The efforts of our laboratory are divided into a number of projects all concerning the use of in vivo NMR spectroscopy and imaging. The research can be classified into three areas: human studies, animal/biochemical studies, and technological development.

We are currently involved in a study to use NMR to monitor the effects of birth asphyxia or neonatal hypoxia. ³¹P NMR spectroscopy provides an excellent monitor of the biochemical energetics of the neonatal rat brain. This allows the examination of the effects of selected drugs and their possible protective actions against hypoxia. T2-weighted magnetic resonance imaging is used to evaluate infarct size and/or edema. The model will eventually be used to evaluate the cerebral damage and subsequent treatment of infants.

A project has recently been initiated in which the behavior of the radiofrequency magnetic field is modeled under the conditions of frequency, dielectric constant, and conductivity that would be expected for an NMR experiment in human tissue. Computer modeling of this type allows for the prediction of artifacts in spectroscopy and imaging due to perturbations caused by induced eddy currents and inductive losses of the radiofrequency coil. These models also allow the generation of specific coil geometries to solve many problems accompanying in vivo NMR applications.

The Center for Nuclear Magnetic Resonance Imaging (NMR) Research at the Hershey Medical Center has a new 3.0 Tesla instrument (MEDSPEC S300) that was built by Bruker Medizintechnik, a German company and a leader in the magnetiresonance field. It has many hardware and software capabilities unavailable to previous whole body systems. The system is equipped with a new design of actively shielded gradient coils whose high speed switching allows ultrafast imaging.

Ultrafast imaging using the echo planar technique allows images of the head or body to be obtained in only 32 msec. The higher magnetic field strength of this new 3.0 Tesla instrument provides greater signal sensitivity and sensitivity to paramagnetic materials, such as iron in blood. Ogawa et al. observed changes in the image intensity with a decrease in blood oxygen. This technique referred to as functional imaging was extended using the rapid speed of echo planar imaging to monitor brain oxygenation in real time. At 3.0 Tesla, contrast changes due to deoxygenation from brain activity should produce intensity changes of up to 20%. Functional imaging produces results very similar to PET (Positron Emission Tomography) without the need of injecting radioactive materials. The work of the laboratory is further supported by computer simulations of magnetic fields in high resolution models of the human body. In the theoretical description of an RF field (B1) in the human body, the dimension of the resonator and human sample are assumed to be small compared to the resonant wavelength. The wavelengths inside the human sample are shorter than in free space. Dielectric resonance inside the human sample further complicates the analysis of the loaded coil and B1 field in the load. A thorough description of these problems requires the use of microwave theory. Using finite element analysis, we have calculated the full wave numerical solution of Maxwell equations for MRI Birdcage resonators with and without load. The threedimensional (3D) electromagnetic field and current distributions corresponding to the various microwave modes can be presented, and the effects of dielectric resonance in the human body can be detailed. This results in both better coil design and analysis of regional radiofrequency field depositions in the tissue.

The new Center for NMR Research is housed in the College of Medicine, adjacent to our outpatient MRI Center. The equipment includes a 9.4 Tesla Bruker AM~400 wide bore spectrometer, an Oxford 1.9 Tesla 26 cm bore horizontal magnet interfaced to a Nicolet 1280 computer, and a new 3.0 Tesla 92 cm spectrometer/imager (MEDSPEC S300). The latter will be the first of its kind. Also included in the Center is an animal preparation area, biochemistry laboratory, radiofrequency electronics shop, a fully equipped machine shop, computing resources, and office space for staff and students.