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 purpose.of this study was to characterize the enhancing patterns of hepatocellular carcinoma (HCC) on two-phase dynamic incremental liver scan with spiral CT. MATERIALS AND METHODS: Two-phase dynamic incremental liver scan using spiral CT was performed on 230 lesions in 107 patients with HCC. CT scanning was performed with a table speed of 13mm/sec and a section thickness of 10 mm;120 mL of contrast medium was injected intravenously with a automatic injector at the rate of 3mL/sec. CT scans were started 35 sec(early phase) and 3 min(delayed phase) after beginning injection of contrast medium. The tumors were divided into 2 groups according to size(< or = 3cm and > 3cm), the contrast enhancement patterns of HCCs and capsules in the early and delayed phases were analyzed in each group. RESULTS: Most of HCCs appeared as high-attenuating lesions in the early phase(75% in tumors smaller than 3cm and 61% in tumors larger than 3cm), and as low-attenuating lesions in the delayed phase(68% in tumors smaller than 3cm and 90% in tumors larger than 3cm). Forty-eight percent of HCCs smaller than 3cm and 58% of HCCs larger than 3cm were high-attenuating in the early phase and low-attenuating in the delayed phase. Thirty-two percent of capsules were low- or iso-attenuating in the early phase and high-attenuating in the delayed phase. Capsules were demonstrated in 22% in HCCs smaller than 3cm and 67% in HCCs larger than 3 cm(p <. 01). CONCLUSION: Two-phase dynamic scan with spiral CT is useful in the diagnosis of HCC because of a precise display of hemodynamic characteristics of HCCs.
Capsules ; Carcinoma, Hepatocellular* ; Diagnosis ; Hemodynamics ; Humans ; Liver ; 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

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.

PURPOSE: To compare the contrast enhancement patterns of hepatocellular carcinomas(HCCs), hemangiomas, and metastases on three-phase images with spiral CT for differential diagnosis. MATERIALS AND METHODS: Three-phasespiral CT scan was performed in 73 patients with hepatic masses. CT scanning was performed with a table speed of 10mm/sec, section thickness of 10mm, and a reconstruction interval of 5mm, 100-150ml of contrast medium was injected intravenously with an automatic injector at a rate of 2-3mL/sec. CT scans were obtained at 30, 70 and 180 seconds after the start of contrast material injection. RESULTS: The enhancement patterns of 136 lesions in 53 patients with HCCs were as follows : 47 lesions(35%) were totally high and 55(40%) were mixed in the early phase ;30 lesions(22%) were mixed and 66(49%) were totally low in the portal phase ; and 105 lesions(78%) were totally low in the delayed phase. In hemangiomas of 23 lesions in 15 patients, 7 lesions(30%) were peripherally high and11(48%) were totally low in the arterial phase ; 4 lesions(17%) were totally high and 12(53%) were peripherally high in the portal phase ; 10 lesions(42%) were totally high and 4(18%) were peripherally high in the deayed phase. In metastatic liver mali gnancies of 42 lesions in 5 patients, 13 lesions(31%) were peripherally high and 22(52%) were totally low in the arterial phase ; 32 lesions(77%) were totally low in the portal phase, and 35(83%)were totally low in the delayed phase. CONCLUSION: Three-phase spiral CT scanning is a useful diagnostic methodin the differential diagnosis of hepatic masses including HCCs, hemangiomas, and hepatic metastases.
Diagnosis, Differential ; Hemangioma ; Humans ; Liver ; Mali ; Neoplasm Metastasis ; Tomography, Spiral Computed* ; Tomography, X-Ray Computed

Conventional angiography has been used to identify detailed vascular anatomy for surgery in which parenchymal salvage should be necessary. Recently, we experienced a case in which 3-dimensional CT was very helpful in salvaging the part of the kidney. A 2 year-old girl was diagnosed as bilateral Wilms` tumor. Conventional CT scan showed right huge mass and left upper pole mass of the kidney. The patient was planned to have neoadjuvant chemotherapy. Spiral CT scan with three-dimensional reconstruction was performed after 3-month chemotherapy and detailed anatomical information regarding vessels, tumor mass and normal parenchyma was obtained. Based on these anatomical information, right radical nephrectomy and left partial nephrectomy was successfully performed. Surgical findings was quite similar to that obtained by preoperative 3-dimensional CT images. Three-dimensional reconstruction of spiral CT imaging is considered to be useful in the evaluation of surgical anatomy in kidney-saving surgery preoperatively.
Angiography ; Child, Preschool ; Drug Therapy ; Female ; Humans ; Kidney ; Nephrectomy ; 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

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