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.
Background: The incidence of liver and pancreatic cancer is rising. Patients benefit from current treatments, but there are limitations in the evaluation of (early) response to treatment. Tumor metabolic alterations can be measured noninvasively with phosphorus ( 31 P) magnetic resonance spectroscopy (MRS). Purpose: To conduct a quantitative analysis of the available literature on 31 P MRS performed in hepatopancreatobiliary cancer and to provide insight into its current and potential for therapy (non-) response assessment. Population: Patients with hepatopancreatobiliary cancer. Field Strength/Sequence: 31 P MRS. Assessment: The PubMed, EMBASE, and Cochrane library databases were systematically searched for studies published to 17 March 17, 2022. All 31 P MRS studies in hepatopancreatobiliary cancer reporting 31 P metabolite levels were included. Statistical Tests: Relative differences in 31 P metabolite levels/ratios between patients before therapy and healthy controls, and the relative changes in 31 P metabolite levels/ratios in patients before and after therapy were determined. Results: The search yielded 10 studies, comprising 301 subjects, of whom 132 (44%) healthy volunteers and 169 (56%) patients with liver cancer of various etiology. To date, 31 P MRS has not been applied in pancreatic cancer. In liver cancer, alterations in levels of 31 P metabolites involved in cell proliferation (phosphomonoesters [PMEs] and phosphodiesters [PDEs]) and energy metabolism (ATP and inorganic phosphate [Pi]) were observed. In particular, liver tumors were associated with elevations of PME/PDE and PME/Pi compared to healthy liver tissue, although there was a broad variety among studies (elevations of 2%-267% and 21%-233%, respectively). Changes in PME/PDE in liver tumors upon therapy were substantial, yet very heterogeneous and both decreases and increases were observed, whereas PME/Pi was consistently decreased after therapy in all studies (À13% to À76%). Data Conclusion: 31 P MRS has great potential for treatment monitoring in oncology. Future studies are needed to correlate the changes in 31 P metabolite levels in hepatopancreatobiliary tumors with treatment response.
Purpose: Inhomogeneous excitation at ultrahigh field strengths (7T and above) compromises the reliability of quantified dynamic contrast-enhanced breast MRI. This can hamper the introduction of ultrahigh field MRI into the clinic. Compensation for this non-uniformity effect can consist of both hardware improvements and postacquisition corrections. This paper investigated the correctable radiofrequency transmit (B + 1 ) range post-acquisition in both simulations and patient data for 7T MRI. Methods: Simulations were conducted to determine the minimum B + 1 level at which corrections were still beneficial because of noise amplification. Two correction strategies leading to differences in noise amplification were tested. The effect of the corrections on a 7T patient data set (N = 38) with a wide range of B + 1 levels was investigated in terms of time-intensity curve types as well as washin, washout and peak enhancement values. Results: In simulations assuming a common amount of T 1 saturation, the lowest B + 1 level at which the SNR of the corrected images was at least that of the original precontrast image was 43% of the nominal angle. After correction, time-intensity curve types changed in 24% of included patients, and the distribution of curve types corresponded better to the distribution found in literature. Additionally, the overlap between the distributions of washin, washout, and peak enhancement values for grade 1 and grade 2 tumors was slightly reduced. Conclusion: Although the correctable range varies with the amount of T 1 saturation, post-acquisition correction for inhomogeneous excitation was feasible down to B + 1 levels of 43% of the nominal angle in vivo. K E Y W O R D S 7T, B + 1 mapping, breast, DCE-MRI, flip-angle correction, RF field inhomogeneity | 1001 van RIJSSEL Et aL.
Alterations in 31P metabolite concentrations in the liver can be a consequence of liver disease and therefore 3D 31P MRSI can help in diagnosis and following progression and treatment response. However, commonly used 31P surface coils have a limited penetration depth and do not provide full coverage of the liver. We used an integrated 31P whole-body transmit coil with a local 31P receive array for 31P MRSI of the liver at a 7T MRI scanner. Here we demonstrate that 31P signals can be measured throughout the liver and 31P metabolite levels can be quantified with good to excellent test-retest reliability.
Early response assessment for patients with pancreatic cancer receiving chemotherapy is limited. Detection of alterations in 31P metabolite levels during treatment could change this perspective. However, to date 31P MRS has not yet been demonstrated in the human pancreas in vivo. Here we show in-vivo 31P MRSI data in the pancreas of healthy subjects, using a 31P whole-body transmit coil in combination with a 16-channel receive array at 7T, and show moderate to good test-retest reliability. In addition, we demonstrate the feasibility of performing 31P MRSI in a patient with pancreatic cancer before and after chemotherapy.
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