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 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 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 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

Inflammatory pseudotumor is a rare benign lesion consisting of inflammatory cells and fibroblastic stroma, and is reported to have occurred. in various organs. Splenic involvement, however, is extremely rare. We report the spiral CT findings of pathologically proven inflammatory pseudotumor of the spleen. The CT scan shows delayed enhancement with central, stellate, low attenuation.
Fibroblasts ; Granuloma, Plasma Cell* ; Spleen* ; Tomography, Spiral Computed ; Tomography, X-Ray Computed

PURPOSE: To evaluate the efficacy of the arterial phase of dynamic spiral CT in the detection of pancreatic adenocarcinoma compared with the late phase. MATERIALS AND METHODS: Two phase spiral CT images of seventeen patients with pathologically proven pancreatic ductal adenocarcinomas were compared retrospectively. CT scans were performed with 5mm collimation at 1:1 pitch table speed. Images of arterial and late phases were obtained at 35 seconds and 180 seconds after initiation of administration of 100mL of contrast material(3mL/sec), respectively. Images of the arterial phase were compared with those of the late phase. RESULTS: Images of the arterial phase showed sufficient contrast between the tumor and adjacent pancreatic parenchyma in 12 cases, insufficient in four cases, and no significant contrast in one case. Images of the late phase showed sufficient contrast in five cases, insufficient in five cases, and no significant contrast in seven cases. Images of the arterial phase was superior to that of the late phase in 12 patients(70.6%). In six of the 12 patients, only the images of the arterial phase showed contrast between the tumor and the adjacent parenchyma. The images of late phase showed only one case of three metastasis detected on the images of the arterial phase. CONCLUSION: The arterial phase of spiral CT is superior to the late phase that is comparable with conventional CT in the detection of pancreatic adenocarcinoma.
Adenocarcinoma* ; Humans ; Neoplasm Metastasis ; Pancreatic Ducts ; Retrospective Studies ; 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*

PURPOSE: To examine the possible measurement errors of lung nodule volumetry at the various scan parameters by using a small nodule phantom. MATERIALS AND METHODS: We obtained images of a nodule phantom using a spiral CT scanner. The nodule phantom was made of paraffin and urethane and its real volume was known. For the CT scanning experiments, we used three different values for both the pitch of the table feed, i.e. 1:1, 1:15 and 1:2, and the tube current, i.e. 40 mA, 80 mA and 120 mA. All of the images acquired through CT scanning were reconstructed three dimensionally and measured with volumetry software. We tested the correlation between the true volume and the measured volume for each set of parameters using linear regression analysis. RESULTS:For the pitches of table feed of 1:1, 1:1.5 and 1:2, the mean relative errors were 23.3%, 22.8% and 22.6%, respectively. There were perfect correlations among the three sets of measurements (Pearson's coefficient = 1.000, p<0.001). For the tube currents of 40 mA, 80 mA and 120 mA, the mean relative errors were 22.6%, 22.6% and 22.9%, respectively. There were perfect correlations among them (Pearson's coefficient = 1.000, p<0.001). CONCLUSION: In the measurement of the volume of the lung nodule using spiral CT, the measurement error was not increased in spite of the tube current being decreased or the pitch of table feed being increased.
Linear Models ; Lung ; Paraffin ; Tomography, Spiral Computed* ; Tomography, X-Ray Computed ; Urethane

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