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 aim of our study was to evaluate the usefulness of high-resolution CT scans in addition tohelical CT for characterizing a solitary pulmonary nodule. MATERIALS AND METHODS: Our study included 49 patientswith a solitary pulmonary nodule ; in each patient this was evaluated by both additional high-resolution CT andhelical scanning. Images were evaluated by three independent observers, each of whom read them twice : initiallywith helical CT images only and then with helical images plus high-resolution CT images. After analysis, theobservers recorded the following : histologic diagnosis, benignancy or malignancy of a nodule, and confidence intheir diagnosis (three scales). RESULTS: In differentiating benign and malignant nodules, the accuracy of helicalscans only was 75% (110/147 readings) whereas that of helical plus high-resolution CT scans was 82% (121/147readings) (p=0.001). Correct histologic diagnosis was made in 47% of cases (69/147 readings) when helical scansonly had been evaluated and in 48% of cases (71/147 readings) for which both helical and high-resolotion CT scanswere available (p=0.815). Diagnosis was more often highly confident on the basis of additional high-resolution CTscans (25%) than helical scans only (5%) (p=0.001) . CONCLUSION: By enhancing differential diagnosticaccuracy between benign and malignant nodules and by increasing confidence in the histologic diagnosis of apulmonary nodule, additional high-resolution CT scans are valuable for the evaluation of a solitary pulmonarynodule.
Diagnosis ; Humans ; Solitary Pulmonary Nodule* ; Tomography, Spiral Computed ; Tomography, X-Ray Computed

OBJECTIVETo develop the method and investigate the value of the application of multislice helical computed tomography (CT) in the maxillofacial distraction osteogenesis.

METHODSTwelve cases of maxillofacial distraction osteogenesis (3 in zygoma, 2 in maxilla, and 7 in mandible) were scanned by the multislice helical CT, then the reconstruction of three dimensional and fault image and the relative measurement were carried out to study the effect of distraction and osteogenesis.

RESULTSThe three dimensional image provided clear and high resolution stereoscopic view that the effect of distraction osteogenesis could be evaluated easily and exactly. The fault image could be set up in private computer by Mimics and the measurements, such as distance, thickness and density, could be performed as expected. The effect of 12 cases was satisfied, and the average distracted distance was 16.73 mm.

CONCLUSIONBasing on multislice helical CT scanning, the high resolution image reconstruction and relative measurement data could be obtained which could meet the need of clear and direct observation. Its application in the maxillofacial distraction osteogenesis is expecting and promising.

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.

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 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