Magnetic resonance spectroscopy: a promising tool for the diagnostics of human prostate cancer?

Ex Vivo High-Resolution Magic Angle Spinning (HRMAS) 1H NMR Spectroscopy for Early Prostate Cancer Detection

Simple Summary

Prostate cancer is the second leading cancer diagnosed in men worldwide. Current diagnostic standards lack sufficient reliability in detecting and characterizing prostate cancer. Due to the cancer’s multifocality, prostate biopsies are associated with high numbers of false negatives. Whereas several studies have already shown the potential of metabolomic information for PCa detection and characterization, in this study, we focused on evaluating its predictive power for future PCa diagnosis. In our study, metabolomic information differed substantially between histobenign patients based on their risk for receiving a future PCa diagnosis, making metabolomic information highly valuable for the individualization of active surveillance strategies.

Abstract

The aim of our study was to assess ex vivo HRMAS (high-resolution magic angle spinning) ¹H NMR spectroscopy as a diagnostic tool for early PCa detection by testing whether metabolomic alterations in prostate biopsy samples can predict future PCa diagnosis. In a primary prospective study (04/2006–10/2018), fresh biopsy samples of 351 prostate biopsy patients were NMR spectroscopically analyzed (Bruker 14.1 Tesla, Billerica, MA, USA) and histopathologically evaluated. Three groups of 16 patients were compared: group 1 and 2 represented patients whose NMR scanned biopsy was histobenign, but patients in group 1 were diagnosed with cancer before the end of the study period, whereas patients in group 2 remained histobenign. Group 3 included cancer patients. Single-metabolite concentrations and metabolomic profiles were not only able to separate histobenign and malignant prostate tissue but also to differentiate between samples of histobenign patients who received a PCa diagnosis in the following years and those who remained histobenign. Our results support the hypothesis that metabolomic alterations significantly precede histologically visible changes, making metabolomic information highly beneficial for early PCa detection. Thanks to its predictive power, metabolomic information can be very valuable for the individualization of PCa active surveillance strategies.

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) B1+| 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 (SI_tumor+SI_zone)/( SI_tumor‐SI_zone).

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 2019;49:1446–1455.

MRS Shimming: An Important Point Which Should not be Ignored

BACKGROUND

Proton magnetic resonance spectroscopy (MRS) is a well-known device for analyzing the biological fluids metabolically. Obtaining accurate and reliable information via MRS needs a homogeneous magnetic field in order to provide well-defined peaks and uniform water suppression. There are lots of reasons which can disturb the magnetic field homogeneity which can be corrected by a process known as shimming. This study is intended to recall the importance of shimming and also the significant role of quality control (QC) in achieving an accurate quantification.

MATERIAL AND METHOD

An acrylic cylindrical quality control phantom was designed as an analog of brain MRS test phantoms in order to control the accuracy of the obtained signal of a 1.5 T Siemens MRI system which belonged to one of Shiraz hospitals. The signal of NAA, Cho, Cr, the combination of these metabolites and also the distilled water, which was used in this study, was evaluated using separate phantoms. A QC test was performed using Siemens QC phantom and a standard test phantom.

RESULTS

The spectrum of our home- made phantom had a significant difference with the expected spectrum. The results of checking the spectrum of metabolites separately also confirmed that there was a systemic problem that affects all the signals originated from all metabolites and even the pure distilled water. The MRS system could not pass QC tests, and peak broadening was common in all spectra. The complex spectrum of standard test phantom was not produced successfully by the MRS system.

DISCUSSION

By a simple check of the water peak characteristics, lots of information can be obtained, one of which is the status of shimming that has a considerable effect on the accuracy of the spectrum. Thus, performing an automatic or manual shimming is not a criterion of the spectrum accuracy, and performing a periodic quality control using a test phantom by a specialist is necessary.

CONCLUSION

Briefly, the quality control of MRS and all the other clinical device must be taken seriously. Sometimes QC can be the boundary of a right or a wrong decision for the patient.

Metabolic atrophy and 3-T 1H-magnetic resonance spectroscopy correlation after radiation therapy for prostate cancer

OBJECTIVE

To correlate 3-T magnetic resonance spectroscopic imaging (MRSI) with prostate-specific antigen (PSA) levels in patients with prostate cancer treated with external beam radiation therapy to assess the potential advantages of MRSI.

MATERIALS AND METHODS

A total of 50 patients (age range 65-83 years) underwent PSA and MRSI surveillance before and at 3, 6, 12, 18 and 24 months after radiotherapy.

RESULTS

Of the 50 patients examined, 13 patients completely responded to therapy showing metabolic atrophy (MA), defined as a choline-plus-creatine/citrate (CC/C) ratio <0.2, at 3 months; in this group none had biochemical relapse (PSA nadir + 2 ng/mL) by the end of the follow-up. Of the 50 patients, 35 showed a partial response to therapy (CC/C ratio between 0.2 and 0.8) at 3 and 6 months and, of these 35 patients, 30 reached MA at 12 months, while five developed a recurrence (CC/C ratio >0.8). Three of those patients with recurrence had a biochemical relapse at 18 months and the other two at 24 months. Two of the 50 patients did not respond to the treatment, showing persistent disease from the 3rd month (CC/C ratio >0.8); one patient had biochemical relapse at 6 and the other at 12 months.

CONCLUSIONS

MRSI was shown to have a greater potential than PSA level in monitoring patients after radiotherapy, because it anticipates PSA nadir, and biochemical relapse in particular.

Magnetic resonance imaging for prostate cancer clinical application

As prostate cancer is a biologically heterogeneous disease for which a variety of treatment options are available, the major objective of prostate cancer imaging is to achieve more precise disease characterization. In clinical practice, magnetic resonance imaging (MRI) is one of the imaging tools for the evaluation of prostate cancer, the fusion of MRI or dynamic contrast-enhanced MRI (DCE-MRI) with magnetic resonance spectroscopic imaging (MRSI) is improving the evaluation of cancer location, size, and extent, while providing an indication of tumor aggressiveness. This review summarizes the role of MRI in the application of prostate cancer and describes molecular MRI techniques (including MRSI and DCE-MRI) for aiding prostate cancer management.