Isotropic 3D fast spin-echo imaging versus standard 2D imaging at 3.0 T of the knee—image quality and diagnostic performance

The objective of this study was to compare a newly developed fat-saturated intermediate-weighted (IM-w) 3D fast spin-echo (FSE) sequence with standard 2D IM-w FSE sequences regarding image quality and diagnostic performance in assessing abnormal findings of the knee. MR imaging was performed at 3.0 T in 50 patients. Images were assessed independently by three radiologists. Image quality was rated significantly higher (p < 0.05) for the 2D versus the 3D FSE sequences. Sensitivity for cartilage lesions was slightly higher for the 3D sequence, but specificity was lower. Low contrast objects were better visualized with 2D sequences, while high contrast objects were better shown with the 3D sequence. Confidence scores were higher for 2D than for 3D sequences, but differences were not significant. In conclusion, isotropic 3D FSE IM-w imaging may enhance standard knee MRI by increased visualization of high contrast lesions; however, 3D FSE image quality was lower.     

Magnetic resonance imaging of hyaline cartilage defects at 1.5T and 3.0T: comparison of medium T2-weighted fast spin echo, T1-weighted two-dimensional and three-dimensional gradient echo pulse sequences

PURPOSE: To evaluate and compare the diagnostic accuracy of appropriate magnetic resonance (MR) sequences in the detection of cartilage lesions at 1.5T and 3.0T. MATERIAL AND METHODS: Twelve chondral defects of varying depths, widths, and locations were created in the retropatellar hyaline cartilage in six sheep cadaver limbs. Axial images employing three fat-suppressed imaging sequences--(1) a T2-weighted fast spin-echo (FSE) sequence, (2) a two-dimensional (2D) and (3) three-dimensional (3D) gradient-echo (GE) sequence at 1.5T and 3.0T using an extremity quadrature coil--were evaluated by three experienced radiologists. Statistical analysis of the results consisted of receiver operating characteristics (ROC) and significant testing using the bivariate chi-square test. In addition, signal-to-noise ratios (SNR) and contrast-to-noise ratios (CNR) were evaluated with significance testing using the Wilcoxon test. RESULTS: The 3D GE sequence compared favorably with other sequences at 3.0T and 1.5T (Az=0.88 at 3.0T and Az=0.85 at 1.5T) missing only one small grade 2 lesion. 2D GE imaging was inferior to 3D imaging at both field strengths (P<0.05) in general. However, compared to 1.5T, lesion detectability was improved at the higher magnetic field of 3.0T (Az=0.81 and 0.73 at 3.0T and 1.5T, respectively). FSE images showed significantly inferior sensitivity and less anatomical detail compared to the GE sequences at both field strengths (Az=0.64 and 0.72 at 3.0T and 1.5T, respectively; P<0.05). However, compared to 1.5T, lesion detectability SNR and CNR values were superior in all sequences tested at 3.0T. CONCLUSION: MRI at 3.0T improves SNR and CNR significantly in the most common sequences for cartilage MRI, resulting in an improvement in chondral lesion detection. GE imaging therefore allows resolution to be increased in an acceptable time manner for patient comfort, and the 3D GE fat-suppressed sequence at 3.0T appears to be best suited for cartilage imaging in a clinical setting.     

Cartilage MR imaging at 3.0 versus that at 1.5 T: preliminary results in a porcine model

PURPOSE: To compare 1.5- and 3.0-T magnetic resonance (MR) images of porcine knee specimens containing artificial cartilage lesions in terms of accuracy of lesion depiction, image quality, and signal-to-noise ratio (SNR). MATERIALS AND METHODS: This Health Insurance Portability and Accountability Act-compliant study had institutional review board approval, and informed consent was obtained from the human volunteers. Two fat-saturated cartilage MR imaging sequences (an intermediate-weighted fast spin-echo [SE] sequence and a spoiled gradient-echo [GRE] sequence) were optimized for imaging at 3.0 T in two human volunteers and then used to image 10 porcine knees in which 29 artificial cartilage lesions had been created. Corresponding sequences were used at 1.5 T for all specimens. Images were assessed by two radiologists in consensus, and diagnostic performance in lesion depiction was determined by using macroscopic findings in specimen slices as a reference standard. SNRs were also calculated. For statistical analysis, the McNemar test of discordant pairs was used with a level of significance of P < .05. RESULTS: The best diagnostic performance for both the intermediate-weighted fast SE and the spoiled GRE sequences was achieved at 3.0 T. With use of corresponding fat-saturated intermediate-weighted fast SE sequences with an identical acquisition time (9 minutes 44 seconds), 26 (90%) of 29 lesions were detected at 3.0 T, while 18 (62%) were detected at 1.5 T. With use of fat-saturated spoiled GRE sequences, 24 (83%) of 29 lesions were detected at 3.0 T (acquisition time, 8 minutes 48 seconds), and 23 (79%) lesions were detected at 1.5 T (acquisition time, 11 minutes 14 seconds). The rate of correct lesion grade assessment was 65% (17 of 26 lesions) at 3.0 T and 61% (11 of 18 lesions) at 1.5 T with the intermediate-weighted fast SE sequences and 83% (20 of 24 lesions) at 3.0 T and 70% (16 of 23 lesions) at 1.5 T with the spoiled GRE sequences. Both subjective evaluation of image quality and SNR values were significantly higher at 3.0 T (P < .05). CONCLUSION: In this animal model, MR imaging at 3.0 T increased the accuracy of cartilage lesion assessment when compared with imaging at 1.5 T. Image quality and SNR were highest at 3.0 T.     

Assessment of cartilage-dedicated sequences at ultra-high-field MRI: comparison of imaging performance and diagnostic confidence between 3.0 and 7.0 T with respect to osteoarthritis-induced changes at the knee joint

Objective  The objectives of the study were to optimize three cartilage-dedicated sequences for in vivo knee imaging at 7.0 T ultra-high-field (UHF) magnetic resonance imaging (MRI) and to compare imaging performance and diagnostic confidence concerning osteoarthritis (OA)-induced changes at 7.0 and 3.0 T MRI. Materials and methods  Optimized MRI sequences for cartilage imaging at 3.0 T were tailored for 7.0 T: an intermediate-weighted fast spin-echo (IM-w FSE), a fast imaging employing steady-state acquisition (FIESTA) and a T1-weighted 3D high-spatial-resolution volumetric fat-suppressed spoiled gradient-echo (SPGR) sequence. Three healthy subjects and seven patients with mild OA were examined. Signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), diagnostic confidence in assessing cartilage abnormalities, and image quality were determined. Abnormalities were assessed with the whole organ magnetic resonance imaging score (WORMS). Focal cartilage lesions and bone marrow edema pattern (BMEP) were also quantified. Results  At 7.0 T, SNR was increased (p < 0.05) for all sequences. For the IM-w FSE sequence, limitations with the specific absorption rate (SAR) required modifications of the scan parameters yielding an incomplete coverage of the knee joint, extensive artifacts, and a less effective fat saturation. CNR and image quality were increased (p < 0.05) for SPGR and FIESTA and decreased for IM-w FSE. Diagnostic confidence for cartilage lesions was highest (p < 0.05) for FIESTA at 7.0 T. Evaluation of BMEP was decreased (p < 0.05) at 7.0 T due to limited performance of IM-w FSE. Conclusion  Gradient echo-based pulse sequences like SPGR and FIESTA are well suited for imaging at UHF which may improve early detection of cartilage lesions. However, UHF IM-w FSE sequences are less feasible for clinical use.     

Magnetic resonance imaging of ankle tendon pathology: benefits of additional axial short-tau inversion recovery imaging to reduce magic angle effects

Objectives

Our goals were to quantify the reduction of the magic angle effect using short-tau inversion recovery (STIR) imaging and to determine the value of adding an axial STIR sequence to the magnetic resonance imaging ankle protocol.

Materials and methods

Axial STIR sequences were used to measure normal tendon T1 and to estimate signal loss due to the inversion recovery preparation of our clinical protocol. In addition, 102 ankles were imaged with axial fat-suppressed intermediate-weighted fast spin echo and STIR sequences. Two radiologists analyzed the tendons for signal intensity, size, abnormalities, and magic angle effect. The diagnostic value and image quality of the two sequences were compared.

Results

We calculated a 50 % reduction of signal intensity in healthy tendons on the STIR sequence at TI?=?170 ms compared with TI?=?0 ms, explaining the decrease in the magic angle effect. Using the STIR sequence, our study demonstrated significantly lower signal intensity within the tendons, more precise tendon size, and a lower magic angle effect compared with the standard intermediate-weighted FSE sequence (p?<?0.001). Diagnostic classification of tendon abnormalities using the STIR sequences showed higher sensitivity (82.35 % vs 75.27 %) and better agreement with a reference standard than the intermediate-weighted sequences, and superior image quality (p?<?0.01).

Conclusions

Axial STIR sequences reduce magic angle effects and improve visualization of ankle tendon pathology.     

Routine clinical brain MRI sequences for use at 3.0 Tesla

PURPOSE: To establish image parameters for some routine clinical brain MRI pulse sequences at 3.0 T with the goal of maintaining, as much as possible, the well-characterized 1.5-T image contrast characteristics for daily clinical diagnosis, while benefiting from the increased signal to noise at higher field. MATERIALS AND METHODS: A total of 10 healthy subjects were scanned on 1.5-T and 3.0-T systems for T(1) and T(2) relaxation time measurements of major gray and white matter structures. The relaxation times were subsequently used to determine 3.0-T acquisition parameters for spin-echo (SE), T(1)-weighted, fast spin echo (FSE) or turbo spin echo (TSE), T(2)-weighted, and fluid-attenuated inversion recovery (FLAIR) pulse sequences that give image characteristics comparable to 1.5 T, to facilitate routine clinical diagnostics. Application of the routine clinical sequences was performed in 10 subjects, five normal subjects and five patients with various pathologies. RESULTS: T(1) and T(2) relaxation times were, respectively, 14% to 30% longer and 12% to 19% shorter at 3.0 T when compared to the values at 1.5 T, depending on the region evaluated. When using appropriate parameters, routine clinical images acquired at 3.0 T showed similar image characteristics to those obtained at 1.5 T, but with higher signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR), which can be used to reduce the number of averages and scan times. Recommended imaging parameters for these sequences are provided. CONCLUSION: When parameters are adjusted for changes in relaxation rates, routine clinical scans at 3.0 T can provide similar image appearance as 1.5 T, but with superior image quality and/or increased speed.     

Hip imaging of avascular necrosis at 7 Tesla compared with 3 Tesla

Objectives

To compare ultra-high field, high-resolution bilateral magnetic resonance imaging (MRI) of the hips at 7 Tesla (T) with 3 T MRI in patients with avascular necrosis (AVN) of the femoral head by subjective image evaluations, contrast measurements, and evaluation of the appearance of imaging abnormalities.

Materials and Methods

Thirteen subjects with avascular necrosis treated using advanced core decompression underwent MRI at both 7 T and 3 T. Sequence parameters as well as resolution were kept identical for both field strengths. All MR images (MEDIC, DESS, PD/T2w TSE, T1w TSE, and STIR) were evaluated by two radiologists with regard to subjective image quality, soft tissue contrasts, B1 homogeneity (four-point scale, higher values indicating better image quality) and depiction of imaging abnormalities of the femoral heads (three-point scale, higher values indicating the superiority of 7 T). Contrast ratios of soft tissues were calculated and compared with subjective data.

Results

7-T imaging of the femoral joints, as well as 3-T imaging, achieved “good” to “very good” quality in all sequences. 7 T showed significantly higher soft tissue contrasts for T2w and MEDIC compared with 3 T (cartilage/fluid: 2.9 vs 2.2 and 3.6 vs 2.6), better detailed resolution for cartilage defects (PDw, T2w, T1w, MEDIC, DESS?>?2.5) and better visibility of joint effusions (MEDIC 2.6; PDw/T2w 2.4; DESS 2.2). Image homogeneity compared with 3 T (3.9–4.0 for all sequences) was degraded, especially in TSE sequences at 7 T through signal variations (7 T: 2.1–2.9); to a lesser extent also GRE sequences (7 T: 2.9–3.5). Imaging findings related to untreated or treated AVN were better delineated at 3 T (≤1.8), while joint effusions (2.2–2.6) and cartilage defects (2.5–3.0) were better visualized at 7 T. STIR performed much more poorly at 7 T, generating large contrast variations (1.5).

Conclusions

7-T hip MRI showed comparable results in hip joint imaging compared with 3 T with slight advantages in contrast detail (cartilage defects) and fluid detection at 7 T when accepting image degradation medially.     

Comparative study of imaging at 3.0 T versus 1.5 T of the knee

Purpose  The objectives of the study were to compare MR imaging at 1.5 and 3.0 T in the same patients concerning image quality and visualization of cartilage pathology and to assess diagnostic performance using arthroscopy as a standard of reference. Materials and methods  Twenty-six patients were identified retrospectively as having comparative 1.5 and 3.0 T MR studies of the knee within an average of 102 days. Standard protocols included T1-weighted and fat-saturated intermediate-weighted fast spin-echo sequences in three planes; sequence parameters had been adjusted to account for differences in relaxation at 3.0 T. Arthroscopy was performed in 19 patients. Four radiologists reviewed each study independently, scored image quality, and analyzed pathological findings. Sensitivities, specificities, and accuracies in diagnosing cartilage lesions were calculated in the 19 patients with arthroscopy, and differences between 1.5 and 3.0 T exams were compared using paired Student’s t tests with a significance threshold of p < 0.05. Results  Each radiologist scored the 3.0 T studies higher than those obtained at 1.5 T in visualizing anatomical structures and abnormalities (p < 0.05). Using arthroscopy as a standard of reference, diagnosis of cartilage abnormalities was improved at 3.0 T with higher sensitivity (75.7% versus 70.6%), accuracy (88.2% versus 86.4%), and correct grading of cartilage lesions (51.3% versus 42.9%). Diagnostic confidence scores were higher at 3.0 than 1.5 T (p < 0.05) and signal-to-noise ratio at 3.0 T was approximately twofold higher than at 1.5 T. Conclusion  MRI at 3.0 T improved visualization of anatomical structures and improved diagnostic confidence compared to 1.5 T. This resulted in significantly better sensitivity and grading of cartilage lesions at the knee.     

Imaging of the wrist at 1.5 Tesla using isotropic three-dimensional fast spin echo cube

Purpose:

To compare three‐dimensional fast spin echo Cube (3D‐FSE‐Cube) with conventional 2D‐FSE in MR imaging of the wrist.

Materials and Methods:

The wrists of 10 volunteers were imaged in a 1.5 Tesla MRI scanner using an eight‐channel wrist coil. The 3D‐FSE‐Cube images were acquired in the coronal plane with 0.5‐mm isotropic resolution. The 2D‐FSE images were acquired in both coronal and axial planes for comparison. An ROI was placed in fluid, cartilage, and muscle for SNR analysis. Comparable coronal and axial images were selected for each sequence, and paired images were randomized and graded for blurring, artifact, anatomic details, and overall image quality by three blinded musculoskeletal radiologists.

Results:

SNR of fluid, cartilage and muscle at prescribed locations were higher using 3D‐FSE‐Cube, without reaching statistical significance. Fluid–cartilage CNR was also higher with 3D‐FSE‐Cube, but not statistically significant. Blurring, artifact, anatomic details, and overall image quality were significantly better on coronal 3D‐FSE‐Cube images (P < 0.001), but significantly better on axial 2D‐FSE images compared with axial 3D‐FSE‐Cube reformats (P < 0.01).

Conclusion:

Isotropic data from 3D‐FSE‐Cube allows reformations in arbitrary scan planes, which may make multiple 2D acquisitions unnecessary, and improve depiction of complex wrist anatomy. However, axial reformations suffer from blurring, likely due to T2 decay during the long echo train, limiting overall image quality in this plane. J. Magn. Reson. Imaging 2011;33:908–915. © 2011 Wiley‐Liss, Inc.     

High-resolution whole-body magnetic resonance imaging applications at 1.5 and 3 Tesla: a comparative study

OBJECTIVES: To analyze the impact of altered magnetic field properties on image quality and on potential artifacts when an established whole-body magnetic resonance imaging (WB-MRI) protocol at 1.5 Tesla (T) is migrated to 3 T. MATERIALS AND METHODS: Fifteen volunteers underwent noncontrast magnetic resonance imaging (MRI) on 32-channel whole body-scanners at 1.5 and 3 T with the use of parallel acquisition techniques (PAT). Coronal T1-weighted TSE- and short tau inversion recovery (STIR)-sequences at 4 body levels including sagittal imaging of the whole spine were performed. Additional axial HASTE-imaging of lung and abdomen, T1-/T2-weighted-TSE- and EPI-sequences of the brain and T2-weighted respiratory-triggered imaging of the liver was acquired. Both data sets were compared by 2 independent readers in respect to artifacts and image quality using a 5-point scale. Regions of pronounced artifacts were defined. RESULTS: Overall image impression was both qualitatively rated as "good" at 1.5 and 3 T for T1-w-TSE- and STIR-imaging of the whole body and spine. At 1.5 T, significantly better quantitative values for overall image quality were found for WB-STIR, T2-w-TSE imaging of the liver and brain (Wilcoxon Mann-Whitney U Test; P < 0.05), overall rated as good at 3 T. Significantly higher dielectric effects at 3 T were affecting T1-w- and STIR-WB-MRI, and HASTE of the abdomen and better image homogeneity at 1.5 T was observed for T1-weighted-/STIR-WB-MRI and T1-w-TSE-imaging of the spine. Pulsation artifacts were significantly increased at 3 T for T1-w WB-MRI. Significantly higher susceptibility artifacts were found for GRE-sequences of the brain at 3 T. Motion artifacts, Gibbs-Ringing, and image distortion was not significantly different and showed slightly higher quantitative values at 3 T (except for HASTE imaging of the abdomen). Overall scan time was 45 minutes and 44 seconds at 1.5 T and 40 minutes and 28 seconds at 3 T at identical image resolution. CONCLUSION: Three Tesla WB-MRI is feasible with good image quality comparable to 1.5 T. 3.0 T WB-MRI shows significantly more artifacts with a mild to moderate impact on image assessment. Therefore 1.5 T WB-MRI is the preferred image modality. Overall scan time at 3 T is reduced with the use of parallel imaging at a constant image resolution.     

MRI of the ankle joint in healthy non-athletes and in marathon runners: image quality issues at 7.0 T compared to 1.5 T

Objective

To present imaging characteristics of the ankle at 7.0 T and to investigate the appearance and image quality of presumed pathologies of ankles without physical strain as well as of ankles after a marathon run in comparison to 1.5 T.

Materials and methods

Appearance of presumed pathologic findings and image quality of TSE (PD, T2, and STIR) and GRE sequences (MEDIC, DESS, and/or CISS) at 7.0 T and 1.5 T MRI were compared by two senior radiologists in consensus in two healthy controls without strain and in six marathon runners after a full-length marathon (eight males, mean age 49.1 years).

Results

Overall, 7.0 T MRI allowed for higher resolution images for most of the sequences while requiring comparable acquisition times and achieving high contrast images mainly in gradient echo sequences. Bursal or presumed peritendineal fluid and/or edematous tissue, which were found in seven of eight subjects, could be best appreciated with 7.0 T MEDIC. Other findings with sharper delineation at 7.0 T included cartilage defects (best: CISS), osseous avulsions, and osteophytes (best: DESS). Nevertheless, 1.5 T STIR imaging enabled assessment of a tibiotalar bone edema-like lesion in two runners, which was barely visible at 7.0 T using STIR, but not with any other sequence at 7.0 T including MEDIC (with frequency selective fat suppression). 7.0 T showed larger image quality variations with challenges especially in the TSE sequences.

Conclusion

Our initial results of ultra-high-field ankle joint imaging demonstrate the improved depiction of ankle anatomy, fluid depositions, and cartilage defects. However imaging of edema-like bone lesions remains challenging at ultra-high magnetic field strength, and TSE coverage in particular is limited by the specific absorption rate.     

Comparison of breath-hold multishot echo-planar and respiratory triggered fast-spin-echo sequences for T2-weighted MRI of liver lesions

The purpose of this study was to evaluate the usefulness of multishot echo-planar imaging in detecting liver tumors in comparison with respiratory triggered T2-weighted fast-spin-echo (FSE) imaging. Thirty-two patients with 70 focal liver lesions were imaged using a 1.5-T high speed MR imager. Eight-shot echo-planar images covering the whole liver were acquired during a single breath-hold period. FSE images were acquired with respiratory triggering in approximately 4 minutes. Lesion detectability and image quality of the two pulse sequences were analyzed qualitatively. Quantitative analysis was performed by means of signal-to-noise and tumor-liver contrast-to-noise analysis. Lesion detectability was comparable in both solid (86.3% vs 90.2%: .3 < P < .5) and nonsolid lesions (89.5% vs 100%: .3 < P < .5) between echo-planar and FSE images. Echo-planar imaging provided significantly reduced image artifact, better lesion conspicuity, and anatomic detail compared with FSE imaging. The signal-to-noise and contrast-to-noise ratios of echo-planar images were significantly higher than those of FSE images. Breath-hold eight-shot echo-planar imaging can be an alternative to T2-weighted FSE imaging because it can provide comparable image quality in a substantially decreased acquisition time.     

High-resolution proton density weighted three-dimensional fast spin echo (3D-FSE) of the knee with IDEAL at 1.5 Tesla: comparison with 3D-FSE and 2D-FSE--initial experience

Purpose:

To assess the feasibility of combining three‐dimensional fast spin echo (3D‐FSE) and Iterative‐decomposition‐of water‐and‐fat‐with‐echo asymmetry‐and‐least‐squares‐estimation (IDEAL) at 1.5 Tesla (T), generating a high‐resolution 3D isotropic proton density‐weighted image set with and without “fat‐suppression” (FS) in a single acquisition, and to compare with 2D‐FSE and 3D‐FSE (without IDEAL).

Materials and Methods:

Ten asymptomatic volunteers prospectively underwent sagittal 3D‐FSE‐IDEAL, 3D‐FSE, and 2D‐FSE sequences at 1.5T (slice thickness [ST]: 0.8 mm, 0.8 mm, and 3.5 mm, respectively). 3D‐FSE and 2D‐FSE were repeated with frequency‐selective FS. Fluid, cartilage, and muscle signal‐to‐noise ratio (SNR) and fluid‐cartilage contrast‐to‐noise ratio (CNR) were compared among sequences. Three blinded reviewers independently scored quality of menisci/cartilage depiction for all sequences. “Fat‐suppression” was qualitatively scored and compared among sequences.

Results:

3D‐FSE‐IDEAL fluid‐cartilage CNR was higher than in 2D‐FSE (P < 0.05), not different from 3D‐FSE (P = 0.31). There was no significant difference in fluid SNR among sequences. 2D‐FSE cartilage SNR was higher than in 3D FSE‐IDEAL (P < 0.05), not different to 3D‐FSE (P = 0.059). 2D‐FSE muscle SNR was higher than in 3D‐FSE‐IDEAL (P < 0.05) and 3D‐FSE (P < 0.05). Good or excellent depiction of menisci/cartilage was achieved using 3D‐FSE‐IDEAL in the acquired sagittal and reformatted planes. Excellent, homogeneous “fat‐suppression” was achieved using 3D‐FSE‐IDEAL, superior to FS‐3D‐FSE and FS‐2D‐FSE (P < 0.05).

Conclusion:

3D FSE‐IDEAL is a feasible approach to acquire multiplanar images of diagnostic quality, both with and without homogeneous “fat‐suppression” from a single acquisition. J. Magn. Reson. Imaging 2012;361‐369. © 2011 Wiley Periodicals, Inc.     

Fast spin-echo MR imaging of the female pelvis. Part I. Use of a whole-volume coil.

In this prospective study, axial and sagittal magnetic resonance (MR) images were obtained with T2-weighted conventional spin-echo (CSE) and fast spin-echo (FSE) sequences in 34 consecutive female patients who underwent clinical pelvic MR examination at 1.5 T. The MR images from each patient were compared side by side, blindly and independently, by two radiologists experienced in MR imaging who used a standardized score sheet for anatomic and pathologic findings. The FSE sequences were rated superior significantly more often than the CSE sequences in most categories of findings (P less than .05), including overall image quality and reduction of motion artifact. The examination time for the FSE sequences was 1 minute 46 seconds versus an examination time of 9 minutes 14 seconds for the CSE sequences. (Both CSE and FSE sequences provided 18 sections.) It is concluded that the FSE sequence provides T2-weighted anatomic and pathologic information superior to that provided by the CSE sequence and requires substantially less imaging time.     

Evaluation of optimised 3D turbo spin echo and gradient echo MR pulse sequences of the knee at 3T and 1.5T

IntroductionTo investigate the impact of parameter optimisation for novel three-dimensional 3D sequences at 1.5T and 3T on resultant image quality.MethodsFollowing institutional review board approval and acquisition of informed consent, MR phantom and knee joint imaging on healthy volunteers (n = 16) was performed with 1.5 and 3T MRI scanners, respectively incorporating 8- and 15-channel phased array knee radiofrequency coils. The MR phantom and healthy volunteers were prospectively scanned over a six-week period. Acquired sequences included standard two-dimensional (2D) turbo spin echo (TSE) and novel three-dimensional (3D) TSE PDW (SPACE) both with and without fat-suppression, and T21W gradient echo (TrueFISP) sequences. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were measured for knee anatomical structures. Two musculoskeletal radiologists evaluated anatomical structure visualisation and image quality. Quantitative and qualitative findings were investigated for differences using Friedman tests. Inter- and intra-observer agreements were determined with κ statistics.ResultsPhantom and healthy volunteer images revealed higher SNR for sequences acquired at 3T (p-value <0.05). Generally, the qualitative findings ranked images acquired at 3T higher than corresponding images acquired at 1.5T (p < 0.05). 3D image data sets demonstrated less sensitivity to partial volume averaging artefact (PVA) compared to 2D sequences. Inter- and intra-observer agreements for evaluation across all sequences ranged from 0.61 to 0.79 and 0.71 to 0.92, respectively.ConclusionBoth 2D and 3D images demonstrated higher image quality at 3T than at 1.5T. Optimised 3D sequences performed better than the standard 2D PDW TSE sequence for contrast resolution between cartilage and joint fluid, with reduced PVA artefact.Implications for practiceWith rapid advances in MRI scanner technology, including hardware and software, the optimisation of 3D MR pulse sequences to reduce scan time while maintaining image quality, will improve diagnostic accuracy and patient management in musculoskeletal MRI.     

Usefulness of IDEAL T2-weighted FSE and SPGR imaging in reducing metallic artifacts in the postoperative ankles with metallic hardware

Purpose

The aim of this work is to prospectively compare the effectiveness of iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL), T2-weighted fast spin-echo (FSE), and spoiled gradient-echo (SPGR) MR imaging to frequency selective fat suppression (FSFS) protocols for minimizing metallic artifacts in postoperative ankles with metallic hardware.

Materials and methods

The T2-weighted and SPGR imaging with IDEAL and FSFS were performed on 21 ankles of 21 patients with metallic hardware. Two musculoskeletal radiologists independently analyzed techniques for visualization of ankle ligaments and articular cartilage, uniformity of fat saturation, and relative size of the metallic artifacts. A paired t test was used for statistical comparisons of MR images between IDEAL and FSFS groups.

Results

IDEAL T2-weighted FSE and SPGR images enabled significantly improved visualization of articular cartilage (p?<?0.05), the size of metallic artifact (p?<?0.05), and the uniformity of fat saturation (p?<?0.05). However, no significant improvement was found in the visibility of ligaments.

Conclusions

IDEAL T2-weighted FSE and SPGR imaging effectively reduces the degree of tissue-obscuring artifacts produced by fixation hardware in ankle joints and improves image quality compared to FSFS T2-weighted FSE and SPGR imaging. However, visibility of ligaments was not improved using IDEAL imaging.

     

Assessment of myocardial viability using delayed enhancement magnetic resonance imaging at 3.0 Tesla

OBJECTIVE: Cardiac magnetic resonance imaging (MRI) at 3.0 T has recently become available and potentially provides a significant improvement of tissue contrast in T1-weighted imaging techniques relying on Gd-based contrast enhancement. Imaging at high-field strength may be especially advantageous for methods relying on strong T1-weighting and imaging after contrast material administration. The aim of this study was to compare cardiac delayed enhancement (DE) MRI at 3.0 T and 1.5 T with respect to image quality, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) between infarcted and normal myocardium. MATERIALS AND METHODS: Forty consecutive patients with history of myocardial infarction were examined at 3.0 T (n = 20) or at 1.5 T (n = 20). Myocardial function was assessed using cine steady-state-free-precession (SSFP) sequences (TR 3.1 milliseconds, TE 1.6 milliseconds, flip angle 70 degrees , and a matrix of 168 x 256 at 1.5 T and TR 3.4 milliseconds, TE 1.7 milliseconds, flip angle 50 degrees and a matrix of 168 x 256 at 3.0 T), acquired in long- and short-axes views. DE images were obtained 15 minutes after the administration of 0.15 mmol of Gd-DTPA/kg body weight using a segmented inversion recovery prepared gradient echo sequence at 1.5 T (TR 9.6 milliseconds, TE 4.4 milliseconds, flip angle 25 degrees , matrix 160 x 256, bandwidth 140 Hertz/pixel) and at 3.0 T (TR 9.8 milliseconds, TE 4.3 milliseconds, flip angle 30 degrees , matrix 150 x 256, bandwidth 140 Hertz/pixel). For image analysis, standardized SNR and CNR measurements were performed in infarcted and remote myocardial regions. Two independent observers rated image quality on a 4-point scale (0 = poor image quality, 1 = sufficient image quality, 2 = good image quality, 3 = excellent image quality). RESULTS: High diagnostic image quality was obtained in all patients. Rating of mean image quality was 2.2 +/- 0.8 at 1.5 T and 2.5 +/- 0.6 at 3.0 T (P = 0.012) for observer 1 and 2.2 +/- 0.7 at 1.5 T and 2.6 +/- 0.6 at 3.0 T (P = 0.003) for observer 2, respectively. Interobserver agreement was good (kappa = 0.68 at 1.5 T and 0.78 at 3.0 T). SNR measurements yielded a mean SNR of 37.8 +/- 13.9/22.9 +/- 6.0 in infarcted myocardium (P < 0.001) and 5.6 +/- 2.2/5.9 +/- 2.4 in normal myocardium (P = 0.45) at 3.0 T/1.5 T, respectively. CNR measurements revealed mean values of 32.4 +/- 13.0/16.7 +/- 5.4 (P< 0.001) at 3.0 T/1.5 T, respectively. CONCLUSIONS: Delayed enhancement MRI at 3.0 T is feasible and provides superior image quality compared with 1.5 T. Furthermore, using identical contrast doses, increased SNR and CNR values were recorded at 3.0 T.     

Prevalence of pathologic findings in asymptomatic knees of marathon runners before and after a competition in comparison with physically active subjects—a 3.0 T magnetic resonance imaging study

PURPOSE: To determine the prevalence of pathologic findings in asymptomatic knees of marathon runners before and after a competition in comparison with physically active subjects. To compare the diagnostic performance of cartilage-dedicated magnetic resonance imaging (MRI) sequences at 3.0 T. MATERIALS AND METHODS: Ten marathon runners underwent 3.0 T MRI 2-3 days before and after competition. Twelve physically active asymptomatic subjects not performing long-distance running were examined as controls. Pathologic condition was assessed with the whole-organ magnetic resonance imaging score (WORMS). Cartilage abnormalities and bone marrow edema pattern (BMEP) were quantified. Visualization of cartilage pathology was assessed with intermediate-weighted fast spin-echo (IM-w FSE), fast imaging employing steady-state acquisition (FIESTA) and T1-weighted three-dimensional (3D) high-spatial-resolution volumetric fat-suppressed spoiled gradient-echo (SPGR) MRI sequences. RESULTS: Eight of ten marathon runners and 7/12 controls showed knee abnormality. Slightly more and larger cartilage abnormalities, and BMEP, in marathon runners yielded higher but not significantly different WORMS (P > 0.05) than in controls. Running a single marathon did not alter MR findings substantially. Cartilage abnormalities were best visualized with IM-w FSE images (P < 0.05). CONCLUSION: A high prevalence of knee abnormalities was found in marathon runners and also in active subjects participating in other recreational sports. IM-w FSE sequences delineated more cartilage MR imaging abnormalities than did FIESTA and SPGR sequences.     

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.     

Magnetic resonance (MR) cholangiography: quantitative and qualitative comparison of 3.0 Tesla with 1.5 Tesla

OBJECTIVES: To determine quantitative and qualitative image quality in patients undergoing magnetic resonance (MR) cholangiography at 3.0 Tesla (T) compared with 1.5 T. MATERIALS AND METHODS: Fifty patients (30 women; mean age, 51 years) underwent MR cholangiography at 1.5 T; another 50 patients (25 women; mean age 51 years) were scanned at 3.0 T. MR sequence protocol consisted of breath-hold single-slice rapid acquisition with relaxation enhancement (RARE) and a respiratory-triggered 3D turbo spin echo (3D TSE) sequence. Maximum intensity projections were generated from the 3D TSE datasets. Contrast-to-noise ratio (CNR) measurements between the common bile duct (CBD), left and right intrahepatic duct (LHD, RHD), and periductal tissue were performed. Three radiologists assessed qualitatively the visibility of the CBD, LHD, and RHD and the overall diagnostic quality. RESULTS: Mean gain in CNR at 3.0 T versus 1.5 T in all 3 locations ranged for the RARE sequence from 7.7% to 38.1% and for the 3D TSE from 0.5% to 26.1% (P > 0.05 for all differences). Qualitative analysis did not reveal any significant difference between the 2 field strengths (P > 0.05). CONCLUSIONS: MR cholangiography at 3.0 T shows a trend toward higher CNR without improving image quality significantly.