Optimization protocols of MRCP imaging for mri 0.4 tesla (open) and comparison image quality with mri 3.0 tesla

Abstract

Magnetic resonance imaging (MRI) at high field strength has become more and more frequently used in recent years. The magnetic field strength is a factor affecting the image quality, spatial resolution, signal to noise ratio, contrast to noise ratio and the efficiency to reduce noise. According to the cost of system, type of magnet, cost of maintenance and several examinations, these items are considered in selecting MRI system. For these reasons, Open MRI has been appropriately selected by the hospital with limited budget in purchasing MRI system. Thus, the aim of this study is to assess the feasibility in optimization protocols of MRCP imaging acquired by MRI 0.4 Tesla (Open) and the factors affecting the image quality on MRCP at 0.4 Tesla in comparison to 3.0 Tesla. The pancreatic duct model made of plastic tube with internal diameter of 2.0 mm was used to determine FWHM (spatial resolution) with parameters affecting the image quality. The improved spatial resolution could be obtained when the slice thickness on 2D image were set at 20 and 30 mm, 280 mm FOV and the number of phase encoding at 288. For 3D images, the best spatial resolution obtained by selecting 2 and 3 mm slice thickness, 300 mm FOV and the number of phase encoding at 288. The syringe with internal diameter of 10 mm was used to evaluate the SNR, CNR and image noise. For 2D images, the highest SNR and CNR with the lowest noise were obtained at 50 mm slice thickness, 320 mm FOV, the number of phase encoding at 288, TR 6,000 ms, the NSA at 4. For 3D images, the highest SNR and CNR with the lowest noise were obtained at a 5 mm slice thickness, 320 mm FOV, 288 number of phase encoding and NSA at 5. The quantitative and qualitative assessment had been performed for both phantom and ten healthy volunteers who had been invited to MRCP examination. The normal subjects were 2 female and 8 male with the age range from 25-57 years (mean 34.7 years). The quantitative assessment was assessed from spatial resolution and signal intensity (FWHM, SNR and CNR) and qualitative assessment by one radiologist with experience over ten years was performed by scoring the MRCP images of seven structures for biliary systems with 2 readings. The intra-class correlation coefficient (ICC) was assessed for consistency or reproducibility of qualitative measurements. The results of quantitative study of MRCP image in phantom and on 2D and 3D at 3.0 T showed a higher SNR and CNR (p-value<0.05) than 0.4 T. Overall image quality on 2D MRCP image at 3.0 T was significant improvement than 0.4 T (p-value < 0.05) except 3D imaging (p-value >0.05) showing no significantly different between 0.4 and 3.0 T. The lowest ICC (0.61) is on 2D image 0.4 T and the highest is on 3D image of 3.0 T. Therefore, the overall MRCP imaging at 0.4 T (Open) with optimal protocols could be beneficial in adding up the confidence at 3D images.