Published online Nov 28, 2013. doi: 10.4329/wjr.v5.i11.411
Revised: September 6, 2013
Accepted: October 18, 2013
Published online: November 28, 2013
AIM: To experimentally investigate the acoustical behavior of different dual-mode nanosized contrast agents (NPCAs) for echographic medical imaging at low ultrasound (US) frequency.
METHODS: We synthesized three different nanosized structures: (1) Pure silica nanospheres (SiNSs); (2) FePt-iron oxide (FePt-IO)-coated SiNSs; and (3) IO-coated SiNSs, employing three different diameter of SiNS-core (160, 330 and 660 nm). Tissue mimicking phantoms made of agarose gel solution containing 5 mg of different NPCAs in 2 mL-Eppendorf tubes, were insonified by a commercial echographic system at three different low US pulse values (2.5, 3.5 and 4.5 MHz). The raw radiofrequency signal, backscattered from each considered NPCA containing sample, has been processed in order to calculate the US average backscatter intensity and compare the acoustic behavior of the different NPCA types.
RESULTS: The highest US contrast was exhibited by pure SiNSs; FePt-IO-coated SiNSs acoustical behavior followed a similar trend of pure SiNSs with a slight difference in terms of brightness values. The acoustic response of the examined NPCAs resulted function of both SiNS diameter and US frequency. Specifically, higher US frequencies determined higher value of the backscatter for a given SiNS diameter. Frequency-dependent enhancement was marked for pure SiNSs and became less remarkable for FePt-IO-coated SiNSs, whereas IO-coated SiNSs resulted almost unaffected by such frequency variations. Pure and FePt-IO-coated SiNSs evidenced an image backscatter increasing with the diameter up to 330 nm. Conversely, among the types of NPCA tested, IO-coated SiNSs showed the lowest acoustical response for each synthesized diameter and employed US frequency, although a diameter-dependent raising trend was evidenced.
CONCLUSION: The US characterization of magnetically covered SiNS shows that FePt-IO, rather than IO, was the best magnetic coating for realizing NPCAs suitable for dual mode imaging of deep organs, combining US and magnetic resonance imaging.
Core tip: In this work we investigated the acoustic response of novel dual-mode nanoparticle contrast agents, detectable through both ultrasound (US) and magnetic resonance imaging (MRI), made of silica nanospheres (SiNSs) of different diameters coated with superparamagnetic nanoparticles [iron-oxide (IO) or FePt-IO nanocrystals]. Magnetically-coated SiNSs were insonified with US pulses in the lower diagnostic range (2.5-4.5 MHz), which are commonly employed for the imaging of deep organs, and the results were compared with those of pure SiNSs. The US characterization of these nanocomposites shows that FePt-IO, rather than IO, was the best magnetic coating for realizing nanosized contrast agents suitable for dual mode imaging of deep targets, combining US and MRI techniques.