ABSTRACT
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.
ABSTRACT
Objective To discuss the changes of correlative ultrasonic parameter index of normal hips and abnormal hips with developmental dislocation of the hip (DDH) in infants of different months in order to provide objective information for the diagnosis. Methods Three-hundred and seventy-eight normal hips and 244 hips with DDH among 622 hips of 311 infants were detected by ultrasonography(US). The morphology and structure information of hips were observed, and the values of ultrasonic parameter index,including angle α,angle 3, acetabular index( AI), femoral head percentage of cover(FHC) of normal hips and abnormal hips were measured. The values of each parameter index were collected by being divided into different groups (3 months a group) ,then the correlation was analyzed. Results Morphology and structure,position relation between femoral head and acetabulum of the hips were demonstrated by US. Normal or abnormal hips,the degrees of abnormal hips and the types of hips could be judged according to the findingsof US. Analysis of values of parameter index of normal hips:①There was significantly statistical significance in the values of ultrasonic parameter index, such as angle α, angle β, AI, FHC of normal hip between the groups of different age (P＜0.01). ②There was correlation between the age and the values of each parameter index, among which angle α, FHC had positive correlations with age ( r = 0. 537, 0. 554,respectively ) while angle β and Al negative correlations ( r = -0. 465, -0.424, respectively ). ③There was correlation between the values of different parameter index. Both angle β and AI had negative correlation with angle α,among which the latter correlation was closely ( r = - 0. 794). No statistical significance was found between the ultrasonic values of each group under different ages of different type abnormal hips( P ＞0.05) ,but closely negative correlations still existed between angle α and AI. ConclusionsUS can be viewed as an early definite and a screening method of diagnosing DDH.For older infants (above 6 months) it will be more accurate to analyze the ultrasonic parameter index together with the age of infants.