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Objective To study algorithm expression of the optimal reconstruction increment with which images could be reconstructed without loss of z-direction spatial resolution for multislice spiral CT.Methods Using Gauss function and signal sampling principle,an algorithm expression was deduced to calculate the optimal reconstruction increment with which images could be reconstructed without loss of zdirection spatial resolution.Spiral slice sensitivity profile (SSP) phantom was scanned using Somatom Sensation 64-slice spiral CT and temporal bone protocol as those used for clinic,axial images were reconstructed with slice thickness of 0.600 mm and increment of 0.100,0.300,0.400 and 0.500 mm respectively.Then SSPs and full width at half maximum (FWHM) were measured and modulation transfer functions were obtained by Fourier transfer from SSPs.Axial CT scan of 7 normal temporal bones in 6 patients were obtained by the same CT system and parameters as above.Coronal MPR images of temporal bone out of different reconstruction increment were obtained and the quality of reconstructed images were independently assessed by three senior radiologists using a four-point scale and blinded the information of reconstruction.Experimental data were processed and two-way ANOVA(in which Dunnett t test was selected for multiple comparisons) was performed with statistic software SPSS10.0.P ＜ 0.05 was considered as significant difference.Results (1) The measured FWHM of reconstruction slice thickness of 0.600 mm was 0.665 mm,so the optimal reconstruction increment calculated with the algorithm expression in this article was 0.296 mm(≈0.300 mm).Objective evaluation showed that there was obviously aliasing in high spatial frequency range of MTF curve when reconstruction increment was more than 0.300 mm,i.e.both 0.400 and 0.500 mm.Clinical scores of coronal MPR images of temporal bone reconstructed with different increment had significant difference(F =505.374,P ＜ 0.01).Treating reconstruction increment of 0.100 mm as a control group and comparing another groups against it,there was no significant difference for reconstruction increment of 0.300 mm (t =-0.222,P ＞ 0.05),while there were significant difference for 0.400 and 0.500 mm (t =-1.333、-15.889,P ＜ 0.05,P ＜ 0.01).Conclusion It was proved that the angorithm expression deduced in this article was proper because of the consistence between the calculated value and the results from objective and clinical evaluation.The optimal reconstruction increment without loss of z-direction spatial resolution is 0.445 times as large as FWHM for multislice CT.
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Objective To compare imaging quality and radiation dose on DR and dual-sided reading of CR system.Methods The TRG of ALVIM statistics phantom was exposed by DR and dual-sided reading of CR with the same radiation dose,then the exposure factor and the entrance surface dose (ESD) were recorded.After that,the phantom was exposed by dual-sided reading of CR with various mAs ( 3.2,4.0,4.3,4.8 and 5.2 mAs) and the same kV,and the ESD was recorded,too.The acquired images were read by three radiologists on the monitor of diagnosis work station with the same window width and window level,then the total points of the images were given with the method of a five-level confidence scale.ROC curves were drawn and probability Pdet was calculated.Then the data was analyzed statistically by analysis of variance (ANOVA).Results The ROC analysis of bone substitute with diameter from 0.5 to 1.0 mm and muscle substitute with diameter from 0.9 to 2.0 mm showed A (z) values of 0.742 to 0.923 and 0.635 to 0.900 for DR system when the radiation dose was 137.5 μGy.The ROC analysis of bone substitute and muscle substitute showed A(z) values of 0.526 to 0.586 and 0.473 to 0.560 for dual-sided reading of CR at the same radiation dose.The probability Pdet discrepancy of bone substitute in two systems was from 0.216 to 0.337,with the highest of 0.337 in the diameter of 1.0 mm.The probability Pdet discrepancy by muscle substitute in two systems was from 0.075 to 0.342,with the highest of 0.342 in the diameter of 2.0 mm.There was significant statistical difference between the two groups ( F =35.30,P ＜ 0.01 ).When the exposure factor of dual-sided reading of CR system was 75 kV,4.8 mAs,the ESD was 180.4 μ Gy,the ROC analysis in the bone substitute with diameter from 0.5 to 1.0 mm and muscle substitute with diameter from 0.9 to 2.0 mm showed A(z) values was the same.The probability Pdet discrepancy of bone substitute in two systems was from - 0.003 to 0.009.The probability Pdet discrepancy of muscle substitute in two systems was from -0.005 to 0.008,and there was no statistical difference between the two groups ( F =5.23,P ＞0.05).When the probability Pdet of two systems was the same,the ESD was 180.4 μGy by dual-sided reading of CR system,and the ESD was 137.5 μGy by DR system.Conclusion Detection with DR system was proved to be superior to dual-sided reading of CR system at the same radiation dose.When the image quality was similar,the radiation dose of DR system was less than the dual-sided reading of CR system.
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Objective To evaluate the parallactic unsharpness caused by flat panel detector in digital radiography using different incident angle of central ray. Methods R-1 square-wave phantom was exposed by Kodak DR3000 system with X-ray tube angled 0°, 10°, 20°, 30°, and 40° respectively. Then,presampled modulation transfer function (MTF) was calculated for each case above. Subsequently,experimental data were processed and Wilcoxon signed ranks test were performed by statistic software SPSS 10. 0, in which P ＜ 0. 05 was considered as statistically significant difference. Results The presampled MTF curves of incident angle of 0°-40° degree, were presented orderly from top to bottom, especially the incident angle of 40° was obviously the lowest. The incident angle of 0° was considered as a control group and other groups were compared against it. There was no statistically significant difference for MTF of incident angle of 10°( Z = - 1. 893 ,P = 0. 058 ), while there were significant difference for MTF of incident angle of 20°, 30°, and 40° ( Z = - 2. 547, - 2. 666, - 2. 666, P ＜ 0. 05 ). Conclusions For flat panel detector in digital radiography, the bigger the incident angle of central ray, the larger the parallactic unsharpness. In addition, this effect has less influence on structures of low spatial frequency than those of high spatial frequency.
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Objective To explore the optimum voltage for digital chest radiography in adult. Methods PMMAs of Different thickness (7.2, 9.0, 10. 8 and 12. 6 cm) were used to simulate chest of different depth ( 17. 5, 22. 5, 27.0 and 32. 5 cm). The combinants of contrast-detail Cdrad 2.0 phantom and above PMMAs were exposed with automatic exposure control (AEC) and different tube voltages. The images of these combinants were obtained and the entrance surface dose (ESD) was recorded. The imaging quality factor (IQF) was calculated and the curves were drawn between the ESD,IQF and kV. The PMMAs of different thickness, on which a contrast object ( PMAA of 5 cm diameter and 1.8 cm thickness ) was placed, were exposed with the same condition used for above test. Their images were obtained and SNRs were calculated. Results The ESD, SNR and IQFinv of different chest depth decreased with increase of kV.When tube voltages of 70, 100 and 140 kV were used, for 17. 5 cm chest depth, the ESD was 0. 22, 0. 09 and 0. 06 mGy, the IQF was 43.3, 58. 8 and 72. 0, the SNR was 7.5, 6. 2 and 5.0; for 22. 5 cm chest depth, the ESD was 0.37, 0.12 and 0.06 mGy, the IQF was 56. 0, 61.4 and 65.3, the SNR was 6. 4, 5.2 and 3. 8; for 27. 0 cm chest depth, the ESD was 0. 52, 0. 20 and 0. 09 mGy, the IQF was 54. 2, 64. 3 and 91. 0, the SNR was 6. 0, 4. 8 and 3. 5; for 31.5 cm chest depth, the ESD was 0.53, 0.24 and 0. 10 mGy,the IQF was 53.2, 66. 8 and 95.3, the SNR was 5. 7, 4. 5 and 3. 0. Conclusion To balance ESD, SNR and IQF, proper tube voltage should be chosen for chest radiography according to thickness and constitution of patients.
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Objective To evaluate diagnostic accuracy of image interpretation using viewboxes at different luminance with ALVIM statistical phantom (TRG).Methods A digital film of TRG image was obtained by exposing the phantom of TRG with Kodak DR 3000 using proper parameter.Viewboxes with three different luminance were selected from those used in daily work.The film of TRG was evaluated with these viewboxes of three different luminance by three different radiologists with experience of five,eight and sixteen years respectively.A grade scale of 5 was used to evaluate each row of signal and noise.According to the results and formula,the probabilities of true-positive [P (S/s)],false-positive [P (S/n)] and true answer(Pdet) were obtained. Results The three kinds of luminance used in viewboxes were: (3489 ± 256),(2231 ± 220),(816 ± 168) cd/m2.When the average luminance of viewbox was 3489 cd/m2,Pdet of 0.6,0.7,0.8 mm in bone substitute was 0.558±0.009,0.788±0.008,0.813±0.006,Pdet of0.9,1.0,1.2 mm in muscle substitute was 0.663 ± 0.010,0.750 ± 0.008,0.933 ± 0.005 ; When the average luminance of viewbox was 2231 cd/m2 ,Pdet of 0.6,0.7,0.8 mm in bone substitute was 0.525 ± 0.013,0.713 ± 0.013,0.775 ± 0.016,Pdet of 0.9,1.0,1.2 mm in muscle substitute was 0.613 ± 0.019,0.650 ± 0.013,0.850±0.019 ;When the average luminance of viewbox was 816 cd/m2 ,Pdet of 0.6,0.7,0.8 mm in bone substitute was 0.475 ± 0.022,0.550 ± 0.018,0.688±0.020,Pdet of 0.9,1.0,1.2 mm in muscle substitute was 0.550 ± 0.025,0.575 ± 0.021,0.725 ± 0.016. Viewboxes of different luminance were compared to one another by paired t-test.The results of comparison all had significant statistical differences (t = 5.057 and 4.681 ,P <0.05).Conclusions The image displayed by viewboxes at different luminance had significant influence on image interpretation. The higher the luminace of viewbox,the richer the information displayed,and the higher the accuracy of diagnosis.
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Objective To establish the mathematical model and perform experimental mensuration on effective slice width for 4-slice spiral CT. Methods First, assuming the spiral slice sensitivity profile (SSP) was Gauss distribution, a formula about effective slice width, defined as the full width at half maximum (FWHM) of SSP, was get. Then, using Philips Mx8000 4-slice spiral CT system and the same CT technique as those used for clinical CT, CTP 528 of Phantom Catphan 500 was scanned with parameters as follows: 120 kV, 150 mAs, 180 mm FOV, 512×512 Matrix, 180° linear interpolation, different pitch and 0.5 mm detector width. Finally, FWHM was got from the coronal multiplanar reconstruction image passing by the center of tungsten ball in CTP528 for each sequence. Results With pitch of 0.500, 0.625, 0.875, 1.000, 1.250, 1.500 and 1.750, the measured FWHM was 0.7, 0.7, 0.7, 0.8, 0.7, 0.7 and 0.7 mm, respectively. With detector width of 0.5, 1.0 and 5.0 mm, the measured FWHM was 0.7, 1.2, and 6.7 mm, respectively. All the measured effective slices were higher than those of theoretical values. Conclusion The relativity between effective slice width and detector width is direct proportion, while that between effective slice width and pitch is non-linear.
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Objective To measure and evaluate slice sensitivity profile(SSP)and the full width at half-maximum(FWHM)for a 64-slice spiral CT system.Methods Using the same CT technique and body mode as those used for clinical CT,delta phantom was scanned with Somatom Sensation 64-slice spiral CT.SSPs and FWHM were measured both with reconstruction slice width of 0.6 mm at pitch = 0.50,0.75,1.00,1.25,1.50 and with reconstruction slice width of 0.6,1.0,1.5 mm at pitch = 1 respectively.Results For normal slice width of 0.6 mm,the measured FWHM,i.e.effective slice width,is 0.67,0.67,0.66,0.69,0.69 mm at different pitch.All the measured FWHM deviate less than 0.1mm from the nominal slice width.The measured SSPs are symmetrical,bell-shaped curves without far-reaching tails,and show only slight variations as a function of the spiral pitch.When reconstruction slice width increase,relative SSP become wider.Conclusions The variation of pitch hardly has effect all on SSP,effective slice width,and z-direction spatial resolution for Sensation 64-slice spiral CT system,which is helpful to optimize CT scanning protocol.