Towards intrinsic R2* imaging in the prostate at 3 and 7tesla

PURPOSE: Hypoxia is an important marker for resistance to therapy. In this study, we quantify the macroscopic effects of R2* mapping in prostate cancer patients incorporating susceptibility matching and field strengths effects. MATERIALS AND METHODS: 91 patients were scanned without endorectal coil (ERC) at 3T. Only when rectal gas was absent, data was included for analysis. Another group of 10 patients was scanned using a susceptibility matched ERC. To assess the residual contamination of R2 and macroscopic field non-uniformities, a group of 10 patients underwent ultra-high resolution 7T MRI. RESULTS: Of the patients scanned at 3T 60% presented rectal gas and were excluded, due to susceptibility artifacts. At 3T the tumor was significantly different (P<0.01) from the healthy surrounding tissue in R2* values at intrapatient level. Using the measured median R2* value of 24.9s(-1) at 3T and 43.2s(-1) at 7T of the peripheral zone, the minimum contribution of macroscopic susceptibility effects is 15% at 3T. CONCLUSION: R2* imaging might be a promising tool for hypoxia imaging, particularly when minimizing macroscopic susceptibility effects contaminating intrinsic R2* of tissue, such as rectal gas. At 3T macroscopic effects still contribute 15% in the R2* value, compared to ultra-high resolution R2* mapping at 7T

Comparing signal-to-noise ratio for prostate imaging at 7T and 3T

\u3cp\u3eBackground: In MRI, the signal-to-noise ratio (SNR) theoretically increases with B \u3csub\u3e0\u3c/sub\u3e field strength. However, because of attenuation of the radiofrequency (RF) fields at 7T, it is not certain if this SNR gain can be realized for prostate imaging. Purpose/Hypothesis: To investigate the SNR gain in prostate imaging at 7T as compared with 3T. It is expected that SNR will improve for prostate imaging at 7T compared with 3T. Study Type: Prospective. Subjects: Four healthy volunteers and one prostate cancer patient. Field Strength/Sequence: All subjects were scanned at 3T and at 7T using optimal coil setups for both field strengths. For all volunteers, proton density-weighted images were acquired for SNR analysis and actual flip angle imaging (AFI) B \u3csub\u3e1\u3c/sub\u3e \u3csup\u3e+|\u3c/sup\u3e maps were acquired for correction of measured SNR values. In the patient, a T \u3csub\u3e2\u3c/sub\u3e -weighted (T \u3csub\u3e2\u3c/sub\u3e w) image was acquired at 3T and at 7T. Assessment: SNR was calculated in the prostate region for all volunteers. SNR was normalized for flip angle, receiver bandwidth, and voxel volume. SNR was also calculated for different sensitivity encoding (SENSE) acceleration factors. Statistical Testing: SNR values are represented as the arithmetic mean of SNR values in the prostate. Estimated SNR in the T \u3csub\u3e2\u3c/sub\u3e w image is calculated as the arithmetic mean of the signal intensity (SI) divided by the standard deviation of the SI in a specified zone. Tumor-to-tissue contrast is calculated as (SI \u3csub\u3etumor\u3c/sub\u3e +SI \u3csub\u3ezone\u3c/sub\u3e )/(SI \u3csub\u3etumor\u3c/sub\u3e -SI \u3csub\u3ezone\u3c/sub\u3e ). Results: An increase in SNR ranging from 1.7-fold to 2.8-fold was measured in the prostate at 7T in comparison to 3T for four volunteers. At 7T, it is possible to achieve a 4-fold SENSE acceleration in the left-right direction with similar SNR to a nonaccelerated 3T image. T \u3csub\u3e2\u3c/sub\u3e w imaging was done at 3T and 7T in one patient, where improved tumor-to-tissue contrast was demonstrated at 7T. Data Conclusion: SNR improves for prostate imaging at 7T as compared with 3T. Level of Evidence: 2. Technical Efficacy: Stage 1. J. Magn. Reson. Imaging 2019;49:1446–1455. \u3c/p\u3

Comparing signal-to-noise ratio for prostate imaging at 7T and 3T

Background: In MRI, the signal-to-noise ratio (SNR) theoretically increases with B0 field strength. However, because of attenuation of the radiofrequency (RF) fields at 7T, it is not certain if this SNR gain can be realized for prostate imaging. Purpose/Hypothesis: To investigate the SNR gain in prostate imaging at 7T as compared with 3T. It is expected that SNR will improve for prostate imaging at 7T compared with 3T. Study Type: Prospective. Subjects: Four healthy volunteers and one prostate cancer patient. Field Strength/Sequence: All subjects were scanned at 3T and at 7T using optimal coil setups for both field strengths. For all volunteers, proton density-weighted images were acquired for SNR analysis and actual flip angle imaging (AFI) (Formula presented.) maps were acquired for correction of measured SNR values. In the patient, a T2-weighted (T2w) image was acquired at 3T and at 7T. Assessment: SNR was calculated in the prostate region for all volunteers. SNR was normalized for flip angle, receiver bandwidth, and voxel volume. SNR was also calculated for different sensitivity encoding (SENSE) acceleration factors. Statistical Testing: SNR values are represented as the arithmetic mean of SNR values in the prostate. Estimated SNR in the T2w image is calculated as the arithmetic mean of the signal intensity (SI) divided by the standard deviation of the SI in a specified zone. Tumor-to-tissue contrast is calculated as (SItumor+SIzone)/(SItumor-SIzone). Results: An increase in SNR ranging from 1.7-fold to 2.8-fold was measured in the prostate at 7T in comparison to 3T for four volunteers. At 7T, it is possible to achieve a 4-fold SENSE acceleration in the left-right direction with similar SNR to a nonaccelerated 3T image. T2w imaging was done at 3T and 7T in one patient, where improved tumor-to-tissue contrast was demonstrated at 7T. Data Conclusion: SNR improves for prostate imaging at 7T as compared with 3T. Level of Evidence: 2. Technical Efficacy: Stage 1. J. Magn. Reson. Imaging 2018

Correlation between genomic index lesions and mpMRI and 68Ga-PSMA-PET/CT imaging features in primary prostate cancer

Abstract Magnetic resonance imaging (MRI) and prostate specific membrane antigen (PSMA)- positron emission tomography (PET)/computed tomography (CT)-imaging of prostate cancer (PCa) are emerging techniques to assess the presence of significant disease and tumor progression. It is not known, however, whether and to what extent lesions detected by these imaging techniques correlate with genomic features of PCa. The aim of this study was therefore to define a genomic index lesion based on chromosomal copy number alterations (CNAs) as marker for tumor aggressiveness in prostate biopsies in direct correlation to multiparametric (mp) MRI and 68Ga-PSMA-PET/CT imaging features. CNA profiles of 46 biopsies from five consecutive patients with clinically high-risk PCa were obtained from radiologically suspicious and unsuspicious areas. All patients underwent mpMRI, MRI/TRUS-fusion biopsy, 68Ga-PSMA-PET/CT and a radical prostatectomy. CNAs were directly correlated to imaging features and radiogenomic analyses were performed. Highly significant CNAs (≥10 Mbp) were found in 22 of 46 biopsies. Chromosome 8p, 13q and 5q losses were the most common findings. There was an strong correspondence between the radiologic and the genomic index lesions. The radiogenomic analyses suggest the feasibility of developing radiologic signatures that can distinguish between genomically more or less aggressive lesions. In conclusion, imaging features of mpMRI and 68Ga-PSMA-PET/CT can guide to the genomically most aggressive lesion of a PCa. Radiogenomics may help to better differentiate between indolent and aggressive PCa in the future