Investigation of cerebral ischemia using magnetization transfer contrast (MTC) MR imaging

Early changes in water diffusion, perfusion, T1, and T2 during focal cerebral ischemia in the rat studied at 8.5 T

“…This effect has been previously suggested (17) as one of the possible explanations for the increases in T 1 and T 2 observed after 2 hr of ischemia, which occur before the development of vasogenic edema. It is possible that the same effect may be responsible for part of the early changes observed at high field.…”

“…However, animal experiments have shown that there is no direct relationship between the temporal evolution of total water content and changes in relaxation times (8)(9)(10). This presumably reflects the fact that there are other factors apart from vasogenic edema that can influence the observed relaxation properties of tissue, such as flow effects (11), alteration in the amounts of oxyhemoglobin and deoxyhemoglobin (6,(12)(13)(14), tissue oxygenation (15), and the exchange of nuclear spin magnetization between the ''free'' and ''bound'' proton pools (16,17). All these effects could also influence T 1 and T 2 in the acute phase of stroke, and so the question arises as to whether early measurements of the relaxation times could provide additional information about the evolving pathophysiology of stroke.…”

Acute changes in MRI diffusion, perfusion,T1, andT2 in a rat model of oligemia produced by partial occlusion of the middle cerebral artery

“…A further possible cause for the initial increase in T 1 is a change in the environment of the water. One MRI measurement of the nature of water is that of magnetization transfer (MT), which indicates magnetization exchange between spins in "free" water and in regions of "restricted" or "bound" water (40). A previous study suggested that changes in MT may be consistent with the increase in T 1 and T 2 after 2 hr of ischemia, which occurred before the onset of vasogenic edema (40).…”

Magnetic Resonance Imaging in Experimental Models of Brain Disorders

“…In experimental cerebral ischemia, a reduction in MTR may be related to breakdown of macromolecular tissue components and vasogenic edema-associated increase in free interstitial water (Ordidge et al, 1991). Ewing et al (1999) reported a drop in the apparent forward transfer rate for magnetization between the free water proton pool and the immobile proton pool during the first 6 hours after middle cerebral artery (MCA) occlusion in rats.…”