Applications of Continuous Wave Free Precession Sequences in Low-Field, Time-Domain NMR

This review discusses the theory and applications of the Continuous Wave Free Precession (CWFP) sequence in low-field, time-domain nuclear magnetic resonance (TD-NMR). CWFP is a special case of the Steady State Free Precession (SSFP) regime that is obtained when a train of radiofrequency pulses, separated by a time interval Tp shorter than the effective transverse relaxation time (T2*), is applied to a sample. Unlike regular pulsed experiments, in the CWFP regime, the amplitude is not dependent on T1. Therefore, Tp should be as short as possible (limited by hardware). For Tp < 0.5 ms, thousands of scans can be performed per second, and the signal to noise ratio can be enhanced by more than one order of magnitude. The amplitude of the CWFP signal is dependent on T1/T2; therefore, it can be used in quantitative analyses for samples with a similar relaxation ratio. The time constant to reach the CWFP regime (T*) is also dependent on relaxation times and flip angle (θ). Therefore, T* has been used as a single shot experiment to measure T1 using a low flip angle (5°) or T2, using θ = 180°. For measuring T1 and T2 simultaneously in a single experiment, it is necessary to use θ = 90°, the values of T* and M0, and the magnitude of CWFP signal |Mss|. Therefore, CWFP is an important sequence for TD-NMR, being an alternative to the Carr-Purcell-Meiboom-Gill sequence, which depends only on T2. The use of CWFP for the improvement of the signal to noise ratio in quantitative and qualitative analyses and in relaxation measurements are presented and discussed.

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Signal-to-noise ratio of heterodyne beats between a comb and a continuous wave laser above the limit of a single mode

CLEO: 2013 ◽

10.1364/cleo_si.2013.ctu2i.6 ◽

2013 ◽

Author(s):

Jean-Daniel Deschênes ◽

Jérôme Genest

Keyword(s):

Continuous Wave ◽

Signal To Noise Ratio ◽

Single Mode ◽

Continuous Wave Laser ◽

Signal To Noise ◽

Wave Laser ◽

Noise Ratio

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Enhancing signal-to-noise ratio and resolution in low-field NMR relaxation measurements using post-acquisition digital filters

Magnetic Resonance in Chemistry ◽

10.1002/mrc.4806 ◽

2018 ◽

Vol 57 (9) ◽

pp. 616-625 ◽

Cited By ~ 2

Author(s):

Tatiana Monaretto ◽

Andre Souza ◽

Tiago Bueno Moraes ◽

Victor Bertucci-Neto ◽

Corinne Rondeau-Mouro ◽

...

Keyword(s):

Digital Filters ◽

Signal To Noise Ratio ◽

Nmr Relaxation ◽

Signal To Noise ◽

Low Field ◽

Relaxation Measurements ◽

Low Field Nmr ◽

Noise Ratio

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Clinical impact of ultra-high b-value (3000 s/mm2) diffusion-weighted magnetic resonance imaging in prostate cancer at 3T: comparison with b-value of 2000 s/mm2

British Journal of Radiology ◽

10.1259/bjr.20210465 ◽

2021 ◽

pp. 20210465

Author(s):

Tsutomu Tamada ◽

Ayumu Kido ◽

Yu Ueda ◽

Mitsuru Takeuchi ◽

Takeshi Fukunaga ◽

...

Keyword(s):

Prostate Cancer ◽

Diagnostic Performance ◽

Signal To Noise Ratio ◽

B Value ◽

Single Shot ◽

Signal To Noise ◽

High B Value ◽

Diffusion Weighted ◽

Significant Difference ◽

Noise Ratio

Objective: High b-value diffusion-weighted imaging (hDWI) with a b-value of 2000 s/mm2 provides insufficient image contrast between benign and malignant tissues and an overlap of apparent diffusion coefficient (ADC) between Gleason grades (GG) in prostate cancer (PC). We compared image quality, PC detectability, and discrimination ability for PC aggressiveness between ultra-high b-value DWI (uhDWI) of 3000 s/mm2 and hDWI. Methods: The subjects were 49 patients with PC who underwent 3T multiparametric MRI. Single-shot echo-planar DWI was acquired with b-values of 0, 2000, and 3000 s/mm2. Anatomical distortion of prostate (AD), signal intensity of benign prostate (PSI), and lesion conspicuity score (LCS) were assessed using a 4-point scale; and signal-to-noise ratio, contrast-to-noise ratio, and mean ADC (×10–3 mm2/s) of lesion (lADC) and surrounding benign region (bADC) were measured. Results: PSI was significantly lower in uhDWI than in hDWI (p < 0.001). AD, LCS, signal-to-noise ratio, and contrast-to-noise ratio were comparable between uhDWI and hDWI (all p > 0.05). In contrast, lADC was significantly lower than bADC in both uhDWI and hDWI (both p < 0.001). In comparison of lADC between tumors of ≤GG2 and those of ≥GG3, both uhDWI and hDWI showed significant difference (p = 0.007 and p = 0.021, respectively). AUC for separating tumors of ≤GG2 from those of ≥GG3 was 0.731 in hDWI and 0.699 in uhDWI (p = 0.161). Conclusion: uhDWI suppressed background signal better than hDWI, but did not contribute to increased diagnostic performance in PC. Advances in knowledge: Compared with hDWI, uhDWI could not contribute to increased diagnostic performance in PC.

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