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.     

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.     

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 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)     

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.     

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.     

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。     

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.     

Hepatic focal nodular hyperplasia: MR imaging at 1.0 and 1.5 T.

Ten cases of hepatic focal nodular hyperplasia (FNH) were studied with magnetic resonance (MR) imaging. Proof of diagnosis was by needle biopsy or follow-up of as long as 5 years. Both short TR/TE and long TR/TE images were obtained. The most common finding was isointensity of the lesion relative to liver parenchyma with all pulse sequences. A central scar was seen in only one patient and was hyperintense on long TR/TE images. Slight hyperintensity of the lesion on short TR/TE and long TR/TE images was seen in two cases. Textural heterogeneity was present in only one of these. The most common presentation in our series was a visually isointense lesion relative to liver on short TR/TE images and an isointense or slightly hyperintense lesion on long TR/TE images. A review of the literature and the present findings suggest that FNH has a variable appearance on MR images.     

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.     

Contrast optimization for the detection of focal hepatic lesions by MR imaging at 1.5 T

The relative efficacies of different spin-echo pulse sequences at 1.5 T were evaluated in the detection of focal hepatic disease. Pulse sequences compared were spin-echo with a repetition time (TR) of 200 msec and echo time (TE) of 20 msec, with six excitations; TR = 300 msec, TE = 20 msec, with 16 excitations (T1-weighted sequences); and a double spin-echo with TR = 2500 and TE = 25 and 70, with two excitations (proton-density-weighted and T2-weighted pulse sequences, respectively). Respiratory-motion compensation, which involved a recording of the phase-encoding gradients (Exorcist), was used for the last two sequences. Spin-echo with TR = 2500 msec and TE = 70 msec was superior in lesion detection and contrast-to-noise ratio. The proton-density-weighted and T2-weighted sequences with respiratory compensation produced better artifact suppression than did the short TR, short TE T1-weighted sequence with temporal averaging. In contradistinction to prior results at 0.6 T, T2-weighted pulse sequences appear superior to T1-weighted pulse sequences with multiple excitations for both lesion detection and artifact suppression at 1.5 T.     

Reduced-bandwidth MR imaging of the head at 1.5 T1

A decrease in the magnetic resonance (MR) imaging bandwidth can be used to increase the signal-to-noise ratio (S/N) at constant imaging time or to maintain the S/N for reduction of imaging time. The effect of bandwidth reduction from the default value of 16 kHz to 8 kHz was evaluated prospectively in 50 patients referred for MR imaging of the head. On intermediate (2,000/30 [repetition time msec/echo time msec]) and more T2-weighted (2,000/90) studies, there were no definite missed diagnoses and no diagnostically important changes in lesion characteristics when the reduced-bandwidth technique was used to obtain half- or quarter-time studies, excluding differences attributable to unintentional changes in patient position between image acquisitions. Chemical shift misregistration artifacts associated with reduced bandwidth are easily recognized with experience and do not interfere with diagnosis, as the artifacts occur in characteristic locations and diminish in most anatomic locations with increasing echo time. This study suggests the feasibility of reduced-bandwidth techniques in clinical MR imaging of the head at high field strength to achieve an increased S/N, to decrease imaging time, or to obtain images in additional projections.