Because breast tissue varies spatially in physical density and elemental content, the effective thickness of breast tissue varies spatially across the imaging field, resulting in a spatially-variant scatter distribution in the imaging field. The data generated in this study can be used to characterize the scatter contribution on a point-by-point basis, for a variety of different techniques.

This study assesses the accuracy of effective atomic number (Z eff ) and electron density measurements acquired from dual energy CT and characterizes the response to clinically relevant variables representative of challenges in patient imaging, including: phantom size, material position within the phantom, variation over time, off-center positioning, and large cone beam angle. Methods: The Gammex Multi-Energy CT head and body phantoms were used to measure Z eff and electron density from 35 rod inserts that mimic tissues and varying concentrations of iodine and calcium. Scans were performed on a Canon Aquilion ONE Genesis CT scanner over a period of 6 months using default dual energy protocols appropriate for each phantom size. Theoretical Z eff and electron density values were calculated using data provided by the phantom manufacturer and compared to the measurements. Sources of variance were separated and quantified to identify the influences of random photon statistics, ROI placement, and variation over time. A subset of measurements were repeated with the phantom shifted in the vertical and horizontal directions, and over all slices in the volumetric scan. Results: All measurements showed strong correlation (r > 0.98) with their corresponding theoretical values; however, the system did demonstrate a bias of −0.58 atomic units in the body phantom and 0.28 atomic units in the head phantom for Z eff measurements. The mean absolute percent error (MAPE) was 6.3% for the body phantom and 3.2% for the head phantom. Electron density measurements of the body and head phantoms gave MAPE values of 4.6% and 1.0%, respectively. Z eff and electron density measurements significantly varied within the solid water background, showing a positional dependence within the phantom that dominated the total standard deviation in measurements. Z eff values dropped by 0.2 atomic units when the phantom was off-center; electron density measurements were less affected by phantom position. Along the z-axis, the accuracy drops off markedly at more than 50-60 mm from the central slice. Conclusion:The Canon dual energy system offers an accurate way of measuring the Z eff and electron density of clinically relevant materials. Accuracy could be improved further by calibration to remove bias, careful attention to centering within the FOV, and avoiding measurements at the edges of the cone beam.

Purpose: Most clinical computed tomography (CT) protocols use helical scanning; however, the traditional method for CTDI vol measurement replaces the helical protocol with an axial scan, which is not easily accomplished on many scanners and may lead to unmatched collimation settings and bowtie filters. This study assesses whether CTDI vol can be accurately measured with a helical scan and determines the impact of pitch, collimation width, and excess scan length. Methods: CTDI vol was measured for 95 helical protocols on 31 CT scanners from all major manufacturers. CTDI vol was measured axially, then again helically, with the scan range set to the active area of the pencil chamber seen on the localizer image. CTDI vol measurements using each method were compared to each other and to the scanner-displayed CTDI vol. To test the impact of scan length, the study was repeated on four scanners, with the scan range set to the phantom borders seen on the localizer. Results: It was not possible to match the collimation width between the axial and helical modes for 12 of the 95 protocols tested. For helical and axial protocols with matched collimation, the difference between the two methods averaged below 1 mGy with a correlation of R 2 = 0.99. The difference between the methods was not statistically significant (P = 0.81). The traditional method produced four measurements that differed from the displayed CTDI vol by >20%; no helical measurements did. The accuracy of the helical CTDI vol was independent of protocol pitch (R 2 = 0.0) or collimation (R 2 = 0.0). Extending the scan range to the phantom borders increased the measured CTDI vol by 2.1%-9.7%. Conclusion: There was excellent agreement between the two measurement methods and to the displayed CTDI vol , without protocol or vendor dependence. The helical CTDI vol measurement can be accomplished more easily than the axial method on many scanners and is reasonable to use for QC purposes.

Objectives:Direct measurement of skin dose of radiation for children using optically stimulated luminescence (OSL) technology using nanoDot® (Landauer, Glenwood, IL, USA).Background:Radiation dose is estimated as cumulative air kerma (AK) and dosearea product based on standards established for adult size patients. Body size of pediatric patients who undergo cardiac catheterization for congenital heart disease vary widely from newborn to adolescence. Direct, skindose measurement applying OSL technology may eliminate errors in the estimate.Materials and Methods:The nanoDot® (1 cm × 1 cm × flat plastic cassette) is applied to patient's skin using adhesive tape during cardiac catheterization and radiation skin doses were read within 24 hrs. nanoDot® values were compared to the currently available cumulative AK values estimated and displayed on fluoroscopy monitor.Results:A total of 12 children were studied, aged 4 months to 18 years (median 1.1 years) and weight range 5.3–86 kg (median 8.4 kg). nanoDot® readings ranged from 2.58 mGy to 424.8 mGy (median 84.1 mGy). Cumulative AK ranged from 16.2 mGy to 571.2 mGy (median 171.1 mGy). Linear correlation was noted between nanoDot® values and AK values (R2 = 0.88, R = 0.94). nanoDot® readings were approximately 65% of the estimated cumulative AK estimated using the International Electrotechnical Commission standards.Conclusions:Application of OSL technology using nanoDot® provides an alternative to directly measure fluoroscopic skin dose in children during cardiac catheterization. Our data show that the actual skin dose for children is approximately one-third lower than the AK estimated using international standards for adult size patients.