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.     

Hepatic arterial and portal venous components of liver blood flow: a dynamic scintigraphic study

Assessment of liver hemodynamics can be obtained by analysis of first pass flow studies through the liver and spleen using 99mTc compounds which are not actually trapped by these organs. This study examines new and existing methods for determining the relevant contribution made by the hepatic artery and portal vein to total liver blood flow, from these first pass studies. Eighty-two studies were performed in 56 patients with both normal and abnormal liver function. Using region of interest analysis, time-activity curves were obtained for the lungs, liver, spleen, and left kidney. These curves were analyzed by four different methods. Two of these methods are based upon measurement of the slopes of the uptake and washout curves from the liver and spleen and the other two methods employ deconvolution analysis to permit area measurement under the deconvolved curves as an indicator of blood flow. All four methods showed a small intraobserver variation after reanalysis. In 11 patients who underwent repeat studies, the correlation between the deconvolution based methods (r = 0.79-0.89) was significantly better than that for the slope based methods (r = 0.55-0.58). The deconvolution based methods provided the most significant separation between normals and patients with various liver disorders and would appear to be the most suitable techniques for monitoring the effects of various drugs and surgical procedures on the relative arterial/portal contribution to hepatic blood flow.     

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.     

氙CT脑血流成像研究

氙CT脑血流成像是将氙气做为增强物质,用其浓度数据和CT图像数据计算脑血流量的影像方法,具有定量准确、同时提供解剖信息、空间分辨率高、无创等优点,对脑缺血的诊断有重要应用价值。本文综述了该方法的原理、检查方法、临床应用及其与其它影像学方法的比较。     

Simultaneous measurements of cerebral blood flow by the xenon/CT method and the microsphere method. A comparison

Simultaneous measurements of cerebral blood flow have been performed in baboons to assess the correlation between the acute and invasive nondiffusible microsphere technique and the noninvasive xenon-enhanced CT method. Blood flows in small tissue volumes (approximately 1 cm3) were directly compared. The results of these studies demonstrate a statistically significant association between the two methods (P less than .001). Similar correlations were obtained by both the Kendall tau (tau) and the Spearman (r) methods. The problems and limitations of such correlations are discussed.     

The role of xenon CT measurements of cerebral blood flow in the clinical determination of brain death

The demonstration of absent blood flow to the brain is often used as a confirmatory test of brain death. Traditionally, cerebral angiography and dynamic radionuclide brain scanning have been used for this purpose. Recently, xenon CT cerebral blood flow techniques have been developed and applied to a wide variety of clinical problems, including the confirmation of brain death. We report our experience with xenon CT studies performed over a 7-year period (1983-1989) in 30 patients with brain injuries. These patients met clinical criteria for brain death within 24 hr of the study. Twenty patients had average global flow values of less than 5 ml/100 ml/min. Seven patients demonstrated mixed flow patterns, whereby large areas of brain showed flow values of less than 5 ml/100 ml/min and residual pockets of flow greater than 5 ml/100/ml/min. Globally symmetric normal to hyperemic flows were seen in three patients. Our study suggests that the demonstration of average global flows of less than 5/ml/100 ml/min is confirmatory of brain death. Demonstration of persistent flow to the entire brain or regions of the brain is not diagnostic of brain death but also does not exclude such an outcome in patients with severe brain injuries. Xenon-derived flow information may be clinically useful in determining the patient's prognosis and in counseling the patient's family.     

Computed tomography perfusion of the liver: assessment of pure portal blood flow studied with CT perfusion during superior mesenteric arterial portography

Purpose: To quantitatively assess the portal component of hepatic blood flow using computed tomography (CT) perfusion studies during superior mesenteric arterial portography. Material and Methods: Thirty-four patients with hepatocellular carcinoma and liver cirrhosis (LC) and 13 patients with liver metastasis without chronic liver disease were enrolled in this study. Ten milliliters of a non-ionic contrast medium (150 mgI) was injected at a rate of 5 ml/s via a catheter placed in the superior mesenteric artery. Single-slice cine CT images at the level of the main trunk or the right/left main trunk of the portal vein were acquired over 40 s. The deconvolution method was then used on these CT images to measure blood flow (BF), blood volume (BV), and mean transit time (MTT) in (a) liver parenchyma in patients with HCC and liver cirrhosis; (b) liver parenchyma in patients with liver metastasis without cirrhosis; (c) directly in the HCC; and (d) directly in one of the metastases. Results: In 34 LC patients (a), BF, BV, and MTT in the liver parenchyma were 44.7±24.5 ml/min/100 g, 3.9±2.4 ml/100 g, and 10.9±5.5 s, respectively. In 13 patients without cirrhosis (b), BF, BV, and MTT in the liver parenchyma were 89.6±52.0 ml/min/100 g, 6.3 ±3.2 ml/100 g, and 8.7±3.6 sec, respectively. A significant difference in BF and BV was seen in patients with liver cirrhosis compared to those without cirrhosis. BF, BV, and MTT measured directly in HCC (c) were 6.5±4.5 ml/min/100 g, 0.4±0.4 ml/100 g, and 3.0±3.1 sec respectively, and BF, BV, and MTT in liver metastases (d) were 19.3 ± 21.7 ml/min/100 g, 0.6±0.8 ml/100 g, and 1.8±1.6 s, respectively. Conclusion: CT perfusion studies during superior mesenteric arterial portography allow quantitative assessment of pure portal blood flow in the liver.     

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.     

Local cerebral blood flow measured by CT after stable xenon inhalation

A safe, practical, clinically applicable, noninvasive method for measuring local cerebral blood flow (LCBF) using inert xenon (Xes) and a 60 sec CT scanner has been developed in the baboon. Direct measurement of expired Xes concentration after short inhalation (4--7 min) of 40% Xes and the use of computer-programmed autoradiographic formulas allow accurate, reproducible measurements of LCBF using serial 60 sec scans of regions as small as 0.04 cm3. LCBF measurements are possible with a single 1 min scan. The method reduces radiation exposure, obviates a costly fourth-generation scanner, avoids anesthetic effects of Xes, and reduces the 30 min/scan saturation period. It is less expensive than emission tomography and minimizes problems of overlap and Compton scatter inherent in 133Xe and positron-emission blood flow measurements. Regions of zero perfusion are demonstrable in three dimensions. Tissue solubility and partition coefficients, as well as LCBF, are measured in vivo with high resolution and reproductibility so that minor regional changes in physical properties of tissue that alter solubility are measured. These enhance the potential clinical usefulness of CT scanning.     

PET/CT测量肝动脉和门静脉血流量方法学进展

肝脏纤维化进展和恶性病变发生时病灶组织肝动脉和门静脉血流量会发生明显改变,测量肝组织血流量对于检测肝脏组织病变进展和监测治疗效果具有重要的价值。PET/CT是将PET与CT有机结合在一起进行解剖、功能和分子成像的先进成像设备。采用PET/CT和正电子核素示踪剂能够无创、精准获得肝脏组织总血流量,以及肝动脉、门静脉所占的血流量比例。特别是采用动脉输入图像派生法替代传统采集动脉血样的方法后,使得测量肝脏血流量的方法更加简便,因此该方法广泛应用于临床前期研究和临床研究。就无创PET/CT分子成像设备测量肝脏总血流量以及肝动脉、门静脉血流量的方法和应用进展予以介绍。     

Quantitative multilevel mapping of hepatic blood flow by xenon computed tomography using aorta

A noninvasive and quantitative technique has been developed to measure human hepatic blood flow by xenon computed tomography (Xe-CT). Accurate data on time-dependent xenon concentrations in the arterial blood are indispensable for Xe-CT to ensure quantitativeness of measured blood flow. A method has been established by our group to use both aorta and end-tidal data to obtain arterial xenon information. Multilevel (3 levels) maps of arterial blood flow (Fa), portal blood flow (Fp), and partition coefficient (lambda) were created for patients with chronic hepatitis. A method to objectively evaluate Fa, Fp, and lambda values for the whole liver has also been developed by our group.     

Difference in regional hepatic blood flow in liver segments —Non-invasive measurement of regional hepatic arterial and portal blood flow in human by positron emission tomography with H2 15O—

Organ blood flow can be quantitatively measured by positron emission tomography (PET). As the liver has dual blood supplies, arterial and portal, regional hepatic blood flow had not been measured quantitatively. However, we succeeded in simultaneously measuring both regional hepatic arterial and portal blood flow by PET in non-stressed patients. Mean regional portal hepatic blood flow in patients with normal liver and cirrhotic liver was 57.5 and 36.7 ml/minutes/100 g, respectively. Mean regional arterial blood flow was 42.5 and 30.7 ml/minutes/100 g, respectively. A significant difference between regional portal hepatic blood flows in normal and cirrhotic patients was noted. Mean regional portal hepatic blood flow in the lateral, medial, anterior, and posterior segments of the liver was 29.8, 43.4, 50.0, and 40.9 ml/minutes/100 g, respectively. Mean regional arterial blood flow in each liver segment was 37.6, 30.0, 28.2, and 31.6 mi/minutes/100 g, respectively. A significant difference between regional portal hepatic blood flows in lateral and anterior segment was noted. The p value was less than 0.025 and the 95 % confidence interval of the difference between means was from ?20.2 to ?2.7 ml/minutes/100 g by ANOVA. These results showed that regional hepatic blood flow is not the same in all the liver segments.     

应用DSA、CT和经肠系膜上动脉门静脉灌注CT成像研究肝转移瘤的血液供应

目的 探讨DSA、CT和经肠系膜上动脉门静脉灌注CT成像对肝转移瘤的血液供应显示状况.方法 回顾性分析100例原发病灶经手术和(或)病理证实的肝转移瘤患者资料,均进行了CT平扫、多期CT增强扫描、选择性腹腔动脉和超选择性肝固有动脉DSA检查,其中,56例还经肠系膜上动脉插管行肠系膜上动脉的门静脉灌注CT成像(P(1TAP)检查,计算转移瘤中心区域、肿瘤边缘、门静脉和正常肝实质的时间-密度曲线(TDC)灰度密度(K值),观察肝转移瘤血液供应来源.DSA图像用Photoshop软件进行定量分析,CT图像用去卷积灌注软件进行分析.结果 DSA表现:肝固有动脉造影TDC显示肿瘤中心K值峰值平均为(67±12)%,肿瘤边缘K值峰值平均为(76±15)%,正常肝实质K值峰值平均为(51±10)%.腹腔动脉造影TDC显示,肿瘤中心及肿瘤边缘K值表现为快速上升,然后为缓慢上升的平台,而正常肝实质则呈现持续缓慢上升的态势.PCTAP扫描表现:肿瘤在30 s的时间内,密度变化几乎呈直线,无增强表现.结论 肝动脉是肝转移瘤的主要血液供应来源,门静脉几乎不参与肝转移瘤血液供应.     

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.     

Scintigraphic estimation of arterial and portal blood supplies to the liver

A technique is described for the measurement of the relative magnitudes of the hepatic-artery and portal-vein components of liver perfusion, using a gamma camera and on-line computer system. This ratio is obtained from analysis of the time variation in liver activity on the first pass following bolus intravenous injection of a Tc-99m-labeled radiocolloid. The arterial and portal components are separated by their times of arrival at the liver. These arrival times are evaluated from activity time variations for spleen, left ventricle, and left kidney. Physiological validation of the technique was provided in a digestion study in which normal volunteers showed a significant increase in the portal-vein component 1 hr after a meal relative to the fasting situation. These results are compared with those from studies by other workers. The uncertainties and limitations of the technique are discussed and potential clinical uses suggested.     

Regional blood flow in human tumours measured with argon, krypton and xenon

Blood perfusion in 19 superficial tumour metastases was measured by injecting three tracers, 41Ar, 85Krm and 135Xe or 133Xe, simultaneously into the tissue. The blood flow rate was calculated from the constants of the biexponential functions fitted to the measured counts. The mean blood flow in the 19 tumours studied was 18 ml/(100 g min) (SD +/- 10). Alternatively, the relative partition coefficients of argon, krypton and xenon were calculated from the equations obtained using compartmental analysis. The mean values for the ratios of the partition coefficients of these nuclides were found to be between 0.82 and 1.07.     

Simultaneous measurement of regional cerebral blood flow by perfusion CT and stable xenon CT: a validation study

BACKGROUND AND PURPOSE: Knowledge of cerebral blood flow (CBF) alterations in cases of acute stroke could be valuable in the early management of these cases. Among imaging techniques affording evaluation of cerebral perfusion, perfusion CT studies involve sequential acquisition of cerebral CT sections obtained in an axial mode during the IV administration of iodinated contrast material. They are thus very easy to perform in emergency settings. Perfusion CT values of CBF have proved to be accurate in animals, and perfusion CT affords plausible values in humans. The purpose of this study was to validate perfusion CT studies of CBF by comparison with the results provided by stable xenon CT, which have been reported to be accurate, and to evaluate acquisition and processing modalities of CT data, notably the possible deconvolution methods and the selection of the reference artery. METHODS: Twelve stable xenon CT and perfusion CT cerebral examinations were performed within an interval of a few minutes in patients with various cerebrovascular diseases. CBF maps were obtained from perfusion CT data by deconvolution using singular value decomposition and least mean square methods. The CBF were compared with the stable xenon CT results in multiple regions of interest through linear regression analysis and bilateral t tests for matched variables. RESULTS: Linear regression analysis showed good correlation between perfusion CT and stable xenon CT CBF values (singular value decomposition method: R(2) = 0.79, slope = 0.87; least mean square method: R(2) = 0.67, slope = 0.83). Bilateral t tests for matched variables did not identify a significant difference between the two imaging methods (P >.1). Both deconvolution methods were equivalent (P >.1). The choice of the reference artery is a major concern and has a strong influence on the final perfusion CT CBF map. CONCLUSION: Perfusion CT studies of CBF achieved with adequate acquisition parameters and processing lead to accurate and reliable results.