Cerebral blood flow evaluation of arteriovenous malformations with stable xenon CT

Twenty patients with supratentorial arteriovenous malformations (AVMs) were evaluated with angiography, conventional CT, and stable xenon CT to determine cerebral blood flow. Contralateral and ipsilateral regions of interest relative to the AVM were evaluated from cerebral blood flow maps and correlated with angiography. A significant decrease in cerebral blood flow was observed in the ipsilateral cortical gray matter adjacent to the AVM relative to the corresponding contralateral cortex (mean difference = 9.52 ml/100 g/min, p less than .01). The larger AVMs (greater than 8 cm3) were associated with a more marked decrease with a mean difference of 12.22 ml/100 g/min (p less than .02). Regions of interest were also chosen on the basis of angiographic findings, which suggested areas of decreased flow. Comparison of these areas with analogous contralateral areas also showed a significant decline in cerebral blood flow (mean difference = 8.86 ml/100 g/min); this decline was greater with larger AVMs (volume greater than 8 cm3), which had a mean difference of 11.38 ml/100 g/min (p less than .01). Our correlative study enabled us to pinpoint the regions most likely to have reduced flow from an AVM.     

Correlation of regional cerebral blood flow measured by stable xenon CT and perfusion MRI

PURPOSE: The purpose of this work was to investigate the validity of perfusion MRI in comparison with stable xenon CT for evaluating regional cerebral blood flow (rCBF). METHOD: The rCBF was measured by xenon CT and perfusion MRI within a 24 h interval in 10 patients (mean +/- SD age 63 +/- 10 years). For perfusion MRI, absolute values of rCBF were calculated based on the indicator dilution theory after injection of 0.1 mmol/kg of Gd-DTPA. Eight to 10 regions of interest (37 mm2) were located in the white and gray matter on the rCBF images for each of the 10 patients. RESULTS: The mean +/- SD values of rCBF in gray matter were 48.5 +/- 14.1 ml/100 g/min measured by xenon CT and 52.2 +/- 16.4 ml/100 g/min measured by perfusion MRI. In the white matter, the rCBF was 22.6 +/- 9.1 ml/100 g/min by xenon CT and 27.4 +/- 6.8 ml/100 g/min by perfusion MRI. There was a good correlation of rCBF values between perfusion MRI and xenon CT (Pearson correlation coefficient 0.83; p < 0.0001). CONCLUSION: Comparable to xenon CT, perfusion MRI provides relatively high resolution, quantitative local rCBF information coupled to MR anatomy.     

Investigation of cerebral blood volume measurement

PURPOSE: Cerebral blood blow (ml/100g/min) (CBF) and cerebral blood volume (%) (CBV) were determined in 102 patients (68 men and 34 women; average age, 55.6 years) with diagnostic cerebral blood flow accident. METHODS: CBF was obtained by xenon inhalation computed tomography (Xe CT) and transit time (TT) by perfusion CT. CBV was calculated under the expression CBV=CBF x TT. The patients were divided into three categories: mild (outpatient), moderate (inpatient), and serious (dead), and CBF and CBV were compared between categories. RESULTS: On regions of interest (ROI) in the thalamus, the value for mild cases was 58.8+/-10.4 ml/100g/min (CBF) and that for moderate cases was 40.2+/-19.4, a significant difference. In serious cases, CBV was decreased in the thalamus, but there was no difference in CBF between mild and moderate cases. CONCLUSION: CBV was useful for determining prognosis in severe cases of diagnostic cerebral blood flow accident.     

Xenon/CT blood flow mapping of the kidney and liver

A noninvasive technique for measuring blood flow by xenon-enhanced X-ray transmission CT has been developed and reported quite extensively in recent years. In this method nonradioactive xenon gas is inhaled, and the temporal changes in radiographic enhancement produced by the inhalation are measured by sequential CT. Time-dependent xenon concentration within various tissue segments is used to derive local blood flow maps. The method has been amply discussed in relation to assessment of local cerebral blood flow. Its application to other body organs is explored in this paper, in which results from six preliminary blood flow studies in the liver and kidneys of nonhuman primates are reported. Blood flow in renal cortex ranged from 150 to 280 ml/100 cc/min and hepatic tissue perfusion from 80 to 120 ml/100 cc/min. The advantages and limitations of the method in such applications are discussed.     

Flow volume in the common carotid artery detected by color duplex sonography: an approach to the normal value and predictability of cerebral blood flow

PURPOSE: To determine normal common carotid artery (CCA) flow volume, its relationship with age, and the predictability of cerebral blood flow (CBF) by color duplex sonography. SUBJECTS AND METHODS: Forty-five healthy subjects (18 men, 27 women, 23-86 years old) and 13 patients (3 men, 10 women, 51-88 years old) without neurological disease underwent color duplex sonography. All 13 patients also underwent xenon CT. CCA flow volume in the healthy subjects was measured to determine normal values. This volume was divided by mean brain weight to estimate CBF, which was correlated with CBF measured by xenon CT in regions of ipsilateral internal carotid arteries (ICA). RESULTS: In healthy subjects, CCA flow volume ranged from 155.0-458.8 ml/min (mean+/-SD: 267.77+/-59.91), corresponding to an estimated CBF of 12.43-32.84 ml/min/100 g brain weight (mean+/-SD: 20.63+/-4.22). No relationship was found between flow volume and age. A good correlation was found between estimated CBF and CBF measured by xenon CT in regions of both ICAs (gamma=0.713, p=0.0062 on the left; gamma=0.686, p=0.0096 on the right). CONCLUSION: By using color duplex sonography, we established a set of normal CCA flow volumes, which do not decline with age. Estimated CBF derived from flow volume can predict actual CBF.     

Quantitative tissue blood flow evaluation of pancreatic tumor: comparison between xenon CT technique and perfusion CT technique based on deconvolution analysis

PURPOSE: There has been one report that tissue blood flow (TBF) quantification with xenon CT was effective in predicting the therapeutic response to an anticancer drug in pancreatic cancer. The purpose of this study was to evaluate the correlation between the TBF of pancreatic tumors calculated with xenon CT and those with perfusion CT, in order to evaluate whether perfusion CT could replace xenon CT. MATERIALS AND METHODS: Nine patients with pathologically proved pancreatic tumors who underwent both xenon CT and perfusion CT were included. Results: Quantitative TBF of pancreatic tumors measured by perfusion CT ranged from 22.1 to 196.2 ml/min/100 g (mean+/-SD, 52.6+/-54.8 ml/min/100 g). In contrast, those obtained by xenon CT ranged from 10.3 to 173.6 ml/min/100 g (mean+/-SD, 47.4+/-49.4 ml/min/100 g). There was a good linear correlation between xenon CT and perfusion CT (y=0.8537x+2.48, R2=0.895: p<0.05). CONCLUSION: The TBF of pancreatic tumors measured by xenon CT and perfusion CT techniques showed a close linear correlation. We can expect that perfusion CT based on the deconvolution algorithm may replace xenon CT to predict the effect of pancreatic tumor treatment with anticancer drugs.     

Blood flow mapping in the human liver by the xenon/CT method

In the noninvasive, nonradioactive xenon/CT method of blood flow measurement, xenon gas is inhaled, and the temporal changes in radiographic enhancement produced by the inhalation are measured by sequential CT; time-dependent xenon concentration within various tissue segments is then used to derive local blood flow maps. The usefulness of the method in the assessment of local cerebral blood flow has been documented. In this paper we explore its application to blood flow measurement in the human liver. In our preliminary clinical studies, hepatic blood flow ranged from 50 to 120 ml/100 cc/min in normal and adequately supplied tissue, and lower flow values were observed in tissue with abnormal function. The advantages and limitations of the method in such applications are discussed.     

Stable xenon CT cerebral blood flow imaging: rationale for and role in clinical decision making

The stable xenon CT method of measuring cerebral blood flow has been investigated in research studies for over 10 years. Recently, it has been gaining clinical acceptance, primarily owing to a combination of several unique advantages it holds over other cerebral blood flow measurement techniques. The accuracy of this technique in quantifying low cerebral blood flow gives it a unique application in cases of brain death and acute stroke and it can be repeated after an interval of 20 min. making it possible to evaluate autoregulation and cerebrovascular reserve. Furthermore, cerebral blood flow information is directly coupled to CT anatomy. Although it is more difficult to administer than a standard CT scan, careful monitoring can ensure patient safety during the examination. In this article we review the physiologic and technical bases for the clinical application of xenon CT-derived quantitative cerebral blood flow information and discuss the advantages and disadvantages of the technique. We also describe its current clinical applications, including its usefulness in the evaluation of acute stroke, occlusive vascular disease, carotid occlusion testing, vasospasm, arteriovenous malformations, and head trauma management.     

Quantitative, non-invasive cerebral blood flow measurements with non-diffusible tracers using a heart-rate-dependent recirculation correction--application in carotid surgery

A general method is described for computation of blood flow from time-activity curves using intravenous injection of the non-diffusible radio-tracer technetium pertechnetate. A technique of recirculation correction is adopted which predicts the start and end of recirculation depending on the patient's heart rate. This method allows one to clearly separate the first transit from the following recirculation. A correction for bolus dispersion of the intravenously injected tracer is also used. The evaluation of cerebral dynamic perfusion studies in 126 unselected adult patients resulted in a normal CBF of 44.5 ml/min/100 g +/- 5% and a decreased CBF of less than 40 ml/min/100 g. The presented method was also applied for flow measurement on the neck vessels. A good correlation between values obtained from these regions and the corresponding cerebral hemispheres was found. The method was also tested in 40 patients with angiographically proven neck vessel stenosis and in 15 patients before and after surgery of carotid stenosis. The results prove that the haemodynamic relevance of carotid stenosis on cerebral blood flow can be quantified. The accuracy of the method is estimated better than 5% for cerebral blood flow values and better than 15% for blood flow values gained over the neck vessel regions.     

A measurement of regional portal blood flow with Xe-133 and balloon catheter in man

This investigation was undertaken to measure regional portal blood flow of the liver. The measurement was performed by injecting 133Xe into the proper hepatic artery through a balloon catheter and then occluding the proper hepatic artery with an inflated balloon. Data were collected using a gamma camera, and washout curves were generated. They were analyzed by the initial slope method and Kety Schmidt equation. The average regional portal blood flows were: 59.31 +/- 13.04 ml/100 g per min, 58.71 +/- 14.14 ml/100 g per min and 37.12 +/- 10.11 ml/100 g per min in hospital controls (11), patients with chronic hepatitis (10) and those with liver cirrhosis (56), respectively. In the patients with cirrhosis, the regional portal blood flow was significantly reduced (P less than 0.01). The reproducibility of this method was satisfactory. The measurement of regional portal blood flow will be useful to evaluate underlying liver injuries and determine indications of a transcatheter arterial embolization of the liver.     

Stroke risk after abrupt internal carotid artery sacrifice: accuracy of preoperative assessment with balloon test occlusion and stable xenon-enhanced CT.

PURPOSETo evaluate stable xenon-enhanced CT cerebral blood flow with balloon test occlusion as a predictor of stroke risk in internal carotid artery sacrifice.METHODSAbrupt internal carotid artery occlusion was performed by surgical or endovascular means below the origin of the ophthalmic artery in 31 normotensive patients who were assessed preoperatively by a 15-minute clinical balloon test occlusion followed by an internal carotid artery-occluded xenon CT cerebral blood flow study.RESULTSOne patient, who passed the clinical test occlusion but exhibited regions of cerebral blood flow less than 30 mL/100 g per minute on the occlusion xenon CT cerebral blood flow study went on to have a fatal stroke corresponding exactly to the region of reduced blood flow. Thirty patients passed both components of the preoperative stroke-risk assessment. Neuroimaging demonstrated possible flow-related infarctions, which subsequently developed in three patients. Two patients were asymptomatic, and one patient was left with a mild residual hemiparesis.CONCLUSIONSOur protocol provided a statistically significant reduction in subsequent infarction rate and infarction-related death rate when compared with a control group of normotensive abrupt internal carotid artery occlusion patients who did not undergo any preoperative stroke-risk assessment (reported in the literature). The estimated false-negative rate for our preoperative assessment protocol ranged from 3.3% to 10% depending on the assessment of the cause of the three potentially flow-related infarctions. Although life-threatening major vascular territory infarctions have been avoided, our protocol is less sensitive to changes predicting smaller, often minimally symptomatic, vascular border zone infarctions and does not predict postoperative thromboembolic strokes.     

Xe/CT cerebral blood flow evaluation of delayed symptomatic cerebral ischemia after subarachnoid hemorrhage.

PURPOSE: We examined the xenon/CT method of measuring cerebral blood flow in assessing the location, pattern of onset, and severity of delayed cerebral ischemia. PATIENTS AND METHODS: Fourteen patients with delayed neurologic deficits due to ischemia were selected from a group of 66 patients with subarachnoid hemorrhage. All blood flow studies were performed within 12 hours of deterioration and at regular intervals during medical management. RESULTS: In 10 of the 14 patients, noncontrast CT did not identify a cause for deterioration, whereas the blood flow study revealed diminished flow values. Location of blood flow reduction was variable. In five of the 14 patients, blood flow reduction was closely related anatomically to the vessel of aneurysm origin. In another three, blood flow reduction was anatomically remote to the vessel of origin. The remaining six experienced local and remote cerebral blood flow reduction. Six of 14 patients suffered sudden, devastating deterioration, refractory to therapy and associated with blood flow of 15 cc/100 g.min or less, resulting in local or widespread infarction. The remaining eight had less severe blood flow reduction and did not infarct those territories. CONCLUSIONS: Vasospasm can affect remote vessels as severely as local vessels and can affect remote vessels alone. Diminished cerebral blood flow correlated closely with clinical vasospasm in this group of patients. Xenon/CT cerebral blood flow studies can identify tissue at risk of infarction when CT is normal.     

Effects of inhaled stable xenon on cerebral blood flow velocity

The effects of inhaled stable xenon gas on cerebral blood flow were studied with 23 transcranial Doppler examinations performed in 13 normal volunteers while breathing, 25, 30, or 35% xenon for 5 min. Doppler velocities from the middle cerebral artery rose significantly during inhalation in 85% of subjects and 78% of studies and decreased significantly in 15% of subjects and 17% of studies. These different velocity responses may represent different responses of pial vasculature to xenon. The mean velocity rise among those studies showing a significant increase was 38 +/- 3.6% (SEM). The velocity rise began 2 min after the start of xenon inhalation and increased rapidly, so that the velocities measured at the four times at which scans were obtained in our xenon CT protocol (0, 1.5, 3, and 5 min after the start of xenon inhalation) were significantly different. A consistent fall in the pulsatility of the Doppler waveform as the velocity increased provided evidence for xenon-induced vasodilation of the small-resistance vessels as the cause of the increase in flow velocity. Most subjects became mildly hyperventilated, so that the observed changes could not be attributed to hypercapnia. Inhalation of 25, 30, or 35% xenon for 5 min induces a delayed but significant rise in cerebral blood velocity. This suggests that cerebral blood flow itself may be rapidly changing during the process of xenon CT scanning. These changes may compromise the ability of the xenon CT technique to provide reliable quantitative measurements of cerebral blood flow.     

Hepatic blood flow measurements with arterial and portal blood flow mapping in the human liver by means of xenon CT

PURPOSE: The purpose of this work was to quantify arterial and portal blood flows in the human liver and to create blood flow maps by means of xenon CT. METHOD: Mathematical procedures were developed based on a simplified model having two tissue components: liver tissue and portal organ tissue. Xe-CT studies were performed on 10 healthy volunteers (ages 33.4 +/- 9.8 years), a patient with hepatocellular carcinoma (HCC), and a liver transplant recipient. RESULTS: Arterial and portal blood flows for the healthy subjects were 36.7 +/- 5.2 and 65.2 +/- 22.0 ml/100 ml/min. In the HCC patient, arterial blood flow was shown to be dominant in the tumoral area. From the results of the liver recipient, it was demonstrated that obtaining lambda values is important for proper evaluation of blood flows. CONCLUSION: Xe-CT can provide substantial information on hepatic blood flow quantitatively and visually with separation of arterial and portal components.     

Comparison of cerebral blood flow with Xe-inhalation CT and perfusion CT

Cerebral blood flow (ml/min/100g) (CBF) was detected by two methods, static xenon inhalation dynamic CT (Xe-CT) and perfusion CT, and a comparison of these two methods (Xe-CBF and perfusion CBF) was carried out in the same cases. Xe CT used 30% static xenon, 4 min wash-in, and 5 min wash-out, while perfusion CT was done by injecting 30 ml of non-ionic contrast medium at a rate of 9 ml/sec. Forty-eight patients underwent these examinations (30 serious cases and 18 mild). The correlation coefficients in the hemispheric area were r=0.713 (p<0.01) with Xe-CBF and perfusion CBF in mild cases and r=0.567 (p<0.01) in serious cases. The two CBF values were especially disparate in serious cases. The value for perfusion CBF was almost double that of Xe-CBF in these cases. Perfusion CT was a useful examination for the detection of CBF, but in serious cases, CBF needs to be determined by Xe-CT as well.     

Clinical significance of the measurement of hepatic blood flow using xenon 133 and balloon catheter in patients undergoing treatment for hepatocellular carcinoma.

Total hepatic blood flow and portal blood flow were measured separately using a modified xenon 133 clearance method during angiography in 71 patients with chronic liver diseases, including 40 with proven hepatocellular carcinoma, and in 12 patients without detectable chronic liver injury who served as controls. Total hepatic and portal blood flow rates in controls were 805 +/- 149 ml/min and 667 +/- 206 ml/min, respectively. Total hepatic blood flow was significantly decreased in patients with compensated and decompensated liver cirrhosis (519 +/- 156 ml/min and 317 +/- 153 ml/min, respectively; P less than 0.01), as was portal blood flow (399 +/- 134 ml/min and 271 +/- 134 ml/min, respectively; P less than 0.01). Following transcatheter arterial embolization or hepatic resection (in 35 and 13 patients, respectively), hepatic failure occurred in 3 cases each. Embolization appeared contraindicated when hepatic portal blood flow was under 125 ml/min, and safe hepatic resection required an anticipated residual hepatic portal blood flow of at least 250 ml/min.     

Method of injection of contrast medium for brain perfusion CT

Perfusion computed tomography (CT) has great value for detecting stroke and evaluating blood flow in the brain. With perfusion CT, it is possible to obtain two absolute values, cerebral blood flow (CBF) (ml/min/100g) and cerebral blood volume (CBV) (%). In using this examination, the main problem is the method of iodine injection. The maximum slope of time-attenuation curve in organs must be reached before the peak enhancement time of the sagittal sinus. To solve this problem, we used a new method in which total injection volume is 30ml, and the rate of injection is 9ml/sec. The data acquisition time is one second for each scan, and the time interval is one second, for 20 scans in total. With this method, we can obtain reliable information on blood flow in the damaged brain. The most common examination used for the detection of brain blood flow is single-phased dynamic CT with Xe inhalation. However, the Xe inhalant examination is difficult to use in the routine clinical setting. Perfusion CT will be more useful for the detection of brain blood flow.     

Evaluation of critically perfused area in acute ischemic stroke for therapeutic reperfusion: A clinical PET study

To evaluate critically perfused areas in the acute ischemic brain, 9 patients were studied by positron emission tomography (PET) within 7–32 hours after the onset. The cerebral blood flow (CBF) and oxygen metabolic rate (CMRO₂) were evaluated and compared with sequential change in CT findings. In all the regions developing subsequent necrosis on CT, CBF dropped below 17 ml/100 g/min. But in some of these lesions, CMRO₂ remained above the minimum value for regions in which infarction did not develop, and the tissue density on CT obviously remained normal for several hours after PET scan. The mean CBF in these lesions (14.0 ml/100 g/min, range: 9.9–17.3 ml/100 g/min) was significantly higher than that in ischemic areas with low density on CT before or just after PET study (～10 ml/100 g/min, range: 7.7–14.1 ml/100 g/min). These findings suggest that a part of the tissue with CBF between 10–17 ml/100 g/min is still viable at least 7 hours after the onset of ischemia, but becomes non-viable in a longer period of ischemia. These lesions should respond to effective treatment, including therapeutic reperfusion.     

A measurement of regional portal blood flow with Xe-133 and balloon catheter in man

This investigation was undertaken to measure regional portal blood flow of the liver. The measurement was performed by injecting ¹³³Xe into the proper hepatic artery through a balloon catheter and then occluding the proper hepatic artery with an inflated balloon. Data were collected using a gamma camera, and washout curves were generated. They were analyzed by the initial slope method and Kety Schmidt equation. The average regional portal blood flows were: 59.31±13.04 ml/100 g per min, 58.71±14.14 ml/100 g per min and 37.12±10.11 ml/100 g per min in hospital controls (11), patients with chronic hepatitis (10) and those with liver cirrhosis (56), respectively. In the patients with cirrhosis, the regional portal blood flow was significantly reduced (P<0.01). The reproducibility of this method was satisfactory. The measurement of regional portal blood flow will be useful to evaluate underlying liver injuries and determine indications of a transcatheter arterial embolization of the liver.Presented in part at the Society of Nuclear Medicine 34th Annual Meeting, June 2–5, 1987, Toronto, Ontario, Canada     

The wash-in/washout protocol in stable xenon CT cerebral blood flow studies.

PURPOSE: We conducted a comparative study to optimize the scanning and inhalation protocols for xenon CT cerebral blood flow (CBF) examination (Xe CT), with the aim of improving the practical performance of Xe CT as a routine clinical examination. MATERIALS AND METHODS: Four different inhalation protocols, including 3-min, 6-min, and 8-min wash-in protocols, and a 3-min wash-in/5-min washout protocol, were compared in five healthy volunteers. Each subject underwent two serial Xe CT examinations with an interval of 30 min between the first one (wash-in) and the second one (wash-in/washout). A computer simulation was also performed to support the results of the clinical study. The rate of success was calculated from our experience of 110 clinical cases examined with the wash-in/washout protocol over the last 9 months. RESULTS: The mean CBF values with 6-min and 8-min wash-in protocols were 59.0 and 59.5 mL/100-g brain per min in the thalamus, and 19.5 and 19.0 mL/100-g brain per min in the frontal white matter, respectively. The mean CBF values with 3-min wash-in/5-min washout protocol were 60.0 mL/100-g brain per min in the thalamus and 18.5 mL/100-g brain per min in the frontal white matter, respectively. Computer simulation showed improved signal-to-noise ratio by employing the 3-min wash-in/5-min washout protocol instead of 8-min wash-in protocol for the same number of data points. The rate of success improved to 99.1% due to the significant decrease in head motion with the shorter period of inhalation. CONCLUSION: A wash-in/washout protocol is a useful alternative in Xe CT CBF measurement and more useful than the wash-in method for clinical purposes.