This gave rise to the concept of the BBB, which is not known to be complex. The function of the BBB is to maintain homeostasis of the neuronal environment (Bradbury I979). Long (1970) suggested that it would be more correct to speak of the complete absence of the BBB as a.
Metastatic tumors in the brain induce proliferation of non-neural capillaries, characteristic of the tissue of origin. Various forms of ionizing radiation have been shown to increase the durability of the BBB (Bradbury L979a). The total dose required to produce acute breakdown of the BBB is large (Uaír t. Roth 1964).
Such enhancement is likely due to changes in BBB integrity induced by acute demyelination that allow extravasation. Experimentally induced severe hypertension leads to increased permeability of the BBB (Byrorn L954), sensitivity is increased by irradiation (Blornstrand et al. I975a) and decreased by dexamethasone. Increased BBB permeability has been documented after carotid injection of various CMs (Harrington et al 1966, Jeppsson &.
Absence of local and systemic toxÍeity;
Clearance of intrathecal CM depends on mixing of the media in the CSF and its rate of absorption by the CSF. In view of the role that spinal arachnoid proliferation plays in the excretion of water-soluble CM from the CSF, the presence of arachnoiditis would be expected to reduce the excretion rate. The common carotid artery divides into external and internal carotid arteries beyond the origin of the thyroid gland.
The external carotid artery is much larger and represents the continuation of the main trunk of the cortmon vessel. Two branches of the internal maxillary artery provide an anastomosis between the external and internal carotid vessels. Selective catheterization of the internal carotid artery via the femoral artery is difficult because of its narrowness.
Thus, in addition to the lingual artery containing the catheter, the internal carotid artery innervated the only patent branch of the common carotid artery. For definitive studies, therefore, it was decided to close the proximal lumen. Sixteen preliminary studies were performed to develop a technique for obtaining CT scans of the canine brain after regeneration.
Intense enhancement of the distribution of the middle cerebral artery, including the basal ganglia (arrow), is not outlined. In conventional human studies, intravenous r^rater-soluble CM was given to demonstrate increased permeability or breakdown of the BBB (Section 1.6). After the CT studies (Section 2.L.4), coronal sections of the brain were cut in the same plane and at corresponding levels as the CT scans.
On the other hand, variable staining of the anterior cerebral and posterior cerebral artery distributions \^ras observed. For this reason, the distribution of the middle cerebral artery was chosen for comparison, between the injected and control hernispheres in the definitive studies.
STUDY NO. ACA MCA PCA BASAL GANGLIA
Definitive Studles
- In Vitro Studies
After injection of water-soluble CM, control radiographs were performed to demonstrate the presence of CM in the subarachnoid space. A technique for performing a post-removal CT scan of the canine brain has been previously developed (Section 2.1.4). Six preliminary studies were performed without intrathecal injection to determine normal cortical density in the dog.
One hour after intrathecal injection of the CM test, the brain was removed and a coronal CT examination was performed (section 2.L.4). The window width of the diagnostic display console was set to "measure" and the level to 24 EMI units. This was the maximum value of the normal dog brain, determined in the six preliminary studies without CT.
The depth of attenuation values above those of normal cortex could then be measured directly perpendicular to the brain surface in the same region of the temporal lobe for each examination (Figure 2.3.4.I). In these preliminary studies, a blind subjective assessment of the penetration depth of CI in both tenporal lobes at adjacent levels was assessed by two independent observers and confirmed the reproducibility of this assessment method. To establish that brain penetration by intrathecal CM is not just a post-mortem phenomenon, four in vivo studies were performed and after an in vivo coronal CT at one hour, the dog was euthanized, the brain removed, and a coronal CT of the brain was performed. . brain running.
Fifteen to sixty minutes after the end of the intrahecal injection, the animals are sacrificed by an intravenous injection of 10-15 sec of saturated potassium chloride solution. With this information, a blind subjective assessment was made of the penetration depth of CM in both temporal lobes, as made at two adjacent levels in each of the eight studies. The window width of the diagnostic display console is set to the size setting and the level is set to 24 EYLI units.
The depth of attenuation values above that of normal gray matter could then be measured directly perpendicular to the brain surface in the same region of the parietal lobe for each examination (Figure 2.4.I.2). The patchy brain penetration at 15 minutes (A) is associated with the cortical sulci, but at 60 minutes (B) a relatively even distribution of the CM throughout the gray matter has occurred.
I Aíns of Study
Subjective assessment of the distribution of meËrizamide and the depth and degree of brain penetration was carried out using the ttmeasuret. The effect of intravenous CM on the integrity of the BBB was detected in rabbits. If the integrity of the BBB is disrupted, the 99nTc-pertenetate crosses freely into the extracellular fluid of the brain parenchyma.
The blood sample and each half of the brain are then counted separately in a Searle gamma counter using a. Visual assessment of the presence and degree of Evans' Blue staining in the distribution of the rníddle cerebral artery by two independent observers is given in Table 3.1.1.1. Visual assessment of the presence and degree of Evans' Blue staining in the distribution of the middle cerebral artery was.
Regions of interest (100 pixels) in the distribution of the middle cerebral artery in the injected and control hemispheres. I have no evidence of Evans blue staining of the parenchyma in the parietal reglon of either. Mean CT attenuation values (nOI = 100 pills) in cortical gray xnatter and white matter in patients.
None of the patients showed a noticeable increase in the density of the white matter at 6 hours or 24 hours of the patient (nurnber 13). Increased permeability of the BBB after intracarotid injections of various ionic water-soluble CM waxes. The effect of cM on the BBB is not related to the iodine content of the CM, since similar non-iodized.
More recently Zamani et al (1981) showed increased BBB permeability in dogs using qualitative Evans' Blue and quantitative CT assessment. Despite a very large intravenous dose of sodium iothalamate (3.36gl/kg)r, a marked increase in BBB permeability to Evans' Blue or 99urTc-pertechnetaÈe was demonstrated. Minor morphological changes in normal cerebral capillaries could not be excluded, however BBB disparity appeared to be maintained despite this large CM level.
Presumably, such extracellular CM contacts the brain side of the blood-brain interface (Figure 1.3.1.1).
An experlmental evaluation of used for cerebral angiographY
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