Recently about 90% of radiographs have been taken by the digital radiographic system in Japan, but the exposure dose of the patients are about ten-times different among the systems. We understood it by a surveytaken in 2007. We studied the visual evaluation with varying exposure doses using the image phantom of the lumber AP, lumber lateral and hip AP. Additionally we measured quantum efficiency (DQE) of the digital systems. We also studied the exposure index (EI) of IEC standard to see whether it is able to be the sensitivity index among the digital systems. DQE in 1.0 cycle/mm of CR, FPD (GOS), FPD (CsI, a-Se) became 0.2–0.25, 0.3, 0.5, respectively. Our results display that the dose reduction is relative to DQE. The visual evaluation results also show that dose reduction is possible among the systems. From these results, we are able to reduce the exposure dose of the patients at the clinical site. We also suggest that we manage the exposure dose using the E.I of the IEC standard.
The purpose of this study is to estimate radiation dose and image quality of ECG-gated coronary 320-area detector CT (ADCT) angiography which was acquired using the protocols that were considered as optimal methods for different heart rates (HR) in 1031 consecutive patients (M/F=580/451, 65±12 yr) without arrhythmias. We set up 5 protocols for 320-ADCT based on the relationship among heart rates, temporal resolution, gantry rotation speed, optimal reconstruction phase and slow filling phase on 64-multidetector-row computed tomography (MDCT), ie, 1) mid-diastolic (75% of RR) 1 beat scan (MD 1 beat, N=761(73.8%)) for HR≤60, 2) mid-diastolic (75% of RR) 2 beat scan (MD 2 beat, N=135) for 61≤HR≤65, 3) end-systolic and mid-diastolic (37–80% of RR) 2 beat scan (ES-MD 2 beat, N=92) for 66≤HR≤75, 4) end-systolic (R+280–430 ms) 2 beat scan (ES 2 beat, N=21) for 76≤HR≤80, and 5) end-systolic (R+250–400 ms) 3 beat scan (ES 3 beat, N=22) for 81≤HR≤105. Image quality was classified into 3 categories (excellent (3 points), acceptable (2 points), and unacceptable (1 point)). Scanning time, DLP.e and image quality score were 1.4±0.1 s, 220±59 mGy·cm, 3.0±0.2 points in MD 1 beat, 2.2±0.2 s, 434±118 mGy·cm, 2.9±0.3 points in MD 2 beat, 2.1±0.2 s, 729±229 mGy·cm, 2.7±0.5 points in ES-MD 2 beat, 1.9±0.1 s, 432±148 mGy·cm, 2.2±0.6 points in ES 2 beat, and 2.4±0.2 s, 669±152 mGy·cm, 2.3±0.6 points in ES 3 beat respectively. In conclusion, the prospective ECG-gated scan protocol for coronary 320-ADCT angiography in any HR group was considered reasonable and proper for image quality and radiation dose.
In diagnostic brain computed tomography (CT) imaging of hyperacute ischemic stroke, the recognition of subtle lesions is difficult and may be missed. The aim of this study was to evaluate quantitatively the effect of the window width on low contrast detectability by using digital phantom images intended for detection of hyperacute ischemic stroke, and clinical CT images. We first derived the digital phantom images by subtracting the simulated signal data (intensity=1–3 hounsfield units (HU), diameter=10–30 mm) from the water phantom images at various mAs values. Observer studies were then performed under the various window widths at 20, 40, 60, and 80 HU by using the 30 digital phantom images and the 30 water phantom images. In addition, observer studies on brain CT images with 30 abnormal cases and 30 normal cases were performed under the window widths at 20 and 80 HU. Studies were also performed under the simultaneous display of the set of brain CT images on each window width. As a result of evaluation by receiver operating characteristic analysis, narrowing of the window width can improve the low contrast detectability in CT images with noticeable noise, and can decrease the variation in the interpretation skills between observers in clinical CT images. Moreover, the interpretation accuracy was improved by displaying simultaneously the clinical CT image set on window widths at 20 and 80 HU.
The purpose of this study was to investigate image quality identification methods among direct- and indirect-type flat panel detectors (FPDs) and a computed radiography (CR) system using two radiation qualities RQA3 and RQA5 defined in the IEC 61267 standard. For each system, the digital characteristic curve, the presampled modulation transfer function (MTF), and the normalized noise power spectrum (NNPS) were measured. Images for a burger phantom and a foot-bone phantom were processed by resolution identification utilizing two-dimensional Fourier transform, and then contrast-to-noise ratio (CNR) for each image was measured. For the RQA3, the direct FPD system indicated the highest DQE value, and for the RQA5 DQE value of indirect FPD system, it was a little higher than that of direct FPD system. The CNR results with the resolution identification displayed good accordance with the DQE results in both phantoms. From the DQE results, dose ratios for image quality identification were determined, and the CNRs of the dose-adjusted images were measured. The results for, the CNRs of all systems showed good coincidence. From these findings, they indicated that the DQE measurement is effective to determine the exposure parameters for equalizing the image quality of different types of radiographic systems.
The purpose of our study was to investigate the relationship between image quality and radiation dose for the filtered backprojection (FBP) with smooth kernel and the iterative reconstruction (iDose) based on image noise, image resolution, CT number, and low-contrast detectability. We used the Catphan phantom and scanned at 65, 45, 32, and 20 mAs on a 64-detector CT. Image reconstruction algorithm and kernel were employed FBP with standard (C type) and FBP with smooth (A type) kernel as images obtained at 20–65 mAs. Regarding to 20–45 mAs, we additionally reconstructed it using the iDose. After scanning, we measured image noise, full width at half maximum (FWHM), and CT number and assessed low-contrast detectability. Image noise acquired at iDose was 10.9, 11.1, and 11.2 HU corresponding to 45, 32, and 20 mAs, respectively. Compared to FBP with standard kernel, FBP with smooth kernel increased the image noise range from 6.7 HU at 65 mAs to 12.3 HU at 20 mAs with decreasing tube current-time product. Unlike iDose and FBP with standard kernel, there was a statistically significant difference between FBP with standard and smooth kernel with respect to image resolution (P=0.002). Reconstruction algorithm of the iDose resulted in the same or better image quality improvements despite a reduction in the radiation dose compared to the FBP with standard or with smooth kernel. From our findings, iDose facilitates the reduction in radiation dose while maintaining image quality.
Exposure indicators of digital radiography systems have been termed by manufacturers individually. The International Electrotechnical Commission (IEC) provided a concept of exposure index (EI) that unified the exposure indicators in order to recognize the deviations from the intended exposure. Although the IEC determined the calibration conditions between the exposure indicator and the air kerma at the detector surface, the tolerance was described was limited concerning the beam conditions. The purpose of this study is to evaluate the calibration error regarding the geometry and the added filtrations. The relative errors of calibrations based on the IEC condition were derived using the value of exposure indicators at EI value of 200, 500 and 1000 for field size of 10×10 cm, 20×20 cm, 30×30 cm and 43×43 cm, and source-image receptor distance (SID) of 100 cm, 120 cm, 150 cm and 200 cm. The beam qualities using added filtrations of 0.5 mm Cu+2 mm Al, 0.6 mm Cu and 21 mm Al were adjusted to RQA 5. The air kerma at the detector surface over the clinical use ranged from 0.18 to 26.3 μGy. Consequently, the relative errors for the calibrations were less than 6% at a field size of more than 10×10 cm and at SID of more than 100 cm with all added filtrations.
The purpose of this study was to optimize X-ray conditions for full spine X-ray examinations in slot-scan digital radiography (SSDR). Follow-up of spinal deformities, such as scoliosis, typically involves many radiographs of the patient throughout childhood and adolescence. The Radiation doses for the full spine X-ray examination should be minimized. Recently, SSDR has been introduced for full spine as well as lower extremity examinations. This system utilizes slot scanning geometry to acquire the radiographic images. X-ray energy characteristics of direct amorphous Selenium (a-Se) digital fluoroscopy and short time X-ray tube loads of this system were investigated. Orthopedists evaluated the irradiation time for full spine radiographs in various conditions using an observer study. Patient doses were measured with radiophotoluminescence glass dosimeters, which were implanted in various tissue and organ positions within an anthropomorphic phantom. In the optimization of conditions for SSDR, patient doses are reduced by approximately 60% compared to default setting.
Angiographic equipment has tended toward using flat-panel detector (FPD). However, the radiation dose varies depending on the size of field of view (FOV) in the FPD. Although we were using 7 inch FOV in cardiac procedures, we examined a way to reduce the patients’ radiation dose by using 8 inch FOV utilizing a digital zoom processing. We measured the absorbed dose rates at an interventional reference point (IRP) with 20 cm acrylic board to compare 8 inch FOV using a digital zoom processing with 7 inch FOV. Additionally we visually evaluated these phantom images. Result of comparison of absorbed dose rates at IRP, 8 inch FOV using a digital zoom processing was reduced more than 7 inch FOV (fluoroscopic 29.0% and digital cine 37.5%). These phantom images were of equivalent quality. The method to use 8 inch FOV utilizing a digital zoom processing technique in cardiac procedures is one of the effective radiation exposure reduction methods.
Philips DigitalDiagnost, a digital radiographic system mounting flat panel detector (FPD), can display dose area data (DiDi dose) calculated by examination parameters. We evaluated its fundamental characteristics and compared the values of DiDi dose andactual measured data obtained by the area dose product meter (PD-4100L). Tendency of varied values of mAs, X-ray tube values and exposure area from both the area dose product meter and the DiDi dose were coincided. Further, in clinical images of chest PA 100 cases, chest lateral 50 cases and abdomen stand 25 cases, the determination coefficient was overly high as R2=0.99. Based on these results, it is clear that the DiDi dose can be treated the same as the area dose product meter. Under increasing of patient X-ray exposure dose is a concern in digital general radiography, this research indicates that maximum values of histogram obtained by DiDi dose contributes dose awareness for radiographer.
Many cases in which the skin complication are caused by increased exposure dose to skin by interventional radiology (IVR) are reported. Therefore, the decrease of patient exposure dose at IVR is important. Patient exposure dose by using IVR-computed tomography (CT) unit is defined as the sum of exposure dose from both angiography and CT scanner. The dose decrease with the CT device was examined in this article. Since the images available during angiography have a high contrast compared to conventional CT scan, best applied standard deviation (SD) values are evaluated by using CT auto exposure control (CT-AEC). Although exposure dose decreased by varying SD values, contrast resolution was kept high. As a result, it became possible to adjust the dose from CT device to about a third by setting a proper CT-AEC value, which led to decrease of the total exposure dose.