Arterial Cerebral Blood Volume Research Articles

Model‐free arterial spin labeling quantification approach for perfusion MRI

In this work a model-free arterial spin labeling (ASL) quantification approach for measuring cerebral blood flow (CBF) and arterial blood volume (aBV) is proposed. The method is based on the acquisition of a train of multiple images following the labeling scheme. Perfusion is obtained using deconvolution in a manner similar to that of dynamic susceptibility contrast (DSC) MRI. Local arterial input functions (AIFs) can be estimated by subtracting two perfusion-weighted images acquired with and without crusher gradients, respectively. Furthermore, by knowing the duration of the bolus of tagged arterial blood, one can estimate the aBV on a voxel-by-voxel basis. The maximum of the residue function obtained from the deconvolution of the tissue curve by the AIF is a measure of CBF after scaling by the locally estimated aBV. This method provides averaged gray matter (GM) perfusion values of 38 +/- 2 ml/min/100 g and aBV of 0.93% +/- 0.06%. The average CBF value is 10% smaller than that obtained on the same data set using the standard general kinetic model (42 +/- 2 ml/min/100 g). Monte Carlo simulations were performed to compare this new methodology with parametric fitting by the conventional model.

Quantification of cerebral arterial blood volume and cerebral blood flow using MRI with modulation of tissue and vessel (MOTIVE) signals

Regional cerebral arterial blood volume (CBVa) and blood flow (CBF) can be quantitatively measured by modulation of tissue and vessel (MOTIVE) signals, enabling separation of tissue signal from blood. Tissue signal is selectively modulated using magnetization transfer (MT) effects. Blood signal is changed either by injection of a contrast agent or by arterial spin labeling (ASL). The measured blood volume represents CBVa because the contribution from venous blood was insignificant in our measurements. Both CBVa and CBF were quantified in isoflurane-anesthetized rats at 9.4T. CBVa obtained using a contrast agent was 1.1 +/- 0.5 and 1.3 +/- 0.6 ml/100 g tissue (N = 10) in the cortex and caudate putamen, respectively. The CBVa values determined from ASL data were 1.0 +/- 0.3 ml/100 g (N = 10) in both the cortex and the caudate putamen. The match between CBVa values determined by both methods validates the MOTIVE approach. In ASL measurements, the overestimation in calculated CBF values increased with MT saturation levels due to the decreasing contribution from tissue signals, which was confirmed by the elimination of blood with a contrast agent. Using the MOTIVE approach, accurate CBF values can also be obtained.

How does the blood leave the brain? A systematic ultrasound analysis of cerebral venous drainage patterns.

The internal jugular veins are considered to be the main pathways of cerebral blood drainage. However, angiographic and anatomical studies show a wide anatomical variability and varying degrees of jugular and non-jugular venous drainage. The study systematically analyses the types and prevalence of human cerebral venous outflow patterns by ultrasound and MRI. Fifty healthy volunteers (21 females; 29 males; mean age 27+/-7 years) were studied by color-coded duplex sonography. Venous blood volume flow was measured in both internal jugular and vertebral veins in the supine position. Furthermore, the global arterial cerebral blood volume flow was calculated as the sum of volume flows in both internal carotid and vertebral arteries. Three types of venous drainage patterns were defined: a total jugular volume flow of more than 2/3 (type 1), between 1/3 and 2/3 (type 2) and less than 1/3 (type 3) of the global arterial blood flow. 2D TOF MR-venography was performed exemplarily in one subject with type-1 and in two subjects with type-3 drainage. Type-1 drainage was present in 36 subjects (72%), type 2 in 11 subjects (22%) and type 3 in 3 subjects (6%). In the majority of subjects in our study population, the internal jugular veins were indeed the main drainage vessels in the supine body position. However, a predominantly non-jugular drainage pattern was found in approximately 6% of subjects.

Myths and Truths in functional MRI: A Basic Guide for Practitioners

Since the first successful demonstration of primary visual cortex "activation" by Sokoloff in 1961, activation studies based on regional blood flow alteration became one of the gold standards for neuroscientific investigation. The rapid advancement of non-invasive imaging techniques provided an appropriate stage for the human application of this original method. Following the tremendous success of positron emission tomography (PET) utilizing O(15) labeled H(2)O (H(2)O(15)-PET), the magnetic resonance imaging (MRI) version, which is now referred to as functional MRI (fMRI), was introduced. fMRI is the method created based on the empirical observation that MRI exhibits spontaneous signal alteration associated with blood flow changes. It is now believed that the principle of fMRI is identical to H(2)O(15)-PET, namely, that it is blood flow based in accordance with the well-known Munro-Kellie doctrine which predicts a decline in cerebral venous blood volume secondary to an increase in cerebral arterial blood volume. The method is inherently qualitative and does not provide quantitative information regarding flow alteration. With the growing use of fMRI, however, exponentially increasing well founded criticism questioning the validity of fMRI data has been raised. The majority of validation issues arise during the process of obtaining raw images, which eventually provides raw numerical data for post-processing statistical analysis. This article provides a distillation of the essential knowledge necessary for the non-MR physicist fMRI investigator.

The Influence of Carbon Dioxide and Body Position on Near-Infrared Spectroscopic Assessment of Cerebral Hemoglobin Oxygen Saturation

Near-infrared spectroscopy may allow continuous and noninvasive monitoring of regional brain hemoglobin oxygen saturation by measuring the differential absorption of infrared light by oxyhemoglobin and deoxyhemoglobin. We have previously examined the correlation between the spectroscopic signal generated by a prototype cerebral oximeter (Invos 3100 Registered Trademark; Somanetics, Troy, MI), and global brain hemoglobin oxygen saturation calculated from arterial and jugular venous bulb oxygen saturations. Because the technology does not distinguish between arterial and venous hemoglobin saturation, changes in the proportion of cerebral arterial and venous blood volume, which may result from changes in blood flow or venous distending pressure, may confound measurements. In eight conscious volunteers breathing hypoxic oxygen mixtures, we examined the influence of supine, 20 degrees Trendeleburg, and 20 degrees reverse Trendelenburg positions on the correlation of the spectroscopic measurement of cerebral oxygen saturation in the field assessed by the probe (CSf O2) and the calculated brain hemoglobin oxygen saturation (CScomb O2), estimated as 0.25 times arterial saturation plus 0.75 times jugular venous bulb oxygen saturation. We found that changes in position did not influence the association between CSf O2 and CScomb O2 (r2 = 0.69-0.885) during hypoxic challenge. In a second set of eight volunteers, we studied the influence of hypercapnia and hypocapnia and body position on the association between CSf O2 and CScomb O2, and found that they were less well correlated (r2 = 0.366-0.976) in individual patients. Because changes in body position and PaCO2 confound the relationship between CSf O2 and CScomb O2, changes in CS (f) O2 can best be assessed if position and PaCO2 are constant. (Anesth Analg 1996;82:278-87)

The influence of carbon dioxide and body position on near-infrared spectroscopic assessment of cerebral hemoglobin oxygen saturation.

Near-infrared spectroscopy may allow continuous and noninvasive monitoring of regional brain hemoglobin oxygen saturation by measuring the differential absorption of infrared light by oxyhemoglobin and deoxyhemoglobin. We have previously examined the correlation between the spectroscopic signal generated by a prototype cerebral oximeter (Invos 3100; Somanetics, Troy, MI), and global brain hemoglobin oxygen saturation calculated from arterial and jugular venous bulb oxygen saturations. Because the technology does not distinguish between arterial and venous hemoglobin saturation, changes in the proportion of cerebral arterial and venous blood volume, which may result from changes in blood flow or venous distending pressure, may confound measurements. In eight conscious volunteers breathing hypoxic oxygen mixtures, we examined the influence of supine, 20 degrees Trendelenburg, and 20 degrees reverse Trendelenburg positions on the correlation of the spectroscopic measurement of cerebral oxygen saturation in the field assessed by the probe (CSfO2) and the calculated brain hemoglobin oxygen saturation (CScombO2), estimated as 0.25 x arterial saturation plus 0.75 x jugular venous bulb oxygen saturation. We found that changes in position did not influence the association between CSfO2 and CScombO2 (r2 = 0.69-0.885) during hypoxic challenge. In a second set of eight volunteers, we studied the influence of hypercapnia and hypocapnia and body position on the association between CSfO2 and CScombO2, and found that they were less well correlated (r2 = 0.366-0.976) in individual patients. Because changes in body position and Paco2 confound the relationship between CSfO2 and CScombO2, changes in CSfO2 can best be assessed if position and Paco2 are constant.

Physiological effects of locally applied reduced pressure in man.

Physiological effects of locally applied reduced pressure in man.

Cerebral blood flow and oxygen consumption in man.

Cerebral blood flow and oxygen consumption in man.