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

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 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 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 evaluate contrast enhancement patterns of hepatomas (HCCs) on arterial dominant, portal dominant,and delayed phase of CT scan by using double spiral CT. MATERIALS AND METHODS: Using double-spiral CT, three-phase dynamic liver scan was performed on 27 patients with 45 nodular HCC lesions. Non-ionic contrast medium(100-120ml) was injected intravenously with an automatic injector at the rate of 2-4 ml/sec. CT scans were obtained at 25-30sec (arterial dominant phase), 60 sec (portal dominant phase), and 5min (delayed phase) afteradministration of the contrast medium. The tumor were divided into two groups according to the diameter(<3cm and > or = 3cm). In each group, contrast enhancement patterns of HCCs were classified as follows : high, central high, peripheral high, iso, low, or mixed attenuation. The incidence and contrast enhancement patterns of thin peripheral rims(psevdocapsules) were also analyzed. RESULTS: There were 23 lesions with a diameter less than 3cm,while 22 lesions were 3cm or larger. On the arterial dominant phase, tumors smaller than 3cm showed high(74%), iso(17%), mixed(4%), and peripheral high(4%) attenuation, while the attenuation of tumors larger than 3cm washigh(73%), mixed(9%), iso(9%), and low(9%). On the portal dominant phase, tumors smaller than 3cm were mostcommonly iso(43%) or high(35%), while tumors larger than 3cm were low(65%) or iso(18%). On the delayed phase, tumors were most commonly low in attenuation regardless of size. A thin peripheral rim was observed in 22% of tumors smaller than 3cm and in 64% of tumors larger than 3cm. The rim showed iso(53%) or low(42%) attenuation onthe arterial dominant phase, high(47%) or iso(47%) attenuation on the portal dominant phase, and high(100%) attenuation on the delayed phase. CONCLUSIONS: For the detection and diagnois of HCCS, an understanding of their contrast enhancement patterns is useful.
Carcinoma, Hepatocellular* ; Humans ; Incidence ; Liver ; Tomography, Spiral Computed* ; Tomography, X-Ray Computed

PURPOSE: To evaluate the mean width of anterior commissure of true vocal cord in Korean adults by measuringits dimension on spiral CT scans. MATERIALS AND METHODS: We reviewed the CT scans of 53 Korean adults(age range,23-73years; mean age 39.2years; M:F=41:12) without laryngeal disorders. Spiral CT scanning was performed aroundthe anterior commissure with 1mm slice thickness and table incrementation for 15 seconds. The anteroposteriorwidth of the anterior commissure was measured on CT scan where the true vocal cord and arytenoid, cricoid andthyroid cartilages were all present. We determined the mean width of the anterior commissure and whether there wasa relationship between age and the width of the anterior commissure. RESULTS: The width of the anteriorcommissure was between 0.9mm and 2.3mm ; mean width was 1.60+/-0.38mm(mean+/-SD). Using two SDs above the mean wouldhave defined 2.36mm as the upper limit of normal width. Statistically, no significant correlation existed betweenthe age and the width of the anterior commissure(p>0.05). CONCLUSION: An awareuess of the normal width range ofthe anterior commissure in Korean adults evaluated by spiral CT enhances the possibility of early detection ofinvasion of the anterior commissure by glottic cancer.
Adult* ; Cartilage ; Humans ; Tomography, Spiral Computed* ; Tomography, X-Ray Computed ; Vocal Cords*