Accuracy and calibration of integrated radiation output indicators in diagnostic radiology: A report of the AAPM Imaging Physics Committee Task Group 190.

Due to the proliferation of disciplines employing fluoroscopy as their primary imaging tool and the prolonged extensive use of fluoroscopy in interventional and cardiovascular angiography procedures, "dose-area-product" (DAP) meters were installed to monitor and record the radiation dose delivered to patients. In some cases, the radiation dose or the output value is calculated, rather than measured, using the pertinent radiological parameters and geometrical information. The AAPM Task Group 190 (TG-190) was established to evaluate the accuracy of the DAP meter in 2008. Since then, the term "DAP-meter" has been revised to air kerma-area product (KAP) meter. The charge of TG 190 (Accuracy and Calibration of Integrated Radiation Output Indicators in Diagnostic Radiology) has also been realigned to investigate the "Accuracy and Calibration of Integrated Radiation Output Indicators" which is reflected in the title of the task group, to include situations where the KAP may be acquired with or without the presence of a physical "meter." To accomplish this goal, validation test protocols were developed to compare the displayed radiation output value to an external measurement. These test protocols were applied to a number of clinical systems to collect information on the accuracy of dose display values in the field.

An investigation into factors affecting the precision of CT radiation dose profile width measurements using radiochromic films.

PURPOSE: To investigate the impact of x-ray beam energy, exposure intensity, and flat-bed scanner uniformity and spatial resolution on the precision of computed tomography (CT) beam width measurements using Gafchromic XR-QA2 film and an off-the-shelf document scanner. METHODS: Small strips of Gafchromic film were placed at isocenter in a CT scanner and exposed at various x-ray beam energies (80-140 kVp), exposure levels (50-400 mA s), and nominal beam widths (1.25, 5, and 10 mm). The films were scanned in reflection mode on a Ricoh MP3501 flat-bed document scanner using several spatial resolution settings (100 to 400 dpi) and at different locations on the scanner bed. Reflection measurements were captured in digital image files and radiation dose profiles generated by converting the image pixel values to air kerma through film calibration. Beam widths were characterized by full width at half maximum (FWHM) and full width at tenth maximum (FWTM) of dose profiles. Dependences of these parameters on the above factors were quantified in percentage change from the baselines. RESULTS: The uncertainties in both FWHM and FWTM caused by varying beam energy, exposure level, and scanner uniformity were all within 4.5% and 7.6%, respectively. Increasing scanner spatial resolution significantly increased the uncertainty in both FWHM and FWTM, with FWTM affected by almost 8 times more than FWHM (48.7% vs 6.5%). When uncalibrated dose profiles were used, FWHM and FWTM were over-estimated by 11.6% and 7.6%, respectively. Narrower beam width appeared more sensitive to the film calibration than the wider ones (R(2) = 0.68 and 0.85 for FWHM and FWTM, respectively). The global and maximum local background variations of the document scanner were 1.2%. The intrinsic film nonuniformity for an unexposed film was 0.3%. CONCLUSIONS: Measurement of CT beam widths using Gafchromic XR-QA2 films is robust against x-ray energy, exposure level, and scanner uniformity. With proper film calibration and scanner resolution setting, it can provide adequate precision for meeting ACR and manufacturer's tolerances for the measurement of CT dose profiles.

Quantitative evaluation of light scattering intensities of the crystalline lens for radiation related minimal change in interventional radiologists: a cross-sectional pilot study.

To evaluate low-dose X-ray radiation effects on the eye by measuring the amount of light scattering in specific regions of the lens, we compared exposed subjects (interventional radiologists) with unexposed subjects (employees of medical service companies), as a pilot study. According to numerous exclusionary rules, subjects with confounding variables contributing to cataract formation were excluded. Left eye examinations were performed on 68 exposed subjects and 171 unexposed subjects. The eye examinations consisted of an initial screening examination, followed by Scheimpflug imaging of the lens using an anterior eye segment analysis system. The subjects were assessed for the quantity of light scattering intensities found in each of the six layers of the lens. Multiple stepwise regression analyses were performed with the stepwise regression for six variables: age, radiation exposure, smoking, drinking, wearing glasses and workplace. In addition, an age-matched comparison between exposed and unexposed subjects was performed. Minimal increased light scattering intensity in the posterior subcapsular region showed statistical significance. Our results indicate that occupational radiation exposure in interventional radiologists may affect the posterior subcapsular region of the lens. Since by its very nature this retrospective study had many limitations, further well-designed studies concerning minimal radiation-related lens changes should be carried out in a low-dose exposure group.

Comparison of topogram-based body size indices for CT dose consideration and scan protocol optimization.

PURPOSE: To retrospectively compare different topogram-based patient body size indices and to determine the optimal topogram-based body size index as a basis for body computed tomography (CT) dose consideration and scan protocol optimization. METHODS: Forty-three routine thorax and abdomen CT scans are studied retrospectively, with patient ages ranging from 18 to 67 yr. The individual patient's water-equivalent diameter (D(w)) of the scanned body region is computed from CT DICOM images as the "gold standard," after first converting from Hounsfield units values to µa values, where µ is the normalized tissue attenuation coefficient and a is the area per pixel. Four topogram-based body size indices [average diameter (D), girth (G), topogram projection area (E(topo)), and improved topogram projection area (E(topo)('))] are computed and correlated with D(w) using linear regression analysis. Specifically, D is calculated by averaging the coronal and sagittal diameters; G is computed by modeling the patient's cross-section as an ellipse; E(topo) is the product of the mean topogram pixel value and the width of the scanned body region; and (E(topo)(')) incorporates E(topo) with correction of patient miscentering and water attenuation coefficient. The accuracy of these four approaches for estimation of D(w) is assessed using linear regression models. Results are given in terms of 95% confidence intervals (CIs). RESULTS: Regression analysis results in four different linear models. The standard error (95% CI) for estimation of D(w) from D and G was ±2.8 and ±3.1 cm, respectively (p = 0.297). The standard error for estimation of D(w) from E(topo) was significantly less than that from D (±2.1 cm, p < 0.01). The standard error for estimation of D(w) from (E(topo)(')) was ±1.3 cm, significantly less than that from E(topo) (p < 0.01). CONCLUSIONS: Among the four topogram-based patient body indices, (E(topo)(')) is the most accurate for estimation of individual x-ray attenuation of the scanned body region. Thus, (E(topo)(')) is an optimal topogram-based patient body size index that is relevant for determining the proper CT dose level for individual patients.

Increased radiation dose to overweight and obese patients from radiographic examinations.

PURPOSE: To estimate the increase in effective radiation dose from diagnostic x-rays for overweight and obese adult patients, as compared with the effective dose for lean reference phantoms. MATERIALS AND METHODS: Relative effective radiation doses (E/E(0)) for the acquisition of chest and abdominal radiographs were calculated by using Monte Carlo computer simulations of effective doses delivered to adult phantoms with (E) and without (E(0)) subcutaneous adipose tissue added to the torso for five fat distributions. Total (anterior plus posterior) fat thicknesses ranged from 0 to 38 cm. RESULTS: For 30 cm of additional fat, E/E(0) values for 120-kVp chest and 80-kVp abdomen radiographs ranged from approximately 2 to 31 and 2 to 83 for male patients, respectively, and from 2 to 45 and 2 to 76 for female patients, respectively, depending on the type of fat distribution and patient orientation in the x-ray beam (anteroposterior or posteroanterior). Orienting the patient such that the thinnest fat layer was facing away from the x-ray tube minimized E/E(0), which was well approximated by using the formula E/E(0) = [B(t)/B(0)] x exp(kt(DF)), where B(t) and B(0) are the antiscatter grid Bucky factors for patient thicknesses of t and t = 20 cm, respectively; k, a constant; and t(DF), the distal (beam exit) fat layer thickness. Reductions in E/E(0) reached 14% and 20% for the thickest phantoms when x-ray tube voltages were increased by 10 and 20 kVp, respectively, for abdominal radiography in the male phantom. CONCLUSION: Effective doses from radiographic examinations in the extremely obese can exceed 100 mSv from only a small number of abdominal examinations and should be minimized to the extent possible and monitored. Exponential dose increases for increased subcutaneous fat thicknesses can be reduced substantially by positioning the patient so that the thinnest fat layer (anterior or posterior) is closest to the image receptor. Increasing the tube voltage also reduces the dose-but to a much smaller extent.

Digital mammographic artifacts on full-field systems: what are they and how do I fix them?

The recent introduction of digital mammography represents a significant technologic advance in breast imaging. However, many radiologists and technologists are unfamiliar with artifacts that are commonly seen with this modality, and recognizing these artifacts is critical for optimizing image quality. Commonly encountered artifacts include patient-related artifacts (motion artifact, antiperspirant artifact, thin breast artifact), hardware-related artifacts (field inhomogeneity, detector-associated artifacts, collimator misalignment, underexposure, grid lines, grid misplacement, vibration artifact), and software processing artifacts ("breast-within-a-breast" artifact, vertical processing bars, loss of edge, high-density artifacts). Although some of these artifacts are similar to those seen with screen-film mammography, many are unique to digital mammography--specifically, those due to software processing errors or digital detector deficiencies. In addition, digital mammographic artifacts depend on detector technology (direct vs indirect) and therefore can be vendor specific. It is important that the technologist, radiologist, and physicist become familiar with the spectrum of digital mammographic artifacts and pay careful attention to digital quality control procedures to ensure optimal image quality.

The impact of increased Al filtration on x-ray tube loading and image quality in diagnostic radiology.

Previous work has shown that for nine common radiographic projections (AP abdomen, AP cervical spine, LAT cervical spine, PA chest, LAT chest, AP hip, AP lumbar spine, LAT lumber spine, and AP pelvis) increasing the total x-ray tube filtration from 2.5 mm Al equivalent (the regulatory minimum for general diagnostic radiology) to 4.0 mm Al equivalent, reduces the average effective dose and average skin entrance dose by 9% and 16%, respectively, using a 400 speed screen-film system. In this study, the effects of this filtration increase on x-ray tube loading and image quality were assessed. For the above projections and filtration increase, mean absolute and percentage increases in tube loading were 2.9 mAs and 15%, respectively, for a constant film density and fixed kVp. Tube current (mA) increases of 25% (a worst case) resulted in no statistically significant loss in focal spot resolution due to blooming for both large (1.2 mm) and small (0.6 mm) focal spot sizes, except at high mA low kVp techniques. The latter losses were below 10%, and when the image receptor blur was incorporated, the total system spatial resolution losses were on the order of one-quarter to one-half these values for typical clinical geometries. Radiographs of a contrast phantom taken with 2.5 and 4.0 mm total Al equivalent x-ray tube filtration were compared at 60, 70, 81, 90, 102, and 121 kVp. No statistically significant changes were observed with regard to (1) test object conspicuity as reported by three observers, (2) image contrast, as measured using a densitometer with a 3 mm aperture (+/-0.0017 OD, 95% confidence level), and (3) pixel value image noise, image contrast-to-noise ratios, and image signal-to-noise ratios, as measured using a scanning densitometer with a 12-bit acquisition depth and 85 micron pixel size (+/-2.5%, +/-3.1%, and +/-2.5%, 95% confidence levels, respectively). These results, combined with the linear no-threshold model for radiation risk and the ALARA principle, suggest that general radiography should be carried out using a minimum of 4.0 mm total Al equivalent filtration.