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: 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

OBJECTIVETo evaluate the value of three-dimensional surface reconstruction of spiral CT-shaded surface display (SSD) to examine the impacted teeth before orthodontic treatment.

METHODSThree-dimensional surface reconstruction of spiral CT and shaded surface display (SSD) was applied to twenty patients whose impacted teeth couldn't be judged clearly through the panorama and occlusal films.

RESULTSThree-dimensional surface reconstruction of spiral CT and SSD could clearly demonstrate the dental surface image including crown, root neck and root bifurcation in three-dimensional way, labial or palatal location, eruption orientation and relation with dentition.

CONCLUSIONIt is concluded that the three-dimensional surface reconstruction is an accurate and effective method to examine impacted teeth before orthodontic treatment.

OBJECTIVETo study the allocation of embedded teeth in jaws using the three-dimensional reconstruction technique of 64-slices spiral CT.

METHODS27 cases were examined by helical scanning of axial view volume scan CT. The exact localization of the embedded teeth in jaws was acquired by using volume rendering (VR), maximum intensity projection (MIP), multiplanar reformation (MPR) and curve plane reconstruction (CPR).

RESULTSThe localization, morphous, size, erupted orientation and relationship between surrounding tissues of the 41 embedded teeth in 27 patients were displayed by effectually using the images of VR, MIP, MPR and CPR. The election of orthodontic treatment or surgical intervention was decided by using 64-slices spiral CT.

CONCLUSIONThe exact data and objective evidence of the treatment plan could be provided by 64-slices spiral CT which will have important clinical application.

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

STUDY DESIGN: A study on the development of an algorithm to enhance computed tomographic images. OBJECTIVE: The purpose of this study was to develop an approach to reduce the metal artifact that appears around pedicle screws, and thus to facilitate the evaluation of pedicle screw positions on CT scan images. SUMMARY OF LITERATURE REVIEW: Metal artifact caused by pedicle screws significantly reduces the interpretability of computed tomography images. MATERIALS AND METHODS: We describe the development of an algorithm that processes CT scan images on a personal computer using a digital image enhancement technique. The algorithm improves CT images by transforming image pixel values using a proper transformation curve that takes into account the characteristic distribution pattern of metal artifact caused by pedicle screws made of titanium alloys. We implemented this algorithm in a program that reconstructs the resulting images in arbitrary planes and in axial, coronal, and sagittal planes. The software was tested with spiral CT scan images of 38 patients containing 190 pedicle screws. RESULTS: In all test cases, our algorithm generated images with less metal artifact, better soft tissue visualization and clearer screw outlines than conventional bone setting. In addition, images reconstructed in arbitrary planes increase the convenience and confidence of localizing screw positions. CONCLUSIONS: The algorithm effectively decreases metal artifact and improved pedicle screw localization.
Alloys ; Artifacts* ; Humans ; Image Enhancement* ; Microcomputers ; Titanium* ; Tomography, Spiral Computed ; Tomography, X-Ray Computed*

PURPOSE: To evaluate the CT findings of tumor in the pyriform sinus, and to assess by functional study of thelarynx the extent the extent to which its characteristic findings differ from those of supraglottic tumor. MATERIALS AND METHODS: CT scans of 14 patients with tumor in the pyriform sinus were reviewed and compared withthose of 17 patients with supraglottic tumor. In all cases, spiral CT scanning linvolved both quiet breathing andmodified breath holding; we evaluated the images and analysed the primary site of tumors and the displacement ofair in the pyriform sinus. Extra and intralaryngeal extension of the tumors was also assessed. RESULTS: In tumorsin the pyriform sinus, CT findings were thickening of more than two walls in 14, the displacement of air in 9,extralaryngeal extension in 13, extension to the post-cricoid space in 11, invasion of the pre-epiglottic space in13, and widening of the cricothyroid space in 8 patients. In supraglottic tumors, CT findings were thickening ofthe medial wall in 17, extralaryngeal extension in 1, extension to the post-cricoid space in 1, invasion of theipsilateral paralaryngeal space in 17, and of the contralateral paralaryngeal space in 6, invasion of thepre-epiglottic space in 11, and widening of the cricothyroid space in 9 patienhts. In this type of tumor thedisplacement of air was not seen. CONCLUSION: The characteristic CT findings of tumor in the pyriform sinus werethickening of more than two walls of the pyriform sinus and the anterior or medial displacement of air. To assessthe site at which a tumor originates, spiral CT scanning is needed, together with functional study.
Breath Holding ; Humans ; Larynx* ; Pyriform Sinus* ; Respiration ; Tomography, Spiral Computed* ; Tomography, X-Ray Computed

PURPOSE: To evaluate the usefulness of spiral CT in predicting the depth of tumor invasion in patients with gastric cancer by comparing with histopathological finding. MATERIALS AND METHODS: We studied spiral CT scans of forty-eight patients, in whom gastric cancer was proven by gastrofibroscopic biopsy and surgery. After distending the stomach with 400ml tap water or effervescent granules, 100ml of contrast media was given intravenously at a rate of 3ml/sec. CT scanning was started at 45 sec after administration of the contrast material. Gastric tumors were subdivided into five types according to enhancing pattern from the inner layer of gastric wall to the outer layer. These pattern were correlated with histopathologic results. RESULT: The tumor masses were detected on CT scan in 10(77%) of 13 patients with early gastric cancer, while, the tumor masses were seen on CT scan in all patients with advanced gastric cancer. Of 9 patients with type 1 or type 2 enhancing pattern, early gastric cancer(T1) were proven in 7 patients(78%), serosal invasion (T3) in 2 patients(22%). In contrast, among 29 patients with type 4 and type 5, 22 patients(76%) were proven as serosal invasion(T3). Of 7 patients with type 3, 3 patients(43%) were proven as serosal invasion(T3), three(43%) as subserosal invasion(T2), one as early gastric cancer(T1). CONCLUSION: Analysis of morphological enhancing pattern on spiral CT is useful in predicting the depth of tumor invasion in patients with gastric cancer.
Biopsy ; Contrast Media ; Humans ; Stomach ; Stomach Neoplasms ; Tomography, Spiral Computed* ; Tomography, X-Ray Computed ; Water

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