Patient Positioning Assistive Technology Applicable to the Existing Computed Tomography System: Estimation by Pixel Value of Scout Image.

ABSTRACT: This study aimed to propose a patient positioning assistive technique using computed tomography (CT) scout images. A total of 210 patients who underwent CT scans in a single center, including on the upper abdomen, were divided into a study set of 127 patients for regression and 83 patients for verification. Linear regression analysis was performed to determine the R2 coefficient and the linear equation related to the mean pixel value of the scout image and ideal table height (TH ideal ). The average pixel values of the scout image were substituted into the regression equation to estimate the TH ideal . To verify the accuracy of this method, the distance between the estimated table height (TH est ) and TH ideal was measured. The medians of age (in years), gender (male/female), height (in centimeters), and body weight (in kilograms) for the regression and verification groups were 68 versus 70, 85/42 versus 55/28, 163.8 versus 163.0, and 59.9 versus 61.9, respectively. Linear regression analysis indicated a high coefficient of determination ( R2 = 0.91) between the mean pixel value of the scout image and TH ideal . The correlation coefficient between TH ideal and TH est was 0.95 (95% confidence interval, 0.92-0.97; P < 0.0001), systematic bias was 0.2 mm, and the limits of agreement were -5.4 to 5.9 ( P = 0.78). The offset of the table height with TH est was 2.8 ± 2.1 mm. The proposed estimation method using scout images could improve the automatic optimization of table height in CT, and it can be used as a general-purpose automatic positioning technique.

Patient dose increase caused by posteroanterior CT localizer radiographs.

INTRODUCTION: The aim of this study was to compare the output dose (volume CT dose index [ CTDIvol], and dose length product [DLP]) of automatic tube current modulation (ATCM) determined by localizer radiographs obtained in the anteroposterior (AP) and posteroanterior (PA) directions. METHODS: One hundred and twenty-four patients who underwent upper abdomen and/or chest-to-pelvis computed tomography (CT) were included. Patients underwent two series of CT examinations, and localizer radiographs were obtained in the AP and PA directions. The horizontal diameter of the localizer radiograph, scan length, CTDIvol, and DLP were measured. RESULTS: There was no significant difference in the scan length; however, all the other values were significantly higher in the PA direction. The mean horizontal diameter was 33.1 ± 2.6 cm and 35.4 ± 2.9 cm in the AP and PA directions of the localizer radiographs, respectively. The CTDIvol and DLP in the PA direction increased by approximately 7-8%. Bland-Altman plots between AP and PA localizer directions in upper abdominal CT showed a positive bias of 1.1 mGy and 30.0 mGy cm for CTDIvol and DLP, respectively. Correspondingly, chest-to-pelvic CT showed a positive bias of 0.93 mGy and 69.3 mGy cm for CTDIvol and DLP, respectively. CONCLUSION: The output dose of ATCM determined by localizer radiographs obtained in the PA direction was increased compared to the AP direction. Localizer radiographs obtained in the AP direction should be preferred for optimizing the output dose using ATCM. IMPLICATIONS FOR PRACTICE: Based on the evidence of this study, localizer radiographs obtained in the AP direction should be preferred for optimizing the output dose in CT examinations.

Inaccurate table height setting affects the organ-specific radiation dose in computed tomography.

PURPOSE: We aimed to prove that the locally absorbed doses in tissues and organs are affected by inaccurate table height in computed tomography. MATERIALS AND METHODS: We compared the volume CT dose index (CTDIvol) and the absorbed doses using an anthropomorphic phantom combined with a breast phantom. The phantom was set at the gantry center, from which the table height was changed every 20 mm between-40 mm and 40 mm. Data acquisition was performed using auto table height correction (AHC) for each table height. The CTDIvol was obtained from the CT console and the tube current value for each image slice (DICOM tag: 0018, 1151). The absorbed dose was measured by a glass dosimeter that was implanted at various positions in the phantom. RESULTS: The tube current values in the lung were lower at a table height of + 40 mm than those at other heights. The CTDIvol was slightly lower at + 40 mm than at the center (12.78 mGy vs. 13.42 mGy, p < 0.05). The CTDIvol values were almost the same at the other table heights (13.30-13.40 mGy). The absorbed doses at the lens and mammary gland were significantly different from those at the gantry center (-27.27%-17.77% and -24.31%-12.83%, respectively). Compared with the center, both the lens and mammary gland had higher absorbed doses at a table height of -40 mm. CONCLUSION: The absorbed dose was affected by the table height, but the CTDIvol was maintained by AHC. The operator should appropriately position patients even when using AHC.

Radiation dose and image quality of CT fluoroscopy with partial exposure mode.

PURPOSE: The present study aimed to evaluate the scan technique of computed tomography (CT)-guided puncture procedures using partial exposure mode (PEM) on the radiation dose of the operator's hand and image quality. METHODS: Radiation dose was evaluated using three types of scanning methods: one-shot scan (OS), OS with a bismuth shield added (OSBismuth), and a half-scan (i.e., PEM) capable of an adjustable exposure angle. Dose evaluation was performed using a torso phantom, while a circular phantom simulating the liver parenchyma and lesions was used for image quality evaluation. For each scanning method, four measurements were made to determine the radiation dose to the operator's hand and the dose distribution on the surface of the patient's torso; the output-dose profile was determined from five measurements. Image quality was evaluated in terms of contrast and contrast-to-noise ratio (CNR). Analysis of variance (ANOVA) or Friedman test were used for comparison between groups as appropriate. The post hoc tests were Tukey's honestly difference (HSD) test for parametric data or Wilcoxon signed rank test with Bonferroni correction for nonparametric data. RESULTS: The PEM yielded a radiation dose to the operator's hand that was 84% (0.35 vs. 2.33 mGy) lower than that of the OS. The dose to the patient's torso was reduced by 35% and 68% for the OSBismuth and PEM, respectively, relative to that of the OS. Compared with the CNR of the other two scanning methods (OS, 2.9±0.1; OSBismuth, 2.9±0.1), the PEM increased the standard deviation and decreased the CNR (2.1±0.04, Tukey's HSD, P < 0.001 for all). Images acquired with PEM showed visibility equivalent to that of other scanning methods when window conditions were adjusted. CONCLUSION: This study demonstrated that CT-guided puncture procedure using PEM effectively reduces the operator's exposure to radiation while minimizing image quality deterioration.

Radiation dose optimization for the bolus tracking technique in abdominal computed tomography: usefulness of real-time iterative reconstruction for monitoring scan.

The purpose of this study was to optimize the monitoring dose, obtained using the conventional filtered back projection (FBP) method and iterative reconstruction algorithms, for the bolus tracking technique. A phantom study was performed to assess the effect of the scan start time in patients grouped according to different body weights. An oval torso phantom was used for simulating the time enhancement curve of the bolus tracking technique. To reproduce image noise levels in the two body weight groups, the phantom diameter was adjusted with a water-equivalent material. The tube currents were 10, 20, 30, and 50 mA. The monitoring scan was performed with the conventional FBP method and real-time adaptive iterative dose reduction by three-dimensional processing (AIDR 3D). The results at different doses were compared with those at 50 mA. The volume computed tomography dose index was 1.31, 2.65, 3.93, and 6.56 mGy at tube currents of 10, 20, 30, and 50 mA, respectively. The scan start time, reconstructed using FBP, was significantly faster at 10 and 20 mA in group A (50-59 kg) and at 20 mA in group B (≥80 kg). The CT values in the region of interest could not be measured at 10 mA because of artifacts. With real-time AIDR 3D, both groups showed no significant differences between the measurements obtained at 30 or 20 mA and those obtained at 50 mA. Our study demonstrated that the real-time AIDR 3D algorithm improved the accuracy of the CT measurements with the bolus tracking technique.

Operator Dose Measurements and Image Quality Assessment in Computed Tomography Fluoroscopy Using Bismuth Sheet.

OBJECTIVE: The purpose of this study was to assess the dose reduction and the image quality using bismuth sheets during the computed tomography fluoroscopy (CTF). MATERIALS AND METHODS: The bismuth sheets of 1-mm thick were put on the upper mylar ring to reduce the frontal X-ray. The dose rates of an operator were measured using a torso phantom in the patient position during the CTF. The torso phantom was set on the gantry rotation center (center) and the lower position from the center (off-center). The image quality of the CTF image was assessed using an original phantom that mimics the normal liver parenchyma and the low attenuation lesions. The image contrast and contrast-to-noise ratio (CNR) were compared with and without the bismuth sheets. RESULTS: The bismuth sheets reduced the dose rate of the operator, regardless of whether the torso phantom was set at the center or the off-center. The reduction rate of exposure at the center and the off-center were 42.3% and 34.5%, respectively. There were no significant differences in the image contrast and the CNR, although the bismuth sheets increased the CT values of the liver parenchyma and the low attenuation lesions. CONCLUSION: The bismuth sheets were effective for the reduction of exposure to the operator without degrading the image quality of CTF images.