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 compare the images of arterial phase (AP) and portal venous phase (PVP) in the evaluation of conspicuousness of lesion and peripancreatic arterial and venous opacification in pancreatic diseases. MATERIALS AND METHODS: Dual-phase spiral CT was performed in 37 patients with pancreatic adenocarcinoma and 21 patients with pancreatitis. CT scans were performed with 5mm collimation at 1 : 1 pitch table feed. Images of AP and PVP were obtained at 30 and 65 seconds after administration of contrast material, was initiated. Using a gradingsystem, images were analalysed for conspicuousness of lesion and vascular opacification(grade 1=good, grade2=fair, grade 3=poor). RESULTS: In pancreatic adenocarcinoma, 35 and 36 of 37 cases showed low attenuation on APand PVP, respectively. With regard to conspicuousness of tumour, PVP(mean grade : 1.24) was superior AP(mean grade: 1.43), but not significantly(p=0.0745). In arterial opacification, AP(mean grade : 1.03) was significantly superior to PVP(mean grade : 1.30, ; p=0.0051). In venous opacification, PVP(mean grade : 1.19) was significautlyto AP(mean grade : 2.41 ; p<0.0001). In pancreatitis, 14 and 15 of 21 cases showed localized hypo-attenuating lesion indicating necrosis or fluid collection, on AP and PVP, respectively. With regard to conspicuousness oflesion, PVP(mean grade : 1.61) was superior to AP(mean grade : 1.81), but not significantly(p=0.1088). In arterial opacification, AP(mean grade : 1.05) was significantly superior to PVP(mean grade: 1.38 ; p=0.0180). In venous opacification, PVP(mean grade : 1.10) was significantly superior to AP(mean grade : 2.33 ; p=0.0005). CONCLUSION: For the diagnosis and staging of pancreatic disease, dual-phase spiral CT in arterial and portal venous phase maybe recommendable. The portal venous phase of spiral CT seems, however, to be superior to the arterial phase because the lesion is more conspicuous and there is venous opacification.
Adenocarcinoma ; Diagnosis ; Humans ; Necrosis ; Pancreas* ; Pancreatic Diseases ; Pancreatitis ; 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

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: 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 determine the factors that are related to local recurrence after Radiofrequency thermal ablation (RFTA) of hepatic tumors. MATERIALS AND METHODS: We selected 30 patients with 51 hepatic nodules less than 5 cm in diameter (HCC, n=33; metastasis, n=18) who underwent RF thermal ablation between May 1999 and April 2000. Ablation was defined as 'complete'if immediately post-procedual CT showed that a nodule's margin was completely covered by ablation. Every three months, follow-up CT scans were examined for signs of local recurrence, and a nodule was assessed in terms of its size, the histologic diagnosis, adjacent vessels, perfect ablation (a safety margin of more than 5mm beyond the tumor margin), and whether hyperemia was observed after ablation. Finally, a group in which there was local recurrence (group A, n=15) and another showing no recurrence (group B, n=36) were compared. RESULTS: Mean nodule size in group A and group B was 3.26 and 2.24 cm, respectively. Local recurrence was noted in 7 of 33 HCC nodules (21.2%), and in 8 of 18 (44.4%) which were metastatic. There was recurrence in 9 of 31 nodules with adjacent vessels (29.0%), and in 6 of 20 (30%) without adjacent vessels. In two of 17 perfectly ablated nodules (11.8%) there was local recurrence, but this was observed in 13 of 34 imperfectly ablated nodules (38.2%). Finally, local recurrence was seen in 14 of 36 nodules showing hyperemia (38.9%) but in one of 15 (6.7%) without hyperemia. Using chi-square analysis, it was thus shown that with regard to local recurrence, tumor size, perfect ablation and peritumoral hyperemia were statistically significant factors (p<0.05). CONCLUSION: Local recurrence after RF thermal ablation of hepatic tumors clearly increases in nodules which are larger. The degree to which ablation is perfect, and the presence of peritumoral hyperemia, may be factors related to the local recurrence observed after RFTA.
Diagnosis ; Follow-Up Studies ; Humans ; Hyperemia ; Neoplasm Metastasis ; Recurrence* ; Tomography, Spiral Computed* ; Tomography, X-Ray Computed

Helical CT has improved with faster gantry rotation, more powerful X-ray tubes, and improved interpolation algorithms; however, the greatest advance has been made by the recent introduction of multi detector-row computed tomography (MDCT) scanners. Fundamental advantages of MDCT include substantially shorter acquisition times, retrospective creation of thinner or thicker sections from the same raw data, and improved threedimensional (3-D) rendering with diminished helical artifacts. While these features will likely be important to many applications of CT scanning, the greatest impact has been on CT angiography. The advantages of MDCT over single detector-row CT scanners when imaging the vascular system can be broken down into three fundamental improvements, that is, speed (faster scan time), distance (longer coverage), and section thickness (better resolution). This article will focus on how the MDCT technology has substantially improved imaging of the vascular system, including pulmonary artery, aorta and extremity vessels.
Angiography ; Aorta ; Artifacts ; Extremities ; Pulmonary Artery ; Retrospective Studies ; Tomography, Spiral Computed ; Tomography, X-Ray Computed

PURPOSE: To measure, using spiral CT, the time interval between intraperitoneal injection of gastrografin and its renal excretion, and to demonstrate sequential change in the urinary bladder. MATERIALS AND METHODS: Five rats underwent serial CT scanning at one minute and every three minutes after the intraperitoneal injection of 0.5ml of 33 % gastrografin until opacification of the urinary bladder occurred. The procedure was repeated 15, 30, and 60mins later. We analyzed sequential change in the attenuation coefficient of the urinary bladder, as seen on CT scans and measured the time interval between gastrografin administration and opacification of the renal collecting system. RESULTS: All rats which received an intraperitoneal injection (n=5) showed opacification of the renal collecting system and urinary bladder 3 -9mins and 6.7 -1 2 .8mins, respectively, after gastrografin administration. The attenuation coefficient increased continuously until 1 hr after administration; its mean maximal level was 1 7 5 1 .6HU. CONCLUSION: The mean period required for opacification of the renal collecting system and of the urinary bladder, as seen on CT scans, was 6 mins and 9 mins, respectively, after intraperitoneal administration of gastro-grafin. The attenuation coefficient of the bladder increased continuously until 1 hr after injection.
Animals ; Diatrizoate Meglumine* ; Injections, Intraperitoneal ; Rats* ; Tomography, Spiral Computed ; Tomography, X-Ray Computed ; Urinary Bladder

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*