Magnetic resonance imaging of the orbit

Technological advances in MRI have resulted in the ability to obtain thin sections with high resolution; thus, MRI has become a serious competitor to CT in the evaluation of the orbit. MRI permits normal and pathologic anatomy to be visualized with exquisite detail in several planes. In addition to precise localization of lesions, in certain cases MRI also adds some specificity.     

T2-weighted cardiovascular magnetic resonance imaging

Technical advances in T2-weighted cardiovascular MR (CMR) imaging allow for accurate identification and quantification of tissue injuries that alter myocardial T2 relaxation. Of these, myocardial edema is of special relevance. Increased myocardial water content is an important feature of ischemic as well as nonischemic cardiomyopathies, which are often associated with acute myocardial inflammation. In this article, we review technical considerations and discuss clinical indications of myocardial T2-weighted imaging.     

3 T magnetic resonance imaging of the musculoskeletal system

The increasing distribution of high-field (3 T) magnetic resonance (MR) systems for clinical use has been accompanied by the need to fully understand the advantages and disadvantages that the increase in signal quality confers. Continuous development of the coils is required to fully express the potential of these systems, especially given the synergy between parallel imaging and the recent multichannel phased-array coils, which are able to improve image quality, spatial resolution and diagnostic accuracy in musculoskeletal imaging. The increase in signal offered by the high field makes possible improved visualisation of bone, cartilage, tendons and ligaments. This advantage, together with increased spatial resolution, is particularly useful when studying joints or some of their components, the evaluation of which has produced suboptimal results in non arthrographic examinations such as the glenoid labrum of the shoulder and the articular cartilage of the knee. Thanks to the greater signal-to-noise ratio and improved spatial resolution, MR imaging at 3 T is able to notably increase diagnostic performance in the musculoskeletal setting, with a consequent improvement in patient treatment and management.     

Update of prostate magnetic resonance imaging at 3 T

More recently, 3-T magnetic resonance (MR) scanner become more clinically available, and clinical application of 3-T MR imaging (MRI) of the abdomen and pelvis is now feasible and being performed at many institutions. However, few prostrate 3-T MRI studies have been published. The increase in signal-to-noise ratio at 3 versus 1.5 T clearly improves spatiotemporal and spectral resolutions of the prostate. Thus, we asked whether 3-T MRI improves the localization and staging of prostate cancer versus 1.5-T MRI. To answer this question, this article reviews the current limitations of prostate 1.5-T MRI and addresses its pros and cons. Moreover, we present preliminary results of prostate 3-T MRI and introduce our experience for prostate 3-T MRI using a phased-array coil, with an emphasis on imaging sequences, for example, T2-weighted, dynamic contrast-enhanced, diffusion-weighted, and MR spectroscopic imaging.     

3．0T磁共振扩散成像在甲状腺的成像分析

目的探讨3．0T磁共振扩散成像在甲状腺的成像技术方法和信号特点。方法分别取b值为0、300、500、700s／mm。对24例志愿者甲状腺行扩散加权成像,对信号强度、信噪比及表观弥散系数（ADC）值进行分析。结果图像信号强度、信噪比及ADC值随b值增大而减低;b值分别为0、300、500、700s／mm2时,信号强度分别为：50±21、30±14、24±11、20±8,F=41．25,P〈0．05;信噪比分别为：49±21、44±17、32±13、29±12,F=15．07,P〈0．05．b值分别为300、500、700s／mm2时,ADC值分别为：（1981±388）、（1647±293）、（1408±211）mm2／s,F=42．323,P〈0．05。结论随着b值增加,图像信号强度、信噪比及ADC值逐渐减小,b值在0—300s／ramz区间信号强度减低明显,b值在300～500s／mm2区间信噪比减低明显;ADC值在300～700s／mm2区间呈逐渐均匀性减小。     

Screening test for detection of metallic foreign objects in the orbit before magnetic resonance imaging.

RATIONALE AND OBJECTIVES. A study was designed to determine whether plain films, used as a screening modality for magnetic resonance imaging (MRI), could reliably detect intraorbital metallic foreign objects. METHODS. In the first experiment, 20 metal particles were placed in five human cadaver orbits. Routine orbital plain film series and computed tomography (CT) were obtained, randomized, and interpreted blinded by three experienced radiologists. RESULTS. The threshold size of particle detection for CT (0.07 mm3) was lower than for plain films (0.12 mm3). Placing metal particles in artificial and true vitreous demonstrated that all particles moved under a magnetic field at 1.5 T. When human globes were exposed to industrial tools (grinder, bandsaw, air hose, etc.), no metal objects penetrated the sclera. CONCLUSIONS. Plain films can be used as a low-cost, low-radiation screening procedure for high-risk patients with occupations involving metal work. CT should be used for patients with a history of eye trauma from other causes.     

Cardiac magnetic resonance imaging using an open 0.35 T system

OBJECTIVE: To evaluate cardiac magnetic resonance imaging (MRI) using a 0.35 T magnetic resonance system with open design. METHODS: Eleven patients were examined in an open MRI system with a field strength of 0.35 T. Myocardial function was assessed with cine true fast imaging with steady-state precession sequences in 2 planes. Perfusion images were acquired with a T1-weighted gradient echo sequence. Late enhancement was performed using an inversion recovery-prepared fast gradient echo technique. Image quality was assessed using a 4-point score in consensus. Signal-noise ratio was measured. RESULTS: For functional imaging, average score was 1.65 (SD, 0.6). For perfusion imaging, the value was 2.25 (SD, 0.68). For late enhancement, quality score was 2.6 (SD, 0.82). Average value of signal-noise ratio for functional, perfusion, and late enhancement imaging was 50.6 (SD, 16.4), 91.8 (SD, 52.8), and 33.2 (SD, 20.4), respectively. CONCLUSIONS: Open MRI with lower field strength can be used for functional imaging of the heart. For perfusion and viability imaging (late enhancement), higher field strength is needed. Open low-field cardiac MRI may provide a helpful alternative for obese or claustrophobic patients or patients who are difficult to move.     

T1rho contrast in functional magnetic resonance imaging.

The application of T1 in the rotating frame (T1rho) to functional MRI in humans was studied at 3 T. Increases in neural activity increased parenchymal T1rho. Modeling suggested that cerebral blood volume mediated this increase. A pulse sequence named spin-locked echo planar imaging (SLEPI) that produces both T1rho and T2* contrast was developed and used in a visual functional MRI (fMRI)experiment. Spin-locked contrast significantly augments the T2* blood oxygen level-dependent (BOLD) contrast in this sequence. The total functional contrast generated by the SLEPI sequence (1.31%) was 54% larger than the contrast (0.85%) obtained from a conventional gradient-echo EPI sequence using echo times of 30 ms. Analysis of image SNR revealed that the spin-locked preparation period of the sequence produced negligible signal loss from static dephasing effects. The SLEPI sequence appears to be an attractive alternative to conventional BOLD fMRI, particularly when long echo times are undesirable, such as when studying prefrontal cortex or ventral regions, where static susceptibility gradients often degrade T2*-weighted images.     

Nuclear magnetic resonance tomography of the orbit at 3.4 MHz

The significantly different signals from the various structures within the orbit suggest that NMR tomography will prove to be a valuable method for the diagnosis of both ocular and orbital disease. The resolution of the technique is initially illustrated by the demonstration of the signal patterns from the normal globe and orbit. The characteristic features of some pathological conditions, including vitreous haemorrhage and retinal detachment, are then shown. The value and limitations of the technique in differentiating conditions such as choroidal haemorrhage from malignant melanoma, and intra-orbital lymphoma from pseudo-tumour, are illustrated and discussed. The absence of artefact from bone, synthetic lens implants and non-ferromagnetic metallic foreign bodies is stressed.     

Malformations of cortical development: 3T magnetic resonance imaging features

Malformation of cortical development (MCD) is a term representing an inhomogeneous group of central nervous system abnormalities, referring particularly to embriyological aspect as a consequence of any of the three developmental stages, i.e., cell proliferation, cell migration and cortical organization. These include cotical dysgenesis, microcephaly, polymicrogyria, schizencephaly, lissencephaly, hemimegalencephaly, heterotopia and focal cortical dysplasia. Since magnetic resonance imaging is the modality of choice that best identifies the structural anomalies of the brain cortex, we aimed to provide a mini review of MCD by using 3T magnetic resonance scanner images.     

Magnetic resonance imaging of hematomas in a 0.02 T magnetic field

One intramuscular calf hematoma, 2 ankle hematomas and 4 cephalhematomas were imaged at various ages in a low magnetic field (0.02 T). At least one spin echo (SE) multislice image and a series of inversion recovery images (IR) were made varying the inversion time for estimation of the relaxation time T1. T1 tended to shorten and T2 to stay unchanged. With an unsuitable pulse sequence the hematomas were not visible. They were best seen with short TIs. The images of one of the ankle hematomas and the calf hematoma were compared with sonographic findings. The appearances of the hematomas varied during aging with both imaging modalities. The hematomas were easier to detect with magnetic resonance imaging than with ultrasound, also when aging.     

Shoulder magnetic resonance imaging

MRI provides excellent soft tissue contrast and allows for multiplanar imaging in anatomic planes. Because of these advantages MRI has become the study of choice for imaging of shoulder pathology. Some structures, such as the rotator cuff, humeral head contour, and glenoid shape, are evaluated well with conventional MRI. When more sensitive evaluation of the labrum, capsule, articular cartilage, and glenohumeral ligaments is required or when a partial-thickness rotator cuff tear is suspected,magnetic resonance arthrography with intra-articular contrast can be performed. For MR arthrography contrast is injected directly into the glenohumeral joint. This article reviews the appearances of normal anatomic structures in MRI of the shoulder and disorders involving the rotator cuff and glenoid labrum.     

Vascular magnetic resonance imaging

Natural contrast from flow void potentiates the diagnosis of the intimal flap of aortic dissection, the dilated contour of aortic aneurysm, the protruding plaque of atherosclerotic disease, the recognition of deep vein thrombosis, and the identification of a number of acquired and congenital vascular abnormalities. Although MRI is costly at the present, the advantages of vascular MRI include noninvasive multiplanar imaging, no ionizing radiation, no contrast material requirements, and its use as an alternative to technically limited ultrasonography or computed tomography. MRI can define anatomy, measure blood flow, and be used for serial examinations in following disease processes and response to treatment. Future research with tissue characterization of atherosclerotic plaque may allow for early diagnosis and treatment of this ubiquitous disease. Not only chemical but also metabolic studies, including tissue perfusion in the heart and other solid viscera, would be of great value. Undoubtedly, MRI will have a permanent role in cardiovascular diagnosis.     

Dynamic magnetic resonance imaging

Among the devices helping with an accurate diagnosis, neither MRI nor arthroscopy is perfect; both delineate pathology in the knee joint with reasonable sensitivity and specificity. MRI, as a noninvasive and nonionizing modality, has made a significant contribution to the understanding of musculoskeletal disturbances. Static images through the patellofemoral joint in different degrees of flexion reveal only the degree of patellar tilt or subluxation, parameters that can be measured also on the axial view of conventional radiography. The accuracy of patellar position on static axial MRI is limited by the absence of muscle contraction, movement, and loading. Dynamic axial images of patellofemoral articulation can demonstrate the degree of flexion where patellar malalignment is maximal and assess whether or not it reduces. Arthroscopy, aside from its diagnostic values, provides the opportunity for treatment of intra-articular changes contributing to knee joint disturbances, but it is an invasive technique with potential risks of complications. The performed cost-effectiveness analysis of MRI is based mainly on estimation of intra-articular pathology of the acutely-injured knee [49,52,56]. There are scarce data on the cost-effectiveness of MRI of patellofemoral alignment in patellofemoral pain knees. Total examination time for active movement dynamic MRI procedure is approximately 8 to 10 minutes, thus it can be performed during routine MRI examination of the knee. In cases of suspected patellofemoral malalignment with symptoms that mimic other types of internal derangement of the knee joint, dynamic MRI can be a procedure of choice for detection of transient patellar dislocation, whereas a single clinical examination cannot differentiate from other internal knee pathologies. Dynamic MRI, although in an experimental phase, gives us a new perspective for dynamic study of the patellofemoral joint.     

Breast magnetic resonance imaging

Mammography has long been considered the gold standard for screening breast cancer. Although it reduces the risk of breast cancer mortality by enabling early diagnosis, it does not detect all breast cancers. Numerous breast imaging technologies are emerging as effective adjunctive diagnostic tools when mammography results are negative or inconclusive. Contrast-enhanced magnetic resonance (CE-MR) imaging, in particular, has demonstrated a high sensitivity and has proven to be most effective, especially with patients at high risk for developing breast cancer. This article discusses the clinical applications for breast MR imaging, use of CE-MR for breast cancer detection, and other emerging breast imaging technologies.     

Gynecologic magnetic resonance imaging

Magnetic resonance imaging (MRI) is an excellent modality with which to delineate normal anatomic structures and a variety of pathologic conditions in the female pelvis. It excels at demonstrating the extent of local tumor involvement in cases of endometrial and cervical cancer. It can help to elucidate the origin and nature of a variety of benign pelvic masses in cases where ultrasound findings are equivocal, and it is an accurate tool in demonstrating congenital abnormalities of the female reproductive tract. As technology continues to evolve, MRI will likely assume an even greater role in evaluating the female pelvis.