Threshold of regional cerebral blood flow for infarction in patients with acute cerebral ischemiaSeuil dedébit sanguin cérébral correspondant à un infarctus chez les patients ayant une ischémie cérébrale aiguë
Threshold of regional cerebral blood flow (rCBF) forcerebral tissue survival in relation to time was studied in patientswith acute cerebral ischemia with xenon-enhanced computed tomography(XeCT). Case 1: A 58-year-old man with right hemiparesis, totalaphasia and a high intensity area of 1cm2 in the leftinsula on diffusion weighted image underwent XeCT CBF study beforeand after intra-arterial local thrombolytic therapy (IALT) on theoccluded middle cerebral artery (MCA) 4 hours and 7 hours afterstroke onset, respectively. Case 2: A 65-year-old woman withrecurrent transient ischemic attacks (TIAs) caused by severe stenosisof the left MCA underwent XeCT CBF study 5 hours after onset of thelast attack. XeCT was conducted by 5-min wash-in method. In Case 1the rCBF in the pre-IALT MCA territory was 4 to19ml/100g/min. The area where rCBF in the post-IALT increasedto above 15ml/100g/min were saved, but the other area whereit remained in the 9 to 14ml/100g/min evolved into infarct onsubsequent CT scan/MR (magnetic resonance) imaging. The patientwas discharged with only mild motor dysphasia. In Case 2 the leftcorona radiata showed rCBF of 7ml/100g/min and this areaevolved into infarct on MR imaging. The patient was discharged homewith right hemiparesis. Our results showed validity of the rCBFthreshold in acute cerebral ischemia reported by Jones et al. Residual rCBF in the acute stage of cerebral ischemic stroke canpredict the fate of the lesion.
Résumé
Le seuil de débitsanguin cérébral (DSC) pour la survie tissulaire enfonction du temps était étudié par le scanner auxénon (XeCT) chez les patients présentant uneischémie cérébrale aiguë. Casn° 1 : un XeCT a été réalisé chezun homme de 58 ans avec une hémiparésie droite,une aphasie mixte et une zone hyperintense de 1 cm2au niveau de l’insula gauche sur l’IRM de diffusion. LeXeCT a été effectué avant et après unethrombolyse intra-artérielle (TIA) de l’occlusion del’artère cérébrale moyenne (ACM) àla 4e et 7e heure de l’accidentischémique. Cas n̊2 : une femme de 65 ans avecune sténose sévère de l’ACM gaucheresponsable des accidents ischémiques transitoires (AIT)répétés. Le XeCT a étéréalisé chez ce patient 5 heure après sonaccident initial. Dans le cas n̊1, le DSC avant la thrombolyseétait de 4 à 19 ml/100g/min. Les zonesavec un DSC > 15 ml/100g/min ontété récupérées et celles< 9 ml/100g/min ont évoluées versl’infarctus aux XeCT et IRM de contrôle. Le patient estsortie de l’hôpital avec une aphasie motricemodérée. Dans le cas n̊2, le DSC de la coronaradiata gauche était 7 ml/100g/min avec uneévolution vers l’infarctus à l’IRM. Lapatiente est sortie de l’hôpital avec unehémiparésie droite. En conclusion, nos résultatsvalident le seuil d’ischémie cérébralerapporté par Jones et al. Le DSC résiduel dans la phaseaiguë de l’ischémie cérébrale peutprédire l’évolution de lalésion.
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Individual CBF maps were next multiplied by the previously generated DMN masks and thresholded at a value of 15 to reduce partial voluming effects. A value of 15 was selected to prevent the inclusion of gray–white matter boundary voxels with CBF values suggestive of physiological ischemia (Hossmann, 1994), while including voxels with values suggestive of viable cerebral tissue (Ohashi et al., 2005; Powers et al., 1985). Figs. 2B and D depict the DMN ROI mask in a single representative subject.
A growing body of evidence indicates that cardiorespiratory fitness attenuates some age-related cerebral declines. However, little is known about the role that myocardial function plays in this relationship. Brain regions with high resting metabolic rates, such as the default mode network (DMN), may be especially vulnerable to age-related declines in myocardial functions affecting cerebral blood flow (CBF). This study explored the relationship between a measure of myocardial mechanics, global longitudinal strain (GLS), and CBF to the DMN. In addition, we explored how cardiorespiratory affects this relationship. Participants were 30 older adults between the ages of 59 and 69 (mean age = 63.73 years, SD = 2.8). Results indicated that superior cardiorespiratory fitness and myocardial mechanics were positively associated with DMN CBF. Moreover, results of a mediation analysis revealed that the relationship between GLS and DMN CBF was accounted for by individual differences in fitness. Findings suggest that benefits of healthy heart function to brain function are modified by fitness.
Could the infarction be diagnosed quickly and accurately at the acute stage by CT perfusion imaging (CTPI) technology? Whether the images of CTPI will correspond with the pathological changes or not? All the questions need to be solved by experimental and clinical studies.
To reveal the rules of perfusion map changes and guide the early diagnosis of hyperacute cerebral infarction by analyzing the correlation of CTPI with pathological manifestations for hyperacute cerebral infarction.
A randomized controlled animal experiment.
Experimental Center of Medical Radiology, Longgang Central Hospital of Shenzhen City.
Forty-two adult New Zealand rabbits of (2.6±0.5) kg, either male or female, were randomly divided into experimental group (n =36) and control group (n =6). Six rabbits in the experimental group were observed after ischemia for 0.5, 1, 2, 3, 4 and 6 hours respectively, and 1 rabbit in the control group was observed at each corresponding time point.
The experiments were carried out in the Experimental Center of Medical Radiology, Longgang Central Hospital of Shenzhen City from March 2003 to July 2004. Rabbit models of cerebral infarction were established by modified O'Brein method. The rabbits in the experimental group were scanned at 0.5, 1, 2, 3, 4 and 6 hours after ischemia respectively. The dynamic CT scan slice was 13 mm from the anterior edge of the frontal cortex, and six fake color functional images were obtained, including cerebral blood flow map (CBF map), cerebral blood volume map (CBV map), peak to enhancement map (PE map), flow without vessels map, time to peak map (TP map), time to start map (TS map). The manifestations and changes of the functional maps in different interval were observed. Bilateral symmetric ranges of interest (ROI) were drawn separately on the CBF map, CBV map, TP map and TS map. The blood flow parameters of focal and contralateral cerebral tissues could be obtained to calculate relative cerebral blood flow (rCBF, rCBF=focal CBF/contralateral CBF), relative cerebral blood volume (rCBV, rCBV= focal CBV/contralateral CBV), a relative time to peak (rTP, rTP= focal TP–contralateral TP), a relative time to start (rTS, rTS= focal TP–contralateral TP). The perfusion maps were input into AutoCAD software. The percents of ischemic cores and peri-ischemic areas accounting for contralateral cerebral hemisphere were calculated. The animals were anesthetized and killed, then the cerebellum and low brain stem were taken out. The brain tissues were cut on coronal plane at 14 mm from the anterior edge of the frontal cortex, a 2-mm piece anterior to the incision, and a 3-mm piece posterior to the incision. The anterior piece was fixed, stained and observed. A 1-mm slice was cut from the front of the posterior piece tissues as electron microscope sample, the remnant was fixed and then taken out, and the location and size of stained “white” areas were observed as the reference for electron microscope sample. The correlation between CTPI and pathological manifestations was observed.
Laws of time and spatial changes of ischemic areas; Pathological changes of the ischemic tissues; Correspondency between CTPI and pathological manifestations.
Laws of time and spatial changes of ischemic areas: Relative ischemic-core areas were consistent in each perfusion map, increased incessantly along with the ischemic times. Relative peri-ischemic areas were inconsistent in each perfusion map, on CBF map from 1 to 6 hours after ischemia, the area of ischemic core increased from (1.503±0.523)% to (7.125±1.054)%, the ascending trend occurred. But the peri-ischemic areas showed a descending trend on CBF map, the areas decreased from (8.960±0.719)% to (5.445±0.884)% from 0.5 to 6 hours; The relative areas were the largest one on TP maps, the average value was (32.796±3.029)% at 0.5 hour after ischemia happening (60.540±1.683)% at 6 hours. The trend of ischemic areas was increased. No obvious change was observed on TS maps. Pathological changes of the ischemic tissues: Under light microscope, there was no obvious change at 0.5–2 hours after ischemia, edema at 3 hours, karyopycnosis at 4 hours and eosinophilous changes at 6 hours; Under electron microscope, there was edema in ischemic cores within 4 hours after ischemia, whereas karyopycnosis or structure vanished after 4 hours; Edema was observed in peri-ischemic areas. Correlation between CTPI and pathological manifestations: On CTPI maps, the ischemic core was blue on CBF and CBV maps, black on TP and TS maps. Along with the ischemic times, the rCBF and rCBV decreased, whereas the rTP and rTS prolonged. Hemodynamic parameters were not significantly different within 2 hours of ischemia and 2 hours after ischemia. The rTP and rTS became 0 after 1 and 2 hours respectively. On CTPI maps the peri-ischemic area was red on CBF and CBV maps, red and yellow on TS maps, red on TP maps. Along with the ischemic times, the rCBF decreased, and the lowest level was always at about 20%, whereas the rTP and rTS prolonged.
CTPI manifestations corresponded well with pathological findings, and it is a sensitive, stable and reliable technique to diagnose hyperacute cerebral infarction. TP map was more sensitive than CBF map and TS map in exhibiting the peri-ischemic areas, thus TP maps could be a good choice for observing peri-ischemic areas.