ABSTRACT
Objective To explore the effect of multi-detector computed tomography (MDCT)scan parameters and imaging post-processing methods on metallic artifacts,so as to achieve the perfection in reduction of artifacts caused by metallic implants.Methods Water phantom with titanium alloy steel plate was scanned under MDCT with alternating scan parameters including tube voltage, tube current,pitch and focal spot.The areas of image artifacts were measured and correlated with the scan parameters.Another 1 5 postoperative patients with vertebral implantation scaned with the conventional scan parameters were also included in the study.Ima-ging post-processing including multi-planar reconstruction (MPR),window width and level adjustment,and volume rendering tech-nique (VRT)was performed by using optimized and conventional methods,respectively,and then the image quality was evaluated. Results The areas of image artifacts under the differnt tube voltage,pitch,and focal spot were statistically different.With the in-crease of the tube voltage or the decrease of the pitch,the area of image artifacts decreased gradually.The area of image artifacts scanned with the small focal spot was smaller than the large one.There was no significant difference for the area of image artifacts scanned with the different tube currents.The metallic artifacts decreased by using the soft tissue algorithm (Kernel B40f)in the bone window reconstruction,wide windows (2 000 HU window width,600 HU window level)in observing,and VRT.Conclusion Selection of appropriate MDCT scan parameters and imaging post-processing methods can reduce the metal artifacts,improve the image quality and diagnosis.
ABSTRACT
Objective:To observe the artifacts produced by dental metal crown made from different materials on magnetic resonance imaging (MRI).Methods:Mental crows made from Co-Gr,Ni-Gr,low-Ti alloy and Pure-Ti were respectively fabricated for upper right second premolar of a ripe crossbreed dog.The 4 different casting crowns were respectively put on experimental tooth and head MRI scan was carried out with 4 sequences of 1.5 T and 6 sequences of 3.0 T MRI respectively.The existence and extent of the arti-facts were assessed and compared.Results:On both 1.5 T and 3.0 T MRI,the Go-Gr alloy crown exhibited significantly wider arti-facts than the others (ANAVO analysis,P0.05).On 3.0 T MRI the artifacts produced by Ni-Gr was larger than that by low-Ti alloy or Pure-Ti(P0.05).By any of the test sequence either on 1.5 T or on 3.0 T,the Co-Gr alloy produced arti-facts in the most slices of MRI imaging and Pure-Ti in the least.Conclusion:Go-Gr alloy may produce larger artifacts than Ni-Gr, low-Ti alloy and Pure-Ti on MRI.
ABSTRACT
PURPOSE: To calculate the appearance of the image distortion from metallic artifacts and to determine the location of a metallic needle from a distorted MR image. MATERIALS AND METHODS: To examine metal artifacts, an infinite metal cylinder in a strong magnetic field are assumed. The cylinder's axis leaned toward the magnetic field along some arbitrary angle. The Laplace equation for this situation was solved to investigate the magnetic field distortion, and the simulation was performed to evaluation the image artifact caused by both readout and slice-selection gradient field. Using the result of the calculation, the exact locations of the metal cylinder were calculated from acquired images. RESULTS: The distances between the center and the folded point are measured from images and calculated. Percentage errors between the measured and calculated distance were less than 5%, except for one case. CONCLUSION: The simulation was successfully performed when the metal cylinder was skewed at an arbitrary tilted angle relative to the main magnetic field. This method will make it possible to monitor and guide both biopsy and surgery with real time MRI.