Optimized high-resolution contrast-enhanced hepatobiliary imaging at 3 tesla: a cross-over comparison of gadobenate dimeglumine and gadoxetic acid

Purpose:

To evaluate the signal to noise ratio (SNR) and contrast to noise ratio (CNR) performance of 0.05 mmol/kg gadoxetic acid and 0.1 mmol/kg gadobenate dimeglumine for dynamic and hepatobiliary phase imaging. In addition, flip angles (FA) that maximize relative contrast‐to‐noise performance for hepatobiliary phase imaging were determined.

Materials and Methods:

A cross‐over study in 10 volunteers was performed using each agent. Imaging was performed at 3 Tesla (T) with a 32‐channel phased‐array coil using breathheld 3D spoiled gradient echo sequences for SNR and CNR analysis, and for FA optimization of hepatobiliary phase imaging.

Results:

Gadobenate dimeglumine (0.1 mmol/kg) had superior SNR performance during the dynamic phase, statistically significant for portal vein and hepatic vein in the portal venous and venous phase (for all, P < 0.05) despite twice the approved dose of gadoxetic acid (0.05 mmol/kg), while gadoxetic acid had superior SNR performance during the hepatobiliary phase. Optimal FAs for hepatobiliary phase imaging using gadoxetic acid and gadobenate dimeglumine were 25–30° and 20–30° for relative contrast liver versus muscle (surrogate for nonhepatocellular tissues), and 45° and 20° (relative contrast liver versus biliary structures), respectively.

Conclusion:

Gadobenate dimeglumine may be preferable for applications that require dynamic phase imaging only, while gadoxetic acid may be preferable when the hepatobiliary phase is clinically important. Hepatobiliary phase imaging with both agents benefits from flip angle optimization. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

Safety characteristics of gadobenate dimeglumine: clinical experience from intra- and interindividual comparison studies with gadopentetate dimeglumine

PURPOSE: To evaluate the safety and tolerability of gadobenate dimeglumine (Gd-BOPTA) relative to that of gadopentetate dimeglumine (Gd-DTPA) in patients and volunteers undergoing MRI for various clinical conditions. MATERIALS AND METHODS: A total of 924 subjects were enrolled in 10 clinical trials in which Gd-BOPTA was compared with Gd-DTPA. Of these subjects, 893 were patients with known or suspected disease and 31 were healthy adult volunteers. Of the 893 patients, 174 were pediatric subjects (aged two days to 17 years) referred for MRI of the brain or spine. Safety evaluations included monitoring vital signs, laboratory values, and adverse events (AE). RESULTS: The rate of AE in adults was similar between the two agents (Gd-BOPTA: 51/561, 9.1%; Gd-DTPA: 33/472, 7.0%; P = 0.22). In parallel-group studies in which subjects were randomized to either agent, the rate of AE was 10.9% for Gd-BOPTA and 7.9% for Gd-DTPA (P = 0.21). In the subset of subjects receiving both agents in intraindividual crossover trials, the rate of AE was 8.0% for Gd-BOPTA and 8.5% for Gd-DTPA (P = 0.84). Results of other safety assessments (laboratory tests, vital signs) were similar for the two agents. CONCLUSION: The safety profile of Gd-BOPTA is similar to Gd-DTPA in patients and volunteers. Both compounds are equally well-tolerated in patients with various disease states undergoing MRI.     

Additional value of gadoxetic acid-DTPA-enhanced hepatobiliary phase MR imaging in the diagnosis of early-stage hepatocellular carcinoma: comparison with dynamic triple-phase multidetector CT imaging

Purpose:

To assess the value of hepatobiliary phase gadoxetic acid (EOB)‐enhanced magnetic resonance imaging (MRI) for the diagnosis of early stage hepatocellular carcinoma (HCC) (<3 cm) compared to triple‐phase dynamic multidetector computed tomography (MDCT).

Materials and Methods:

In all, 52 patients with 60 pathologically proven HCCs underwent both EOB‐enhanced MRI and triple‐phase dynamic MDCT. Two radiologists independently and blindly reviewed three image sets: 1) MDCT, 2) dynamic MRI (unenhanced and EOB‐enhanced dynamic MR images), and 3) combined MRI (dynamic MRI + hepatobiliary phase images) using a five‐point rating scale on a lesion‐by‐lesion basis. Receiver operating characteristics (ROC) analysis was performed, and sensitivity and specificity were calculated.

Results:

The area under the ROC curve (Az) of dynamic MRI was equivalent to that of MDCT for both readers. For both readers, Az and sensitivity of combined MRI for smaller lesions (<1.5 cm) were significantly higher than that of dynamic MRI and MDCT (P < 0.0166). The majority of false‐negative nodules on dynamic MRI or MDCT (75% and 62%, respectively) were due to a lack of identified washout findings.

Conclusion:

Hepatobiliary phase images can increase the value of EOB‐enhanced MRI in the diagnosis of early stage HCC. The sensitivity and accuracy were significantly superior to MDCT for the diagnosis of lesions less than 1.5 cm. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

Enhancement of the liver and pancreas in the hepatic arterial dominant phase: Comparison of hepatocyte‐specific MRI contrast agents,gadoxetic acid and gadobenate dimeglumine,on 3 and 1.5 tesla MRI in the same patient

Purpose:

To evaluate the relative enhancement of liver, pancreas, focal nodular hyperplasia (FNH), pancreas‐to‐liver index, and FNH‐to‐liver index in the hepatic arterial dominant phase (HADP) after injection of hepatocyte‐specific MRI contrast agents, gadoxetic acid and gadobenate dimeglumine, on 3 and 1.5 Tesla (T) MRI in the same patient.

Materials and Methods:

The MRI database was retrospectively searched to identify consecutive patients who underwent abdominal MRI at 3T and 1.5T systems, using both 0.025 mmol/kg gadoxetic acid‐enhanced and 0.05 mmol/kg gadobenate dimeglumine‐enhanced MRI at the same magnetic strength field system. 22 patients were identified, 10 were scanned at 3T system and 12 at 1.5T system. The enhancement of liver, pancreas, and FNH was evaluated quantitatively on MR images.

Results:

The relative enhancement of liver in HADP in the gadobenate dimeglumine‐enhanced group in all subjects was significantly higher than that in gadoxetic acid‐enhanced group (P = 0.023). The gadobenate dimeglumine‐enhanced group in HADP had better relative enhancement of pancreas and FNH, pancreas‐to‐liver index, and FNH‐to‐liver index than gadoxetic acid‐enhanced group, but the difference was not statistically significant.

Conclusion:

The 0.05 mmol/kg gadobenate dimeglumine‐enhanced abdominal MRI studies at 3T and 1.5T MR systems are superior in relative enhancement of the liver in HADP to 0.025 mmol/kg gadoxetic acid‐enhanced MRI. This type of assessment may provide comparative effectiveness data. J. Magn. Reson. Imaging 2013;37:903–908. © 2012 Wiley Periodicals, Inc.     

Evaluation of gadobutrol,a macrocyclic,nonionic gadolinium chelate in a brain glioma model: Comparison with gadoterate meglumine and gadopentetate dimeglumine at 1.5 T,combined with an assessment of field strength dependence,specifically 1.5 versus 3 T

Purpose:

To evaluate in a rat brain glioma model intraindividual tumor enhancement at 1.5 T using gadobutrol (Gadovist), a nonionic, macrocyclic chelate currently in clinical trials in the United States, in comparison with both an ionic macrocyclic chelate, gadoterate meglumine (Dotarem), and an ionic linear chelate, gadopentetate dimeglumine (Magnevist), and to compare the degree of tumor enhancement with gadobutrol at 1.5 and 3 T.

Materials and Methods:

A total of 24 rats, divided into three groups with n = 8 animals per group, were evaluated. Animals in group 1 received injections of gadobutrol and gadopentetate dimeglumine, whereas those in group 2 received gadobutrol and gadoterate meglumine. Injections were performed in random order and separated by 24 hours. Magnetic resonance imaging (MRI) examinations were performed immediately following each contrast injection with a 1.5 T MR system. Animals in group 3 received gadobutrol injections using the same protocol but with scans performed at 1.5 and 3 T. In all examinations, T1‐weighted images were acquired precontrast, 1 minute postcontrast, and at 4 consecutive 2‐minute intervals thereafter. A contrast dose of 0.1 mmol/kg was used in all instances.

Results:

In groups 1 and 2, tumor signal‐to‐noise ratio (SNR) and contrast‐to‐noise ratio (CNR) were higher for gadobutrol compared to both other agents at each timepoint postcontrast injection. The improvement in tumor CNR with gadobutrol, depending on time, was between 12% and 40% versus gadopentetate dimeglumine, with the difference achieving statistical significance at 7 minutes. The improvement in tumor CNR with gadobutrol, depending on time, was between 15% and 27% versus gadoterate meglumine, with the difference statistically significant at 5 and 9 minutes. In group 3 the improvement in tumor SNR and CNR seen with the increase in field strength from 1.5 to 3 T for gadobutrol was statistically significant at all acquired timepoints (P < 0.002). CNR mean values ranged from 10.4 ± 2.9 to 24.6 ± 5.0 at 1.5 T and from 20.5 ± 5.9 to 47.8 ± 15.7 at 3 T depending on the timepoint postcontrast.

Conclusion:

Consistently greater tumor enhancement was noted at all measured timepoints following contrast injection with gadobutrol compared to both gadopentetate dimeglumine and gadoterate meglumine at 1.5 T. A substantial further improvement in tumor enhancement was noted using gadobutrol at 3 T. J. Magn. Reson. Imaging 2010;31:549–555. © 2010 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.     

MRA of intracranial aneurysms embolized with platinum coils: a vascular phantom study at 1.5T and 3T

PURPOSE: To analyze the influence of matrix and echo time (TE) of three-dimensional time-of-flight (3D TOF) magnetic resonance angiography (MRA) on the depiction of residual flow in aneurysms embolized with platinum coils at 1.5T and 3T. MATERIALS AND METHODS: A simulated intracranial aneurysm of the vascular phantom was loosely packed to maintain the patency of some residual aneurysmal lumen with platinum coils and connected to an electromagnetic flow pump with pulsatile flow. MRAs were obtained altering the matrix and TE of 3D TOF sequences at 1.5T and 3T. RESULTS: The increased spatial resolution and the shorter TE offered better image quality at 3T. For the depiction of an aneurysm remnant, the high-spatial-resolution 3T MRA (matrix size of 384 x 224 and 512 x 256) with a short TE of < or =3.3 msec were superior to the 1.5T MRA obtained with any sequences. CONCLUSION: 3T MRA is superior to 1.5T MRA for the assessment of aneurysms embolized with platinum coils; the combination of the 512 x 256 matrix and short TE (3.3 msec or less) seems feasible at 3T.     

Double inversion black-blood fast spin-echo imaging of the human heart: a comparison between 1.5T and 3.0T

PURPOSE: To evaluate the effectiveness of blood suppression and the quality of black-blood cardiac images acquired at 3.0 Tesla using a double-inversion recovery fast spin-echo sequence by comparing data acquired at 3.0T to data acquired at 1.5T. MATERIALS AND METHODS: Black-blood T2-weighted fast spin-echo images of the heart were acquired from five normal volunteers at 1.5T and five normal volunteers at 3.0T. Region-of-interest signal intensity measurements were performed at several locations in the suppressed blood regions of the left and right ventricles and around the left ventricle walls to assess the effectiveness and uniformity of the blood suppression, the myocardial signal-to-noise ratio (SNR), and the signal uniformity at both field strengths. B1 field maps were produced in phantoms and in subjects at both field strengths. RESULTS: Blood suppression performance is equivalent at 1.5T and 3.0T. The improvement in SNR at 3.0T compared with 1.5T is less than has been predicted in previous studies. The signal uniformity is significantly poorer at 3.0T than at 1.5T due to dielectric effects and shorter radio frequency wavelengths (P < 0.005). CONCLUSION: Spin-echo and spin-echo echo-train sequences that perform well at 1.5T will produce large signal variations in the chest cavity at 3.0T without modifications. B1 insensitive methods must be explored and implemented for spin-echo sequences to fully realize the advantages of using these sequences for high-field MRI.     

Myocardial T mapping free of distortion using susceptibility‐weighted fast spin‐echo imaging: A feasibility study at 1.5 T and 3.0 T

This study demonstrates the feasibility of applying free‐breathing, cardiac‐gated, susceptibility‐weighted fast spin‐echo imaging together with black blood preparation and navigator‐gated respiratory motion compensation for anatomically accurate T mapping of the heart. First, T maps are presented for oil phantoms without and with respiratory motion emulation (T = (22.1 ± 1.7) ms at 1.5 T and T = (22.65 ± 0.89) ms at 3.0 T). T relaxometry of a ferrofluid revealed relaxivities of R = (477.9 ± 17) mM^?1s^?1 and R = (449.6 ± 13) mM^?1s^?1 for UFLARE and multiecho gradient‐echo imaging at 1.5 T. For inferoseptal myocardial regions mean T values of 29.9 ± 6.6 ms (1.5 T) and 22.3 ± 4.8 ms (3.0 T) were estimated. For posterior myocardial areas close to the vena cava T‐values of 24.0 ± 6.4 ms (1.5 T) and 15.4 ± 1.8 ms (3.0 T) were observed. The merits and limitations of the proposed approach are discussed and its implications for cardiac and vascular T‐mapping are considered. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Quantitative and qualitative comparison of 3.0T and 1.5T MR imaging of the liver in patients with diffuse parenchymal liver disease

Purpose

The purpose of our study was to compare signal characteristics and image qualities of MR imaging at 3.0 T and 1.5 T in patients with diffuse parenchymal liver disease.

Materials and methods

25 consecutive patients with diffuse parenchymal liver disease underwent abdominal MR imaging at both 3.0 T and 1.5 T within a 6-month interval. A retrospective study was conducted to obtain quantitative and qualitative data from both 3.0 T and 1.5 T MRI. Quantitative image analysis was performed by measuring the signal-to-noise ratios (SNRs) and the contrast-to-noise ratios (CNRs) by the Students t-test. Qualitative image analysis was assessed by grading each sequence on a 3- and 4-point scale, regarding the presence of artifacts and image quality, respectively. Statistical analysis consisted of the Wilcoxon signed-rank test.

Results

the mean SNRs and CNRs of the liver parenchyma and the portal vein were significantly higher at 3.0 T than at 1.5 T on portal and equilibrium phases of volumetric interpolated breath-hold examination (VIBE) images (P < 0.05). The mean SNRs were significantly higher at 3.0 T than at 1.5 T on T1-weighted spoiled gradient echo (SGE) images (P < 0.05). However, there were no significantly differences on T2-weighted short-inversion-time inversion recovery (STIR) images. Overall image qualities of the 1.5 T non-contrast T1- and T2-weighted sequences were significantly better than 3.0 T (P < 0.01). In contrast, overall image quality of the 3.0 T post-gadolinium VIBE sequence was significantly better than 1.5 T (P < 0.01).

Conclusions

MR imaging of post-gadolinium VIBE sequence at 3.0 T has quantitative and qualitative advantages of evaluating for diffuse parenchymal liver disease.     

Diagnostic value of gadopentetate dimeglumine for 1.5-T MR imaging of musculoskeletal masses: comparison with unenhanced T1- and T2-weighted imaging.

Three magnetic resonance (MR) imaging techniques (T1-weighted, T2-weighted, and T1-weighted gadopentetate dimeglumine--enhanced) were compared in 32 consecutive MR imaging studies of 26 patients with suspected musculoskeletal masses. T2-weighted images were superior to T1-weighted enhanced images with respect to detection and definition of lesions in 12% of cases (n = 4) and were equal in 88% of cases (n = 28). T2-weighted images were also superior to T1-weighted images in 38% of cases (n = 12). In no cases were T1-weighted enhanced images superior to T2-weighted images. In two cases, T1-weighted images were superior to both T1-weighted enhanced and T2-weighted images. The authors conclude that gadopentetate dimeglumine did not provide much value in lesion detection above that obtained with T2-weighted images. They also conclude that T1-weighted images were occasionally superior to T1-weighted enhanced images and T2-weighted images because of loss of definition between fat and lesion on the latter.     

MR lymphangiography using dendrimer-based contrast agents: a comparison at 1.5T and 3.0T.

Most macromolecular contrast agents (CAs) show lower r1 and higher r2 relaxivities at 3.0T than at 1.5T. MR lymphangiography in mice using a macromolecular G6 dendrimer-based CA was serially performed and compared at both 1.5T and 3.0T. The r1 and r2 relaxivities of the G6 CA were 25 and 78/s/mM at 1.5T and 17 and 82/s/mM at 3.0T, respectively. The lymph node (LN)-to-fat ratios (LN signal intensity (SI)/fat SI) of T1-weighted 3D-fast spoiled gradient-echo (3D-FSPGR) were 3.2+/-0.4 (mean+/-standard deviation (SD)) at 1.5T and 2.7+/-0.3 at 3.0T (P=0.021), and the LN-to-fat ratios of T2/T1-weighted 3D-fast imaging employing steady-state acquisition with phase cycling (3D-FIESTA-C) were 1.8+/-0.2 at 1.5T and 1.2+/-0.4 at 3.0T (P=0.003). Although 3D-FSPGR successfully delineated the LNs at both 1.5T and 3.0T, 3D-FIESTA-C at 3.0T failed to visualize the LNs.     

Multicenter,double‐blind,randomized, intra‐individual crossover comparison of gadobenate dimeglumine and gadopentetate dimeglumine in MRI of brain tumors at 3 tesla

Purpose

To prospectively compare 0.1 mmol/kg doses of gadobenate dimeglumine and gadopentetate dimeglumine for contrast‐enhanced MRI of brain lesions at 3 Tesla (T).

Materials and Methods

Forty‐six randomized patients underwent a first examination with gadobenate dimeglumine (n = 23) or gadopentetate dimeglumine (n = 23) and then, after 2–7 days, a second examination with the other agent. Contrast administration (volume, rate), sequence parameters (T1wSE; T1wGRE), and interval between injection and image acquisition were identical for examinations in each patient. Three blinded neuroradiologists evaluated images qualitatively (lesion delineation, lesion enhancement, global preference) and quantitatively (lesion‐to‐brain ratio [LBR], contrast‐to‐noise ratio [CNR], % lesion enhancement). Differences were assessed using Wilcoxon's signed‐rank test. Reader agreement was determined using kappa (κ) statistics.

Results

There were no demographic differences between groups. The three readers preferred gadobenate dimeglumine globally in 22 (53.7%), 21 (51.2%), and 27 (65.9%) patients, respectively, compared with 0, 1, and 0 patients for gadopentetate dimeglumine. Similar significant (P < 0.001) preference was expressed for lesion border delineation and enhancement. Reader agreement was consistently good (κ = 0.48–0.64). Significantly (P < 0.05) higher LBR (+43.5– 61.2%), CNR (+51.3–147.6%), and % lesion enhancement (+45.9–49.5%) was noted with gadobenate dimeglumine.

Conclusion

Brain lesion depiction at 3T is significantly improved with 0.1 mmol/kg gadobenate dimeglumine. J. Magn. Reson. Imaging 2009;29:760–767. © 2009 Wiley‐Liss, Inc.     

Segmented echo planar MR imaging of the brachial plexus with inversion recovery magnetization preparation at 3.0T

PURPOSE: To evaluate the image quality of segmented echo planar MRI with inversion recovery magnetization preparation (seg-IR-EPI) to depict the anatomy and pathologic changes involving the brachial plexus. MATERIALS AND METHODS: The coronal seg-IR-EPI sequence was performed on 30 healthy volunteers and 20 patients. Postprocessing techniques were used to generate images of brachial plexus and the images acquired were qualitatively evaluated by two experienced radiologists based on grading of the morphological images. Signal-to-noise ratios (SNRs) and nerve soft tissue contrast-to-noise-ratios (CNRs) were calculated and the normalized SNR (SNRn) and the normalized CNR (CNRn) were compared with the STIR TSE sequence. RESULTS: Although seg-IR-EPI had more ghosting artifacts than STIR TSE, excellent general image appearance with minor blurring can be achieved with seg-IR-EPI. In all healthy volunteers the means of CNRn were significantly greater for seg-IR-EPI than for STIR-TSE, while the means of SNRn were significantly lower for seg-IR-EPI than for STIR-TSE. CONCLUSION: In the present study the seg-IR-EPI sequence obtained uniform fat suppression and high-contrast T2-weighted images of brachial plexus. Our data suggest that the seg-IR-EPI sequence may provide high fidelity in evaluating brachial plexus.     

MR colonoscopy at 3.0 T: comparison with 1.5 T in vivo and a colon model

PURPOSE: Retrospectively, magnetic resonance (MR) colonography images obtained from a colon model and in routine examinations of patients screened for polyps were compared in terms of whether, and to what degree, image quality improved at a higher field strength of 3.0 T compared to 1.5 T. MATERIALS AND METHODS: One hundred twenty-eight MR colonography images from 40 patients, of whom 20 had each been scanned at 1.5 and 3.0 T, respectively, using a four-element phased-array torso coil, were compared. At both field strengths, imaging included T1-weighted fat-suppressed spoiled gradient-echo (T1-fs-GE), T2/T1-weighted fast imaging employing steady-state acquisition (FIESTA), and T2-weighted single-shot fast spin-echo (T2-SSFSE), with breath-hold technique. Using receiver operating characteristic analysis performed by seven readers, the three types of images from the colon model and from 20 patients each at 1.5 and 3.0 T were compared. While a time window of 20 s was allowed for picture assessment in a chance-generated succession of images on a monitor, image quality was rated with a score of 1-5 (1=very good; 5=very bad). Statistical significance was calculated with Mann-Whitney U test. RESULTS: At both field strengths, T2-SSFSE images received the best ratings, followed by FIESTA images (P=.001). Although, overall, the 3.0-T images obtained scores worse than those of the 1.5-T images, a better detection of phantom polyps was noted in the colon model (P=.001). CONCLUSION: Although MR colonography with the breath-hold technique using the same four-element phased-array coil at 3.0 and 1.5 T does not perform better at a higher field strength in general, an improved detection of small polyps may be obtained.     

Multislice dark-blood carotid artery wall imaging: a 1.5 T and 3.0 T comparison

PURPOSE: To compare two multislice turbo spin-echo (TSE) carotid artery wall imaging techniques at 1.5 T and 3.0 T, and to investigate the feasibility of higher spatial resolution carotid artery wall imaging at 3.0 T. MATERIALS AND METHODS: Multislice proton density-weighted (PDW), T2-weighted (T2W), and T1-weighted (T1W) inflow/outflow saturation band (IOSB) and rapid extended coverage double inversion-recovery (REX-DIR) TSE carotid artery wall imaging was performed on six healthy volunteers at 1.5 T and 3.0 T using time-, coverage-, and spatial resolution-matched (0.47 x 0.47 x 3 mm3) imaging protocols. To investigate whether improved signal-to-noise ratio (SNR) at 3.0 T could allow for improved spatial resolution, higher spatial resolution imaging (0.31 x 0.31 x 3 mm3) was performed at 3.0 T. Carotid artery wall SNR, carotid lumen SNR, and wall-lumen contrast-to-noise ratio (CNR) were measured. RESULTS: Signal gain at 3.0 T relative to 1.5 T was observed for carotid artery wall SNR (223%) and wall-lumen CNR (255%) in all acquisitions (P < 0.025). IOSB and REX-DIR images were found to have different levels of SNR and CNR (P < 0.05) with IOSB values observed to be larger. Normalized to a common imaging time, the higher spatial resolution imaging at 3.0 T and the lower spatial resolution imaging at 1.5 T provided similar levels of wall-lumen CNR (P = NS). CONCLUSION: Multislice carotid wall imaging at 3.0 T with IOSB and REX-DIR benefits from improved SNR and CNR relative to 1.5 T, and allows for higher spatial resolution carotid artery wall imaging.     

Paradoxical signal pattern of mediastinal cysts on T2-weighted MR imaging: phantom and clinical study

Purpose

To evaluate the intracystic MRI (magnetic resonance imaging) signal intensity of mediastinal cystic masses on T2-weighted images.

Materials and methods

A phantom study was performed to evaluate the signal intensity of a mediastinal cystic mass phantom (rubber balloon containing water) adjacent to a cardiac phantom pulsing at the rate of 60/min. T2-weighted images (sequence, fast spin echo [FSE] and single shot fast spin echo [SSFSE]) were acquired for the mediastinal cystic mass phantom. Further, a clinical study was performed in 33 patients (16 men, 17 women; age range, 19-85 years; mean, 65years) with thymic cysts or pericardial cysts. In all patients, T2-weighted images (FSE and SSFSE) were acquired. The signal intensity of cystic lesion was evaluated and was compared with that of muscle. A region of interest (ROI) was positioned on the standard MR console, and signal intensity of the cystic mass (cSI), that of the muscle (mSI), and the rate of absolute value of cSI–mSI to standard deviation (SD) of background noise (|cSI–mSI|/SD = CNR [contrast-to-noise ratio]) were measured.

Results

The phantom study demonstrated that the rate phantom-ROI/saline-ROI was higher in SSFSE (0.36) than in FSE (0.19). In clinical cases, the degree of the signal intensity was higher in SSFSE than in FSE. The CNR was significantly higher in SSFSE (mean ± standard deviation, 111.0 ± 47.6) than in FSE (72.8 ± 36.6) (p < 0.001, Wilcoxon signed-rank test).

Conclusions

Anterior mediastinal cysts often show lower signal intensity than the original signal intensity of water on T2-weighted images. SSFSE sequence reduces this paradoxical signal pattern on T2-weighted images, which may otherwise cause misinterpretation when assessing cystic lesions.