Pathophysiologic study of chronic infarcts with I-123 isopropyl iodo-amphetamine (IMP): the importance of periinfarct area.

Abstract

Seventeen chronic cerebral Infarcts were investigated by a highly sensitive, dedicated brain single photon emission computerized tomography system using li3 I-isopropyl iodoamphetamine (IMP) and LU Xe. IMP uptake was measured 10 minutes, 2 hours, and 5 hours after injection, and regional cerebral blood flow was measured with 133 Xe. In 4 cases a positron emission tomography system was used to measure the rCBF and the regional metabolic rate of oxygen with C 15 O 2 and '*O 2 -The results obtained allowed us to identify 2 abnormal zones. One, the "central area," was characterized by a severe decrease in IMP uptake and rCBF averaging 34% and 46% respectively and by a hypodense image on the x-ray computerized tomography scan. The second, the periinfarct or "peripheral area" was characterized by a moderate decrease in IMP uptake and regional cerebral blood flow averaging 13 and 19% respectively; this area extended around the central area and had a normal density on computerized tomography scan. The IMP hypofixation of the peripheral area observed at the 10th minute tended to disappear at the 5th hour. The volume of this area was often found to be quite large, covering more than 30% of a hemisphere whereas the central area did not exceed 25%. C EREBRAL single photon emission tomography (SPECT) has benefited from two major improvements in recent years. The first was the advent of I-123-isopropyl-iodoamphetamine (IMP), which can be considered the first real brain agent 1 placed at the disposition of every nuclear medicine center. Its usefulness is recognized in cerebrovascular patients in obtaining both the localization and the extent of infarcts whether such infarcts are visible or not by x-ray computerized tomography (CT).2 " 7 The second was the introduction of a high-sensitivity SPECT system. 89 Because its sensitivity is so much higher than that of rotating cameras, acquisitions take only a few minutes and can be repeated easily. With this system, regional cerebral blood flow (rCBF) measured with 133 Xe and IMP values can be obtained on the same areas of the tomographic slices.Using this high-sensitivity SPECT system we studied 17 patients with chronic infarcts; a few were also studied with a positron emission tomography (PET) system. The results obtained emphasize the pathophysiological importance of the periinfarct area in Received October 18, 1985; accepted July 29, 1986. which IMP uptake, CBF, and metabolic activity are decreased. Subjects and MethodsTwo SPECT systems were used. All patients were studied with the Tomomatic 64, a hybrid bar-camera array system; a few were also studied using a rotating camera (GE-400 A) connected to a SIMIS 4 computer. Physical characteristics of both systems have been described in detail elsewhere.8 "" We will only detail here the "relative ' sensitivity of the Tomomatic, which we found to be 20-25 times higher than that of the GE-400 A for 123 I allowing for shorter acquisition times. With both systems "relative" sensitivity represents the count number of a 2-cm-thick...

Mapping brain function in freely moving subjects

“…Differences in the gray-matter-to-white-matter ratios of HMPAO and ECD underscore the differences underlying the chemical reactions required for tissue retention of these tracers, as well as how closely these tracers may approximate true cerebral perfusion, as compared to that measured using PET. Unlike earlier tracers such as the 123 Ilabeled amines [74,75], neither ECD nor HMPAO redistributes in the brain.…”

“…This stability of distribution within the brain is essential during image acquisition, and is one reason why earlier perfusion agents such as 123 I-labeled iodoamphetamine (IMP, Spectamine, Medi-Physics, Inc., Emeryville, CA) have fallen into disuse. IMP, while demonstrating a high first-pass extraction fraction (85-95%), shows substantial washout and redistribution, such that perfusion patterns at an hour post-administration no longer represent perfusion at the time of injection [73][74][75][76]. By comparison, imaging with HMPAO can take place from 2 min to 4 h post injection.…”

SPECT analysis of recent cerebral infarction.

“…Although values from the chronic period were reported in detail elsewhere, 1 we summarize them here because they may be compared with the subacute values in every patient ( Table 2). rCBF of the central area was very low, with a mean decrease of 49%, identical to that observed in Phase 3b.…”

“…Despite the slight decrease in rCBF and uptake of IMP at 10 minutes in the peripheral area, neither CT hypodensity nor contrast enhancement was observed in the subacute period. 1 Two of the three patients examined by PET and SPECT had a peripheral area large enough to be studied. Both had a slight but not significant Xe and rCMR0 2 (Table 3); rOEF was normal as in chronic infarct.…”

“…1 The central area was characterized by a marked decrease in [ l23 I]iodoamphetamine (IMP) uptake, in regional cerebral blood flow (rCBF), and in regional cerebral metabolic rate for oxygen (rCMROi), corresponding to the infarct core and hypodensity on the x-ray computed tomogram (CT scan). The peripheral or peri-infarct area was characterized by slight decreases in IMP uptake, rCBF, and rCMRO 2 , with a normal image on the x-ray CT scan that we attributed to diaschisis or selective neuronal loss and not to a chronic ischemic penumbra.…”