X-Band Equipment

Two X-Band spectrometers are available for in vitro measurements.

1) A Bruker spectrometer with EMX console is equipped with two cavities: one of them is standard, and the other has two sets of coils.  One set is used to provide H-field modulation; the other set is used to provide a rapid field sweep.  Additional equipment includes: a Research Specialties 728 6570 variable temperature unit, an ER-033M Field/Frequency Lock and a data acquisition system based on a Pentium III 500 MHz computer with WinEPR 3.01 Acquisition software. 

2) A Varian E109E spectrometer with a standard TE 102 and a loop-gap XPO 202 Jagmar, Inc. resonator.  The latter is used for samples with high water content and diameter up to 2 mm. Additional equipment includes a variable temperature controller, a Field/Frequency Lock, and the data acquisition system based on an IBM clone computer and software written in the EPR Center.

 L-Band Equipment:

The EPR Center has two L-band spectrometers for collaborative users operating at a frequency of about 1.2 GHz and configured for small animal measurements.

1)  One consists of a modified standard receiver (a console produced by MicroNow, Chicago, IL) and a magnetic field controller connected with a microwave bridge (both instruments were custom-built in our lab). The field controller is based on an ultra-stable computer controlled stabilizer of the current for the electromagnet and our specially-built Field/Frequency Lock. This design improves the long-term and short-term stability of the magnetic field, which is especially important for measuring very narrow EPR signals, such as of LiPc and carrying out extensive averaging to resolve weak spectra.

2)  The second L-band spectrometer has been constructed more recently and incorporates most of the features of the other spectrometer plus some improvements. It uses a permanent magnet (Sumitomo Special Metals, Japan), which provides a wide gap (12'', 30 cm) and has better homogeneity of the magnetic field. The microwave bridge has a special design for using low microwave power to avoid saturation of paramagnetic materials. This spectrometer has an Automatic Matching Control (AMC) system built in our laboratory. All parts of the spectrometer, including a receiver, a magnetic field modulator, a field sweeper, Field/Frequency Lock, computer-based control/acquisition and software, a microwave bridge with AFC and AMC and a set of resonators were constructed in our lab. Additional equipment includes a temperature control/stabilization system based on air flow, and a custom-built gas mixture supply system with calibrated concentration of oxygen and nitrogen. 

There are an additional three L-Band spectrometers being used for developmental projects.

These spectrometers can be used with any of three types of resonators that have been built in our lab to provide specific configurations for various experiments on living objects. The external loop resonator is designed for general use, with the loop positioned over the area of interest. A new unique external loop resonator with electrical control of matching in addition to electrical control of resonance frequency has been developed recently. The cylindrical loop gap resonator is used for whole body measurements. The third resonator is a surface coil based on a dielectric resonator.

 Clinical whole body L-band EPR spectrometer based on permanent magnet:

The whole body clinical L-band EPR spectrometer uses a permanent magnet which was manufactured by Sumitomo Special Metals Co., Ltd, Torrence, CA to our specifications for a clinical EPR spectrometer:

• magnetic field:  410 Gs

• homogeneity:  25 ppm in a 40 mm sphere

• gap between poles:   50 cm

• weight:   »2000 kg

The system has the following (nonmagnetic) accessories:

• modulation coils with a 50 cm gap

• large amplitude modulation coils with a 20 cm gap

• sweep coils with a 50 cm gap

• rails to support insertion of full cart for subject (same cart that is used to position subjects into the adjacent hyperbaric chamber)

• patient bed with mattress on cart for measurements made in the prone position

• a special chair for measurements made with the subject in a sitting position

• a holder for the resonators to achieve precise and stable positioning of  resonator with six degrees of freedom

• an additional holder for resonators for tooth dosimetry

• a  holder for positioning the foot reliably and comfortably

• a holder for positioning the head reliably and comfortably

• an oxygen line for increasing the inhalation mixture and for local oxygen enrichment

• vacuum line for removing saliva in conjunction with measurements made with an intraoral resonator

• air flow heater to control the temperature in a region of interest (e.g. the skin of the foot)

 Whole body electromagnet for new clinical multi frequency EPR spectrometer:

A whole human body electromagnet has been purchased and is scheduled to be delivered by the end of 2006. The magnet has been designed specially for clinical multi‑frequency EPR spectrometer by Resonance Research, Inc., Billerica, MA.  The electromagnet has a quasi Helmholtz design with water cooling and with additional shimming and gradient coils nested inside larger magnet coils. The magnet has rails for a patient bed. The magnet has the following parameters:

• diameter of coils:    1,200 mm

• gap between coils:   500 mm

• homogeneity of 400 Gs magnetic field: +/- 20 ppm   in   300 mm sphere

• current and voltage for 400 Gs field:  90 A, 180 V

• weight:  950 kG

The magnet will be equipped with a commercial power supply capable of delivering regulated current and voltage up to 17 kW.

The spectrometer system is placed in Dartmouth - Hitchcock Medical Center in a specially constructed room that will include RF shielding. The complete spectrometer system will be constructed by the EPR Center, incorporating the latest version of the electronics and software in the center. It is expected to be operational in 2007