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Chemical exchange saturation transfer (CEST) has been explored for differentiation between tumour and benign tissue in prostate cancer (PCa) patients. With ultrahigh field strengths such as 7-T, the increase of spectral resolution and sensitivity could allow for selective detection of amide proton transfer (APT) at 3.5 ppm and a group of compounds that resonate at 2 ppm (i.e., [poly]amines and/or creatine). The potential of 7-T multipool CEST analysis of the prostate and the detection of PCa was studied in patients with proven localised PCa who were scheduled to undergo robot-assisted radical prostatectomy (RARP). Twelve patients were prospectively included (mean age 68.0 years, mean serum prostate-specific antigen 7.8ng/mL). A total of 24 lesions larger than 2 mm were analysed. Used were 7-T T2-weighted (T2W) imaging and 48 spectral CEST points. Patients received 1.5-T/3-T prostate magnetic resonance imaging and galium-68-prostate-specific membrane antigen-positron emission tomography/computerised tomography to determine the location of the single-slice CEST. Based on the histopathological results after RARP, three regions of interest were drawn on the T2W images from a known malignant zone and benign zone in the central and peripheral zones. These areas were transposed to the CEST data, from which the APT and 2-ppm CEST were calculated. The statistical significance of the CEST between the central zone, the peripheral zone, and tumour was calculated using a Kruskal-Wallis test. The z-spectra showed that APT and even a distinct pool that resonated at 2 ppm were detectable. This study showed a difference trend in the APT levels, but no difference in the 2-ppm levels when tested between the central zone, the peripheral zone, and tumour (H(2) = 4.8, p = 0.093 and H(2) = 0.86, p = 0.651, respectively). Thus, to conclude, we could most likely detect APT and amines and/or creatine levels noninvasively in prostate using the CEST effect. At group level, CEST showed a higher level of APT in the peripheral versus the central zone; however, no differences of APT and 2-ppm levels were observed in tumours., (© 2023 The Authors. NMR in Biomedicine published by John Wiley & Sons Ltd.)

Immobilization masks are used to prevent patient movement during head and neck (H&N) radiotherapy. Motion restriction is beneficial both during treatment, as well as in the pre-treatment simulation phase, where magnetic resonance imaging (MRI) is often used for target definition. However, the shape and size of the immobilization masks hinder the use of regular, close-fitting MRI receive arrays. In this work, we developed a mask-compatible 8-channel H&N array that consists of a single-channel baseplate, on which the mask can be secured, and a flexible 7-channel anterior element that follows the shape of the mask. The latter uses high impedance coils to achieve its flexibility and radiolucency. A fully-functional prototype was manufactured, its radiolucency was characterized, and the gain in imaging performance with respect to current clinical setups was quantified. Dosimetry measurements showed an overall dose change of -0.3%. Small, local deviations were up to -2.7% but had no clinically significant impact on a full treatment plan, as gamma pass rates (3%/3 mm) only slightly reduced from 97.9% to 97.6% (clinical acceptance criterion: ≥95%). The proposed H&N array improved the imaging performance with respect to three clinical setups. The H&N array more than doubled (+123%) and tripled (+246%) the signal-to-noise ratio with respect to the clinical MRI-simulation and MR-linac setups, respectively. G -factors were also lower with the proposed H&N array. The improved imaging performance resulted in a clearly visible signal-to-noise ratio improvement of clinically used TSE and DWI acquisitions. In conclusion, the 8-channel H&N array improves the imaging performance of MRI-simulation and MR-linac acquisitions, while dosimetry suggests that no clinically significant dose changes are induced., (© 2022 Institute of Physics and Engineering in Medicine.)

Deuterium metabolic imaging (DMI) is a novel MR-based method to spatially map metabolism of deuterated substrates such as [6,6'- 2 H 2 ]-glucose in vivo. Compared with traditional 13 C-MR-based metabolic studies, the MR sensitivity of DMI is high due to the larger 2 H magnetic moment and favorable T 1 and T 2 relaxation times. Here, the magnetic field dependence of DMI sensitivity and transmit efficiency is studied on phantoms and rat brain postmortem at 4, 9.4 and 11.7 T. The sensitivity and spectral resolution on human brain in vivo are investigated at 4 and 7 T before and after an oral dose of [6,6'- 2 H 2 ]-glucose. For small animal surface coils (Ø 30 mm), the experimentally measured sensitivity and transmit efficiency scale with the magnetic field to a power of +1.75 and -0.30, respectively. These are in excellent agreement with theoretical predictions made from the principle of reciprocity for a coil noise-dominant regime. For larger human surface coils (Ø 80 mm), the sensitivity scales as a +1.65 power. The spectral resolution increases linearly due to near-constant linewidths. With optimal multireceiver arrays the acquisition of DMI at a nominal 1 mL spatial resolution is feasible at 7 T., (© 2019 John Wiley & Sons, Ltd.)

Phosphorus ( 31 P) MRSI provides opportunities to monitor potential biomarkers. However, current applications of 31 P MRS are generally restricted to relatively small volumes as small coils are used. Conventional surface coils require high energy adiabatic RF pulses to achieve flip angle homogeneity, leading to high specific absorption rates (SARs), and occupy space within the MRI bore. A birdcage coil behind the bore cover can potentially reduce the SAR constraints massively by use of conventional amplitude modulated pulses without sacrificing patient space. Here, we demonstrate that the integrated 31 P birdcage coil setup with a high power RF amplifier at 7 T allows for low flip angle excitations with short repetition time (T R ) for fast 3D chemical shift imaging (CSI) and 3D T 1 -weighted CSI as well as high flip angle multi-refocusing pulses, enabling multi-echo CSI that can measure metabolite T 2 , over a large field of view in the body. B 1 + calibration showed a variation of only 30% in maximum B 1 in four volunteers. High signal-to-noise ratio (SNR) MRSI was obtained in the gluteal muscle using two fast in vivo 3D spectroscopic imaging protocols, with low and high flip angles, and with multi-echo MRSI without exceeding SAR levels. In addition, full liver MRSI was achieved within SAR constraints. The integrated 31 P body coil allowed for fast spectroscopic imaging and successful implementation of the multi-echo method in the body at 7 T. Moreover, no additional enclosing hardware was needed for 31 P excitation, paving the way to include larger subjects and more space for receiver arrays. The increase in possible number of RF excitations per scan time, due to the improved B 1 + homogeneity and low SAR, allows SNR to be exchanged for spatial resolution in CSI and/or T 1 weighting by simply manipulating T R and/or flip angle to detect and quantify ratios from different molecular species., (© 2019 The Authors. NMR in Biomedicine published by John Wiley & Sons Ltd.)

The differentiation grade of cervical cancer is histologically assessed by examining biopsies or surgical specimens. MRS is a highly sensitive technique that images tissue metabolism and can be used to increase the specificity of tissue characterization in a non-invasive manner. We aim to explore the feasibility of using in vivo 1 H-MRS at 7 T in women with cervical cancer to study tissue fatty acid composition. 10 women with histologically proven Stage IB1-IIB cervical cancer were scanned with a whole-body 7 T MR system with a multi-transmit system and an internal receive only monopole antenna. A STEAM sequence was used to obtain 1 H-MRS data. Fatty acid resonances were fitted with Lorentzian curves and the 2.1 ppm/1.3 ppm ratios were calculated. 1 H-MRS data showed fatty acid signals resonating at 2.1 ppm, 1.9 ppm, 1.5 ppm, 1.3 ppm and 0.9 ppm. Mean 2.1/1.3 ppm ratios were 0.019 ± 0.01, 0.021 ± 0.006, 0.12 ± 0.089 and 0.39 ± 0.27 for normal, Grade I, Grade II and Grade III groups respectively. Poorly differentiated tumor tissue (Grade III) showed elevated fatty acid ratios when compared with the well differentiated tumor (Grade I) or normal tissue. 1 H-MRS in cervical cancer at 7 T is feasible and individual fatty acid signals were detected. In addition, poorly differentiated tumors show more fatty acid unsaturation. The 2.1 ppm/1.3 ppm ratio has potential for tumor characterization in a non-invasive manner for uterine cervical cancer., (© 2018 The Authors. NMR in Biomedicine published by John Wiley & Sons Ltd.)

The combination of functional MRI (fMRI) and MRS is a promising approach to relate BOLD imaging to neuronal metabolism, especially at high field strength. However, typical scan times for GABA edited spectroscopy are of the order of 6-30 min, which is long compared with functional changes observed with fMRI. The aim of this study is to reduce scan time and increase GABA sensitivity for edited spectroscopy in the human visual cortex, by enlarging the volume of activated tissue in the primary visual cortex. A dedicated setup at 7 T for combined fMRI and GABA MRS is developed. This setup consists of a half volume multi-transmit coil with a large screen for visual cortex activation, two high density receive arrays and an optimized single-voxel MEGA-sLASER sequence with macromolecular suppression for signal acquisition. The coil setup performance as well as the GABA measurement speed, SNR, and stability were evaluated. A 2.2-fold gain of the average SNR for GABA detection was obtained, as compared with a conventional 7 T setup. This was achieved by increasing the viewing angle of the participant with respect to the visual stimulus, thereby activating almost the entire primary visual cortex, allowing larger spectroscopy measurement volumes and resulting in an improved GABA SNR. Fewer than 16 signal averages, lasting 1 min 23 s in total, were needed for the GABA fit method to become stable, as demonstrated in three participants. The stability of the measurement setup was sufficient to detect GABA with an accuracy of 5%, as determined with a GABA phantom. In vivo, larger variations in GABA concentration are found: 14-25%. Overall, the results bring functional GABA detections at a temporal resolution closer to the physiological time scale of BOLD cortex activation., (© 2018 The Authors. NMR in Biomedicine published by John Wiley & Sons Ltd.)

The aim of this study was to investigate the signal-to-noise ratio (SNR) gain in early-stage cervical cancer at ultrahigh-field MRI (e.g. 7 T) using a combination of multiple external antennas and a single endorectal antenna. In particular, we used an endorectal monopole antenna to increase the SNR in cervical magnetic resonance imaging (MRI). This should allow high-resolution, T 2 -weighted imaging and magnetic resonance spectroscopy (MRS) for metabolic staging, which could facilitate the local tumor status assessment. In a prospective feasibility study, five healthy female volunteers and six patients with histologically proven stage IB1-IIB cervical cancer were scanned at 7 T. We used seven external fractionated dipole antennas for transmit-receive (transceive) and an endorectally placed monopole antenna for reception only. A region of interest, containing both normal cervix and tumor tissue, was selected for the SNR measurement. Separated signal and noise measurements were obtained in the region of the cervix for each element and in the near field of the monopole antenna (radius < 30 mm) to calculate the SNR gain of the endorectal antenna in each patient. We obtained high-resolution, T 2 -weighted images with a voxel size of 0.7 × 0.8 × 3.0 mm 3 . In four cases with optimal placement of the endorectal antenna (verified on the T 2 -weighted images), a mean gain of 2.2 in SNR was obtained at the overall cervix and tumor tissue area. Within a radius of 30 mm from the monopole antenna, a mean SNR gain of 3.7 was achieved in the four optimal cases. Overlap between the two different regions of the SNR calculations was around 24%. We have demonstrated that the use of an endorectal monopole antenna substantially increases the SNR of 7-T MRI at the cervical anatomy. Combined with the intrinsically high SNR of ultrahigh-field MRI, this gain may be employed to obtain metabolic information using MRS and to enhance spatial resolutions to assess tumor invasion., (Copyright © 2017 John Wiley & Sons, Ltd.)

Purpose: Improved diagnostic sensitivity could be obtained in cancer detection and staging when individual compounds of the choline pool can be detected. Therefore, a novel coil design is proposed, providing the ability to acquire both (1) H and (31) P magnetic resonance spectroscopic imaging (MRSI) in patients with prostate cancer., Methods: A two-element (1) H/(31) P endorectal coil was designed by adjusting a commercially available 3T endorectal coil. The two-element coil setup was interfaced as a transceiver to a whole body 7T MR scanner. Simulations and phantom measurements were performed to compare the efficiency of the coil. (1) H MRSI and (31) P MRSI were acquired in vivo in prostate cancer patients., Results: The efficiency of the (1) H/(31) P coil is comparable to the dual channel (1) H coil previously published. Individually distinguishable phospholipid metabolites in the in vivo (31) P spectra were: phosphoethanolamine, phosphocholine, phosphate, glycerophosphoethanolamine, glycerophosphocholine, phosphocreatine, and adenosine triposphate. (1) H MRSI was performed within the same scan session, visualizing choline, polyamines, creatine, and citrate., Conclusion: (1) H MRSI and (31) P MRSI can be acquired in the human prostate at 7T within the same scan session using an endorectal coil matched and tuned for (1) H (quadrature) and (31) P (linear) without the need of cable traps and with negligible efficiency losses in the (1) H and (31) P channel., (© 2013 Wiley Periodicals, Inc.)

Spectral degradations as a result of temporal field variations are observed in MRSI of the human prostate. Moving organs generate substantial temporal and spatial field fluctuations as a result of susceptibility mismatch with the surrounding tissue (i.e. periodic breathing, cardiac motion or random bowel motion). Nine patients with prostate cancer were scanned with an endorectal coil (ERC) on a 7-T MR scanner. Temporal B0 field variations were observed with fast dynamic B0 mapping in these patients. Simulations of dynamic B0 corrections were performed using zero- to second-order shim terms. In addition, the temporal B0 variations were applied to simulated MR spectra causing, on average, 15% underestimation of the choline/citrate ratio. Linewidth distortions and frequency shifts (up to 30 and 8 Hz, respectively) were observed. To demonstrate the concept of observing local field fluctuations in real time during MRSI data acquisition, a field probe (FP) tuned and matched for the (19)  F frequency was incorporated into the housing of the ERC. The data acquired with the FP were compared with the B0 field map data and used to correct the MRSI datasets retrospectively. The dynamic B0 mapping data showed variations of up to 30 Hz (0.1 ppm) over 72 s at 7 T. The simulated zero-order corrections, calculated as the root mean square, reduced the standard deviation (SD) of the dynamic variations by an average of 41%. When using second-order corrections, the reduction in the SD was, on average, 56%. The FP data showed the same variation range as the dynamic B0 data and the variation patterns corresponded. After retrospective correction, the MRSI data showed artifact reduction and improved spectral resolution. B0 variations can degrade the MRSI substantially. The simple incorporation of an FP into an ERC can improve prostate cancer MRSI without prior knowledge of the origin of the dynamic field distortions., (Copyright © 2014 John Wiley & Sons, Ltd.)

γ-Aminobutyric acid (GABA) and lactate are metabolites which are present in the brain. These metabolites can be indicators of psychiatric disorders or tumor hypoxia, respectively. The measurement of these weakly coupled spin systems can be performed using MRS editing techniques; however, at high field strength, this can be challenging. This is due to the low available B1 (+) field at high fields, which results in narrow-bandwidth refocusing pulses and, consequently, in large chemical shift displacement artifacts. In addition, as a result of the increased chemical shift displacement artifacts and chemical shift dispersion, the efficiency of the MRS method is reduced, even when using adiabatic refocusing pulses. To overcome this limitation, frequency offset corrected inversion (FOCI) pulses have been suggested as a mean to substantially increase the bandwidth of adiabatic pulses. In this study, a Mescher-Garwood semi-localization by adiabatic selection and refocusing (MEGA-sLASER) editing sequence with refocusing FOCI pulses is presented for the measurement of GABA and lactate in the human brain. Metabolite detection efficiencies were improved by 20% and 75% for GABA and lactate, respectively, when compared with editing techniques that employ adiabatic radiofrequency refocusing pulses. The highly efficient MEGA-sLASER sequence with refocusing FOCI pulses is an ideal and robust MRS editing technique for the measurement of weakly coupled metabolites at high field strengths., (Copyright © 2013 John Wiley & Sons, Ltd.)

Higher magnetic field strengths, such as 7 T, offer increased spectral resolution and higher signal-to-noise ratio. These properties can be very advantageous for MRSI. In particular, signals that generally overlap at lower fields, such as choline, polyamines and creatine, can be resolved at 7 T. However, higher magnetic field strengths suffer from strong radiofrequency (RF) field nonuniformities. These nonuniformities become even stronger when using surface transceivers, such as an endorectal coil for prostate imaging. In order to obtain uniform excitations for accurate MRSI measurements, adiabatic sequences are therefore recommended. Conventional adiabatic MRS sequences (i.e. localization by adiabatic selective refocusing, LASER) have relatively long TEs, especially when optimized to measure the strongly coupled spins of citrate in the prostate. The semi-LASER (sLASER) sequence has a significantly shorter TE, although it does not provide adiabatic excitation. Therefore, we propose an adiabatic sLASER sequence that either has a composite adiabatic slice-selective excitation (cLASER) or a non-slice-selective adiabatic excitation (nsLASER), allowing for shorter TEs, whilst maintaining the adiabatic spin excitation. Furthermore, the spatial properties of the composite adiabatic excitation allow for a high slice excitation bandwidth, resulting in negligible chemical shift displacement artifacts. Exclusion of the slice selection can be considered once the field of view extends beyond the transmit field of the RF coil. The use of a transceiver at high magnetic field strengths has shown that the cLASER and nsLASER sequences are suitable for MRSI of the prostate in both phantom and in vivo validations., (Copyright © 2012 John Wiley & Sons, Ltd.)

At high field (7 T) spectral editing of γ-aminobutyric acid with MEGA-point-resolved spectroscopy is inefficient due to the large chemical shift displacement error. In this article, a new pulse sequence is designed which has minimal chemical shift displacement error to perform an efficient spectral editing of the γ-aminobutyric acid 3.0 ppm resonance at 7 T. The sequence consists of the conventional MEGA editing pulses and a semi-localized by adiabatic selective refocusing sequence. Phantom and in vivo measurements demonstrated an efficient detection of γ-aminobutyric acid. Using ECG triggering, excellent in vivo performance of the MEGA-semi-localized by adiabatic selective refocusing (MEGA-sLASER) provided well-resolved γ-aminobutyric acid signals in 27 mL volumes in the human brain at an echo time of 74 ms within a relatively short acquisition time (5 min). Furthermore, the high efficiency of the MEGA-sLASER was demonstrated by acquiring small volumes (8 mL) at an echo time of 74 ms, as well as long echo time measurements (222 ms in 27 mL volume)., (Copyright © 2011 Wiley Periodicals, Inc.)

Higher magnetic field strengths like 7 T and above are desirable for MR spectroscopy given the increased spectral resolution and signal to noise ratio. At these field strengths, substantial nonuniformities in B(1)(+/-) and radiofrequency power deposition become apparent. In this investigation, we propose an improvement on a conventionally used endorectal coil, through the addition of a second element (stripline). Both elements are used as transceivers. In the center of the prostate, approximately 40% signal to noise ratio increase is achieved. In fact, the signal to noise ratio gain obtained with the quadrature configuration locally can be even greater than 40% when compared to the single loop configuration. This is due to the natural asymmetry of the B(1)(+/-) fields at high frequencies, which causes destructive and constructive interference patterns. Global specific absorption rate is reduced by almost a factor of 2 as expected. Furthermore, approximately a 4-fold decrease in local specific absorption rate is observed when normalized to the B(1) values in the center of the prostate. Because of the 4-fold local specific absorption rate decrease obtained with the dual channel setup for the same reference B(1) value (20 μT at 3.5 cm depth into the prostate) as compared to the single loop, the transmission power B(1) duty cycle can be increased by a factor 4. Consequently, when using the two-element endorectal coil, the radiofrequency power deposition is significantly reduced and radiofrequency intense sequences with adiabatic pulses can be safely applied at 7 T for (1)H magnetic resonance spectroscopy and MRI in the prostate. Altogether, in vivo (1)H magnetic resonance spectroscopic imaging of prostate cancer with a fully adiabatic sequence operated at a minimum B(1)(+) of 20 μT shows insensitivity to the nonuniform transmit field, while remaining within local specific absorption rate guidelines of 10 W/kg., (Copyright © 2011 Wiley Periodicals, Inc.)