High-resolution MRI of the wrist and finger joints in patients with rheumatoid arthritis: comparison of 1.5 Tesla and 3.0 Tesla

The goal of this study was to compare magnetic resonance (MR) image quality at different field strengths for evaluating lesions in wrist and finger joints of patients with rheumatoid arthritis (RA) in order to determine whether the higher field strength provides diagnostic gain. The hand mainly affected in 17 RA patients was examined at 1.5 Tesla (T) and 3.0 T with comparable MR imaging (MRI) protocols. MR images were reviewed twice by two experienced radiologists using the Rheumatoid Arthritis MRI Scoring System (RAMRIS) of the OMERACT (Outcome Measures in Rheumatoid Arthritis Clinical Trials) group. Image quality was rated on a five-point scale using Friedmann’s test and Kendall’s W-test for statistical analysis. Image comparison revealed better image quality at higher field strength. Image quality of T1-weighted images was rated 14–22% better at 3.0 T compared with 1.5 T by both readers. Moreover, the rating for the T2-weighted-images acquired at 3.0 T was one point better in the five-point scale used. Inter-reader correlation for image quality, bone erosions/defects, edema and synovitis ranged between 0.6 and 0.9 at 3.0 T and between 0.6 and 0.8 at 1.5 T. Intra-reader correlation for these parameters was high at 0.8–1.0. MRI image quality of RA hands is superior at 3.0 T, while an acceptable image quality is achieved at 1.5 T, which improves the evaluation of extent of bone edema, synovitis and identification of small bone erosions.     

Creutzfeldt-Jakob disease: comparative analysis of MR imaging sequences

BACKGROUND AND PURPOSE: MR imaging has played an increasingly important role in the diagnosis of Creutzfeldt-Jakob disease (CJD) since basal ganglia abnormalities on T2-weighted images have been described; thus, the aim of our study was to compare the value of different MR images in the diagnosis of CJD. METHODS: One hundred fifty-seven patients with CJD underwent MR imaging examinations. Ninety-two patients were neuropathologically confirmed, and 65 were clinically classified as having CJD through the CJD Surveillance Unit (probability of 95%). There was no standardized MR imaging protocol; thus, the examinations included 143 T2-weighted, 43 proton attenuation (PD)-weighted, 84 fluid-attenuated inversion recovery (FLAIR), and 44 diffusion-weighted images (DWI). The MR images were reviewed for pathologic changes of the basal ganglia, thalamus, and cerebral cortex. RESULTS: Cortical abnormalities were present in 70 patients (45%) and were visible in 80% (35/44) of all available DWI examinations. The basal ganglia were affected in 94 patients (60%), in particular in the caudate nucleus; the most sensitive sequences were DWI (64%) and PD-weighted (63%). A thalamic involvement was more frequently diagnosed on PD-weighted images (19%) and DWI (14%) than on FLAIR or T2-weighted images. CONCLUSION: PD-weighted images and DWI showed better results in the diagnosis of signal intensity changes in the basal ganglia compared with T2-weighted or FLAIR images; however, in the diagnosis of cortical changes, DWI was clearly superior. Our data suggest that DWI is the most sensitive MR imaging technique in the diagnosis of CJD.     

Abdominal Magnetic Resonance Imaging at 3.0 T: What Is the Ultimate Gain in Signal-to-Noise Ratio?

RATIONALE AND OBJECTIVES: The purpose of this study was to calculate the gain in signal-to-noise ratio (SNR) of four human abdominal tissues at 3.0 Tesla (T) compared with standard 1.5 T and to validate this calculation in vivo. MATERIALS AND METHODS: The expected gain in SNR at 3.0 T in the liver, pancreas, spleen, and kidney compared with standard 1.5 T was approximated theoretically for a T2-weighted HASTE (half-Fourier acquisition single-shot turbo spin-echo) and a T1-weighted gradient-echo in- and opposed-phase sequence. Fifteen healthy male subjects underwent abdominal MR imaging using a 1.5 T and 3.0 T scanner. Coronal T2-weighted HASTE images and axial T1-weighted gradient-echo in- and opposed-phase images were acquired using the sequence parameters optimized by the vendor. RESULTS: Except for opposed-phased imaging of pancreatic tissue, in vivo adjusted SNR values of all abdominal tissues were significantly higher at 3.0 T for all sequences (P < .05). The highest overall gain in SNR was achieved with the HASTE sequence ranging from 3.8-fold for renal imaging to 7.4-fold for hepatic imaging. The theoretical calculation of SNR gain was in good agreement with the experimentally measured gain in SNR for the HASTE and the in-phase sequence. CONCLUSION: High-field abdominal MR imaging at 3.0 T offers significantly higher SNR compared with standard 1.5 T MR imaging.     

Acute and subacute intracerebral hemorrhages: comparison of MR imaging at 1.5 and 3.0 T--initial experience

PURPOSE: To assess and describe the appearance of intracerebral hemorrhage (ICH) at 3.0-T magnetic resonance (MR) imaging as compared with the appearance of this lesion type at 1.5-T MR imaging. MATERIALS AND METHODS: Sixteen patients with 21 parenchymal ICHs were examined. ICHs were classified as hyperacute, acute, early subacute, late subacute, or chronic. Patients underwent 1.5- and 3.0-T MR imaging with T2-weighted fast spin-echo, fluid-attenuated inversion-recovery (FLAIR), and T1-weighted spin-echo (1.5-T) and gradient-echo (3.0-T) sequences within 4 hours of each other. The central (ie, core) and peripheral (ie, body) parts of the ICHs were analyzed quantitatively by using contrast-to-noise ratio (CNR) calculations derived from signal intensity (SI) measurements; these values were statistically evaluated by using the Mann-Whitney U test. Two readers qualitatively determined SIs of the cores and bodies of the ICHs, degrees of apparent susceptibility artifacts, and lesion ages. The chi(2) test was used to determine statistically significant differences. RESULTS: With the exception of the bodies of late subacute ICHs at 3.0-T T2-weighted imaging, which had increased positive CNRs and SI scores (P .05). With the exception of minor susceptibility artifacts seen in acute and early subacute ICHs at 3.0-T T1-weighted gradient-echo imaging, no susceptibility artifacts were noticed. The ages of most lesions were identified correctly without significant differences between the two field strengths (P >.05), with the exception of the ages of acute ICHs, which were occasionally misinterpreted as early subacute lesions at 3.0 T. CONCLUSION: At 3.0 T, all parts of acute and early subacute ICHs had significantly increased hypointensity on FLAIR and T2-weighted MR images as compared with the SIs of these lesions at 1.5 T. However, 1.5- and 3.0-T MR images were equivalent in the determination of acute to late subacute ICHs.     

MR imaging in carotid artery atherosclerosis plaque characterization.

AIM: To evaluate the potential role of carotid artery atherosclerosis plaque magnetic resonance (MR) microimaging as magnetic resonance imaging (MRI) marker, ex vivo MR images were acquired at optimized parameters on 9.4T Bruker animal imager for occluded tissue resected by carotid endarterectomy (CEA) and corresponding histopathological analysis was made. METHODS AND MATERIALS: For imaging, CEA tissues of size 2-6 cm long and 0.5-1.5 cm wide, were transferred to 15 ml co-polymer laboratory culture tubes containing either 10% formalin in phosphate buffered saline (PBS) or in 50% glycerol in PBS. Imaging protocol was set at TE=30 ms, TR=1.5 s, matrix size=265 x 512, NEX=128, slice thickness=1 mm and in-plane resolution=0.1 mm for total sample size 2.5 cm. Soon after imaging done, carotid artery tissues were cut into 5-mm segments and processed for histological section for successive 5-micrometer slices. To compare morphology of 5 mum thin CEA section with that of 1 mm MR slices, registration was obtained between histologic sections and MR slices. Contrast and magnetic resonance relaxation characteristics were analyzed. RESULTS: Total carotid artery area computed by MR imaging was correlated with areas determined from histologic sections (r(2)=0.989, p=0.0001). For the lumen area, the correlation between MR images and histologic area was (r(2)=0.942, p=0.0001). Relaxation times and T(2) parametric images of different plaque components were determinant for contrast resolution. Scan parameters were optimized for fibrous cap and atheroma. Scan parameters were characteristic for comparison at 1.5T and 9.4T MR imagers. CONCLUSION: The observed correlation validated MR microimaging to assess morphological features of carotid artery plaques and contrast resolution highlighted the potential of in vivo MR imaging as non-invasive MRI marker to monitor carotid artery plaque morphometry and plaque composition.     

Comparison of phased-array 3.0-T and endorectal 1.5-T magnetic resonance imaging in the evaluation of local staging accuracy for prostate cancer

OBJECTIVE: To retrospectively evaluate local staging accuracy for prostate cancer at 3.0-T magnetic resonance imaging (MRI) by comparing with that at 1.5-T MRI. METHODS: Two groups, each consisting of 54 patients, were included by matching for age, prostate specific antigen, and Gleason score. Before radical prostatectomy, 1 group underwent 3.0-T MRI using a phased-array coil, and the other 1.5-T MRI using an endorectal coil. T2-weighted MR images at 3.0 and 1.5 T were analyzed in consensus by 2 radiologists, and their staging accuracy was compared with histology. Artifact and overall image quality were compared at both 3.0 and 1.5 T. RESULTS: Accuracy for T3 stage at 3.0 and 1.5 T were 72% (39/54) and 70% (38/54), respectively (P > 0.05). The 3.0-T MRI had a lower incidence of MR artifacts than the 1.5-T MRI (P < 0.05). However, overall imaging quality at both 3.0 and 1.5 T had no significant difference (P > 0.05). CONCLUSIONS: The 3.0-T phased-array MRI is equivalent to the 1.5-T endorectal MRI in evaluating local staging accuracy for prostate cancer without significant loss of imaging quality.     

Quantification of human atherosclerotic plaques using spatially enhanced cluster analysis of multicontrast-weighted magnetic resonance images.

One of the current limitations of magnetic resonance imaging (MRI) is the lack of an objective method to classify plaque components. Here we present a cluster analysis technique that can objectively quantify and classify MR images of atherosclerotic plaques. We obtained three-dimensional (3D) images from 12 human coronary artery specimens on a 9.4T imaging system using multicontrast-weighted fast spin-echo (T1-, proton density-, and T2-weighted) imaging with an isotropic voxel size of 39 micro. Spatially enhanced cluster analysis (SECA) was performed on multicontrast MR images, and the resulting segmentation was evaluated against histological tracings. To visualize the overall structure of plaques, the MR images were rendered in 3D. The specimens exhibited lesions of American Heart Association (AHA) plaque classification types I-VI. Both MR images and histological sections were independently reviewed, categorized, and compared. Overall, the classification obtained from the cluster-analyzed MR and histopathology images showed very good agreement for all AHA types (92%, Cohen's kappa = 0.89, P < 0.0001). All plaque types were identified and quantified by SECA with a high degree of correlation between cluster-analyzed MR and manually traced histopathology data. MRI combined with SECA provides an objective method for atherosclerotic plaque component characterization and quantification.     

Human peripheral arteries: feasibility of transvenous intravascular MR imaging of the arterial wall

Feasibility of in vivo transvenous intravascular magnetic resonance (MR) imaging of the human arterial wall was determined. All subjects provided written informed consent, and institutional review board approved the study. Six arteries in six patients were imaged with a guidewire placed in the iliac vein (n = 5) or left renal vein (n = 1). Pre- and postcontrast T1-weighted and T2-weighted transvenous MR imaging were performed. An atherosclerotic plaque with a fibrous cap was identified on 27 (42%) of 64 images of veins without stents; intimal hyperplasia in a renal artery with a stent was identified on 12 images. Contrast-to-noise ratios (CNRs) on arterial wall postcontrast T1-weighted images were superior to those on images obtained with other sequences (P < .001), and the postcontrast images demonstrated the greatest number of plaques with a low-signal intensity core and fibrous cap. Preliminary results show that transvenous MR imaging is feasible for high-spatial-resolution imaging of the arterial wall and atherosclerotic plaque. Postcontrast T1-weighted imaging affords greatest CNR for the arterial wall.     

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.     

MR imaging of acute hemorrhagic brain infarction

Six patients with acute hemorrhagic brain infarct were imaged using spin-echo (SE) pulse sequences on a 1.5 Tesla MR scanner. Including two patients with repeated MR imaging, a total of eight examinations, all performed within 15 days after stroke, were analyzed retrospectively. Four patients revealed massive hemorrhages in the basal ganglia or cerebellum and three cases demonstrated multiple linear hemorrhages in the cerebral cortex. On T1-weighted images, hemorrhages were either mildly or definitely hyperintense relative to gray matter, while varied from mildly hypointense to hyperintense on T2-weighted images. T1-weighted images were superior to T2-weighted images in detection of hemorrhage. CT failed to detect hemorrhages in two of five cases: indicative of MR superiority to CT in the diagnosis of acute hemorrhagic infarcts.     

Vulnerable plaque detection by 3.0 tesla magnetic resonance imaging

RATIONALE AND OBJECTIVES: A clinical case report is presented on a 76-year-old man who volunteered for a 3.0 T magnetic resonance (MR) carotid protocol. The subject was referred for carotid endarterectomy and histology was performed on the ex vivo specimen and compared with the in vivo images. METHODS: The 3.0 and 1.5 T (obtained for comparison) MR protocol consisted of 2-dimensional (2D) and 3-dimensional (3D) multicontrast bright and black blood imaging for detecting the lumen and vessel wall. RESULTS: The combination of multicontrast black blood transverse images and the 3D time of flight transverse images provided visualization of a narrowed internal carotid artery lumen 4 mm above of the bifurcation and the presence of a complex atherosclerotic plaque containing a large lipid pool, calcification, and intact fibrous cap. Quantitative comparisons including vessel lumen and plaque area, signal-to-noise (SNR) and contrast-to-noise (CNR) ratios were obtained for 1.5 and 3.0 T image data. Plaque composition was verified with histology. Macrophages were also detected in the shoulders of the plaque as demonstrated by CD68 staining and corresponded with a small hyperintense area in the T2W images at 3.0 T, but not observed in comparable 1.5 T images. CONCLUSIONS: High field 3.0 T multicontrast MRI of atherosclerotic plaque has been validated with histology comparison and provides improved detection of complex atherosclerotic plaque with increased SNR and CNR compared with 1.5 T. Further studies validating contrast mechanisms of plaque at 3.0 T are required, but atherosclerotic plaque imaging has clear benefit from application at the higher magnetic field strength.     

MR imaging of the ankle at 3 Tesla and 1.5 Tesla: protocol optimization and application to cartilage, ligament and tendon pathology in cadaver specimens

The objective of this study was to optimize ankle joint MR imaging in volunteers at 1.5 Tesla (T) and 3.0 T, and to compare these optimized sequences concerning image quality and performance in assessing cartilage, ligament and tendon pathology in fresh human cadaver specimens. Initially our clinical ankle protocol consisting of T1-weighted (-w), fat-saturated (fs) T2-w, and short τ inversion-recovery fast spinecho (FSE) sequences was optimized at 1.5 T and 3.0 T by two radiologists. For dedicated cartilage imaging, fs-intermediate (IM)-w FSE, fs spoiled gradient echo, and balanced free-precession steady-state sequences were optimized. Using the optimized sequences, thirteen cadaver ankle joints were imaged. Four radiologists independently assessed these images concerning image quality and pathology. All radiologists consistently rated image quality higher at 3.0 T (all sequences p<0.05). For detecting cartilage pathology, diagnostic performance was significantly higher at 3.0 T (ROC-values up to 0.93 vs. 0.77; p<0.05); the fs-IM FSE sequence showed highest values among the different sequences. Average sensitivity for detecting tendon pathology was 63% at 3.0 T vs. 41% at 1.5 T and was significantly higher at 3.0 T for 2 out of 4 radiologists (p<0.05). Compared to 1.5 T, imaging of the ankle joint at 3.0 T significantly improved image quality and diagnostic performance in assessing cartilage pathology. Cameron Barr and Jan S. Bauer both equally contributed to this work.     

Comparison of multiple sclerosis lesions at 1.5 and 3.0 Tesla

OBJECTIVE: To evaluate the relative sensitivity of MR scanning for multiple sclerosis (MS) at 1.5 Tesla (T) and 3.0 T using identical acquisition conditions, as is typical of multicenter clinical trials. METHODS: Twenty-five subjects with MS were scanned at 1.5 T and 3.0 T using fast spin echo, and T(1)-weighted SPGR with and without gadolinium contrast injections. Image data, blinded to field strength, were analyzed using automated segmentation and lesion counting. RESULTS: Relative to scanning at 1.5 T, the 3.0 T scans showed a 21% increase in the number of detected contrast enhancing lesions, a 30% increase in enhancing lesion volume and a 10% increase in total lesion volume. DISCUSSION: The improved detection ability using high-field MR imaging is prominent even when sequence parameters are optimized around the midfield units. Multicenter trials using both 1.5 T and 3.0 T instruments may be affected by these sensitivity differences.     

High-Resolution 3 T MR Microscopy Imaging of Arterial Walls

Purpose To achieve a high spatial resolution in MR imaging that allows for clear visualization of anatomy and even histology and documentation of plaque morphology in in vitro samples from patients with advanced atherosclerosis. A further objective of our study was to evaluate whether T2-weighted high-resolution MR imaging can provide accurate classification of atherosclerotic plaque according to a modified American Heart Association classification. Methods T2-weighted images of arteries were obtained in 13 in vitro specimens using a 3 T MR unit (Medspec 300 Avance/Bruker, Ettlingen, Germany) combined with a dedicated MR microscopy system. Measurement parameters were: T2-weighted sequences with TR 3.5 sec, TE 15–120 msec; field of view (FOV) 1.4 × 1.4; NEX 8; matrix 192; and slice thickness 600 μm. MR measurements were compared with corresponding histologic sections. Results We achieved excellent spatial and contrast resolution in all specimens. We found high agreement between MR images and histology with regard to the morphology and extent of intimal proliferations in all but 2 specimens. We could differentiate fibrous caps and calcifications from lipid plaque components based on differences in signal intensity in order to differentiate hard and soft atheromatous plaques. Hard plaques with predominantly intimal calcifications were found in 7 specimens, and soft plaques with a cholesterol/lipid content in 5 cases. In all specimens, hemorrhage or thrombus formation, and fibrotic and hyalinized tissue could be detected on both MR imaging and histopathology. Conclusion High-resolution, high-field MR imaging of arterial walls demonstrates the morphologic features, volume, and extent of intimal proliferations with high spatial and contrast resolution in in vitro specimens and can differentiate hard and soft plaques.     

Characterization of coronary atherosclerotic plaque using multicontrast MRI acquired under simulated in vivo conditions

PURPOSE: To compare coronary atherosclerotic plaque characterization using multicontrast MRI on: 1) freshly excised vessels under simulated in vivo conditions, and 2) preserved vessels. MATERIALS AND METHODS: T1-weighted (T1W), T2-weighted (T2W), proton density-weighted (PDW), and diffusion-weighted (DW) MR images were acquired on 13 freshly excised human coronary arteries from explanted hearts. Vessels were imaged in an MR-compatible tissue culture chamber using a 4.7 Tesla small-bore MR scanner. Eight vessels were then preserved in buffered formalin and rescanned following the same imaging protocol. A three-dimensional spatially penalized fuzzy C-means (3D-SPFCM) technique was applied to classify different plaque constituents. The classification results from vessels under "fresh" and "preserved" conditions were compared with corresponding histological sections. RESULTS: For most plaque constituents, the plaque characterization results show no significant difference between fresh and preserved scans, and little difference between scans and the histological reference standard. In the case of thrombus, apparent signal changes between fresh and preserved images were identified. Overall, MR scans conducted under preserved conditions provided a 1.8% to 17.5% greater signal-to-noise ratio (SNR) than those conducted in the fresh stage. CONCLUSION: Preservation of coronary vessels did not alter the contrast between plaque tissues on multicontrast MRI, and did not significantly change the results of plaque constituent characterization.     

Comprehensive cardiac magnetic resonance imaging at 3.0 Tesla: feasibility and implications for clinical applications

OBJECTIVE: The objective of this study was to examine the applicability of high magnetic field strengths for comprehensive functional and structural cardiac magnetic resonance imaging (MRI). SUBJECTS AND METHODS: Eighteen subjects underwent comprehensive cardiac MRI at 1.5 T and 3.0 T. The following imaging techniques were implemented: double and triple inversion prepared FSE for anatomic imaging, 4 different sets of echocardiographic-gated CINE strategies for functional and flow imaging, inversion prepared gradient echo for delayed enhancement imaging, T1-weighted segmented EPI for perfusion imaging and 2-dimensional (2-D) spiral, and volumetric SSFP for coronary artery imaging. RESULTS:: Use of 3 Tesla as opposed to 1.5 Tesla provided substantial baseline signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) improvements for anatomic (T1-weighted double IR: DeltaSNR = 29%, DeltaCNR = 20%, T2-weighted double IR: DeltaSNR = 39%, DeltaCNR = 33%, triple IR: DeltaSNR = 74%, DeltaCNR = 60%), functional (conventional CINE: DeltaSNR = 123%, DeltaCNR = 74%, accelerated CINE: DeltaSNR = 161%, DeltaCNR = 86%), myocardial tagging (DeltaSNRsystole = 54%, DeltaCNRsystole = 176%), phase contrast flow measurements (DeltaSNR = 79%), viability (DeltaSNR = 48%, DeltaCNR = 40%), perfusion (DeltaSNR = 109%, DeltaCNR = 87%), and breathhold coronary imaging (2-D spiral: DeltaSNRRCA = 54%, DeltaCNRRCA = 69%, 3-D SSFP: DeltaSNRRCA = 60%, DeltaCNRRCA = 126%), but also revealed image quality issues, which were successfully tackled by adiabatic radiofrequency pulses and parallel imaging. CONCLUSIONS: Cardiac MRI at 3.0 T is feasible for the comprehensive assessment of cardiac morphology and function, although SAR limitations and susceptibility effects remain a concern. The need for speed together with the SNR benefit at 3.0 T will motivate further advances in routine cardiac MRI while providing an image-quality advantage over imaging at 1.5 Tesla.     

MRI of prostate cancer at 1.5 and 3.0 T: comparison of image quality in tumor detection and staging

OBJECTIVE: This prospective study was performed to compare the image quality, tumor delineation, and depiction of staging criteria on MRI of prostate cancer at 1.5 and 3.0 T. SUBJECTS AND METHODS: Twenty-four patients with prostate cancer underwent MRI at 1.5 T using the combined endorectal-body phased-array coil and at 3.0 T using the torso phased-array coil, among them 22 before undergoing radical prostatectomy. The prostate was imaged with T2-weighted sequences in axial and coronal orientations at both field strengths and, in addition, with an axial T1-weighted sequence at 1.5 T. Preoperative analysis of all MR images taken together was compared with the histologic findings to determine the accuracy of MRI for the local staging of prostate cancer. In a retroanalysis, the image quality, tumor delineation, and conspicuity of staging criteria were determined separately for both field strengths and compared. Statistical analysis was performed using Wilcoxon's and the McNemar tests. RESULTS: In the preoperative analysis, MRI (at both 1.5 and 3.0 T) had an accuracy of 73% for the local staging of prostate cancer. The retroanalysis yielded significantly better results for 1.5-T MRI with the endorectal-body phased-array coil in terms of image quality (p < 0.001) and tumor delineation (p = 0.012) than for 3.0-T MRI with the torso phased-array coil. Analysis of the individual staging criteria for extracapsular disease did not reveal a superiority of either of the two field strengths in the depiction of any of the criteria. CONCLUSION: Intraindividual comparison shows that image quality and delineation of prostate cancer at 1.5 T with the use of an endorectal coil in a pelvic phased-array is superior to the higher field strength of 3.0 T with a torso phased-array coil alone. As long as no endorectal coil is available for 3-T imaging, imaging at 1.5 T using the combined endorectal-body phased-array coil will continue to be the gold standard for prostate imaging.     

Atherosclerotic plaques: classification and characterization with T2-weighted high-spatial-resolution MR imaging-- an in vitro study

PURPOSE: To evaluate if T2-weighted high-spatial-resolution magnetic resonance (MR) imaging (117 microm per pixel) can help accurate classification of atherosclerotic plaques. MATERIALS AND METHODS: Thirty human arteries and 11 carotid endarterectomy specimens from 31 patients underwent T2-weighted MR imaging (2-T magnet; repetition time, 2,000 msec; echo time, 50 msec) at room temperature. After imaging, Bouin fixative was used to fix 26 arteries, and the other 15 arteries were fixed by means of freezing. Specimens were stained with hematoxylin-eosin and safranin or Sudan lipid stain. MR images and histologic slices were classified independently by two radiologists and a pathologist, respectively, on the basis of the American Heart Association classification. RESULTS: Results with MR imaging were the following: type I-II plaques, sensitivity of 67% and specificity of 100%; type IV-Va plaques, sensitivity of 74% and specificity of 85%; type Vb plaques, sensitivity of 90% and specificity of 100%; type Vc plaques, sensitivity of 80% and specificity of 90%. No type III plaque was diagnosed in the study. The overall kappa value was 0.68. CONCLUSION: High-spatial-resolution MR imaging with T2 weighting alone can help accurate classification of fibrocalcic plaques (type Vb), but it is subject to limitations for the classification and analysis of other types of atherosclerotic plaques.     

Detection of hepatic metastases by superparamagnetic iron oxide-enhanced MR imaging: prospective comparison between 1.5-T and 3.0-T images in the same patients

Objective:

To prospectively compare the diagnostic performance of superparamagnetic iron oxide (SPIO)-enhanced magnetic resonance (MR) imaging at 3.0 T and 1.5 T for detection of hepatic metastases.

Methods:

A total of 28 patients (18 men, 10 women; mean age, 61 years) with 80 hepatic metastases were prospectively examined by SPIO-enhanced MR imaging at 3.0 T and 1.5 T. T1-weighted gradient-recalled-echo (GRE) images, T2*-weighted GRE images and T2-weighted fast spin-echo (SE) images were acquired. The tumour-to-liver contrast-to-noise ratio (CNR) of the lesions was calculated. Three observers independently reviewed each image. Image artefacts and overall image quality were analysed, sensitivity and positive predictive value for the detection of hepatic metastases were calculated, and diagnostic accuracy using the receiver-operating characteristics (ROC) method was evaluated.

Results:

The tumour-to-liver CNRs were significantly higher at 3.0 T. Chemical shift and motion artefact were more severe, and overall image quality was worse on T2-weighted fast SE images at 3.0 T. Overall image quality of the two systems was similar on T1-weighted GRE images and T2*-weighted GRE images. Sensitivity and area under the ROC curve for the 3.0-T image sets were significantly higher.

Conclusion:

SPIO-enhanced MR imaging at 3.0 T provided better diagnostic performance for detection of hepatic metastases than 1.5 T.     

Intracranial contrast-enhanced magnetic resonance venography with 6.4-fold sensitivity encoding at 1.5 and 3.0 Tesla

PURPOSE: To prospectively compare vessel conspicuity and diagnostic image quality between three-dimensional intracranial contrast-enhanced MR venography acquired at 1.5 Tesla (T) and 3.0T, with 6.4-fold sensitivity encoding. MATERIALS AND METHODS: Ten healthy volunteers were imaged on 1.5T and 3.0T MR scanners using eight-element head coil arrays. The intracranial venous vasculature was divided into five groups for evaluation based on vessel size and anatomical location. Two radiologists independently assessed vessel conspicuity, level of artifacts, and diagnostic image quality. Informed consent was obtained, and the study was approved by the institutional review board. RESULTS: With the exception of large cerebral sinuses where 1.5T and 3.0T results were rated as equivalent, 3.0T images demonstrated superior vessel continuity, sharpness, and signal contrast to background tissue than 1.5T for all other intracranial venous vasculature (P < 0.01). No statistical significance in overall image quality was found between 1.5T and 3.0T venograms, and all data sets were deemed sufficient for diagnostic interpretation. CONCLUSION: Whole brain contrast-enhanced venography with 6.4-fold sensitivity encoding is robust and has the potential to become the method of choice for fast visualization of the intracranial venous vasculature. At 3.0T, demonstration of small cerebral vessels is superior to 1.5T.