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: 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 determine the hemodynamics of the pancreas by investigating the enhancement patterns of pancreaticparenchyma, as seen on spiral CT, after the administration of various amounts of contrast medium, and to determineoptimal scan time by knowing the peak time of normal pancreatic parenchyma. MATERIALS AND METHODS: Between January1995 and April 1997 55 cases of normal abdominal CT with dynamic enhancement study on pancreas, the subject were38 cases(28 persons) with good image, aged 21-65 years, men were twenty-one and women were seven. Non-ioniccontrast medium, 30ml(n=15), 60ml(n=9), 990ml(n=7), and 120ml(n=7) were injected at a rate of 3ml/sec. From 20sec. after the start of injection, 15 images were obtained at 3-sec intervals. Before and after injection, R.O.I.was applied to each image, and for the aorta and pancreatic parenchyma, Hounsfield units(H.U.) were measured; timeof enhancement and maximal H.U. were also measured. RESULTS: After 30, 60, 90, and 120ml of contrast mediuminjection, mean maximal H.U. of pancreatic parenchyma was 36+/-7, 54+/-6, 68V13, and 92+/-8, respectively; mean valueat peak parenchymal enhancement of the pancreas was 27+/-3, 32+/-3, 42+/-3, and 52+/-3, respectively. Time intervalsof maximal enhancement of aorta and pancreatic parenchyma could not be obtained in 30ml injection, but 5,4+/-2.5,4.2+/-1.6, and 6.0+/-2.1sec in 60, 90, and 120ml injection, respectively. CONCLUSION: Maximal H.U. of parenchymalenhancement of the pancreas is directly proportional to the amount of injected contrast medium and the peak timeof parenchymal enhancement was 12sec after the injection of contrast material. Time interval of maximalenhancement of aorta and pancreatic parenchyma was 5.2+/-2.1sec.
Aorta ; Contrast Media ; Female ; Hemodynamics ; Humans ; Male ; Pancreas* ; Tomography, Spiral Computed* ; Tomography, X-Ray Computed

PURPOSE: To evaluate the usefulness of dynamic CT during the hepatic arterial phase with rapid IV injection ofcontrast material in distinguishing hepatocellular carcinoma (HCC) from intrahepatic cholangiocarcinoma (ICAC) asthe cause of biliary obstruction. MATERIALS AND METHODS: We retrospectively reviewed two-phase dynamic incrementalCT or helical CT findings in 22 patients with intrahepatic duct obstruction secondary to pathologically provenHCCs (n=12) or ICACs (n=10). Two-phase CT scans were obtained 20-45 seconds (hepatic arterial phase) or 2 minutes(equilibrium phase) after the initiation of a bolus injection of contrast material (5 mL/sec, 150 mL). Theenhancement patterns of tumors, as seen on two-phase images, were classified as hypo-, iso-, or hyperattenuated,relative to surrounding liver parenchyma. Two-phase images were compared and correlated with pathologic findings. RESULTS: During the hepatic arterial phase, diffuse high-enhancement was seen in nine HCCs (75%) and partialenhancement in three (25%); five (50%) of the ten ICACs were hypodense and five (50%) were hypodense withperipheral enhancement. During the equilibrium phase, however, all HCCs were hypodense and capsular enhancementwas seen in four cases (33.3%). All ICACs were hypodense with mild peripheral or central heterogeneousenhancement. Contrast enhancement patterns of HCCs during the hepatic arterial phase were significantly different(P<.0001) from those of ICACs. CONCLUSION: Our results suggest that dynamic CT during the hepatic arterial phase,with rapid IV injection of contrast material, is useful for the differentiation of HCC from ICAC as the cause ofbiliary obstruction.
Carcinoma, Hepatocellular* ; Cholangiocarcinoma* ; Humans ; Liver ; Retrospective Studies ; Tomography, Spiral Computed ; Tomography, X-Ray Computed

PURPOSE: To assess the relationship between splenic transient inhomogeneous contrast enhancement(CE) on the arterial phase of spiral CT, and splenic volume, and to classify the CE pattern in liver cirrhosis. MATERIALS AND METHODS: We measured the splenic volume of 120 patients, 60 showed inhomogeneous splenic CE on arterial phase,and 60 showed homogeneous splenic CE. CT scans with intrinsic splenic pathology were excluded. Sixteen patients with clinically confirmed liver cirrhosis were included. Splenic volumes of the inhomogeneous and homogeneous CE group were compared. The inhomogeneous group was divided into three grades according to areas of non-enhanced portion (grade I, focal geographic ; grade II, multifocal patchy, grade III, extensive serpentine inhomogeneous CE) , and these were correlated with splenic volume. RESULTS: Among the 60 inhomogeneous CE scans, 23 cases(38.3%) showed splenomegaly (spleen volume>220cm3); in contrast, this applied to only 8 cases (13.3%) of the 60 homogeneous CE scans. Mean splenic volume in the inhomogeneous CE group (226.74+/-129.78cm3) was greater than in the homogeneous CE group (184.56+/-77.44cm3) (p<0.033). A larger splenic volume and extensive inhomogeneous CE(grade III) were noted, and most liver cirrhosis patients(14/16) were grade III. Three such patients who had shown inhomogeneous splenic CE on arterial phase showed inhomogeneous CE even on portal phase. CONCLUSION: Inhomogeneous splenic CE on arterial phase was more common in cases of an enlarged spleen, and more extensive in liver cirrhosis. These findings suggest hemodynamic change of the spleen may be a contributory factor.
Hemodynamics ; Humans ; Liver Cirrhosis ; Pathology ; Spleen* ; Splenomegaly ; 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 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 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