Measurement Of Blood Flow Volume Research Articles

Analysis of partial volume effects on arterial input functions using gradient echo: A simulation study

Absolute blood flow and blood volume measurements using perfusion weighted MRI require an accurately measured arterial input function (AIF). Because of limited spatial resolution of MR images, AIF voxels cannot be placed completely within a feeding artery. We present a two-compartment model of an AIF voxel including the relaxation properties of blood and tissue. Artery orientations parallel and perpendicular to the main magnetic field were investigated and AIF voxels were modeled to either include or be situated close to a large artery. The impact of partial volume effects on quantitative perfusion metrics was investigated for the gradient echo pulse sequence at 1.5 T and 3.0 T. It is shown that the tissue contribution broadens and introduces fluctuations in the AIF. Furthermore, partial volume effects bias perfusion metrics in a nonlinear fashion, compromising quantitative perfusion estimates and profoundly effecting local AIF selection.

Respiratory self‐gating for free‐breathing abdominal phase‐contrast blood flow measurements

To demonstrate the feasibility of using a free-breathing (FB) respiratory self-gated (RSG) approach for abdominal phase-contrast (PC) blood flow measurements. PC-magnetic resonance imaging (MRI) flow measurements were performed within the right renal artery, common hepatic artery, and main portal vein during breath-hold (BH) and FB with both signal averaging and RSG in eight healthy volunteers. The resultant images were qualitatively scored by two independent reviewers blinded to acquisition techniques. Blood flow volume and cross-sectional vessel size measurements were compared for three techniques. The overall efficiency for the RSG-PC sequence was 38.9% +/- 4.7%. Images acquired with RSG effectively mitigated respiratory motion artifacts, which were clearly evident within FB signal-averaged images. RSG produced similar image quality to that of BH techniques (P > 0.146) and resulted in similar vessel size measurements (P = 0.694). Flow results for both FB RSG and signal-averaged reconstructions correlated well with BH flow measurements (r = 0.97 and 0.92, P < 0.001). However, only the RSG methods demonstrated excellent absolute agreement with BH-PC flow measurements (P = 0.600), with signal-averaged methods resulting in significant overestimations. RSG methods can limit respiratory motion artifacts to reduce flow measurement inaccuracies during free-breathing PC measurements in the abdomen.

The development of cerebral perfusion during the first three years of life: Long-term follow-up study of cerebral blood flow volume measurement in two healthy children

The development of cerebral perfusion during the first three years of life: Long-term follow-up study of cerebral blood flow volume measurement in two healthy children

Mensuração do volume de fluxo portal em pacientes esquistossomóticos: avaliação da reprodutibilidade do ultra-som Doppler

OBJETIVO: Avaliar a reprodutibilidade do ultra-som Doppler na quantificação do volume de fluxo portal em pacientes esquistossomóticos. MATERIAIS E MÉTODOS: Estudo prospectivo, transversal, observacional e autopareado, avaliando 21 pacientes portadores de esquistossomose hepatoesplênica, submetidos a mensuração do fluxo portal pelo ultra-som Doppler por três observadores, de forma independente, sendo calculada a concordância entre estes, dois a dois, pelo coeficiente de correlação intraclasse, teste t-pareado e grau de linearidade de Pearson. RESULTADOS: A concordância interobservador foi excelente. O coeficiente de correlação intraclasse variou entre 80,6% e 93,0% (IC a 95% [65,3% ; 95,8%]), com coeficiente de correlação de Pearson variando entre 81,6% e 92,7% e sem diferença estatisticamente significante entre os observadores quanto à média do fluxo portal mensurado pelo ultra-som Doppler (p = 0,954 / 0,758 / 0,749). CONCLUSÃO: O ultra-som Doppler é um método confiável para quantificar o fluxo portal em pacientes portadores de hipertensão porta de origem esquistossomótica, apresentando boa concordância interobservador.

OC078: Agreement between umbilical vein volume blood flow measurements obtained at the intra‐abdominal portion and free‐loop of the umbilical cord

Umbilical vein (UV) is a single vessel and theoretically the volume of blood flowing through it should be equal whether it is measured at the intra-abdominal portion (IA) or free-loop of the umbilical cord (FL). However, reported values vary considerably depending on the technique and site of measurement. We investigated the correlation and agreement between Quv measured at the IA and FL. Blood flow velocities and inner diameter of the UV were measured at the IA and FL in 131 pregnant women cross-sectionally at 22–24 weeks, and 41 of them were examined longitudinally at 4-weekly intervals until delivery. For each sampling site, UV blood flow (Quv) was calculated as: Quv = (0.5 × time-averaged maximum velocity) × π (UV diameter/2)2. The mean Quv measured at the IA (61.5 ± 23 mL/min) and FL (60.6 ± 17 mL/min) were similar at 22–24 weeks, but the correlation between them was poor (R = 0.38; P < 0.0001). When the agreement between 131 pairs of ln-transformed Quv measurements were tested with Bland-Altman analysis, the geometric mean of the ratio IA Quv/FL Quv was found to be 1.05 (i.e. IA Quv exceeded FL Quv on average by 5%) with 95% limits of agreement 0.467–2.027. We further evaluated the 164 pairs of Quv measurements obtained at the IA and FL longitudinally from 41 fetuses at 22–42 weeks. The mean Quv measurements obtained at two sites were similar, i.e. 152 ± 83 (range, 30–470) mL/min versus 161 ± 99 (range, 25–531) mL/min, and the bivariate correlation between them was slightly better (R = 0.75; P < 0.0001). However, the correlation adjusted for gestational age was poor (R = 0.461; P < 0.0001). The geometric mean of the ratio IA Quv/FL Quv was 1.08 (i.e. IA Quv exceeded FL Quv on average by 8%) with 95% limits of agreement 0.51–2.02. Average Quv measured at the IA and FL were similar, but the correlation and agreement between them was not particularly good. Quv measured at different sampling sites cannot be used interchangeably.

Brain perfusion CT: Principles, technique and clinical applications

The imaging of brain haemodynamics and its applications are generating growing interest. By providing quantitative measurements of cerebral blood flow (CBF) and cerebral blood volume (CBV), dynamic perfusion computed tomography (p-CT) allows visualisation of cerebral autoregulation mechanisms and represents a fast, available and reliable imaging option for assessing cerebral perfusion. Thanks to its feasibility in emergency settings, p-CT is considered most useful, in combination with CT angiography, in acute ischaemic patients, as it is able to provide a fast and noninvasive assessment of cerebral perfusion impairment. In addition, p-CT can play a diagnostic role in other types of cerebrovascular disease to assess functional reserve, and in intracranial neoplasms, where it has a role in diagnosis, grading, biopsy guidance, and follow-up during treatment. This article illustrates the principles, technique and clinical applications of p-CT cerebral perfusion studies.

Course of cerebral blood flow and metabolism following severe brain injury. Correlation with neurological function and outcome

This study was carried out investigate the course of cerebral blood flow and metabolism in fifty five head-injured patients and to specifically characterize the changes in oxidative and glucose indices in the acute post-traumatic period with regard to neurological condition and functional outcome. Blood flow volume (BFV) measurements were obtained from the extracranial internal carotid artery using a dual-beam angle-independent digital Doppler ultrasound. Cerebral metabolism was studied using blood sample, blood gas, blood saturation, hemoglobin, hematocrit, pH and glucose plasma concentrations. Arterial jugular differences were then calculated and used to determine global cerebral metabolic rates of oxygen (gCMRO2) and glucose (gCMRGlc). In patients with good outcome, CBF remained stable within the normal range whereas in patients with poor outcome, the course of CBF was characterized by a triphasic pattern defined by a secondary decrease on the third day. CMRO2 showed a significant and progressive correlation with level of consciousness expressed by means of GCS. Lower CBF values were significantly associated with poorer outcome.

Doppler ultrasound measurement of blood flow volume in the extracranial internal carotid artery for evaluation of brain perfusion after aneurysmal subarachnoid hemorrhage

Monitoring of cerebral blood flow (CBF) is an essential part in the early diagnosis of cerebral vasospasm following aneurysmal subarachnoid hemorrhage (SAH). Several methods have been established to monitor cerebral perfusion in these patients. During last few years, a new sonographic approach has been introduced, the so called 'angle independent ultrasound system' for monitoring volume flow in the internal carotid artery (ICA). The angle independent Doppler ultrasound system Quantix ND (Cardiosonix Ltd, Israel) determines the diameter of the ICA as well as the velocity of blood flow in the extracranial part of this vessel. Thus, a determination of the global CBF in the anterior circulation can be achieved. Aim of our study was to compare the Quantix ND system and the commonly used transcranial Doppler sonography (TCD) in patients suffering from aneurysmal SAH.We included 11 patients (eight female and three male; Hunt and Hess I–V) and performed post-operatively/post-interventionally daily measurement of blood flow volume in the ICA, and determined the blood flow velocity in middle and anterior cerebral artery (MCA and ACA) with TCD. Six patients post-operatively/post-interventionally developed cerebral vasospasm, resulting in ischemia and territorial infarction. Three patients were chosen as case studies.In contrast to the TCD, we found a strong significant correlation of blood flow volume with Quantix ND in the ICA and the occurrence of cerebral infarction (p<0.001).These preliminary data justify further investigation of this angle independent Doppler ultrasound device. We postulate that this new tool might be effective for monitoring the CBF in the critical post-operative/post-interventional interval following aneurysmal SAH.

Thrombin effectuates therapeutic arteriogenesis in the rabbit hindlimb ischemia model: A quantitative analysis by computerized in vivo imaging

We report on an experimental mammalian controlled study that documents arteriogenic capacity of thrombin and utilizes computerized algorithms to quantify the newly formed vessels. Hindlimb ischemia was surgically invoked in 10 New Zealand white rabbits. After quiescence of endogenous angiogenesis heterologous bovine thrombin was intramuscularly injected (1500 units) in one hindlimb per rabbit (Group T). Contralateral limbs were infused with normal saline (Group C). Digital subtraction angiography (DSA) of both limbs was performed after thrombin infusion by selective cannulation of the abdominal aorta and digital images were post-processed with computerized algorithms in order to enhance newly formed vessels. Total vessel area and total vessel length were quantified. In vivo functional evaluation included measurements of blood flow volume at the level of the external iliac artery by Doppler ultrasonography both at baseline and at 20 days after thrombin infusion. Total vessel area and length (in pixels) were 14,713±1023 and 5466±1327 in group T versus 12,015±2557 and 4598±1269 in group C ( p = 0.0062 and 0.1526, respectively). Blood flow volumes (ml/min) at baseline and at 20 days after thrombin infusion were 25.87±11.09 and 38.06±11.72 in group T versus 26.57±11.19 and 20.35±7.20 in group C ( p = 0.8898 and 0.0007, respectively). Intramuscular thrombin effectuates an arteriogenic response in the rabbit hindlimb ischemia model. Computerized algorithms may enable accurate quantification of the neovascularization outcome.

Validating Volume Flow Measurements From a Novel Semiautomated Four-Dimensional Doppler Ultrasound Scanner

Accurate measurement of blood volume flow (in ml/min) is an important clinical goal. This project compared in vitro and in vivo volume flow measurements obtained with a novel, real-time three-dimensional (i.e., four-dimensional) ultrasound scanner (Encore PV; Vuesonix Sensors, Wayne, PA) with those from an invasive transit time flowmeter. A flow pump was used to generate pulsatile flow rates from 60 to 600 ml/min. The Encore detected absolute blood velocity vectors within a volume. The scanner determined the centerline of the vessel and volume flow was then automatically calculated. Results were compared with those of an invasive technique for volumetric blood flow measurements utilizing a transit-time flowmeter (TS420; Transonic Systems Inc., Ithaca, NY). In vivo, 10 second datasets of the volume flow in the distal aorta of six rabbits were obtained simultaneously with the Encore PV and the flowmeter. Data were compared using linear regression and Bland-Altman analysis (due to the lack of independence). In vitro, Encore and flowmeter measurements both matched the flow pump (r2 > 0.99; P < .0001) with mean errors of -11.8% and -0.3%, respectively. Marked underestimation of the true flow rates was encountered with the Encore at the lowest pump setting. In vivo mean volume flows between 10.6 and 79.3 ml/min were measured. Mean and maximum volume flows obtained with the two techniques correlated significantly (P < .0001) with r2 values of 0.86 and 0.62, respectively. The corresponding root-mean-square errors were 6.9% for mean flow and 61.2% for maximum volume flow measurements. A new semiautomated four-dimensional Doppler device has been tested in vitro and in vivo. Mean volume flow measurements with this unit are comparable to those of an invasive flowmeter.

2D Cine Phase-Contrast MRI for Volume Flow Evaluation of the Brain-Supplying Circulation in Moyamoya Disease

The purpose of this study was to evaluate and quantify hemodynamic compromise in patients with moyamoya disease by measuring blood volume flow in the brain-supplying arteries. Thirty-five patients with angiographically proven moyamoya disease (31 women, 4 men; mean age, 39.4 +/- 12.2 years; range, 15-58 years; adult moyamoya disease) and 15 age-matched healthy controls were examined prospectively with 2D cine phase-contrast MRI. Blood volume flow was measured in both common carotid arteries (CCAs), both internal carotid arteries (ICAs), and the basilar artery. The diagnosis of moyamoya disease was based on results of selective intraarterial digital subtraction angiography. Blood volume flow of the brain-supplying arteries in age-matched controls was 435.6 +/- 47.9 mL/min for the CCA, 254.1 +/- 25.3 mL/min for the ICA, and 173.3 +/- 13.2 mL/min for the basilar artery. Patients with bilateral moyamoya disease had decreased mean blood flow in the CCA (309.4 +/- 89.9 mL/min) and ICA (117.9 +/- 64.0 mL/min) and increased blood volume flow in the basilar artery (433.7 +/- 165.9 mL/min). Moyamoya disease causes a significant decrease in carotid artery circulation, particularly ICA blood volume flow, with a compensatory increase in blood flow in the basilar artery to nearly 2.5 times normal basilar artery blood flow. 2D cine phase-contrast MRI with measurement of blood volume flow in the brain-supplying arteries is useful in the initial evaluation of moyamoya disease and in continuing assessment of hemodynamics in patients with this disease.

Identification of Penumbra and Infarct in Acute Ischemic Stroke Using Computed Tomography Perfusion–Derived Blood Flow and Blood Volume Measurements

We investigated whether computed tomography (CT) perfusion-derived cerebral blood flow (CBF) and cerebral blood volume (CBV) could be used to differentiate between penumbra and infarcted gray matter in a limited, exploratory sample of acute stroke patients. Thirty patients underwent a noncontrast CT (NCCT), CT angiography (CTA), and CT perfusion (CTP) scan within 7 hours of stroke onset, NCCT and CTA at 24 hours, and NCCT at 5 to 7 days. Twenty-five patients met the criteria for inclusion and were subsequently divided into 2 groups: those with recanalization at 24 hours (n=16) and those without (n=9). Penumbra was operationally defined as tissue with an admission CBF <25 mL x 100 g(-1) x min(-1) that was not infarcted on the 5- to 7-day NCCT. Logistic regression was applied to differentiate between infarct and penumbra data points. For recanalized patients, CBF was significantly lower (P<0.05) for infarct (13.3+/-3.75 mL x 100 g(-1) x min(-1)) than penumbra (25.0+/-3.82 mL x 100 g(-1) x min(-1)). CBV in the penumbra (2.15+/-0.43 mL x 100 g(-1)) was significantly higher than contralateral (1.78+/-0.30 mL x 100 g(-1)) and infarcted tissue (1.12+/-0.37 mL x 100 g(-1)). Logistic regression using an interaction term (CBFxCBV) resulted in sensitivity, specificity, and accuracy of 97.0%, 97.2%, and 97.1%, respectively. The interaction term resulted in a significantly better (P<0.05) fit than CBF or CBV alone, suggesting that the CBV threshold for infarction varies with CBF. For patients without recanalization, CBF and CBV for infarcted regions were 15.1+/-5.67 mL x 100 g(-1) x min(-1) and 1.17+/-0.41 mL x 100 g(-1), respectively. We have shown in a limited sample of patients that CBF and CBV obtained from CTP can be sensitive and specific for infarction and should be investigated further in a prospective trial to assess their utility for differentiating between infarct and penumbra.

Cerebral perfusion computerized tomography: influence of reference vessels, regions of interest and interobserver variability

There are still no standardized guidelines for perfusion computerized tomography (PCT) analysis. A total of 61 PCT studies were analyzed using either the anterior cerebral artery (ACA) or the middle cerebral artery (MCA) as the arterial reference, and the superior sagittal sinus (SSS) or the vein of Galen (VG) as the venous reference. The sizes of regions of interest (ROI) were investigated comparing PCT results obtained using a hemispheric ROI combined with vascular pixel elimination with those obtained using five smaller ROIs located over the cortex and basal ganglia. In addition, interobserver variations were explored using a standardized protocol. MCA-based measurements of cerebral blood flow (CBF) and blood volume (CBV) were in accordance with those obtained with the ACA except in 16 patients with ischemic stroke, in whom CBF was overestimated by the ipsilateral MCA. Venous maximal intensity was significantly lower with the VG when compared with the SSS, resulting in overestimation of CBF and CBV. However, in 13.3% of patients the VG ROI yielded higher maximal intensities than the SSS ROI. There was no difference in PCT results between hemispheric ROI and averaged separate ROI when vascular pixel elimination was used. Finally, interobserver variations were as high as 11% for CBF and 12% for CBV. The present results suggest that pathological rather than anatomical considerations should dictate the choice of the arterial ROI. For venous ROI, although SSS seems to be adequate in most instances, deep cerebral veins may occasionally generate higher maximal intensities and should therefore be selected. Importantly, significant user-dependency should be taken into account.

The fetal circulation and essential organs—a new twist to an old tale

The fetal circulation and essential organs—a new twist to an old tale

Automated Technique for Angiographic Determination of Coronary Blood Flow and Lumen Volume

Visual interpretation of angiographic images has been shown to be inadequate for assessing the severity of intermediate coronary stenoses. An approach for evaluating both the anatomic and functional impact of a stenosis is needed. An automated technique for determining both coronary blood flow and lumen volume based on a first-pass analysis (FPA) of coronary angiograms and a template matching algorithm was evaluated. Coronary angiograms of a swine animal model were obtained during power injections of contrast material into the left coronary ostium. Background anatomy was subtracted with an automated phase matching program. A template matching algorithm and first-pass analysis were then used to quantify coronary blood flow and lumen volume. Coronary blood flow and lumen volume measurements were validated with a transit-time ultrasound flow probe and a polymer cast of the coronary arteries, respectively. In 14 independent comparisons, the mean coronary blood flow measured with FPA showed strong correlation with the mean flow measured with the ultrasound flow probe (Q(FPA) = 0.88Q(probe) - 1.99; r = 0.977; standard error of estimate = 3.23 mL/minute). The lumen volumes determined with FPA and cast measurements demonstrated excellent correlation and can be related to each other by V(FPA) = 0.95V(C) - 0.01 (r = 0.997; standard error of estimate = 0.01 mL). The proposed automated method for accurate determination of coronary blood flow and lumen volume can supplement visual evaluation of coronary anatomy with quantitative physiologic data. This automated technique potentially offers a clinically feasible method of quantifying coronary blood flow and lumen volume in conjunction with routine cardiac catheterization.

Potential Value of Poststroke Extracranial Arterial Blood Flow Volume in the Prediction of Stroke Functional Outcome

Background and Purpose: Cerebral vasoreactivity and collateral circulation are important protective mechanisms against cerebral ischemia. Previous studies suggest that the efficiency of these mechanisms can be reflected by extracranial arterial blood flow volume. Brain damage leading to neurological impairments can influence patients’ functional recovery after stroke. This study attempted to explore the potential value of poststroke extracranial arterial blood flow volume in the prediction of stroke patients’ functional outcome. Methods: We prospectively studied 362 consecutive patients who were hospitalized for recent acute strokes. All patients underwent extracranial arterial blood flow volume measurement of the carotid and vertebral arteries by color velocity imaging quantification within 3 days after admission. Their functional recovery was assessed 6 months after stroke. The effect of poststroke extracranial arterial blood flow volume on patients’ functional outcome was tested by multivariate ordinal regression after controlling for other independent variables. Significance was at p < 0.05. Results: Poststroke extracranial arterial blood flow volume together with age, prestroke modified Rankin scale, the National Institutes of Health Stroke Scale and diabetes mellitus had significant effects on the patients’ 6-month functional outcome as measured by the modified Rankin scale after controlling for other independent variables (p < 0.05). Conclusions: Poststroke extracranial arterial blood flow volume is an independent outcome predictor. The graded predictive power of this parameter is potentially more superior than other outcome predictors by allowing classification of stroke outcome according to the degree of severity. A large prospective study is thus warranted to investigate its clinical value in the management of stroke patients.

Development of Cerebral Blood Flow Volume in Preterm Neonates during the First Two Weeks of Life

To investigate the postnatal development of cerebral perfusion in preterm neonates with normal brains over the first 2 wk of life, a prospective longitudinal study was designed. Quantitative measurement of cerebral blood flow (CBF) volume was performed using ultrasound flowmetry of the extracranial, brain-feeding arteries in 32 preterm infants of 28-35 wk gestational age. Measurements were done in the internal carotid and vertebral arteries of both sides on d 1, 2, 3, 7, and 14 after birth. A 10.0-MHz linear transducer of a computed sonography system (Acuson 128/XP10) was used. Intravascular flow volumes were calculated as the product of angle-corrected time-averaged flow velocity and the cross-sectional area of the vessel. Mean CBF volume increased markedly over the first 2 wk. One-third of this rise already occurred from the first to the second postnatal day, thereafter there was a continuous increase from d 2 to d 14 of life. Whereas the absolute level of CBF volume was primarily determined by postmenstrual age, the pattern of postnatal changes in CBF volume was found to be independent of gestational age. Arterial carbon dioxide tension, mean arterial blood pressure, and hematocrit had no influence on the development of CBF volume. The pronounced increase of CBF volume from d 1 to d 2 is likely to represent a normal adaptive response of the cerebral circulation to postnatal life. The data presented here may serve as the basis for further studies to investigate whether deviations from this adaptive response are associated with an increased risk of brain injury.

The use of fetal Doppler cerebroplacental blood flow and amniotic fluid volume measurement in the surveillance of postdated pregnancies

This prospective observational study aims at determining the distribution of fetal cerebro-placental Doppler indices and amniotic fluid volume in a homogenous group of uncomplicated postdated pregnancies at 41 weeks. The correlation with incidence of passage of thick meconium-stained liquor in labor was analyzed to decide which parameter would be useful in the surveillance of postdated pregnancies. The amniotic fluid volume, middle cerebral artery pulsatility index, umbilical artery pulsatility index, and cerebroplacental ratio were measured and distribution determined in 118 well-dated singleton pregnancies admitted for routine induction of labor at 41 weeks. The 10th centile and the 90th centile in each Doppler parameter and amniotic fluid volume were chosen to divide each parameter into three centile groups. The prevalence of thick meconium-stained liquor in labor in different Doppler and amniotic fluid volume centile groups was compared using Chi-square test for trend with P < 0.05 taken as statistically significant. The prevalence of thick meconium-stained liquor in labor was significantly inversely correlated with the middle cerebral artery pulsatility index (P = 0.008), with significant difference across different middle cerebral artery pulsatility index centile groups (P = 0.02). There was no significant difference in the prevalence of thick meconium-stained liquor in labor or oligohydramnios across different umbilical artery pulsatility index centile groups. Neither was there significant difference in the prevalence of thick meconium-stained liquor in labor and oligohydramnios across different cerebroplacental ratio and amniotic fluid volume centile groups. Logistic regression using the 10th centile of middle cerebral artery pulsatility index confirmed that it was a significant independent predicting factor for risk of thick meconium-stained liquor in labor with adjusted odds ratio (95th CI) of 6.14 (1.6-24.1). Middle cerebral artery pulsatility index is better than amniotic fluid volume or umbilical artery pulsatility index in predicting the risk of thick meconium-stained liquor in labor in uncomplicated postdated pregnancy at 41 weeks.

Cerebral blood flow volume measurements with ultrasound: Interobserver reproducibility in preterm and term neonates

Cerebral blood flow (CBF) volume can be measured quantitatively by colour duplex sonography. To test the reliability of CBF volume measurements in newborns, two “blinded” examiners performed a prospective test-retest study in 32 neonates (postmenstrual age 32 to 42 weeks). Measurements were done in the internal carotid and vertebral arteries. Intravascular flow volumes (FV) were calculated as the product of angle-corrected time-averaged flow velocity and the cross-sectional area of the vessel. The CBF volumes measured by the two examiners were very close (mean ± SD, 62.6 ± 20.6 vs. 62.1 ± 21.2 mL/min, NS; coefficient of variation, 6.3%; intraclass correlation coefficient, 0.98). The 95% limits of agreement, according to Bland and Altman, ranged from −7.3 to +8.4 mL/min. In comparison with other test-retest studies, the reproducibility of quantitative CBF measurements reported here is among the best ever found. We conclude that CBF volume can be measured reliably even in preterm neonates. (E-mail: martin.schoening@med.uni-tuebingen.de)

The use of fetal Doppler cerebroplacental blood flow and amniotic fluid volume measurement in the surveillance of postdated pregnancies

Background. This prospective observational study aims at determining the distribution of fetal cerebro-placental Doppler indices and amniotic fluid volume in a homogenous group of uncomplicated postdated pregnancies at 41 weeks. The correlation with incidence of passage of thick meconium-stained liquor in labor was analyzed to decide which parameter would be useful in the surveillance of postdated pregnancies. Methods. The amniotic fluid volume, middle cerebral artery pulsatility index, umbilical artery pulsatility index, and cerebroplacental ratio were measured and distribution determined in 118 well-dated singleton pregnancies admitted for routine induction of labor at 41 weeks. The 10th centile and the 90th centile in each Doppler parameter and amniotic fluid volume were chosen to divide each parameter into three centile groups. The prevalence of thick meconium-stained liquor in labor in different Doppler and amniotic fluid volume centile groups was compared using Chi-square test for trend with P < 0.05 taken as statistically significant. Results. The prevalence of thick meconium-stained liquor in labor was significantly inversely correlated with the middle cerebral artery pulsatility index (P = 0.008), with significant difference across different middle cerebral artery pulsatility index centile groups (P = 0.02). There was no significant difference in the prevalence of thick meconium-stained liquor in labor or oligohydramnios across different umbilical artery pulsatility index centile groups. Neither was there significant difference in the prevalence of thick meconium-stained liquor in labor and oligohydramnios across different cerebroplacental ratio and amniotic fluid volume centile groups. Logistic regression using the 10th centile of middle cerebral artery pulsatility index confirmed that it was a significant independent predicting factor for risk of thick meconium-stained liquor in labor with adjusted odds ratio (95th CI) of 6.14 (1.6–24.1). Conclusion. Middle cerebral artery pulsatility index is better than amniotic fluid volume or umbilical artery pulsatility index in predicting the risk of thick meconium-stained liquor in labor in uncomplicated postdated pregnancy at 41 weeks.