Magnetic Resonance Imaging (MRI)

Accurate determination of relaxation times has become increasingly important in efforts to determine the diagnostic specificity of nuclear magnetic resonance (NMR) imaging. Techniques used in NMR imaging, not routinely employed in conventional NMR spectroscopy, can significantly affect the resulting relaxation time determinations. For the saturation recovery (SR) approach of T1 measurement used in our laboratory, these include selective excitation to define the image plane and magnetization refocusing for NMR signal acquisition.

We used three-dimensional proton NMR images to study ischemic infarction in the territory of the vertebral-basilar posterior cerebral circulation. The study includes sixteen cases, eight of which are presented in detail. In seven cases, the infarctions were secondary to demonstrable large artery occlusive disease -- vertebral, basilar, or posterior cerebral. In nine cases, the infarctions were secondary to what was presumably small vessel disease.

Proton nuclear magnetic resonance (NMR) imaging was performed on normal volunteers and patients with various types of clinical strokes. True three-dimensional volumetric data were obtained for subsequent reconstruction of images at various orientations, including transverse, coronal, and sagittal, and for specific matching to x-ray computed tomographic planes. A variety of radiofrequency pulse sequences was used to generate images weighted by the NMR parameters spin density (p) and spin-lattice (T1) and spin-spin (T2) relaxation times.

Electrocardiographically gated magnetic resonance images were acquired in 20 subjects using a spin-echo pulse sequence. For optimizing the display of cardiac anatomy, a technique was developed which uses patient positioning in addition to alteration of gradient angle to select image planes.

Magnetic resonance imaging (MRI) techniques provide a versatile method of manipulating soft tissue contrast in the extremities. Different pulse sequence techniques are discussed with respect to the optimization of contrast differences between muscle, marrow, and abnormal tissue.

Proton (hydrogen-1) magnetic resonance imaging techniques have potential for the detection and characterization of changes associated with myocardial ischemia. Since image contrast is dependent on T1 and T2 relaxation times, we examined these parameters in a canine preparation of occlusion of the left anterior descending coronary artery. Of 16 dogs studied, seven underwent 3 hr of coronary artery occlusion and nine underwent 3 hr of occlusion followed by 1 hr of reperfusion. After the dogs were killed, the hearts of four from each group were imaged in a small bore, 1.4 tesla magnet.

A patient with a high grade malignant fibrous histiocytoma of the leg is presented. Staging studies included a 99mTc diphosphonate bone scan, an arteriogram, a computed tomogram (CT) and a proton (1H) magnetic resonance imaging (MRI) study. By manipulating imaging parameters to enhance contrast between normal and neoplastic tissues, the latter technique more accurately delineated the extent of the soft tissue sarcoma than the other imaging modalities.

Magnetic resonance imaging (MRI) was compared to computed tomography (CT) in four cases of sacrococcygeal chordoma. Both techniques yielded important anatomic information and represented important advances over early radiologic imaging methods. MRI provides superior contrast with surrounding soft tissues because of the prolonged T1 and T2 times of the tumors. This was especially important in a case of recurrent chordoma. The direct sagittal images obtained by MRI were valuable in determining the extent of lesions.

A phase-contrast method of chemical shift imaging was used to evaluate bone marrow in normal volunteers and in patients with metabolic, inflammatory, traumatic, and neoplastic disorders. Five normal volunteers were examined in order to obtain preliminary data on normal patterns of signal intensity in hematopoietic and fatty marrow using both conventional magnetic resonance imaging and proton chemical shift imaging.