OBJECTIVE: To build a helical CT projection data restoration model at random low-dose levels. METHODS: We used a noise estimation module to achieve noise estimation and obtained a low-dose projection noise variance map, which was used to guide projection data recovery by the projection data restoration module. A filtering back-projection algorithm (FBP) was finally used to reconstruct the images. The 3D wavelet group residual dense network (3DWGRDN) was adopted to build the network architecture of the noise estimation and projection data restoration module using asymmetric loss and total variational regularization. For validation of the model, 1/10 and 1/15 of normal dose helical CT images were restored using the proposed model and 3 other restoration models (IRLNet, REDCNN and MWResNet), and the results were visually and quantitatively compared. RESULTS: Quantitative comparisons of the restored images showed that the proposed helical CT projection data restoration model increased the structural similarity index by 5.79% to 17.46% compared with the other restoration algorithms (P < 0.05). The image quality scores of the proposed method rated by clinical radiologists ranged from 7.19% to 17.38%, significantly higher than the other restoration algorithms (P < 0.05). CONCLUSION The proposed method can effectively suppress noises and reduce artifacts in the projection data at different low-dose levels while preserving the integrity of the edges and fine details of the reconstructed CT images.
Algorithms ; Artifacts ; Tomography, Spiral Computed ; Tomography, X-Ray Computed/methods*

OBJECTIVE: To quantitatively analyze image quality of two sets of phantom (CatPhan504 and Cheese) Megavoltage computed tomography (MVCT) images acquired by Helical Tomotherapy with three scanning modes (Fine, Normal and Coarse), and to explore and validate a semi-automatic quality assurance procedure for MVCT images of Helical Tomotherapy. METHODS: On Helical Tomotherapy, CatPan504 and Cheese phantoms were scanned with three pitch levels (Fine, Normal, Coarse: 4 mm, 8 mm, 12 mm/circle) respectively. Pylinac, Matlab and Eclipse were used to calculate and compare spatial resolution, noise level and low contrast resolution of images obtained under three scanning modes respectively. The spatial resolution can be evaluated by the blurring of line-pair CT value in the images of CatPhan504's CTP528 module. The noise level can be evaluated by the integral non-uniformity in the images of Cheese's uniformity module. the low contrast resolution can be evaluated by contrast-to-noise ratio of both phantoms' plug-in module, or visibility of the region of interest (Supra-Slice) in the images of CatPhan504's CTP515 module. RESULTS: Analyses on CatPhan504's line pair module(CTP528 module) showed that the first three line pairs(the gap size are 0.500 cm, 0.250 cm and 0.167 cm respectively) could be clearly observed but blurring began to occur from the fourth line pair(the gap size is 0.125 cm) under Coarse mode. Meanwhile, the first four line pairs were all observable under the Normal and Fine modes. Integral non-integrity index(the value negatively correlated with the noise level) were 0.155 7, 0.136 8 and 0.122 9 for Coarse, Normal and Fine modes respectively. None of the Supra-Slice in CatPhan504's CTP515 module could be observed under three imaging modes. Low contrast contrast-to-noise ratio of Cheese phantom was similar under three modes and the insert visibility exhibited nearly linear growth with the increasing difference between CT average value of the insert material and background. CONCLUSION Superiority and inferiority of three image modes in terms of the three image quality index was not consistent. Evaluation results above could provide reference for more rational decision on scanning modes selection of helical tomotherapy, which was based on image visualization demands in clinical practice. The proposed method could also provide guidance for similar image quality assessment and periodic quality assurance.
Cone-Beam Computed Tomography ; Phantoms, Imaging ; Radiotherapy, Intensity-Modulated ; Tomography, Spiral Computed ; Tomography, X-Ray Computed

PURPOSE: The purpose.of this study was to characterize the enhancing patterns of hepatocellular carcinoma (HCC) on two-phase dynamic incremental liver scan with spiral CT. MATERIALS AND METHODS: Two-phase dynamic incremental liver scan using spiral CT was performed on 230 lesions in 107 patients with HCC. CT scanning was performed with a table speed of 13mm/sec and a section thickness of 10 mm;120 mL of contrast medium was injected intravenously with a automatic injector at the rate of 3mL/sec. CT scans were started 35 sec(early phase) and 3 min(delayed phase) after beginning injection of contrast medium. The tumors were divided into 2 groups according to size(< or = 3cm and > 3cm), the contrast enhancement patterns of HCCs and capsules in the early and delayed phases were analyzed in each group. RESULTS: Most of HCCs appeared as high-attenuating lesions in the early phase(75% in tumors smaller than 3cm and 61% in tumors larger than 3cm), and as low-attenuating lesions in the delayed phase(68% in tumors smaller than 3cm and 90% in tumors larger than 3cm). Forty-eight percent of HCCs smaller than 3cm and 58% of HCCs larger than 3cm were high-attenuating in the early phase and low-attenuating in the delayed phase. Thirty-two percent of capsules were low- or iso-attenuating in the early phase and high-attenuating in the delayed phase. Capsules were demonstrated in 22% in HCCs smaller than 3cm and 67% in HCCs larger than 3 cm(p <. 01). CONCLUSION: Two-phase dynamic scan with spiral CT is useful in the diagnosis of HCC because of a precise display of hemodynamic characteristics of HCCs.
Capsules ; Carcinoma, Hepatocellular* ; Diagnosis ; Hemodynamics ; Humans ; Liver ; Tomography, Spiral Computed* ; Tomography, X-Ray Computed

PURPOSE: To evaluate clinical usefulness of facial soft tissue thickness measurement using 3D computed tomographic images. MATERIALS AND METHODS: One cadaver that had sound facial soft tissues was chosen for the study. The cadaver was scanned with a Helical CT under following scanning protocols about slice thickness and table speed; 3 mm and 3 mm/sec, 5 mm and 5 mm/sec, 7 mm and 7 mm/sec. The acquired data were reconstructed 1.5, 2.5, 3.5 mm reconstruction interval respectively and the images were transferred to a personal computer. Using a program developed to measure facial soft tissue thickness in 3D image, the facial soft tissue thickness was measured. After the ten-time repeation of the measurement for ten times, repeated measure analysis of variance (ANOVA) was adopted to compare and analyze the measurements using the three scanning protocols. Comparison according to the areas was analyzed by Mann-Whitney test. RESULTS: There were no statistically significant intraobserver differences in the measurements of the facial soft tissue thickness using the three scanning protocols (p>0.05). There were no statistically significant differences between measurements in the 3 mm slice thickness and those in the 5 mm, 7 mm slice thickness (p>0.05). There were statistical differences in the 14 of the total 30 measured points in the 5 mm slice thickness and 22 in the 7mm slice thickness. CONCLUSION: The facial soft tissue thickness measurement using 3D images of 7 mm slice thickness is acceptable clinically, but those of 5 mm slice thickness is recommended for the more accurate measurement.
Cadaver ; Imaging, Three-Dimensional ; Microcomputers ; Tomography, Spiral Computed ; Tomography, X-Ray Computed

PURPOSE: To determine the number of multiple alternating layers of liver abscess, and changes in this number, as revealed by spiral CT, and to ascertain which factors are related to changes occurring during the three phases of this modality. MATERIALS AND METHODS: Using three-phase spiral CT imaging we studied 26 cases of liver abscess (pyogenic:amebicm=23:3). The number of layers comprising the abscess, as seen on postcontrast CT scans, was determined during the arterial (30sec), portal (70sec), and delayed (220sec) phase, and all cases were assigned to one of two groups according to changes in the number of layers observed during the three phases. With regard to underlying disease, the two groups were compared in terms of the presence of abscess and of diabetes mellitus,CT interval (time from onset of symptoms to CT scanning), microbial agent (pyogenic vs. amebic), and the largest diameter of abscess as revealed by CT. RESULTS: Except in one case, three or four alternating layers [in 13(50%) and 7(27%) cases, respectively] were seen only during the arterial and portal phase. During each of the three phases-and especially the delayed phase, where it was present in 25 of cases (96%)-two alternating layers (2:2:2) was the most common pattern, with a 3:3:3 pattern occurring in one case. All 12 cases (46%) in the unchanging-layer group showed one of these two patterns. All changing-layer group cases (14;54%) demonstrated three or four layers during the arterial and portal phase but only two during the delayed phase. The CT interval was the only significantly different factor between the two groups. During the first week, the number of cases in the unchanging-layer group was much higher than in the changing-layer group (86%,14%), but during the second week this situation reversed (25%, 75%). CONCLUSION: Our study reveals that on three-phase dynamic CT images, a characteristic enhancement feature of liver abscesses is three or four layers during the arterial and portal phases, with reduction to two layers during the delayed phase. This change, as revealed by spiral CT, is rare during the week following the onset of symptoms, but common during the second week.
Abscess ; Liver Abscess ; Liver* ; Tomography, Spiral Computed ; Tomography, X-Ray Computed

Inflammatory pseudotumor is a rare benign lesion consisting of inflammatory cells and fibroblastic stroma, and is reported to have occurred. in various organs. Splenic involvement, however, is extremely rare. We report the spiral CT findings of pathologically proven inflammatory pseudotumor of the spleen. The CT scan shows delayed enhancement with central, stellate, low attenuation.
Fibroblasts ; Granuloma, Plasma Cell* ; Spleen* ; Tomography, Spiral Computed ; Tomography, X-Ray Computed

PURPOSE: To evaluate the contrast enhancement patterns and mass detection rate of metastatic adenocarcinoma of the liver in the early and late phase of spiral bolus dynamic CT. MATERIALS AND METHODS: Two-phase spiral bolus dynamic CT of the liver was performed on 34 patients with clinically or pathologically proved metastatic adenocarcinoma of the liver after bolus administration of 120 mL of contrast material intravenously. CT scanning was started at 45 seconds and 6 minutes after I~eginning of injection in 23 patients, and at 35 seconds and 3 minutes in another 11 patients. The enhancement patterns of the tumors were classified into 6 types compared with attenuation of surrounding normal liver parenchyma, as diffusely high, peripherally high, centrally high, mixed, iso, diffusely low. The enhancement patterns of 76 tumors in 34 patients were analysed. RESULTS: In the early phase, peripherally high attenuation was seen in 34(45%) and diffusely low attenuation in 23(30%). In the late phase, diffusely low attenuation was seen in 27(36%) followed by iso and mixed in 14 (18%), in each, and peripherally high in 13(17%). The appearances of enhancement pattern from the early to the late phase were variable. 12(16%) were diffusely low in both phases, 11(14%) were peripherally high in the early phase and diffusely low in the late phase, and 10(13%) were peripherally high in both phases. Number of tumor lesions detected were more in the early phase in 12(35%)patients, and in the late phase in 3(9%) patients. CONCLUSION: Metastatic adenocarcinoma of the liver showed variable enhancement patterns in the early and late phases of spiral bolus dynamic CT, although the most common pattern was peripherally high in early phase, and diffusely low in the late phase. The detection rate of masses was higher in early phase than late. The two-phase spiral bolus dynamic CT should be good method in detection and differential diagnosis of metastatic adenocarcinoma of the liver.
Adenocarcinoma* ; Diagnosis, Differential ; Humans ; Liver* ; Tomography, Spiral Computed* ; Tomography, X-Ray Computed

PURPOSE: To evaluate the contrast enhancement patterns and mass detection rate of metastatic adenocarcinoma of the liver in the early and late phase of spiral bolus dynamic CT. MATERIALS AND METHODS: Two-phase spiral bolus dynamic CT of the liver was performed on 34 patients with clinically or pathologically proved metastatic adenocarcinoma of the liver after bolus administration of 120 mL of contrast material intravenously. CT scanning was started at 45 seconds and 6 minutes after I~eginning of injection in 23 patients, and at 35 seconds and 3 minutes in another 11 patients. The enhancement patterns of the tumors were classified into 6 types compared with attenuation of surrounding normal liver parenchyma, as diffusely high, peripherally high, centrally high, mixed, iso, diffusely low. The enhancement patterns of 76 tumors in 34 patients were analysed. RESULTS: In the early phase, peripherally high attenuation was seen in 34(45%) and diffusely low attenuation in 23(30%). In the late phase, diffusely low attenuation was seen in 27(36%) followed by iso and mixed in 14 (18%), in each, and peripherally high in 13(17%). The appearances of enhancement pattern from the early to the late phase were variable. 12(16%) were diffusely low in both phases, 11(14%) were peripherally high in the early phase and diffusely low in the late phase, and 10(13%) were peripherally high in both phases. Number of tumor lesions detected were more in the early phase in 12(35%)patients, and in the late phase in 3(9%) patients. CONCLUSION: Metastatic adenocarcinoma of the liver showed variable enhancement patterns in the early and late phases of spiral bolus dynamic CT, although the most common pattern was peripherally high in early phase, and diffusely low in the late phase. The detection rate of masses was higher in early phase than late. The two-phase spiral bolus dynamic CT should be good method in detection and differential diagnosis of metastatic adenocarcinoma of the liver.
Adenocarcinoma* ; Diagnosis, Differential ; Humans ; Liver* ; Tomography, Spiral Computed* ; Tomography, X-Ray Computed

PURPOSE: To compare the enhancement characteristics of small hemangiomas seen on multiphase spiral CT anddynamic MR imaging MATERIALS AND METHODS: Thirteen patients with 20 hepatic hemangiomas less than 25mm indiameter underwent both multiphase spiral CT and dynamic MR imaging. All lesions were assigned to one of threeclassified into 3 categories according to the enhancement pattern seen on multiphase spiral CT : typical delayedpooling, atypical early enhancement, or continuous low attenuation. The enhancement patterns seen on spiral CT andon dynamic MRI were correlated. RESULTS: On CT scans, ten lesions (50%) showed delayed pooling. Six(30%) showedearly arterial enhancement and four(20%) showed continuous low attenuation. On delayed-phase MRI, all lesionsshowed delayed high signal intensity compared to adjacent liver parenchyma. Four of six lesions with earlyenhancement on CT showed peripheral globular enhancement on early arterial-phase MRI. CONCLUSION: On multiphasespiral CT scans, small hemangiomas can show variable atypical enhancement features. In this situation,contrast-enhanced dynamic MRI is helpful for the diagnosis of hemangiomas.
Diagnosis ; Hemangioma* ; Humans ; Liver ; Magnetic Resonance Imaging* ; Tomography, Spiral Computed* ; Tomography, X-Ray Computed

PURPOSE: To evaluate accuracy and reliability of program to measure facial soft tissue thickness using 3D computed tomographic images by comparing with direct measurement. MATERIALS AND METHODS: One cadaver was scanned with a Helical CT with 3 mm slice thickness and 3 mm/sec table speed. The acquired data was reconstructed with 1.5 mm reconstruction interval and the images were transferred to a personal computer. The facial soft tissue thickness were measured using a program developed newly in 3D image. For direct measurement, the cadaver was cut with a bone cutter and then a ruler was placed above the cut side, The procedure was followed by taking pictures of the facial soft tissues with a high-resolution digital camera. Then the measurements were done in the photographic images and repeated for ten times. A repeated measure analysis of variance was adopted to compare and analyze the measurements resulting from the two different methods. Comparison according to the areas was analyzed by Mann-Whitney test. RESULTS: There were no statistically significant differences between the direct measurements and those using the 3D images (p>0.05). There were statistical differences in the measurements on 17 points but all the points except 2 points showed a mean difference of 0.5 mm or less. CONCLUSION: The developed software program to measure the facial soft tissue thickness using 3D images was so accurate that it allows to measure facial soft tissues thickness more easily in forensic science and anthropology.
Anthropology ; Cadaver ; Forensic Sciences ; Imaging, Three-Dimensional ; Microcomputers ; Tomography, Spiral Computed ; Tomography, X-Ray Computed