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M Hoehn

Publications and source records attributed to M Hoehn.

At least 19 recordsLinked to original sources
PubMed2006

A responsive MRI contrast agent to monitor functional cell status.

It has been shown that insoluble Gd chelates are suitable MRI contrast agents for conditional activation by intracellular lipases. The DTPA-based, insoluble, inactive contrast agent was internalized into dendritic cells by phagocytosis. Cleavage of long aliphatic side chains by intracellular lipase activity leads to the contrast agents solubility and hereby its activation depending on the enzyme expression. Uptake and activation of the contrast agent was much reduced in Flt3+ CD11b+ progenitor cells. Detectability limits in the T(1)-weighted MR images were estimated in phantoms and in vivo in the rat brain. Marginal toxic effects were only observed at very high concentrations of the contrast agent. The chelate can easily be modified to be targeted by enzymes expressed during specific change of cell status like activation or differentiation. Such a system is suitable for functional cellular in vivo MR imaging.

Animals↗
PubMed2002

Dynamic changes of ADC, perfusion, and NMR relaxation parameters in transient focal ischemia of rat brain.

The potential of multiparametric MRI parameters for differentiating between reversibly and irreversibly damaged brain tissue was investigated in an experimental model of focal brain ischemia in the rat. The middle cerebral artery (MCA) was occluded by intraluminal suture insertion for 60 or 90 min, followed by 4.5 h of reperfusion. The apparent diffusion coefficient (ADC) of brain water, T(1) and T(2) relaxation times, and CBF(i), an MR-derived index of cerebral perfusion, were repeatedly measured and correlated with the outcome from the ischemic impact. A novel user-independent approach for segmentation of ADC maps into classes of increasing injury was introduced to define regions of interest (ROIs) in which these parameters were evaluated. MCA occlusion led to a graded decline of ADC, which corresponded with both the severity of flow reduction and an increase in T(1) and T(2) relaxation times. Removal of the suture led to a triphasic restitution of blood flow consisting of a fast initial rise, a secondary decline, and final normalization. Postischemic reperfusion led to a rise of ADC irrespective of the duration of ischemia. However, the quality of recovery declined with increasing severity of the ischemic impact. Throughout the observation time, T(1) and T(2) showed a continuous increase, the intensity of which correlated with the severity of ADC decline during ischemia. Particularly with longer ischemia time, elevated T(2) in combination with reduced ADC yielded a lower probability of recovery during recirculation, while intraischemic perfusion information contributed less to the prediction of outcome. In conclusion, the combination of MR parameters at the end of ischemia correlated with the probability of tissue recovery but did not permit reliable differentiation between reversibly and irreversibly damaged tissue.

Animals↗
PubMed2002

Prediction of hemorrhagic transformation after thrombolytic therapy of clot embolism: an MRI investigation in rat brain.

BACKGROUND AND PURPOSE: Thrombolytic treatment of stroke carries the risk of hemorrhagic transformation. Therefore, the potential of MRI for prediction of recombinant tissue plasminogen activator (rtPA)-induced bleeding is explored to identify patients in whom rtPA treatment may provoke such complications. METHODS: Spontaneously hypertensive rats (SHR) (n=9) were submitted to middle cerebral artery (MCA) clot embolism, followed 3 hours later by intra-arterial infusion of 10 mg/kg rtPA. Untreated SHR (n=9) were infused with saline. MRI imaging was performed before treatment and included apparent diffusion coefficient (ADC), T2, and perfusion mapping and contrast enhancement with gadolinium-DTPA. The distribution of intracerebral hemorrhages was studied 3 days later by histological staining. RESULTS: Clot embolism led to the rapid decline of ADC in the territory of the occluded artery. Tissue lesion volume derived from ADC imaging increased by 155+/-69% in the untreated animals and by 168+/-87% in the treated animals (P=NS), determined on the histological sections after 3 days. This same lesion growth in both groups indicated absence of therapeutic effect after 3-hour treatment delay. Hemorrhagic transformations were significantly more frequent in treated SHR (P<0.05). In untreated rats, hemorrhages were found in the border zone of the ischemic territory; in treated animals, hemorrhagic transformations occurred in the ischemic core region. rtPA-induced hemorrhages were predicted by a disturbance of the blood-brain barrier in 3 of 4 animals before treatment by Gd-DTPA contrast enhancement but not by ADC, T2, or perfusion imaging. The region of contrast enhancement colocalized with subsequent bleeding in these animals. CONCLUSIONS: The disturbance of blood-brain barrier but not of other MR parameters allows risk assessment for hemorrhagic transformation induced by subsequent thrombolytic treatment.

Animals↗
PubMed2001

Application of magnetic resonance to animal models of cerebral ischemia.

The present review has been compiled to highlight the role of magnetic resonance imaging (MRI) and MR spectroscopy (MRS) for the investigation of cerebral ischemia in the animal experimental field of basic research. We have focused on stroke investigations analyzing the pathomechanisms of the disease evolution and on new advances in both nuclear MR (NMR) methodology or genetic engineering of transgenic animals for the study of complex molecular relationships and causes of the disease. Furthermore, we have tried to include metabolic and genetic aspects, as well as the application of functional imaging, for the investigation of the disturbance or restitution of functional brain activation under pathological conditions as relates to controlled animal experiments.

Animals↗
PubMed2001

MR angiographic investigation of transient focal cerebral ischemia in rat.

Contrast agent free time-of-flight magnetic resonance angiography (TOF-MRA) was applied to the intraluminal thread occlusion model of experimental stroke in rat. It was combined with perfusion- and diffusion-weighted imaging (PWI and DWI) sequences to correlate occlusion and reopening of the middle cerebral artery with alterations in these well-established magnetic resonance sequences. Since TOF-MRA can be repeated without limitations, the time course of vascular patency is demonstrated during an experimental period of up to 8 h (2 h control, 1 h ischemia, 3-6 h reperfusion). With an acquisition time of 10 min, TOF-MRA proved to be suitable to analyze the vascular state of occlusion and reperfusion repetitively in longitudinal studies. Spatial resolution was sufficient to observe neurovascular structural details. In eight out of 10 animals complete vessel occlusion by the intraluminal thread could be validated by an entirely extinguished signal of the ipsilateral middle cerebral artery (MCA) in the angiograms. This was in accordance with a perfusion deficit in the MCA vascular territory detected by PWI (reduction to 30.4 +/- 7.4% relative to contralateral side) and a disturbance of water ion homeostasis monitored by DWI in this area. One animal showed a delayed occlusion after 30 min of MCA occlusion, in another animal vessel occlusion failed. In seven out of the eight successful occlusion experiments there was immediate reperfusion after withdrawal of the thread. One animal showed a delayed reperfusion after suture retraction. Remarkable hemispheric differences in vascular branching of the MCA could be recognized in three out of 10 animals. In conclusion, TOF-MRA is considered a helpful method to survey even in small laboratory animals the correct time course of vascular occlusion and reopening in experimental ischemia, and provides complementary information to the tissue perfusion status monitored by PWI and the ischemic lesion territory detected by DWI.

Animals↗
PubMed2001

1H- and (31)P-MR spectroscopy of primary and recurrent human brain tumors in vitro: malignancy-characteristic profiles of water soluble and lipophilic spectral components.

In vitro NMR spectroscopy was performed on specimen of human brain tumors. From all patients, tissue samples of primary tumors and their first recurrences were examined. (31)P- and (1)H-spectra were recorded from samples of meningioma, astrocytoma and glioblastoma. A double extraction procedure of the tissue samples permitted acquisition of information from the membrane fraction and from the cytosolic fraction. (31)P-spectra were used to analyze the lipophilic fraction (phospholipids of the membrane) of the tissue extracts, while the (1)H-spectra reflected information on the metabolic alterations of the hydrophilic, cytosolic fraction of the tissue. The tumor types showed distinctive spectral patterns in both the (31)P- and the (1)H-spectra. Based on the total detectable (31)P signal, the level of phosphatidylcholine was about 34% lower in primary astrocytomas than in primary glioblastomas (p = 0.0003), whereas the level of sphingomyelin was about 45% lower in primary glioblastomas than in primary astrocytomas (p = 0.0061). A similar tendency of these phospholipids was observed when comparing primary and recurrent astrocytoma samples from the same individuals [+15% (p = 0.0103) and -23% (p = 0.0314) change, respectively]. (1)H-spectra of gliomas were characterized by an increase of the ratios of alanine, glycine and choline over creatine as a function of the degree of malignancy. In agreement with findings in the (31)P-spectra, the (1)H-spectra of recurrent astrocytomas showed metabolic profiles of increased malignancy in comparison to their primary occurrence. Since gliomas tend to increase in malignancy upon recurrence, this may reflect evolving tumor metabolism. (1)H-spectra of meningiomas showed the highest ratio of alanine over creatine accompanied by a near absence of myo-inositol. Phospholipid profiles of meningiomas showed higher fractional contents of phosphatidylcholine along with lower phosphatidylserine compared to astrocytomas, while higher phosphatidylethanolamine and sphingomyelin fractional contents distinguished meningiomas from glioblastomas. The extraction method being used in this study combined with high-resolution (1)H- and (31)P-MRS provides a wide range of biochemical information, which enables differentiation not only between tumor types but also between primary and recurrent gliomas, reflecting an evolving tumor metabolism.

Analysis of Variance↗
PubMed2001

Dynamic changes of magnetic resonance imaging abnormalities in relation to inflammation and glial responses after photothrombotic cerebral infarction in the rat brain.

This investigation analyzed the potential of high-resolution magnetic resonance imaging (MRI) at a field strength of 7T to depict leukocyte infiltration and glial responses after focal cerebral ischemia induced by photothrombotic occlusion of cerebral microvessels. For this purpose we superimposed multiparametric MRI (apparent diffusion coefficient, T2, perfusion-weighted, and gadolinium-DTPA-enhanced T1-weighted imaging) on tissue sections stained for phagocytes and astrocytes and, moreover, assessed the regional distribution of tissue pH and ATP content by invasive biochemical methods. Comparing the histological data with the various MRI parameters, high-resolution MRI did not allow a spatial discrimination between distinct areas of phagocyte accumulation or astroglial scar formation, based on image contrast or even quantitative parameter value differences. However, MRI parameters underwent characteristic changes and differentiated distinct stages of tissue remodeling between days 3 and 14 after photothrombosis. Low apparent diffusion coefficient (ADC) and high T2 values indicated an early stage (3 days) with necrosis and beginning glial activation. Normal ADC and reduced T2 elevation characterized an infarct with advanced glial activation and infiltration of hematogenous cells at 7 days after photothrombosis. Heterogeneous ADC together with T2 elevation reflected a late infarct stage (14 days) when pseudocystic degeneration and scar formation had occurred.

Animals↗
PubMed2001

Magnetic resonance prediction of outcome after thrombolytic treatment.

Treatment of clinical stroke with recombinant tissue plasminogen activator (rt-PA) carries the risk of hemorrhagic complications. Hence, predictors of therapeutic outcome with respect to (a) reperfusion and (b) tissue recovery would be very useful to identify potentially salvageable brain tissue. Magnetic resonance (MR) parameters, especially the apparent diffusion coefficient of water (ADC), perfusion-weighted imaging (PWI) and T(2) relaxometry are thought to provide this information. We evaluated the prognostic implications of ADC, PWI and T(2) relaxometry immediately before initiation of thrombolytic treatment in a model of clot embolism in rats. Animals (n = 14) were treated with intraarterial rt-PA (10 mg/kg) at 90 min after embolism. MR imaging was repeatedly performed at 4.7 T before and up to 5.5 h after embolism. ADC was calculated from diffusion-weighted images (b-values: 30, 765, 1500 s/mm(2)), arterial spin tagging was used for PWI, and quantitative T(2) relaxometry was performed with a Carr-Purcell-Meiboom-Gill (CPMG) sequence. A reperfusion index was calculated to assess the quality of thrombolytic recanalization. The decline of ADC at the end of the experiment to below 80% of control was defined as unfavorable outcome. The probability of tissue injury at the end of the experiments increased with the severity of ADC changes before the initiation of treatment (probability of unfavorable outcome: 21%, 44%, 65% for ADC values of 80-90%, 70-80% and <70% of control, respectively). Pretreatment PWI or T(2) relaxometry also correlated with outcome but-alone or in combination with pretreatment ADC maps-did not improve injury prediction over that obtained by ADC alone. Outcome was influenced positively by successful reperfusion the quality of which, however, could not be predicted by pre-treatment MR characteristics. The data demonstrate that ADC mapping performed before the initiation of thrombolytic treatment provides reliable risk assessment of impeding brain injury but due to uncertainties of postischemic reperfusion does not allow precise outcome prediction in individual experiments.

Animals↗
PubMed2001

Relation of apparent diffusion coefficient changes and metabolic disturbances after 1 hour of focal cerebral ischemia and at different reperfusion phases in rats.

Changes in apparent diffusion coefficients (ADC) were compared with alterations of adenosine triphosphate (ATP) concentration and pH in different phases of transient focal cerebral ischemia to study the ADC threshold for breakdown of energy metabolism and tissue acidosis during ischemia and reperfusion. Male Wistar rats underwent 1 hour of middle cerebral artery occlusion without recirculation (n = 3) or with 1 hour (n = 4) or 10 hours of reperfusion (n=5) inside the magnet, using a remotely controlled thread occlusion model. ADC maps were calculated from diffusion-weighted images and normalized to the preischemic value to obtain relative ADC maps. Hemispheric lesion volume (HLV) was determined on the last relative ADC maps at different relative ADC thresholds and was compared to the HLV measured by ATP depletion and by tissue acidosis. The HLVs, defined by ATP depletion and tissue acidosis, were 26.0% +/- 10.6% and 38.1% +/- 6.5% at the end of ischemia, 3.3% +/- 2.4% and 4.8% +/- 3.5% after 1 hour of reperfusion, and 11.2% +/- 4.7% and 10.9% +/- 5.2% after 10 hours of recirculation, respectively. The relative ADC thresholds for energy failure were consistently approximately 77% of the control value in the three different groups. The threshold for tissue acidosis was higher at the end of ischemia (86% of control) but was similar to the results obtained for ATP depletion after 1 hour (78% of control) and 10 hours (76% of control) of recirculation. These results indicate that the described relative ADC threshold of approximately 77% of control provides a good estimate for the breakdown of energy metabolism not only during middle cerebral artery occlusion but also at the early phase of reperfusion, when recovery of energy metabolism is expected to occur, or some hours later, when development of secondary energy failure was described.

Acidosis↗
PubMed2001

Intensive voice treatment (LSVT) for patients with Parkinson's disease: a 2 year follow up.

OBJECTIVES: To assess long term (24 months) effects of the Lee Silverman voice treatment (LSVT), a method designed to improve vocal function in patients with Parkinson's disease. METHODS: Thirty three patients with idiopathic Parkinson's disease were stratified and randomly assigned to two treatment groups. One group received the LSVT, which emphasises high phonatory-respiratory effort. The other group received respiratory therapy (RET), which emphasises high respiratory effort alone. Patients in both treatment groups sustained vowel phonation, read a passage, and produced a monologue under identical conditions before, immediately after, and 24 months after speech treatment. Change in vocal function was measured by means of acoustic analyses of voice loudness (measured as sound pressure level, or SPL) and inflection in voice fundamental frequency (measured in terms of semitone standard deviation, or STSD). RESULTS: The LSVT was significantly more effective than the RET in improving (increasing) SPL and STSD immediately post-treatment and maintaining those improvements at 2 year follow up. CONCLUSIONS: The findings provide evidence for the efficacy of the LSVT as well as the long term maintenance of these effects in the treatment of voice and speech disorders in patients with idiopathic Parkinson's disease.

Aged↗
PubMed2000

The effect of transient hypercapnia on task-related changes in cerebral blood flow and blood oxygenation in awake normal humans: a functional magnetic resonance imaging study.

It has recently been reported in alpha-chloralose anesthetized rats that the hemodynamic response to somatosensory stimulation almost doubled following transient hypercapnia (THC). In principle, this effect could be employed to enhance the sensitivity of perfusion-based fMRI experiments. To investigate whether a comparable effect was detectable in awake normal humans, changes in cerebral blood flow (DeltaCBF) and the effective transverse relaxation time (DeltaT(2)*) induced by a visual search task were measured in 10 healthy volunteers before and after THC. Concerning DeltaT(2)* no significant differences were found, whereas in four subjects DeltaCBF was significantly decreased (p < 0.01) following THC. These results demonstrate no increase in the CBF response following THC for awake humans. We conclude that the most likely explanation for this discrepancy with the earlier results obtained with animals is an as yet unknown mechanism of modulation of the cholinergic system by the anesthesia.

Adult↗
PubMed2000

Facilitation of electric forepaw stimulation-induced somatosensory activation in rats by additional acoustic stimulation: an fMRI investigation.

The influence of scanner acoustic noise on somatosensory activation pattern in rat cortex was investigated by functional magnetic resonance imaging (fMRI) using the blood oxygenation level-dependent (BOLD) contrast. This was achieved by two approaches. The first approach was to compare a conventional, loud fMRI sequence with a new sequence, in which the noise level was reduced by about 30 dB. In the second approach, the inner ear of the animal was destroyed, resulting in deafness. We compared the activation patterns obtained with both sequences before and after cochleotomy. The activated area was larger when data were sampled with background noise, and was also larger before cochleotomy than after. Thus, facilitation of somatosensory activation is induced by additional acoustic stimulation. Magn Reson Med 44:317-321, 2000.

Acoustic Stimulation↗
PubMed2000

Functional MRI at 4.7 tesla of the rat brain during electric stimulation of forepaw, hindpaw, or tail in single- and multislice experiments.

Stimulation of peripheral nerves activates corresponding regions in sensorimotor cortex. We have applied functional magnetic resonance imaging (fMRI) techniques to monitor activated brain regions by means of measuring changes of blood oxygenation level-dependent contrast during electric stimulation of the forepaw, hindpaw, or tail in rats. During alpha-chloralose anesthesia, artificial respiration, and complete muscle relaxation, stimulations were delivered at 3 Hz via subcutaneous bipolar electrodes with 500-microseconds-current pulses of 0.2-2.0 mA. Single- or multislice gradient echo images were collected during recording sessions consisting of five alternating rest and stimulation periods. Stimulation of the right and left forepaws and hindpaws repeatedly led to robust activation of the contralateral sensorimotor cortex. There was a significant correlation (P < 0.05) between current pulse strength and amount of activation of the sensory cortex during forepaw stimulation. The center of the main cortical representation of the forepaw was situated 3.4 mm lateral to the midline and 5 mm posterior to the rhinal fissure. The main representation of the hindpaw was 2.0 mm lateral to the midline and 6 mm posterior to the rhinal fissure. Tail stimulation gave rise to a strikingly extended bilateral cortical activation, localized along the midline in medial parietal and frontal cortex 4 and 5 mm posterior to the rhinal fissure. In conclusion, the experiments provide evidence that peripheral nerve stimulation induces a fMRI signal in the respective division of the somatosensory cortex in a stimulus-related manner. The marked cortical activation elicited by tail stimulation underlines the key importance of the tail.

Afferent Pathways↗
PubMed2000

Arterial spin tagging perfusion imaging of rat brain: dependency on magnetic field strength.

Perfusion-weighted imaging (PWI), using the method of arterial spin tagging, is strongly T(1)-dependent. This translates into a high field dependency of the perfusion signal intensity. In order to determine the expected signal improvement at higher magnetic fields we compared perfusion-weighted images in rat brain at 4.7 T and 7 T. Application of PWI to focal ischemia and functional activation of the brain and the use of two different anesthetics allowed the observation of a wide range of flow values. For all these (patho-)physiological conditions switching from 4.7 T to 7 T resulted in a significant increase of mean perfusion signal intensity by a factor of 2.96. The ratio of signal intensities of homotopic regions in the ipsi- and contralateral hemisphere was field-independent. The relative contribution of a) T(1) relaxation time, b) net magnetization, c) the Q-value of the receiver coils and d) the degree of adiabatic inversion to the signal improvement at higher field strength were discussed. It was shown that the main parameters contributing to the higher signal intensity are the lengthening of T(1) and the higher magnetization at the higher magnetic field.

Animals↗
PubMed2000

Probability of metabolic tissue recovery after thrombolytic treatment of experimental stroke: a magnetic resonance spectroscopic imaging study in rat brain.

The effect of thrombolytic therapy on metabolic changes was studied in rats submitted to thromboembolic stroke. Reperfusion was initiated at three different time points, 1.5, 3, and 4.5 hours after embolism (n = 3 each), by injection of recombinant tissue-type plasminogen activator (rt-PA). Recovery was observed during 5 hours of reperfusion using perfusion-weighted images and a two-dimensional 1H magnetic resonance spectroscopic imaging (MRSI) technique. Temporal evolution of the cerebral metabolites lactate and N-acetyl-aspartate (NAA) was determined. To analyze the chances of metabolic tissue recovery, the outcome of treatment, defined by a reversal of lactate concentration, was compared with the lactate intensity before treatment. In untreated animals (n = 4), clot embolism resulted in a drop of perfusion signal intensity in the occluded hemisphere followed by an increase of lactate concentration and a decrease of NAA that persisted throughout the observation period. Thrombolysis partially restored blood flow, but the mean lactate concentration decreased only slightly after successful lysis in animals treated 1.5 hours after embolism. If treatment was initiated later, no decline of lactate level was observed. Five hours after initiation of thrombolysis, the average tissue lactate amounted to 95 +/- 6, 111 +/- 17, and 139 +/- 60% of the early ischemic value (40 minutes after embolization) if treatment began 1.5, 3, and 4.5 hours after embolism, respectively. The NAA level declined slightly but never showed a recovery after rt-PA treatment. In individual pixels, the probability of metabolic tissue recovery clearly declined with increasing lactate concentration before thrombolysis. Interestingly, this probability was independent of treatment delay, but the number of pixels with low lactate declined with increasing ischemia time. Potential clinical applications of MRSI include monitoring of therapeutic intervention as well as support for prognosis of outcome after rt-PA treatment.

Animals↗
PubMed2000

Secondary deterioration of apparent diffusion coefficient after 1-hour transient focal cerebral ischemia in rats.

Recent investigations on transient focal cerebral ischemia suggested recovery of energy metabolism during early reperfusion, but followed by secondary energy failure. As disturbances of energy metabolism are reflected by changes of the apparent diffusion coefficient (ADC) of water, the aim of the current study was to follow the dynamics of the ADC during 1 hour of middle cerebral artery occlusion (MCAO) and 10 hours of reperfusion. The right MCA was occluded in male Wistar rats inside the magnet using a remotely controlled thread occlusion model. Diffusion-, perfusion-, and T2-weighted images were performed repetitively, and ADC, perfusion, and T2 maps were calculated and normalized to the respective preischemic value. The lesion volume at each time point was defined by ADC < 80% of control. At the end of 1-hour MCAO the hemispheric lesion volume was 22.3 +/- 9.0%; it decreased to 6.4 +/- 5.7% in the first 2 hours of reperfusion (P < 0.01), but then increased again, and by the end of 10 hours of reperfusion reached 17.3 +/- 9.3%. The mean relative ADC in the end ischemic lesion volume significantly improved within 2 hours of reperfusion (from 65.7 +/- 1.2% to 90.1 +/- 6.7% of control), but later declined and decreased to 75.4 +/- 7.3% of control by the end of the experiment. Pixels with secondary deterioration of ADC showed a continuous increase of T2 value during the first 2 hours of reperfusion in spite of ADC improvement, indicating improving cytotoxic, but generation of vasogenic edema during early reperfusion. A significant decrease of the perfusion level was not observed during 10 hours of recirculation. The authors conclude that the improvement of ADC in the early phase of reperfusion may be followed by secondary deterioration that was not caused by delayed hypoperfusion.

Animals↗
PubMed2000

CO(2) reactivity measured by perfusion MRI during transient focal cerebral ischemia in rats.

BACKGROUND AND PURPOSE: CO(2) response was examined in rats undergoing 60 minutes of middle cerebral artery occlusion (MCAO) and 4.5 hours of reperfusion. Because it is not clear whether the vasoreactivity improves during reperfusion in parallel with tissue recovery, CO(2) response was determined spatially resolved, sequentially in the initially ischemic but later recovered areas and in the permanently damaged areas. METHODS: Apparent diffusion coefficient (ADC) maps were calculated from diffusion-weighted images, whereas CO(2) reactivity maps were determined from the difference in perfusion signal intensity before and after CO(2) stimulation. CO(2) reactivity (administration of 6% CO(2) for 5 minutes) was expressed in % change of perfusion signal intensity/mm Hg of PCO(2) increase. ATP levels of tissue were used as a measure of outcome. The recovered and permanently damaged tissues were differentiated by combined use of end-ischemic ADC map and ATP image at the end of the experiment. RESULTS: The preischemic (control) CO(2) reactivity of 3.5+/-0.9%/mm Hg decreased dramatically during MCAO in the ischemic hemisphere. During reperfusion, it remained <1%/mm Hg in the region with end-ischemic ADC <80% of the preischemic control value, but showed gradual recovery in the region with end-ischemic ADC >80% of control. Although at the end of the experiment the CO(2) reactivity was significantly higher in the recovered tissue than in the permanently damaged tissue (1.15+/-0.44 and 0.13+/-0.47%/mm Hg, respectively; P:<0.01), it still remained far below the normal control value (P:<0.01). CONCLUSIONS: The noninvasive perfusion-weighted MR imaging in combination with a CO(2) challenge permits the investigation of the spatially resolved vascular reactivity during a longitudinal study of cerebral ischemia. Our data suggest that severe ischemia is followed by a prolonged disturbance of CO(2) reactivity, despite already normalized energy metabolism.

Adenosine Triphosphate↗