ABSTRACT
Objective To evaluate the value of gemstone spectral imaging (GSI)and multi artifact reduction system(MARs)in re-ducing metallic implants artifacts,and find the best monochromatic images.Methods Twenty-one patients with metal implants in our hospital receievd GSI examination ,MARS reconstruction and polychromatic images(140 kVp).Eleven groups of monochromatic and MARS images were obtained from 40 keV to 140 keV every interval of 10 keV by the special GSI viewer ,respetively.Subjective image quality of two methods were assessed by 3 radiologists in consensus.For every patient one group monochromatic images and blend enery images were selected two heaviest artifacts level and no artifacts level,the CT value and the standard deviations(SD)value of the region of interest(ROI)were meatured of artifacts.Contrast-to-noise ratio(CNR)and artifacts index(AI)were also caculated and were analyzed with paired-t test.Results There was significant statistical differences of CNR between energy spectral images and blend energy images in energy level of 40 to 120 keV(P 0.05),and the optimal CNR was acquired at the energy level of 70 keV(CNR=8.75±3.28).The value of AI for two mehtods has no difference in energy level scope 40 to 60 keV(P >0.05),there was significant statistical differences of AI between energy spectral images and blend energy images in energy level of 70 to 140 keV(P <0.05),and the lowest of AI(AI=26.95±9.64)was ac-quired at 1 10 keV images.Conclusion The energy spectral CT possess superiority in decreasing the artifacts and will provide high image quality in the metal implants.Gemstone spectral CT has great significance for postoperative patients with metal implants in imaging diagnosis.
ABSTRACT
Objective To study the effects of gantry rotation time on image quality in 64-slice spiral CT. Methods Using the same CT technique and body mode as those used for 64-slice spiral CT, delta phantom was firstly layed on the isocenter, then scanned and reconstructed with SOMATOM Sensation 64-slice spiral CT. Slice sensitivity profile(SSP) was measured from which modulation transfer function (MTF) were got by Fourier transfer. The Catphan500 phantom was layed on the table, then scanned and reconstructed with SOMATOM Sensation 64-slice spiral CT. The maximum linepair and minimum size of the targets visualized. Results The MTF curve was nearly overlapped on 0.5 s and 1.0 s gantry rotation time, the values of 5% MTF were 11.3 LP/cm and 11.9 LP/cm. Their spatial resolution and low contrast resolution were completely identical.Conclusion The image quality is no distinction on 0.5 s group and 1.0 s group of gantry rotation time. In order to shorten the scan time and eliminate the breath defect, we suggest that the 0.5 s gantry rotation time be used routinely at body spiral scan mode.