"Protocol timings can also differ. Labelling duration (LD) is how long the labelling pulse or train is applied for. The recommended LD for PCASL at 3T is 1800 ms 3. Post-labelling delay (PLD) is the time elapsed between the end of labelling and the start of imaging acquisition. For adults < 70 years, a PLD of 1800 ms is also recommended. ASL can be acquired with a single PLD or with multiple PLDs. Multiple PLDs can be used to estimate arterial transit time 4."
"Protocol timings can also differ. Labelling duration (LD) is how long the labelling pulse or train is applied for. The recommended LD for PCASL at 3T is 1800 ms 3. Post-labelling delay (PLD) is the time elapsed between the end of labelling and the start of imaging acquisition. For adults < 70 years, a PLD of 1800 ms is also recommended. ASL can be acquired with a single PLD or with multiple PLDs. Multiple PLDs can be used to estimate arterial transit time 4."
"Basic principles "
"Clinical applications "
"pulsed (PASL)"
"pseudocontinuous (PCASL)"
"The PCASL technique is recommended because it provides superior labelling efficiency and better signal-to-noise ratio (SNR) when compared to the other methods 3."
"Protocol timings can also differ. Labelling duration (LD) is how long the labelling pulse or train is applied for. The recommended LD for PCASL at 3T is 1800 ms 3. Post-labelling delay (PLD) is the time elapsed between the end of labelling and the start of imaging acquisition. For adults < 70 years, a PLD of 1800 ms is also recommended. ASL can be acquired with a single PLD or with multiple PLDs. Multiple PLDs can be used to estimate arterial transit time 4."
"The main idea in ASL is to obtain a labelled image or tagged image and a control image, in which the static tissue signals are identical but the magnetisation of the inflowing blood is different. The water molecules in the arterial blood are magnetically labelled (tagged) by using a radiofrequency pulse that saturates water protons. Subtraction between labelled (tagged) and control images eliminate the static signals and the remaining signals are linear measures to the perfusion, which is proportionate to the cerebral blood flow (CBF). ASL SNR is very low because the signal from the tagged blood is only 0.5-1.5% of the entire tissue signal. As such, a 3T field strength is recommended to improve SNR along with background suppression, best achieved using 3D segmented readout methods such as 3D GRASE or 3D multiecho (RARE) stack of spirals 3. ASL data must be acquired before gadolinium administration since gadolinium will cause T1 shortening leading to a decrease in the measurable signals in both the labelled and controlled images 1,5."
"The main idea in ASL is to obtain a labelled image or tagged image and a control image, in which the static tissue signals are identical but the magnetisation of the inflowing blood is different. The water molecules in the arterial blood are magnetically labelled (tagged) by using a radiofrequency pulse that saturates water protons. Subtraction between labelled (tagged) and control images eliminate the static signals and the remaining signals are linear measures to the perfusion, which is proportionate to the cerebral blood flow (CBF). ASL SNR is very low because the signal from the tagged blood is only 0.5-1.5% of the entire tissue signal. As such, a 3T field strength is recommended to improve SNR along with background suppression, best achieved using 3D segmented readout methods such as 3D GRASE or 3D multiecho (RARE) stack of spirals 3. ASL data must be acquired before gadolinium administration since gadolinium will cause T1 shortening leading to a decrease in the measurable signals in both the labelled and controlled images 1,5."
Expected headings
"Basic principles "
"Clinical applications "
"Arterial spin labelling (ASL) MR perfusion is an MR perfusion technique which does not require intravenous administration of contrast (unlike DSC perfusion and DCE perfusion). 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-ionising MRI technique that measures tissue perfusion (blood flow) by using magnetically-labelled arterial blood water protons as an endogenous tracer."
"The main idea in ASL is to obtain a labelled image or tagged image and a control image, in which the static tissue signals are identical but the magnetisation of the inflowing blood is different. The water molecules in the arterial blood are magnetically labelled (tagged) by using a radiofrequency pulse that saturates water protons. Subtraction between labelled (tagged) and control images eliminate the static signals and the remaining signals are linear measures to the perfusion, which is proportionate to the cerebral blood flow (CBF). ASL SNR is very low because the signal from the tagged blood is only 0.5-1.5% of the entire tissue signal. As such, a 3T field strength is recommended to improve SNR along with background suppression, best achieved using 3D segmented readout methods such as 3D GRASE or 3D multiecho (RARE) stack of spirals 3. ASL data must be acquired before gadolinium administration since gadolinium will cause T1 shortening leading to a decrease in the measurable signals in both the labelled and controlled images 1,5."
"ASL is a very suitable technique to use in paediatrics, patients with impaired renal function, pregnancy and those who may need serial follow-up 1."