Leon ter Beek

Magnetic Resonance Elastography for the Noninvasive Staging of Liver Fibrosis

BACKGROUND & AIMS The purpose of our study was to prospectively compare the success rate and diagnostic accuracy of magnetic resonance elastography, ultrasound elastography, and aspartate aminotransferase to platelets ratio index (APRI) measurements for the noninvasive staging of fibrosis in patients with chronic liver disease. METHODS We performed a prospective blind comparison of magnetic resonance elastography, ultrasound elastography, and APRI in a consecutive series of patients who underwent liver biopsy for chronic liver disease in a university-based hospital. Histopathologic staging of liver fibrosis according to the METAVIR scoring system served as the reference. RESULTS A total of 141 patients were assessed. The technical success rate of magnetic resonance elastography was higher than that of ultrasound elastography (133/141 [94%] vs 118/141 [84%]; P = .016). Magnetic and ultrasound elastography, APRI measurements, and histopathologic analysis of liver biopsy specimens were technically successful in 96 patients. The areas under the receiver operating characteristic curves of magnetic resonance elasticity (0.994 for F >or= 2; 0.985 for F >or= 3; 0.998 for F = 4) were larger (P < .05) than those of ultrasound elasticity, APRI, and the combination of ultrasound elasticity and APRI (0.837, 0.709, and 0.849 for F >or= 2; 0.906, 0.816, and 0.936 for F >or= 3; 0.930, 0.820, and 0.944 for F = 4, respectively). CONCLUSIONS Magnetic resonance elastography has a higher technical success rate than ultrasound elastography and a better diagnostic accuracy than ultrasound elastography and APRI for staging liver fibrosis.

Hepatic viscoelastic parameters measured with MR elastography: correlations with quantitative analysis of liver fibrosis in the rat.

To determine the correlations between the viscoelastic parameters of the liver measured with in vivo MR elastography and quantitative analysis of liver fibrosis.

Rapid acquisition of multifrequency, multislice and multidirectional MR elastography data with a fractionally encoded gradient echo sequence

In MR elastography (MRE), periodic tissue motion is phase encoded using motion‐encoding gradients synchronized to an externally applied periodic mechanical excitation. Conventional methods result in extended scan time for quality phase images, thus limiting the broad application of MRE in the clinic. For practical scan times, researchers have been relying on one‐dimensional or two‐dimensional motion‐encoding, low‐phase sampling and a limited number of slices, and artifact‐prone, single‐shot, echo planar imaging (EPI) readout. Here, we introduce a rapid multislice pulse sequence capable of three‐dimensional motion encoding that is also suitable for simultaneously encoding motion with multiple frequency components. This sequence is based on a gradient‐recalled echo (GRE) sequence and exploits the principles of fractional encoding. This GRE MRE pulse sequence was validated as capable of acquiring full three‐dimensional motion encoding of isotropic voxels in a large volume within less than a minute. This sequence is suitable for monofrequency and multifrequency MRE experiments. In homogeneous paraffin phantoms, the eXpresso sequence yielded similar storage modulus values as those obtained with conventional methods, although with markedly reduced variances (7.11 ± 0.26 kPa for GRE MRE versus 7.16 ± 1.33 kPa for the conventional spin‐echo EPI sequence). The GRE MRE sequence obtained better phase‐to‐noise ratios than the equivalent spin‐echo EPI sequence (matched for identical acquisition time) in both paraffin phantoms and in vivo data in the liver (59.62 ± 11.89 versus 27.86 ± 3.81, 61.49 ± 14.16 versus 24.78 ± 2.48 and 58.23 ± 10.39 versus 23.48 ± 2.91 in the X, Y and Z components, respectively, in the case of liver experiments). Phase‐to‐noise ratios were similar between GRE MRE used in monofrequency or multifrequency experiments (75.39 ± 14.93 versus 86.13 ± 18.25 at 28 Hz, 71.52 ± 24.74 versus 86.96 ± 30.53 at 56 Hz and 95.60 ± 36.96 versus 61.35 ± 26.25 at 84Hz, respectively). Copyright

Improved focal liver lesion detection: comparison of single-shot spin-echo echo-planar and superparamagnetic iron oxide (SPIO)-enhanced MRI.

To prospectively compare single‐shot spin‐echo echo‐planar imaging (SSSE‐EPI) using b = 0, 10, 150, and 400 seconds/mm2 with standard MRI techniques after intravenous super paramagnetic iron oxide (SPIO) in the detection and characterization of focal liver lesions with focus on small (<10 mm) focal liver lesions.

Focal liver lesion detection and characterization: Comparison of non-contrast enhanced and SPIO-enhanced diffusion-weighted single-shot spin echo echo planar and turbo spin echo T2-weighted imaging

PURPOSE To compare lesion conspicuity and image quality between single-shot spin echo echo planar imaging (SS SE-EPI) before, immediately and 5min after intravenous (IV) injection of superparamagnetic iron oxide (SPIO) for detecting and characterizing focal liver lesions (FLLs). MATERIALS AND METHODS Twenty-five patients suspected for colorectal liver metastases were prospectively included. Lesion detection and characterization were compared between all SS SE-EPI and T2-weighted turbo spin echo (T2w TSE) sets (two-sided Fishers exact test). Image quality and lesion conspicuity were compared for SS SE-EPI sets using rank order statistic (RIDIT). Reference standard comprised of surgery, biopsy and/or follow-up. RESULTS Reference standard demonstrated 18 benign and 43 malignant FLLs. Best lesion detection (p<0.05) was achieved with non-contrast-enhanced SS SE-EPI. Lesion characterization was best using all T2w TSE sequences. Best image quality and lesion conspicuity (p<0.05) was achieved with non-contrast-enhanced SS SE-EPI. CONCLUSION Non-contrast-enhanced SS SE-EPI was best for lesion detection. SS SE-EPI sequences were not useful for lesion characterization (differentiation between benign and malignant lesions). Unenhanced SS SE-EPI did not allow differentiation especially as many benign FLLs were hyperintense on the highest b-value images. Combining unenhanced and SPIO-enhanced SS SE-EPI performed better but still was not clinically useful due to variable degree of uptake and vascular pooling of SPIO for (especially) benign FLLs. T2w TSE with SPIO-enhancement was needed for characterization.

Prostate MR elastography with transperineal electromagnetic actuation and a fast fractionally encoded steady-state gradient echo sequence

Our aim is to develop a clinically viable, fast‐acquisition, prostate MR elastography (MRE) system with transperineal excitation. We developed a new actively shielded electromagnetic transducer, designed to enable quick deployment and positioning within the scanner. The shielding of the transducer was optimized using simulations. We also employed a new rapid pulse sequence that encodes the three‐dimensional displacement field in the prostate gland using a fractionally encoded steady‐state gradient echo sequence, thereby shortening the acquisition time to a clinically acceptable 8–10 min. The methods were tested in two phantoms and seven human subjects (six volunteers and one patient with prostate cancer). The MRE acquisition time for 24 slices, with an isotropic resolution of 2 mm and eight phase offsets, was 8 min, and the total scan, including positioning and set‐up, was performed in 15–20 min. The phantom study demonstrated that the transducer does not interfere with the acquisition process and that it generates displacement amplitudes that exceed 100 µm even at frequencies as high as 300 Hz. In the in vivo human study, average wave amplitudes of 30 µm (46 µm at the apex) were routinely achieved within the prostate gland at 70 Hz. No pain or discomfort was reported. Results in a single patient suggest that MRE can identify cancer tumors, although this result is preliminary. The proposed methods allow the integration of prostate MRE with other multiparametric MRI methods. The results of this study clearly motivate the clinical evaluation of transperineal MRE in patients. Copyright

Reproducibility of rapid short echo time CSI at 3 tesla for clinical applications.

To validate the reproducibility of a chemical shift imaging (CSI) acquisition protocol with parallel imaging, using automated repositioning software.