This healthy 52-year-old patient presented with mild language difficulties that brought him to our emergency department 2h after symptom onset. Neurologically, there was no focal deficit of the extremities. The National Institute of Health (NIH) stroke scale score was 3. An emergency CT scan was performed and showed no hemorrhage, but a slight left frontal opercular hypodensity (Figure 1). Based on this, it was decided to proceed to MRI, which was performed on a 3.0-T Magnetom Trio (Siemens; Erlangen, Germany). Arterial spin labeling (ASL) was carried out with a pulsed arterial spin labeling (PASL) sequence, using a QUIPS-II perfusion mode and the following parameters: 16 slices; voxel size: 3.4×3.4×6mm; TA=5/55min; lambda=0.9mL/g; alpha=95%; TE/TR/TI1/TI2/T1 (blood, 3T)=15/5000/700/1800/1496.19ms. Relative cerebral blood flow (relCBF) maps for ASL were calculated online by the MRI scanner, and offline for contrast-enhanced perfusion-weighted imaging (cePWI) using syngo perfusion (MR) software. Susceptibility-weighted imaging (SWI) was done using 3D acquisition with an in-plane resolution of 1×1×1mm. cePWI was also acquired as well as diffusion-weighted imaging (DWI) with a 30°-direction scan. Initially, MRI showed a small focus of hyperintensity on DWI and hypoperfusion in the left middle cerebral artery (MCA) territory on gadolinium (Gd)-perfusion images (Fig.1).
Non-enhanced brain CT shows the beginnings of a left frontal hypodensity (A) that corresponds to hyperintensity on the diffusion images with a maximum b value (B) and a corresponding decrease in the apparent diffusion coefficient (ADC) (C). A large area of hypoperfusion can be seen on the gadolinium-enhanced perfusion MRI (D).
Scanner cérébral sans injection. Hypodensité frontale gauche (A) correspondant à l’hypersignal visible sur les images de diffusion avec valeur de b maximale (B) et diminution correspondante de l’ apparent diffusion coefficient (C). Il existe une large zone d’hypoperfusion en IRM de perfusion de premier passage. Zoom
Angiography was performed using a transfemoral approach. The left carotid artery was supraselectively accessed and revealed an occlusion at the level of M2. Intra-arterial thrombolysis was carried out and was followed by revascularization of the vessel; indeed, the distal MCA branches were slightly hyperperfused afterwards (Figure 2). On repeating MRI, the hypoperfusion was no longer evident. However, the ASL images revealed the presence of small cortical areas of hyperperfusion (Figure 3). Clinically, the patient’s language problems were reversed and his Rankin score at discharge was 1.
Cerebral angiography shows an occlusion at the level of the M1 portion of the left middle cerebral artery (MCA) (A). This was supraselectively catheterized and thrombolysis was performed locally (B). Later angiography shows recanalization (C) as well as hyperperfusion in the distal MCA branches.
Angiographie cérébrale. Occlusion du segment M1 de l’artère cérébrale moyenne (ACM) gauche (A). Celui-ci a été cathétérisé sélectivement et une thrombolyse in situ a été réalisée (B). Le contrôle angiographique montre ensuite la recanalisation (C) ainsi que l’hyperperfusion dans les branches distales de l’ACM. Zoom
Arterial spin labeling before (A) and after (B) thrombolysis. A large perfusion deficit can be seen in the left middle cerebral artery territory (A). After recanalization (B), the deficit has regressed and additional cortical hyperperfusion can be seen (arrow).
Imagerie de perfusion par marquage des spins avant (A) et après (B) thrombolyse. Avant thrombolyse, il existe un déficit important de la perfusion dans le territoire de l’artère cérébrale moyenne gauche. Après recanalisation, celui-ci a régressé et il existe une hyperperfusion corticale additionnelle. Zoom
We have shown here that ASL not only reproduces the imaging findings seen with Gd-based perfusion techniques, but can also demonstrate reperfusion. This is of great importance in cases where interventional neurovascular procedures have been undertaken. It is also of interest in the face of the challenges posed by nephrogenic systemic fibrosis (NFS).
Reperfusion is one of the aims of stroke therapy. Although neuroimaging in stroke has taken great strides in the last 10 years, there remains much that needs to be improved [1, 2]. In addition to demonstrating hypoperfusion and its reversibility, and the appearance–disappearance of lesions, imaging after interventions has been inadequate, as reperfusion is still not well characterized by MR techniques .
ASL is a promising new technique that may help to reveal the presence of small collaterals or cortical revascularization [4, 5]. It is based on the possibility of performing MRI studies of brain perfusion (to obtain flow images) without the use of contrast agents. ASL can demonstrate collateral flow , and the presence or absence of collaterals plays an important role in the survival of tissue after stroke.