MRI's role in evaluating knee anatomy and injuries.

Because its function is related to its bony anatomy, ligamentous structures and integrated muscle groups, the knee is one of the most complex joints in the human body. Not surprisingly, knee injuries rank as one of the major causes of physical disability. Prior to the introduction of magnetic resonance imaging, prompt and accurate diagnosis of knee injuries was a challenge. Now, using MRI, a highly accurate diagnosis can be made in 30 minutes or less without patient discomfort. This article reviews knee anatomy, discusses common injuries and describes magnetic resonance techniques for imaging the knee.

MR and CT imaging of ethanol-treated liver tumors in an animal model.

To characterize the radiographic appearance of liver lesions over time following ethanol injection, seven New Zealand white rabbits underwent surgical implantation of small fragments of VX-2 carcinoma within the liver. Upon reaching 1 cm in diameter, a tumor nodule was directly injected with absolute ethanol. Another nodule in the same animal was injected with saline as a control. Imaging was performed 6-24 days after the injections by high resolution CT and MRI, and correlation obtained with the pathologic specimens. Long TR spin-echo MR sequences were found to characterize the ethanol-treated regions of liver most accurately. Liver tissue infarcted by alcohol could be differentiated from tumor and necrosis by virtue of its short T2 relaxation value. There were no distinguishing features by other imaging techniques between the ethanol-treated and control tumor nodules. Peripheral contrast enhancement was demonstrated in both, corresponding to fibrous tissue around the ethanol-injected regions, and to viable tumor in the case of controls.

MRI of the upper abdomen using motion artifact suppression technique (MAST).

Magnetic resonance imaging of the upper abdomen has been hampered by motion artifacts that cause suboptimal image quality. A promising software solution to this problem, motion artifact suppression technique (MAST), is described. Using mathematically determined refocussing gradients, it has improved image clarity significantly. Unlike alternate techniques such as respiratory gating, there is no increase in scan time, and patient throughput is expedited.

Motion artifact suppression technique (MAST) for MR imaging.

A technique has been developed that significantly improves the image resolution and reduces motion artifacts in conventional two-dimensional Fourier transform and three-dimensional Fourier transform magnetic resonance imaging sequences. Modifications on the gradient waveforms completely refocus the transverse magnetization at the echo time, regardless of the motion occurring between the time of the 90 degrees radiofrequency excitation and the echo time (within-view). This accomplishes suppression of motion artifacts and regains the signal from flowing blood and CSF. Images of the head, abdomen, chest, and spine are reproduced which show the increase in signal and anatomical detail that would otherwise be degraded and lost in artifact noise. This technique has reduced the practical difficulty of obtaining clinically diagnostic T2-weighted abdominal images. It also has allowed diagnostic quality T1- and T2-weighted images to be obtained with one acquisition per view, thus reducing the total scan time.

Contiguous computed tomography angiography (CTA) of the chest.

Contiguous computed tomography angiography (CTA) of the chest is a useful diagnostic adjunct to the overall process of mediastinal imaging. The authors' method, termed Chiu-Dynamic, which includes multiple bolus injection of contrast material and advanced software programming for rapid scanning, produces excellent opacification of mediastinal vasculature and allows easier assessment of vascular anomalies and pathological soft tissue lesions.