Tao, Ashley T

PurposeWhile scatter from the patient is assumed to be the primary source of occupational radiation dose associated with fluoroscopically guided interventional procedures, the potential contribution of scatter from the x‐ray collimator assembly is unknown. The purpose of this work was to survey clinical x‐ray angiography systems to assess the potential contribution of collimator assembly scatter on occupational radiation dose.MethodsExperimental methods were designed to measure the relative contributions of scatter originating from within the collimator assembly of the x‐ray tube to total scatter, which included scatter from a patient‐simulating phantom. Measurements were acquired as a function of lateral distance from the x‐ray beam center using a posterior anterior (PA) projection and at a fixed location for variable right anterior oblique to left anterior oblique projections in the range −90º to 90º. For one system, the collimator assembly was partially disassembled to assess the scatter contribution of individual components. For two systems, 0.5 mm Pb was added to the inner surface of the collimator assembly cover and tested for efficacy to block collimator assembly scatter.ResultsConsidering all x‐ray systems and only the PA projection, collimator assembly scatter contributed 20–50% to total scatter. For x‐ray projection angles of −90º to 90º, the relative contribution of collimator assembly to total scatter was dependent on projection angle and ranged from 5% to 56%. X‐ray systems with kerma‐area product meters demonstrated higher collimator assembly scatter than those without. Considering all projection angles, the addition of 0.5 mm Pb to the inside of the collimator assembly cover reduced collimator assembly scatter from 28% to 16% of total scatter for both systems.ConclusionFindings from this work suggest that contemporary radiation safety practices and guidelines should be revised to account for scatter originating from the collimator assembly of angiographic x‐ray tubes.

BackgroundGradient nonlinearity (GNL) leads to biased apparent diffusion coefficients (ADCs) in diffusion‐weighted imaging. A gradient nonlinearity correction (GNLC) method has been developed for whole body systems, but is yet to be tested for the new compact 3T (C3T) scanner, which exhibits more complex GNL due to its asymmetrical design.PurposeTo assess the improvement of ADC quantification with GNLC for the C3T scanner.Study TypePhantom measurements and retrospective analysis of patient data.Phantom/SubjectsA diffusion quality control phantom with vials containing 0–30% polyvinylpyrrolidone in water was used. For in vivo data, 12 patient exams were analyzed (median age, 33).Field Strength/SequenceImaging was performed on the C3T and two commercial 3T scanners. A clinical DWI (repetition time [TR] = 10,000 msec, echo time [TE] = minimum, b = 1000 s/mm2) sequence was used for phantom imaging and 10 patient cases and a clinical DTI (TR = 6000–10,000 msec, TE = minimum, b = 1000 s/mm2) sequence was used for two patient cases.AssessmentThe 0% vial was measured along three orthogonal axes, and at two different temperatures. The ADC for each concentration was compared between the C3T and two whole‐body scanners. Cerebrospinal fluid and white matter ADCs were quantified for each patient and compared to values in literature.Statistical TestsPaired t‐test and two‐way analysis of variance (ANOVA).ResultsFor all PVP concentrations, the corrected ADC was within 2.5% of the reference ADC. On average, the ADC of cerebrospinal fluid and white matter post‐GNLC were within 1% and 6%, respectively, of values reported in the literature and were significantly different from the uncorrected data (P < 0.05).Data ConclusionThis study demonstrated that GNL effects were more severe for the C3T due to the asymmetric gradient design, but our implementation of a GNLC compensated for these effects, resulting in ADC values that are in good agreement with values from the literature.Level of Evidence: 4Technical Efficacy: Stage 2J. Magn. Reson. Imaging 2018;48:1498–1507