A retrospective cohort study evaluating the incidence of herpes zoster and postherpetic neuralgia after a live attenuated Oka-strain herpes zoster vaccine in a real-world setting in Japan.

BACKGROUND: In Japan, freeze-dried live attenuated Oka-strain varicella-zoster virus vaccine, VVL (BIKEN), is available for adults aged ≥50 years to prevent herpes zoster (HZ). Although an increase in the antibody titer and cellular immune response has been demonstrated following vaccination with VVL (BIKEN), to date, no clinical studies have shown that the vaccine decreases the incidence of HZ and postherpetic neuralgia (PHN). This study investigated the incidence of HZ and PHN among adults aged ≥50 years who received a single dose of VVL (BIKEN) to prevent HZ. METHODS: This retrospective cohort study investigated the incidence of HZ and PHN among adults aged ≥50 years who received a single dose of VVL (BIKEN) at a large hospital and affiliated clinics in Japan. A dispensing database and electronic medical records were used to identify vaccine recipients and cases of HZ and PHN. The end date of the follow-up period and the reason to end the follow-up were defined to avoid underestimating the incidence. The analysis was stratified according to age, sex, immunocompromising conditions, and use of immunosuppressant therapy. Vaccine effectiveness was estimated using published estimates of the incidence of HZ and PHN in the unvaccinated population in Japan. RESULTS: A total of 1175 patients were enrolled in the study. During a median follow-up period of 3.36 years, HZ was diagnosed in 27 participants (15 men [2.8%] and 12 women [1.9%]). The incidence of HZ among VVL (BIKEN) recipients was 7.67/1000 person-years. The incidence of PHN was 0.82/1000 person-years. The vaccine effectiveness was estimated as 27.8% [95% confidence interval (CI), -29.8 to 63.9%] and 73.8% [95% CI, 38.6-100%] against HZ and PHN, respectively. CONCLUSIONS: The VVL (BIKEN) had limited effectiveness at preventing HZ, but relatively good effectiveness at preventing PHN. VVL (BIKEN) might have a role as an affordable alternative.

[Subjective Contrast of Pulmonary Tissues in CsI-FPD Chest Radiography Using Model Phantom by Monte Carlo Simulation].

OBJECTIVE: Subject contrast of pulmonary tissues was investigated for five X-ray beams (70 kV without filter, 90 kV with 0.15 mm Cu filter, 90 kV with 0.2 mm Cu filter, 120 kV without filter, and 120 kV with 0.2 mm Cu filter) in CsI-FPD chest radiography using two types of model phantoms by Monte Carlo simulation. METHODS: A total of 72 million photons were entered to the model lung phantom (width, 300 mm; length, 300 mm; thickness, 200 mm; air space, 120 mm) and model mediastinum phantom (width, 300 mm; length, 300 mm; thickness, 200 mm; air space, 40 mm). Individual primary and secondary photon's process (absorption, scattering, and penetration) in the phantom and CsI-detector was recorded by Monte Carlo simulation. Subject contrast was calculated by entered and absorbed photon's number in the CsI-detector. RESULTS: Subject contrast pulmonary tissues were high to low energy X-ray beam; however, the ones of soft tissue and soft tissue overlaying bone had few differences for beam quality except 70 kV without filter. Moreover, the subject contrast by absorbed photons was higher compared to the one by entered photons in CsI. CONCLUSION: It was shown that the subject contrast study by Monte Carlo calculation can be replaced by the way of physical chest phantom, and that the subject contrast by absorbed photons and by injected photons in CsI was different. Furthermore, be verified that the subject contrast of soft tissue and soft tissue overlaying bone differs hardly.

[Study of X-ray Beam Quality and Contrast-to-Noise Ratio of Lung Nodules in Chest FPD Radiography: Monte Carlo Simulation Using Chest Model Phantom].

OBJECTIVES: Contrast-to-noise ratio (CNR) of four X-ray beams (90 kV with 0.15-mm Cu filter, 90 kV with 0.2-mm Cu filter, 120 kV without filter and 120 kV with 0.2-mm Cu filter) in CsI-flat panel detector (FPD) radiography for lung cancer diagnosis was investigated using Monte Carlo simulation. METHOD: Two billion photons were injected to the chest phantom model (width: 300 mm, length: 300 mm, thickness: 200 mm) with imitated lung nodules (10 mm diameter, CT value: +30 Hounsfield unit (HU), -375 HU, and -620 HU). Individual primary and secondary photon's process (absorption, scattering and penetration) in the phantom and CsI-detector was recorded by Monte Carlo simulation. CNR was calculated using primary and secondary absorbed photon's number in the CsI-detector. RESULTS: CNR of 90 kV X-ray beam with 0.15 mm and 0.2 mm Cu filters was higher to 120 kV X-ray beam because of higher primary object contrast and photon's contribution, and high photon's absorption to CsI. CONCLUSION: By Monte Carlo calculation, it was verified that 90 kV X-ray beam with 0.15 mm and 0.2 mm Cu filters yielded higher CNR to 120 kV X-ray beam.

Simultaneous treatment for M ycobacterium-avium complex lung disease and allergic bronchopulmonary aspergillosis: A case report.

Recently, there are several reports of simultaneous allergic bronchopulmonary aspergillosis (ABPA) and Mycobacterium-avium complex (MAC) lung disease. However, the strategies for early diagnosis and appropriate treatment for patients with both ABPA and MAC lung disease have not been established. Here, we report a case with ABPA complicated by MAC lung disease, which was successfully diagnosed and treated by simultaneous administration of systemic steroids and antimycobacterial drugs. Bronchoscopy can be useful in the diagnosis of such cases. Furthermore, in a patient with concurrent ABPA and MAC lung disease, simultaneous treatments for both diseases could reduce both diseases.

[Optimal Beam Quality in Chest Radiography Using CsI-flat Panel Detector for Detection of Pulmonary Nodules].

OBJECTIVES: Optimal beam quality for detection of pulmonary nodules in digital chest radiography using CsI-flat panel detector (FPD) was investigated in consideration of image quality and patient dose. METHODS: The human chest phantom with inserted imitated nodules (diameter: 10 mm, CT value: +30 Hounsfield unit (HU), -375 HU, -620 HU) was used for the measurement of contrast-to-noise ratio (CNR) of imitated nodules by twenty beams arranged by five tube voltages and four filters. RESULTS: The CNR varies with X-ray tube voltage and added filter. CNR correlates weakly to the tube voltage, fairly to the effective energy in second-order polynomial and strongly to the quality index (effective energy divided X-ray tube voltage). In order to improve the CNR, the effective energy and the quality index are kept about 50 keV and more than 0.5, respectively, using an 80-100 kV beam with a copper filter. CONCLUSION: A 90 kV (2.5 mm Al inherent filtration) beam with a 0.15 mm copper filter and a 90 kV or 100 kV (2.5 mm Al inherent filtration) beam with a 0.2 mm copper filter are appropriate for chest radiography using CsI-FPD.

[Evaluation of 90 kV Beam with 0.15 mm Cu Filter in Chest Radiography Using CsI-flat Panel Detector].

PURPOSE: To compare the visibility of anatomic structure in chest radiography acquired with different beam quality (120 kV beam and 90 kV beam with 0.15 mmCu) using CsI-flat panel detector. METHOD: Pair image obtained by different beam quality of 100 person's chest radiographies which were taken periodical health examination were compared with the visibility of normal structures (pulmonary vessels) and abnormal opacities by two pulmonologists and four radiological technologists. Moreover, the spectrum of the two beam quality were calculated using Monte Carlo simulation. RESULT: Dominant observers gave high score significantly (p<0.01) to the 90 kV beam's image in spite of 20% less dose. Monte Carlo simulation showed that 90 kV beam with 0.15 mmCu were much absorbed primary photon than 120 kV beam to CsI detector, and less absorbed secondary photon. CONCLUSION: The visibility of anatomic structure and abnormal opacities in FPD chest radiography was improved by using the 90 kV beam with 0.15 mmCu than traditional 120 kV beam's chest radiography.

Optimal beam quality for chest flat panel detector system: realistic phantom study.

OBJECTIVE: To investigate optimal beam quality for chest flat panel detector (FPD) system by semi-quantitatively assessment using a realistic lung phantom. MATERIALS AND METHODS: Chest FPD radiographs were obtained on a realistic lung phantom with simulated lung opacities using various X-ray tube voltage levels (90-140 kV) with/without copper filter. Entrance skin dose was set to maintain identical for all images (0.1 mGy). Three chest radiologists unaware of the exposure settings independently evaluated the image quality of each simulated opacity and normal structure using a 5-point scale (+ 2: clearly superior to the standard; + 1: slightly superior to the standard; 0: equal to the standard; - 1: slightly inferior to the standard; - 2: clearly inferior to the standard). The traditional FPD image obtained at a tube voltage of 120 kV was used as the standard. The scores of image quality were statistically compared using the Wilcoxon rank test with Bonferroni correction. RESULTS: FPD images using 90-kV shot with copper filter were superior to the traditional 120-kV shot without filter with respect to the visibility of vertebra, pulmonary vessels, and nodules overlapping diaphragm and heart (p < 0.05). There was no significant difference with respect to the visibility of all other simulated lung opacities (lung nodules except for overlying diaphragm/heart and honeycomb opacity) between each tube voltage level with/without copper filter and the traditional 120-kV shot without filter. CONCLUSION: Image quality of FPD images using 90 kV with copper filtration is superior to that using standard tube voltage when dose is identical. KEY POINTS: • FPD image quality using 90 kV with filter is superior to that using traditional beam. • Ninety-kilovolt shot with copper filter may be suitable for chest FPD image. • Clinical study dealing with chest FPD beam optimization would be warranted.

[Optimal beam quality for chest digital radiography].

To investigate the optimal beam quality for chest computed radiography (CR), we measured the radiographic contrast and evaluated the image quality of chest CR using various X-ray tube voltages. The contrast between lung and rib or heart increased on CR images obtained by lowering the tube voltage from 140 to 60 kV, but the degree of increase was less. Scattered radiation was reduced on CR images with a lower tube voltage. The Wiener spectrum of CR images with a low tube voltage showed a low value under identical conditions of amount of light stimulated emission. The quality of chest CR images obtained using a lower tube voltage (80 kV and 100 kV) was evaluated as being superior to those obtained with a higher tube voltage (120 kV and 140 kV). Considering the problem of tube loading and exposure in clinical applications, a tube voltage of 90 to 100 kV (0.1 mm copper filter backed by 0.5 mm aluminum) is recommended for chest CR.

Usefulness of computerized method for lung nodule detection on digital chest radiographs using similar subtraction images from different patients.

PURPOSE: The purpose of this study is to evaluate the usefulness of a novel computerized method to select automatically the similar chest radiograph for image subtraction in the patients who have no previous chest radiographs and to assist the radiologists' interpretation by presenting the "similar subtraction image" from different patients. MATERIALS AND METHODS: Institutional review board approval was obtained, and the requirement for informed patient consent was waived. A large database of approximately 15,000 normal chest radiographs was used for searching similar images of different patients. One hundred images of candidates were selected according to two clinical parameters and similarity of the lung field in the target image. We used the correlation value of chest region in the 100 images for searching the most similar image. The similar subtraction images were obtained by subtracting the similar image selected from the target image. Thirty cases with lung nodules and 30 cases without lung nodules were used for an observer performance test. Four attending radiologists and four radiology residents participated in this observer performance test. RESULTS: The AUC for all radiologists increased significantly from 0.925 to 0.974 with the CAD (P=.004). When the computer output images were available, the average AUC for the residents was more improved (0.960 vs. 0.890) than for the attending radiologists (0.987 vs. 0.960). CONCLUSION: The novel computerized method for lung nodule detection using similar subtraction images from different patients would be useful to detect lung nodules on digital chest radiographs, especially for less experienced readers.

Usefulness of computerized method for lung nodule detection in digital chest radiographs using temporal subtraction images.

RATIONALE AND OBJECTIVES: The aim of this study was to evaluate the usefulness of a novel computerized method for lung nodule detection on digital chest radiographs using temporal subtraction images. MATERIALS AND METHODS: To significantly reduce the number of false-positive results while maintaining high sensitivity, temporal subtraction images, which can enhance interval changes on sequential chest radiographs, were used. Fifty-one cases with lung nodules <3 cm and 51 cases without lung nodules were selected for an observer performance test. Twelve radiologists participated in this observer performance test. The radiologists' performance was evaluated using receiver-operating characteristic analysis, on a continuous rating scale. To estimate the numbers of cases affected beneficially and those affected detrimentally using this computerized method, the computer output was assumed to have an effect on an observer's diagnosis when there was a difference in rating score of ≥30% between the first and second ratings. RESULTS: The average area under the curve for all radiologists increased significantly from 0.849 to 0.950 with the computerized method (P < .001). The mean number of cases affected beneficially was significantly higher than that of cases affected detrimentally (8.92 vs 1.25, P < .001). CONCLUSIONS: The novel computerized method using temporal subtraction images would be useful in detecting lung nodules on digital chest radiographs.

Radiation dose evaluation in tomosynthesis and C-arm cone-beam CT examinations with an anthropomorphic phantom.

PURPOSE: The objective of this study was to evaluate organ dose and the effective dose to patients undergoing tomosynthesis (TS) and C-arm cone-beam computed tomography (CBCT) examinations and to compare the doses to those in multidetector CT (MDCT) scans. METHODS: Patient doses were measured with small sized silicon-photodiode dosimeters, 48 in number, which were implanted at various tissue and organ positions within an anthropomorphic phantom. Output signals from photodiode dosimeters were read out on a personal computer, from which organ and effective doses were computed. The doses in head, chest, abdomen, and hip-joint TS, and in head and abdomen C-arm CBCT were evaluated for routine protocols on Shimadzu TS and C-arm CBCT systems, and the doses in MDCT with the same scan regions as in TS and CBCT were on Toshiba 64-detector-row CT scanners. RESULTS: In TS examination of the head, chest, abdomen, and hip-joint, organ doses for organs within scan ranges were 1-4 mGy, and effective doses were 0.07 mSv for the head scan and around 1 mSv for other scans. In C-arm CBCT examinations of the head and abdomen, organ doses within scan range were 2-37 mGy, and effective doses were 1.2 mSv for the head scan and 4-5 mSv for abdominal scans. Effective doses in TS examinations were approximately a factor of 10 lower, while the doses in CBCT examinations were nearly the same level, compared to the doses in the corresponding MDCT examinations. CONCLUSIONS: TS examinations with low doses and excellent resolutions in coronal images compared to recent MDCT would widely be used in tomographic examinations of the chest, abdomen, pelvis, skeletal-joints, and knee instead of MDCT examinations with significantly high doses. Since patient dose in C-arm CBCT was nearly the same level as that in recent MDCT, the same consideration for high radiation dose would be required for the use of CBCT.

[Feasibility of a new initial check-up program for medical X-ray and computed radiography systems].

We investigated the feasibility of a simple, easy method that uses a digital radiography (DR) phantom for daily operational checks of the medical X-ray system and computed radiography (CR) system. First, we measured exposure indicator calibration (S value) from 12 seconds to 11 minutes after irradiation to examine the effect of fading of the photostimulable phosphor screen. We then examined the management width of the exposure indicator calibration ratio and limiting resolution of the CR system. Finally, we studied the exposure indicator calibration ratio, limiting the resolution and time necessary for the initial check-up by running the program 20 times for five weeks. Under the influence of the fading, the S value increased gradually, although the level of variation was small. From the mean and coefficient of variation of the exposure indicator calibration ratio, the management width was determined as +/-10%. The exposure indicator calibration ratio and limiting resolution were within +/-10% and +/-20%, respectively. It took three minutes to accomplish the initial check-up. The initial check-up using a DR phantom is simple and can perform the operational check of the medical X-ray system and the CR system with sufficient accuracy in only 3 minutes.

[Effect of diagnostic X-rays on implantable cardiac pacemakers and implantable cardioverter defibrillators, and its management].

The effects of diagnostic X-rays on implantable cardiac pacemakers and implantable cardioverter defibrillators (ICDs) were investigated. A total of 33 pacemakers from six manufacturers and nine ICDs from four manufacturers were irradiated using several X-ray units (plain X-ray diagnostic unit, under-table system fluoroscopy unit, over-table system fluoroscopy unit, biplane cardiac digital angiography unit, DSA unit and cone-beam CT unit). No systematic reset phenomena were observed in any pacemakers and ICDs under the X-ray irradiation. Nevertheless, over-sensing associated with the lack of a few pulses was observed in three of 33 pacemakers under radiation exposure. It has been proven that diagnostic X-rays might affect pacemaker function. Since the duration of the over-sensing under the radiation was very short and included transient episodes, this sensing failure, therefore, induced by radiation exposure would not affect the health of pacemaker recipients. ICDs were not affected by radiation exposure at a clinical dose. It is recommended that caution be exercised in direct irradiation to the pacemaker. Using a copper sheet of 2.0 mm thickness or more prevented over-sensing of pacemakers in the present study, especially when serial X-ray exposures were used with an over-table fluoroscopy system or cone-beam CT unit.

The usefulness of three-dimensional angiography with a flat panel detector of direct conversion type in a transcatheter arterial chemoembolization procedure for hepatocellular carcinoma: initial experience.

The purpose of this study was to assess the usefulness of a three-dimensional (3D) angiography system using a flat panel detector of direct conversion type in treatments with subsegmental transcatheter arterial chemoembolization (TACE) for hepatocellular carcinomas (HCCs). Thirty-six consecutive patients who underwent hepatic angiography were prospectively examined. First, two radiologists evaluated the degree of visualization of the peripheral branches of the hepatic arteries on 3D digital subtraction angiography (DSA). Then the radiologists evaluated the visualization of tumor staining and feeding arteries in 25 patients (30 HCCs) who underwent subsegmental TACE. The two radiologists who performed the TACE assessed whether the additional information provided by 3D DSA was useful for treatments. In 34 (94.4%) of 36 patients, the subsegmental branches of the hepatic arteries were sufficiently visualized. The feeding arteries of HCCs were sufficiently visualized in 28 (93%) of 30 HCCs, whereas tumor stains were sufficiently visualized in 18 (60%). Maximum intensity projection images were significantly superior to volume recording images for visualization of the tumor staining and feeding arteries of HCCs. In 27 (90%) of 30 HCCs, 3D DSA provided additional useful information for subsegmental TACE. The high-quality 3D DSA with flat panel detector angiography system provided a precise vascular road map, which was useful for performing subsegmental TACE of HCCs.

Usefulness of cone-beam volume CT with flat panel detectors in conjunction with catheter angiography for transcatheter arterial embolization.

PURPOSE: To assess the usefulness of cone-beam volume computed tomography (CT) (cone-beam CT) with use of flat panel detectors of the direct conversion type in conjunction with conventional digital subtraction angiography (DSA) in the diagnosis and treatment of patients with hepatocellular carcinoma (HCC). MATERIALS AND METHODS: Forty-nine consecutive patients (52 suspicious lesions) were prospectively examined. All patients underwent intraarterial rotational angiography with a flat panel detector system, and the cone-beam CT scans were reconstructed from the volume data set. The authors evaluated the diagnostic quality of cone-beam CT for the transcatheter arterial chemoembolization (TACE) procedure. RESULTS: The diagnostic quality of conventional DSA plus cone-beam CT with regard to tumor staining was superior to that of DSA alone. Cone-beam CT showed tumor staining in five lesions that were difficult to diagnose with confidence on the basis of the DSA findings alone. The extent of contrast medium perfusion was sufficiently visualized on all cone-beam CT scans at the tip of the catheter positioned in either the segmental or subsegmental hepatic arteries. In 42 of the 52 lesions (81%), cone-beam CT provided additional useful information for therapeutic decision making or TACE compared with DSA. CONCLUSIONS: Intraarterial cone-beam CT with a flat panel detector can provide clinically acceptable image quality in the assessment of HCC, thereby improving the detection of tumor staining due to HCC and the visualization of the extent of contrast medium perfusion.

Intracranial 2D and 3D DSA with flat panel detector of the direct conversion type: initial experience.

The purpose of this study was to compare the image quality of two-dimensional (2D) digital subtraction angiography (DSA) between a flat panel detector (FPD) of the direct conversion type with low radiation dose and a conventional image intensifier (I.I.)-TV system, and to assess 3D DSA with the FPD system in the depiction of intracranial vessels. Fifteen consecutive patients (five men, ten women; age range: 18-82 years; mean age: 55.5 years) were prospectively included in this study. All patients underwent 2D DSA with both the FPD and I.I.-TV system in one projection. The radiation doses during angiography were evaluated using a phantom. The 3D DSA images were created from the rotational DSA data with the FPD system. Two blinded radiologists independently evaluated 2D DSA with the FPD system and I.I.-TV system using a 5-point assessment scale (excellent to not visible) to assess the depiction of intracranial vessels. MIP and volume rendering (VR) images of 3D DSA with the FPD system were also evaluated using a 5-point scale (excellent to not visible). DSA and fluoroscopy dose measurements with the phantom showed a dose reduction of approximately 85% and 9% with the FPD system compared with the I.I.-TV system, respectively. For 2D DSA, the FPD system was significantly superior to the I.I.-TV system with respect to the visibility of the peripheral and perforating vessels (p<0.05). The peripheral and perforating vessels were also sufficiently visualized on MIP images of 3D DSA in all 15 cases. Our FPD system was found to be superior to the I.I.-TV system in visualizing small intracranial vessels combined with a significant reduction of radiation dose, and was able to create high-quality 3D DSA images on which high spatial resolution allowed precise visualization of small vessels such as perforating ones.

Investigation of misfiled cases in the PACS environment and a solution to prevent filing errors for chest radiographs.

RATIONALE AND OBJECTIVE: The aim of the study was to survey misfiled cases in a picture archiving and communication system environment at two hospitals and to demonstrate the potential usefulness of an automated patient recognition method for posteroanterior chest radiographs based on a template-matching technique designed to prevent filing errors. MATERIALS AND METHODS: We surveyed misfiled cases obtained from different modalities in one hospital for 25 months, and misfiled cases of chest radiographs in another hospital for 17 months. For investigating the usefulness of an automated patient recognition and identification method for chest radiographs, a prospective study has been completed in clinical settings at the latter hospital. RESULTS: The total numbers of misfiled cases for different modalities in one hospital and for chest radiographs in another hospital were 327 and 22, respectively. The misfiled cases in the two hospitals were mainly the result of human errors (eg, incorrect manual entries of patient information, incorrect usage of identification cards in which an identification card for the previous patient was used for the next patient's image acquisition). The prospective study indicated the usefulness of the computerized method for discovering misfiled cases with a high performance (ie, an 86.4% correct warning rate for different patients and 1.5% incorrect warning rate for the same patients). CONCLUSION: We confirmed the occurrence of misfiled cases in the two hospitals. The automated patient recognition and identification method for chest radiographs would be useful in preventing wrong images from being stored in the picture archiving and communication system environment.

Improved detection of lung cancer arising in diffuse lung diseases on chest radiographs using temporal subtraction.

RATIONALE AND OBJECTIVES: The purpose of this study was to evaluate the usefulness of temporal subtraction for the detection of lung cancer arising in pneumoconiosis, idiopathic pulmonary fibrosis, and pulmonary emphysema. MATERIALS AND METHODS: Fifteen cases of lung cancer arising in diffuse lung diseases, including three cases of pneumoconiosis, six of idiopathic pulmonary fibrosis, and six of pulmonary emphysema, were evaluated. Pathologic proof was obtained by surgery or transbronchial lung biopsy. The average interval between previous and current radiographs was 356 days (range, 31-947 days). All chest radiographs were obtained with a computed radiography system, and temporal subtraction images were produced by subtracting of a previous image from a current one with a nonlinear image-warping technique. The effect of the temporal subtraction image was evaluated by observer performance study with receiver operating characteristic analysis. RESULTS: The average observer performance with temporal subtraction was significantly improved (Az = 0.935) compared with that without temporal subtraction (Az = 0.857, P < .0001). CONCLUSION: The temporal subtraction technique is useful for the detection of lung cancer arising in pneumoconiosis, idiopathic pulmonary fibrosis, and pulmonary emphysema.

Improved detection of lung nodules on chest radiographs using a commercial computer-aided diagnosis system.

OBJECTIVE: The aim of this study was to evaluate the usefulness of a new commercially available computer-aided diagnosis (CAD) system with an automated method of detecting nodules due to lung cancers on chest radiograph. MATERIALS AND METHODS: For patients with cancer, 45 cases with solitary lung nodules up to 25 mm in diameter (nodule size range, 8-25 mm in diameter; mean, 18 mm; median, 20 mm) were used. For healthy patients, 45 cases were selected on the basis of confirmation on chest CT. All chest radiographs were obtained with a computed radiography system. The CAD output images were produced with a newly developed CAD system, which consisted of an image server including CAD software called EpiSight/XR. Eight radiologists (four board-certified radiologists and four radiology residents) participated in observer performance studies and interpreted both the original radiographs and CAD output images using a sequential testing method. The observers' performance was evaluated with receiver operating characteristic analysis. RESULTS: The average area under the curve value increased significantly from 0.924 without to 0.986 with CAD output images. Individually, the use of CAD output images was more beneficial to radiology residents than to board-certified radiologists. CONCLUSION: This CAD system for digital chest radiographs can assist radiologists and has the potential to improve the detection of lung nodules due to lung cancer.