Table 2 Nanocarriers applied in molecular imaging methods to visualize the ischemic brain

Magnetic resonance imaging (MRI)

Low signal intensity and sensitivity

MNPs conjugated with antibodies

Become both a MRI contrast enhancement agent and a selective biological recognizer of target molecules

[64]

Lipid-encapsulated perflurocarbon NPs

Detect the microthrombin that form on the intimal surfaces of unstable atherosclerotic plaque sensitively and specifically

[67]

An integrin α_vβ₃-specific Fe₃O₄ nanoprobe modified with RGD tripeptide

Visualize the collaterals during acute IS

[68]

PEGylated ultrasma paramagnetic Gd2O3 NPs

Label and track cells in brain

[69]

Positron emission spectroscopy (PET)

Always used together with MRI and CT

NPs consisted of a SPIO core labelled with ⁶⁴Cu and coated with PEGylated phospholipids

Show high initial blood retention with moderate liver uptake

[72]

¹⁸F-modified polyglucose NPs

Exhibit high affinity for macrophages

[73]

Computed tomography (CT)

Not sensitive within the differentiation of penumbral and infarct core region

Au NPs grown in the PEGylated dendrimer

Achieve a blood pool imaging better than a commercial iodine agent

[77]

PEGylated BaHoF₅ nanoprobes

Much lower dosage required, main metabolism through liver and better imaging efficiency at different voltages

[78]

Exosome-labeled with glucose coated gold nanoparticles

Exhibit better accumulation of particles in the ischemic region

[81]

Ultrasonography

Difficult to penetrate the cranium

PDI NPs conjugated with cRGD

Monitor the obstructive degree of thrombus and the thrombolysis effect in time

[84]