

Research paper thumbnail of A method to create an optimum current distribution and homogeneous B1 field for elliptical birdcage coils

Magnetic Resonance in Medicine, 1997

For a birdcage coil with elliptical cross-section, a sinusoidal current pattern does not provide ... more For a birdcage coil with elliptical cross-section, a sinusoidal current pattern does not provide a homogeneous B, field. A simple theory was developed to create an optimized current distribution for elliptical birdcage coils. This optimized current pattern can create a perfectly homogeneous 8, field inside any elliptical shape. To verify the theory, a 16-element highpass elliptical birdcage coil was built inside a circular RF shield. The current was optimized by using the inductance characteristics of the coil components to calculate the endring capacitances. The B, field was theoretically calculated and experimentally mapped for the optimized elliptical birdcage coil and a nonoptimized coil. The results demonstrate that by optimizing the current distribution, a very homogeneous B, field is produced. This method can be directly applied in design and construction of elliptical birdcage coils for imaging of the naturally occurring elliptical cross-sectional geometries in the human body.

Research paper thumbnail of A computer simulation of the static magnetic field distribution in the human head

Magnetic Resonance in Medicine, 1995

Distortion of the static magnetic field inside the human head is dependent on regional tissue sus... more Distortion of the static magnetic field inside the human head is dependent on regional tissue susceptibility variations and geometrical shape. These effects result in resonance line broadening and frequency shifts and consequently, intensity and spatial errors in both magnetic resonance imaging (MRI) and magnetic resonance (MR) spectroscopy. To calculate the field distortion due to the susceptibility's geometry, two dimensional (2D) finite element analysis was applied to simulate the field distribution in a 2D model of the human head, placed in a uniform magnetic field. The model contains air-filled cavities and sinuses, and the remainder is treated as water. The magnetic field deviation was evaluated using gray scale plots and histograms of the magnetic field. The shifts in parts/ million and broadening of the histograms correspond to the NMR of the sampled region. The field distribution of the human head was also experimentally mapped using the DANTE tagging sequence. The calculated and experimental field maps are in good agreement. Thus, geometric considerations with uniform susceptibilities are sufficient to explain most of the static magnetic field distribution in the human head.

Research paper thumbnail of Different excitation and reception distributions with a single-loop transmit-receive surface coil near a head-sized spherical phantom at 300 MHz

Magnetic Resonance in Medicine, 2002

Calculations and experiments were used to examine the B 1 field behavior and signal intensity dis... more Calculations and experiments were used to examine the B 1 field behavior and signal intensity distribution in a 16-cm diameter spherical phantom excited by a 10-cm diameter surface coil at 300 MHz. In this simple system at this high frequency very complex RF field behavior exists, resulting in different excitation and reception distributions. Included in this work is a straightforward demonstration that coil receptivity is proportional to the magnitude of the circularly polarized component of the B 1 field that rotates in the direction opposite to that of nuclear precession. It is clearly apparent that even in very simple systems in head-sized samples at this frequency it is important to consider the separate excitation and reception distributions in order to understand the signal intensity distribution. Magn Reson Med 47:1026 -1028, 2002.

Research paper thumbnail of 7T vs. 4T: RF power, homogeneity, and signal-to-noise comparison in head images

Magnetic Resonance in Medicine, 2001

Signal-to-noise ratio (SNR), RF field (B 1 ), and RF power requirement for human head imaging wer... more Signal-to-noise ratio (SNR), RF field (B 1 ), and RF power requirement for human head imaging were examined at 7T and 4T magnetic field strengths. The variation in B 1 magnitude was nearly twofold higher at 7T than at 4T (ϳ42% compared to ϳ23%). The power required for a 90°pulse in the center of the head at 7T was approximately twice that at 4T. The SNR averaged over the brain was at least 1.6 times higher at 7T compared to 4T. These experimental results were consistent with calculations performed using a human head model and Maxwell's equations. Magn Reson Med 46:24 -30, 2001.

Research paper thumbnail of Direct magnetic resonance imaging of histological tissue samples at 3.0T

Magnetic Resonance in Medicine, 2007

Direct imaging of a histological slice is challenging. The vast difference in dimension between p... more Direct imaging of a histological slice is challenging. The vast difference in dimension between planar size and the thickness of histology slices would require an RF coil to produce a uniform RF magnetic (B1) field in a 2D plane with minimal thickness. In this work a novel RF coil designed specifically for imaging a histology slice was developed and tested. The experimental data demonstrate that the coil is highly sensitive and capable of producing a uniform B1 field distribution in a planar region of histological slides, allowing for the acquisition of high-resolution T2 images and T2 maps from a 60-microm-thick histological sample. The image intensity and T2 distributions were directly compared with histological staining of the relative iron concentration of the same slice. This work demonstrates the feasibility of using a microimaging histological coil to image thin slices of pathologically diseased tissue to obtain a precise one-to-one comparison between stained tissue and MR images.

Research paper thumbnail of Analysis of wave behavior in lossy dielectric samples at high field

Magnetic Resonance in Medicine, 2002

Radiofrequency (RF) field wave behavior and associated nonuniform image intensity at high magneti... more Radiofrequency (RF) field wave behavior and associated nonuniform image intensity at high magnetic field strengths are examined experimentally and numerically. The RF field produced by a 10-cm-diameter surface coil at 300 MHz is evaluated in a 16-cm-diameter spherical phantom with variable salinity, and in the human head. Temporal progression of the RF field indicates that the standing wave and associated dielectric resonance occurring in a pure water phantom near 300 MHz is greatly dampened in the human head due to the strong decay of the electromagnetic wave. The characteristic image intensity distribution in the human head is the result of spatial phase distribution and amplitude modulation by the interference of the RF traveling waves determined by a given sample-coil configuration. The numerical calculation method is validated with experimental results. The general behavior of the RF field with respect to the average brain electrical properties in a frequency range of 42-350 MHz is also analyzed. Magn Reson Med 47: 982-989, 2002.

Research paper thumbnail of Radio frequency magnetic field mapping of a 3 Tesla birdcage coil: Experimental and theoretical dependence on sample properties

Magnetic Resonance in Medicine, 2001

The RF B 1 distribution was studied, theoretically and experimentally, in phantoms and in the hea... more The RF B 1 distribution was studied, theoretically and experimentally, in phantoms and in the head of volunteers using a 3 T MRI system equipped with a birdcage coil. Agreement between numerical simulation and experiment demonstrates that B 1 distortion at high field can be explained with 3D full-Maxwell calculations. It was found that the B 1 distribution in the transverse plane is strongly dependent on the dielectric properties of the sample. We show that this is a consequence of RF penetration effects combined with RF standing wave effects. In contrast, along the birdcage coil z-axis the B 1 distribution is determined mainly by the coil geometry. In the transverse plane, the region of B 1 uniformity (within 10% of the maximum) was 15 cm with oil, 6 cm with distilled water, 11 cm with saline, and 10 cm in the head. Along z the B 1 uniformity was 9 cm with phantoms and 7 cm in the head. Magn Reson Med 46:379 -385, 2001.

Research paper thumbnail of Multi-gradient echo with susceptibility inhomogeneity compensation (MGESIC): Demonstration offMRI in the olfactory cortex at 3.0 T

Magnetic Resonance in Medicine, 1997

Short image acquisition times and sensitivity to magnetic susceptibility favor the use of gradien... more Short image acquisition times and sensitivity to magnetic susceptibility favor the use of gradient echo imaging methods in functional MRI (fMRI). However, magnetic susceptibility effects attributed to air-tissue interfaces also lead to severe signal loss in images of the large inferior frontal and lateral temporal cortices of the human brain, which renders these regions inaccessible to IMRI. The signal loss is caused by the local field gradients in the slice selection direction. A multigradient echo with magnetic susceptibility inhomogeneity compensation method (MGESIC) is proposed to overcome this problem. The MGESIC method effectively corrects the susceptibility artifacts and maintains the advantages of gradient echo methods to both BOLD sensitivity and fast image acquisition. The effectiveness of the MGESIC method is demonstrated by f MRI experimental results within the olfactory cortex.

Research paper thumbnail of B1 destructive interferences and spatial phase patterns at 7 T with a head transceiver array coil

Magnetic Resonance in Medicine, 2005

RF behavior in the human head becomes complex at ultrahigh magnetic fields. A bright center and a... more RF behavior in the human head becomes complex at ultrahigh magnetic fields. A bright center and a weak periphery are observed in images obtained with volume coils, while surface coils provide strong signal in the periphery. Intensity patterns reported with volume coils are often loosely referred to as "dielectric resonances," while modeling studies ascribe them to superposition of traveling waves greatly dampened in lossy brain tissues, raising questions regarding the usage of this term. Here we address this question experimentally, taking full advantage of a transceiver coil array that was used in volume transmit mode, multiple receiver mode, or single transmit surface coil mode. We demonstrate with an appropriately conductive sphere phantom that destructive interferences are responsible for a weak B(1) in the periphery, without a significant standing wave pattern. The relative spatial phase of receive and transmit B(1) proved remarkably similar for the different coil elements, although with opposite rotational direction. Additional simulation data closely matched our phantom results. In the human brain the phase patterns were more complex but still exhibited similarities between coil elements. Our results suggest that measuring spatial B(1) phase could help, within an MR session, to perform RF shimming in order to obtain more homogeneous B(1) in user-defined areas of the brain.

Research paper thumbnail of Polarization of the RF field in a human head at high field: A study with a quadrature surface coil at 7.0 T

Magnetic Resonance in Medicine, 2002

The RF field intensity distribution in the human brain becomes inhomogeneous due to wave behavior... more The RF field intensity distribution in the human brain becomes inhomogeneous due to wave behavior at high field. This is further complicated by the spatial distribution of RF field polarization that must be considered to predict image intensity distribution. An additional layer of complexity is involved when a quadrature coil is used for transmission and reception. To study such complicated RF field behavior, a computer modeling method was employed to investigate the RF field of a quadrature surface coil at 300 MHz. Theoretical and experimental results for a phantom and the human head at 7.0 T are presented. The results are theoretically important and practically useful for high-field quadrature coil design and application. Magn Reson Med 48:362-369, 2002.

Research paper thumbnail of Hexagonal zero mode TEM coil: A single-channel coil design for imaging multiple small animals

Magnetic Resonance in Medicine, 2005

A novel hexagonal coil design for simultaneous imaging of multiple small animals is presented. Th... more A novel hexagonal coil design for simultaneous imaging of multiple small animals is presented. The design is based on a coaxial cavity and utilizes the magnetic field formed between two coaxial conductors with hexagonal cross-sections. An analytical solution describing the B(1) field between conductors of the hexagonal coil was found from the Biot-Savart law. Both experimental results and analytical calculations showed a variation in the B(1) field within the imaging region of less than 10%. Numerical calculations predicted approximately 35% improvement in B(1) field homogeneity with the hexagonal coil design compared to a cylindrical coaxial cavity design. The experimentally-measured signal-to-noise ratio (SNR) of the hexagonal coil loaded with six 50-mM phantoms was only 4-5% lower than that of a single parallel plate resonator loaded with one phantom. In vivo spin-echo (SE) images of six 7-day-old rat pups acquired simultaneously demonstrated sufficient SNR for microimaging. The construction scheme of the coil, simple methods for tuning and matching, and an anesthesia device and animal holder designed for the coil are described. The hexagonal coil design utilizes a single receiver and allows for simultaneous imaging of six small animals with no significant compromise in SNR.

Research paper thumbnail of Predicting Hiring Managers' Intentions to Use I.T. Certification in the Selection Process

International Journal of Information Technology and Management, 2005

Individuals applying for jobs differ in terms of knowledge, skills, abilities and other character... more Individuals applying for jobs differ in terms of knowledge, skills, abilities and other characteristics, which challenges managers to assess the capabilities of candidates. Certification is used in some Information Technology fields to ensure that job candidates possess certain knowledge and proficiencies. This research investigates the factors that influence a given hir- ing manager's intention to use IT certification as part

Research paper thumbnail of A framework of the use of certifications by hiring personnel in it hiring decisions

ACM SIGMIS Database, 2010

IT certification represents a common and growing practice with significant implications for manag... more IT certification represents a common and growing practice with significant implications for managing in-house IT workers and outsourcing contracts. Prior research is of limited value in understanding its use in common personnel decisions, such as hiring, and its role in the IS profession because of possible sponsor bias, conflicting findings, and inattention to the hiring process or the value of

Research paper thumbnail of Predicting the Intention of Undergraduate IS Students to Earn IT Certification

proc.isecon.org

IT/IS hiring managers have indicated that they may use certification to differentiate between job... more IT/IS hiring managers have indicated that they may use certification to differentiate between job candidates with similar levels of education and experience. Some studies and salary surveys have indicated that certified employees make more money and bonuses than noncertified workers. Despite the obvious benefits, some IS students choose not to pursue certification. This study will use the Theory of Planned Behavior to identify the factors that influence students' intentions to earn an IS-related certification. The different effects of cognitive beliefs and affect (feelings) will be explored. Results will be compared to those of a similar study of hiring managers to identify differences.

Research paper thumbnail of Neuroinflammation and Both Cytotoxic and Vasogenic Edema Are Reduced in Interleukin-1 Type 1 Receptor-Deficient Mice Conferring Neuroprotection

Stroke, 2005

Background and Purpose-Interleukin-1 (IL-1) is a proinflammatory cytokine implicated in multiple ... more Background and Purpose-Interleukin-1 (IL-1) is a proinflammatory cytokine implicated in multiple neurodegenerative diseases, including stroke. However, to date, there is no consensus regarding which receptor(s) mediates the detrimental effects of IL-1. We hypothesized that abrogating IL-1 type 1 receptor (IL-1R1) signaling would reduce edema, chemokine expression, and leukocyte infiltration; lower levels of iNOS; and, consequently, decrease free radical damage after mild hypoxia/ischemia (H/I), thus preserving brain cells. Methods-IL-1R1 null mice and wild-type mice were subjected to a mild H/I insult. MRI was used to measure the area affected at 30 minutes and 48 hours after H/I. An RNAse protection assay was used to evaluate changes in chemokine mRNA expression. RT-PCR was used to assess inducible nitric oxide synthase (iNOS) and endothelial nitric oxide synthase mRNA levels. Immunohistochemistry was used to assess leukocyte infiltration. Western blots were used to assess iNOS and glutamate aspartate transporter protein levels. Results-IL-1R1 null mice had reduced cytotoxic and vasogenic edema. The volume of hyperintense signal on T 2 -weighted images was reduced on average by 90% at 48 hours after H/I. The induction of multiple chemokine mRNAs was significantly reduced in IL-1R1 null mice compared with wild-type mice at 18 and 72 hours after H/I, which correlated with fewer infiltrating CD3ϩ leukocytes. Levels of iNOS protein and mRNA (but not glutamate aspartate transporter) were significantly reduced in the IL-1R1 mouse brain. Conclusions-These findings indicate that abrogating IL-1R1 signaling could protect brain cells subsequent to a mild stroke by reducing edema and immune cell recruitment, as well as by limiting iNOS-mediated free radical damage. (Stroke. 2005;36:2226-2231.)

Research paper thumbnail of Increased Plasma Beta-Hydroxybutyrate, Preserved Cerebral Energy Metabolism, and Amelioration of Brain Damage During Neonatal Hypoxia Ischemia with Dexamethasone Pretreatment

Pediatric Research, 2000

Dexamethasone (DEX) pretreatment has been shown to be neuroprotective in a neonatal rat model of ... more Dexamethasone (DEX) pretreatment has been shown to be neuroprotective in a neonatal rat model of hypoxia ischemia (HI). The exact mechanism of this neuroprotection is still unknown. This study used 31 P nuclear magnetic resonance spectroscopy to monitor energy metabolism during a 3-h episode of HI in 7-d-old rat pups in one of two groups. The first group was pretreated with 0.1 mL saline (i.p.) and the second group was treated with 0.1 mL of 0.1mg/kg DEX (i.p.) 22 h before HI. Animals pretreated with DEX had elevated nucleoside triphosphate and phosphocreatine levels during HI when compared with controls. Salinetreated animals had significant decreases in nucleoside triphosphate and phosphocreatine and increases in inorganic phosphate over this same period. 31 P nuclear magnetic resonance data unequivocally demonstrate preservation of energy metabolism during HI in neonatal rats pretreated with DEX. Animals pretreated with DEX had little or no brain damage following 3 h of HI when compared with matched controls, which experienced severe neuronal loss and cortical infarction. These same pretreated animals had an increase in blood beta-hydroxybutyrate levels before ischemia, suggesting an increase in ketone bodies, which is the neonate's primary energy source. Elevation of ketone bodies appears to be one of the mechanisms by which DEX pretreatment provides neuroprotection during HI in the neonatal rat. Abbreviations DEX, dexamethasone HI, hypoxia ischemia NTP, nucleoside triphosphate NMR, nuclear magnetic resonance NMRS, nuclear magnetic resonance spectroscopy BHB, beta-hydroxybutyrate D-␤-HBA, D-␤-hydroxybutyrate dehydrogenase ABSTRACT 248

Research paper thumbnail of Regional activation in the rat brain during visceral stimulation detected by c-fos expression and fMRI

Neurogastroenterology and Motility, 2005

Aim: The aim of the study was to determine and compare the areas of brain activated in response t... more Aim: The aim of the study was to determine and compare the areas of brain activated in response to colorectal distention (CRD) using functional magnetic resonance imaging (fMRI) and c-fos protein expression. Methods: For fMRI study (3.0 T magnet), anaesthetized rats underwent phasic CRD, synchronized with fMRI acquisition. Stimulation consisted of eight cycles of balloon deflation (90 s) and inflation (30 s), at 40, 60 or 80 mmHg of pressure. For c-fos study two sets of experiments were performed on anaesthetized rats: comparing (A) brain activation in rats with the inserted colorectal balloon (n ¼ 5), to the rats without the balloon (n ¼ 5); and (B) rats with inserted balloon (n ¼ 10), to the rats with inserted and distended balloon (n ¼ 10). The pressure of 80 mmHg was applied for 2 h of 30 s inflation and 90 s deflation, alternating cycles. Results: Functional MRI revealed significant activation in the amygdala, hypothalamus, thalamus, cerebellum and hippocampus. Significant increase in c-fos expression was observed in amygdala and thalamus in the first set of experiments, and hypothalamus and parabrachial nuclei in the second. Conclusion: The two methods are not interchangeable but appeared to be complementary: fMRI was more sensitive, whereas c-fos had much greater resolution.

Research paper thumbnail of Progress in high field MRI at the University of Florida

Magma: Magnetic Resonance Materials in Physics, Biology, and Medicine, 2001

In this article we report on progress in high magnetic field MRI at the University of Florida in ... more In this article we report on progress in high magnetic field MRI at the University of Florida in support of our new 750MHz wide bore and 11.7T/40cm MR instruments. The primary emphasis is on the associated rf technology required, particularly high frequency volume and phased array coils. Preliminary imaging results at 750MHz are presented. Our results imply that the pursuit of even higher fields seems warranted.

Research paper thumbnail of Three-dimensional mapping of the static magnetic field inside the human head

Magnetic Resonance in Medicine, 1996

Finite element analysis was used to calculate the static magnelic field within the three-dimensio... more Finite element analysis was used to calculate the static magnelic field within the three-dimensional head model. Localized field distributions were evaluated by using the magnetic field histogram technique. Experimental field maps and histograms of ithe human head were also obtained to validate the simulation results. Field deviations and gradients inside the human head cause NMR signal frequency shifts and line broadening, respectively. Voxels 2 x 2 x 0.5 cm may have frequency diflerences of more than 2.0 ppm. The linewidth of a single voxeel may be broadened by more than 0.5 ppm. Calculated and experimental field maps are in excellent agreement. The global field distortion in the human head is primarily due to the susceptibility difference between air and tissues and their corresponding geometrical shapes.

Research paper thumbnail of Consideration of magnetically-induced and conservative electric fields within a loaded gradient coil

Magnetic Resonance in Medicine, 2006

We present a method to calculate the electric (E)-fields within and surrounding a human body in a... more We present a method to calculate the electric (E)-fields within and surrounding a human body in a gradient coil, including E-fields induced by the changing magnetic fields and "conservative" E-fields originating with the scalar electrical potential in the coil windings. In agreement with previous numerical calculations, it is shown that magnetically-induced E-fields within the human body show no real concentration near the surface of the body, where nerve stimulation most often occurs. Both the magnetically-induced and conservative E-fields are shown to be considerably stronger just outside the human body than inside it, and under some circumstances the conservative Efields just outside the body can be much larger than the magnetically-induced E-fields there. The order of gradient winding and the presence of conductive RF shield can greatly affect the conservative E-field distribution in these cases. Though the E-fields against the outer surface of the body are not commonly considered, understanding gradient E-fields may be important for reasons other than peripheral nerve stimulation (PNS), such as potential interaction with electrical equipment. Magn Reson Med 55:1424 -1432, 2006.

Research paper thumbnail of A method to create an optimum current distribution and homogeneous B1 field for elliptical birdcage coils

Magnetic Resonance in Medicine, 1997

For a birdcage coil with elliptical cross-section, a sinusoidal current pattern does not provide ... more For a birdcage coil with elliptical cross-section, a sinusoidal current pattern does not provide a homogeneous B, field. A simple theory was developed to create an optimized current distribution for elliptical birdcage coils. This optimized current pattern can create a perfectly homogeneous 8, field inside any elliptical shape. To verify the theory, a 16-element highpass elliptical birdcage coil was built inside a circular RF shield. The current was optimized by using the inductance characteristics of the coil components to calculate the endring capacitances. The B, field was theoretically calculated and experimentally mapped for the optimized elliptical birdcage coil and a nonoptimized coil. The results demonstrate that by optimizing the current distribution, a very homogeneous B, field is produced. This method can be directly applied in design and construction of elliptical birdcage coils for imaging of the naturally occurring elliptical cross-sectional geometries in the human body.

Research paper thumbnail of A computer simulation of the static magnetic field distribution in the human head

Magnetic Resonance in Medicine, 1995

Distortion of the static magnetic field inside the human head is dependent on regional tissue sus... more Distortion of the static magnetic field inside the human head is dependent on regional tissue susceptibility variations and geometrical shape. These effects result in resonance line broadening and frequency shifts and consequently, intensity and spatial errors in both magnetic resonance imaging (MRI) and magnetic resonance (MR) spectroscopy. To calculate the field distortion due to the susceptibility's geometry, two dimensional (2D) finite element analysis was applied to simulate the field distribution in a 2D model of the human head, placed in a uniform magnetic field. The model contains air-filled cavities and sinuses, and the remainder is treated as water. The magnetic field deviation was evaluated using gray scale plots and histograms of the magnetic field. The shifts in parts/ million and broadening of the histograms correspond to the NMR of the sampled region. The field distribution of the human head was also experimentally mapped using the DANTE tagging sequence. The calculated and experimental field maps are in good agreement. Thus, geometric considerations with uniform susceptibilities are sufficient to explain most of the static magnetic field distribution in the human head.

Research paper thumbnail of Different excitation and reception distributions with a single-loop transmit-receive surface coil near a head-sized spherical phantom at 300 MHz

Magnetic Resonance in Medicine, 2002

Calculations and experiments were used to examine the B 1 field behavior and signal intensity dis... more Calculations and experiments were used to examine the B 1 field behavior and signal intensity distribution in a 16-cm diameter spherical phantom excited by a 10-cm diameter surface coil at 300 MHz. In this simple system at this high frequency very complex RF field behavior exists, resulting in different excitation and reception distributions. Included in this work is a straightforward demonstration that coil receptivity is proportional to the magnitude of the circularly polarized component of the B 1 field that rotates in the direction opposite to that of nuclear precession. It is clearly apparent that even in very simple systems in head-sized samples at this frequency it is important to consider the separate excitation and reception distributions in order to understand the signal intensity distribution. Magn Reson Med 47:1026 -1028, 2002.

Research paper thumbnail of 7T vs. 4T: RF power, homogeneity, and signal-to-noise comparison in head images

Magnetic Resonance in Medicine, 2001

Signal-to-noise ratio (SNR), RF field (B 1 ), and RF power requirement for human head imaging wer... more Signal-to-noise ratio (SNR), RF field (B 1 ), and RF power requirement for human head imaging were examined at 7T and 4T magnetic field strengths. The variation in B 1 magnitude was nearly twofold higher at 7T than at 4T (ϳ42% compared to ϳ23%). The power required for a 90°pulse in the center of the head at 7T was approximately twice that at 4T. The SNR averaged over the brain was at least 1.6 times higher at 7T compared to 4T. These experimental results were consistent with calculations performed using a human head model and Maxwell's equations. Magn Reson Med 46:24 -30, 2001.

Research paper thumbnail of Direct magnetic resonance imaging of histological tissue samples at 3.0T

Magnetic Resonance in Medicine, 2007

Direct imaging of a histological slice is challenging. The vast difference in dimension between p... more Direct imaging of a histological slice is challenging. The vast difference in dimension between planar size and the thickness of histology slices would require an RF coil to produce a uniform RF magnetic (B1) field in a 2D plane with minimal thickness. In this work a novel RF coil designed specifically for imaging a histology slice was developed and tested. The experimental data demonstrate that the coil is highly sensitive and capable of producing a uniform B1 field distribution in a planar region of histological slides, allowing for the acquisition of high-resolution T2 images and T2 maps from a 60-microm-thick histological sample. The image intensity and T2 distributions were directly compared with histological staining of the relative iron concentration of the same slice. This work demonstrates the feasibility of using a microimaging histological coil to image thin slices of pathologically diseased tissue to obtain a precise one-to-one comparison between stained tissue and MR images.

Research paper thumbnail of Analysis of wave behavior in lossy dielectric samples at high field

Magnetic Resonance in Medicine, 2002

Radiofrequency (RF) field wave behavior and associated nonuniform image intensity at high magneti... more Radiofrequency (RF) field wave behavior and associated nonuniform image intensity at high magnetic field strengths are examined experimentally and numerically. The RF field produced by a 10-cm-diameter surface coil at 300 MHz is evaluated in a 16-cm-diameter spherical phantom with variable salinity, and in the human head. Temporal progression of the RF field indicates that the standing wave and associated dielectric resonance occurring in a pure water phantom near 300 MHz is greatly dampened in the human head due to the strong decay of the electromagnetic wave. The characteristic image intensity distribution in the human head is the result of spatial phase distribution and amplitude modulation by the interference of the RF traveling waves determined by a given sample-coil configuration. The numerical calculation method is validated with experimental results. The general behavior of the RF field with respect to the average brain electrical properties in a frequency range of 42-350 MHz is also analyzed. Magn Reson Med 47: 982-989, 2002.

Research paper thumbnail of Radio frequency magnetic field mapping of a 3 Tesla birdcage coil: Experimental and theoretical dependence on sample properties

Magnetic Resonance in Medicine, 2001

The RF B 1 distribution was studied, theoretically and experimentally, in phantoms and in the hea... more The RF B 1 distribution was studied, theoretically and experimentally, in phantoms and in the head of volunteers using a 3 T MRI system equipped with a birdcage coil. Agreement between numerical simulation and experiment demonstrates that B 1 distortion at high field can be explained with 3D full-Maxwell calculations. It was found that the B 1 distribution in the transverse plane is strongly dependent on the dielectric properties of the sample. We show that this is a consequence of RF penetration effects combined with RF standing wave effects. In contrast, along the birdcage coil z-axis the B 1 distribution is determined mainly by the coil geometry. In the transverse plane, the region of B 1 uniformity (within 10% of the maximum) was 15 cm with oil, 6 cm with distilled water, 11 cm with saline, and 10 cm in the head. Along z the B 1 uniformity was 9 cm with phantoms and 7 cm in the head. Magn Reson Med 46:379 -385, 2001.

Research paper thumbnail of Multi-gradient echo with susceptibility inhomogeneity compensation (MGESIC): Demonstration offMRI in the olfactory cortex at 3.0 T

Magnetic Resonance in Medicine, 1997

Short image acquisition times and sensitivity to magnetic susceptibility favor the use of gradien... more Short image acquisition times and sensitivity to magnetic susceptibility favor the use of gradient echo imaging methods in functional MRI (fMRI). However, magnetic susceptibility effects attributed to air-tissue interfaces also lead to severe signal loss in images of the large inferior frontal and lateral temporal cortices of the human brain, which renders these regions inaccessible to IMRI. The signal loss is caused by the local field gradients in the slice selection direction. A multigradient echo with magnetic susceptibility inhomogeneity compensation method (MGESIC) is proposed to overcome this problem. The MGESIC method effectively corrects the susceptibility artifacts and maintains the advantages of gradient echo methods to both BOLD sensitivity and fast image acquisition. The effectiveness of the MGESIC method is demonstrated by f MRI experimental results within the olfactory cortex.

Research paper thumbnail of B1 destructive interferences and spatial phase patterns at 7 T with a head transceiver array coil

Magnetic Resonance in Medicine, 2005

RF behavior in the human head becomes complex at ultrahigh magnetic fields. A bright center and a... more RF behavior in the human head becomes complex at ultrahigh magnetic fields. A bright center and a weak periphery are observed in images obtained with volume coils, while surface coils provide strong signal in the periphery. Intensity patterns reported with volume coils are often loosely referred to as "dielectric resonances," while modeling studies ascribe them to superposition of traveling waves greatly dampened in lossy brain tissues, raising questions regarding the usage of this term. Here we address this question experimentally, taking full advantage of a transceiver coil array that was used in volume transmit mode, multiple receiver mode, or single transmit surface coil mode. We demonstrate with an appropriately conductive sphere phantom that destructive interferences are responsible for a weak B(1) in the periphery, without a significant standing wave pattern. The relative spatial phase of receive and transmit B(1) proved remarkably similar for the different coil elements, although with opposite rotational direction. Additional simulation data closely matched our phantom results. In the human brain the phase patterns were more complex but still exhibited similarities between coil elements. Our results suggest that measuring spatial B(1) phase could help, within an MR session, to perform RF shimming in order to obtain more homogeneous B(1) in user-defined areas of the brain.

Research paper thumbnail of Polarization of the RF field in a human head at high field: A study with a quadrature surface coil at 7.0 T

Magnetic Resonance in Medicine, 2002

The RF field intensity distribution in the human brain becomes inhomogeneous due to wave behavior... more The RF field intensity distribution in the human brain becomes inhomogeneous due to wave behavior at high field. This is further complicated by the spatial distribution of RF field polarization that must be considered to predict image intensity distribution. An additional layer of complexity is involved when a quadrature coil is used for transmission and reception. To study such complicated RF field behavior, a computer modeling method was employed to investigate the RF field of a quadrature surface coil at 300 MHz. Theoretical and experimental results for a phantom and the human head at 7.0 T are presented. The results are theoretically important and practically useful for high-field quadrature coil design and application. Magn Reson Med 48:362-369, 2002.

Research paper thumbnail of Hexagonal zero mode TEM coil: A single-channel coil design for imaging multiple small animals

Magnetic Resonance in Medicine, 2005

A novel hexagonal coil design for simultaneous imaging of multiple small animals is presented. Th... more A novel hexagonal coil design for simultaneous imaging of multiple small animals is presented. The design is based on a coaxial cavity and utilizes the magnetic field formed between two coaxial conductors with hexagonal cross-sections. An analytical solution describing the B(1) field between conductors of the hexagonal coil was found from the Biot-Savart law. Both experimental results and analytical calculations showed a variation in the B(1) field within the imaging region of less than 10%. Numerical calculations predicted approximately 35% improvement in B(1) field homogeneity with the hexagonal coil design compared to a cylindrical coaxial cavity design. The experimentally-measured signal-to-noise ratio (SNR) of the hexagonal coil loaded with six 50-mM phantoms was only 4-5% lower than that of a single parallel plate resonator loaded with one phantom. In vivo spin-echo (SE) images of six 7-day-old rat pups acquired simultaneously demonstrated sufficient SNR for microimaging. The construction scheme of the coil, simple methods for tuning and matching, and an anesthesia device and animal holder designed for the coil are described. The hexagonal coil design utilizes a single receiver and allows for simultaneous imaging of six small animals with no significant compromise in SNR.