Thyroid imaging with high-field-strength surface-coil MR

Magnetic resonance (MR) imaging of the thyroid was performed with a 1.5-T system and local receiver coil in 19 "healthy" subjects and 34 patients with various focal and diffuse thyroid disorders. The normal gland was typically homogeneous with increased intensity relative to that of muscle on images obtained with long repetition times (TRs) and long echo times (TEs). Adjacent structures in the neck and upper mediastinum were well displayed. Thyroid nodules as small as 4-5 mm were identified. Follicular adenomas appeared as well-circumscribed nodules of heterogeneous intensity, increasing significantly in signal with long TRs/TEs. Colloid cysts and hemorrhagic cysts had homogeneous high signal with both short and long TRs/TEs. Two of three carcinomas were seen as poorly marginated lesions with associated cervical lymphadenopathy clearly depicted as increased intensity with long TRs/TEs. A follicular adenoma containing microscopic papillary carcinoma appeared similar to other benign adenomatoid nodules. A functioning nodule was isointense with normal gland at all pulse sequences. Characteristic patterns of diffuse abnormality were observed in cases of multinodular goiter, Hashimoto thyroiditis, and Graves disease, although additional cases are required to determine specificity. High-field-strength surface-coil MR imaging appears to be a sensitive method for identifying gross morphology of focal, multinodular, and diffuse disorders of the thyroid and involvement of surrounding structures in the neck.     

Tendons: high-field-strength, surface coil MR imaging

High-resolution magnetic resonance (MR) images of the tendons of the hands, wrists, feet, and ankles of six healthy volunteers and six cadavers were obtained using receive-only surface coils and reduced-field-of-view imaging. Normal anatomy was identified and compared with gross anatomic sections of the six cadavers. Experimentally produced tears of the calcaneal (Achilles) tendon in domestic swine were identified on MR images. The hands and feet of 11 patients were examined, and a variety of pathologic lesions were identified, including acute posttraumatic rupture, acute tenosynovitis, chronic tendonitis, and postsurgical complications. MR imaging provides inherently greater soft-tissue contrast than any other currently available imaging modality. With the use of surface coils and reduced-field-of-view imaging to enhance spatial resolution, MR imaging has become a valuable tool for imaging tendons. Advantages over other available modalities include excellent depiction of anatomic detail, superior contrast resolution, and the potential for multiplanar imaging.     

Infections of the musculoskeletal system: high-field-strength MR imaging

Twenty-two patients with clinical findings consistent with osteomyelitis, soft-tissue infection, or both were studied with magnetic resonance (MR) imaging at 1.5 T. Another 15 patients with joint effusion but no clinical or laboratory signs of infection served as controls. Soft-tissue abscesses, osteomyelitis, joint and tendon sheath effusion, and cellulitis were well depicted on MR imaging, allowing the correct diagnosis of presence and extent of infection in all but two cases. MR imaging was as sensitive as technetium-99m methylene diphosphonate bone scintigraphy in demonstrating osteomyelitis and was more specific and more sensitive than other scintigraphic techniques in demonstrating soft-tissue infections, primarily because of its superior spatial resolution. Computed tomography, performed in seven cases, was as accurate as MR imaging in demonstrating bone and soft-tissue infections. Infected and noninfected synovial effusions had the same signal intensity, but associated findings such as soft-tissue fluid collections or osteomyelitis made the distinction possible.     

慢性多发性硬化病灶:高场MRI特征

目的阐明多发性硬化(MS)病灶在磁敏感加权成像MR影像对比的机制以及评估铁及髓磷脂对产生MR影像对比的组织关联性。方法每例病人均提供了机构审查委员会批准的个人受试者协议的书面同意书。21例MS病人进行了     

Heating of the scrotum by high-field-strength MR imaging

Sterility can occur in mammals if spermatogenic tissue is acutely or chronically heated to levels equal to or greater than body temperature. High-field-strength MR imaging has been shown to elevate tissue temperatures, particularly if high levels of RF radiation are used. To determine if MR imaging above the recommended level for RF radiation is associated with heating of the scrotum, scrotal skin temperatures were measured in eight subjects immediately before and after MR imaging of the scrotum with a 1.5-T, 64-MHz MR scanner at mean whole-body average specific absorption rates ranging from 0.56 to 0.84 W/kg (mean, 0.72 W/kg). The average imaging time was 23 min. A statistically significant (p less than .01) increase in average scrotal skin temperature was associated with MR imaging (before MR imaging, 30.8 degrees C; after MR imaging, 32.3 degrees C). The largest change in temperature was 3.0 degrees C, and the highest temperature measured was 34.1 degrees C. MR imaging at relatively high specific absorption rates produced a statistically significant increase in average scrotal skin temperature. However, the recorded temperatures were below the threshold known to affect spermatogenesis in mammals.     

Cortical deactivation in mild cognitive impairment: high-field-strength functional MR imaging

PURPOSE: To prospectively identify brain regions in which task-related changes in activation during a memory encoding task, measured with functional magnetic resonance (MR) imaging, correlate with degree of memory impairment across Alzheimer disease (AD), mild cognitive impairment (MCI), and elderly control subjects. MATERIALS AND METHODS: The institutional review board approved this HIPAA-compliant study, and each patient gave written informed consent. Seventy-five subjects (mean age, 72.9 years+/-7.2 [standard deviation]; 37 men, 38 women)-13 patients with mild AD, 34 individuals with amnestic MCI, and 28 healthy elderly control subjects-were imaged at 4.0 T during novel encoding (NE) and familiar encoding (FE) of face-name pairs presented within a block design for later retrieval. Blood oxygen level-dependent (BOLD) changes were assessed across the entire brain for each group. Between-subject analysis identified brain regions demonstrating a monotonic increase or decrease in activation magnitude, from control subjects to patients with MCI to patients with mild AD. BOLD response was also correlated with score on the delayed portion of the California Verbal Learning Test (CVLT). RESULTS: In controls, the task elicited positive activation (NE>FE) in the dorsolateral prefrontal, lateral parietal, and medial temporal regions, and negative activation (FE>NE) in the midline frontal and parietal regions. Along the spectrum from control subjects to patients with AD, there was decreasing activation in the medial temporal lobe (MTL), including the hippocampus and parahippocampal and fusiform gyri, and increasing activation in the posteromedial cortices (PMCs), primarily in the precuneus and posterior cingulate gyrus. Activation magnitude in the PMCs significantly (P<.001, r=-0.502) correlated with CVLT score. CONCLUSION: Compared with activation in the MTL, deactivation in the PMCs could be a more sensitive marker of early AD at functional MR imaging.     

Intraoperative high-field-strength MR imaging: implementation and experience in 200 patients

PURPOSE: To review the initial clinical experience with intraoperative high-field-strength magnetic resonance (MR) imaging of brain lesions in 200 patients. MATERIALS AND METHODS: Two hundred patients (mean age, 46.1 years; range, 7-84 years), most of whom had glioma or pituitary adenoma, were examined with a 1.5-T MR imager equipped with a rotating operating table and located in a radiofrequency-shielded operating theater. A navigation microscope placed inside the 0.5-mT zone and used in combination with a ceiling-mounted navigation system enabled integrated microscope-based neuronavigation. The extent of resection depicted at intraoperative imaging, the surgical consequences of intraoperative imaging, and the clinical practicability of the operating room setup were analyzed. RESULTS: Seventy-seven resections with a transsphenoidal approach, 100 craniotomies, and 23 burr-hole procedures were performed. In 55 (27.5%) of 200 patients, intraoperative MR imaging had immediate surgical consequences (eg, extension of resection in 39% of patients with pituitary adenoma or glioma). In 108 patients the navigation system was used, and for 37 of those patients, functional imaging data were integrated into the navigation system. There was nearly no difference in quality between pre- and intraoperative images. Intraoperative workflow with intraoperative patient transport for imaging was straightforward, and imaging in most cases began less than 2 minutes after sterile covering of the surgical site. No complications resulted from high-field-strength MR imaging. CONCLUSION: The high-field-strength MR imager was successfully adapted for intraoperative use with the integrated neuronavigation system. Intraoperative MR imaging provided valuable information that allowed intraoperative modification of the surgical strategy.     

Development of the human cerebellum observed with high-field-strength MR imaging

A retrospective study of 160 pediatric subjects, aged 32-410 weeks after conception, was conducted to determine the normal developmental patterns of the human cerebellum by means of magnetic resonance (MR) imaging. On the basis of axial T2-weighted spin-echo images (repetition time, 3,000 msec; echo time, 120 msec), which provided the best contrast between gray matter and white matter, five distinct developmental stages were defined. At term, the medial lemnisci as well as the parasagittal cerebellum were myelinated. The appearance of myelin in the middle cerebellar peduncles and the basilar pons preceded that in the corpus medullare of the cerebellum. The normal age ranges for the different stages were defined with statistical analysis. These ranges are applicable to the daily routine of image interpretation. The sequence of myelination in the cerebellum observed at MR imaging correlates with the known patterns observed in pathologic studies but lags behind by an average of 6 months.     

Comparison of CT, low-field-strength MR imaging, and high-field-strength MR imaging. Work in progress

To assess objectively the sensitivity and specificity of low-field-strength (0.064 T) magnetic resonance (MR) imaging, a prospective blind study of 280 examinations was performed to compare low-field-strength MR imaging with computed tomography (CT) and with high-field-strength (1.5-T) MR imaging of the cranium. The sensitivity (defined as the true-positive rate) with high-field MR imaging was superior to that with low-field MR imaging and CT in helping detect overall abnormalities. Sensitivities were generally similar over a broad range of specific cranial central nervous system diseases. Low-field and high-field MR imaging were equivalent in the blind diagnoses of neoplasms and white matter disease, whereas low-field MR and CT were equivalent in the blind diagnoses of contusion, subdural and epidural hematoma, sinus disease, normality, and abnormality. The specificities with low-field MR imaging and CT were substantially better than those with high-field MR imaging.     

Avascular necrosis of the femoral head: high-field-strength MR imaging with histologic correlation

Magnetic resonance (MR) images, contact radiographs, and histologic sections of six femoral head specimens with avascular necrosis were correlated. A low-signal-intensity band or ring represented the repair tissue interface surrounding a high-signal-intensity necrotic marrow segment. Large segmental areas of low signal intensity were observed on T1-weighted images when the lesion consisted of necrotic bone with amorphous marrow debris and adjacent thickened trabecular bone with mesenchymal repair tissue infiltration. On intermediate-weighted images, however, mesenchymal repair tissue, which was located inferior to the necrotic zone, increased markedly in signal intensity, permitting distinction from low-intensity necrotic bone with amorphous marrow debris. When trabecular thickening with collapse predominated, segmental areas of low signal intensity with both sequences were found. MR signal intensities used in combination with anatomic configuration and location may provide information of potential therapeutic importance regarding tissue composition and stage of disease.     

Superparamagnetic iron oxide: Detection of focal liver lesions at high-field-strength MR imaging

AMI-25 was evaluated at 1.5 T as a superparamagnetic iron oxide contrast agent for the liver. Sixteen patients with up to five suspected focal liver lesions were examined with T1-, proton-density—, and T2-weighted spin-echo sequences before and after intravenous administration of AMI-25 (15 μmol/kg iron). The contrast-to-noise ratio (C/N) increased from 1.8 to 3.5 on 600/15 (TR msec/TE msec) images and from 1.7 to 7.9 on 2,500/15 images after AMI-25 administration (P <.01). C/N did not change significantly on 2,500/90 images. Two blinded readers counted the number of lesions visible on unenhanced and contrast-enhanced images, with the 32 sets of images of the 16 patients presented in random order. Both readers identified more lesions on AMI-25–enhanced images, but the difference was not statistically significant (P >.05). Two patients reported minor side effects (flushing, sensation of heat, lower back pain). On the basis of the results obtained in a limited number of patients, the authors conclude that at 1.5 T, AMI-25 does not significantly improve the detection of focal liver lesions on conventional spin-echo images.     

MR imaging of mucocutaneous malignant melanoma in the head and neck

MR imaging was performed in three patients with mucocutaneous malignant melanoma of the head and neck, and surgical specimens were investigated in MR-pathological correlation. Two of 3 cases were revealed to be melanotic melanoma; one arose in the maxillary sinus, and another in the bulbar conjunctiva. The remaining case was amelanotic melanoma originating in the nasal cavity. Two cases of melanotic melanoma showed different intensity on T1WI according to the melanin concentration; the more the melanin-producing process existed, the higher intensity in the tumor was shown. On T2WI there were also some differences in signal intensity; the case having more concentration of melanin changed lower partially in the areas where very high intensity was noted on T1WI, while another case remained unchanged. These findings are based on the inherent paramagnetic effect mostly compatible with the previous reports. On the other hand, the amelanotic melanoma was demonstrated as an intermediate intensity both on T1- and T2WI. Because of the higher incidence of hemorrhage in/around the tumor, it is an important diagnostic clue to this tumor, as in our case of amelanotic type. On reviewing the three cases, we consider that MR imaging offers a useful adjunct in the diagnosis of malignant melanoma.     

MR imaging of malignant uveal melanoma: role of pulse sequence and contrast agent

To determine the most sensitive pulse sequence and to clarify the role of each pulse sequence in the MR diagnosis of uveal malignant melanoma, noncontrast T1- and T2-weighted, and postcontrast T1-weighted, spin-echo images were compared blindly and independently by two experienced observers. Thirty uveal malignant melanomas, preselected by ophthalmoscopy and sonography for size greater than 2 mm, were examined with a 1.5-T superconducting MR unit with an orbital surface coil. Fifteen tumor studies were done after the patient was injected with gadopentetate dimeglumine. Postcontrast T1-weighted images were the most sensitive in detecting melanomas, demonstrating tumors 2 mm in height accurately on axial planes and 1.6 mm in height on combined orthogonal planes. The contrast-to-noise ratio between melanoma and vitreous fluid was greatest on postcontrast T1-weighted images (average, 72.1), followed by noncontrast T1-weighted images (average, 32.9), and then by T2-weighted images (average, -21.2). Postcontrast T1-weighted images also proved useful in differentiating melanomas from subretinal fluid collections when combined with noncontrast images. We conclude that postcontrast T1-weighted images are most helpful in detecting small uveal melanomas and in differentiating melanomas from subretinal fluid collections.     

Intramuscular metastasis from malignant melanoma: MR findings

We present a rare case of intramuscular metastasis from malignant melanoma. The lesion showed intermediate to high signal intensity on T1-weighted magnetic resonance (MR) images and mixed signal intensities containing high and low signals on T2-weighted images. The signal intensity on T1-weighted images, which is due to the paramagnetic effect of melanin, is a characteristic MR finding of this entity. Received: 10 June 1999 Revision requested: 7 July 1999 Revision received: 9 August 1999 Accepted: 9 August 1999     

MR imaging of intracranial metastatic melanoma

Ten patients with intracerebral metastases from malignant melanoma were evaluated with magnetic resonance (MR) imaging performed at 1.5 T using spin-echo techniques. On the basis of histopathologic findings in three of 10 cases and CT appearances in all 10 cases, three patterns were identified on analysis of MR signal intensities in both short repetition time/echo time (TR/TE) and long TR/TE spin-echo scans. In comparison to normal cortex, nonhemorrhagic melanotic melanoma appeared markedly hyperintense on short TR/TE images and isointense, mildly hypointense on long TR/TE images. Nonhemorrhagic, amelanotic melanoma appeared isointense or mildly hypointense on short TR/TE and isointense or mildly hyperintense on long TR/TE images. Hemorrhagic melanoma varied in appearance, depending on the stage of hemorrhage. Melanotic, nonhemorrhagic melanoma can be distinguished from early and late subacute hemorrhage by its signal intensity on long TR/TE images. Spin-echo MR appears to be the method of choice for diagnosing melanotic metastases.     

Hemorrhagic intracranial malignant neoplasms: spin-echo MR imaging

Twelve patients with 15 separate, spontaneously hemorrhagic, intracranial malignant lesions (seven primary gliomas, eight metastatic lesions) were examined with spin-echo magnetic resonance imaging at 1.5 T, and with computed tomography. The signal intensity patterns of these lesions, as seen on both short repetition time (TR)/short echo time (TE) and long-TR/long-TE spin-echo pulse sequences, were compared with the previously described appearance at 1.5 T of non-neoplastic intracerebral hematomas. The images of hemorrhagic intracranial malignancies showed notable signal heterogeneity, often with identifiable nonhemorrhagic tissue corresponding to tumor; diminished, irregular, or absent hemosiderin deposition; delayed hematoma evolution; and pronounced or persistent edema, compared with non-neoplastic hematomas. The demonstration of these characteristics in the appropriate clinical setting may suggest malignancy as the cause of an intracranial hematoma.     

Lower extremity MR angiography: universal retrofitting of high-field-strength systems with stepping kinematic imaging platforms initial experience.

In 15 volunteers and 84 patients with clinically suspected peripheral vascular disease, a stepping kinematic imaging platform, a manual retrofit stepping magnetic resonance (MR) imaging table, was used with three high-field-strength MR imaging systems to perform multistation peripheral contrast material-enhanced MR angiography in the lower extremity with the existing system phased-array coil. Each examination was performed in less than 45 minutes. Mounting of the stepping kinematic imaging platform was quick and simple and allowed rapid repositioning of a patient relative to the phased-array coil and acquisition of high-spatial-resolution MR angiograms of the peripheral vasculature with use of one injection of MR imaging contrast agent.