Table of Contents
What is arterial spin Labelling ASL?
Arterial spin labeling (ASL) is a magnetic resonance imaging technique for measuring tissue perfusion using a freely diffusible intrinsic tracer. As compared with other perfusion techniques, ASL offers several advantages and is now available for routine clinical practice in many institutions.
What is ASL sequence?
Arterial spin labeling (ASL) will soon be available as a routine clinical perfusion imaging sequence for a significant number of MRI scanners. The ASL perfusion technique offers similar information as conventional dynamic susceptibility sequences; however, it does not require intravenous contrast and can be quantified.
How do you measure CBV?
CBV calculation. Under idealized conditions, it is possible to calculate relative regional CBV in each brain voxel simply by summing the contrast concentrations measured at each time point during the scan, i.e., calculating the area under Ct.
What is ASL perfusion MRI?
Arterial spin labeling (ASL) perfusion is a MRI technique to quantify tissue blood flow. ASL is a non-invasive technique that labels the protons in the arterial blood by radiofrequency pulses, without the exogenous injection of contrast media.
What is ASL radiology?
Arterial spin labeling (ASL) is a non-invasive MRI technique to measure cerebral blood flow (CBF). This review provides a practical guide and overview of the clinical applications of ASL of the brain, as well its potential pitfalls. The technical and physiological background is also addressed.
What is pseudo continuous arterial spin labeling?
Pseudo-continuous ASL (pcASL) is a pulse sequence strategy that can achieve continuous labeling without special hardware. Before describing pcASL, it is helpful to have some intuition for the basic principle of flow-driven adiabatic inversion.
What is CBV in radiology?
Cerebral blood volume (CBV) (often relative CBV: see below) is one of the parameters generated by perfusion techniques (CT perfusion and MR perfusion). CBV is defined as the volume of blood in a given amount of brain tissue, most commonly milliliters of blood per 100 g of brain tissue 1.
What is T2 Relaxometry?
T2 relaxometry involves measuring the T2 relaxation rate in the area of interest. The relaxation rate is best described by a combination of exponential decay curves in part due to different compartments of water in tissue but for simplicity a first approximation using a single curve is used.
What does BOLD imaging show in the brain?
Blood Oxygenation Level Dependent (BOLD) imaging is a technique that is commonly used for measuring brain activity in humans using magnetic resonance imaging (MRI). Blood supplies oxygen to brain cells. When these cells are active, there is an increase in blood flow and blood oxygen in the surrounding area.
What is CBV blood test?
CBV is defined as the volume of blood in a given amount of brain tissue, most commonly milliliters of blood per 100 g of brain tissue 1.
What is Tmax on CTP?
Time-to-Maximum (Tmax) is a perfusion parameter used both in CT perfusion and MRI perfusion and reflects the time delay between the contrast bolus arriving in the proximal large vessel arterial circulation (arterial input function) and the brain parenchyma 1.
What is T1 and T2 sequence?
The most common MRI sequences are T1-weighted and T2-weighted scans. T1-weighted images are produced by using short TE and TR times. The contrast and brightness of the image are predominately determined by T1 properties of tissue. Conversely, T2-weighted images are produced by using longer TE and TR times.
What is a good perfusion index?
5,6 The perfusion index is measured by a finger probe. The normal limits are not defined very well by the manufacturer. We accept the perfusion index value of 5 as the border for description of low or high (ie, 0–5 is low, >5 is high).
What is arterial spin labeling (ASL)?
Arterial spin labeling (ASL), also known as arterial spin tagging, is a magnetic resonance imaging technique used to quantify cerebral blood perfusion by labelling blood water as it flows throughout the brain.
What does arterial spin labeling tell us about cerebral perfusion?
Arterial spin labeling cerebral blood flow maps (bottom row) demonstrate no perfusion to the encephalomalacic brain (white arrowhead) and decreased perfusion in the mildly atrophic right cerebellar hemisphere (white arrow), consistent with cross cerebellar diaschisis. CONCLUSION ASL provides an important method for measuring cerebral perfusion.
What is continuous arterial spin labelling (CASL)?
In continuous arterial spin labelling (CASL), the blood water is inverted as it flows through the brain in one plane. CASL is characterized by one single long pulse (around 1-3) seconds.
What is a magnetically labeled arterial blood tracer?
Instead it exploits the ability of MRI to magnetically label arterial blood below the imaging slab. The parameter most commonly derived is cerebral blood flow (CBF). It is a non-invasive and non-ionizing MRI technique that measures tissue perfusion (blood flow), by using magnetically-labeled arterial blood water protons as an endogenous tracer.