Improving the Signal-to-noise Ratio of Surface-NMR Measurements by Reference Channel Based Noise Cancellation

Mueller-Petke, M.; Yaramanci, U.

doi:10.3997/2214-4609.20144767

Cited by 8 publications

(7 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…As seen S N 1 (z) and S N 2 (z) are not identical as tacitly assumed in the standard method of noise cancelling of multichannel MRS signals (Walsh 2008;Mueller-Petke & Yaramanci 2010;Dalgaard et al 2012). To improve on this matter, more advanced signal processing schemes must be devised where the contributions from different sources are thoroughly separated and independently cancelled.…”

Section: N O I S E I N M R S R E C O R D I N G Smentioning

confidence: 99%

“…The noise in the primary loop and the reference loops are correlated and, through filtering, the signals from the reference loops can be transformed into an estimate of the noise in the primary loop. The estimate is subtracted from the primary loop signal leaving only the desired signal (Walsh 2008;Mueller-Petke & Yaramanci 2010;Dalgaard et al 2012). However, as will be demonstrated below, this approach is not always optimum.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Noise cancelling of MRS signals combining model-based removal of powerline harmonics and multichannel Wiener filtering

Larsen

Dalgaard

Auken

2013

Geophysical Journal International

109

View full text Add to dashboard Cite

The fidelity of magnetic resonance sounding signals is often severely degraded by noise, primarily electrical interference from powerline harmonics and short electromagnetic discharges. In many circumstances, the noise originates from multiple sources. We show that noise cancelling can be improved if the multiple origins of noise are taken into account. In particular, a method is developed where powerline harmonics are efficiently removed through a modelbased approach. Subsequently, standard multichannel Wiener filtering can be used to provide a further noise reduction. The performance of the method depends on the distribution of noise on the particular site of measurement. Simulations on synthetic signals embedded in real noise recordings show that the combined approach can improve the signal-to-noise ratio with an accompanying improvement in retrieval of model parameters.

show abstract

Section: N O I S E I N M R S R E C O R D I N G Smentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Noise cancelling of MRS signals combining model-based removal of powerline harmonics and multichannel Wiener filtering

Larsen

Dalgaard

Auken

2013

Geophysical Journal International

109

View full text Add to dashboard Cite

show abstract

“…Methods that mitigate EMI effects such as spiking in an image have been proposed using machine learning and other such advanced signal processing algorithms, 35,36 but are model based and generally require training datasets. Common EMI suppression methods for surface NMR include the use of an external or "remote" reference loop wherein a global transfer function is formed from "noise" data (calibration data) both in frequency 30 and time domain. 25 This has been extended to an arbitrary number of external reference loops for more robust performance.…”

Section: Introductionmentioning

confidence: 99%

“…Active and post processing cancellation approaches to EMI mitigation that are more flexible and are less intrusive to the subject have been developed for Magnetotellurics, [20][21][22] transient electromagnetics, 23 SQUID MRI, 24 surface NMR instrumentation, [25][26][27][28][29][30][31][32] ECG, 33 EEG 34 and MRI. [35][36][37][38][39][40][41][42][43] Large "figure 8"-shaped surface coils have also been used to cancel EMI actively 26,31 for surface NMR groundwater surveys, but this method is not easily translated to in vivo brain imaging.…”

Section: Introductionmentioning

confidence: 99%

External Dynamic InTerference Estimation and Removal (EDITER) for low field MRI

Srinivas

Cauley

Stockmann

et al. 2021

Magnetic Resonance in Med

View full text Add to dashboard Cite

Purpose Point‐of‐care MRI requires operation outside of Faraday shielded rooms normally used to block image‐degrading electromagnetic interference (EMI). To address this, we introduce the EDITER method (External Dynamic InTerference Estimation and Removal), an external sensor‐based method to retrospectively remove image artifacts from time‐varying external interference sources. Theory and Methods The method acquires data from multiple EMI detectors (tuned receive coils as well as untuned electrodes placed on the body) simultaneously with the primary MR coil during and between image data acquisition. We calculate impulse response functions dynamically that map the data from the detectors to the time varying artifacts then remove the transformed detected EMI from the MR data. Performance of the EDITER algorithm was assessed in phantom and in vivo imaging experiments in an 80 mT portable brain MRI in a controlled EMI environment and with an open 47.5 mT MRI scanner in an uncontrolled EMI setting. Results In the controlled setting, the effectiveness of the EDITER technique was demonstrated for specific types of introduced EMI sources with up to a 97% reduction of structured EMI and up to 76% reduction of broadband EMI in phantom experiments. In the uncontrolled EMI experiments, we demonstrate EMI reductions of up to 99% using an electrode and pick‐up coil in vivo. We demonstrate up to a nine‐fold improvement in image SNR with the method. Conclusion The EDITER technique is a flexible and robust method to improve image quality in portable MRI systems with minimal passive shielding and could reduce the reliance of MRI on shielded rooms and allow for truly portable MRI.

show abstract

“…Only little information is available about the technique implemented in Vista‐Clara software (Walsh ). Müller‐Petke and Yaramanci () presented a time‐ domain approach based on a single reference loop and optimal filtering that has been extended to an arbitrary number of references by Neyer (). An adaptive filter in the time domain was presented by Dalgaard et al () and compared to the time‐domain optimal filter.…”

Section: Introductionmentioning

confidence: 99%

Comparison and optimal parameter settings of reference‐based harmonic noise cancellation in time and frequency domains for surface‐NMR

Müller‐Petke

Costabel

2013

Near Surface Geophysics

View full text Add to dashboard Cite

The technique of surface nuclear magnetic resonance (surface-NMR) provides information on porosity and hydraulic conductivity that is highly valuable in a hydrogeological context. However, the applicability of surface-NMR is often limited due to a bad signal-to-noise ratio. In this paper we provide a detailed insight into the technique of harmonic noise cancellation based on remote references to improve the signal-to-noise ratio. We give numerous synthetic examples to study the influence of various parameters such as optimal filter length for time-domain approaches or the necessary record length for frequency-domain approaches, all of which evaluated for different types of noise conditions. We show that the frequency-domain approach is superior to time-domain approaches. We demonstrate that the parameter settings in the frequency domain and the decision whether or not to use separated noise measurement depend on the actual noise properties, i.e., frequency content or stability with time. We underline our results using two field examples. netic noise. Such techniques have been used e.g., in magnetotellurics (MT) and transient electromagnetics (TEM) since the 1980s (Gamble et al. 1979a,b;Goubau et al. 1984;Spies 1988). A similar approach has become popular with the latest developments in surface-NMR instrumentation that provides the necessary multichannel data acquisition systems (Radic 2006;Walsh 2008).Several methods using a reference loop based system have been developed. Radic (2006) presented a remote reference approach operating in the frequency domain and using vertical loops as references. Only little information is available about the technique implemented in Vista-Clara software (Walsh 2008). Müller-Petke and Yaramanci (2010b) presented a time-domain approach based on a single reference loop and optimal filtering that has been extended to an arbitrary number of references by Neyer (2010). An adaptive filter in the time domain was presented by Dalgaard et al. (2012) and compared to the timedomain optimal filter. They showed that both approaches led to similar results. All approaches have demonstrated a useful capability to improve the S/N ratio of surface-NMR data.However, a comparison that allows for determining the performance, i.e., pro et contra of each approach concerning different measurement conditions, is missing. Thus, to compare the time-domain with the frequency-domain approach, we developed a frequency-domain code beside the existing time-domain code and distinguished two strategies within the frequency domain. We present and describe in detail noise cancellation

show abstract

Improving the Signal-to-noise Ratio of Surface-NMR Measurements by Reference Channel Based Noise Cancellation

Cited by 8 publications

References 0 publications

Noise cancelling of MRS signals combining model-based removal of powerline harmonics and multichannel Wiener filtering

Noise cancelling of MRS signals combining model-based removal of powerline harmonics and multichannel Wiener filtering

External Dynamic InTerference Estimation and Removal (EDITER) for low field MRI

Comparison and optimal parameter settings of reference‐based harmonic noise cancellation in time and frequency domains for surface‐NMR

Contact Info

Product

Resources

About