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

Congenital bronchial atresia is a rare anomaly, which results from a congenital focal obliteration of a proximal segmental or subsegmental bronchus, with normal development of the distal structures. The short atretic segment leads to the accumulation of mucus within the distal bronchi, forming a bronchocele and air trapping of the alveoli supplied by these bronchi. The diagnostic CT features include the presence of a branching opacity and the bronchocele, which radiate from the hilum and are surrounded by an area of hyperlucency.
Bronchi ; Bronchial Diseases ; Mucus ; Tomography, Spiral Computed ; Tomography, X-Ray Computed

PURPOSE: Central lucency of pelvic phleboliths is frequently observed on plain pelvic radiographs. When it is also present on noncontrast helical CT images, pelvic phleboliths may be easily diagnosed, with no suspicion of distal ureteral calculi. The objective of this study was to determine the frequency with which this phenome-non is seen on plain radiographs and noncontrast helical CT images. MATERIALS AND METHODS: During a recent two-year period we identified 70 patients with renal colic who under-went both abdomino-pelvic radiography and noncontrast helical CT scanning. Radiographs were obtained at 70 -85 kVp and 30 -40 mA; CT scans were preformed within one month of plain radiography with parameters of 120 kVp, 200 -220 mA, 5-mm collimation, and pitch of 1 -1.6, and using soft tissue and bone window settings. With regared to the central lucency of pelvic phleboliths, as seen on both on radiographs and CT im-ages, two experienced radiologists reached a consensus. RESULTS: Among the 70 patients, a total of 150 pelvic phleboliths was found. In all cases except one, pelvic radi-ography and noncontrast helical CT revealed the same number of phleboliths. The exception was a case in which one of two phleboliths demonstrated by CT was not seen on radiographs. Pelvic radiography revealed central lucency in 95 of these 150 phleboliths (63%), but noncontrast helical CT failed to depict a hypodense center in any phlebolith. CONCLUSION: Central lucency of pelvic phleboliths, as frequently seen on plain pelvic radiographs, was not revealed by routine noncontrast helical CT in any patient.The presence or absence of central lucency on these CT images cannot, therefore, be used to differentiate phleboliths from distal ureteral calculi.
Consensus ; Humans ; Radiography ; Renal Colic ; Tomography, Spiral Computed* ; Tomography, X-Ray Computed ; Ureteral Calculi

PURPOSE: To evaluate the radiologic findings for complete and partial ablation after percutaneous CT-guided transthoracic radiofrequency ablation (RFA) of lung VX2 tumor implanted in rabbits. MATERIALS AND METHODS: Thirteen rabbits with successfully implanted lung VX2 were used. Three rabbits as controls did not receive RFA while the other ten rabbits underwent RFA; 5 complete and 5 partial. RFA was performed using an internally cooled, 17-gauge electrode (Radionics, Burlington, MA) with a 1-cm active tip under CT guidance. Postprocedural CT was performed within 3 days, and we analyzed the ablated size, enhancement pattern, shape, margin, and complications of the complete and partial ablation groups. Rabbits were sacrificed after postprocedural CT with an overdose of ketamine, and pathologic findings of the ablated groups were compared with those of the control group. RESULTS: The size of the ablated lesions and the enhancement pattern differed between the completely and partially ablated groups on chest CT. The size of the ablated lesions was increased by 47.1% in the completely ablated group and by 2.1% in the partially ablated group. In the completely ablated group, VX2 tumor showed absolutely no enhancement, whereas only ablated pulmonary parenchyma outside VX2 showed mild enhancement on enhanced CT. In the partial ablated group, a part of VX2 became strongly enhanced on enhanced CT. On microscopic examination, the completely ablated group demonstrated that a viable tumor cell was not visible. In the partially ablated group, however, a viable tumor cell within the surrounding fibrous capsule on the peripheral area of the VX2 was observed. CONCLUSION: The important CT findings for evaluation of complete and partial RFA are the ablated size and enhancement pattern of the ablated lesion.
Animals ; Catheter Ablation ; Electrodes ; Ketamine ; Lung* ; Rabbits ; 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 evaluate the diagnostic accuracy of computed tomography(CT) and magnetic resonance imaging(MRI)in the staging of rectosigmoid carcinoma according to the new AJCC classification. MATERIALS AND METHODS: BetweenAugust 1997 and October 1998, 36 patients with pathologically proven rectosigmoid carcinoma who underwent preoperative CT and MRI were evaluated. CT scans were performed with spiral CT in 27 cases and with conventional CT in nine. In all cases, MR images were obtained using a 1.5T unit and a body arrayed coil. T1- and T2-weightedimages were obtained in axial, sagittal, and coronal planes. On the basis of the results of CT scanning and MRI,tumor stage was determined by two radiologists using the AJCC cancer staging manual(1997). They reached aconsensus and compared their results with the pathologic stage. The T-stage was T1 in three cases, T2 in two, T3in 26, and T4 in five. The N-stage was N0 in 16 cases, N1 in seven, and N2 in 13. RESULTS: In the case of CT, thediagnostic accuracy of T-staging was 67%, and that of N-staging, 44%. For MRI, the corresponding figures were 83%and 67%. For T-staging, MRI was more accurate than CT(P=0.006), but for N-staging, the diagnostic accuracy of CT and MRI was statistically equivalent (P>0.05). CONCLUSION: MRI using a body arrayed coil is a useful preoperative diagnostic tool for the local staging of rectosigmoid carcinoma.
Classification* ; Humans ; Magnetic Resonance Imaging* ; Neoplasm Staging ; 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 distinguish the spiral CT findings of Borrmann type IV adenocarcinoma from those of gastric lymphoma with diffuse gastric wall thickening. MATERIALS AND METHODS: We retrospectively reviewed the spiral CT scans of 30 patients with Borrmann type IV adenocarcinoma and nine with gastric lymphoma with diffuse gastric wall thickening. In all patients the respective condition was pathologically confirmed by gastrectomy. CT scanning was performed after peroral administration of 500-700ml of water. A total of 120-140ml bolus of nonionic contrast material was administered intravenously at a flow rate of 3ml/sec and two-phase images were obtained at 35-45 sec(early phase) and 180 sec(delayed phase) after the start of bolus injection. Spiral CT was performed with 10mm collimation, 10mm/sec table feed and 10mm reconstruction. We evaluated the degree and homogeneity of enhancement of thickened entire gastric wall, and the enhancement pattern of gastric inner layer, as seen on earlyphase CT scans. On early and delayed views, the thickness of gastric wall and the presence of perigastric fat infiltration were determined. The enhancement patterns of gastric inner layer were classified as either continuous or discontinuous thick enhancement, thin enhancement, or nonenhancement. RESULTS: The thickness of gastric wall was 1.2-3.5cm(mean 2.2cm) in cases of adenocarcinoma and 1.2-7.6c m (mean 4cm) in lymphoma. Perigastric fat infiltration was seen in 24 patients with adenocarcinoma(80 %) and four with lymphoma(44%). In those with adenocarcinoma, the degree of enhancement of entire gastric wall was hyperdense in fifteen patients(50%) and isointense in eleven (37 %). Seven patients with lymphoma(78 % ) showed hypodensity. In those with adenocarcinoma, continuous thick enhancement of gastric inner layer was seen in 18 patients(60 %) and discontinuous thick enhancement in nine(30%). In lymphoma cases, no thick enhancement was observed. Thin enhancement of gastric inner layer was demonstrated in three patients with adenocarcinoma( 10 %) and two with lymphoma(22 %). In seven patients with lymphoma(78 %), there was no enhancement. CONCLUSION: The following early-phase findings are highly suggestive of gastric lymphoma: a gastric wall thickness of more than 3 cm; no or minimal perigastric fat infiltration, hypodense enhancement of thickened entire gastric wall; and no or thin enhancement of gastric inner layer.
Adenocarcinoma* ; Gastrectomy ; Humans ; Lymphoma* ; Retrospective Studies ; Tomography, Spiral Computed* ; Tomography, X-Ray Computed ; Water