Ankle: surface coil MR imaging at 1.5 T

High-field surface coil magnetic resonance (MR) images were obtained of 12 ankles: two from healthy volunteers, seven from patients, and three from fresh cadavers. The cadaver ankles were sectioned in the coronal, sagittal, and axial planes for direct comparison with the MR images. Plain film confirmation of pathologic conditions was obtained in all patients, and five underwent arthroscopy or surgery, or both. MR imaging provided excellent delineation of ligaments and cartilaginous structures in all cases.     

Intracranial hemorrhage: gradient-echo MR imaging at 1.5 T. Comparison with spin-echo imaging and clinical applications

Fifty-seven patients with hemorrhagic intracranial lesions were examined with magnetic resonance (MR) imaging at 1.5 T with use of both spin-echo (SE) and gradient-echo-acquisition (GEA) techniques to assess the clinical applications and limitations of GEA in evaluation of intracranial hemorrhage at high field strength. All GEA images were obtained with a long echo time and short flip angle to emphasize T2*-based contrast. In 30 of 61 cases, GEA images demonstrated more hemorrhagic lesions than SE images. In 14 of 61 cases, GEA images failed to depict the lesion or obscured the specific diagnosis (as depicted by SE MR imaging). The authors believe that GEA imaging in its current form has a limited but definite adjunctive role in the evaluation of intracranial hemorrhage at high field strength.     

Integrated MR imaging and spectroscopy with chemical shift imaging of P- 31 at 1.5 T: initial clinical experience

A section-selective three-dimensional phosphorus-31 chemical shift imaging (CSI) experiment was evaluated as the spatial localization method for spectroscopy in an integrated clinical magnetic resonance (MR) imaging and spectroscopy examination. The results of a CSI experiment can be displayed as either spectra related to specific voxels or "metabolite maps," in which the relative concentration of a given metabolite is displayed as an overlay of the MR image. This method was applied to the study of a soft-tissue mass and to a meningioma. The total imaging time in each case was 17 minutes with a voxel size of 27 cm3 in the extremity and 64 cm3 in the brain. The total time to set up this part of the study was about 10 minutes. No additional shimming was necessary when the center of the field of view selected for the CSI experiment was located at or near isocenter. The promising results obtained with this approach make the CSI method an attractive choice of spatial localization method.     

Intracranial hemorrhagic lesions: evaluation with spin-echo and gradient-refocused MR imaging at 0.5 and 1.5 T

Twenty patients with intracranial hemorrhage were examined with magnetic resonance (MR) imaging at 0.5 and 1.5 T within 2 hours on the two imagers for lesions less than 30 days old and within 24 hours for lesions older than 30 days. MR studies included T1- and T2-weighted spin-echo (SE) and T2*-weighted gradient-refocused (GR) pulse sequences at each field strength. The number of lesions identified and the characteristics (ie, signal intensity of the margin, body, and core) of each hemorrhagic lesion were assessed and compared by means of the three pulse sequences at each field strength. Lesion depiction and characterization were superior (P less than .01) at 1.5 T with T2-weighted SE sequences. Improved depiction and characterization of lesions 300 or more days old (P less than .01) accounted for this result. With the GR sequence, depiction and characterization were similar at both field strengths. The GR sequence did not provide significant additional information about hemorrhage at 1.5 T in this series, but it improved depiction and characterization of hemorrhage at 0.5 T.     

Diffusion-tensor MR imaging at 1.5 and 3.0 T: initial observations.

Diffusion-tensor MR imaging was compared at 1.5 and 3.0 T. With sufficient signal-to-noise ratio, we found no differences in fractional anisotropy. With a 40% higher signal-to-noise ratio at 3.0 T, higher resolution could be obtained without introduction of noise-related errors, albeit at the cost of increased geometric distortions caused by 3.0-T magnetic field inhomogeneities.     

Dynamic sequential MR imaging of focal liver lesions: initial experience in 22 patients at 1.5 T

The feasibility of dynamic sequential magnetic resonance (MR) imaging of focal hepatic lesions using Gd-diethylenetriamine pentaacetic acid (DTPA) was evaluated in this study. Three patients with hepatocellular carcinoma, 12 patients with metastases, and 7 patients with hemangiomas were studied with pre- and postcontrast multislice spin echo (SE) images using a repetition time of 500 ms and an echo time of 15 ms. The dynamic distribution phase of Gd-DTPA (0.1 mmol/kg) was investigated by using a sequential, transverse partial flip imaging sequence [fast low angle shot (FLASH)] before and after intravenous administration of Gd-DTPA. The lesion-liver contrast-to-noise ratio showed a great variability in patients with metastases and was significantly improved following administration of Gd-DTPA in patients with hemangiomas, two patients with hepatocellular carcinoma, and eight patients with metastases both on FLASH and SE images. Hemangiomas appeared darker than liver parenchyma on precontrast SE and FLASH images, increasingly enhanced over 5 min postinjection (pi) on FLASH images, and were still greatly enhanced at 10 min pi on SE images. During the dynamic sequential image acquisition the contrast enhancement of hemangiomas was significantly different from the enhancement observed in malignant lesions. The results of this study indicate the clinical potential of dynamic sequential imaging for the MR assessment of focal hepatic lesions.     

High-resolution MR imaging of pituitary microadenomas at 1.5 T: experience with Cushing disease

The MR images of 27 patients with clinically and biochemically suspected Cushing disease were evaluated retrospectively in a blinded fashion. The MR interpretation was compared with detailed operative diagrams and operative and pathologic reports. The examinations were performed on a 1.5-T MR system with thin-section sagittal and coronal T1-weighted (short TR/TE) images. Each pituitary half was considered separately (54 "halves"). Twenty-one pituitary halves were considered to have glandular abnormalities on MR. Compared with surgical findings, 17 MR findings were true positives and four were false positives (one pars intermedia cyst, three normal tissue). Of the 33 pituitary halves considered normal on MR, 26 were true negatives and seven were false negatives. MR had an overall sensitivity of 71% and a specificity of 87% for these adrenocorticotropic hormone (ACTH)-secreting pituitary adenomas. A focal glandular hypointensity identified on coronal images was the most sensitive predictor of adenoma location. Sagittal images were not useful in either detection or localization. Upward convexity of the gland and deviation of the stalk were less useful indicators. Abnormalities of the sellar floor were the least reliable. In comparison with the capabilities of CT detection of microadenomas described in the current literature, it appears that high-field thin-section MR of the sella is the most sensitive imaging method for preoperative localization of ACTH-secreting adenomas in patients with Cushing disease.     

Improved MR imaging of the orbit at 1.5 T with surface coils

A method for obtaining localized high-resolution magnetic resonance (MR) images of the eye and orbit is demonstrated. The method uses modified surface receiver coils placed immediately adjacent to the anatomy to detect the MR signal. Surface coils provide enhanced sensitivity for imaging voxels close to the surface of the body while limiting the received patient-generated noise. The resulting improvement in signal-to-noise ratio allows for a reduction in the imaging voxel size to about 0.5 X 0.5 X 5 mm in scan times of 3.4-5 min. At this level of resolution, anatomic detail in the orbital region previously unobservable in MR images is seen.     

Contrast-enhanced MR imaging of the breast at 3.0 and 1.5 T in the same patients: initial experience

PURPOSE: To establish a pulse sequence for dynamic contrast material-enhanced magnetic resonance (MR) imaging of the breast at 3.0 T and to prospectively compare MR imaging at 3.0 T with MR imaging at 1.5 T in the same patients. MATERIALS AND METHODS: A prospective intraindividual internal review board-approved study was performed in 37 women with 53 lesions (25 breast cancers, 28 benign focal lesions) who underwent contrast-enhanced dynamic bilateral subtraction MR imaging twice, once at 1.5 T with a standard technique (voxel size, 1.44 mm3) and once at 3.0 T (voxel size, 0.45-0.72 mm3) with variable repetition time and flip angle settings. Written informed consent was obtained. Sagittal single breast high-spatial-resolution MR imaging was performed with active fat suppression. Image quality, number and features of enhancing lesions, and Breast Imaging Reporting and Data System categories were compared by using the Wilcoxon matched-pairs signed rank test and Student t test for matched pairs. Diagnostic confidence was compared by using a receiver operating characteristic (ROC) analysis. RESULTS: With repetition time prolonged to account for longer T1 relaxation times at 3.0 T and a flip angle of 60 degrees, enhancement rates at 3.0 T were substantially below those at 1.5 T. In two patients with benign lesions, enhancement was rated as insufficient to establish diagnosis. When parameter settings were kept equivalent, equivalent enhancement rates were observed with both systems. With these settings, 3.0-T MR imaging yielded homogeneous signal intensity over the entire field of view. No dielectric resonance effects were observed. Overall image quality scores for the dynamic series were slightly higher at 3.0 T (P<.01). A total of 49 lesions were prospectively identified with both systems. Owing to substantial patient motion at 1.5 T, two malignant lesions in one patient were visualized at 3.0 T only. At 3.0 T, differential diagnosis of enhancing lesions was possible with higher diagnostic confidence, as reflected by a larger area under the ROC curve (P<.05). CONCLUSION: Initial experiences indicate that contrast-enhanced MR imaging at 3.0 T is nearing readiness for clinical use.     

Achilles tendon: MR imaging at 1.5 T

Thirty magnetic resonance (MR) examinations of the Achilles tendon were performed: 20 from patients without suspected tendon abnormalities; ten from patients with suspected tendon abnormalities. The appearance of the normal Achilles tendon is hypointense and flattened. Partial tears appeared as high-signal intratendinous collections, complete acute ruptures appeared as tendinous discontinuity, and uncomplicated surgical repairs appeared as areas of tendinous continuity with inhomogeneous signal in the operative site. Chronic tendinitis appeared as a diffuse thickening of the tendon. MR imaging of the Achilles tendon at 1.5 T enabled the determination of the degree of tendinous continuity, which may help with diagnosis, treatment, and the pacing of rehabilitation.     

Prostatic disorders: MR imaging at 1.5 T

Pelvic magnetic resonance (MR) images obtained at 1.5 T of 31 men with known genitourinary disease were reviewed retrospectively. In most, peripheral and central prostatic zones could be seen on axial images obtained with long repetition times/echo times (TRs/TEs). The prostate had no specific signal intensity that enabled differentiation between benign and malignant changes. Each patient with known extracapsular prostatic carcinoma had a peripheral zone defect--1 cm or greater in diameter with ill-defined borders and relatively lower signal intensity than that of the remainder of the peripheral zone--that correlated with the site of clinical-pathologic involvement. Correlation of a peripheral zone defect on long TR/TE images as a sign for extracapsular spread of prostatic cancer was 100% sensitive, yet 54% specific, with excellent interobserver agreement. Stage A2 and B1 prostatic carcinoma was not detected. Benign prostatic hyperplasia was seen as centrally located proliferation and nodularity, usually with discrete margins and a wide spectrum of low- to high-signal-intensity features. MR imaging may have a role in differentiating between intracapsular and extracapsular prostatic carcinoma.     

Prostatic carcinoma: staging with MR imaging at 1.5 T

Magnetic resonance (MR) imaging was used to stage prostatic carcinoma in 81 patients with a proved diagnosis. MR imaging findings were correlated with histologic findings regarding the local extent of disease (37 patieNts) and the presence of nodal metastases (51 patients). Tumor nodules were detected in the peripheral zone (PZ) in 34 of 37 patients and were of low signal intensity compared with the signal of the PZ. Hemorrhage in the PZ represented a problem in tumor detection and in tumor volume measurement. When multiple criteria for local tumor spread were combined, MR imaging had a sensitivity of 72%, a specificity of 84%, and an accuracy of 78% in the differentiation of stage A or B from Stage C or D disease. Assessment of seminal vesicle invasion was more accurate than assessment of direct extracapsular spread. In five patients, microscopic invasion of the capsule (stage C) was classified as stage B with MR imaging; from a clinical standpoint, this should not affect patient treatment and prognosis. The MR imaging sensitivity in the detection of lymph node metastases was 69%, with a specificity of 95% and an accuracy of 88%. In this study MR imaging proved reliable in the comprehensive evaluation and staging of prostatic carcinoma.     

Aneurysmal bone cysts: MR imaging at 1.5 T

Two patients with aneurysmal bone cysts of the pelvis were imaged using a 1.5-T magnetic resonance imaging device. Findings included multiple internal septations, cysts with fluid-fluid levels of varying intensity, and an intact rim of low-intensity signal completely surrounding the lesion. These findings allow a specific diagnosis of aneurysmal bone cyst to be made.     

Pituitary adenomas: high-resolution MR imaging at 1.5 T

The magnetic resonance (MR) images of 28 patients with surgically confirmed pituitary adenomas were retrospectively evaluated. The examinations were performed on a 1.5-T superconducting MR system using a multisection spin-echo technique with 3-mm-thick sections and a 256 X 256 matrix. T1- and T2-weighted images were obtained in sagittal and coronal planes. The MR findings were correlated with detailed operative reports and diagrams. There were 11 microadenomas and 17 macroadenomas. Ten of the microadenomas and all of the macroadenomas were accurately localized and their extent delineated, particularly on T1-weighted coronal sections. Adenomas typically appeared hypointense on T1-weighted coronal sections. The appearance on T2-weighted images was variable, and generally the lesions were less well seen. Involvement of parasellar structures, particularly the optic chiasm and cavernous sinuses, was accurately depicted. Cyst formation and hemorrhage could be characterized in some instances. In general, there was excellent correlation between MR imaging and operative findings.     

Testes and scrotum: MR imaging at 1.5 T

Magnetic resonance (MR) images of the scrotum were obtained at 1.5 T in 20 subjects, 13 patients with intrascrotal pathologic conditions and seven healthy subjects. Characteristic MR imaging signals obtained on T1- and T2-weighted images allowed differentiation of testis from epididymis and spermatic cord. Masses were differentiated from normal testicular parenchyma in all cases. Atrophic or ischemic testes had lower signal intensity than normal testes on T2-weighted images. Hematoma displayed a characteristic high intensity on both T1- and T2-weighted images. Intratesticular and extratesticular pathologic conditions were readily differentiated. These results suggest that MR imaging is useful in the diagnosis of scrotal and testicular abnormalities.     

MR imaging-guided prostate biopsy with a closed MR unit at 1.5 T: initial results

The authors evaluated a magnetic resonance (MR) imaging-compatible biopsy device comprising a needle guide that can be visualized with MR imaging and manipulated mechanically from outside the MR unit. With approval from the local ethics committee and patient consent, this device was tested in 12 patients by using a closed 1.5-T MR unit and a body phased-array coil. Patients had elevated prostate-specific antigen levels (6-60 ng/mL) and one or more areas in the prostate that were suspicious for carcinoma at prebiopsy MR imaging. Biopsy was performed with transrectal access and with the patient prone. A 16-gauge MR imaging-compatible needle was successfully positioned with the device, and between six and nine tissue cores were obtained in each patient. In one patient, two suspicious basal areas could not be reached with the device. Histologic analysis showed prostate cancer in five patients and prostatitis in six. No complications were observed. The device enabled MR imaging-guided core-needle biopsy of prostate areas suspicious for cancer on MR images.     

Comparison of single-shot fast spin-echo and conventional spin-echo sequences for MR imaging of the heart: initial experience

A conventional T1-weighted spin-echo (SE) magnetic resonance (MR) imaging sequence was compared with breath-hold and non-breath-hold half- Fourier single-shot fast SE MR sequences with black-blood preparation and high spatial resolution for imaging of various cardiac diseases. The optimized single-shot fast SE sequence provided better or equal image quality in less time. Breath-hold and non-breath-hold single-shot fast SE sequences may replace the conventional T1-weighted SE sequence for first-line cardiac MR imaging.