Ehman, Richard L.

Purpose The stiffness of a myocardial infarct affects the left ventricular pump function and remodeling. Magnetic resonance elastography (MRE) is a noninvasive imaging technique for measuring soft‐tissue stiffness in vivo. The purpose of this study was to investigate the feasibility of assessing in vivo regional myocardial stiffness with high‐frequency 3D cardiac MRE in a porcine model of myocardial infarction, and compare the results with ex vivo uniaxial tensile testing. Methods Myocardial infarct was induced in a porcine model by embolizing the left circumflex artery. Fourteen days postinfarction, MRE imaging was performed in diastole using an echocardiogram‐gated spin‐echo echo‐planar‐imaging sequence with 140‐Hz vibrations and 3D MRE processing. The MRE stiffness and tensile modulus from uniaxial testing were compared between the remote and infarcted myocardium. Results Myocardial infarcts showed increased in vivo MRE stiffness compared with remote myocardium (4.6 ± 0.7 kPa versus 3.0 ± 0.6 kPa, P = 0.02) within the same pig. Ex vivo uniaxial mechanical testing confirmed the in vivo MRE results, showing that myocardial infarcts were stiffer than remote myocardium (650 ± 80 kPa versus 110 ± 20 kPa, P = 0.01). Conclusions These results demonstrate the feasibility of assessing in vivo regional myocardial stiffness with high‐frequency 3D cardiac MRE. Magn Reson Med 79:361–369, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

PurposeTo evaluate if cardiac magnetic resonance elastography (MRE) can measure increased stiffness in patients with cardiac amyloidosis. Myocardial tissue stiffness plays an important role in cardiac function. A noninvasive quantitative imaging technique capable of measuring myocardial stiffness could aid in disease diagnosis, therapy monitoring, and disease prognostic strategies. We recently developed a high‐frequency cardiac MRE technique capable of making noninvasive stiffness measurements.Materials and MethodsIn all, 16 volunteers and 22 patients with cardiac amyloidosis were enrolled in this study after Institutional Review Board approval and obtaining formal written consent. All subjects were imaged head‐first in the supine position in a 1.5T closed‐bore MR imager. 3D MRE was performed using 5 mm isotropic resolution oblique short‐axis slices and a vibration frequency of 140 Hz to obtain global quantitativein vivoleft ventricular stiffness measurements. The median stiffness was compared between the two cohorts. An octahedral shear strain signal‐to‐noise ratio (OSS‐SNR) threshold of 1.17 was used to exclude exams with insufficient motion amplitude.ResultsFive volunteers and six patients had to be excluded from the study because they fell below the 1.17 OSS‐SNR threshold. The myocardial stiffness of cardiac amyloid patients (median: 11.4 kPa, min: 9.2, max: 15.7) was significantly higher (P = 0.0008) than normal controls (median: 8.2 kPa, min: 7.2, max: 11.8).ConclusionThis study demonstrates the feasibility of 3D high‐frequency cardiac MRE as a contrast‐agent‐free diagnostic imaging technique for cardiac amyloidosis.Level of Evidence:2Technical Efficacy:Stage 2J. Magn. Reson. Imaging 2017;46:1361–1367.

PurposeTo investigate the ability of slip interface imaging (SII), a recently developed magnetic resonance elastography (MRE)‐based technique, to predict the degree of meningioma–brain adhesion, using findings at surgery as the reference standard.Materials and MethodsWith Institutional Review Board approval and written informed consent, 25 patients with meningiomas >2.5 cm in maximal diameter underwent preoperative SII assessment. Intracranial shear motions were introduced using a soft, pillow‐like head driver and the resulting displacement field was acquired with an MRE pulse sequence on 3T MR scanners. The displacement data were analyzed to determine tumor–brain adhesion by assessing intensities on shear line images and raw as well as normalized octahedral shear strain (OSS) values along the interface. The SII findings of shear line images, OSS, and normalized OSS were independently and blindly correlated with surgical findings of tumor adhesion by using the Cohen's κ coefficient and chi‐squared test.ResultsNeurosurgeons categorized the surgical plane as extrapial (no adhesion) in 15 patients, mixed in four, and subpial (adhesion) in six. Both shear line images and OSS agreed with the surgical findings in 18 (72%) cases (fair agreement, κ = 0.37, 95% confidence interval [CI]: 0.05–0.69), while normalized OSS was concordant with the surgical findings in 23 (92%) cases (good agreement, κ = 0.86, 95% CI: 0.67–1). The correlation between SII predictions (shear line images, OSS, and normalized OSS) and the surgical findings were statistically significant (chi‐squared test, P = 0.02, P = 0.02, and P < 0.0001, respectively).ConclusionSII preoperatively evaluates the degree of meningioma–brain adhesion noninvasively, allowing for improved prediction of surgical risk and tumor resectability.Level of Evidence: 1Technical Efficacy: Stage 1J. Magn. Reson. Imaging 2017;46:1007–1016.

PurposeTo investigate the use of magnetic resonance elastography (MRE) in the quantitative assessment of pulmonary fibrosis by comparing quantitative shear stiffness measurements of lung parenchyma in patients diagnosed with fibrotic interstitial lung disease (ILD) and healthy controls.Materials and MethodsA 1.5T spin‐echo, echo planar imaging MRE (SE‐EPI MRE) pulse sequence was utilized to assess absolute lung shear stiffness in 15 patients with diagnosed ILD and in 11 healthy controls. Data were collected at residual volume (RV) and total lung capacity (TLC). Spirometry data were obtained immediately prior to scanning. To test for statistical significance between RV and TLC shear stiffness estimates a two‐sample t‐test was performed. To assess variability within individual subject shear stiffness estimates, the intraclass correlation coefficient (ICC) and Krippendorff's alpha were calculated.ResultsPatients with ILD exhibited an average (±1 standard deviation) shear stiffness of 2.74 (±0.896) kPa at TLC and 1.32 (±0.300) kPa at RV. The corresponding values for healthy individuals were 1.33 (±0.195) kPa and 0.849 (±0.250) kPa, respectively. The difference in shear stiffness between RV and TLC was statistically significant (P < 0.001). At TLC, the ICC and alpha values were 0.909 and 0.887, respectively. At RV, the ICC and alpha values were 0.852 and 0.862, respectively.ConclusionIn subjects with known fibrotic interstitial lung disease, parenchymal shear stiffness is increased when compared to normal controls at both RV and TLC, with TLC demonstrating the most significant difference. MRE‐derived parenchymal shear stiffness is a promising new noninvasive imaging‐based biomarker of interstitial lung disease.Level of Evidence: 1Technical Efficacy: Stage 2J. MAGN. RESON. IMAGING 2017;46:365–374

PurposeTo evaluate the effect of imaging sequence (spin‐echo echo‐planar imaging [EPI] and gradient‐echo [GRE]) and postprocessing method (two‐dimensional [2D] and 3D inversion algorithms) on liver MR elastography (MRE) and to validate the diagnostic performance of EPI‐MRE3D versus conventional GRE‐MRE2D for liver fibrosis staging.Materials and MethodsThree MRE methods (EPI‐MRE3D, EPI‐MRE2D, and GRE‐MRE2D) were performed on soft and mildly stiff phantoms and 58 patients with chronic liver disease using a 3 Tesla clinical MRI scanner, and stiffness values were compared among the three methods. A validation study comprised 73 patients with histological liver fibrosis (F0–4, METAVIR system). Areas under the receiver operating characteristic curves (AUCs) and accuracies for diagnosing significant fibrosis (F3–4) and cirrhosis (F4) were compared between EPI‐MRE3D and GRE‐MRE2D.ResultsStiffness values of the soft and mildly stiff phantoms were 2.4 kPa and 4.0 kPa by EPI‐MRE3D; 2.6 kPa and 4.2 kPa by EPI‐MRE2D; and 2.7 kPa and 4.2 kPa by GRE‐MRE2D. In patients, EPI‐MRE3D provided significantly lower stiffness values than other methods (P < 0.001). However, there was no significant difference between GRE‐MRE2D and EPI‐MRE2D (P = 0.12). The AUCs and accuracies of EPI‐MRE3D and GRE‐MRE2D were statistically equivalent in the diagnoses of significant fibrosis (F3–4) and cirrhosis (F4) (all P < 0.005).ConclusionEPI‐MRE3D showed modestly lower liver stiffness values than conventional GRE‐MRE2D. The diagnostic performances of EPI‐MRE3D and GRE‐MRE2D were equivalent for liver fibrosis staging.Level of Evidence: 3J. Magn. Reson. Imaging 2017;45:1163–1170