Staging uterine cervical carcinoma with low-field MR imaging

PURPOSE: To assess the validity of low-field MR in staging cervical cancer compared to clinical staging. MATERIAL AND METHODS: A total of 95 women entered the study over a 3-year period. MR examinations with a 0.1 T resistive magnet using a body coil and clinical staging according to the FIGO recommendations (1988) were performed within 2 weeks from clinical diagnosis. T1- and T2-weighted sequences were obtained in transversal and sagittal acquisitions, and an additional T1 before and after contrast (randomisation to 0.1 or 0.3 mmol/kg b.w. gadodiamide). Treatment decisions on surgery or radiation therapy were made solely on the clinical staging. RESULTS: Sixty-one patients were found to be eligible for surgery. In 5 women, the pathological results revealed a more advanced stage of the disease than assessed by clinical staging. MR correctly staged 4 of the 5 but otherwise tended to overstate the disease. Contrast enhancement significantly reduced this trend (p<0.05) regardless of the contrast medium dose used. Divided into two groups, an operable (less than stage 2b) and an inoperable group (more than stage 2a), the clinical staging correctly classified 57 patients (accuracy 92%) compared to 52 patients with MR using contrast enhancement (accuracy 84%). The specificity was no higher than 31%, whereas the reproducibility of the MR assessment was fairly good with kappa values around 0.65 for both intra- and inter-observer variations. Conclusion: In the present set-up, clinical assessment was superior to low-field MR in staging cervical cancer. When using contrast enhancement, the staging accuracies of low-field MR were comparable to the ones reported for techniques with higher tesla values, whereas the specificity and reproducibility errors were lower. The method, therefore, needs to be optimised.     

Evaluation of treatment response of chemoembolization in hepatocellular carcinoma with diffusion-weighted imaging on 3.0-T MR imaging

PurposeTo assess the treatment response of hepatocellular carcinoma (HCC) after transarterial chemoembolization with diffusion-weighted imaging and dynamic contrast-enhanced magnetic resonance (MR) imaging with a 3-T system.Materials and MethodsBetween February 2010 and November 2010, 74 patients were treated with chemoembolization in our interventional radiology unit. Twenty-two patients (29%) who had liver MR imaging including diffusion and dynamic contrast-enhanced MR imaging on a 3-T system before and after transarterial chemoembolization were evaluated retrospectively. Tumor size, arterial enhancement, venous washout, and apparent diffusion coefficient (ADC) values of lesions, peritumoral parenchyma, normal liver parenchyma, and spleen were recorded before and after treatment. The significance of differences between ADC values of responding and nonresponding lesions was calculated.ResultsThe study included 77 HCC lesions (mean diameter, 31.4 mm) in 20 patients. There was no significant reduction in mean tumor diameter after treatment. Reduction in tumor enhancement in the arterial phase was statistically significant (P = .01). Tumor ADC value increased from 1.10 × 10^?3 mm²/s to 1.27 × 10^?3 mm²/s after treatment (P < .01), whereas the ADC values for liver and spleen remained unchanged. ADC values from cellular parts of the tumor and necrotic areas also increased after treatment. However, pretreatment ADC values were not reliable to identify responding lesions according to the results of receiver operating characteristic analysis.ConclusionsAfter transarterial chemoembolization, responding HCC lesions exhibited decreases in arterial enhancement and increases in ADC values in cellular and necrotic areas. Pretreatment ADC values were not predictive of response to chemoembolization.     

Superficial esophageal carcinoma: an in vitro study of high-resolution MR imaging at 1.5T

The purpose of this study was to determine the diagnostic accuracy of high-resolution MR imaging at 1.5T for evaluating the mural invasion of superficial esophageal carcinoma. Forty-one esophageal specimens taken from patients suspected of having superficial carcinoma were studied using a 1.5T MR system with a surface coil. Spin-echo MR images were obtained with a field of view of 50mm, matrix of 256 x 256, and section thickness of 2mm (voxel size = 0.08 mm3). MR findings were compared with histopathologic findings. T2-weighted images clearly depicted the normal esophageal wall as consisting of 8 layers. In 39 (95%) of 41 carcinomas, the depth of mural invasion determined by MR imaging correlated well with that determined with histopathologic examination. The MR-based stage was higher in 2 (5%) cases than the histopathologic stage. High-resolution MR imaging at 1.5T shows a high diagnostic accuracy for evaluating the mural invasion of superficial esophageal carcinoma, thus potentially enabling preoperative histopathologic staging.     

Early gastric carcinoma: evaluation with high-spatial-resolution MR imaging in vitro.

PURPOSE: To determine signal intensity characteristics of the gastric wall layers and to assess the accuracy of the evaluation of early gastric carcinomas in vitro by using resected specimens studied with high-spatial-resolution magnetic resonance (MR) imaging. MATERIALS AND METHODS: Fifteen gastric specimens obtained from patients suspected of having early gastric carcinoma were studied with a 1.5-T MR system with a 4-cm-diameter loop coil. High-spatial-resolution spin-echo MR images were obtained with a field of view of 50 mm, a matrix of 256 x 256, and a section thickness of 2 mm, resulting in a voxel size of 0.08 mm(3). Findings from MR images were compared with histopathologic findings. RESULTS: T1- and T2-weighted MR images clearly depicted the normal gastric wall as consisting of four and six layers, respectively, which corresponded well to the histologic layers. In 14 (93%) of 15 gastric carcinomas, the depth of mural invasion visualized with MR imaging correlated well with the histopathologic stage. The stage determined with MR imaging, however, was lower in one instance (7%) than the histopathologic stage. MR imaging also depicted the gross features of the tumor, presence of ulceration, and adjacent lymph node swelling. CONCLUSION: High-spatial-resolution MR imaging has a high diagnostic accuracy in the evaluation of the mural invasion of early gastric carcinoma in vitro and thus potentially enables preoperative histopathologic staging.     

MR imaging of the brachial plexus: comparison between 1.5-T and 3-T MR imaging: preliminary experience

Objective  

To compare 1.5-T and 3-T magnetic resonance (MR) imaging of the brachial plexus.     

Thin-section MR imaging of rat brain at 4.7 T.

The brains of anesthetized 7-month-old male hooded rats were imaged in coronal, sagittal, and horizontal planes at 4.7 T. Images were obtained with a section thickness of 0.6 mm and in-plane pixel size of 0.18-0.20 mm, resulting in finer combined spatial and contrast resolution than in most previously published reports. This allowed detailed anatomic assignment of many brain structures on the basis of comparison with a histologic brain atlas. T1, apparent T2, and water proton density values of gray matter, white matter, and cerebrospinal fluid (CSF) were derived from saturation-recovery and multi-echo measurements. These values were used to calculate expected contrast-to-noise ratios as a function of TR and TE in spin-echo imaging sequences. The optimal simultaneous contrast between gray and white matter and between CSF and gray matter was obtained on images with moderate T2 weighing, with a TR of 3.6 seconds and a TE of 45 msec. The use of thin sections was found to be essential for resolving many fine structures, and the improved sensitivity provided by the high magnetic field strength was crucial for imaging such thin sections at adequate signal-to-noise ratios.     

Evaluation of the acetabular labrum at 3.0-T MR imaging compared with 1.5-T MR arthrography: preliminary experience

Institutional review board approval and informed consent were obtained for this HIPAA-compliant study. The purpose of this study was to prospectively compare imaging of the acetabular labrum with 3.0-T magnetic resonance (MR) imaging and 1.5-T MR arthrography. Eight patients (four male, four female; mean age, 38 years) with hip pain suspicious for labral disease were examined at both MR arthrography and MR imaging. Presence of labral lesions, paralabral cysts, articular cartilage lesions, subchondral cysts, osteophytes, and synovial herniation pits was recorded. There was arthroscopic correlation of findings in five patients. MR imaging depicted four surgically confirmed labral tears that were identified at MR arthrography, as well as one that was not visualized at MR arthrography. MR imaging helped identify all other pathologic conditions that were diagnosed at MR arthrography and helped identify one additional surgically confirmed focal articular cartilage lesion. These results provide encouraging support for evaluation with 3.0-T MR imaging over 1.5-T MR arthrography.     

Whole-body MR imaging and spectroscopy with a 4-T system

The clinical potential and limitations of magnetic resonance imaging and spectroscopy at 4 T were investigated with the use of a newly constructed system, which has been in use since January 1987. The magnet has a warm bore that measures 1.25 m in diameter, and its homogeneity in a sphere with a diameter of 50 cm is better than +/- 2.5 ppm. It was hypothesized that the improvement in the signal-to-noise ratio (S/N) afforded by the higher field strength would be useful in reducing imaging time and in improving spatial resolution. In experiments in human volunteers, believed to be the first in which an entire human body was exposed to a magnetic flux density of that magnitude, the subjects were exposed to 4 T for 10-30 minutes. They showed no changes in well-being or heart activity. The expected gain in spectral resolution due to chemical-shift scaling was achieved with the 4-T system, and an improvement in S/N was verified for phosphorus at 34 and 68 MHz. In sodium imaging, the high flux density appears to be useful in reducing imaging time, which should increase the usefulness of sodium imaging in evaluating brain tumors and strokes. In spectroscopy, the increase in flux density improves the quality of the spectra.     

Visualization of microvascularity in glioblastoma multiforme with 8-T high-spatial-resolution MR imaging

We used 8-T high-spatial-resolution gradient-echo MR imaging to directly visualize microvascularity in pathologically proved glioblastoma multiforme. Images were compared with 1.5-T high-spatial-resolution fast spin-echo T2-weighted images and digital subtraction angiograms. Preliminary data indicate that 8-T high-spatial-resolution MR imaging may enable the identification of areas of abnormal microvascularity in glioblastoma multiforme that are not visible with other routine clinical techniques.     

MR imaging of the knee with a 0.064-T permanent magnet

Magnetic resonance (MR) imaging has proved beneficial in the evaluation of internal derangements of the knee. A limitation to general acceptance of MR imaging of the knee has been availability and cost. The recent introduction of low-field-strength MR imaging has shown promise in decreasing the cost and increasing the availability of this modality. High-resolution (pixel size, 0.7 mm2), three-dimensional Fourier transform (3DFT), thin-section (3.5 mm) imaging performed on a 0.064-T permanent magnet was used to evaluate 117 knees in 114 consecutive patients. The appearance of normal anatomy and internal derangements of the knee at low-field-strength imaging is described. Arthroscopic correlation was available for 28 knees. Findings from low-field-strength MR imaging and arthroscopy agreed in 79% of cases in the determination of meniscal tears. Partial-flip-angle techniques with 3DFT produced thin-section images of the knee of diagnostic quality. The authors conclude that in patients with internal derangements of the knee, low-field-strength (0.064-T) MR imaging may provide useful information.     

Mild cognitive impairment: evaluation with 4-T functional MR imaging

PURPOSE: To prospectively assess abnormalities in brain activation patterns during encoding and retrieval in subjects with mild cognitive impairment by using 4-T functional magnetic resonance (MR) imaging. MATERIALS AND METHODS: The institutional review board approved this HIPAA-compliant study; all subjects gave written informed consent. Twenty patients with mild cognitive impairment (12 men, eight women; mean age, 75.0 years +/- 7.6 [standard deviation]) and 20 elderly control subjects (nine men, 11 women; mean age, 71.2 years +/- 4.5) underwent functional MR imaging at 4 T during a novel-versus-familiar face-name encoding-retrieval task. The magnitude of blood oxygen level-dependent brain responses across the entire brain were compared within and between subjects with mild cognitive impairment and control subjects by using a voxelwise random-effects model. A one-sample t test was used for within-group analysis; an analysis-of-covariance model (with age as a covariate) was used for between-group analysis. RESULTS: Brain regions activated by the task (prefrontal, medial temporal, and parietal regions) during encoding were similar to those activated during retrieval, with larger areas activated during retrieval. Subjects with mild cognitive impairment showed decreased magnitude of activation in bilateral frontal cortex regions (during encoding and retrieval), the left hippocampus (during retrieval), and the left cerebellum (during encoding) compared with magnitude of activation in control subjects (P < .001). Patients with mild cognitive impairment showed increased activation in the posterior frontal lobes (during retrieval) (P < .001). Lower hippocampal activation during retrieval was the most significant correlate of clinical severity of memory loss in mild cognitive impairment (P < .001). CONCLUSION: A difference exists in the response of brain regions underlying encoding and retrieval in mild cognitive impairment. Memory deficits in mild cognitive impairment may be linked to functional alterations in several specific brain regions both inside and outside the medial temporal lobe.     

Acute cervical spine trauma: evaluation with 1.5-T MR imaging

Twenty-one patients with acute neurologic deficits following cervical spine trauma were evaluated with magnetic resonance (MR) imaging (n = 21), computed tomography enhanced with intrathecal contrast material (CT myelography) (n = 18), myelography (n = 13), cervical spine radiography (n = 21), and intraoperative sonography (n = 7). MR imaging proved superior to other modalities in demonstrating parenchymal spinal cord injuries and cervical intervertebral disk herniation. Although both T1- and T2-weighted studies appear necessary to evaluate the anatomic relationship of the spinal cord, thecal space, intervertebral disks, and surrounding osseous and ligamentous structures, T2-weighted sequences were more sensitive than T1-weighted studies for detection of spinal cord injury. CT myelography was superior to MR imaging in demonstrating cervical spine fractures. In most cases, myelography revealed no information that was not apparent from both CT and MR imaging studies. Preliminary experience with MR imaging of acute cervical spine trauma suggests that it should be the study of choice in symptomatic patients who are otherwise clinically stable. CT may still be required in selected patients to evaluate complex fractures.     

Diffusion-tensor fiber tractography: intraindividual comparison of 3.0-T and 1.5-T MR imaging

PURPOSE: To prospectively evaluate the depiction of brain fiber tracts at 3.0- versus 1.5-T diffusion-tensor (DT) fiber tractography performed with parallel imaging. MATERIALS AND METHODS: Institutional review board approval was obtained, and each subject provided written informed consent. Subjects were 30 healthy volunteers (15 men, 15 women; mean age, 28 years; age range, 21-46 years). Single-shot spin-echo echo-planar magnetic resonance (MR) sequences with parallel imaging were applied. Four fiber tracts were reconstructed: corticospinal tract (CST), superior longitudinal fasciculus (SLF), corpus callosum (CC), and fornix. Two neuroradiologists compared 3.0- and 1.5-T tractography in terms of fiber tract depiction by using five depiction scores (scores 0-4) and numbers of reconstructed tract fibers and in terms of lateral asymmetry in the CST by using numbers of reconstructed fibers. The Wilcoxon signed rank test was applied for statistical analysis. RESULTS: Visual scores for both CST hemispheres (P < .001), the right SLF (P = .005), the CC (P = .01), and the right fornix (P = .04) were higher at 3.0-T DT tractography. Larger numbers of CST (right, P = .008; left, P < .001), SLF (right, P = .001; left, P = .02), and fornix (bilaterally, P = .02) tract fibers were depicted at 3.0 T. The asymmetry index for the CST was lower (P < .001) at 3.0 T. Visual scores for the left SLF and the left fornix and numbers of CC tract fibers were not significantly different. CONCLUSION: Depiction of most fiber tracts was improved at 3.0-T DT tractography compared with depiction at 1.5-T tractography.     

Time-of-flight MR angiography: comparison of 3.0-T imaging and 1.5-T imaging--initial experience

Intracranial three-dimensional time-of-flight (TOF) magnetic resonance (MR) angiography was performed in seven healthy volunteers and eight patients with both 1.5-T and 3.0-T MR systems with standard and high spatial resolutions (true voxel sizes, 0.48 x 0.75 x 2.00 mm and 0.30 x 0.44 x 1.00 mm, respectively). Superior image quality and significantly better depiction of small vessel segments and vascular disease were observed at high-spatial-resolution 3.0-T TOF MR angiography but not at standard 1.5-T or standard 3.0-T TOF MR angiography (P <.01, respectively). Intracranial high-spatial-resolution TOF MR angiography at 3.0-T imaging provides diagnostic improvement in studies of cerebrovascular disease.     

Bone marrow patterns in aplastic anemia: observations with 1.5-T MR imaging

Six patients diagnosed as having aplastic anemia underwent magnetic resonance (MR) imaging. The bone marrow in the lumbar spine, pelvis, and proximal femora was examined in each case. One patient had a normal marrow signal intensity (SI) and pattern and was considered cured of disease. The other patients had varying numbers of focal low-SI areas interspersed with high-SI areas in the marrow of the spine. The pelves and proximal femora of all patients had diffuse high-SI marrow without focal abnormalities. Biopsy of a lumbar vertebral body in one patient demonstrated that the focal low-SI areas may have been islands of active hematopoietic cells scattered in otherwise fatty marrow. MR may prove to be a valuable, noninvasive method of following the response of patients with aplastic anemia to therapy; more investigation is necessary before this can be definitely concluded.     

Gallbladder carcinoma: evaluation with MR imaging

Magnetic resonance (MR) images of 19 patients with histologically proved gallbladder carcinoma were retrospectively reviewed to determine the appearance of the primary tumor, and to assess the ability of MR imaging to demonstrate the various modes of tumor spread beyond the gallbladder. The primary tumor, as well as tumor spread beyond the gallbladder, was hyperintense on T2-weighted images and hypointense on T1-weighted images when compared with the liver parenchyma. Liver invasion and metastasis could be depicted by MR imaging with both sequences, unless the tumors were small or the extent of invasion was minimal. Duodenal invasion was difficult to evaluate because of motion artifacts, paucity of fat, and partial volume effects. T1-weighted images readily demonstrated extension of the tumor to the hepatoduodenal ligament and para-aortic region with good contrast between tumor and surrounding tissue. The extent of tumor extension to the blood vessels was also easily evaluated because of flow void in the vasculature. MR imaging can help determine the extent of gallbladder carcinoma and can contribute to the staging of this disease.     

Feasibility study of 3-T MR imaging of the skin

The purpose of this study was to assess the quality of 3-T magnetic resonance (MR) imaging of the skin, to describe skin anatomy at 3 T and to discuss future prospects of skin MRI. A 7-cm single-element surface receiver coil was developed for our 3-T MRI system. Thin sections were obtained with a three-dimensional FIESTA acquisition sequence and a spin-echo T1-weighted sequence (SET1). Prospective analysis was performed twice by two radiologists independently. Thirty-six healthy volunteers were included and underwent MRI on the face and the calf. Image quality was assessed regarding visibility of skin layers and quantification of artefacts. High field strength MR enables imaging of the skin with a high spatial in-plane resolution (87–180 μm), the total examination lasting 15–20 min. Image quality was excellent for the calf (mean SET1 quality = 96%) with a high intra- and interobserver correlation (SET1 kappa coefficient concerning visibility of epidermis, dermis and hypodermis ≥ 0.84). Motion artefacts resulted in a small loss of quality and reproducibility for the face. In conclusion, 3-T MR allows high spatial resolution imaging of the skin and can potentially provide an accurate noninvasive means of analysing the skin.