Fetal radiation dose in computed tomography

Estimation of maternal and foetal risk of radiation-induced cancer from a survey of computed tomography pulmonary angiography and ventilation/perfusion lung scanning for diagnosing pulmonary embolism during pregnancy

INTRODUCTION

While there are many papers on maternal and foetal radiation doses from computed tomography pulmonary angiography (CTPA) and ventilation/perfusion (V/Q) lung scanning examinations for diagnosing pulmonary embolism in pregnant patients, few have used clinical data to examine the patient lifetime attributable risk (LAR) of different cancer types. This paper aims to estimate the cancer risk from maternal radiation doses from CTPA and V/Q examinations and associated foetal doses.

METHODS

Dosimetric data were determined for 267 pregnant patients who received CTPA and/or V/Q examinations over 8 years. Organ and foetal doses were determined using software allowing patient size variations for CTPA and using two different activity-to-organ dose conversion methods for V/Q scans. The LAR of cancer incidence was estimated using International Commission on Radiological Protection (ICRP) modelling including estimates of detriment.

RESULTS

Estimated total cancer incidence was 23 and 22 cases per 100,000 for CTPA and V/Q examinations, respectively, with detriment estimates of 18 and 20 cases. Cancer incidence was evenly divided between lung and breast cancer for CTPA with lung cancer being 80% of all cancer for V/Q. The median foetal doses were 0.03 mSv for CTPA and 0.29 mSv for V/Q. Significant differences in estimated foetal dose for V/Q scans were obtained by the two different methods used. The differences in dose between the modes of CTPA scan acquisition highlight the importance of optimisation.

CONCLUSION

Maternal cancer incidence and detriment were remarkably similar for each examination. Optimisation of examinations is critical for low-dose outcomes, particularly for CTPA examination.

Management of pregnant or potentially pregnant patients undergoing diagnostic and interventional radiology procedures: Investigation of clinical routine practice

It is well known that foetuses are highly sensitive to ionising radiation and special attention to justification and optimisation of radiological procedures involving a pregnant patient is required. A task to review, validate and compare different approaches to managing the pregnant patient and to estimating the associated foetal doses arising from a diagnostic or interventional radiology (DIR) procedure was designed in the framework of EURADOS working group 12. As a first step, a survey of radiation protection practice including dosimetry considerations among EURADOS members was performed using online questionnaire. Then, to evaluate the possible differences in the estimated foetal doses, a comparison of assessed dose values was made for three cases of pregnant patients that underwent different CT procedures. More than 120 professionals from 108 institutions and 17 countries that are involved in managing pregnant patients undergoing DIR procedures answered the questionnaire. Most of the respondents use national or hospital guidelines on the management of pregnant patients undergoing DIR procedures. However, the guidelines differ considerably among respondents. Comparison of foetal dose assessments performed by dosimetry experts showed the variety of methods used as well as large variability of estimated foetal doses in all three cases. Although European and International commission on radiation protection guidelines already exist, they are more than 20 years old and, in some aspects, they are obsolete. This paper shows that there is a need to revise and update these guidelines.

Pericardial Diseases in Pregnancy

Pericardial effusion is the most common manifestation of pericardial diseases during pregnancy. This effusion is benign, mild, or moderate, well tolerated, with spontaneous resolution after delivery; no specific treatment is required. Acute pericarditis is the second most common condition, usually requiring medical therapy during pregnancy. Cardiac tamponade and constrictive pericarditis are rare in pregnancy. Pre-pregnancy counselling is essential in women of childbearing age with recurrent pericarditis to plan pregnancy in a phase of disease quiescence and to review therapy. High-dose aspirin or nonselective nonsteroidal anti-inflammatory drugs, such as ibuprofen and indomethacin, can be used up to the 20th week of gestation. Low-dose prednisone (2.5-10 mg/d) can be administered throughout pregnancy. All of these medications, apart from high-dose aspirin, may be used during lactation. Colchicine is compatible with pregnancy and breastfeeding, and it can be continued throughout pregnancy to prevent recurrences. Appropriate follow-up with a multidisciplinary team with experience in the field is recommended throughout pregnancy to ensure good maternal and fetal outcomes.

Evaluation of radiation dose for inferior vena cava filter placement during pregnancy: A comparison of dosimetry and dose calculation software

Numerous medical conditions are associated with pregnancy in women, including pulmonary thromboembolism, which can be fatal. An effective treatment of this condition is the positioning of an inferior vena cava filter (IVC-F) under the guidance of X-ray imaging. However, this procedure involves the risk of high radiation exposure to pregnant women and fetuses. Moreover, there are no published reports comparing the values of fetal dose, received during IVC-F placement in pregnant women, determined using dose calculation software and actual measurements. To address this issue, we compared the fetal radiation dose and entrance surface dose (ESD) for pregnant women for gestation periods of 6 and 9 months based on software calculations and actual measurements. The ESD and fetal doses were estimated for a pregnant woman for gestation periods of 6 and 9 months during IVC-F placement. For actual measurements, one pregnant model phantom was constructed using an anthropomorphic phantom, and two custom-made different-sized abdomen phantoms were used to simulate pregnancy. The custom-made abdomen phantoms were constructed using polyurethane. For software calculations, the software utilized a set of anatomically realistic pregnant patient phantoms. The ESD estimated using the software was consistent with the measured ESD, but the fetal dose estimations were more complicated due to fetal positioning. During fetal dose evaluation using software calculations, the user must carefully consider how much of the fetal length is in the irradiation field to prevent underestimation or overestimation. Despite the errors, the software can assist the user in identifying the magnitude of the dose approaching critical limits.

Radiation exposure to fetus from extremity CBCT examinations

PURPOSE

To evaluate fetal doses from extremity CBCT examinations at different stages of pregnancy and to investigate different methods of fetal dose optimization.

METHOD

Fetal doses were measured in an anthropomorphic phantom for two CBCT examination protocols - knee and elbow. The measurements were made at three different heights representing the three trimesters during pregnancy and three different depths in the phantom. The effect of soft tissue layer, tube voltage, add-on device shield and body angulation on fetal dose were investigated.

RESULTS

The fetal doses in clinical examination protocols were in the range of 3.4 to 6.0 µGy during knee examinations and 2.9 to 7.7 µGy during elbow examinations depending on the depth of the fetus and the stage of pregnancy. A soft tissue layer representing variative body composition above abdomen region decreased the fetal dose up to 19 % in knee and up to 21 % in elbow examinations. Using lower tube voltage decreased the fetal doses up to 45 % (knee) and 51 % (elbow). An add-on device shield decreased the fetal doses up to 91 % (knee) and up to 75 % (elbow). Turning the body away from the device bore reduced the fetal doses up to 62 %. The conversion factor to convert an entrance surface dose to the fetal dose ranged from 0.4 to 0.6.

CONCLUSIONS

The fetal doses from CBCT examinations of extremities are low and do not produce a concern about radiation detriment to the fetus. The most efficient way found to reduce the fetal dose was to use the add-on device shielding.

Construction of A Digital Fetus Library for Radiation Dosimetry

PURPOSE

Accurate estimation of fetal absorbed dose and radiation risks are crucial for radiation protection and important for radiological imaging research owing to the high radio-sensitivity of the fetus. Computational anthropomorphic models have been widely used in patient-specific radiation dosimetry calculations. In this work, we aim to build the first digital fetal library for more reliable and accurate radiation dosimetry studies.

ACQUISITION AND VALIDATION METHODS

Computed tomography (CT) images of abdominal and pelvic regions of 46 pregnant females were segmented by experienced medical physicists. The segmented tissues/organs include the body contour, skeleton, uterus, liver, kidney, intestine, stomach, lung, bladder, gall bladder, spleen and pancreas for maternal body, and placenta, amniotic fluid, fetal body, fetal brain and fetal skeleton. Non-Uniform Rational B-Spline (NURBS) surfaces of each identified region was constructed manually using 3D modeling software. The Hounsfield unit (HU) values of each identified organs were gathered from CT images of pregnant patients and converted to tissue density. Organ volumes were further adjusted according to reference measurements for the developing fetus recommended by the World Health Organization (WHO) and International Commission on Radiological Protection (ICRP). A series of anatomical parameters, including femur length (FL), humerus length (HL), biparietal diameter (BPD), abdominal circumference (FAC) and head circumference (HC) were measured and compared with WHO recommendations.

DATA FORMAT AND USAGE NOTES

The first fetal patient-specific model library was developed with the anatomical characteristics of each model derived from the corresponding patient whose gestational age varies between 8-weeks and 35-weeks. Voxelized models are represented in the form of MCNP matrix input files representing the three-dimensional model of the fetus. The size distributions of each model are also provided in text files. All data are stored on Zenodo and are publicly accessible on the following link: https://zenodo.org/record/6471884.

POTENTIAL APPLICATIONS

The constructed fetal models and maternal anatomical characteristics are consistent with the corresponding patients. The resulting computational fetus could be used in radiation dosimetry studies to improve the reliability of fetal dosimetry and radiation risks assessment. The advantages of NURBS surfaces in terms of adapting fetal postures and positions enable us to adequately assess their impact on radiation dosimetry calculations. This article is protected by copyright. All rights reserved.

SIZE-SPECIFIC DOSE ESTIMATES IN FETAL COMPUTED TOMOGRAPHY

During fetal computed tomography (CT) imaging, because of differences in the pregnancy period and scanning conditions, different doses of radiation are absorbed by the fetus. We propose a correction coefficient for determining the fetal size-specific dose estimate (SSDE) from the CT dose index (CTDI) displayed on the console at tube voltages of 80-135 kVp. The CTDIs corresponding to pregnant women and fetuses were evaluated using a Monte Carlo (MC) simulation, and the ratio of these CTDIs was defined as the Fetus-factor. When the effective diameter of a fetus was approximately 10 cm, the Fetus-factor was 1.0. The estimated pregnant SSDE was multiplied by the Fetus-factor to estimate the fetal SSDE, which was compared with the fetal dose obtained by the MC simulation of the image of the fetal CT examination. The fetal dose could be estimated with an error of 31.5% in fetal examinations conducted using helical CT.

Management of acute and recurrent pericarditis in pregnancy

This review summarizes the currently available evidence on the management of acute and recurrent pericarditis during pregnancy, focusing on the safety of diagnostic procedures and treatment options for the mother and foetus. Family planning should be addressed in women with recurrent pericarditis of reproductive age and adjustment of therapy should be considered before a planned pregnancy. The treatment of pericarditis in pregnancy is similar to that for non-pregnant women but considers current knowledge on drug safety during pregnancy and lactation. The largest case series on this topic described 21 pregnancies with idiopathic recurrent pericarditis. Pregnancy should be planned in a phase of disease quiescence. Non-steroidal anti-inflammatory drugs can be used at high dosages until the 20th week of gestation (except low-dose aspirin 100 mg/die). Colchicine is allowed until gravindex positivity; after this period, administration of this drug during pregnancy and lactation should be discussed with the mother if its use is important to control recurrent pericarditis. Prednisone is safe if used at low-medium doses (2,5 - 10 mg/die). General outcomes of pregnancy in patients with pericarditis are good when the mothers are followed by a multidisciplinary team with experience in the field.

Evaluation of exposure dose in fetal computed tomography using organ-effective modulation

Organ-effective modulation (OEM) is a computed tomography scanning technique that reduces the exposure dose to organs at risk. Ultrasonography is commonly used for prenatal imaging, but its reliability is reported to be limited. Radiography and computed tomography (CT) are reliable but pose risk of radiation exposure to the pregnant woman and her fetus. Although there are many reports on the exposure dose associated with fetal CT scans, no reports exist on OEM use in fetal CT scans. We measured the basic characteristics of organ-effective modulation (X-ray output modulation angle, maximum X-ray output modulation rate, total X-ray output modulation rate, and noise modulation) and used them in a Monte Carlo simulation to evaluate the effect of this technique on fetal CT scans in terms of image quality and exposure dose to the pregnant woman and fetus. Using ImPACT MC software, Monte Carlo simulations of OEMON and OEMOFF were run on 8 cases involving fetal CT scans. We confirmed that the organ-effective modulation X-ray output modulation angle was 160°; the X-ray output modulation rate increased with increasing tube current; and no modulation occurred at tube currents of 80 mA or below. Our findings suggest that OEM has only a minimal effect in reducing organ exposure in pregnant women; therefore, it should be used on the anterior side (OEMON,front) to reduce the exposure dose to the fetus.

Fetal Dosimetry at CT: A Primer

CT scanning of a pregnant patient is often a source of distress for both patient and staff. Despite having expertise in image interpretation, a radiologist may not feel equipped to discuss the radiation-related safety issues during CT scanning of the fetus. In addition, patients are frequently concerned about the risk of adverse effects on the fetus from exposure to ionizing radiation. Recognizing the possibility of adverse effects from fetal exposure and the impossibility of direct in vivo measurement, medical physicists have developed several methods to estimate the amount of radiation reaching the fetus. A physician should know the potential biologic effects of fetal irradiation and at what radiation dose thresholds they occur. Physicians should also have an understanding of these methods and how the numbers they produce relate to potential fetal bioeffects. Furthermore, radiologists should have some understanding of how a qualified medical physicist calculates the fetal dose, how much they should trust those numbers, and the relevant variables that can affect the outcomes. Finally, the radiologist should know the magnitude of doses for CT scans commonly used in pregnant patients. Armed with this knowledge, a radiologist should be confident when discussing fetal dose and determining the best course of action for the pregnant patient. Online supplemental material is available for this article. ^©RSNA, 2020.

Computed Tomography Pulmonary Angiography during Pregnancy: Radiation Dose of Commonly Used Protocols and the Effect of Scan Length Optimization

Objective

To evaluate the radiation dose for pregnant women and fetuses undergoing commonly used computed tomography of the pulmonary arteries (CTPA) scan protocols and subsequently evaluate the simulated effect of an optimized scan length.

Materials and Methods

A total of 120 CTPA datasets were acquired using four distinctive scan protocols, with 30 patients per protocol. These datasets were mapped to Cristy phantoms in order to simulate pregnancy and to assess the effect of an effective radiation dose (in mSv) in the first, second, or third trimester of pregnancy, including a simulation of fetal dose in second and third trimesters. The investigated scan protocols involved a 64-slice helical scan at 120 kVp, a high-pitch dual source acquisition at 100 kVp, a dual-energy acquisition at 80/140 kVp, and an automated-kV-selection, high pitch helical scan at a reference kV of 100 kV_ref. The effective dose for women and fetuses was simulated before and after scan length adaptation. The original images were interpreted before and after scan length adaptations to evaluate potentially missed diagnoses.

Results

Large inter-scanner and inter-protocol variations were found; application of the latest technology decreased the dose for non-pregnant women by 69% (7.0–2.2 mSv). Individual scan length optimization proved safe and effective, decreasing the fetal dose by 76–83%. Nineteen (16%) cases of pulmonary embolism were diagnosed and, after scan length optimization, none were missed.

Conclusion

Careful CTPA scan protocol selection and additional optimization of scan length may result in significant radiation dose reduction for a pregnant patient and her fetus, whilst maintaining diagnostic confidence.

Estimation of the radiation dose in pregnancy: an automated patient-specific model using convolutional neural networks

OBJECTIVES

The conceptus dose during diagnostic imaging procedures for pregnant patients raises health concerns owing to the high radiosensitivity of the developing embryo/fetus. The aim of this work is to develop a methodology for automated construction of patient-specific computational phantoms based on actual patient CT images to enable accurate estimation of conceptus dose.

METHODS

We developed a 3D deep convolutional network algorithm for automated segmentation of CT images to build realistic computational phantoms. The neural network architecture consists of analysis and synthesis paths with four resolution levels each, trained on manually labeled CT scans of six identified anatomical structures. Thirty-two CT exams were augmented to 128 datasets and randomly split into 80%/20% for training/testing. The absorbed doses for six segmented organs/tissues from abdominal CT scans were estimated using Monte Carlo calculations. The resulting radiation doses were then compared between the computational models generated using automated segmentation and manual segmentation, serving as reference.

RESULTS

The Dice similarity coefficient for identified internal organs between manual segmentation and automated segmentation results varies from 0.92 to 0.98 while the mean Hausdorff distance for the uterus is 16.1 mm. The mean absorbed dose for the uterus is 2.9 mGy whereas the mean organ dose differences between manual and automated segmentation techniques are 0.07%, - 0.45%, - 1.55%, - 0.48%, - 0.12%, and 0.28% for the kidney, liver, lung, skeleton, uterus, and total body, respectively.

CONCLUSION

The proposed methodology allows automated construction of realistic computational models that can be exploited to estimate patient-specific organ radiation doses from radiological imaging procedures.

KEY POINTS

• The conceptus dose during diagnostic radiology and nuclear medicine imaging procedures for pregnant patients raises health concerns owing to the high radiosensitivity of the developing embryo/fetus. • The proposed methodology allows automated construction of realistic computational models that can be exploited to estimate patient-specific organ radiation doses from radiological imaging procedures. • The dosimetric results can be used for the risk-benefit analysis of radiation hazards to conceptus from diagnostic imaging procedures, thus guiding the decision-making process.

Estimating fetal dose from tube current-modulated (TCM) and fixed tube current (FTC) abdominal/pelvis CT examinations

PURPOSE

The purpose of this work was to estimate scanner-independent CTDI_vol -to-fetal-dose coefficients for tube current-modulated (TCM) and fixed tube current (FTC) computed tomography (CT) examinations of pregnant patients of various gestational ages undergoing abdominal/pelvic CT examinations.

METHODS

For 24 pregnant patients of gestational age from <5 to 36 weeks who underwent clinically indicated CT examinations, voxelized models of maternal and fetal (or embryo) anatomy were created from abdominal/pelvic image data. Absolute fetal dose (D_fetus ) was estimated using Monte Carlo (MC) simulations of helical scans covering the abdomen and pelvis for TCM and FTC scans. Estimated TCM schemes were generated for each patient model using a validated method that accounts for patient attenuation and scanner output limits for one scanner model and were incorporated into MC simulations. FTC scans were also simulated for each patient model with multidetector row CT scanners from four manufacturers. Normalized fetal dose estimates, nD_fetus , was obtained by dividing D_fetus from the MC simulations by CTDI_vol . Patient size was described using water equivalent diameter (D_w ) measured at the three-dimensional geometric centroid of the fetus. Fetal depth (DE_f ) was measured from the anterior skin surface to the anterior part of the fetus. nD_fetus and D_w were correlated using an exponential model to develop equations for fetal dose conversion coefficients for TCM and FTC abdominal/pelvic CT examinations. Additionally, bivariate linear regression was performed to analyze the correlation of nD_fetus with D_w and fetal depth (DE_f ). For one scanner model, nD_fetus from TCM was compared to FTC and the size-specific dose estimate (SSDE) conversion coefficients (f-factors) from American Association of Physicists in Medicine (AAPM) Report 204. nD_fetus from FTC simulations was averaged across all scanners for each patient ( n D fetus ¯ ) . n D fetus ¯ was then compared with SSDE f-factors and correlated with D_w using an exponential model and with D_w and DE_f using a bivariate linear model.

RESULTS

For TCM, the coefficient of determination (R² ) of nD_fetus and D_w was observed to be 0.73 using an exponential model. Using the bivariate linear model with D_w and DE_f , an R² of 0.78 was observed. For the TCM technology modeled, TCM yielded nD_fetus values that were on average 6% and 17% higher relative to FTC and SSDE f-factors, respectively. For FTC, the R² of n D fetus ¯ with respect to D_w was observed to be 0.64 using an exponential model. Using the bivariate linear model, an R² of 0.75 was observed for n D fetus ¯ with respect to D_w and DE_f . A mean difference of 0.4% was observed between n D fetus ¯ and SSDE f-factors.

CONCLUSION

Good correlations were observed for nD_fetus from TCM and FTC scans using either an exponential model with D_w or a bivariate linear model with both D_w and DE_f . These results indicate that fetal dose from abdomen/pelvis CT examinations of pregnant patients of various gestational ages may be reasonably estimated with models that include (a) scanner-reported CTDI_vol and (b) D_w as a patient size metric, in addition to (c) DE_f if available. These results also suggest that SSDE f-factors may provide a reasonable (within ±25%) estimate of nD_fetus for TCM and FTC abdomen/pelvis CT exams.

Patient-Specific Computational Model and Dosimetry Calculations for PET/CT of a Patient Pregnant with Twins

The radiation dose delivered to pregnant patients during radiologic imaging procedures raises health concerns because the developing embryo and fetus are considered to be highly radiosensitive. To appropriately weigh the diagnostic benefits against the radiation risks, the radiologist needs reasonably accurate and detailed estimates of the fetal dose. Expanding our previously developed series of computational phantoms for pregnant women, we here describe a personalized model for twin pregnancy, based on an actual clinical scan. Methods: The model is based on a standardized hybrid pregnant female and fetus phantom and on a clinical case of a patient who underwent an ¹⁸F-FDG PET/CT scan while expecting twins at 25 weeks' gestation. This model enabled us to produce a realistic physical representation of the pregnant patient and to estimate the maternal and fetal organ doses from the ¹⁸F-FDG and CT components. The Monte Carlo N-Particle Extended general-purpose code was used for radiation transport simulation. Results: The ¹⁸F-FDG doses for the 2 fetuses were 3.78 and 3.99 mGy, and the CT doses were 0.76 and 0.70 mGy, respectively. Therefore, the relative contribution of ¹⁸F-FDG and CT to the total dose to the fetuses was about 84% and 16%, respectively. Meanwhile, for ¹⁸F-FDG, the calculated personalized absorbed dose was about 40%-50% higher than the doses reported by other dosimetry computer software tools. Conclusion: Our approach to constructing personalized computational models allows estimation of a patient-specific radiation dose, even in cases with unusual anatomic features such as a twin pregnancy. Our results also show that, even in twins, the fetal organ doses from both ¹⁸F-FDG and CT present a certain variability linked to the anatomic characteristics. The CT fetal dose is smaller than the ¹⁸F-FDG PET dose.

Fetal radiation dose in three common CT examinations during pregnancy - Monte Carlo study

PURPOSE

To determine fetal doses in different stages of pregnancy in three common computed tomography (CT) examinations: pulmonary CT angiography, abdomino-pelvic and trauma scan with Monte Carlo (MC) simulations.

METHODS

An adult female anthropomorphic phantom was scanned with a 64-slice CT using pulmonary angiography, abdomino-pelvic and trauma CT scan protocols. Three different sized gelatin boluses placed on the phantom's abdomen simulated different stages of pregnancy. Intrauterine dose was used as a surrogate to a dose absorbed to the fetus. MC simulations were performed to estimate uterine doses. The simulation dose levels were calibrated with volumetric CT dose index (CTDI_vol) measurements and MC simulations in a cylindrical CTDI body phantom and compared with ten point doses measured with metal-oxide-semiconductor field-effect-transistor dosimeters. Intrauterine volumes and uterine walls were segmented and the respective dose volume histograms were calculated.

RESULTS

The mean intrauterine doses in different stages of pregnancy varied from 0.04 to 1.04mGy, from 4.8 to 5.8mGy, and from 9.8 to 12.6mGy in the CT scans for pulmonary angiography, abdomino-pelvic and trauma CT scans, respectively. MC simulations showed good correlation with the MOSFET measurement at the measured locations.

CONCLUSIONS

The three studied examinations provided highly varying fetal doses increasing from sub-mGy level in pulmonary CT angiography to notably higher levels in abdomino-pelvic and trauma scans where the fetus is in the primary exposure range. Volumetric dose distribution offered by MC simulations in an appropriate anthropomorphic phantom provides a comprehensive dose assessment when applied in adjunct to point-dose measurements.

Contemporary Modalities to Image the Fetal Brain

Fetal brain ultrasound remains as the mainstay for screening fetal intracranial anatomy. One of its main advantages is the availability of 3 dimensional and other ultrasound modalities for a better understanding of fetal neurodevelopment. Neurosonography is performed when findings, suggestive of an abnormality, are present on a screening ultrasound or if a high-risk situation of brain injury is present. This technique offers the use of complementary imaging planes, axial, coronal and sagittal, and the ability to image intracranial anatomy from the transabdominal and transvaginal approaches. Fetal brain magnetic resonance imaging is more sensitive than ultrasound. As an adjunctive imaging modality, magnetic resonance imaging offers additional sequences to complete the information on neurodevelopment from different perspectives, such as brain metabolism, microstructure, and connectivity.

Trauma in pregnant women: assessing detection of post-traumatic placental abruption on contrast-enhanced CT versus ultrasound

OBJECTIVES

To evaluate detection of post-traumatic placental abruption with contrast-enhanced CT (CECT) and comparison with Ultrasound (US).

METHODS

Picture Archive and Date System database at a level-1 trauma center was retrospectively reviewed using keywords pregnancy, trauma, and/or placental abruption over 10 years. CT was compared to US, if performed within 24 h. Two subspecialty-trained radiologists blindly reviewed the studies. Placental features on delivery and pregnancy outcomes were used as reference standard. Lack of adverse pregnancy/fetal outcome was treated as the absence of abruption.

RESULTS

CECT was performed in 36 patients, with 27 US within 24 h. There were three complete and eight partial abruptions. Reader sensitivity for CT was 100% for both reviewers; however, specificity was 54.5% and 56.7%. No sonographic abnormality was noted in both partial and complete abruption. Using kappa statistics, inter-observer agreement was low for both CT (0.169) and US (0.078). False-positive reads were from misinterpretation of normal placental structures like cotyledons, age-related infarcts, and marginal sinus of the placenta.

CONCLUSIONS

CECT identifies post-traumatic placental abruption with high sensitivity but low specificity for clinically significant abruptions, and performs better than US. Pitfalls from normal placental structures mimicking abruption should be avoided. US markedly underdiagnoses abruption.

Comparing different methods for estimating radiation dose to the conceptus

PURPOSE

To compare different methods available in the literature for estimating radiation dose to the conceptus (D_conceptus) against a patient-specific Monte Carlo (MC) simulation and a commercial software package (CSP).

METHOD

Eight voxel models from abdominopelvic CT exams of pregnant patients were generated. D_conceptus was calculated with an MC framework including patient-specific longitudinal tube current modulation (TCM). For the same patients, dose to the uterus, D_uterus, was calculated as an alternative for D_conceptus, with a CSP that uses a standard-size, non-pregnant phantom and a generic TCM curve. The percentage error between D_uterus and D_conceptus was studied. Dose to the conceptus and percent error with respect to D_conceptus was also estimated for three methods in the literature.

RESULTS

The percentage error ranged from -15.9% to 40.0% when comparing MC to CSP. When comparing the TCM profiles with the generic TCM profile from the CSP, differences were observed due to patient habitus and conceptus position. For the other methods, the percentage error ranged from -30.1% to 13.5% but applicability was limited.

CONCLUSIONS

Estimating an accurate D_conceptus requires a patient-specific approach that the CSP investigated cannot provide. Available methods in the literature can provide a better estimation if applicable to patient-specific cases.

KEY POINTS

• A patient's internal anatomy affects the dose to the conceptus. • Conceptus position has an influence on its dose estimation. • Patient anatomy and specific TCM must be considered for accurate conceptus dosimetry. • D _uterus to a standard-size phantom should not be used as D _conceptus .