Fourier transform electron spin resonance imaging

Ewert, Uwe; Crepeau, Richard H.; Dunnam, Curt R.; Xu, Dajiang; Lee, Sanghyuk; Freed, Jack H.

doi:10.1016/0009-2614(91)87159-9

Cited by 25 publications

(12 citation statements)

References 18 publications

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“…This permits one to obtain the Fourier-transformed concen tration distribution C(K,t) directly from the experiment, unlike in cw DID-ESR where one must first Fourier transform Jg(g,!) andJo(g) (17,18,47).…”

Section: Fourier Transform Esr Imagingmentioning

confidence: 99%

Field Gradient ESR and Molecular Diffusion in Model Membranes

Freed¹

1994

Annu. Rev. Biophys. Biomol. Struct.

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Section: Fourier Transform Esr Imagingmentioning

confidence: 99%

Field Gradient ESR and Molecular Diffusion in Model Membranes

Freed¹

1994

Annu. Rev. Biophys. Biomol. Struct.

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“…In addition, with the increasing sensitivity of EPRI at clinically relevant tissue oxygenation levels encountered in pathological conditions, EPRI may well find a unique place to detect and map hypoxic volumes. 27,28 Such measurements should provide valuable physiologic information with respect to the pO 2 status of tumor versus normal tissue. This information may help in devising more aggressive therapeutic regimens for patients with large hypoxic fractions in tumors.…”

Section: Discussionmentioning

confidence: 99%

A broadband pulsed radio frequency electron paramagnetic resonance spectrometer for biological applications

Murugesan

Afeworki

Cook

et al. 1998

Review of Scientific Instruments

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A time-domain radio frequency (rf) electron paramagnetic resonance (EPR) spectrometer/imager (EPRI) capable of detecting and imaging free radicals in biological objects is described. The magnetic field was 10 mT which corresponds to a resonance frequency of 300 MHz for paramagnetic species. Short pulses of 20–70 ns from the signal generator, with rise times of less than 4 ns, were generated using high speed gates, which after amplification to 283 Vpp, were deposited into a resonator containing the object of interest. Cylindrical resonators containing parallel loops at uniform spacing were used for imaging experiments. The resonators were maintained at the resonant frequency by tuning and matching capacitors. A parallel resistor and overcoupled circuit was used to achieve Q values in the range 20–30. The transmit and receive arms were isolated using a transmit/receive diplexer. The dead time following the trailing edge of the pulse was about 450 ns. The first stage of the receive arm contained a low noise, high gain and fast recovery amplifier, suitable for detection of spin probes with spin-spin relaxation times (T2) in the order of μs. Detection of the induction signal was carried out by mixing the signals in the receiver arm centered around 300 MHz with a local oscillator at a frequency of 350 MHz. The amplified signals were digitized and summed using a 1 GHz digitizer/summer to recover the signals and enhance the signal-to-noise ratio (SNR). The time-domain signals were transformed into frequency-domain spectra, using Fourier transformation (FT). With the resonators used, objects of size up to 5 cm3 could be studied in imaging experiments. Spatial encoding of the spins was accomplished by volume excitation of the sample in the presence of static field gradients in the range of 1.0–1.5 G/cm. The spin densities were produced in the form of plane integrals and images were reconstructed using standard back-projection methods. The image resolution of the phantom objects containing the spin probe surrounded by lossy biologic medium was better than 0.2 mm with the gradients used. To examine larger objects at local sites, surface coils were used to detect and image spin probes successfully. The results from this study indicate the potential of rf FT EPR for in vivo applications. In particular, rf FT EPR may provide a means to obtain physiologic information such as tissue oxygenation and redox status.

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“…Use of shaped pulses for slice selection and selective uniform excitation in MRI and MRS is well established [29][30][31][32]. But the selective pulses used in MRI/MRS need to cover relatively small bandwidths (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20). Because of the low bandwidth requirements, Q-profile artifacts are negligible in MRI.…”

Section: Pulse Shaping For Q-profile Compensationmentioning

confidence: 98%

“…EPR methods in time-domain has the potential to reduce acquisition times, making image data collection times compatible with the biological half-life of commonly used EPR spin probes. Although the feasibility of Fourier domain EPR imaging has been demonstrated [15][16][17], the short T Ã 2 of biologically viable EPR spin probes make Fourier EPR imaging using pulsed field gradients challenging. Therefore, in time-domain EPR imaging, projections are collected in the presence of static magnetic field gradients in a polar grid and images are reconstructed using filtered back projection (FBP) method [18][19][20].…”

Section: Introductionmentioning

confidence: 99%