Improved sensitivity of computed tomography towards iodine and gold nanoparticle contrast agents via iterative reconstruction methods.

Ally Leigh Bernstein,David Peter Cormode,Martina Jurcova,Amar Dhanantwari,Pratap Chandra Naha,Thomas Ivanc,Efrat Shefer,Rabee Cheheltani

doi:10.1038/srep26177

Abstract

Computed tomography is a widely used medical imaging technique that has high spatial and temporal resolution. Its weakness is its low sensitivity towards contrast media. Iterative reconstruction techniques (ITER) have recently become available, which provide reduced image noise compared with traditional filtered back-projection methods (FBP), which may allow the sensitivity of CT to be improved, however this effect has not been studied in detail. We scanned phantoms containing either an iodine contrast agent or gold nanoparticles. We used a range of tube voltages and currents. We performed reconstruction with FBP, ITER and a novel, iterative, modal-based reconstruction (IMR) algorithm. We found that noise decreased in an algorithm dependent manner (FBP > ITER > IMR) for every scan and that no differences were observed in attenuation rates of the agents. The contrast to noise ratio (CNR) of iodine was highest at 80 kV, whilst the CNR for gold was highest at 140 kV. The CNR of IMR images was almost tenfold higher than that of FBP images. Similar trends were found in dual energy images formed using these algorithms. In conclusion, IMR-based reconstruction techniques will allow contrast agents to be detected with greater sensitivity, and may allow lower contrast agent doses to be used.

Highlights

T-values were compared to the 5% reference value, which is 2.14 when using fourteen degrees of freedom, to determine significant differences
We used an synthesized gold nanoparticle formulation in this study as a model CT contrast agent. 3.6 nm gold nanoparticles were used in this study that were synthesized via previously reported methodology[7,39]
Gold nanoparticle concentration was determined via inductively coupled plasma mass spectrometry (ICP-MS)

Summary

Methods

Gold nanoparticle synthesis.We used an synthesized gold nanoparticle formulation in this study as a model CT contrast agent. 3.6 nm gold nanoparticles were used in this study that were synthesized via previously reported methodology[7,39]. We used an synthesized gold nanoparticle formulation in this study as a model CT contrast agent. 3.6 nm gold nanoparticles were used in this study that were synthesized via previously reported methodology[7,39]. Hydrophobically coated gold nanocrystals that were synthesized by the method of Brust[40] were subsequently coated with myristoyl hydroxy phosphatidylcholine (MHPC). The gold nanocrystals and MHPC (1:1 weight ratio) were dissolved in a 9:1 chloroform:methanol solvent mixture. This solution was dripped slowly into hot (80 °C) deionized water. Concentrations are given as the number of gold atoms. The highest concentration used in this study, 95 mM of gold atoms, corresponds to 67 μM on a nanoparticle basis

Results

Discussion

Conclusion