Acute NMR changes during MCA occlusion: a preliminary study in primates.

Abstract

SUMMARY Advancements in computer science and magnet design have resulted in the recent development of high resolution NMR imaging systems. Using our primate model we evaluated the ability of NMR scanning to detect early changes following middle cerebral artery (MCA) occlusion.Serial NMR scans documented progressive changes secondary to edema and swelling beginning ninety minutes after MCA occlusion. NMR was also able to readily demonstrate the area of cerebral infarct 10 days after a six hour episode of MCA occlusion.Soft tissue contrast and image resolution were superb. Correlation with pathologic sections was excellent.Stroke, Vol 14, No 2, 1983 THE PHENOMENON OF NUCLEAR MAGNETIC RESONANCE (NMR) was first reported for the hydrogen nuclei of water and paraffin in 1946. '• 2 Hydrogen nuclides (protons, deuterium, and tritium) and the isotopes of certain other elements ( 13 C, 31 P, etc.) share the common property of having an intrinsic nuclear magnetic dipole moment. As a result they can be thought of as behaving like small bar magnets. Normally in a sample containing the nuclides, these nuclear magnets are randomly orientated so that the net nuclear magnetism is zero ( fig. la). When such a sample is placed in a strong static magnetic field, however, the nuclear magnets tend to realign themselves with the direction of the lines of force in the magnetic field (fig. lb) so that the nuclear magnetic forces are additive ( fig. lb). Thermal motions within the sample tend to disturb this alignment. The net effect of these opposing forces is a macroscopic quantity called magnetization. At equilibrium the magnitude of this nuclear magnetization vector is directly proportional to the strength of the applied magnetic field, and inversely proportional to the absolute temperature (Curie's Law). One of the most common ways to obtain an NMR signal is to use a short, intense radio frequency (RF) pulse applied transverse to the direction of the static magnetic field. By choosing an appropriate frequency for the RF pulse the nuclei of interest (e.g. the hydrogen proton, 'H) can be forced to rotate (or precess) about the axis of the static magnetic field ( fig. 2). Following the RF pulse, then, the magnetization of these stimulated nuclei (the sum of the rotating nuclear magnetic vector moments) is no longer in alignment with the static field and undergoes free precession in the magnetic field at an

Evolving focal cerebral ischemia in cats: spatial correlation of nuclear magnetic resonance imaging, cerebral blood flow, tetrazolium staining, and histopathology.

“…Studies in baboons have shown that NMRI changes can be seen as soon as 90 minutes using Tl-weighted images 10 and are quite apparent by 5 hours as increased signal intensity using spin-echo, T2-weighted images, and decreased signal intensity on inversion recovery, Tl-weighted images." Our findings are slightly different in that we did not find early (90 minutes) or late changes in the Tl-weighted images.…”

Focal parenchymal lesions in transient ischemic attacks: correlation of computed tomography and magnetic resonance imaging.

“…Other formal studies on TIA patients are still lacking. Because of the high sensitivity of MRI in experimental 8 ' 9 and clinical 10 ' " infarction, some authors have predicted a similarly high sensitivity in TIA patients. 12 Proton MRI has detected parenchymal changes as early as 30 minutes after experimental artery occlusion in animals, presumably prior to histologically detectable infarction.…”

Photochemically-induced cerebral infarction in the rat: Comparison of NMR imaging and histologic changes

“…Several studies have documented the improved ability to detect infarction with NMR as compared to Xray CT even within the first hours after vascular occlusion 3, t4, 16. At present, X-ray CT is the standard imaging method for detecting cerebral infarction.…”