Liver diffusivity in healthy volunteers and patients with chronic liver disease: comparison of breathhold and free-breathing techniques

Purpose:

To compare liver ADC obtained with breathhold and free‐breathing diffusion weighted imaging (DWI) in healthy volunteers and patients with liver disease.

Materials and Methods:

Twenty‐eight subjects, 12 healthy volunteers and 16 patients (9 NAFLD, 7 chronic active HCV), underwent breathhold (BH) and free‐breathing (FB) DWI MRI at 1.5 Tesla. Pearson's correlation coefficient was used to determine correlation while paired t‐tests assessed differences between BH and FB ADC. Estimated bias was calculated using the Bland‐Altman method.

Results:

Liver ADC (×10^?3 mm²/s) was lower on BH for all groups (mean difference 0.36 ± 0.20; P < 0.01). ADC was higher in healthy volunteers (BH 1.80 ± 0.18; FB 2.24 ± 0.20) compared with NAFLD patients (BH 1.43 ± 0.27; FB 1.78 ± 0.28) (P < 0.001) and HCV patients (BH 1.63 ± 0.191; FB 1.88 ± 0.12). Overall correlation between BH and FB ADC was (r = 0.75), greatest in NAFLD (r = 0.90) compared with the correlation in HCV (r = 0.24) and healthy subjects (r = 0.34). Bland‐Altman plots did not show agreement in mean absolute difference and estimated bias between subjects.

Conclusion:

Correlation between BH and FB liver ADC is moderate indicating that BH and FB should not be used interchangeably. Additionally, the lower ADC values in BH versus FB should be accounted for when comparing different liver DWI studies. J. Magn. Reson. Imaging 2012;35:103‐109. © 2011 Wiley Periodicals, Inc.

     

Correlation of apparent diffusion coefficient values measured by diffusion MRI and MGMT promoter methylation semiquantitatively analyzed with MS‐MLPA in patients with glioblastoma multiforme

Purpose:

To retrospectively determine whether the apparent diffusion coefficient (ADC) values correlate with O⁶‐methylguanine DNA methyltransferase (MGMT) promoter methylation semiquantitatively analyzed by methylation‐specific multiplex ligation‐dependent probe amplification (MS‐MLPA) in patients with glioblastoma.

Materials and Methods:

The study was approved by the Institutional Review Board and was Health Insurance Portability and Accountability Act (HIPAA) compliant. Newly diagnosed patients with glioblastoma (n = 26) were analyzed with an ADC histogram approach based on enhancing solid portion. The methylation status of MGMT promoter was assessed by methylation‐specific polymerase chain reaction (MSP) and by MS‐MLPA. MS‐MLPA is a semiquantitative method that determines the methylation ratio. The Ki‐67 labeling index was also analyzed. The mean and 5th percentile ADC values were correlated with MGMT promoter methylation status and Ki‐67 labeling index using a linear regression model. Progression‐free survival (PFS) was also correlated with the ADC values using Kaplan–Meier survival analysis.

Results:

The mean methylation ratio was 0.21 ± 0.20. By MSP, there were 5 methylated and 21 unmethylated tumors. The mean ADC revealed a positive relationship with MGMT promoter methylation ratio (P = 0.015) and was also significantly different according to MSP‐determined methylation status (P = 0.011). Median PFS was significantly related with methylation ratio (P = 0.017) and MSP‐derived methylation status (P = 0.025). A positive relationship was demonstrated between PFS and the mean ADC value (P = 0.001). The 5th percentile ADC values showed a significant negative relationship with Ki‐67 labeling index (P = 0.036).

Conclusion:

We found that ADC values were significantly correlated with PFS as well as with MGMT promoter methylation status. We believe that ADC values may merit further investigation as a noninvasive biomarker for predicting treatment response. J. Magn. Reson. Imaging 2013;37:351–358. © 2012 Wiley Periodicals, Inc.     

In vivo spatially localized high resolution 1H MRS via intermolecular single‐quantum coherence of rat brain at 7 T

Purpose:

To compare the conventional localized point‐resolved spectroscopy (PRESS) with localized 2D intermolecular single‐quantum coherence (iSQC) magnetic resonance spectroscopy (MRS) and obtain in vivo MRS spectrum of rat brain using the latter technique.

Materials and Methods:

A brain phantom, an intact pig brain tissue, and mature Sprague–Dawley rat were studied by PRESS, Nano magic‐angle spinning spectroscopy, and iSQC MRS.

Results:

Using PRESS, high‐resolution MRS can be obtained from the brain phantom and pig brain tissue with a small voxel in a relatively homogeneous field. When a large voxel is selected, the field homogeneity is distinctly reduced. No useful information is obtained from the PRESS spectra. However, using the iSQC MRS, high‐resolution spectra can be obtained from the two samples with a relatively large voxel. In the same way, an iSQC MRS spectrum can be obtained from a relatively large voxel of in vivo rat brain with a comparable resolution to the PRESS spectrum with a small voxel.

Conclusion:

Compared to PRESS, the iSQC MRS may be more feasible and promising for detection of strongly structured tissues with relatively large voxels. J. Magn. Reson. Imaging 2013;37:359–364. © 2012 Wiley Periodicals, Inc.     

Loss of fine structure and edge sharpness in fast-spin-echo carotid wall imaging: measurements and comparison with multiple-spin-echo in normal and atherosclerotic subjects

Purpose:

To test whether the k‐space acquisition strategy used by fast‐spin‐echo (FSE) is a major source of blurring in carotid wall and plaque imaging, and investigate an alternative acquisition approach.

Materials and Methods:

The effect of echo train length (ETL) and T₂ on the amount of blurring was studied in FSE simulations of vessel images. Edge sharpness was measured in black‐blood T₁ and proton‐density weighted (T₁W and PDW) carotid images acquired from 5 normal volunteers and 19 asymptomatic patients using both FSE and multiple‐spin‐echo (Multi‐SE) sequences at 3 Tesla. Plaque images were classified and divided in group α (tissues' average T₂ ～40–70 ms) and group β (plaque components with shorter T₂).

Results:

Simulations predicted 26.9% reduction of vessel edge sharpness from Multi‐SE to FSE images (ETL = 9, T₂ = 60 ms). This agreed with in vivo measurements in normal volunteers (27.4%) and in patient group α (26.2%), while in group β the loss was higher (31.6%).

Conclusion:

FSE significantly reduced vessel edge sharpness along the phase‐encoding direction in T₁W and PDW images. Blurring was stronger in the presence of plaque components with short T₂ times. This study shows a limitation of FSE and the potential of Multi‐SE to improve the quality of carotid imaging. J. Magn. Reson. Imaging 2011;33:1136–1143. © 2011 Wiley‐Liss, Inc.     

Diffusion tensor imaging (DTI) with retrospective motion correction for large-scale pediatric imaging

Purpose:

To develop and implement a clinical DTI technique suitable for the pediatric setting that retrospectively corrects for large motion without the need for rescanning and/or reacquisition strategies, and to deliver high‐quality DTI images (both in the presence and absence of large motion) using procedures that reduce image noise and artifacts.

Materials and Methods:

We implemented an in‐house built generalized autocalibrating partially parallel acquisitions (GRAPPA)‐accelerated diffusion tensor (DT) echo‐planar imaging (EPI) sequence at 1.5T and 3T on 1600 patients between 1 month and 18 years old. To reconstruct the data, we developed a fully automated tailored reconstruction software that selects the best GRAPPA and ghost calibration weights; does 3D rigid‐body realignment with importance weighting; and employs phase correction and complex averaging to lower Rician noise and reduce phase artifacts. For select cases we investigated the use of an additional volume rejection criterion and b‐matrix correction for large motion.

Results:

The DTI image reconstruction procedures developed here were extremely robust in correcting for motion, failing on only three subjects, while providing the radiologists high‐quality data for routine evaluation.

Conclusion:

This work suggests that, apart from the rare instance of continuous motion throughout the scan, high‐quality DTI brain data can be acquired using our proposed integrated sequence and reconstruction that uses a retrospective approach to motion correction. In addition, we demonstrate a substantial improvement in overall image quality by combining phase correction with complex averaging, which reduces the Rician noise that biases noisy data. J. Magn. Reson. Imaging 2012;36:961–971. © 2012 Wiley Periodicals, Inc.     

Quantitative 2D and 3D phase contrast MRI: Optimized analysis of blood flow and vessel wall parameters

Quantification of CINE phase contrast (PC)‐MRI data is a challenging task because of the limited spatiotemporal resolution and signal‐to‐noise ratio (SNR). The method presented in this work combines B‐spline interpolation and Green's theorem to provide optimized quantification of blood flow and vessel wall parameters. The B‐spline model provided optimal derivatives of the measured three‐directional blood velocities onto the vessel contour, as required for vectorial wall shear stress (WSS) computation. Eight planes distributed along the entire thoracic aorta were evaluated in a 19‐volunteer study using both high‐spatiotemporal‐resolution planar two‐dimensional (2D)‐CINE‐PC (～1.4 × 1.4 mm²/24.4 ms) and lower‐resolution 3D‐CINE‐PC (～2.8 × 1.6 × 3 mm³/48.6 ms) with three‐directional velocity encoding. Synthetic data, error propagation, and interindividual, intermodality, and interobserver variability were used to evaluate the reliability and reproducibility of the method. While the impact of MR measurement noise was only minor, the limited resolution of PC‐MRI introduced systematic WSS underestimations. In vivo data demonstrated close agreement for flow and WSS between 2D‐ and 3D‐CINE‐PC as well as observers, and confirmed the reliability of the method. WSS analysis along the aorta revealed the presence of a circumferential WSS component accounting for 10–20%. Initial results in a patient with atherosclerosis suggest the potential of the method for understanding the formation and progression of cardiovascular diseases. Magn Reson Med 60:1218–1231, 2008. © 2008 Wiley‐Liss, Inc.     

Magnetic resonance (MR) differential diagnosis of breast tumors using apparent diffusion coefficient (ADC) on 1.5‐T

To review the published reports concerning the apparent diffusion coefficient (ADC) value evaluation for the differentiation between malignant and benign breast tumors, articles were searched with the inclusion criteria: (a) a 1.5‐T unit was used; (b) the diagnostic criteria were clearly stated; (c) diffusion‐weighted images (DWIs) were obtained, and ADC value was calculated; (d) ADC values of breast tumors were reported with mean ± standard deviation (SD). Meta‐analysis from 12 articles revealed that the pooled sensitivity and specificity were 0.89 (95% confidence interval [CI], 0.85–0.91) and 0.77 (95% CI, 0.69–0.84), respectively, and that only the maximum b factor correlated with the mean ADC values of malignant and benign tumors, and the noncancerous breast tissue (P< 0.05,P < 0.01,P< 0.05, respectively). In conclusion, ADC evaluation is useful for the differentiation between malignant and benign breast tumors. J. Magn. Reson. Imaging 2009;30:249–255. © 2009 Wiley‐Liss, Inc.