A high-resolution NMR probe in which the coil and preamplifier are cooled with liquid helium

Styles, Peter; Soffe, Nick; Scott, Christopher A.; Crag, D.A; Row, F.; White, David J.; White, P.C.

doi:10.1016/0022-2364(84)90050-7

Cited by 128 publications

(97 citation statements)

References 8 publications

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“…Cyclotron Mode-The electron beam supports cyclotron modes that obey the equation, (1) where ω is the radiation frequency, k z is the wave vector, v z is the axial electron velocity, s is the cyclotron harmonic number, and γ′ is the relativistic mass factor, (2) Here is the total electron velocity. The beam pitch factor α = (v ⊥ /v z ) determines the transverse energy in the electron beam, where v ⊥ and v z are the parallel and perpendicular velocities respectively of the electron beam with respect to the external DC magnetic field B 0 .…”

Section: Theorymentioning

confidence: 99%

See 1 more Smart Citation

250GHz CW gyrotron oscillator for dynamic nuclear polarization in biological solid state NMR

Bajaj

Hornstein

Kreischer

et al. 2007

Journal of Magnetic Resonance

162

130

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In this paper, we describe a 250 GHz gyrotron oscillator, a critical component of an integrated system for magic angle spinning (MAS) dynamic nuclear polarization (DNP) experiments at 9T, corresponding to 380 MHz 1 H frequency. The 250 GHz gyrotron is the first gyro-device designed with the goal of seamless integration with an NMR spectrometer for routine DNP-enhanced NMR spectroscopy and has operated under computer control for periods of up to 21 days with a 100% duty cycle. Following a brief historical review of the field, we present studies of the membrane protein bacteriorhodopsin (bR) using DNP-enhanced multidimensional NMR. These results include assignment of active site resonances in [U-13 C, 15 N]-bR and demonstrate the utility of DNP for studies of membrane proteins. Next, we review the theory of gyro-devices from quantum mechanical and classical viewpoints and discuss the unique considerations that apply to gyrotron oscillators designed for DNP experiments. We then characterize the operation of the 250 GHz gyrotron in detail, including its long-term stability and controllability. We have measured the spectral purity of the gyrotron emission using both homodyne and heterodyne techniques. Radiation intensity patterns from the corrugated waveguide that delivers power to the NMR probe were measured using two new techniques to confirm pure mode content: a thermometric approach based on the temperaturedependent color of liquid crystalline media applied to a substrate and imaging with a pyroelectric camera. We next present a detailed study of the mode excitation characteristics of the gyrotron. Exploration of the operating characteristics of several fundamental modes reveals broadband continuous frequency tuning of up to 1.8 GHz as a function of the magnetic field alone, a feature that may be exploited in future tunable gyrotron designs. Oscillation of the 250 GHz gyrotron at the second harmonic of cyclotron resonance begins at extremely low beam currents (as low 12 mA) at frequencies between 320-365 GHz, suggesting an efficient route for the generation of even higher frequency radiation. The low starting currents were attributed to an elevated cavity Q, which is confirmed by cavity thermal load measurements. We conclude with an appendix containing a detailed description of the control system that safely automates all aspects of the gyrotron operation.

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Section: Theorymentioning

confidence: 99%

“…coil and lower noise figures in the detection r.f. preamplifiers have become routinely available, improving the sensitivity by a factor of 1.5-3 depending on the conductivity of the sample [2].…”

Section: Introductionmentioning

confidence: 99%

250GHz CW gyrotron oscillator for dynamic nuclear polarization in biological solid state NMR

Bajaj

Hornstein

Kreischer

et al. 2007

Journal of Magnetic Resonance

162

130

View full text Add to dashboard Cite

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“…SNR improvements with a cryo-cooled NMR probe designed for 13 C NMR spectroscopy at 45.9 MHz of roomtemperature samples were first demonstrated by Styles, et al (2). Subsequently, SNR gains have been observed with large coils in low-field MRI systems, but the greatest gains are expected with small coils since sample noise voltage scales roughly as frequency ϫ (diameter) 3/2 (3).…”

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confidence: 99%

In vivo MR micro imaging with conventional radiofrequency coils cooled to 77�K

2000

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“…Since GE sequences are less sensitive to pulse angle variations across the ROI, a slightly higher SNR gain was obtained for the GE sequences when comparing the cryo- The estimated SNR gains were calculated on the basis of the measured Q-factors according to Eqs. [5,6]. The temperatures used were T KT,coil ϭ 293K, T RT,coil ϭ 30 K, T sample ϭ 293K (DMSO and NaCl phantom), and T sample ϭ 310K (mouse head).…”

Section: Discussionmentioning

confidence: 99%

“…[5,6], the estimated gains in SNR between the two coils are 3.02 Ϯ 0.20 for the DMSO sample, 2.37 Ϯ 0.15 for the NaCl sample, and 2.01 Ϯ 0.17 for the mouse brain (Table 2). Equations [5,6] are based on the assumption that exactly the same magnetization is available for the room temperature and cryogenic coil, and thus the SNR gain can be determined by the ratio of the respective Johnson noise terms. To verify this assumption, the B 1 maps of the two surface coils were compared.…”

Section: Animal Experimentsmentioning

confidence: 99%

Performance of a 200‐MHz cryogenic RF probe designed for MRI and MRS of the murine brain

Ratering

Baltes

Nordmeyer-Massner

et al. 2008

Magnetic Resonance in Med

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A cryogenic 200-MHz RF transmit/receive probe (CryoProbe) made of copper and designed for murine brain studies is described. The probe operates at 30K and its performance was compared to a home-made surface coil of equal dimensions and a mouse head volume resonator, both operating at room temperature (RT). Since for small volumes of tissue interrogated (<5 mL) sample noise and thermal noise of the receiver are of comparable magnitude, considerable noise reduction can be achieved by cooling of the receiver system, e.g., using cold helium gas. The effect of temperature lowering on the signal-to-noise ratio (SNR) was assessed in phantom and in vivo murine brain studies using conventional MRI sequences (spin and gradient echo) and single voxel MR spectroscopy. Consistent sensitivity increases were observed for the CryoProbe. SNR increases by a factor ≥2 for the phantom experiments and by factors of 1.8 to 1.9 for in vivo experiments when compared to the RT surface coil for both MRI and MRS experiments. These results are in good agreement with estimated SNR gains for a circular surface coil probe cooled to 30K. The use of a cryogenic probe represents an economically attractive option to enhance the sensitivity in small animal MRI/MRS.

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A high-resolution NMR probe in which the coil and preamplifier are cooled with liquid helium

Cited by 128 publications

References 8 publications

250GHz CW gyrotron oscillator for dynamic nuclear polarization in biological solid state NMR

250GHz CW gyrotron oscillator for dynamic nuclear polarization in biological solid state NMR

In vivo MR micro imaging with conventional radiofrequency coils cooled to 77�K

Performance of a 200‐MHz cryogenic RF probe designed for MRI and MRS of the murine brain

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