SQUID-Detected Magnetic Resonance Imaging in Microtesla Fields

Clarke, John; Hatridge, Michael; Mößle, M.

doi:10.1146/annurev.bioeng.9.060906.152010

Cited by 197 publications

(129 citation statements)

References 48 publications

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“…Since both the signal and the flux noise of the two configurations depend on the overall geometry of the detection channel, we compared the performances of the double-D receiver and the stand-alone MS in terms of the SNR obtained at specific frequencies, instead of simply comparing the magnetic flux detected by them [1,19]. Indeed, both the signal and the magnetic noise sensed by the double-D channel are larger (but with a different ratio) than those of the stand-alone MS, as shown in Figure 6(a).…”

Section: Comparison Between the Sensitivity Of The Superconducting Domentioning

confidence: 99%

“…MRI has evolved towards ever-higher applied field strengths with the aim at increasing the signal to noise ratio (SNR). However, during the last decade, some advantages of working at very low static fields (below 100 mT) have been suggested [1,2]. Such low-field NMR apparatuses, as compared to conventional high-field scanners, provide a higher frequency resolution of NMR lines [3,4], are less prone to susceptibility artefacts, require only moderate relative homogeneity of the static field [5] and, notably, the possibility of exploiting enhanced T1 contrast at low-field strengths, e.g., for the detection of tumours, has been recently suggested [6].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

NMR Detection at 8.9 Mt With a GMR Based Sensor Coupled to a Superconducting Nb Flux Transformer

Sinibaldi¹,

Luca²,

Nieminen³

et al. 2013

PIER

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Abstract-This study presents NMR signal detection by means of a superconducting channel consisting of a Nb surface detection coil inductively coupled to a YBCO mixed sensor. The NMR system operates at a low-field (8.9 mT) in a magnetically shielded room suitable for magnetoencephalographic (MEG) recordings. The main field is generated by a compact solenoid and the geometry of the pick-up coil has been optimized to provide high spatial sensitivity in the NMR field of view. The Nb detection coil is coupled to the mixed sensor through a Nb input coil. The mixed sensor consists of a superconducting YBCO loop with 2-µm constriction above which two Giant MagnetoResistance sensors are placed in a half-bridge configuration to detect changes of the bridge voltage as a function of the flux through the YBCO loop. The sensitivity of the receiving channel is calibrated experimentally. The measured spatial sensitivity is in agreement with the simulations and is ∼10 times better than that of the stand-alone mixed sensor. A NMR echo at 375 kHz shows a SNR only a factor 4 smaller than a tuned room temperature coil tightly wound around the sample, with a noise level which is a factor 3 better than for the volume coil. Our results suggest that mixed sensors are suitable for the integration of low-field MRI and MEG in a hybrid apparatus, where MEG and MRI would be recorded by SQUIDs and mixed sensors, respectively.

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Section: Comparison Between the Sensitivity Of The Superconducting Domentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

NMR Detection at 8.9 Mt With a GMR Based Sensor Coupled to a Superconducting Nb Flux Transformer

Sinibaldi¹,

Luca²,

Nieminen³

et al. 2013

PIER

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“…At the still lower …eld of 0.03 mT maintained by a conventional, room-temperature solenoid, Connolly and coworkers [18,19] obtain good spatial resolution and SNR by prepolarizing the protons in a …eld B p of 0.3 T. Prepolarization enhances the magnetic moment of an ensemble of protons over that produced by the lower precession …eld; after the polarizing …eld is removed, the higher magnetic moment produces a correspondingly larger signal during its precession in B 0 . The ultralow …eld MRI system developed by the Clarke group extends the technique of prepolarized MRI to even lower precession …elds [20]. Detection at these very weak …elds (typically 132 T, corresponding to a resonant frequency of 5.6 kHz) is enabled by use of dc SQUID readout, which outperforms conventional Faraday detections at low frequencies [21].…”

Section: Mri Of Human Subjects Open Challengesmentioning

confidence: 99%

“…Our current generation gradiometer is balanced to the part per few A second key feature of the input circuit is the array of current-limiting Josephson tunnel junctions connected in series with the gradiometer. If their critical current (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) A) is exceeded due to a large ‡ux change in the gradiometer, they switch to the normal state with a k resistance, preventing potentially damaging …elds from being coupled into the SQUID loop. When the current falls below the retrapping current, the junctions switch back to the superconducting state, so that the current-limiter, or 'Q-spoiler'as it is sometimes called, to functions as a self-resetting fuse in the input circuit.…”

Section: Squid Detector Chainmentioning

confidence: 99%

SQUID magnetometry from nanometer to centimeter length scales

Hatridge

2010

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Information stored in magnetic …elds plays an important role in everyday life. This information exists over a remarkably wide range of sizes, so that magnetometry at a variety of length scales can extract useful information. Examples at centimeter to millimeter length scales include measurement of spatial and temporal character of …elds generated in the human brain and heart, and active manipulation of spins in the human body for non-invasive magnetic resonance imaging (MRI). At micron length scales, magnetometry can be used to measure magnetic objects such as ‡ux qubits; at nanometer length scales it can be used to study individual magnetic domains, and even individual spins. The development of Superconducting QUantum Interference Device (SQUID) based magnetometer for two such applications, in vivo prepolarized, ultra-low …eld MRI of humans and dispersive readout of SQUIDs for micro-and nanoscale magnetometry, are the focus of this thesis.Conventional MRI has developed into a powerful clinical tool for imaging the human body. This technique is based on nuclear magnetic resonance of protons with the addition application of three-dimensional magnetic …eld gradients to encode spatial information. Most clinical MRI systems involve magnetic …elds generated by superconducting magnets, and the current trend is to higher magnetic …elds than the widely used 1.5-T systems. Nonetheless, there is ongoing interest in the development of less expensive imagers operating at lower …elds. The prepolarized, SQUID detected ultra-low …eld MRI (ULF MRI) developed by the Clarke group allows imaging in very weak …elds (typically 132 T, corresponding to a resonant frequency of 5.6 kHz). At these low …eld strengths, there is enhanced contrast in the longitudinal relaxation time of various tissue types, enabling imaging of objects which are not visible to conventional MRI, for instance prostate cancer. We are currently investigating the contrast between normal and cancerous prostate tissue in ex vivo prostate specimens in collaboration with the UCSF Genitourinary Oncology/Prostate SPORE Tissue Core. In characterizing pairs of nominally normal and cancerous tissue, we measure a marked di¤erence in the longitudinal relaxation times, with an average value of cancerous tissue 0.66 times shorter than normal prostate tissue. However, in vivo imaging is required to de…nitively demonstrate the feasibility of ULF MR imaging of prostate cancer. To that end, we have worked to improve the performance of the system to facilitate human imaging. This is accomplished by increasing the prepolarizing …eld amplitude, and minimizing magnetic noise in the SQUID detector. We have achieved polarizing …elds as high 2 as 150 mT and SQUID e¤ective …eld noise below 1 fT Hz 1=2 , enabling us to demonstrate proof-of-principle in vivo images of the human forearm with 2 x 2 x 10 mm 3 resolution in 6 minutes.On a much smaller spatial scale, there is currently fundamental and technological interest in measuring and manipulating nanoscale magnets, particularly in the qua...

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“…At LF/ULF, some techniques were developed to improve SNR. For example, a pre-polarization technique involving a current-pulsed coil [1] and an ultra-sensitive detector superconducting quantum interference device (SQUID) were combined to build a low-cost MRI system with acceptable SNR [2,3]. The first SQUID-based ultra-low field (ULF) MRI system was built by the Clarke group at Berkeley, and operated at 132 μT [4].…”

Section: Introductionmentioning

confidence: 99%

Adaptive suppression of power line interference in ultra-low field magnetic resonance imaging in an unshielded environment

Huang

Dong

Qiu

et al. 2018

Journal of Magnetic Resonance

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Power-line harmonic interference and fixed-frequency noise peaks may cause stripeartifacts in ultra-low field (ULF) magnetic resonance imaging (MRI) in an unshielded environment and in a conductively shielded room. In this paper we describe an adaptive suppression method to eliminate these artifacts in MRI images. This technique utilizes spatial correlation of the interference from different positions, and is realized by subtracting the outputs of the reference channel(s) from those of the signal channel(s) using wavelet analysis and the least squares method. The adaptive suppression method is first implemented to remove the image artifacts in simulation. We then experimentally demonstrate the feasibility of this technique by adding three orthogonal superconducting quantum interference device (SQUID) magnetometers as reference channels to compensate the output of one 2 nd -order gradiometer. The experimental results show great improvement in the imaging quality in both 1D and 2D MRI images at two common imaging frequencies, 1.3 kHz and 4.8 kHz. At both frequencies, the effective compensation bandwidth is as high as 2 kHz. Furthermore, we examine the longitudinal relaxation times of the same sample before and after compensation, andshow that the MRI properties of the sample did not change after applying adaptive suppression. This technique can effectively increase the imaging bandwidth and be applied to ULF MRI in both an unshielded environment and a shielded room made from aluminum sheets.

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SQUID-Detected Magnetic Resonance Imaging in Microtesla Fields

Cited by 197 publications

References 48 publications

NMR Detection at 8.9 Mt With a GMR Based Sensor Coupled to a Superconducting Nb Flux Transformer

NMR Detection at 8.9 Mt With a GMR Based Sensor Coupled to a Superconducting Nb Flux Transformer

SQUID magnetometry from nanometer to centimeter length scales

Adaptive suppression of power line interference in ultra-low field magnetic resonance imaging in an unshielded environment

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