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 correlate the enhancement pattern of hepatocellular carcinoma during the arterial phase of spiral CT with vascularity on angiography. MATERIALS AND METHODS: Forty-Two patients with hepatocellular carcinoma underwent spiral CT and angioigraphy. spiral CT was performed with a section thickness of 10mm and a table speedof 10 or 13 mm/sec. 120mL of contrast medium was injected at 3 mL/sec. Spiral CT scans during the arterial phase were obtained 35 seconds after the injection of contrast medium. CT findings of 78 lesions less than 4cm indiameter were correlated with angiographic findings. RESULTS: The attenuation of lesions was high(n=69),iso(n=5), and low(n=4) compared with liver parenchyma during the arterial phase of spiral CT. in lesions with high-, iso-, and low-attenuation during the arterial phase of spiral CT, hypervascularity on angiograms was foundin 63 of 69(91.3%), three of five(60%), and three of four lesions(75%), respectively. Six lesions with high-attenuation on the arterial phase of spiral CT were not seen on angiography. Two iso-attenuated and onelow-attenuated lesion were hypovascular on angiograms. CONCLUSION: The results of this study suggest that with some exceptions there was good correlation between the arterial phase of spiral CT and angiography.
Angiography* ; Carcinoma, Hepatocellular* ; Humans ; Liver ; Tomography, Spiral Computed* ; Tomography, X-Ray Computed*

PURPOSE: To correlate the preoperative staging of gastric adenocarcinoma using two-phase spiral CT withpathologic staging. MATERIALS AND METHODS: One hundred and eighty patients with gastric cancers confirmed duringsurgery underwent two-phase spiral CT, and were evaluated retrospectively. CT scans were obtained in the proneposition after ingestion of water. Scans were performed 35 and 80 seconds after the start of infusion of 120mL ofnon-ionic contrast material with the speed of 3mL/sec. Five mm collimation, 7mm/sec table feed and 5mmreconstruction interval were used. T- and N-stage were determined using spiral CT images, without knowledge of thepathologic results. Pathologic staging was later compared with CT staging. RESULTS: Pathologic T-stage was T1 in70 cases(38.9%), T2 in 33 (18.3%), T3 in 73 (40.6%), and T4 in 4 (2.2%). Type-I or IIa elevated lesions accountedfor 10 of 70 T1 cases(14.3%) and flat or depressed lesions(type IIb, IIc, or III) for 60 (85.7%). PathologicN-stage was N0 in 85 cases(47.2%), N1 in 42 (23.3%), N2 in 31 (17.2%), and N3 in 22 (12.2%). The detection rate ofearly gastric cancer using two-phase spiral CT was 100.0%(10 of 10 cases) among elevated lesions and 78.3%(47 of60 cases) among flat or depressed lesions. With regard to T-stage, there was good correlation between CT image andpathology in 86 of 180 cases (47.8%). Overstaging occurred in 23.3%(42 of 180 cases) and understaging in 28.9%(52of 180 cases). With regard to N-stage, good correlation between CT image and pathology was noted in 94 of 180cases (52.2%). The rate of understaging(31.7%, 57 of 180 cases) was higher than that of overstaging(16.1%, 29 of180 cases)(p<0.001). CONCLUSION: The detection rate of early gastric cancer using two-phase spiral CT was 81.4%,and there was no significant difference in detectability between elevated and depressed lesions. Two-phase spiralCT for determing the T- and N-stage of gastric cancer was not effective ; it was accurate in abont 50% of casesunderstaging tended to occur.
Adenocarcinoma* ; Eating ; Humans ; Pathology ; Retrospective Studies ; Stomach Neoplasms ; Tomography, Spiral Computed* ; Tomography, X-Ray Computed ; Water

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

PURPOSE: To evaluate the effect of variable scanning protocols of computed tomography for evaluation of pre-implant site of the mandible through the comparison of the reformatted cross-sectional images of helical CT scans obtained with various imaging parameters versus those of conventional CT scans. MATERIALS AND METHODS: A dry mandible was imaged using conventional nonoverlapped CT scans with 1 mm slice thickness and helical CT scans with 1 mm slice thickness and pitches of 1.0, 1.5, 2.0, 2.5 and 3.0. All helical images were reconstructed at reconstruction interval of 1 mm. DentaScan reformatted images were obtained to allow standardized visualization of cross-sectional images of the mandible. The reformatted images were reviewed and measured separately by 4 dental radiologists. The image qualities of continuity of cortical outline, trabecular bone structure and visibility of the mandibular canal were evaluated and the distance between anatomic structures were measured by 4 dental radiologists. RESULTS: On image qualities of continuity of cortical outline, trabecular bone structure and visibility of the mandibular canal and in horizontal measurement, there was no statistically significant difference among conventional and helical scans with pitches of 1.0, 1.5 and 2.0. In vertical measurement, there was no statistically significant difference among the conventional and all imaging parameters of helical CT scans with pitches of 1.0, 1.5, 2.0, 2.5 and 3.0. CONCLUSION: The images of helical CT scans with 1 mm slice thickness and pitches of 1.0, 1.5 and 2.0 are as good as those of conventional CT scans with 1 mm slice thickness for evaluation of pre-dental implant site of the mandible. Considering the radiation dose and patient comfort, helical CT scans with 1 mm slice thickness and pitch of 2.0 is recommended for evaluation of pre-implant site of the mandible.
Dental Implants ; Humans ; Mandible ; Tomography, Spiral Computed ; Tomography, X-Ray Computed

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.

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.

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 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