WO2025212950A1 - High-speed, high-memory nmr spectrometer and hyperpolarizer - Google Patents

Abstract

A magnetic resonance (MR) spectrometer includes a magnet configured to hold one or more samples, an arbitrary waveform transceiver/generator (AWT/G) configured to generate a waveform at the Larmor frequency to apply to the sample, a duplexer to receive the waveform from theAWT/G, apply the signal to the sample, receive a signal from the sample, and send the signal from the sample to the AWT/G at the Larmor frequency in a phase sensitive manner, and a control computing device comprising one or more processors configured to receive the signal from the sample and to execute code that causes the one or more processors to analyze the sample.

Description

HIGH-SPEED, HIGH-MEMORY NMR SPECTROMETER AND HYPERPOLARIZER

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to and the benefit of US Provisional Application No. 63/575,307 filed April 5, 2024, which is incorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

[0002] This invention was made with Government support under grant number N00014-20- 1-2806 awarded by the Office of Naval Research, and grant FA9550-23-1-0106 awarded by the Air Force Office of Scientific Research. The Government has certain rights in this invention.

TECHNICAL FIELD

[0003] This disclosure relates to nuclear magnetic resonance (NMR) spectrometers and Electron Paramagnetic Resonance (EPR) spectroscopy, more particularly to NMR and EPR spectrometers with integrated control of electron and nuclear spins.

BACKGROUND

[0004] Advances in NMR spectroscopy and adjacent fields have historically often been spurred by innovations in instrumentation. Several transformative developments have emerged from such progress. These include Fourier Transform (FT) techniques that enabled multidimensional NMR, strong gradients that have enabled single-shot NMR spectroscopy methods, integrated electron-nuclear spin control for dynamic nuclear polarization (DNP), and infrastructure supporting non-traditional NMR pulse sequences that have resulted in numerous advancements.

[0005] However, as the science of NMR has matured and commercial NMR instruments have become widely accessible, they have been increasingly focused on traditional applications. This has resulted a reduction in their hardware and software flexibility as a result. A greater need is being felt for customizable NMR instrumentation that can be adapted to a wide range of applications, including towards emerging methodology for DNP and quantum sensing.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIG. 1 shows an embodiment of a high-speed, high-memory NMR spectrometer.

[0007] FIG. 2 shows an embodiment of a transmit-receive circuit.

[0008] FIG. 3 shows graphical representations of pulse shaping of signals during phasesensitive detection.

[0009] FIG. 4 shows graphs of free induction decay (FID) and Rabi oscillations.

[0010] FIG. 5 shows graphs of signals during digital down-conversion for phase-sensitive detection.

[0011] FIG. 6 shows a signal-to-comparison.

[0012] FIG. 7 shows a schematic of an experiment involving hyperpolarization and NMR.

[0013] FIG. 8 shows results of a DTC experiment.

[0014] FIG. 9 shows a diagram, and graphs related to an embodiment of a programmable TTL pulse generation circuit.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0015] The embodiments here introduce a new nuclear magnetic resonance (NMR), or electron paramagnetic resonance (EMR), both referred to here as magnetic resonance (MR), spectrometer architecture that capitalizes on the evolving capabilities of commercially available arbitrary waveform transceivers (AWTs) for the integrated control of electron and nuclear spins. While the use of AWT technology is established, having seen considerable recent developments in areas such as radar and communication systems, the enhancement in AWT capability over the past decade is remarkable, and has become the basis for spin control infrastructure in the adjacent field of quantum computing (QC). The increasing number of vendors in this field, partly driven by growth of the QC technologies, has rendered the technology more accessible, cost-effective, and functionally robust.

[0016] The embodiments here involve a novel magnetic resonance (MR) spectrometer, incorporating a high-speed, commercially available arbitrary waveform transceiver (AWT). In one embodiment, the AWT used is a Tabor Proteus P9484M AWT. However, the system may use any AWT having the same or similar capabilities as the Tabor model, as long as the AWT contains one or more arbitrary waveform generators (AWG) or may comprise a combination of an AWG and a receiver of some kind. For purposes of this discussion, the term AWT/G is defined to include both AWGs and AWTs.

[0017] No limitation to any particular configuration of the AWT/G is intended nor should it be implied. The AWT/G may be comprise one instrument, or a combination of instruments, commonly referred to as a composite instrument. The AWT/G characteristics include the ability to generate microwave signals with a particular pulse shape, either downloadable into a processor of the AWT/G or definable at a user interface of the AWT/G, and to receive signals, convert them as necessary, and store them signals in return.

[0018] The AWT/G device embodiments integrate an arbitrary waveform generator (AWG) with a fast analog-to-digital converter (ADC) and high-capacity on-board memory. One should note that AWT/Gs have traditionally found use in radar and communication systems, and more recently for quantum computation hardware. The same capabilities used in these applications are attractive in an NMR / DNP context.

[0019] As a representative example to demonstrate the flexibility of the embodiments, one can apply the spectrometer to experiments on a system of hyperpolarized ¹³C nuclear spins in diamond, which are polarized via optically pumped nitrogen-vacancy (NV) centers. A more detailed discuss of this type of system can be found in U.S. Patent Nos. 11,531,076, “WIDE DYNAMIC RANGE MAGNETIC FIELD CYCLER AND ULTRA PORTABLE OPTICAL NANODIAMOND HYPERPOLARIZER, issued December 20, 2022, and 12,017,919, “ORIENTATION INDEPENDENT, ROOM TEMPERATURE, HYPERPOLARIZATION OF DIAMOND NANO- AND MICRO-PARTICLES,” issued June 24, 2024. The AWT/G generates microwaves for low-field hyperpolarization, RF pulses for high-field NMR, and digitizes NMR signals.

[0020] The embodiment shown in FIG. 1 uses an FPGA-based AWT/G 10 similar to the Proteus system, but other systems with other types of processors, such as Application Specific Integrated Circuits (ASICs), general-purpose processors, digital signal processors, etc., may be used. As will be discussed in more detail, a control computer 12 having one or more processors and memory communicates with the processor and memory of the AWT/G. In one embodiment, the control computer 12 may communicate with the processor 16 through a high-speed serial bus such as a Peripheral Component Interface Express bus (PCIe). The processor 16 may include the processor and memory. The processor may have its own internal memory 18, and a faster memory 20 for output, or these may be separate structures on a processor board.

[0021] The AWT/G will employ digital-to-analog converters (DACs) 26. These may have a signal output speed of up to 9 GHz in the second Nyquist zone. This speed may remove the need for external mixers and reduces the associated insertion losses. Built-in I/Q (in-phase and quadrature) modulation is supported by two numerically controlled oscillators (NCOs) per channel in the output module 30, with waveforms stored in the processor memory for digital up-conversion. The Trigger System 24 provides deterministic control of the output signal, while the Transistor-Transistor Logic (TTL) Marker System 22 can provide transmit waveform coherent control of external equipment such as amplifier blanking, shuttle, laser control, and external AC-field sources.

[0022] The AWT/G cam generate microwave (MW) signal for electronic control. The DAC sampling rate of 9 GS/s facilitates direct MW generation up to 9 GHz, encompassing both the first (0-4.5 GHz) and second (4.5-9.0 GHz) Nyquist zones. This approach eliminates the need for external mixing infrastructure and reduce insertion losses. Higher Nyquist zones can also be utilized to extend the frequency range, such as generating signals in the third Nyquist zone (9-13.5 GHz), although this results in a reduced amplitude that falls off as sinc(nf '/ f _s), where f is the frequency of interest and f_s is the sampling frequency. For example, a continuous-wave tone at 9.8 GHz can be generated by setting an NCO in output module 30 to 4.9 GHz and using the image frequency. Output power can be boosted using an accessory PXIe amplifier, not shown, that spans from 100 kHz to 20 GHz. This versatility potentially broadens the device’s application range beyond NMR and DNP, especially towards X-band Electron Paramagnetic Resonance (EPR).

[0023] To illustrate the MW capabilities, one can implement DNP sequence designed to exploit the optical polarization of NV centers for hyperpolarizing local ¹³C nuclei. This process involves a series of cascaded Landau-Zener anti-crossings, achieved experimentally through MW chirps across the NV center EPR spectrum at low fields, combined with continuous laser excitation. The AWT/G generates the MW chirp waveform and outputs it to a sample of 13C nuclei 38.

[0024] At a polarizing “low” field, in one embodiment the low field is 38mT, this involves a chirp waveform with a linear frequency sweep from 3.4265 GHz to 3.4515 GHz at 750 sweeps per second. To implement this, the waveform is downloaded to the AWT/G and digitally up converted to 3.775 GHz ± 20 MHz using an NCO set at 0.34 GHz. The chirped MWs may then be amplified by a series of high-gain power amplifiers and applied simultaneously with 532 nm green laser 36 excitation for ~60 s, depending on the ¹³C T1 times at the polarizing field, to yield hyperpolarization. The sample may then be shuttled by shuttle 40 to the “high” field of the magnet shown by position 42.

[0025] The sample may then produce an output signal sent to the AWT/G 10 from the duplexer 32 to the input module 44. The received signal undergoes conversion back to an analog with one or more analog-to-digital converters (ADCs) 46. In one embodiment, two inputs share a 5.4 GS/s ADC, enabling one channel to operate at full rate or two channels at 2.7 GS/s each. The captured NMR data is stored in shared AWT/G memory 18, which permits multiple acquisitions per measurement. The raw data may occupy waveform memory space alongside the AWT/G, facilitating the collection of several acquisitions within a single measurement. Although the raw data can be transmitted directly to a measurement PC for analysis, the AWT/G processor could provide additional features, including decimation, filtering, averaging, and potentially real-time decision-making. The data is then analyzed to identify the sample.

[0026] In one embodiment, the AWT/G may have a “task table” feature to simplify programming and support memory efficiency. Each waveform is assigned a segment number, allowing playback in any order, and can be repeated up to IM times, skipped, or triggered externally. Task entries contain instructions for playback, repetitions, and triggers, enabling seamless transitions between tasks and supporting complex pulse and DNP sequences. The processor programming blocks further allow real-time decision -making, such as selecting waveforms based on ADC input levels.

[0027] In the DNP example, a single chirp sequence can be programmed into an instrument channel, with playback time adjusted through segment repetitions without rewriting the waveform. This feature enables more complex or customized sequences, such as a second chirp pulse sweeping in the opposite direction, by saving memory for additional waveform down-loads.

[0028] The AWT/G may also support digital demodulation of raw data using the NCO output as a reference, eliminating external down-conversion and ensuring coherent phase sensitive detection throughout measurements. This functionality underpins direct rotating frame interrogation of nuclear spins in sequences con-trolled by the device, discussed in more detail later. Triggers for data capture can be manual, external, or automated via AWG waveform play-back. Command and control are streamlined through standard Virtual Instrument Software Architecture (VISA) protocols that are compatible with Python, MATLAB, and Lab VIEW, ensuring seamless integration into existing workflows.

[0029] Having discussed electron control applications, the discussion now turns to the capabilities of the AWT/G for RF control and readout of nuclear spins that do not involve DNP. FIG. 2 shows a schematic of an embodiment of a transmit-receive RF circuit employed to probe samples held in an RF coil in a high magnetic field. The AWT/G 10 sends RF pulses, digitally synthesized using techniques similar to MW pulse generation, to an NMR saddle coil in the probe 52 via a cross- diode duplexer 32 and amplified with an amplifier 50. In one embodiment the amplifier comprises a traveling wave tube (TWT) amplifier. For ¹³C nuclei in a 300 MHz superconducting NMR magnet, the Larmor frequency (75 MHz) is directly synthesized by the AWT/G’ s digital -to-analog converter.

[0030] The pulses generated by the AWT/G 10 may take many forms. Fig. 3 A illustrates representative examples of generated RF pulses. The data in Fig. 3 A shows the produced pulses digitized by the same AWT/G, from left to right, including rectangular, Gaussian, secant, and Hermite pulse shapes. Fig. 3B shows the corresponding Fourier transform of these pulses, indicating high spectral purity. These pulse shapes are easy to generate as data arrays in Matlab or Python, making implementation straightforward.

[0031] To provide more details of pulse generation and data acquisition, the AWT/G may employ interpolation to reduce waveform size, and decimation to decrease the read-out memory window by down sampling at an integer factor. Interpolation and decimation significantly reduce memory usage while preserving the essential characteristics of the pulse.

[0032] Pulse generation for the implementation in Fig. 3 begins by drawing a pulse envelope, represented by an array with 16-bit resolution. Each data point in the array corresponds to the envelope shape at intervals of 1/675 x 10⁶ seconds, resulting in sampling frequency of 675 MHz This pulse envelope is then downloaded into the memory of the AWT/G.

[0033] When outputting the pulse, the AWT/G uses the downloaded pulse envelope and applies interpolation to increase the sampling rate, in one embodiment the interpolation factor of 8 was used to increase the sampling rate to 5.4 GHz. Subsequently, the AWT/G can digitally mix this interpolated signal with the AWT/G’ s on-chip NCO, which is set to the system’s Larmor frequency. The advantage of this on-chip mixing is that it simplifies the pulse generation process, requiring only the drawing of the pulse envelope without needing to account for the carrier frequency.

[0034] In one embodiment, to capture the produced pulse shape, the AWT/G’s output channel is directly connected to the ADC channel. In one embodiment the sampling rate of the AWT/G’s ADC is set to 2.7 GHz. The AWT/G digitizes the pulse from its output while simultaneously digitally mixing it down using the receiver NCO, locked with the pulsegenerating NCO, ensuring accurate capture and demodulation to baseband with 12-bit vertical resolution. The AWT/G then saves the mixed-down pulse in its memory with a 16x decimation factor, resulting in data points being obtained every 16 seconds.

[0035] Returning to FIG. 2, the produced RF pulses following FIG. 3 are delivered to the probe by means of the traveling wave tube (TWT) amplifier 50 via a cross-diode duplexer 32. The NMR probe 54 features a saddle coil inductor (NMR coil) with tuning and 50-ohm impedance matching. In one embodiment, the coil is fabricated from 1 mm thick oxygen free high-conductivity (OFHC) copper via laser cutting. Design considerations, such as short capacitor leads and proper grounding to brass and copper ribs, ensure robust RF shielding.

[0036] The NMR receive circuit is designed to detect weak nuclear induction signals generated on the same saddle coil. The probe 54 transmits the RF signal to the coil 52 that holds the sample in the field of the magnet 34. The probe also receives the weak nuclear induction signals from the sample the result from the response of the sample to the application of the RF pulses. These signals first pass through a 75 MHz quarter-wave line and a cross-diode duplexer. The duplexer ensures that only the intended signals pass through the transmit path, preventing the sensitive preamplifiers in the receive circuit from detecting the amplified pulses meant for the probe.

[0037] Subsequently, the signal is amplified by a series of amplifiers 56 and 60, such as low- noise amplifiers. For optimal performance, these amplifiers may be powered by a low-noise DC voltage and current source. Additionally, an attenuator, such as a 9 dB attenuator 58, is inserted between the two amplifiers to reduce intermodulation distortion. The amplified signal is then digitized using the same process described above. In one embodiment, the AWT/G employs a 2.7GS/s sampling rate for good performance.

[0038] FIG. 4A shows the results of standard experiments using the constructed spectrometer, an FID and Rabi oscillations of the hyperpolarized ¹³C nuclear spins at 7 T. FIG. 4A(i) presents single-shot time-domain FID data comparing cases where the NCO is either on-resonant or off-resonant, while FIG. 4A(ii) shows the corresponding Fourier transforms. The FID decay time T2* = 1.5 ms, and corresponding spectrum linewidth 660Hz is dominated by internuclear dipolar interactions. FIG. 4B displays a typical ¹³C Rabi oscillation obtained by varying the length of the excitation pulse. RF inhomogeneity is believed to have caused slightly non-sinusoidal behavior to RF inhomogeneity across the diamond sample and also the pulse ring-down that is unaccounted for when changing the length of the pulse to change its angle 19.

[0039] In one embodiment, the AWT/G has direct phase-sensitive digitization of the NMR signal at the Larmor frequency, leveraging the device’s rapid sampling rate, and eliminating the need for down-mixing elements. FIG. 5A illustrates how this feature enables the extraction of both the phase and the signal of the NMR signal in a windowed acquisition for a representative multipulse sequence consisting of a series of multiple spinlocking TT/2 pulses. The NMR signal is interrogated in tacq windows between the pulses.

[0040] FIG. 5B(i) and (ii) present real (I) and imaginary (Q) raw data acquired by the AWT/G for one representative tacq ~ 13.6/zs signal window, sampled every approximately 5.9 ns, meaning a rate of 168.75Ms/s from decimation. The sequence in FIG. 5A itself entails 2M such windows. In Fig. 5B(i-ii), the 75 MHz Larmor signal is digitally down-converted to DC by mixing with an in-phase and 90° off-phase NCO on-chip, operating at the Larmor frequency. Insets in FIG. 5B(i) and (ii) show a zoom in a 0.3/zs window. The high sampling of the data is evident. A Fourier transform of the signal exhibits a peak at or around zerofrequency, this represents the NMR signal.

[0041] FIG. 5B(iii) illustrates the IQ signals for the same window plotted simultaneously on a 2D plot. One can identify the radial position S of the centroid in this plot, effectively the net signal intensity, and its phase (p, respectively as the net projection of the spin vector on the x — y plane of the Bloch sphere directly in the rotating frame. FIG. 5 A(ii) shows this schematically. AWT/G sampling at the Larmor frequency and digital mixing with a matched NCO provides a simple and effective way to translate the spin dynamics from the lab frame to the rotating frame. This is especially powerful when combining the S and (p information from each acquisition window in the multi-pulse sequence in FIG. 5A. Since each window is referenced to the NCO, the phase evolution during pulse periods is inherently accounted for, enabling the ability to precisely discern S and (p directly in the rotating frame. [0042] To combine the multipulse data efficiently, the I and Q components of the raw data are averaged within each acquisition window. These average values, denoted henceforth as (I) and (Q), are denoted in FIG. 5B(iii) as the respectively intercepts on the 2D plot. The signal intensity and phase associated with each window are then directly extracted from these averages.

[0043] Fig. 5C presents the amplitude S and phase (p data from the spin-lock sequence in FIG. 5A(i) with 2M x-pulses. The phase is represented after the first n/2 x-pulse to be (p = 0. FIG. 5C(i) presents the corresponding amplitude signal S over t = 160s; this trace also contains 2M points. The dashed line denotes the 1/e decay time of T2 = 40.8s, significantly extended over the typical T₂* time, as shown in FIG. 4A. FIG. 5C(ii) displays the corresponding phase points and reveals slight dephasing from (p = 0 at long times due to the decay of the spin-locked state. Combining this amplitude and phase data, together with a unitary constraint of the nuclear spin vector, can facilitate the quasi -continuous tracking of spins on a (half) Bloch sphere.

[0044] To benchmark the performance of the AWT/G-based spectrometer, its signal-to-noise ratio (SNR) was compared to that of a commercial Varian system (Agilent DD2 Spectrometer) under identical experimental conditions. This comparison involved systematically swapping individual components to assess their impact on SNR.

[0045] Fig. 6A illustrates the hyperpolarized pulsed spinlock ¹³C signal, similar to FIG. 5C, measured using the AWT/G spectrometer, which serves as a benchmark for the comparison. The inset in FIG. 6 A shows the pulse sequence with T = 43 ps and t_acq ~ 33.6/zs, and a total of 563,064 pulses and acquisition windows for a total of 60 s. Fig. 6C(i)-(iii) displays the Fourier trans-form of the spin-lock decay signal acquired under three configurations, with corresponding schematics shown in FIG. 6B(i)-(iii). In these schematics, the receiver, sample and probe in FIG. 6B(i), the receiver, sample, probe and duplexer in FIG. 6B(ii), and all components in FIG. 6B(iii), were home-built components as outlined in FIG. 2, while other boxes represent components from the commercial Varian system.

[0046] The first configuration in FIG. 6B(i) utilized the Varian pulse sequencer and transmit/receive (T/R) circuit but digitized the signal through the AWT/G spectrometer. The second configuration in FIG. 6B(ii)) replaced the Varian T/R circuit with a home-built T/R and preamplifier circuit, shown in FIG. 2, while maintaining the Varian pulse sequencer. Finally, the third configuration of FIG. 6B(iii)) employed the AWT/G pulse sequencer discussed above along with the homebuilt T/R and preamplifier circuit of FIG. 2. To ensure comparability, the transmit amplifier’s input signal and the nuclear Rabi frequency is maintained identical across all configurations.

[0047] For each configuration, the measured signal was normalized to 1, and the noise was calculated by averaging 10,000 points from the wings of the log-scale power spectrum. The SNR values obtained are depicted in the SNR numbers alongside the Fourier spectra in FIG. 6C. Using the fully commercial system, an SNR of 2.9xl0⁵ was achieved in FIG. 6C(i)). Replacing the Varian T/R circuit with the homebuilt circuit modestly improved the SNR to 3.2* 10⁵, an approximate 1. lx increase, demonstrating that the homebuilt circuit performs comparably to the commercial counterpart. When the Varian pulse sequencer was substituted with the Proteus AWT/G as in FIG. 6C(iii), the SNR increased to 7.1 * 10⁵, representing a 2.2x improvement over the configuration with the Varian pulse sequencer and a 2.4x improvement over the fully commercial system.

[0048] We describe the applications of AWT/G-based NMR spectroscopy for a few representative experiments. One notable example is their role in constructing discrete time crystals (DTCs) with hyperpolarized ¹³C nuclear spins. DTCs exhibit a robust perioddoubling response that is inherently resilient to pulse errors and disorder. Unlike other demonstrations of DTC-like phenomena that rely on point-by-point measurements, the AWT/G allows for quasi-continuous signal acquisition, shown in FIG. 5C, over extended durations without reinitialization. This capability permits real-time observation of DTC formation and melting in a single shot, streamlining the experimental mapping of the DTC phase diagram.

[0049] The AWT/G is employed here for controlling both electron and nuclear spins, as shown in FIG. 7. During hyperpolarization in the upper left block of FIG. 7, one AWT/G channel delivers chirped MW excitation, as described in FIG. 1, applied with 532 nm laser pumping at low magnetic fields for 60 s. The sample is then transferred, or shuttled, to a 7T superconducting magnet, where a different AWT/G channel generates NMR pulses applied to ¹³C nuclei, and the digitizer captures signals between pulses.

[0050] The DTC sequence, in one embodiment implemented through the task table mentioned above, is displayed in the lower right block of FIG. 7. Spins initially aligned along the x-axis are tipped alternately between the x and -x axes using y_y pulses, interspersed with 6000 spin-locking pulses. The digitizer is activated during the time indicated as T in FIG. 7. The DTC demonstrates robustness against imperfections in the y_y flip angle; a spin-flipping response is achieved even for deviations y_y = n+e.

[0051] A generalized variant of the DTC pulse sequence is that recently referred to as “time rondeau” crystal. This can be considered to be a type of nonequilibrium order that contains long-time stroboscopic order but short-time disorder. As shown in Fig. 8A, it involves defining two distinct blocks: the first block consists of (A ~n) n/2 x-pulses, one n y-pulse, and n x-pulses, while the second block contains n n/2 x-pulses, one n y-pulse, and (A ~ri) x- pulses. A and n are integers such that 0 < n < N/2. After the initial 6000 n/2 x-pulses, these two blocks are randomly arranged in any order. The AWT simplifies the implementation of these complex and/or randomized sequences.

[0052] Representative single-shot decay curves of the lx magnetization and the corresponding measured rotating frame phase, (p = arctan(J_y/I_x ), are illustrated in FIG. 8B-C for an exemplary case of y = 0.98TT. Traces 70 and 72 represent DTC and time rondeau crystal sequences, respectively. As shown in Fig. 8B, the spins consistently switch between +x and the -x axes despite the pulse error, achieving over 150 spin flips during the 16-second period. The inset in Fig. 8B offers a closer view of the experimental data, emphasizing a 0.3 s window where the periodic (i) and random (ii) changes in the sign of lx are clearly visible.

[0053] The phase response, illustrated in Fig. 8C, exhibits periodic switching between rails, shown at 76 and 78, that correspond to phase values of 0 (x) and n (-x), respectively, with each y-pulse. Insets (i) and (ii) provide a magnified view. The phase remains stable over hundreds of cycles, displaying minimal dephasing after t = 16s. This stability highlights the AWT’s capability to facilitate extended studies of dipolar-coupled systems, utilizing its high sampling rate and memory capacity.

[0054] A second representative example demonstrates, the application of the AWT for the sensing of time-varying (AC) magnetic fields using hyperpolarized ¹³C nuclei. It works on the principle that the nuclei when spin-locked, undergo secondary precessions in the rotating frame when exposed to an AC magnetic field; the precession carrying a direct imprint of the sensing field, and allowing its sensitive detection.

[0055] These experiments employ the AWT’s capability to synchronize external devices with the pulse sequence it produces, specifically, here a function generator producing the AC magnetic field to be detected. As shown in FIG. 9A, the AWT 10 generates pulses on a first channel. Labeled Ch 1, while a trigger signal from Marker 1 of a different channel, labeled Ch 2, synchronizes the AC field produced by function generator 80 with the pulse sequence. The two channels are connected to input channels of an oscilloscope 82.

[0056] The pulse sequence for sensing, illustrated in Fig. 9B, involves a train of 19 spinlocking pulses on the hyperpolarized ¹³C nuclei. Here shown is a CPMG sequence as a representative example. A marker was programmed to activate the AC field halfway through the 1000th x-pulse. A 20 s trigger shown in the middle pulse diagram is utilized to switch on the AC field 84 on an edge trigger. The AC field itself is delivered along the z direction through a circular coil in the probe as shown in FIG. 2.

[0057] Traces of the pulses and the synchronized AC field, captured by the oscilloscope 82, are shown in Fig. 9C for clarity. It indicates the triggered AC field midway through the 1000th x-pulse. The programmable pulse length and spacing provide precise adjustment of the AC field frequency and phase, allowing for alignment of its nodes (anti-nodes) at a 0° (90°) phase at the pulse midpoint. While this example uses a single trigger, the AWT can manage up thousands, even tens of thousands, synchronized triggers over extended durations.

[0058] Fig. 9D shows the resulting phase (<p) signal of the spin-locked hyperpolarized ¹³C nuclei analogous to FIG. 5C(ii), but when exposed to the AC field. Here 19 = TT/2, t_acq ~ 13.6/zs, T = 36/zs and the signal is measured continuously for t = 18 s. The AC field is applied precisely at the 2 s mark. The phase signal serves as a direct imprint of the AC field; this is seen clearly in the 4ms zoomed-in inset in Fig. 9D. In addition to sensing, this setup is capable of manipulating spins along specific 3D Bloch sphere trajectories while continuously monitoring them. Overall, this example underscores the precision of the AWT in activating external devices and synchronizing pulse sequences with data acquisition blocks.

[0059] All features disclosed in the specification, including the claims, abstract, and drawings, and all the steps in any method or process disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. Each feature disclosed in the specification, including the claims, abstract, and drawings, can be replaced by alternative features serving the same, equivalent, or similar purpose, unless expressly stated otherwise.

[0060] Additionally, this written description makes reference to particular features. It is to be understood that the disclosure in this specification includes all possible combinations of those particular features. For example, where a particular feature is disclosed in the context of a particular aspect, that feature can also be used, to the extent possible, in the context of other aspects.

[0061] Also, when reference is made in this application to a method having two or more defined steps or operations, the defined steps or operations can be carried out in any order or simultaneously, unless the context excludes those possibilities.

[0062] Although specific aspects of this disclosure have been illustrated and described for purposes of illustration, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, the invention should not be limited except as by the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A magnetic resonance (MR) spectrometer, comprising: a magnet configured to hold one or more samples; an arbitrary waveform transceiver/generator (AWT/G) configured to generate a waveform at the Larmor frequency to apply to the sample; a duplexer to receive the waveform from theAWT/G, apply the signal to the sample, receive a signal from the sample, and send the signal from the sample to the AWT/G at the Larmor frequency in a phase sensitive manner; and a control computing device comprising one or more processors configured to receive the signal from the sample and to execute code that causes the one or more processors to analyze the sample.

2. The MR spectrometer as claimed in claim 1, wherein the magnet comprises a super conducting magnet.

3. The MR spectrometer as claimed in claim 1, wherein further comprising a radio frequency (RF) coil in the magnetic field of the super conducting magnet, the coil configured to hold the sample.

4. The MR spectrometer as claimed in claim 2, wherein the MR spectrometer comprises a nuclear magnetic spectrometer.

5. The MR spectrometer as claimed in claim 2, further comprising a probe connected to the duplexer to apply the waveform to the sample and receive the signal from the sample.

6. The MR spectrometer as claimed in claim 2, further comprising an amplifier between the duplexer and the AWT/G to amplify the waveform.

7. The MR spectrometer as claimed in claim 6, wherein the amplifier comprises a traveling wave tube (TWT) amplifier.

8. The MR spectrometer as claimed in claim 2, further comprising one or more low noise amplifiers between the duplexer and the AWT/G to amplify the signal received from the sample.

9. The MR spectrometer as claimed in claim 7, wherein the one or more low noise amplifiers comprise two low noise amplifiers, and the MR spectrometer further comprises an attenuator between the two low noise amplifiers.

10. The MR spectrometer as claimed in claim 1, wherein the MR spectrometer comprises a hyperpolarizer and comprises: a mechanism to shuttle the samples between low and high magnetic fields the AWT/G having at least one channel configured to apply a microwave signal to the sample in the low magnetic field region adjacent the super conducting magnet; and a laser to optically pump the sample in the low magnetic field region.

11. The MR spectrometer as claimed in claim 1, wherein the magnet is an electromagnet.

12. The MR spectrometer as claimed in claim 1, wherein the MR spectrometer comprises an electron paramagnetic resonance spectrometer.

13. The MR spectrometer as claimed in claim 1, further comprising a control computer connected to the AWT/G, the control computer to allow a user to program pulse shapes and transfer the pulse shapes to the AWT/G.

14. The MR spectrometer as claimed in claim 13, wherein the control computer receives the signal from the sample from the AWT/G and identifies the sample.