Deuterium metabolic imaging (DMI) is a novel noninvasive method to assess tissue metabolism and organ (patho)physiology in vivo using deuterated substrates, such as 6,6’‐2H2‐glucose. The liver and ...kidneys play a central role in whole‐body glucose homeostasis, and in type 2 diabetes, both hepatic and renal glucose metabolism are dysregulated. Diabetes is also associated with gastric emptying abnormalities. In this study, we developed a four‐channel 2H transmit/receive body array coil for DMI in the human abdomen at 7 T and assessed its performance. In addition, the feasibility of simultaneously measuring gastric emptying, and hepatic and renal glucose uptake and metabolism with dynamic 3D DMI upon administration of deuterated glucose, was investigated. Simulated and measured B1+ patterns were in good agreement. The intrasession variability of the natural abundance deuterated water signal in the liver and right kidney, measured in nine healthy volunteers, was 5.6% ± 0.9% and 4.9% ± 0.7%, respectively. Dynamic 3D DMI scans with oral administration of 6,6’‐2H2‐glucose showed similar kinetics of deuterated glucose appearance and disappearance in the liver and kidney. The measured gastric emptying half time was 80 ± 10 min, which is in good agreement with scintigraphy measurements. In conclusion, DMI with oral administration of 6,6’‐2H2‐glucose enables simultaneous assessment of gastric emptying and liver and kidney glucose uptake and metabolism. When applied in patients with diabetes, this approach may advance our understanding of the interplay between disturbances in liver and kidney glucose uptake and metabolism and gastric emptying, at a detail that cannot be achieved by any other method.
The development of a four‐channel deuterium body array coil enabled dynamic DMI in the human abdomen with a FOV covering the liver, kidney, and stomach. Upon oral administration of 6,6’‐2H2‐glucose, liver and kidney glucose uptake and metabolism could be determined, together with the assessment of gastric emptying.
Purpose
Metabolic MRI is a noninvasive technique that can give new insights into understanding cancer metabolism and finding biomarkers to evaluate or monitor treatment plans. Using this technique, a ...previous study has shown an increase in pH during neoadjuvant chemotherapy (NAC) treatment, while recent observation in a different study showed a reduced amide proton transfer (APT) signal during NAC treatment (negative relation). These findings are counterintuitive, given the known intrinsic positive relation of APT signal to pH.
Methods
In this study we combined APT MRI and 31P‐MRSI measurements to unravel the relation between the APT signal and pH in breast cancer. Twenty‐two breast cancer patients were scanned with a 7 T MRI before and after the first cycle of NAC treatment. pH was determined by the chemical shift of inorganic phosphate (Pi).
Results
While APT signals have a positive relation to pH and amide content, we observed a direct negative linear correlation between APT signals and pH in breast tumors in vivo.
Conclusions
As differentiation of cancer stages was confirmed by observation of a linear correlation between cell proliferation marker PE/Pi (phosphoethanolamine over inorganic phosphate) and pH in the tumor, our data demonstrates that the concentration of mobile proteins likely supersedes the contribution of the exchange rate to the APT signal.
31P‐MRS and CEST‐MRI were acquired in 22 breast cancer patients with a 7 T MRI. While APT signals have a positive relation to pH and amide content, we observed a direct negative linear correlation between APT signals and pH in breast tumors in vivo. Our data demonstrates that the concentration of mobile proteins likely supersedes the contribution of the exchange rate to the APT signal.
The purpose of this work was to investigate whether noninvasive early detection (after the first cycle) of response to neoadjuvant chemotherapy (NAC) in breast cancer patients was possible. 31P‐MRSI ...at 7 T was used to determine different phosphor metabolites ratios and correlate this to pathological response.
31P‐MRSI was performed in 12 breast cancer patients treated with NAC. 31P spectra were fitted and aligned to the frequency of phosphoethanolamine (PE). Metabolic signal ratios for phosphomonoesters/phosphodiesters (PME/PDE), phosphocholine/glycerophosphatidylcholine (PC/GPtC), phosphoethanolamine/glycerophosphoethanolamine (PE/GPE) and phosphomonoesters/in‐organic phosphate (PME/Pi) were determined from spectral fitting of the individual spectra and the summed spectra before and after the first cycle of NAC. Metabolic ratios were subsequently related to pathological response. Additionally, the correlation between the measured metabolic ratios and Ki‐67 levels was determined using linear regression.
Four patients had a pathological complete response after treatment, five patients a partial pathological response, and three patients did not respond to NAC. In the summed spectrum after the first cycle of NAC, PME/Pi and PME/PDE decreased by 18 and 13%, respectively. A subtle difference among the different response groups was observed in PME/PDE, where the nonresponders showed an increase and the partial and complete responders a decrease (P = 0.32). No significant changes in metabolic ratios were found. However, a significant association between PE/Pi and the Ki‐67 index was found (P = 0.03).
We demonstrated that it is possible to detect subtle changes in 31P metabolites with a 7 T MR system after the first cycle of NAC treatment in breast cancer patients. Nonresponders showed different changes in metabolic ratios compared with partial and complete responders, in particular for PME/PDE; however, more patients need to be included to investigate its clinical value.
We demonstrated that changes in 31P metabolites can be detected by 7 T MRI after the first cycle of neoadjuvant chemotherapy in breast cancer patients. Already, after the first cycle, patient groups with different pathological responses can potentially be distinguished based on the different metabolic ratios, of which phosphomonoesters/phosphodiesters is most likely to discriminate nonresponders from the partial and complete responders.
Methods for early treatment response evaluation to systemic therapy of liver metastases are lacking. Tumor tissue often exhibits an increased ratio of phosphomonoesters to phosphodiesters (PME/PDE), ...which can be noninvasively measured by phosphorus magnetic resonance spectroscopy (
P MRS), and may be a marker for early therapy response assessment in liver metastases. However, with commonly used
P surface coils for liver
P MRS, the liver is not fully covered, and metastases may be missed. The objective of this study was to demonstrate the feasibility of
P MRS imaging (
P MRSI) with full liver coverage to assess
P metabolite levels and chemotherapy-induced changes in liver metastases of gastro-esophageal cancer, using a
P whole-body birdcage transmit coil in combination with a
P body receive array at 7 T. 3D
P MRSI data were acquired in two patients with hepatic metastases of esophageal cancer, before the start of chemotherapy and after 2 (and 9 in patient 2) weeks of chemotherapy. 3D
P MRSI acquisitions were performed using an integrated
P whole-body transmit coil in combination with a 16-channel body receive array at 7 T, with a field of view covering the full abdomen and a nominal voxel size of 20-mm isotropic. From the
P MRSI data, 12
P metabolite signals were quantified. Prior to chemotherapy initiation, both PMEs, that is, phosphocholine (PC) and phosphoethanolamine (PE), were significantly higher in all metastases compared with the levels previously determined in the liver of healthy volunteers. After 2 weeks of chemotherapy, PC and PE levels remained high or even increased further, resulting in increased PME/PDE ratios compared with healthy liver tissue, in correspondence with the clinical assessment of progressive disease after 2 months of chemotherapy. The suggested approach may present a viable tool for early therapy (non)response assessment of tumor metabolism in patients with liver metastases.
Ultrahigh field magnetic resonance imaging facilitates high spatiotemporal resolution that benefits from increasing the number of receiver elements. Because high‐density receiver arrays have a ...relatively small element size compared with the transmitter, a side effect is that such setups cause low flux coupling between the transmitter and receiver. Moreover, when transmitters are designed in a multitransmit configuration, their relative size is much smaller than the sample, reducing coupling to the sample and thereby potentially also the coupling to the receivers. Transmitters are traditionally detuned during reception. In this study, we investigate, for a 32‐channel receiver head array at 7 T, if transmitter detuning of a quadrature birdcage or of an eight‐channel transmit coil can be omitted without substantially sacrificing signal‐to‐noise ratio (SNR). The transmit elements are operated once with and once without detuning and, in the latter, the received signals are either merged with the array or excluded for image reconstruction. For each of the three measurements, SNR and 1/g‐factor maps are investigated. The tuning of the quadrature and eight‐channel transmit coils during signal reception introduced a 10.1% and 6.5% penalty in SNR, respectively, relative to the SNR received with detuned transmitters. When also incorporating the signal of the transmit coils, the SNR was regained to 98.5% or 101.4% for the quadrature and eight‐channel coil, respectively, relative to the detuned transmitters, while the 1/g‐factor maps improved slightly. For the 32‐channel receive coil used the SNR penalty can become negligible when omitting detuning of the transmit coils. This not only simplifies transmit coil designs, potentially increasing their efficiency, but also enables the transmitters to be used as receivers in parallel to the receiver array, thus increasing parallel imaging performance.
Traditionally, transmitter coils are detuned from receivers during acquisition to exclude their noise contribution. However, with high‐density arrays that have smaller elements, this noise contribution can become negligible and can even be overcompensated by acquiring the signal from the tuned transmit elements as well. We demonstrate the effect of a tuned quadrature birdcage and an eight‐channel transmit coil on a 32‐channel receiver array at 7 T in terms of signal‐to‐noise ratio and 1/g‐factor performance when loaded with a human head.
Purpose
Assess the potential gain in acceleration performance of a 256‐channel versus 32‐channel receive coil array at 7 T in combination with a 2D CAIPIRINHA sequence for 3D data sets.
Methods
A ...256‐channel receive setup was simulated by placing 2 small 16‐channel high‐density receive arrays at 2 × 8 different locations on the head of healthy participants. Multiple consecutive measurements were performed and coil sensitivity maps were combined to form a complete 256‐channel data set. This setup was compared with a standard 32‐channel head coil, in terms of SNR, noise correlation, and acceleration performance (g‐factor).
Results
In the periphery of the brain, the receive SNR was on average a factor 1.5 higher (ranging up to a factor 2.7 higher) than the 32‐channel coil; in the center of the brain the SNR was comparable or lower, depending on the size of the region of interest, with a factor 1.0 on average (ranging from 0.7 up to a factor of 1.6). The average noise correlation between coil elements was 3% for the 256‐channel coil, and 5% for the 32‐channel coil. At acceptable g‐factors (< 2), the achievable acceleration factor using SENSE and 2D CAIPIRINHA was 24 and 28, respectively, versus 9 and 12 for the 32‐channel coil.
Conclusion
The receive performance of the simulated 256 channel array was better than the 32‐channel reference. Combined with 2D CAIPIRINHA, a peak acceleration factor of 28 was assessed, showing great potential for high‐density receive arrays.
Quantitative three‐dimensional (3D) imaging of phosphorus (31P) metabolites is potentially a promising technique with which to assess the progression of liver disease and monitor therapy response. ...However, 31P magnetic resonance spectroscopy has a low sensitivity and commonly used 31P surface coils do not provide full coverage of the liver. This study aimed to overcome these limitations by using a 31P whole‐body transmit coil in combination with a 16‐channel 31P receive array at 7 T. Using this setup, we determined the repeatability of whole‐liver 31P magnetic resonance spectroscopic imaging (31P MRSI) in healthy subjects and assessed the effects of principal component analysis (PCA)‐based denoising on the repeatability parameters. In addition, spatial variations of 31P metabolites within the liver were analyzed. 3D 31P MRSI data of the liver were acquired with a nominal voxel size of 20 mm isotropic in 10 healthy volunteers twice on the same day. Data were reconstructed without denoising, and with PCA‐based denoising before or after channel combination. From the test–retest data, repeatability parameters for metabolite level quantification were determined for 12 31P metabolite signals. On average, 31P MR spectra from 100 ± 25 voxels in the liver were analyzed. Only voxels with contamination from skeletal muscle or the gall bladder were excluded and no voxels were discarded based on (low) signal‐to‐noise ratio (SNR). Repeatability for most quantified 31P metabolite levels in the liver was good to excellent, with an intrasubject variability below 10%. PCA‐based denoising increased the SNR ~ 3‐fold, but did not improve the repeatability for mean liver 31P metabolite quantification with the fitting constraints used. Significant spatial heterogeneity of various 31P metabolite levels within the liver was observed, with marked differences for the phosphomonoester and phosphodiester metabolites between the left and right lobe. In conclusion, using a 31P whole‐body transmit coil in combination with a 16‐channel 31P receive array at 7 T allowed 31P MRSI acquisitions with full liver coverage and good to excellent repeatability.
31P MRS can be used in liver disease diagnosis and treatment monitoring. However, 31P MRS has a low intrinsic sensitivity and commonly used 31P surface coils do not provide full liver coverage. We demonstrated that a 31P whole‐body transmit coil in combination with a 16‐channel 31P receive array improves field‐of‐view coverage, allowing full liver 31P MRSI acquisitions. We showed good repeatability for most quantified 31P metabolite levels, and significant differences for PME and PDE between the left and right lobe.
Background:
Patients with psychotic disorders often show prominent cognitive impairment. Glutamate seems to play a prominent role, but its role in deep gray matter (DGM) regions is unclear.
Aims:
To ...evaluate glutamate levels within deep gray matter structures in patients with a psychotic disorder in relation to cognitive functioning, using advanced spectroscopic acquisition, reconstruction, and post-processing techniques.
Methods:
A 7-Tesla magnetic resonance imaging scanner combined with a lipid suppression coil and subject-specific water suppression pulses was used to acquire high-resolution magnetic resonance spectroscopic imaging data. Tissue fraction correction and registration to a standard brain were performed for group comparison in specifically delineated DGM regions. The brief assessment of cognition in schizophrenia was used to evaluate cognitive status.
Results:
Average glutamate levels across DGM structures (i.e. caudate, pallidum, putamen, and thalamus) in mostly medicated patients with a psychotic disorder (n = 16, age = 33, 4 females) were lower compared to healthy controls (n = 23, age = 24, 7 females; p = 0.005, d = 1.06). Stratified analyses showed lower glutamate levels in the caudate (p = 0.046, d = 0.76) and putamen p = 0.013, d = 0.94). These findings were largely explained by age differences between groups. DGM glutamate levels were positively correlated with psychomotor speed (r(30) = 0.49, p = 0.028), but not with other cognitive domains.
Conclusions:
We find reduced glutamate levels across DGM structures including the caudate and putamen in patients with a psychotic disorder that are linked to psychomotor speed. Despite limitations concerning age differences, these results underscore the potential role of detailed in vivo glutamate assessments to understand cognitive deficits in psychotic disorders.
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