Orbit: initial experience with surface coil spin-echo MR imaging at 1.5 T

Fifty-nine cases in which surface coil MR imaging of the orbit was performed were reviewed. MR imaging was performed with spin-echo techniques at 1.5 T with both short repetition time/echo time (TR/TE) and long TR/TE sequences in all cases. In all patients short TR/TE images were obtained with small-diameter surface coils; long TR/TE images were usually obtained with a standard head coil. Surface coil MR appears to be an important adjunct in state-of-the-art orbital imaging. Orbital MR imaging may be most useful, providing information not available on computed tomography (CT), in identifying lesions in the orbital apex, superior orbital fissure, and optic canal; differentiating inflammatory pseudotumor from malignancy in clinically similar patients; characterizing lesions containing hemorrhage or other paramagnetic material; defining the posterior extent of optic pathway gliomas; and detecting abnormal flow in intraorbital vascular structures. CT seems to be superior to MR imaging in the evaluation of small perioptic meningiomas, especially those that are calcified.     

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.     

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.     

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.     

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.     

MR imaging of the larynx at 1.5 T

The normal magnetic resonance (MR) anatomy of the larynx at high field strength (1.5 T) was studied in 2 normal excised larynges and 62 subjects without laryngopharyngeal disease. The two normal excised larynges were imaged using a 1.5 T MR scanner with a 3 in diameter circular surface coil and a GE 9800 CT scanner. The larynges were sectioned transversely and the MR and CT images compared to gross and histologic sections. Unossified hyaline cartilage was intermediate in signal intensity on T1-weighted and proton density images and low in intensity on T2-weighted images. The signal intensity from ossified cartilage was determined by the amount of fatty marrow and was high in intensity on T1-weighted and proton density images and low to intermediate in intensity on T2-weighted images. A chemical shift artifact from high intensity fatty marrow obscured the calcified or ossified cortex of the major laryngeal cartilages along the frequency encoding axis. The epiglottic cartilage demonstrated an intermediate signal intensity on T1-weighted images and higher intensity on proton density and T2-weighted images. The intralaryngeal muscles were well demonstrated as low intensity structures. The conus elasticus and the vocal ligaments were not recognized as distinct structures. However, the quadrangular membrane and a previously undescribed membrane separating the preepiglottic and paralaryngeal spaces were shown on MR as low intensity linear structures. In the 62 subjects, MR at 1.5 T proved excellent for demonstrating the anatomical details of the major laryngeal cartilages, extra- and intralaryngeal muscles, ligaments, and soft tissues including the vocal cords, false vocal cords, laryngeal ventricles, aryepiglottic folds, preepiglottic space, and paralaryngeal spaces. Visibility and intensity of muscles, ligaments, and soft tissues did not depend on age or sex. The intensity pattern of the thyroid and cricoid cartilages demonstrated wide variations in the same sex and age groups, depending on the degree of ossification. However, they did show more high intensity foci in older men than in younger women. Magnetic resonance showed better contrast resolution and finer detail than CT scans in the same subjects. Magnetic resonance imaging at 1.5 T, with either a saddle-shaped neck surface coil or a 3 in diameter circular surface coil, provides high contrast and high spatial resolution images and could be useful for the diagnosis of lesions of the larynx.(ABSTRACT TRUNCATED AT 400 WORDS)     

Surface coil proton MR imaging at 2 T

We describe the design and application of surface coils for magnetic resonance (MR) imaging at high resonance frequencies (85 MHz). Circular, rectangular-frame, and reflector-type surface coils were used in the transmit-and-receive mode. With these coils, the required radio frequency power is reduced by factors of two up to 100 with respect to head and body coils. With the small, circular coils, high-resolution images of a small region of interest can be obtained that are free of foldback and motion artifacts originating outside the field of interest. With the rectangular-frame and reflector coils, large fields of view are also accessible. As examples of applications, single- and multiple-section images of the eye, knee, head and shoulder, and spinal cord are provided.     

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.     

Acute spinal cord injury: MR imaging at 1.5 T

Thirty-seven magnetic resonance (MR) imaging studies were performed with a 1.5-T magnet and surface coils in 27 patients with suspected spinal cord injuries. Imaging was performed 1 day to 6 weeks after injury. Cord abnormalities were seen with MR in 19 patients, while skeletal and/or ligamentous injuries were seen in 21 (78%). Three types of MR signal patterns were seen in association with cord injuries. Acute intraspinal hemorrhage was seen in five patients with cord injuries and demonstrated decreased signal intensity on T2-weighted images obtained within 24 hours of injury. Cord edema and contusion had high signal intensity on T2-weighted images and were observed in 12 cases with cord injury. Neurologic recovery, determined in 16 patients, was insignificant in patients with intraspinal hemorrhage; however, patients with cord edema or contusion recovered significant neurologic function. MR at 1.5 T is extremely useful in the diagnosis of acute cord injury and also demonstrates potential in predicting neurologic recovery.     

Acute hypertensive intracranial hemorrhage: MR imaging at 1.5T

Twelve patients with acute hypertensive intracranial hemorrhage underwent magnetic resonance (MR) imaging within 7 days after the ictus. T1-weighted (TR = 400 msec; TE = 20 msec) and T2-weighted (TR = 2000 msec; TE = 80 msec) images were obtained on a 1.5 Tesla MR system. Signal intensities of hematomas were carefully evaluated and were compared with white matter intensity. A 9-hour-old hematoma was mildly hypointense on T1-weighted images, and was mildly hyperintense on T2-weighted images, suggesting a reflection of the high water content. On T2-weighted images, thin peripheral hypointense rim, probably due to deoxyhemoglobin, was also observed. Both of 15-hour-old hematoma and 21-hour-old hematoma had peripheral hypointensity on T2-weighted images. Both of 39-hour-old hematoma and 43-hour-old hematoma had central hyper-intensity on T1-weighted images and iso-to-mild central hypointensity on T2-weighted images, suggesting a reflection of decreased water content. A 3-day-old hematoma had thin peripheral iso-to-mild hyperintense rim on T1-weighted images, presumably due to intracellular methomoglobin. A 5-day-old hematoma had thin peripheral hyperintense rim on T2-weighted images, probably due to free methemoglobin. A 7-day-old hematoma was hyperintense on T1-weighted images and was mildly hypointense to hyperintense on T2-weighted images, presumably due to mixed intracellular methemoglobin and free methemoglobin.     

The knee: surface-coil MR imaging at 1.5 T1

Seven normal knees (in five volunteers) and seven injured knees (in seven patients) were examined by high-resolution magnetic resonance (MR) imaging at 1.5 T with a surface coil. Seven medial meniscal tears, three anterior cruciate ligament tears, one posterior cruciate ligament avulsion, an old osteochondral fracture, femoral condylar chondromalacia, and one case of semimembranous tendon reinsertion were identified. MR images correlated well with recent double-contrast arthrograms or results of surgery. All tears were identified in both the sagittal and coronal planes. Because of its ability to demonstrate small meniscal lesions and ligamentous injuries readily, MR imaging with a surface coil may eventually replace the more invasive arthrography.     

Orbital fractures: surface coil MR imaging

Twenty-six patients with orbital fractures diagnosed with plain radiography and computed tomography were examined with surface coil magnetic resonance (MR) imaging. Fifteen patients had blow-out fractures, and 11 had maxillofacial complex fractures. In all patients with blow-out fractures, the location of the fracture was precisely indicated by the presence of prolapsed orbital fat. Incarceration of the extraocular muscle or orbital fat was correctly diagnosed with MR imaging, which was less sensitive in depicting maxillofacial fractures but was useful in assessment of soft-tissue involvement. Postoperative follow-up MR studies provided valuable information about the cause of motility impairment. While T1-weighted images are useful for the detection of the fracture site, both T1- and T2-weighted images are usually necessary for evaluating soft-tissue lesions. The results of this study indicate that surface coil MR imaging is an important adjunct procedure in the diagnosis and treatment of orbital fractures.     

高场强原发性肝癌MR表现及分析

目的：分析高场强下原发性肝癌的MRI表现。方法：收集经手术或尸检病理证实的原发性肝癌MR资料43例，其中巨块型肝癌32例，其中伴子灶3例，结节型5例，小肝癌6例。设备为GE1．5T超导signa advantage MR。应用SET1WI，FSEPDWI，T2WI进行轴位扫描，所有病均行增强扫描。结果：肝癌在T1WI呈高、等、低信号，在T2WI呈高信号，部分肿瘤内部信号不均，肝癌的强化程度主要取决于肿瘤血供的多少，肝癌的包膜由纤维组织构成，表现为低信号环，无包膜的肿瘤门静脉侵犯发生率高，肿瘤的信号及包膜与其病理分级有一定的相关性。结论：MRI对反映原发性肝癌的病理特征有其独特的优越性。     

Normal prostate and adjacent structures: MR imaging at 1.5 T

Pelvic magnetic resonance images obtained at 1.5 T of 29 male patients with no known genitourinary tract disease were retrospectively reviewed. Normal anatomic features of the prostate and its adjacent structures were studied with spin echo techniques with short and long repetition times/echo times (TR/TE). Long TR/TE (T2-weighted) images routinely showed differentiation of peripheral and central prostatic zones, as well as a separate periprostatic venous plexus. Guidelines were developed to optimize imaging of the relationship of the prostate to adjacent structures.     

Interventional MR imaging at 1.5 T: quantification of sound exposure

Sound pressure levels (SPLs) during interventional magnetic resonance (MR) imaging may create an occupational hazard for the interventional radiologist (ie, the potential risk of hearing impairment). Therefore, A-weighted and linear continuous-equivalent SPLs were measured at the entrance of a 1.5-T MR imager during cardiovascular and real-time pulse sequences. The SPLs ranged from 81.5 to 99.3 dB (A-weighted scale), and frequencies were from 1 to 3 kHz. SPLs for the interventional radiologist exceeded a safe SPL of 80 dB (A-weighted scale) for all sequences; therefore, hearing protection is recommended.