Measurement of metabolite levels and treatment-induced changes in hepatic metastases of gastro-esophageal cancer using 7-T phosphorus magnetic resonance spectroscopic imaging.

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 (31P MRS), and may be a marker for early therapy response assessment in liver metastases. However, with commonly used 31P surface coils for liver 31P MRS, the liver is not fully covered, and metastases may be missed. The objective of this study was to demonstrate the feasibility of 31P MRS imaging (31P MRSI) with full liver coverage to assess 31P metabolite levels and chemotherapy-induced changes in liver metastases of gastro-esophageal cancer, using a 31P whole-body birdcage transmit coil in combination with a 31P body receive array at 7 T. 3D 31P 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 31P MRSI acquisitions were performed using an integrated 31P 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 31P MRSI data, 12 31P 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.

31 P MR Spectroscopy in the Pancreas: Repeatability, Comparison With Liver, and Pilot Pancreatic Cancer Data.

BACKGROUND: Non-invasive evaluation of phosphomonoesters (PMEs) and phosphodiesters (PDEs) by 31-phosphorus MR spectroscopy (31 P MRS) may have potential for early therapy (non-)response assessment in cancer. However, 31 P MRS has not yet been applied to investigate the human pancreas in vivo. PURPOSE: To assess the technical feasibility and repeatability of 31 P MR spectroscopic imaging (MRSI) of the pancreas, compare 31 P metabolite levels between pancreas and liver, and determine the feasibility of 31 P MRSI in pancreatic cancer. STUDY TYPE: Prospective cohort study. POPULATION: 10 healthy subjects (age 34 ± 12 years, four females) and one patient (73-year-old female) with pancreatic ductal adenocarcinoma. FIELD STRENGTH/SEQUENCE: 7-T, 31 P FID-MRSI, 1 H gradient-echo MRI. ASSESSMENT: 31 P FID-MRSI of the abdomen (including the pancreas and liver) was performed with a nominal voxel size of 20 mm (isotropic). For repeatability measurements, healthy subjects were scanned twice on the same day. The patient was only scanned once. Test-retest 31 P MRSI data of pancreas and liver voxels (segmented on 1 H MRI) of healthy subjects were quantified by fitting in the time domain and signal amplitudes were normalized to γ-adenosine triphosphate. In addition, the PME/PDE ratio was calculated. Metabolite levels were averaged over all voxels within the pancreas, right liver lobe and left liver lobe, respectively. STATISTICAL TESTS: Repeatability of test-retest data from healthy pancreas was assessed by paired t-tests, Bland-Altman analyses, and calculation of the intrasubject coefficients of variation (CoVs). Significant differences between healthy pancreas and right and left liver lobes were assessed with a two-way analysis of variance (ANOVA) for repeated measures. A P-value <0.05 was considered statistically significant. RESULTS: The intrasubject CoVs for PME, PDE, and PME/PDE in healthy pancreas were below 20%. Furthermore, PME and PME/PDE were significantly higher in pancreas compared to liver. In the patient with pancreatic cancer, qualitatively, elevated relative PME signals were observed in comparison with healthy pancreas. DATA CONCLUSION: In vivo 31 P MRSI of the human healthy pancreas and in pancreatic cancer may be feasible at 7 T. EVIDENCE LEVEL: 3 TECHNICAL EFFICACY: Stage 2.

In vivo phosphorus magnetic resonance spectroscopic imaging of the whole human liver at 7 T using a phosphorus whole-body transmit coil and 16-channel receive array: Repeatability and effects of principal component analysis-based denoising.

Quantitative three-dimensional (3D) imaging of phosphorus (31 P) metabolites is potentially a promising technique with which to assess the progression of liver disease and monitor therapy response. However, 31 P magnetic resonance spectroscopy has a low sensitivity and commonly used 31 P surface coils do not provide full coverage of the liver. This study aimed to overcome these limitations by using a 31 P whole-body transmit coil in combination with a 16-channel 31 P receive array at 7 T. Using this setup, we determined the repeatability of whole-liver 31 P magnetic resonance spectroscopic imaging (31 P MRSI) in healthy subjects and assessed the effects of principal component analysis (PCA)-based denoising on the repeatability parameters. In addition, spatial variations of 31 P metabolites within the liver were analyzed. 3D 31 P 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 31 P metabolite signals. On average, 31 P 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 31 P 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 31 P metabolite quantification with the fitting constraints used. Significant spatial heterogeneity of various 31 P 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 31 P whole-body transmit coil in combination with a 16-channel 31 P receive array at 7 T allowed 31 P MRSI acquisitions with full liver coverage and good to excellent repeatability.

Prospective of 31 P MR Spectroscopy in Hepatopancreatobiliary Cancer: A Systematic Review of the Literature.

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 (-13% to -76%). 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. EVIDENCE LEVEL: 3 TECHNICAL EFFICACY: Stage 2.

Correcting time-intensity curves in dynamic contrast-enhanced breast MRI for inhomogeneous excitation fields at 7T.

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 post-acquisition corrections. This paper investigated the correctable radiofrequency transmit ( B1+ ) range post-acquisition in both simulations and patient data for 7T MRI. METHODS: Simulations were conducted to determine the minimum B1+ 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 B1+ 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 T1 saturation, the lowest B1+ 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 T1 saturation, post-acquisition correction for inhomogeneous excitation was feasible down to B1+ levels of 43% of the nominal angle in vivo.