Comparison of a single shot T1-weighted in- and out-of-phase magnetization prepared gradient recalled echo with a standard two-dimensional gradient recalled echo: preliminary findings

Purpose:

To compare in‐phase (IP) /out‐of‐phase (OP) single shot magnetization‐prepared gradient‐recalled‐echo (MP‐GRE) with a standard two‐dimensional gradient‐recalled‐echo (2D‐GRE), and to compare image quality of MP‐GRE in cooperative and noncooperative subjects.

Materials and Methods:

Ninety‐six consecutive subjects (52 males, 44 females; mean age, 53.2 ± 16.7 years), both cooperative (n = 73) and noncooperative (n = 23) subjects who had MRI examinations including precontrast T1‐weighted IP/OP MP‐GRE with or without IP/OP 2D‐GRE were included in the study. The sequences were independently qualitatively evaluated by two radiologists. Quantitative analysis of liver fat index, signal‐to‐noise ratio (SNR) and liver‐lesion contrast‐to‐noise ratio (CNR) was also performed. Data were subjected to statistical analysis.

Results:

The visual detection of the presence or absence of liver steatosis showed no differences between 2D‐GRE and MP‐GRE imaging (k = 1). Minor differences were observed on image quality between MP‐GRE and 2D‐GRE in cooperative subjects, and between MP‐GRE sequences performed in cooperative and noncooperative subjects. Liver fat index results were strongly positively correlated (r = .98; 95% confidence interval [CI] 0.97 to 0.98; P < .0001). Intercept (.14; 95% CI .13 to .15; P < .0001) and slope (.83; 95% CI .79 to .86; P < .0001) were statistically significant.

Conclusion:

IP/OP MP‐GRE and 2D‐GRE comparably demonstrate the presence or absence of hepatic steatosis. Image quality of MP‐GRE was also comparable to 2D‐GRE, and was not substantially adversely affected if subjects were unable to cooperate with breathholding instructions. J. Magn. Reson. Imaging 2011;33:1482–1490. © 2011 Wiley‐Liss, Inc.     

Three-dimensional contrast-enhanced hepatic MR imaging: comparison between a centric technique and a linear approach with partial Fourier along both slice and phase directions

Purpose

To compare the image quality of two variants of a three‐dimensional (3D) gradient echo sequence (GRE) for hepatic MRI.

Materials and Methods

Thirty‐nine patients underwent hepatic MRI on a 3.0 Tesla (T) magnet (Intera Achieva; Philips Medical Systems). The clinical protocol included two variants of a 3D GRE with fat suppression: (i) a “centric” approach, with elliptical centric k‐space ordering and (ii) an “enhanced” approach using linear sampling and partial Fourier in both the slice and phase encoding direction. “Centric” and “Enhanced” 3D GRE images were obtained both precontrast (n = 32) and after gadoxetic acid injection (n = 39). Two reviewers jointly reviewed MR images for anatomic sharpness, overall contrast, homogeneity, and absence of artifacts. The liver‐to‐lesion signal difference ratio (SDR) was measured. Paired sample Wilcoxon test and paired t‐tests were used.

Results

Enhanced 3D GRE images performed better than centric 3D GRE images with respect to anatomic sharpness (P = 0.0156), overall contrast (P = 0.0195), homogeneity (P < 0.0001), and absence of artifacts (P = 0.0003) on precontrast images. For postcontrast MRI, enhanced 3D GRE images showed better quality in terms of overall contrast (P = 0.0195), homogeneity (P < 0.0001), and absence of artifacts (P = 0.009). Liver‐to‐lesion SDR on enhanced 3D GRE images (0.48 ± 0.13) was significantly higher than that of conventional 3D GRE images (0.40 ± 0.19, P = 0.0004) on postcontrast images, but not on precontrast images.

Conclusion

The enhanced 3D GRE sequence available on our scanner provided better hepatic image quality than the centric variant, without compromising lesion contrast. J. Magn. Reson. Imaging 2011;33:160–166. © 2010 Wiley‐Liss, Inc.     

Liver MRI in the hepatocyte phase with gadolinium‐EOB‐DTPA: Does increasing the flip angle improve conspicuity and detection rate of hypointense lesions?

Purpose:

To compare conspicuity and detection rate of hypointense lesions on T1‐weighted (T1w) gradient echo (GRE) sequences with low and high flip angles (FA) in hepatocyte phase magnetic resonance imaging (MRI) using gadoxetate disodium.

Materials and Methods:

This Health Insurance Portability and Accountability Act (HIPAA)‐compliant study was Institutional Review Board (IRB)‐approved. The study population consisted of patients with hypointense liver lesions undergoing MRI with gadoxetate disodium, with hepatocyte‐phase fat suppressed 3D T1w GRE sequences at both low (10–12°) and high (30–35°) FA. Contrast‐to‐noise ratios (CNRs) were calculated for liver parenchyma vs. large lesions and common bile duct (CBD) vs. liver. Three radiologists each assigned a conspicuity score (CS) for each lesion detected at low or high FA. Paired Student's t‐tests compared the lesion detection (LD) rate using only the hepatocyte phase data set compared with the entire MRI examination, and CS for low and high FA.

Results:

In all, 57 large and 70 small lesions were identified in 18 patients. Average LD and CS were significantly greater at high FA versus low FA overall (LD 89.0% vs. 79.5%; CS 2.8 vs. 2.2; P < 0.05) and for small lesions (81.4% vs. 65.7%; 2.5 vs. 1.8; P < 0.05). Average liver‐to‐lesion CNR for large lesions and CBD‐to‐liver CNR was significantly greater at high FA (P < 0.05).

Conclusion:

Increasing the FA in hepatocyte phase MRI with gadoxetate disodium improves hypointense lesion detection and conspicuity, particularly for small lesions. J. Magn. Reson. Imaging 2012;35:611‐616. © 2011 Wiley Periodicals, Inc.     

Quantitative and qualitative comparison of 1.5 and 3.0 tesla MRI in patients with chronic liver diseases

Purpose

To compare the quantitative and qualitative image quality intra‐individually, at 1.5 and 3.0 Tesla (T) in patients with chronic liver diseases.

Materials and Methods

The study group included 24 consecutive patients (17 males, 7 females; mean age ± standard deviation 56.5 ± 11.5) who had chronic liver diseases and underwent abdominal MRI for the liver evaluation at both 1.5 and 3.0T within a 4‐month period. All MRI studies were retrospectively evaluated quantitatively and qualitatively. Quantitative analysis was performed by measuring signal to noise ratio (SNR) on various abdominal organs. Qualitative analysis was performed by two reviewers to assess image quality, artifacts, and imaging findings of chronic liver diseases. Quantitative and qualitative analyses findings were compared between 1.5 and 3.0T using the paired Student t‐test and Wilcoxon signed rank test, respectively.

Results

The statistically significant increase in SNRs in various abdominal tissues ranged from 1.3‐ to 3.5‐fold at 3.0T compared to 1.5T. Three‐dimensional gradient echo (3D‐GE) sequences demonstrated significantly higher image quality at 3.0T (P < 0.01), whereas precontrast spoiled gradient echo (SGE) sequences demonstrated significantly higher image quality at 1.5T (P < 0.01). T2‐weighted sequences did not show any significant difference in image quality between 1.5 and 3.0T (P > 0.05).

Conclusion

The SNRs of various abdominal tissues demonstrated significant increases at 3.0T. The image quality of 3D‐GE sequences was higher at 3.0T, whereas the image quality of precontrast SGE sequences was higher at 1.5T. J. Magn. Reson. Imaging 2009;29:869–879. © 2009 Wiley‐Liss, Inc.     

Detection of hepatic hypovascular metastases: 3D gradient echo MRI using a hepatobiliary contrast agent

Purpose:

To assess the diagnostic performance of gadobenate dimeglumine‐enhanced 3D gradient echo (3D‐GRE) magnetic resonance imaging (MRI) for the detection of hepatic hypovascular metastases.

Materials and Methods:

We retrospectively analyzed the initial radiologic reports of MRI of 41 patients with suspected hepatic metastases. Seventy‐nine metastatic lesions were confirmed by histopathology or intraoperative ultrasound (IOUS). The sensitivity and positive predictive values for the diagnosis of hepatic metastasis were determined among each MRI set (hepatobiliary phase, precontrast images, dynamic imaging). The diagnostic performance of dynamic image set and combined dynamic and hepatobiliary image set was also evaluated by two radiologists using alternative free response receiver operating characteristic (ROC) analysis.

Results:

The overall detection rate and positive predictive value of MR were 96.2% (76/79) and 96.2% (76/79), respectively. Images obtained with hepatobiliary phase 3D‐GRE showed a significantly better detection rate compared to those with precontrast sequences or dynamic imaging (P = 0.008 and 0.016, respectively). Regarding lesions 1 cm or smaller, the detection rate was 90.3% (28/31). Each reader showed a higher Az value of the combined hepatobiliary image set than those of the dynamic image set.

Conclusion:

3D‐GRE MRI using a hepatobiliary contrast agent is an accurate tool in the detection of hepatic hypovascular metastases and improves detection rate compared with precontrast and dynamic imaging. J. Magn. Reson. Imaging 2010;31:571–578. © 2010 Wiley‐Liss, Inc.     

Secuencia de disparo único eco de gradiente en fase y fase opuesta con preparación de la magnetización: descripción y optimización de la técnica con equipo de 1,5 T

Purpose

To implement in-phase and out-of-phase (IP/OP) techniques with Magnetization-Prepared Gradient Recalled Echo (MP-GRE) and to evaluate the feasibility and diagnostic image quality among pre and post-optimized MP-GRE sequences, including patients unable to cooperate with breath-hold requirements.

Materials and methods

Institutional review board approval with waiver of informed consent was obtained for this HIPAA-compliant retrospective study. Two groups of patients were included in the study, before and after optimization of MP-GRE parameters, with seventy-three (24 noncooperative/49 cooperative) and sixty-four (22 noncooperative/42 cooperative) consecutive patients, respectively. The motion-insensitive sequence used in this study was a single-shot 2D MP-GRE. Two radiologists qualitatively evaluated the sequences to identify the presence of phase cancellation artifact in OP images and to determine image quality, extent of artifacts (respiratory ghosting, bounce-point artifact, spatial misregistration and pixel graininess) and lesion conspicuity on the various sequences. The ability to visually detect liver steatosis and fatty adrenal adenomas was evaluated. Qualitative analyses were compared using the Wilcoxon and Mann-Whitney tests.

Results

There were statistically significant differences between all MP-GRE sequences concerning phase cancellation artifact (P<.0001) which was present in MP-GRE OP sequences and negligible to absent in the pre (IP₁) and post-optimized (IP₂) MP-GRE IP sequences, respectively, in all patients.Bounce point artifacts were significantly more pronounced in MP-GRE IP₁ (P<.0001). Spatial misregistration was slightly more prominent in noncooperative patients with MP-GRE IP₂ (P=.0027). MP-GRE OP and MP-GRE IP₂ showed significantly higher overall image quality (P<.0001).MP-GRE sequences subjectively identified hepatic steatosis (n=20) and adrenal adenomas (n=5) based on signal loss from IP to OP sequence.

Conclusion

Single shot IP/OP MP-GRE is feasible and allows motion resistant imaging with adequate diagnostic image quality. This technique is able to provide IP and OP information in patients unable to suspend respiration.     

Free-breathing contrast-enhanced T1-weighted gradient-echo imaging with radial k-space sampling for paediatric abdominopelvic MRI

Objective

To compare the image quality of contrast-enhanced abdominopelvic 3D fat-suppressed T1-weighted gradient-echo imaging with radial and conventional Cartesian k-space acquisition schemes in paediatric patients.

Methods

Seventy-three consecutive paediatric patients were imaged at 1.5 T with sequential contrast-enhanced T1-weighted Cartesian (VIBE) and radial gradient echo (GRE) acquisition schemes with matching parameters when possible. Cartesian VIBE was acquired as a breath-hold or as free breathing in patients who could not suspend respiration, followed by free-breathing radial GRE in all patients. Two paediatric radiologists blinded to the acquisition schemes evaluated multiple parameters of image quality on a five-point scale, with higher score indicating a more optimal examination. Lesion presence or absence, conspicuity and edge sharpness were also evaluated. Mixed-model analysis of variance was performed to compare radial GRE and Cartesian VIBE.

Results

Radial GRE had significantly (all P?<?0.001) higher scores for overall image quality, hepatic edge sharpness, hepatic vessel clarity and respiratory motion robustness than Cartesian VIBE. More lesions were detected on radial GRE by both readers than on Cartesian VIBE, with significantly higher scores for lesion conspicuity and edge sharpness (all P?<?0.001).

Conclusion

Radial GRE has better image quality and lesion conspicuity than conventional Cartesian VIBE in paediatric patients undergoing contrast-enhanced abdominopelvic MRI.

Key Points

? Numerous techniques are required to provide optimal MR images in paediatric patients. ? Radial free-breathing contrast-enhanced acquisition demonstrated excellent image quality. ? Image quality and lesion conspicuity were better with radial than Cartesian acquisition. ? More lesions were detected on contrast-enhanced radial than on Cartesian acquisition. ? Radial GRE can be used for performing abdominopelvic MRI in paediatric patients.     

Distinguishing hemangiomas from malignant solid hepatic lesions: a comparison of heavily T2-weighted images obtained before and after administration of gadoxetic acid

Purpose:

To compare the use of heavily T2‐weighted images obtained before and after administration of gadoxetic acid in differentiating hemangiomas from malignant solid hepatic lesions.

Materials and Methods:

Heavily T2‐weighted images (TE = 150 msec) were obtained for 70 patients (42 men and 28 women) with 74 focal hepatic lesions (25 hepatocellular carcinomas [HCC], 22 metastases, and 27 hemangiomas) ≤3 cm in diameter before and after gadoxetic acid‐enhanced dynamic magnetic resonance imaging (MRI). Quantitative analysis was performed using receiver operating characteristic (ROC) curves with lesion‐to‐liver signal intensity difference‐to‐noise ratio (SDNR) on precontrast and postcontrast images. Qualitative analysis was also performed by two blinded reviewers.

Results:

The SDNR of the solid lesions was significantly higher on the postcontrast (1.66 ± 1.18) than on the precontrast (1.38 ± 1.07) images (P = 0.0012), while the SDNR of hemangiomas was comparable for pre‐ and postcontrast images (P = 0.8164). The best SDNR cutoff values for distinguishing solid lesions from hemangiomas were ≤1.85 (Az = 0.948) for precontrast and ≤2.58 (Az = 0.901) for postcontrast images (P = 0.057). Reader performances for distinguishing hemangiomas from solid lesions were comparable between the precontrast (Az = 0.975 and 0.970 for readers 1 and 2) and postcontrast (Az = 0.977 and 0.972) images (P = 0.899 and 0.946).

Conclusion:

Heavily T2‐weighted images obtained after administration of gadoxetic acid have a diagnostic capability comparable to precontrast images for differentiating between small hemangiomas and malignant solid lesions of the liver. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

Flow‐sensitive 4D MRI of the thoracic aorta: Comparison of image quality,quantitative flow,and wall parameters at 1.5 T and 3 T

Purpose:

To evaluate the effect of field strength on flow‐sensitive 4D magnetic resonance imaging (MRI) of the thoracic aorta. A volunteer study at 1.5 T and 3 T was conducted to compare phase‐contrast MR angiography (MRA) and 3D flow visualization quality as well as quantification of aortic hemodynamics.

Materials and Methods:

Ten healthy volunteers were examined by flow‐sensitive 4D MRI at both 1.5 T and 3 T MRI with identical imaging parameters (TE/TR = 6/5.1 msec, spatial/temporal resolution ≈2 mm/40.8 msec). Analysis included assessment of image quality of derived aortic 3D phase contrast (PC) angiography and 3D flow visualization (semiquantitative grading on a 0–2 scale, two blinded observers) and quantification of blood flow velocities, net flow per cardiac cycle, wall shear stress (WSS), and velocity noise.

Results:

Quality of 3D blood flow visualization (average grading = 1.8 ± 0.4 at 3 T vs. 1.1 ± 0.7 at 1.5 T) and the depiction of aortic lumen geometry by 3D PC‐MRA (1.7 ± 0.5 vs. 1.2 ± 0.6) were significantly (P < 0.01) improved at 3 T while velocity noise was significantly higher (P < 0.01) at 1.5 T. Velocity quantification resulted in minimally altered (0.05 m/s, 3 mL/cycle and 0.01 N/m²) but not statistically different (P = 0.40, P = 0.39, and P = 0.82) systolic peak velocities, net flow, and WSS for 1.5 T compared to 3 T.

Conclusion:

Flow‐sensitive 4D MRI at 3 T provided improved image quality without additional artifacts related to higher fields. Imaging at 1.5 T MRI, which is more widely available, was also feasible and provided information on aortic 3D hemodynamics of moderate quality with identical performance regarding quantitative analysis. J. Magn. Reson. Imaging 2012;36:1097–1103. © 2012 Wiley Periodicals, Inc.     

Two- versus three-dimensional dual gradient-echo MRI of the liver: a technical comparison

Objective

To compare 2D spoiled dual gradient-echo (SPGR-DE) and 3D SPGR-DE with fat and water separation for the assessment of focal and diffuse fatty infiltration of the liver.

Methods

A total of 227 consecutive patients (141 men; 56?±?14 years) underwent clinically indicated liver MRI at 1.5 T including multiple-breath-hold 2D SPGR-DE and single-breath-hold 3D SPGR-DE with automatic reconstruction of fat-only images. Two readers assessed the image quality and number of fat-containing liver lesions on 2D and 3D in- and opposed-phase (IP/OP) images. Liver fat content (LFC) was quantified in 138 patients without chronic liver disease from 2D, 3D IP/OP, and 3D fat-only images.

Results

Mean durations of 3D and 2D SPGR-DE acquisitions were 23.7?±?2.9 and 97.2?±?9.1 s respectively. The quality of all 2D and 3D images was rated diagnostically. Three-dimensional SPGR-DE revealed significantly more breathing artefacts resulting in lower image quality (P?<?0.001); 2D and 3D IP/OP showed a similar detection rate of fat-containing lesions (P?=?0.334) and similar LFC estimations (mean: +0.4 %; P?=?0.048). LFC estimations based on 3D fat-only images showed significantly higher values (mean: 2.7 % + 3.5 %) than those from 2D and 3D IP/OP images (P?<?0.001).

Conclusion

Three dimensional SPGR-DE performs as well as 2D SPGR-DE for the assessment of focal and diffuse fatty infiltration of liver parenchyma. The 3D SPGR-DE sequence used was quicker but more susceptible to breathing artefacts. Significantly higher LFC values are derived from 3D fat-only images than from 2D or 3D IP/OP images.

Key Points

? Magnetic resonance imaging can assess focal and diffuse hepatic fatty infiltration ? Both 2D and 3D dual-echo MRI techniques can be used for chemical shift imaging of the liver. ? The single breath-hold 3D dual-echo technique is faster but more susceptible to breathing artefacts. ? Three-dimensional fat-only images show higher fat estimates than in- and out-of-phase images.     

Detection and characterization of focal hepatic tumors: A comparison of T2‐weighted MR images before and after the administration of gadoxectic acid

Purpose

To evaluate if T2‐weighted images (T2WI) after administration of gadoxetic acid have diagnostic capability comparable to precontrast T2WI in the detection and characterization of focal liver lesions.

Materials and Methods

Eighty patients with 128 liver lesions (71 hepatocellular carcinomas, 35 metastases, and 22 hemangiomas) underwent gadoxetic acid‐enhanced T1WI and precontrast and postcontrast turbo spin echo‐short tau inversion recovery (TSE‐STIR) and respiratory triggered (RT)‐TSE. The sensitivity for malignancy with combining T2WIs and enhanced T1WIs was evaluated and percentage of signal intensity loss (PSIL) and lesion‐liver contrast to noise ratio (CNR) were calculated for T2WIs. Lesion characterization with T2WIs as solid and nonsolid was evaluated using kappa statistics.

Results

The PSIL was higher with TSE‐STIR than with RT‐TSE (P = 0.0001). The malignancy‐liver CNRs on postcontrast T2WIs were higher than on precontrast T2WIs (P = 0.0001). Sensitivity for malignancy by combining postcontrast T2WIs and T1WIs (93.0% [hepatocellular carcinoma, HCC]; 97.1% [metastases]) was comparable to sensitivity of combining precontrast T2WIs and postcontrast T1WIs (91.6% [HCC]; 88.6% [metastases]). Kappa values for T2WIs indicated excellent agreement (k = 0.935).

Conclusion

Gadoxetic acid‐enhanced T2WIs showed a comparable diagnostic capability to precontrast T2WIs for the detection and characterization of hepatic tumors. J. Magn. Reson. Imaging 2009;30:437–443. © 2009 Wiley‐Liss, Inc.     

Assessment of fast dynamic imaging and the use of Gd‐EOB‐DTPA for MR‐guided liver interventions

Purpose:

1) To analyze and compare fast dynamic imaging sequences to biopsy suspect liver lesions. 2) To evaluate the additional use of hepatocyte‐specific contrast agent compared to the nonenhanced fast dynamic scans and diagnostic liver imaging.

Materials and Methods:

Image acquisition was performed using a 1T open‐configured scanner suitable for interventional purposes. Transversal postcontrast T1‐weighted (T1w) fat‐saturated 3D high‐resolution examination (THRIVE) images were acquired >20 minutes postintravenous application of gadolinium ethoxybenzyl diethylenetriaminepentaacetic acid (Gd‐EOB‐DTPA). A single slice, crossing the level of the lesion, was acquired using intermediate‐weighted steady‐state free‐precession (bTFE), T1w‐gradient echo and spin echo (T1FFE/TSE), T2w‐spin echo (sshTSE) sequences. T1w imaging was acquired prior and after contrast media application. Diagnostic and fast dynamic images were compared based on a 10‐point rating scale. In addition, the liver‐to‐lesion‐contrast ratio was measured.

Results:

A total of 39 malignant lesions with a mean diameter of 13 mm (5–30 mm) in 39 patients were included. Concerning a test of noninferiority, there was no significant difference between rating score values of fast dynamic imaging employing contrast‐enhanced T1FFE‐sequences compared to diagnostic THRIVE (P = 0.001). Calculated liver‐to‐lesion contrast also showed no difference for either imaging sequence (P = 1.0). All other sequences tested showed significant inferiority (P ≤ 0.001).

Conclusion:

T1w Gd‐EOB‐DTPA contrast‐enhanced fast dynamic GRE imaging significantly improves the contrast behavior of malignant liver lesions comparable to diagnostic imaging and is best suited for liver intervention, especially at 1T open magnetic resonance imaging. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

Preoperative evaluation of pancreatic cancer: Comparison of gadolinium‐enhanced dynamic MRI with MR cholangiopancreatography versus MDCT

Purpose

To determine the accuracy of magnetic resonance imaging (MRI) including dynamic imaging using three‐dimensional gradient‐echo (3D‐GRE) sequences and MR cholangiopancreatograpy (MRCP) compared with that of multidetector row CT (MDCT) with regard to resectability in pancreas cancer.

Materials and Methods

From February 2004 to July 2008, 54 patients (32 men, 22 women: age range, 28–83 years; mean age, 63.1 years old) with surgically proven pancreatic carcinoma, who had undergone preoperative gadolinium‐enhanced 3D‐GRE MRI with MRCP and triple‐phase MDCT, were included in this retrospective study. Two, clinically experienced attending radiologists independently reviewed the two image sets. These readers evaluated the tumor conspicuity, presence of vascular invasion, choledochal and duodenal invasion, lymph node metastases, distant metastasis, and tumor resectability. The results were compared with the surgical and histopathologic findings using receiver operating characteristic analysis (Az) and kappa statistics.

Results

Curative resections were performed on 42 patients. Regarding the tumor conspicuity, MRI had a significantly higher Az value compared with MDCT according to both reviewers (P < 0.05). The accuracy of resectability was Az = 0.753 and 0.768 on MRI and Az = 0.829 and 0.762 on MDCT for each reviewer, and the difference in the accuracy of resectability was not significant between MRI and MDCT for either reviewer (P > 0.05). Two imaging sets showed a similar diagnostic performance in the evaluation of vascular involvement, lymph node metastasis, and distant metastasis.

Conclusion

Dynamic 3D‐GRE MRI with MRCP shows superior tumor conspicuity and similar diagnostic performance compared with MDCT in evaluating the resectability of pancreatic cancer. J. Magn. Reson. Imaging 2009;30:586–595. © 2009 Wiley‐Liss, Inc.     

Effect of superparamagnetic iron oxide on tumor‐to‐liver contrast at T2*‐weighted gradient‐echo MRI: Comparison between 3.0T and 1.5T MR systems

Purpose

To compare 3.0T and 1.5T MR systems in terms of the effect of superparamagnetic iron oxide (SPIO) on tumor‐to‐liver contrast in T2*‐weighted gradient‐echo MRI.

Materials and Methods

SPIO‐enhanced gradient‐echo MR images of the liver with four different TEs (3, 5.3, 6.5, and 8.5 msec) were obtained by means of 1.5T and 3.0T systems. Quantitative analyses of relative signal intensities (SIs) and relative tumor contrast and qualitative analyses of image quality and lesion conspicuity of the liver were performed in 22 patients, 16 of whom had malignant liver tumors.

Results

With both 1.5T and 3.0T, at TE = 8.4 msec, the relative SI of liver and relative tumor contrast were significantly (P < 0.01) lower and higher, respectively, than that for any of the other TEs. There were no significant differences in the relative SI of the liver, relative tumor contrast, image quality, and tumor conspicuity for the same TE between the 1.5T and 3.0T systems.

Conclusion

Our results showed that the effect of SPIO on tumor‐to‐liver contrast at T2*‐weighted gradient‐echo imaging was similar for the 1.5T and 3.0T systems, and that the 8.4‐msec TE was optimal of the four TEs used in this study at 3.0T. J. Magn. Reson. Imaging 2009;29:595–600. © 2009 Wiley‐Liss, Inc.     

Optimization of single injection liver arterial phase gadolinium enhanced MRI using bolus track real-time imaging

Purpose:

To measure contrast agent enhancement kinetics in the liver and to further evaluate and develop an optimized gadolinium enhanced MRI using a single injection real‐time bolus‐tracking method for reproducible imaging of the transient arterial‐phase.

Materials and Methods:

A total of 18 subjects with hypervascular liver lesions were imaged with four dimensional (4D) perfusion scans to measure time‐to‐peak (TTP) delays of arterial (aorta‐celiac axis), liver parenchyma, liver lesion, portal, and hepatic veins. Time delays were calculated from the TTP‐aorta signal, and then related to the gradient echo (GRE) k‐space acquisition design, to determine optimized timing for real‐time bolus‐track triggering methodology. As another measure of significance, 200 clinical patients were imaged with 3D‐GRE using either a fixed time‐interval or by individualized arterial bolus real‐time triggering. Bolus TTP‐aorta was calculated and arterial‐phase acquisitions were compared for accuracy and reproducibility using specific vascular enhancement indicators.

Results:

The mean bolus transit‐time to peak‐lesion contrast was 8.1 ± 2.7 seconds following arterial detection, compared to 32.1 ± 5.4 seconds from contrast injection, representing a 62.1% reduction in the time‐variability among subjects (N = 18). The real‐time bolus‐triggered technique more consistently captured the targeted arterial phase (94%), compared to the fixed timing technique (73%), representing an expected improvement of timing accuracy in 28% of patients (P = 0.0001389).

Conclusion:

Our results show detailed timing window analysis required for optimized arterial real‐time bolus‐triggering acquisition of transient arterial phase features of liver lesions, with optimized arterial triggering expected to improve reproducibility in a significant number of patients. J. Magn. Reson. Imaging 2011;33:110–118. © 2010 Wiley‐Liss, Inc.     

Comparison between gadolinium-enhanced 2D T1-weighted gradient-echo and spin-echo sequences in the detection of active multiple sclerosis lesions on 3.0T MRI

Objectives

To compare the sensitivity of enhancing multiple sclerosis (MS) lesions in gadolinium-enhanced 2D T1-weighted gradient-echo (GRE) and spin-echo (SE) sequences, and to assess the influence of visual conspicuity and laterality on detection of these lesions.

Methods

One hundred MS patients underwent 3.0T brain MRI including gadolinium-enhanced 2D T1-weighted GRE and SE sequences. The two sets of contrast-enhanced scans were evaluated in random fashion by three experienced readers. Lesion conspicuity was assessed by the image contrast ratio (CR) and contrast-to-noise ratio (CNR). The intracranial region was divided into four quadrants and the impact of lesion location on detection was assessed in each slice.

Results

Six hundred and seven gadolinium-enhancing MS lesions were identified. GRE images were more sensitive for lesion detection (0.828) than SE images (0.767). Lesions showed a higher CR in SE than in GRE images, whereas the CNR was higher in GRE than SE. Most misclassifications occurred in the right posterior quadrant.

Conclusions

The gadolinium-enhanced 2D T1-weighted GRE sequence at 3.0T MRI enables detection of enhancing MS lesions with higher sensitivity and better lesion conspicuity than 2D T1-weighted SE. Hence, we propose the use of gadolinium-enhanced GRE sequences rather than SE sequences for routine scanning of MS patients at 3.0T.

Key Points

? 2D SE and GRE sequences are useful for detecting active MS lesions. ? Which of these sequences is more sensitive at high field remains uncertain. ? GRE sequence showed better sensitivity for detecting active MS lesions than SE. ? We propose GRE sequence for detecting active MS lesions at 3.0T.

     

Hypointense hepatocellular nodules on hepatobiliary phase of Gd‐EOB‐DTPA‐enhanced MRI: Can increasing the flip angle improve conspicuity of lesions?

Purpose:

To compare the conspicuity of hypointense hepatocellular nodules in patients with chronic liver disease on hepatobiliary phase (HP) of gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid (Gd‐EOB‐DTPA)‐enhanced magnetic resonance imaging (MRI) acquired with low to high flip angles (FAs).

Materials and Methods:

A total of 95 patients with chronic liver disease who underwent Gd‐EOB‐DTPA‐enhanced MRI were included. HP images were obtained at 20 minutes, with 15°, 20°, and 30° FAs. For the detected hepatocellular nodule, liver‐to‐lesion contrast‐to‐phantom ratios (CPR) and lesion conspicuity (LCS) were assessed.

Results:

In all examinations, 96 hepatocellular nodules showing hypointensity on HP were identified. These lesions included 39 hypovascular nodules and 57 hypervascular nodules. Mean CPR and LCS showed the highest value on the 30° FA, followed by 20° and 15° FAs. CPR and LCS of 15° FA were significantly lower than those of 20° and 30° FAs (P < 0.001 to P = 0.007). CPR of 30° FA for hypervascular nodules was significantly greater than that of 20° FA (P < 0.001).

Conclusion:

In the evaluation of hypointense hepatocellular nodules on HP of Gd‐EOB‐DTPA‐enhanced MRI, higher FA such as 30° should be used rather than low FA such as 15°. J. Magn. Reson. Imaging 2013;37:1093–1099. © 2012 Wiley Periodicals, Inc.     

Comparison of ferucarbotran‐enhanced fluid‐attenuated inversion‐recovery echo‐planar,T2‐weighted turbo spin‐echo,T2*‐weighted gradient‐echo,and diffusion‐weighted echo‐planar imaging for detection of malignant liver lesions

Purpose:

To compare the diagnostic accuracy of superparamagnetic iron oxide (SPIO)‐enhanced fluid‐attenuated inversion‐recovery echo‐planar imaging (FLAIR EPI) for malignant liver tumors with that of T2‐weighted turbo spin‐echo (TSE), T2*‐weighted gradient‐echo (GRE), and diffusion‐weighted echo‐planar imaging (DW EPI).

Materials and Methods:

SPIO‐enhanced magnetic resonance imaging (MRI) that included FLAIR EPI, T2‐weighted TSE, T2*‐weighted GRE, and DW EPI sequences was performed using a 3 T system in 54 consecutive patients who underwent surgical exploration with intraoperative ultrasonography. A total of 88 malignant liver tumors were evaluated. Images were reviewed independently by two blinded observers who used a 5‐point confidence scale to identify lesions. Results were correlated with results of histopathologic findings and surgical exploration with intraoperative ultrasonography. The accuracy of each MRI sequence was measured with jackknife alternative free‐response receiver operating characteristic analysis. The sensitivity of each observer with each MRI sequence was compared with McNemar's test.

Results:

Accuracy values were significantly higher with FLAIR EPI sequence (0.93) than with T2*‐weighted GRE (0.80) or DW EPI sequences (0.80) (P < 0.05). Sensitivity was significantly higher with the FLAIR EPI sequence than with any of the other sequences.

Conclusion:

SPIO‐enhanced FLAIR EPI sequence was more accurate in the diagnosis of malignant liver tumors than T2*‐weighted GRE and DW EPI sequences. SPIO‐enhanced FLAIR EPI sequence is helpful for the detection of malignant liver tumors. J. Magn. Reson. Imaging 2010;31:607–616. ©2010 Wiley‐Liss, Inc.     

Comparison of high spatial resolution respiratory triggered inversion recovery‐prepared spoiled gradient echo sequence with standard breathhold T1 sequence MRI of the liver using gadoxetic acid

Purpose:

To assess if a high resolution respiratory triggered inversion recovery prepared GRE sequence (RT) improved image quality and detection of lesions compared with breathhold GRE T1 weighted MR sequence (BH) in the hepatobiliary uptake phase of MR of the liver using gadoxetic acid (Gd‐EOB‐DTPA).

Materials and Methods:

Thirty‐eight consecutive patients from July 2009 to September 2010 who had undergone Gd‐EOB‐DTPA enhanced liver exams were retrospectively identified. Qualitative assessment performed on reference lesions and background liver by two independent readers. Quantitative assessment performed by one reader.

Results:

Liver parenchyma signal‐to‐noise ratio for BH was 90.3 ± 23.9 (mean ± SD) and RT, 106.1 ± 40.4 (P = 0.119). For BH, 320 lesions were detected compared with 257 for RT. Lesion to liver contrast was significantly better on RT sequences (0.26 ± 0.24; mean ± SD) compared with BH sequence (0.21 ± 0.20; P = 0.044). Fifty‐seven reference lesions assessed. Both reviewers rated BH better for lesion margin and hepatic vessel sharpness. BH was rated with less artifact (P < 0.05). Lesion to liver contrast on BH was significantly better for one reviewer.

Conclusion:

BH sequence had better overall image quality than RT in several quantitative and qualitative factors including number of lesions detected and level of artifact. J. Magn. Reson. Imaging 2013;37:700—706. © 2013 Wiley Periodicals, Inc.     

Usefulness of the application of the BLADE technique to reduce motion artifacts on navigation‐triggered prospective acquisition correction (PACE) T2‐weighted MRI (T2WI) of the liver

Purpose

To evaluate the effects of the application of the BLADE (Siemens, Siemens Medical Systems, Erlangen, Germany) technique, a technique to reduce motion artifacts, on navigator‐triggered prospective acquisition correction (PACE) T2‐weighted MRI (T2WI) of the liver.

Materials and Methods

Twenty‐three consecutive patients with a total of 57 localized hepatic diseases (39 malignant, 18 benign) and 57 patients without hepatic lesion underwent MR study during eupnea. The images were assessed quantitatively by calculating the liver–lesion contrast. Two subjective analyses were also performed. Two observers independently assessed the image quality and the confidence level of the detection and characterization of hepatic nodules using a five‐point scale. Statistical analysis was performed with the Wilcoxon matched‐pairs test except for the diagnostic performance evaluated with jackknife alternative free‐response receiver operating characteristic (JAFROC) analysis.

Results

There was no significant difference in the mean liver–lesion contrast between the PACE T2WI with BLADE (T2WI‐BLADE) (mean ± SD = 0.29 ± 0.14) and that without BLADE (0.30 ± 0.14) (P = 0.39). Visual assessment of PACE T2WI‐BLADE (4.8 ± 0.47) was superior to that without BLADE (4.3 ± 0.8) (P < 0.0001), although there were no significant differences in detecting and characterizing hepatic lesions using JAFROC analysis.

Conclusion

The BLADE technique could improve image quality by reducing motion artifacts on hepatic MRI without affecting the diagnostic performance. J. Magn. Reson. Imaging 2009;30:321–326. © 2009 Wiley‐Liss, Inc.