Fast gradient echo magnetic resonance imaging of the normal diaphragm.

To determine the ability of fast gradient-recalled echo (GRE), breath-hold magnetic resonance imaging (MRI) to depict all regions of the diaphragm, 13 volunteers were scanned in coronal and sagittal planes. The central to anterior left hemidiaphragm and the posterior lumbar portions were each demonstrated in 12 subjects (92%). The crura were visible crossing anterior to the aorta in the sagittal plane in eight subjects (62%) and in the coronal plane in six subjects (46%). In the sagittal plane, the right crus was evident in eight subjects (62%). Muscular portions of the diaphragm in contact with the liver or body wall were less frequently discernible, and the central tendon could not be confidently resolved. Several artifacts occurred that interfered with visualization of the diaphragm. These observations indicate that many regions of the diaphragm can be seen with fast GRE, breath-hold MRI, but there are some limitations in depicting the diaphragm in its entirety.

Diaphragmatic motion: fast gradient-recalled-echo MR imaging in healthy subjects.

PURPOSE: To investigate the feasibility of imaging diaphragmatic motion with a fast gradient-recalled-echo (GRE) magnetic resonance (MR) pulse sequence. MATERIALS AND METHODS: Fast GRE pulse sequences in sagittal and coronal planes were used to acquire repeated, single-level, 1.2-second scans in 10 healthy volunteers during deliberately slowed, approximate-vital-capacity breathing. Motion was analyzed subjectively by viewing the image sequences as cine loops and quantitatively by measuring the displacement of different points on the diaphragm at a workstation. RESULTS: Temporal and spatial resolutions were adequate in all subjects. Absolute excursion of the domes was 4.4 cm on the right and 4.2 cm on the left. Analysis of diaphragmatic displacement at different locations revealed a gradient of excursion that increased from anterior to middle to posterior (P < .05-.001; paired t test). Excursion of the lateral aspects was greater than that of the medial aspect (P < .001). CONCLUSION: Fast GRE MR imaging can be reliably used to demonstrate diaphragmatic motion and may prove useful in the investigation of normal and abnormal respiratory mechanics.

Three-dimensional time-of-flight MR angiography with a surface coil: evaluation in 12 subjects.

We compared three-dimensional time-of-flight MR angiograms obtained with head coils and then with surface coils in five patients with intracranial vascular lesions and in seven normal volunteers to determine if imaging of intracranial vascular anatomy could be improved with the use of a surface coil. Visualization of small peripheral vessels was consistently better with a surface coil than with a head coil at identical small fields of view (FOVs). The surface-coil technique allowed small-FOV imaging of peripheral vascular lesions with higher spatial resolution and signal-to-noise ratio similar to that of large-FOV head-coil images. The use of a surface coil introduced the problem of signal falloff; centrally located vessels were visualized as well or better when a standard head coil was used. We conclude that surface-coil MR angiography can serve as a useful adjunct to routine head-coil MR angiography in the evaluation of peripheral vascular abnormalities.

Effect of tendon orientation on MR imaging signal intensity: a manifestation of the "magic angle" phenomenon.

To determine whether orientation in the static field may be responsible for the frequent occurrence of increased signal intensity within normal tendons at magnetic resonance (MR) imaging, seven healthy volunteers were imaged by means of a 1.5-T unit and standard clinical pulse sequences. The wrist, ankle, and shoulder regions were evaluated with local coils. Imaging was performed with tendon orientations ranging from 0 degree to 90 degrees in relation to the constant magnetic induction field (B0). Markedly increased intratendinous signal intensity was observed at the "magic angle" of 55 degrees, intermediate signal intensity was observed at 45 degrees and 65 degrees, and no signal intensity was observed at 0 degree and 90 degrees. Signal intensity was evident only when a short echo time was used. The authors believe that tendon orientation greatly affects tendon signal intensity in vivo. Increased signal intensity due to the magic angle effect may be misdiagnosed as tendinous degeneration, tendinitis, or frank tear.

Canine intervertebral disks: correlation of anatomy and MR imaging.

Because the structure, maturation, and degeneration of canine intervertebral disks resemble those of humans, the authors developed a model of acute intervertebral disk degeneration in dogs. Herniated disks of 18 dogs were examined with magnetic resonance (MR) imaging and then sectioned with a freezing microtome. On the basis of their morphologic appearance in the freezing microtome sections, most of the lumbar intervertebral disks could be categorized as one of six types. Each type has characteristic features and a distinctive appearance on MR images. Findings of this study--including decreased signal intensity from the intervertebral disk, altered signal intensity in contiguous bone marrow, bulging of the anulus fibrosus, herniation of the nucleus pulposus, and contrast enhancement after intravenous administration of gadolinium diethylenetriaminepentaacetic acid (DTPA)--resemble observations from human clinical studies. Classification of degenerating disks and identification of MR imaging characteristics of each type may improve the interpretation of MR images and recognition of early disk degeneration in humans.

An experimental model to study contrast enhancement in MR imaging of the intervertebral disk.

MR imaging after IV gadolinium-DTPA administration has demonstrated contrast enhancement in traumatized lumbar intervertebral disks. To characterize the morbid anatomy that correlates with the contrast enhancement, we developed a canine model of traumatized intervertebral disks. Diskectomy was performed with a nucleotome and the spines were imaged biweekly with MR and Gd-DTPA. The spines were studied at necropsy, and their anatomic abnormalities correlated with contrast enhancement detected by MR imaging. Our preliminary results indicate that contrast enhancement occurs where granulation tissue develops in traumatized intervertebral disks.

Magnetic susceptibility artifacts in gradient-recalled echo MR imaging.

Artifacts related to magnetic susceptibility differences between bone and soft tissue are prevalent on gradient-recalled echo images, particularly when long echo delay times are used. These susceptibility artifacts spatially distort and artifactually enlarge bone contours. This can alter the apparent shape of the spinal canal and exaggerate the degree of spinal stenosis seen in patients with cervical spondylosis. The effects of magnetic susceptibility artifacts in gradient echo imaging were studied in a phantom model and the results were correlated with MR images obtained in patients with cervical spondylosis.

Truncation artifact in MR images of the intervertebral disk.

A cadaver's vertebral column, a phantom, and a volunteer were imaged on a 1.5-T MR scanner to study the thin, uniform, dark, transverse lines that characterize some intervertebral disks. An artifactual dark line appears when the field of view (FOV) and matrix steps (n) are chosen so that d = FOV/n, where d equals the intervertebral disk height, or spacing between phantom vertebrae. The artifact is caused by the truncation effect. An artifactual dark line is differentiated from a dark line caused by anatomic variables, and means for reducing such lines by modifying imaging parameters are discussed.

The MR appearance of gray and white matter in the cervical spinal cord.

Artifacts that can distort the appearance of the cervical spinal cord are caused by data truncation during MR image reconstruction. We used a phantom and then correlated anatomic sections with MR images in cadavers and normal volunteers to evaluate the effect of truncation artifacts on the MR appearance of the spinal cord. When truncation artifacts are minimized, the gray matter and major white-matter columns in the cervical cord can be recognized. T2-weighted gradient-echo MR techniques can best differentiate gray from white matter.

"Truncation" artifact in MR images of the internal auditory canal.

Dry skulls and a phantom were studied to determine whether an intracanalicular dark band in MR images of some acoustic neuromas could be artifactual. A "truncation" artifact was detected in the internal auditory canals of the dry skulls and in a simulated internal auditory canal of the phantom when the width of the canal approximately equaled 4 X (field of view) /N, where N equals 128 or 256, depending on the number of gradient steps chosen. The "truncation" artifact should not be confused with CSF between normal nerves when a canal contains tumor.