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 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 determine the number of multiple alternating layers of liver abscess, and changes in this number, as revealed by spiral CT, and to ascertain which factors are related to changes occurring during the three phases of this modality. MATERIALS AND METHODS: Using three-phase spiral CT imaging we studied 26 cases of liver abscess (pyogenic:amebicm=23:3). The number of layers comprising the abscess, as seen on postcontrast CT scans, was determined during the arterial (30sec), portal (70sec), and delayed (220sec) phase, and all cases were assigned to one of two groups according to changes in the number of layers observed during the three phases. With regard to underlying disease, the two groups were compared in terms of the presence of abscess and of diabetes mellitus,CT interval (time from onset of symptoms to CT scanning), microbial agent (pyogenic vs. amebic), and the largest diameter of abscess as revealed by CT. RESULTS: Except in one case, three or four alternating layers [in 13(50%) and 7(27%) cases, respectively] were seen only during the arterial and portal phase. During each of the three phases-and especially the delayed phase, where it was present in 25 of cases (96%)-two alternating layers (2:2:2) was the most common pattern, with a 3:3:3 pattern occurring in one case. All 12 cases (46%) in the unchanging-layer group showed one of these two patterns. All changing-layer group cases (14;54%) demonstrated three or four layers during the arterial and portal phase but only two during the delayed phase. The CT interval was the only significantly different factor between the two groups. During the first week, the number of cases in the unchanging-layer group was much higher than in the changing-layer group (86%,14%), but during the second week this situation reversed (25%, 75%). CONCLUSION: Our study reveals that on three-phase dynamic CT images, a characteristic enhancement feature of liver abscesses is three or four layers during the arterial and portal phases, with reduction to two layers during the delayed phase. This change, as revealed by spiral CT, is rare during the week following the onset of symptoms, but common during the second week.
Abscess ; Liver Abscess ; Liver* ; 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 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

PURPOSE: To distinguish the spiral CT findings of Borrmann type IV adenocarcinoma from those of gastric lymphoma with diffuse gastric wall thickening. MATERIALS AND METHODS: We retrospectively reviewed the spiral CT scans of 30 patients with Borrmann type IV adenocarcinoma and nine with gastric lymphoma with diffuse gastric wall thickening. In all patients the respective condition was pathologically confirmed by gastrectomy. CT scanning was performed after peroral administration of 500-700ml of water. A total of 120-140ml bolus of nonionic contrast material was administered intravenously at a flow rate of 3ml/sec and two-phase images were obtained at 35-45 sec(early phase) and 180 sec(delayed phase) after the start of bolus injection. Spiral CT was performed with 10mm collimation, 10mm/sec table feed and 10mm reconstruction. We evaluated the degree and homogeneity of enhancement of thickened entire gastric wall, and the enhancement pattern of gastric inner layer, as seen on earlyphase CT scans. On early and delayed views, the thickness of gastric wall and the presence of perigastric fat infiltration were determined. The enhancement patterns of gastric inner layer were classified as either continuous or discontinuous thick enhancement, thin enhancement, or nonenhancement. RESULTS: The thickness of gastric wall was 1.2-3.5cm(mean 2.2cm) in cases of adenocarcinoma and 1.2-7.6c m (mean 4cm) in lymphoma. Perigastric fat infiltration was seen in 24 patients with adenocarcinoma(80 %) and four with lymphoma(44%). In those with adenocarcinoma, the degree of enhancement of entire gastric wall was hyperdense in fifteen patients(50%) and isointense in eleven (37 %). Seven patients with lymphoma(78 % ) showed hypodensity. In those with adenocarcinoma, continuous thick enhancement of gastric inner layer was seen in 18 patients(60 %) and discontinuous thick enhancement in nine(30%). In lymphoma cases, no thick enhancement was observed. Thin enhancement of gastric inner layer was demonstrated in three patients with adenocarcinoma( 10 %) and two with lymphoma(22 %). In seven patients with lymphoma(78 %), there was no enhancement. CONCLUSION: The following early-phase findings are highly suggestive of gastric lymphoma: a gastric wall thickness of more than 3 cm; no or minimal perigastric fat infiltration, hypodense enhancement of thickened entire gastric wall; and no or thin enhancement of gastric inner layer.
Adenocarcinoma* ; Gastrectomy ; Humans ; Lymphoma* ; Retrospective Studies ; Tomography, Spiral Computed* ; Tomography, X-Ray Computed ; Water

PURPOSE: To evaluate the diagnostic accuracy of computed tomography(CT) and magnetic resonance imaging(MRI)in the staging of rectosigmoid carcinoma according to the new AJCC classification. MATERIALS AND METHODS: BetweenAugust 1997 and October 1998, 36 patients with pathologically proven rectosigmoid carcinoma who underwent preoperative CT and MRI were evaluated. CT scans were performed with spiral CT in 27 cases and with conventional CT in nine. In all cases, MR images were obtained using a 1.5T unit and a body arrayed coil. T1- and T2-weightedimages were obtained in axial, sagittal, and coronal planes. On the basis of the results of CT scanning and MRI,tumor stage was determined by two radiologists using the AJCC cancer staging manual(1997). They reached aconsensus and compared their results with the pathologic stage. The T-stage was T1 in three cases, T2 in two, T3in 26, and T4 in five. The N-stage was N0 in 16 cases, N1 in seven, and N2 in 13. RESULTS: In the case of CT, thediagnostic accuracy of T-staging was 67%, and that of N-staging, 44%. For MRI, the corresponding figures were 83%and 67%. For T-staging, MRI was more accurate than CT(P=0.006), but for N-staging, the diagnostic accuracy of CT and MRI was statistically equivalent (P>0.05). CONCLUSION: MRI using a body arrayed coil is a useful preoperative diagnostic tool for the local staging of rectosigmoid carcinoma.
Classification* ; Humans ; Magnetic Resonance Imaging* ; Neoplasm Staging ; Tomography, Spiral Computed ; Tomography, X-Ray Computed

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

PURPOSE: To evaluate the efficacy of each phases in two and three phase spiral CT in the detection of pancreatic adenocarcinoma. MATERIALS AND METHODS: Two phase spiral CT images of 18 patients and three phasespiral CT images of 12 patients with pathologically-proven pancreatic ductal adenocarcinoma were retrospectively compared. Using a single spiral scan, images of early and delayed phases were obtained at 43 seconds and 2 ~ 3 minutes respectively initiating the after administration of 100-120 cc of contrast material (2 ~ 3 cc/sec),Images of arterial, portal and delayed phases were also obtained at 25 and 60 seconds, and 3 ~ 4 minutes,respectively, by the use of a double spiral scan. CT scans were performed with 10 mm collimation at 1 : 1 pitchtable speed. Contrast between the tumor and adjacent pancreatic parenchyma were compared and graded and enhancement pattern of the tumor were analysed together. RESULTS: In 12 patients (66.7%), images of the earlyphase were superior to those of the delayed phase. images of the portal phase were superior to those of thearterial phase. Enhancement of tumor was seen in four patients ; all tumors were less than 3cm in size. CONCLUSION: The early phase of two phase spiral CT is superior to the delayed phase and the portal phase of three phasespiral CT is superior to the arterial phase. Both arterial and portal phases are superior to the delayed phase.
Adenocarcinoma* ; Humans ; Pancreatic Ducts ; Tomography, Spiral Computed* ; Tomography, X-Ray Computed