Koichi Chida

Background: Accurate assessment of fetal radiation dose during diagnostic X‐ray examinations remains challenging because commercially available pregnancy phantoms do not adequately reproduce fetal anatomy or permit organ‐specific dose measurements. Purpose: The purpose of this study was to develop a pregnant phantom with adjustable fetal presentation and to evaluate its anatomical realism and applicability for fetal dose assessment during pelvic radiography. Methods: The developed phantom comprised an anthropomorphic phantom, a whole‐body fetal phantom, acrylic components, and water‐filled plastic bags. The fetal phantom was fabricated using three‐dimensional printing technology and incorporated bone‐equivalent and soft‐tissue‐equivalent materials. Fetal presentations could be adjusted to cephalic or breech presentations by repositioning the fetal phantom within the abdominal phantom. Computed tomography (CT) images were acquired to measure CT numbers of the fetal brain, thorax, abdomen, pelvic bone, and surrounding water‐filled regions. Absorbed doses were measured using real‐time dosimeters placed at five locations in the fetal head and three locations in the fetal abdomen. Dose measurements were performed during pelvic radiography and compared with those obtained using a conventional homogeneous pregnancy phantom. Results: The mean CT numbers of the fetal brain, thorax, abdomen, pelvic bone, and water‐filled regions were 2.1, ‐0.8, ‐0.4, 323.8, and 1.6 HU, respectively. These values were within the expected ranges for soft tissue and bone and were comparable to those of a conventional homogeneous phantom. During pelvic radiography, the mean absorbed doses measured using the adjustable fetal‐presentation phantom were 1.34 mGy in the fetal head and 0.07 mGy in the fetal abdomen for the cephalic presentation, and 0.05 mGy and 1.67 mGy, respectively, for the breech presentation. In comparison, the mean absorbed dose measured in the fetal region of the conventional homogeneous phantom was 2.05 mGy. The findings demonstrated substantial differences in regional fetal dose distribution according to fetal presentation. In particular, the fetal head dose in the cephalic presentation was lower than that measured using the conventional phantom. This difference may be partly attributable to attenuation by the fetal skull; however, the comparison should be interpreted with caution given differences in phantom geometry, internal materials, and dosimeter locations between the two phantoms. Conclusion: A novel pregnant phantom with adjustable fetal presentation was successfully developed. The phantom reproduced anatomically relevant structures using realistic bone‐equivalent and soft‐tissue‐equivalent materials and enabled direct dose measurements in specific fetal anatomical regions. Compared with a conventional homogeneous phantom, the developed phantom provided a more detailed assessment of fetal dose distributions and allowed evaluation of the effects of fetal presentation on radiation exposure during pelvic radiography.

This study evaluated fetal-region doses and dose distributions for X-ray pelvimetry (Guthmann and Martius methods) using exposure conditions from a nationwide survey in Japan and compared them with those of a low-dose computed tomography (CT) protocol using a realistic late-pregnancy phantom. A pregnancy model phantom combining an anthropomorphic phantom with a custom-made abdominal phantom was used. Real-time dosimeters were placed at 18 sites across three abdominal levels. The low-dose CT protocol showed a nearly uniform fetal-region dose distribution, whereas the X-ray methods showed heterogeneous distributions depending on beam direction and irradiation field. The reported mean fetal-region doses were 1.16 mGy for Guthmann, 4.05 mGy for Martius, 5.21 mGy for the combined X-ray examinations, and 0.69 mGy for low-dose CT. These results indicate that the low-dose CT protocol evaluated in this study produced a lower fetal-region dose than the Guthmann and Martius methods evaluated in this study.

To evaluate the image quality and clinical radiation dose of a cerebral angiography system featuring contrast-to-noise ratio (CNR)-based exposure control for neurovascular endovascular treatment (EVT). Image quality was evaluated using a quality control phantom under fluoroscopy and digital subtraction angiography (DSA). Clinical radiation dose was retrospectively compared between a conventional angiography system using detector dose-based exposure control (61 cerebral aneurysm EVT procedures) and a new angiography system using CNR-based exposure control (99 procedures). Patient entrance reference air kerma (K _a,r ) and air kerma–area product (P _KA ) were analyzed. The new system demonstrated significantly higher observer scores than the conventional system for both fluoroscopy and DSA, including spatial resolution, low-contrast resolution, and dynamic range. The median total K _a,r was 1818 [1301–2744] mGy with the new system and 2283 [1580–3184] mGy with the conventional system, representing a 20% reduction (p < 0.05). Conversely, the median total P _KA increased by 26% (173 [120–237] vs. 137 [93–207] Gy·cm ² , p < 0.05), but remained below the current Japanese diagnostic reference level for cerebral aneurysm EVT. Compared with the conventional system, the new angiography platform demonstrated superior image quality under phantom conditions and was associated with a 20% reduction in total K _a,r during cerebral aneurysm EVT. Although the total P _KA increased by 26%, this increase may have reflected differences in the magnification strategy between the two systems, suggesting a need for further optimization.

Radioactive materials are released into the environment and then transferred to animals and humans whenever atmospheric nuclear tests or nuclear disasters occur (Suzuki et al. 2019). Radioactive pa...

Medical personnel performing endoscopic retrograde cholangiopancreatography (ERCP) are at a high risk of developing radiation-induced injuries, such as cataracts, due to scattered radiation, making the use of appropriate radiation protection equipment essential. We developed two types of upright shields attached to a C-arm system (under-couch tube position): one for the operator and the other for the anesthesiologist. The purpose of this study was to evaluate the protective effect of these upright shields. We conducted a phantom study in typical ERCP settings and compared the scattered radiation doses between the C-arm system equipped with the upright shields and an over-couch tube system equipped with an ERCP-specific lead curtain. It was found that the upright shield for the operator reduced scattered radiation exposure by 90%, and the upright shield for the anesthesiologist reduced scattered radiation exposure by 86%. The upright shields for a C-arm system could be just as effective as the ERCP-specific curtain for an over-couch tube system. The use of the novel upright shields may eliminate the need for protective glasses and is expected to not only protect the eyes but also safeguard the thyroid and brain.

With expanding indications for interventional neuroradiology, patient radiation exposure remains a significant concern. This study aimed to identify predictors of high peak skin dose and left lens doses using directly measured patient radiation data. We retrospectively analyzed patient doses and performed multivariate logistic regression. Treatment of a posterior circulation aneurysm [odds ratio (OR) = 7.491; 95% confidence interval (CI), 1.217–46.110] and stent use (OR = 5.516; 95% CI, 1.318–23.085) were identified as independent predictors of peak skin dose exceeding 1.0 Gy. Stent use was also a significant predictor of left lens dose exceeding 100 mGy (OR = 3.141; 95% CI, 1.488–7.851). These findings provide a robust, evidence-based framework for identifying high-risk patients preprocedurally. This knowledge is crucial for enhancing the informed consent process and justifying the timely implementation of dose-reduction strategies to minimize the risk of radiation-induced injuries.