[en] The method of the continuous inhalation technique of oxygen-15 labelled CO₂ coupled with positron emission tomography for the measurement of cerebral blood flow (C.B.F.) is described. An indirect experimental verification that this technique allowed the measurement of C.B.F. has been carried out in baboons by showing the expected change in the measured parameter with variations in the PaCO₂. A critical investigation of the C¹⁵O₂ model was performed. The amount of tracer present in the cerebral vascular pool has a negligible effect on C.B.F. value. The use of a mean brain-blood partition coefficient of water instead of that specific to gray or to white matter is commented upon, and its influence on the final C.B.F. value is studied. Lastly, the problem of the limited diffusion of water across the blood-brain-barrier is discussed. The study of the combined effects of gray-white mixing and limited wates extraction of the C.B.F. value shows that the C¹⁵O₂ technique tends to understimate real C.B.F., and that this error is more severe with high flows and even gray white mixing. These limitations do not depart from the possibility to estimate in the same brain locus not only C.B.F. but oxygen utilization as well by the consecutive inhalation of C¹⁵O₂ and ¹⁵O₂. The advantages of this possibility has already been shown in a number of clinical studies

[en] Published in summary form only

[en] Short communication

[en] This report is concerned with the case of a man afflicted by multiple cerebral arteriovenous malformations. The rCBF measurement with Xe-133 inhalation was relatively elevated. However, I-123 iodoamphetamine imaging showed a relative reduction in radioactivity, and was a more accurate reflection of the clinical situation

[en] The isolated measurement of cerebral blood flow can lead to gross errors in vascular disease, particularly ischaemic disease, because of disruption of the relations between blood flow and metabolism. In contrast, the measurement of cerebral blood flow combined with measurement of the haemodynamic reserve overcomes these difficulties, regardless of the method of evaluation: reactivity to CO₂ or to acetazolamide; measurement of the flow/volume ratio. The author demonstrates that these measurements are even more valuable in situations in which morphological examinations (MRI or computed tomography) are of little value: transient ischaemic attacks, asymptomatic carotid artery stenosis, etc. However, these measurements are useful in constituted infarctions or in vasospasm to assess the distant effects or to guide the therapeutic adjustment or even to provide prognostic elements. Combined measurement of perfusion and haemodynamic reserve, although it does not constitute a formal proof, is now largely accessible by means of non-specialized gamma cameras with determination of the flow/volume ratio

[en] The concept of haemodynamic reserve (H.R.) understands two steps: the increase of the cerebral blood volume (C.B.V.) in compensation to the decrease of the brain central blood pressure, and then after, the increase of the oxygen extraction rate (OER), that insures the steady state of the consumption metabolic rate of O₂ (CMRO₂). The main methods of H.R. measurement are presented and discussed. The most often used is the acetazolamide challenge, but without overall technical consensus. The main indications of the coupled C.B.F. - H.R. measurements are presented: in transient ischemic attacks (TIAs), in assistance with the surgical decision (endarterectomy, extra-intracranial By-pass). It appears that CBF-HR measurement is useful to depicts abnormalities in TIAs (when CT or MRI are normals), to help the surgical decision when the carotid stenosis is lower than 70%, or even to manage the operative methodology (extra-corporal shunting) when the stenosis is higher than 70% with alterations of abolition of the H.R. values. (author)

[en] The isolated measurement of cerebral blood flow can lead to gross errors in vascular disease, particularly ischaemic disease, because of disruption of the relations between blood flow and metabolism. In contrast, the measurement of cerebral blood flow combined with measurement of the haemodynamic reserve overcomes these difficulties, regardless of the method of evaluation: reactivity to CO₂ or to acetazolamide; measurement of the flow volume ratio. The author demonstrates that these measurements are even more valuable in situations in which morphological examinations (MRI or computed tomography) are of little value: transient ischaemic attacks, asymptomatic carotid artery stenosis, etc. However, these measurements are useful in constituted infarctions or in vasospasm to assess the distant effects or to guide the therapeutic adjustment or even to provide prognostic elements. Combined measurement of perfusion and haemodynamic reserve, although it does not constitute a formal proof, is now largely accessible by means of non-specialized gamma cameras with determination of the flow/volume ratio

[en] Short communication

No abstract available

[en] We report a clinical case of a new type of discrepancy between two tracers usable for brain functional imaging: the Xenon 133 and the HmPAO-^99mTc. A 66 year old men had presented a brutal left hemiplegia with transient troubles of consciousness in relation with a right protuberant infarct without hemispheric lesions. The functional studies were performed 4 months after the onset, successively by the Xe inhalation method and immediately after the HmPAO study. On a patient kept still on the camera bed when cerebral blood flow (CBF) study depicted both a right cerebellar low flow and a slightly decreased CBF in the controlateral hemisphere ('hemispheric diaschisis'), the HmPAO SPECT was normal. This observation illustrates both the crossed hemispheric diaschisis and a new type of discrepancy: indeed, the known cases were until now in relation with alterations of the blood: brain barrier, which doses not exist in our report. The explanation of this type of discrepancy remains unclear but is probably linked with the HMPAO retention mechanisms. (author)