Radiation Dose Reduction for Computed Tomography Localizer Radiography Using an Ag Additional Filter.

OBJECTIVE: This study aimed to assess the potential of an Ag additional filter attached to the bow tie filter of a computed tomography (CT) scanner to reduce the radiation dose in CT localizer radiography. METHODS: Radiation doses in CT localizer radiography with Cu and Ag additional filters were evaluated based on dose measurements and Monte Carlo simulations. Image quality evaluations of an adult torso phantom were performed, and the automatic exposure control performance was evaluated in terms of the water-equivalent thickness estimated from CT localizer radiographs. RESULTS: With the Ag additional filter, effective doses were approximately 72% to 75% lower than those with the Cu additional filter. The image quality and water-equivalent thickness with the Ag additional filter were similar to those with the Cu additional filter. CONCLUSIONS: The Ag additional filter helped significantly reduce radiation doses in CT localizer radiography while maintaining image quality and performance.

Usability of the lateral decubitus position on four-dimensional ultra-low-dose computed tomography for the detection of localized pleural adhesion in the pulmonary apical region.

BACKGROUND: Localized pleural adhesion (LPA) evaluation in the apical region is difficult even with four-dimensional ultra-low-dose computed tomography (4D-ULDCT) in the supine position due to smaller pleural movements. PURPOSE: To assess usability of 4D-ULDCT in the lateral decubitus (LD) position for LPA detection in the apical region. MATERIAL AND METHODS: Forty-seven patients underwent 4D-ULDCT of a single respiration cycle with 16-cm coverage of body axis in supine and LD positions with the affected lung uppermost. Intraoperative thoracoscopic findings confirmed LPA presence. A pleural point and a corresponding point on costal outer edge were placed in identical axial planes at end-inspiration. Pleuro-chest wall distance between two points (PCD) was calculated at each respiratory phase. In the affected lung, average change in amount of PCD (PCDACA) was compared between patients with and without LPA in total and two sub-groups (non-COPD and COPD, non-emphysematous and emphysematous patients) in supine and non-dependent (ND) LD positions. Receiver operating characteristic (ROC) curve analysis was performed to determine optimal thresholds in PCDACA for differentiating patients with LPA from those without. RESULTS: In COPD/emphysematous patients and total population, PCDACA with LPA was smaller than in those without in the supine and NDLD positions for overall, lateral, and dorsal regions. For the lateral region in COPD patients, area under ROC curve (AUC) increased from supine (0.64) to NDLD position (0.81). For the dorsal region in emphysematous patients, AUC increased from supine (0.76) to NDLD position (0.96). CONCLUSION: 4D-ULDCT in LD position may be useful for LPA detection in apical regions for COPD and/or emphysematous patients.

Preoperative assessment of localized pleural adhesion: Utility of software-assisted analysis on dynamic-ventilation computed tomography.

PURPOSE: To assess the usefulness of software analysis using dynamic-ventilation CT for localized pleural adhesion (LPA). MATERIALS AND METHODS: Fifty-one patients scheduled to undergo surgery underwent both dynamic-ventilation CT and static chest CT as preoperative assessments. Five observers independently evaluated the presence and severity of LPA on a three-point scale (non, mild, and severe LPA) for 9 pleural regions (upper, middle, and lower pleural aspects on ventral, lateral, and dorsal areas) on the chest CT by three different methods by observing images from: static high-resolution CT (static image); dynamic-ventilation CT (movie image), and dynamic-ventilation CT while referring to the adhesion map (movie image with color map), which was created using research software to visualize movement differences between the lung surface and chest wall. The presence and severity of LPA was confirmed by intraoperative thoracoscopic findings. Parameters of diagnostic accuracy for LPA presence and severity were assessed among the three methods using Wilcoxon signed rank test in total and for each of the three pleural aspects. RESULTS: Mild and severe LPA were confirmed in 14 and 8 patients. Movie image with color map had higher sensitivity (56.9 ±â€¯10.7 %) and negative predictive value (NPV) (91.4 ±â€¯1.7 %) in LPA detection than both movie image and static image. Additionally, for severe LPA, detection sensitivity was the highest with movie image with color map (82.5 ±â€¯6.1 %), followed by movie image (58.8 ±â€¯17.0 %) and static image (38.8 ±â€¯13.9 %). For LPA severity, movie image with color map was similar to movie image and superior to static image in accuracy as well as underestimation and overestimation, with a mean value of 80.2 %. CONCLUSION: Software-assisted dynamic-ventilation CT may be a useful novel imaging approach to improve the detection performance of LPA.

Ultra high-resolution computed tomography with 1024-matrix: Comparison with 512-matrix for the evaluation of pulmonary nodules.

PURPOSE: To determine whether a 1024-matrix provides superior image quality for the evaluation of pulmonary nodules. MATERIALS AND METHODS: Prospective evaluation conducted between December 2017 and April 2018, during which CT images showing lung nodules of more than 6 mm and less than 30 mmm were reconstructed with 2 different protocols: 0.5-mm thickness, 512 × 512 matrix, 34.5-cm field of view (FOV) (0.5-512 protocol); and 2-mm thickness, 1024 × 1024 matrix, 34.5-cm FOV (2-1024 protocol). Lung nodule characteristics such as margin, lobulation, pleural indentation, spiculation as well as peripheral vessels and bronchioles visibility and overall image quality were evaluated by three chest radiologists, using a 5-point scale. Image noise was evaluated by measuring the standard deviation in the region of interest for each image. RESULTS: A total of 89 nodules were evaluated. The 2-1024 protocol performed significantly better for the subjective evaluation of pulmonary nodules (p = 0.006 ∼ p < 0.0001). However, image noise was significantly higher both subjectively and objectively (p = 0.036, p < 0.0001). CONCLUSION: The use of a 2-1024 protocol does not increase the amount of images and allows better assessment of pulmonary nodules, despite noise increase.

Peripheral bronchial luminal conspicuity on dynamic-ventilation computed tomography: association with radiation doses and temporal resolution by using an ex vivo porcine lung phantom.

BACKGROUND: It is still unclear which image reconstruction algorithm is appropriate for peripheral bronchial luminal conspicuity (PBLC) on dynamic-ventilation computed tomography (DVCT). PURPOSE: To assess the influence of radiation doses and temporal resolution (TR) on the association between movement velocity (MV) and PBLC on DVCT. MATERIAL AND METHODS: An ex vivo porcine lung phantom with simulated respiratory movement was scanned by 320-row CT at 240 mA and 10 mA. Peak and dip CT density and luminal area adjusted by values at end-inspiration (CTDpeak and CTDdip, luminal area ratio [LAR]) for PBLC and MVs were measured and visual scores (VS) were obtained at 12 measurement points on 13 frame images obtained at half and full reconstructions (TR 340 and 190 ms) during expiration. Size-specific dose estimate (SSDE) was applied to presume radiation dose. VS, CTDpeak, CTDdip, LAR, and their cross-correlation coefficients with MV (CCC) were compared among four methods with combinations of two reconstruction algorithms and two doses. RESULTS: The dose at 10 mA was presumed as 26 mA by SSDE for standard proportion adults. VS, CTDdip, CTDpeak, and LAR with half reconstruction at 10 mA (2.52 ± 0.59, 1.016 ± 0.221, 0.948 ± 0.103, and 0.990 ± 0.527) were similar to those at 240 mA except for VS, and different from those with full reconstruction at both doses (2.24 ± 0.85, 0.830 ± 0.209, 0.986 ± 0.065, and 1.012 ± 0.438 at 240 mA) (P < 0.05). CCC for CTDdip with half reconstruction (-0.024 ± 0.552) at 10 mA was higher compared with full reconstruction (-0.503 ± 0.291) (P < 0.05). CONCLUSION: PBLC with half reconstruction at 10 mA was comparable to that at 240 mA and better than those with full reconstruction on DVCT.

Continuous quantitative measurement of the main bronchial dimensions and lung density in the lateral position by four-dimensional dynamic-ventilation CT in smokers and COPD patients.

PURPOSE: The purpose of this study was to measure changes in lung density and airway dimension in smokers in the lateral position using four-dimensional dynamic-ventilation computed tomography (CT) during free breathing and to evaluate their correlations with spirometric values. MATERIALS AND METHODS: Preoperative pleural adhesion assessments included dynamic-ventilation CT of 42 smokers (including 22 patients with COPD) in the lateral position, with the unoperated lung beneath (dependent lung). The scanned lungs' mean lung density (MLD) and the bilateral main bronchi's luminal areas (Ai) were measured automatically (13-18 continuous image frames, 0.35 seconds/frame). Calculations included cross-correlation coefficients (CCCs) between the MLD and Ai time curves, and correlations between the quantitative measurements and spirometric values were evaluated by using Spearman's rank coefficient. RESULTS: The ΔMLD1.05 (from the peak inspiration frame to the third expiratory frame, 1.05 seconds later) in the nondependent lung negatively correlated with FEV1/FVC (r=-0.417, P<0.01), suggesting that large expiratory movement of the nondependent lung would compensate limited expiratory movement of the dependent lung due to COPD. The ΔAi1.05 negatively correlated with the FEV1/FVC predicted in both the lungs (r=-0.465 and -0.311, P<0.05), suggesting that early expiratory collapses of the main bronchi indicate severe airflow limitation. The CCC correlated with FEV1/FVC in the dependent lung (r=-0.474, P<0.01), suggesting that reduced synchrony between the proximal airway and lung occurs in patients with severe airflow limitation. CONCLUSION: In COPD patients, in the lateral position, the following abnormal dynamic-ventilation CT findings are associated with airflow limitation: enhanced complementary ventilation in the nondependent lung, early expiratory airway collapses, and reduced synchrony between airway and lung movements in the dependent lung.

Association of Focal Radiation Dose Adjusted on Cross Sections with Subsolid Nodule Visibility and Quantification on Computed Tomography Images Using AIDR 3D: Comparison Among Scanning at 84, 42, and 7 mAs.

RATIONALE AND OBJECTIVES: The objectives of this study were to compare the visibility and quantification of subsolid nodules (SSNs) on computed tomography (CT) using adaptive iterative dose reduction using three-dimensional processing between 7 and 42 mAs and to assess the association of size-specific dose estimate (SSDE) with relative measured value change between 7 and 84 mAs (RMVC7-84) and relative measured value change between 42 and 84 mAs (RMVC42-84). MATERIALS AND METHODS: As a Japanese multicenter research project (Area-detector Computed Tomography for the Investigation of Thoracic Diseases [ACTIve] study), 50 subjects underwent chest CT with 120 kV, 0.35 second per location and three tube currents: 240 mA (84 mAs), 120 mA (42 mAs), and 20 mA (7 mAs). Axial CT images were reconstructed using adaptive iterative dose reduction using three-dimensional processing. SSN visibility was assessed with three grades (1, obscure, to 3, definitely visible) using CT at 84 mAs as reference standard and compared between 7 and 42 mAs using t test. Dimension, mean CT density, and particular SSDE to the nodular center of 71 SSNs and volume of 58 SSNs (diameter >5 mm) were measured. Measured values (MVs) were compared using Wilcoxon signed-rank tests among CTs at three doses. Pearson correlation analyses were performed to assess the association of SSDE with RMVC7-84: 100 × (MV at 7 mAs - MV at 84 mAs)/MV at 84 mAs and RMVC42-84. RESULTS: SSN visibilities were similar between 7 and 42 mAs (2.76 ± 0.45 vs 2.78 ± 0.40) (P = .67). For larger SSNs (>8 mm), MVs were similar among CTs at three doses (P > .05). For smaller SSNs (<8 mm), dimensions and volumes on CT at 7 mAs were larger and the mean CT density was smaller than 42 and 84 mAs, and SSDE had mild negative correlations with RMVC7-84 (P < .05). CONCLUSIONS: Comparable quantification was demonstrated irrespective of doses for larger SSNs. For smaller SSNs, nodular exaggerating effect associated with decreased SSDE on CT at 7 mAs compared to 84 mAs could result in comparable visibilities to CT at 42 mAs.

Subjective and objective comparisons of image quality between ultra-high-resolution CT and conventional area detector CT in phantoms and cadaveric human lungs.

OBJECTIVES: To compare the image quality of the lungs between ultra-high-resolution CT (U-HRCT) and conventional area detector CT (AD-CT) images. METHODS: Image data of slit phantoms (0.35, 0.30, and 0.15 mm) and 11 cadaveric human lungs were acquired by both U-HRCT and AD-CT devices. U-HRCT images were obtained with three acquisition modes: normal mode (U-HRCTN: 896 channels, 0.5 mm × 80 rows; 512 matrix), super-high-resolution mode (U-HRCTSHR: 1792 channels, 0.25 mm × 160 rows; 1024 matrix), and volume mode (U-HRCTSHR-VOL: non-helical acquisition with U-HRCTSHR). AD-CT images were obtained with the same conditions as U-HRCTN. Three independent observers scored normal anatomical structures (vessels and bronchi), abnormal CT findings (faint nodules, solid nodules, ground-glass opacity, consolidation, emphysema, interlobular septal thickening, intralobular reticular opacities, bronchovascular bundle thickening, bronchiectasis, and honeycombing), noise, artifacts, and overall image quality on a 3-point scale (1 = worst, 2 = equal, 3 = best) compared with U-HRCTN. Noise values were calculated quantitatively. RESULTS: U-HRCT could depict a 0.15-mm slit. Both U-HRCTSHR and U-HRCTSHR-VOL significantly improved visualization of normal anatomical structures and abnormal CT findings, except for intralobular reticular opacities and reduced artifacts, compared with AD-CT (p < 0.014). Visually, U-HRCTSHR-VOL has less noise than U-HRCTSHR and AD-CT (p < 0.00001). Quantitative noise values were significantly higher in the following order: U-HRCTSHR (mean, 30.41), U-HRCTSHR-VOL (26.84), AD-CT (16.03), and U-HRCTN (15.14) (p < 0.0001). U-HRCTSHR and U-HRCTSHR-VOL resulted in significantly higher overall image quality than AD-CT and were almost equal to U-HRCTN (p < 0.0001). CONCLUSIONS: Both U-HRCTSHR and U-HRCTSHR-VOL can provide higher image quality than AD-CT, while U-HRCTSHR-VOL was less noisy than U-HRCTSHR. KEY POINTS: • Ultra-high-resolution CT (U-HRCT) can improve spatial resolution. • U-HRCT can reduce streak and dark band artifacts. • U-HRCT can provide higher image quality than conventional area detector CT. • In U-HRCT, the volume mode is less noisy than the super-high-resolution mode. • U-HRCT may provide more detailed information about the lung anatomy and pathology.

[Development of Audio Indicator System for Respiratory Dynamic CT Imaging].

We created the device, which can conduct a radiological technologist's voice to a subject during CT scanning. For 149 lung cancer, dynamic respiratory CT were performed. 92 cases were performed using this device, the others were without this device. The respiratory cycle and respiratory amplitude were analyzed from the lung density. A stable respirating cycle was obtained by using the audio indicator system. The audio indicator system is useful for respiratory dynamic CT.

Preoperative assessment of pleural adhesion by Four-Dimensional Ultra-Low-Dose Computed Tomography (4D-ULDCT) with Adaptive Iterative Dose Reduction using Three-Dimensional processing (AIDR-3D).

PURPOSE: To assess the feasibility of Four-Dimensional Ultra-Low-Dose Computed Tomography (4D-ULDCT) for distinguishing pleural aspects with localized pleural adhesion (LPA) from those without. METHODS: Twenty-seven patients underwent 4D-ULDCT during a single respiration with a 16cm-coverage of the body axis. The presence and severity of LPA was confirmed by their intraoperative thoracoscopic findings. A point on the pleura and a corresponding point on the outer edge of the costal bone were placed in identical axial planes at end-inspiration. The distance of the two points (PCD), traced by automatic tracking functions respectively, was calculated at each respiratory phase. The maximal and average change amounts in PCD (PCDMCA and PCDACA) were compared among 110 measurement points (MPs) without LPA, 16MPs with mild LPA and 10MPs with severe LPA in upper lung field cranial to the bronchial bifurcation (ULF), and 150MPs without LPA, 17MPs with mild LPA and 9MPs with severe LPA in lower lung field caudal to the bronchial bifurcation (LLF) using the Mann-Whitney U test. RESULTS: In the LLF, PCDACA as well as PCDMCA demonstrated a significant difference among non-LPA, mild LPA and severe LPA (18.1±9.2, 12.3±6.2 and 5.0±3.3mm) (p<0.05). Also in the ULF, PCDACA showed a significant difference among three conditions (9.2±5.5, 5.7±2.8 and 2.2±0.4mm, respectively) (p<0.05), whereas PCDMCA for mild LPA was similar to that for non-LPA (12.3±5.9 and 17.5±11.0mm). CONCLUSIONS: Four D-ULDCT could be a useful non-invasive preoperative assessment modality for the detection of the presence or severity of LPA.

Study of Preoperative 3D-CT Angiography of Uterine Artery in Patients with Uterine Cervical Cancer.

Depiction of the fine vessel can provide useful preoperative information for patients with uterine cervical cancer. Although angiography can visualize vessels in detail, it is invasive. MR-angiography is a minimally invasive method to depict vessels, but the resolution of images is insufficient for preoperative evaluation. In this study, we used less invasive three-dimensional CT angiography (3D-CTA) and reconstructed images of adaptive iterative dose resolution 3D (AIDR 3D) with display field of view (D-FOV), which are suitable for arteries with large and small diameters, and created the fusion images. Created images allowed the observation of vessel branch in wide area compared with angiography, and it was less invasive. We evaluated the utility of 3D-CTA for visualizing fine vessels branching from uterine artery as preoperative evaluation for radial hysterectomy. 3D-CTA was obtained in nine patients. Conventional reconstruction and magnification reconstruction (D-FOV: 320‒360 mm, 150 mm) was made using arterial phase. Normal volume rendering image (N-VR) was made from conventional reconstruction image, and hybrid volume rendering image (H-VR) was made from conventional and magnification reconstruction image. Visual evaluation of each VR image was performed by 5 trained radiologists. A Wilcoxon rank sum test was performed for each result. No statistical significance was found in the visualization of vessels with large diameter (p=0.81), but statistical significance was detected in the visualization of the uterine artery and its ascending/descending branches (p<0.05). H-VR could visualize fine vessels clearer than N-VR, and H-VR could depict a vascular map including fine vessels in a large field. Therefore, H-VR could provide useful information for surgical operation. Additional depiction of vein and ureter could clearly visualize the anatomical relationship of each structure, and new clinical finding of anatomical relationship between uterine artery and ureter was suggested. This new clinical finding was useful in radical hysterectomy in which crossing site of the uterine artery and ureter is dissected. This method is simple to create and useful for various clinical surgery.

Ultra-High-Resolution Computed Tomography of the Lung: Image Quality of a Prototype Scanner.

PURPOSE: The image noise and image quality of a prototype ultra-high-resolution computed tomography (U-HRCT) scanner was evaluated and compared with those of conventional high-resolution CT (C-HRCT) scanners. MATERIALS AND METHODS: This study was approved by the institutional review board. A U-HRCT scanner prototype with 0.25 mm x 4 rows and operating at 120 mAs was used. The C-HRCT images were obtained using a 0.5 mm x 16 or 0.5 mm x 64 detector-row CT scanner operating at 150 mAs. Images from both scanners were reconstructed at 0.1-mm intervals; the slice thickness was 0.25 mm for the U-HRCT scanner and 0.5 mm for the C-HRCT scanners. For both scanners, the display field of view was 80 mm. The image noise of each scanner was evaluated using a phantom. U-HRCT and C-HRCT images of 53 images selected from 37 lung nodules were then observed and graded using a 5-point score by 10 board-certified thoracic radiologists. The images were presented to the observers randomly and in a blinded manner. RESULTS: The image noise for U-HRCT (100.87 ± 0.51 Hounsfield units [HU]) was greater than that for C-HRCT (40.41 ± 0.52 HU; P < .0001). The image quality of U-HRCT was graded as superior to that of C-HRCT (P < .0001) for all of the following parameters that were examined: margins of subsolid and solid nodules, edges of solid components and pulmonary vessels in subsolid nodules, air bronchograms, pleural indentations, margins of pulmonary vessels, edges of bronchi, and interlobar fissures. CONCLUSION: Despite a larger image noise, the prototype U-HRCT scanner had a significantly better image quality than the C-HRCT scanners.

Usefulness of a glass-free medical three-dimensional autostereoscopic display in neurosurgery.

PURPOSE: Many stereoscopic displays require glasses that are awkward or inappropriate for use in a neurosurgical operating room. A glass-free three-dimensional autostereoscopic display (3DAD) monitor was developed and tested for neurosurgical applications. METHODS: Our 3DAD system uses images acquired from nine directions projected into the viewer's eyes through 1,280 lenticular lenses (1,280 x 720 pixels). The viewer interprets these as a single stereoscopic image. To evaluate the 3D visualization capabilities of the 3DAD system, 3D images of blood vessels created from brain magnetic resonance angiography were presented to 20 neurosurgeons on both a standard medical two-dimensional (2D) monitor and our 3DAD monitor. Discrimination of the positional relationships for each vessel was recorded. The observers were asked to identify blood vessels located in front of three pairs of points on each image. RESULTS: The neurosurgeon observers achieved significantly higher correct responses using the 3DAD monitor compared with the 2D monitor (91.7 vs. 56.7 %, p< 0.0001). There were no reports of problems such as eye fatigue or discomfort. CONCLUSION: Displaying 3D volume rendered multimodality images with a 3DAD monitor is useful for anatomical discrimination of 3D vessels in MR angiography. This technology may be useful for a wide variety of clinical applications such as rapid and precise diagnosis, surgical simulation, and medical education.

Whole-breast volume perfusion images using 256-row multislice computed tomography: visualization of lesions with ductal spread.

BACKGROUND: The aim of this study was to apply perfusion techniques to breast tumors using a prototype 256-row multislice computed tomography (CT) scanner (which allows a wide range of 128 mm to be scanned and can provide whole-breast perfusion maps without any dead angles) to improve contrast and assess the possibility of precisely depicting the extent of breast cancer. PATIENTS AND METHODS: The study group included seven patients with breast cancer who were scheduled to undergo radical surgery and radiotherapy. Dynamic scanning was performed using a 256-row multislice CT scanner during normal respiration. Volume perfusion images of the entire breast were obtained using the maximum slope method. Perfusion map images and early-phase breast CT images at 54 s were compared by means of pathological examination. RESULTS: All breast cancers could be distinguished from normal mammary glands based on the perfusion value. The extent of cancer depicted in perfusion images showed excellent agreement with the pathology findings for invasive ductal carcinoma and ductal carcinoma in situ. In three patients, all ductal spread, parts of which were not visualized by early-phase CT, were depicted in volume perfusion images. Simulation analysis suggested that perfusion maps could be generated with fewer scanning points. CONCLUSION: The results of the present study suggest that volume perfusion imaging may be useful for depicting the extent of breast cancer, with excellent sensitivity. Further research is needed to determine the clinical relevance of these findings.

Three-dimensional perfusion imaging of hepatocellular carcinoma using 256-slice multidetector-row computed tomography.

PURPOSE: The aim of this study was to evaluate the clinical capability of three-dimensional (3D) perfusion imaging of hepatocellular carcinoma (HCC) by performing dynamic scanning using a 256-slice multidetector-row CT (MDCT) scanner. MATERIALS AND METHODS: Two patients with HCC were examined in this study. They were scheduled to undergo transcatheter arterial infusion therapy using an arterial infusion reservoir system. The CT system used was a newly developed prototype scanner of 256-slice MDCT. Dynamic CT scanning was performed with intraarterial injection via the reservoir route, and perfusion analysis was done based on the 3D data. RESULTS: The blood flow volume per unit volume in the tumors was significantly increased compared with that in normal hepatic parenchyma. Using a 3D workstation, 3D perfusion images could be displayed by fusing CT images with perfusion images about blood flow volume. CONCLUSION: Three-dimensional perfusion images, which enable 3D evaluation of perfusion in HCCs, can be generated using 256-slice MDCT.

Fluctuation in measurements of pulmonary nodule under tidal volume ventilation on four-dimensional computed tomography: preliminary results.

The present study aimed to assess the feasibility of four-dimensional (4D) chest computed tomography (CT) under tidal volume ventilation and the impact of respiratory motion on quantitative analysis of CT measurements. Forty-four pulmonary nodules in patients with metastatic disease were evaluated. CT examinations were performed using a 256 multidetector-row CT (MDCT) unit. Volume data were obtained from the lower lung fields (128 mm) above the diaphragm during dynamic CT acquisition. The CT parameters used were 120 kV, 100 or 150 mA, 0.5 s(-1), and 0.5 mm collimation. Image data were reconstructed every 0.1 s during one respiratory cycle by a 180 degrees reconstruction algorithm for four independent fractions of the respiratory cycle. Pulmonary nodules were measured along their longest and shortest axes using electronic calipers. Automated volumetry was assessed using commercially available software. The diameters of long and short axes in each frame were 9.0-9.6 mm and 7.1-7.5 mm, respectively. There was fluctuation of the long axis diameters in the third fraction. The mean volume in each fraction ranged from 365 to 394 mm(3). Statistically significant fluctuation was also found in the third fraction. 4D-CT under tidal volume ventilation is feasible to determine diameter or volume of the pulmonary nodule.

Low-dose CT screening for lung cancer with automatic exposure control: phantom study.

We conducted a study to determine optimal scan conditions for automatic exposure control (AEC) in computed tomography (CT) of low-dose chest screening in order to provide consistent image quality without increasing the collective dose. Using a chest CT phantom, we set CT-AEC scan conditions with a dose-reduction wedge (DR-Wedge) to the same radiation dose as those for low-tube current, fixed-scan conditions. Image quality was evaluated with the use of the standard deviation of the CT number, contrast-noise ratios (CNR), and receiver-operating characteristic (ROC) analysis. At the same radiation dose, in the scan conditions using CT-AEC with the DR-Wedge, the SD of the CT number of each slice position was stable. The CNR values were higher at the lung apex and lung base under CT-AEC with the DR-Wedge than under standard scan conditions (p < 0.0002). In addition, ROC analysis of blind evaluation by four radiologists and three technologists showed that the image quality was improved for the lung apex (p < 0.009), tracheal bifurcation (p < 0.038), and lung base (p < 0.022) in the scan conditions using CT-AEC with the DR-Wedge. We achieved improvement of image quality without increasing the collective dose by using CT-AEC with the DR-Wedge under low-dose scan conditions.