Fetal Radiation Dose in Common Diagnostic Radiology Procedures for Pregnant Patients: Findings from In-Phantom Measurements

Abstract

The diagnosis of emergent conditions during pregnancy can be delayed due to insufficient knowledge of fetal radiation doses in different imaging modalities. The aim of this article is to investigate the ranges of fetal doses in most common diagnostic and interventional radiology procedures. Procedures were carried out on an anthropomorphic phantom, Tena, representing a pregnant woman in the 18th week of pregnancy with the fetus in breech position. Different clinical scenarios using computer tomography (CT), radiography, fluoroscopy and digital subtraction angiography were selected in three teaching hospitals. Measurements were performed using radiophotoluminescent glass dosimeters placed in dedicated holes in the fetal head and fetal body. Measured fetal doses were below 1 mGy when the fetus was not in the primary beam. The highest fetal doses, up to 47 mGy, were measured after a CT scan for polytrauma and up to 24 mGy after a CT scan of the abdomen and pelvis. Significant variability in fetal doses for the same procedure was found between different hospitals but within the same hospital also. All obtained results are below the threshold for deterministic effects given by the International Commission for Radiation Protection but can be reached with two or more imaging procedures employed. The variability in fetal doses for the same procedures highlights the need for the improved optimization of imaging protocols.

1. Introduction

Emergent, potentially life-threatening conditions during pregnancy can also be of non-obstetric etiology. Due to the physiological and anatomical changes that occur during pregnancy, the female body becomes five times more susceptible to thrombotic incidents, with venous thromboembolism being the leading cause of maternal death in developed countries [1,2,3]. Pregnancy-associated stroke is known to cause 18% of strokes in women under the age of 35, causing up to 15% of the deaths of pregnant women worldwide [4,5,6]. Other potentially life-threatening conditions can be singled out, such as appendicitis, being the most common non-obstetric complication in pregnancy that requires surgical intervention with a reported frequency of 1 in 500–2000 pregnancies [7]. The second most common cause of acute abdomen that requires surgical treatment in pregnant women is cholecystitis, with the incidence being the same as that in the general population [8,9]. Nephrolithiasis is also one of the causes of abdominal pain in pregnancy, with the reported incidence varying from 1 in 250 to 300 [10]. Furthermore, 1 in 12 pregnant women experience trauma during pregnancy, which often requires the use of extensive diagnostics [11].

Although current guidelines state that diagnostic imaging procedures using ionizing radiation should not be avoided in pregnant patients if there is a good risk–benefit ratio, the diagnosis of such conditions can often be delayed due to the fear of using ionizing radiation during pregnancy and the unavailability of other diagnostic modalities such as magnetic resonance imaging [12,13]. A lack of knowledge coupled with patients’ fears can result in the avoidance of procedures or even unnecessary pregnancy terminations, underscoring the importance of knowledge of fetal doses in different clinical scenarios, as well as optimization of the procedures [14,15]. This fear is present due to a known deterministic effect on fetuses which occurs with doses above 100 mGy and includes growth restriction, cognitive impairment, congenital malformations, etc. [16]. Besides deterministic effects, stochastic effects may occur. For stochastic effects, no dose threshold exists, but the risk increases with radiation dose. It has been reported that with higher fetal doses such as doses delivered during a CT scan of the pelvis, the risk of carcinogenesis increases, but it is still low in absolute terms, approximately 1 in 250 [17].

It is considered unethical to conduct dosimetry experiments involving ionizing radiation on pregnant patients due to the potential risks to the fetus. Instead, researchers often rely on phantom measurements, computational models, or some other fetal dose estimation methods, reporting a wide range of values for different scanning protocols [18,19,20,21,22].

The aim of this study was to investigate the range of fetal doses in the most common clinical scenarios using diagnostic and interventional radiology procedures during pregnancy in three large teaching hospitals. The obtained data will contribute to the general knowledge of fetal doses in different clinical scenarios and reasons for their variations. This will help in raising awareness about the need for the optimization of radiological procedures and can help to avoid unnecessary delays in providing the necessary diagnostic procedures in pregnancy in some cases.

2. Materials and Methods

The imaging procedures were carried out on an anthropomorphic phantom, Tena, representing a pregnant woman in the 18th week of pregnancy with the fetus in breech position in the uterus [23,24]. The phantom includes the head and neck, thorax, abdomen, and pelvis to the proximal thighs. It is 88.9 cm high, without holding brackets, and divided into 18.5 cm thick slices. It consists of three types of substitute tissues, soft tissue substitution (STS), bone tissue substitution (BTS), and lung tissue substitution (LTS), as seen in Figure 1, with the physical and radiological properties listed in Table 1.

Research was conducted in two large teaching hospitals in Croatia and one in Italy (herein randomly named Hospital 1, Hospital 2, and Hospital 3). Considering the occurrence of non-obstetric emergencies in pregnancy, five clinical scenarios were selected for the research in the first stage in Hospital 1—nephrolithiasis/ileus/abdominal pain, nephrostomy placement due to nephrolithiasis/urolithiasis, polytrauma, pulmonary embolism, and ischemic stroke. Conventional radiography, CT, fluoroscopy, and fluoroscopy/digital subtraction angiography were chosen as imaging modalities.

For the clinical scenario of non-specific abdominal pain, two protocols were simulated—abdomen and pelvis radiography in two positions and non-contrast CT (NCCT) of the abdomen and pelvis, with a scanning volume from the lung bases to the greater trochanters. Pulsed fluoroscopy was simulated in a clinical scenario of nephrostomy tube placement. In a clinical scenario of polytrauma, an institutional protocol was used consisting of a non-contrast CT of the head and cervical spine, thorax and abdomen (simulating arterial phase), and abdomen and pelvis (simulating venous phase). CT angiography (CTA) of the pulmonary arteries with bolus tracking (5×) was simulated in a clinical scenario of pulmonary embolism. For the clinical scenario of ischemic stroke, a stroke protocol for diagnosis was simulated consisting of an NCCT of the head and CTA of the aortic arch up to the vertex. In the therapeutic part, a mechanical thrombectomy for stroke was simulated, consisting of pulsed fluoroscopy for selective catheterization and mechanical thrombectomy with two passes of aspiration catheter and a DSA for pre- and post-procedural angiography. This simulation was based on a real-life stroke case in a female of a similar age to the physical phantom patient’s age.

Selected clinical scenarios, imaging modalities, used devices, scanning protocols, and imaging parameters used in Hospital 1 are summarized in Table 2.

Significant fetal doses were expected only in clinical scenarios with the fetus in the primary beam [14,18,19,20,21,22], and these scenarios were further investigated in all three hospitals. Fetal doses were measured for conventional radiography of the abdomen, CT of the abdomen, and CT for polytrauma in an additional 3 radiography and 7 CT units in all hospitals using their own protocols. Selected clinical scenarios, imaging modalities, equipment used, scanning protocols, and imaging parameters are summarized in Table 3 for all three hospitals.

Tena phantom is designed to have 51 possible dosimetry positions in total. For this specific research, dosimeters were positioned only in place of the fetal head and fetal body. Measurements were made using radiophotoluminescent (RPL) dosimeters (ATGC, Tokyo, Japan) which are silver-activated phosphate glass rods encapsulated in plastic holders. In recent years, RPL glass dosimeters have been recognized and more widely used as they possess good characteristics such as low fading effects, excellent dose linearity, no need for individual sensitivity correction factor, and they are easy to handle. In our previous study, the energy dependence of the GD-352M RPL dosimeter system in air was found to be better than that of the TLD systems for N-series quality beam [25]. One of their main advantages over the conventionally used TLD is the possibility for multiple readout repeatability which enhances measurement accuracy. In this study, GD-352M types were used, consisting of a glass rod (Φ 1.5 mm × 12 mm) packed in a plastic holder (Φ 4.3 × 14.5 mm). A plastic holder contains an energy compensation filter necessary for dosimetry in medium- and low-energy photon fields usually used in diagnostic radiology. The RPL measurements were performed with a Dose Ace FGD-1000 reader (ATGC, Tokyo, Japan) [26]. The calibration of dosimeters was performed in the 137Cs gamma field in the “Secondary Standard Dosimetry Laboratory” (SSDL) of the Ruđer Bošković Institute, Zagreb, Croatia [27]. Results are expressed as absorbed dose to water. For the dose range in this study, the uncertainty of RPL dosimeters is ~2.1% [25]. More information about the characterization and measuring cycle of RPL dosimeters can be found in Knežević et al., 2011 and 2013 [25,28]. Due to time limitations when performing measurements in hospitals, only three measurements per protocol and per unit for all clinical scenarios and hospitals were performed in order to have as many protocols and units included. The results were presented as a mean of three measurements. The uncertainty in the estimate of the mean was quantified and presented by standard error of the mean (SEM).

3. Results

Fetal doses measured in each clinical scenario in Hospital 1 are listed in Table 4.

Since, as expected, measured fetal doses were always below 1 mGy if the fetus was not in the primary beam, only clinical scenarios with a fetus in the primary beam were additionally investigated. Fetal doses in all clinical scenarios with the fetus positioned in the primary beam are presented in Figure 2 for all three hospitals.

The highest measured absorbed dose in the fetus was measured in a polytrauma CT scan scenario (consisting of head, cervical spine, thorax/abdomen, and pelvis CT) resulting in absorbed doses to the fetal head and to the fetal body of 45.7 mGy and 47.4 mGy, respectively.

4. Discussion

The simulation of the most frequent clinical scenarios involving pregnant patients and ionizing radiation diagnostic and interventional procedures (Table 2) showed a large range of possible fetal doses (Table 4) in these procedures. Nevertheless, in scenarios when the fetus is not in the primary beam, such as CTPA, CT for ischemic stroke, nephrostomy placement, or two-pass mechanical thrombectomy, the fetal head and body doses were well below 1 mGy (Table 4). This is in line with already reported values [18,19,20,21,22,30,31,32]. Such radiation doses further reinforce the fact that these procedures should not be postponed if the only contraindication is fear of fetal radiation.

Since fetal dose estimation is usually not necessary unless the dose to the fetus is expected to be above 1 mGy [14,15,20], further investigation of fetal doses was focused on clinical scenarios with a fetus within the beam. These scenarios included abdominal radiography and CT for polytrauma in three large teaching hospitals using four radiography units and eight CT units (Table 3).

Measured fetal doses ranged from 0.9 mGy to 1.9 mGy in abdominal radiography (Figure 2). This is in line with previous findings where fetal doses of up to 3 mGy were reported [17]. Although fetal doses in abdominal radiography were rather consistent in all three hospitals, it is worth noting that different imaging protocols were used. Protocols consisted of one or two patient positions. This difference was found between hospitals, but also in Hospital 1 (Table 3). Although still in use, abdominal radiography is of limited diagnostic value in a patient presenting with abdominal pain. According to the guidelines, anteroposterior projection with a patient in the supine position is a preferred method, used in a clinical scenario of suspected bowel obstruction and urinary tract calculosis [33]. If there is a clinical suspicion of possible bowel perforation, additional anteroposterior projection with a patient in an erect position adds valuable clinical information; therefore, in several instances in this study, both patient positions were used. This underlines importance of a clear clinical question in referral. Nevertheless, the largest fetal dose was found in Hospital 2, which used imaging in only one patient position. This shows that attention toward the optimization of imaging procedures is required.

When a clinical question for abdominal pain was set, NCCT was a preferred scanning protocol since it also allows for the detection of urinary tract calculi, which might not always be detected on post-contrast scans. After the evaluation of NCCT scans, the radiologist might add an additional scan in the post-contrast arterial or portovenous phase. Although the standardization of all protocols is of utmost importance, it is particularly challenging in a pregnant patient, where the presentation of various clinical scenarios can differ from a non-pregnant patient. Therefore, individualized scanning protocols based on relevant clinical information are often used. In Hospital 2, a specific low-dose protocol for kidney stones was used with the low fetal dose of 2.2 mGy in one CT unit. All abdomen protocols used were routine abdomen protocols with fetal doses ranging from 8.6 mGy to 23.7 mGy (Figure 2). This reveals a fetal dose max/min ratio of approximately three if the procedure is performed in a different hospital or even in the same hospital, but on a different unit.

Similar findings to those in CT for abdominal pain were found in CT for polytrauma (Figure 2). The dose ranged from 15.9 mGy to 47.4 mGy when all hospitals and all eight CT units were taken into account. These differences are mainly due to different protocols with different numbers of phases used (Table 3). This was expected since a whole-body tomography scan is performed in various protocols and there is no agreement as to which protocol is optimal in an emergency situation [34,35]. An unenhanced scan is sometimes built into the protocol [36,37], but the Royal College of Radiologists [38] is of the opinion that an unenhanced scan of the body is of no benefit to polytrauma patients. Nevertheless, a narrower range of fetal doses was found in polytrauma than in abdominal CT within the same hospitals. This is due to the similar CT protocols used within one hospital for polytrauma, while for abdominal CT, protocols differed in doses per phase, but also in the number of phases (Table 3). This again shows the need for the optimization and harmonization of radiological practice.

The results presented in this study are always below 100 mGy, which is the threshold for deterministic effects indicated by the International Commission for Radiation Protection [14]. Nevertheless, in the case of repeated CT procedures of the abdomen or additional phases used, fetal doses could reach higher values that could lead to possible deterministic radiation effects on the fetus. Since different clinical scenarios justify the use of the aforementioned diagnostic procedures, especially in the case of scarce diagnostic information gained from ultrasound examination and/or the inadequacy of magnetic resonance imaging [12,13], it is important to use well-optimized imaging protocols. This underlines another finding of this study: large variability in fetal doses for the same procedures between different hospitals, but also within the same hospital. Besides large fetal dose differences, this can also imply significant differences in diagnostic information obtained. Although the fetal risk of developing malignant disease in childhood is small, it can be changed using different protocols, which raises the importance of the implementation of strategies for reducing radiation exposure, without compromising the quality of diagnostic data obtained [19].

Through using the freely available, inexpensive physical phantom, Tena, developed by our group [23,24], fetal dosimetry data in diagnostic imaging procedures were further improved. Additionally, the fetal dose dependance of imaging protocols was confirmed. Nevertheless, exposure of the fetus also depends on the gestational age, maternal body habitus, and fetal depth. In addition, a fetus in the second trimester can freely move within the placenta, and there is a possibility that the radiation dose for fetuses in the cephalic position could differ for different positions. For this reason, further studies of fetal dose for differently constructed phantoms and acquisition parameters are needed.

Patient doses in diagnostic and interventional radiology procedures are optimized, and in most imaging modalities, reduced nowadays. This calls for repeated measurements of patient doses. The results presented in this work could help to better understand the radiation safety of pregnant patients and improve radiation protection measures and the optimization of imaging procedures for pregnant patients. The obtained data contribute to the general knowledge of fetal doses during diagnostic and interventional radiology procedures and to the prevention of unnecessary delays in providing the necessary procedures in pregnancy. Additionally, the presented variability in fetal doses for the same procedures highlights the need for the improved optimization of imaging protocols.

Author Contributions

Conceptualization, D.F., A.T. and V.K.; methodology, H.B., I.K., M.K., Ž.K., M.M., M.H. and T.T.; validation, I.B. and M.Š.; formal analysis, D.F. and Z.M.; investigation I.B., I.K., F.D.M., N.Z. and R.L.; data curation, All; writing—original draft preparation, A.T., V.K. and D.F.; writing—review and editing, all; supervision, D.F.; project administration, H.B.; funding acquisition, D.F. and H.B. All authors have read and agreed to the published version of the manuscript.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Footnotes

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Figures and Tables

Table 1

Physical and radiological properties of substitution tissues used in the Tena physical phantom. PU—polyurethane, HU—Hounsfield units, Z_eff—effective atomic number.

Anatomical Region	Head, Neck, Thorax, Abdomen, Pelvis, Proximal Parts of the Thighs
Height (cm)/Mass (kg)	88.9/49.7
Substitutional Tissues
STS	PU rubber, CaCO3
Mass density (g/cm3)	1.03
CT number (HU)	30 ± 5
Zeff	6.94
BTS	Epoxy resin, CaCO3, SiO2
Mass density (g/cm3)	1.274
CT number (HU)	450 ± 45
Zeff	10.78
LTS	STS, polystyrene (Styrofoam) balls
Mass density (g/cm3)	0.29
CT number (HU)	−750 ± 80
Zeff	6.9

Table 2

Clinical scenarios performed in Hospital 1, imaging modalities, scanning protocols, and imaging parameters used in Hospital 1. N/A—not available, CT—computed tomography, NCCT—non-contrast CT, CECT—contrast-enhanced CT, CTA—CT angiography, PA—pulmonary artery, MT—mechanical thrombectomy, DSA—digital subtraction angiography.

Clinical Scenario	Imaging Modality	Unit	Imaging Protocol	Imaging Parameters
Non-specific abdominal pain	Radiography	Siemens Luminos dRF Max	Abdomen and pelvis in two positions	80.8 kV; 18.85 mAs
				72.9 kV; 40.7 mAs
Nephrostomy tube placementNephro/urolithiasis	Fluoroscopy	Siemens Uroskop Omnia Max	Pulsed fluoroscopy, collimated field	N/A
Nephrolithiasis, appendicitis, abdominal pain	CT	GE Revolution Frontier	NCCT abdomen and pelvis (lung bases—great trochanters)	120 kV; auto mAs (range 50–750); noise index 13.3; section thickness 5 mm; pitch 1.375:1
Polytrauma	CT	GE Revolution Frontier	NCCT head	120 kV; auto mAs (range 100–335); noise index 3.23; section thickness 2.5 mm; pitch 0.531:1
			NCCT C spine	120 kV; 335 mAs; section thickness 0.625 mm; pitch 0.516:1
			CECT (35 s) thorax and abdomen	120 kV; auto mAs (range 100–600), noise index 18; section thickness 5 mm; pitch 1.375:1
			CECT (75 s) abdomen and pelvis	120 kV; auto mAs (range 100–600), noise index 18; section thickness 5 mm; pitch 1.375:1
Pulmonary embolism	CT	GE Revolution Frontier	CT angiography of PA with “bolus tracking” (5×)	120 kV; auto mAs (range 150–800); noise index 28; section thickness 0.625 mm; pitch 1.375:1
Ischemic stroke	CT	GE Revolution Frontier	NCCT head	120/140 kV; 400/600 mAs;
			CTA aortic arch–vertex	120 kV; auto mAs (range 80–700), noise index 8.94; section thickness 1.25 mm; pitch 0.984:1
	Fluoroscopy and DSA	Philips Azurion	2 pass MT:Pulsed fluoroscopy for selective catheterization and MTDSA run for pre- and post-procedure angiography (6 fps)	75 kV; 7–22 mAsRotation 0°, LAO 45°, LAO 89°Angulation: 0° and CRAN 15°SID: 100–111 cm

Table 3

Clinical scenarios, imaging modalities, scanning protocols, and imaging parameters used in dosimetry measurements. CT—computed tomography, NCCT—non-contrast CT, CECT—contrast-enhanced CT. Radiography and CT units are labeled to facilitate its use further in the figures.

Clinical Scenario	Imaging Modality	Hospital	Unit	Imaging Protocol	Imaging Parameters
Non-specific abdominal pain	Radiography	1	Siemens Luminos (R1)	Abdomen and pelvis in two positions	80.8 kV; 18.85 mAs
					72.9 kV; 40.7 mAs
		1	Siemens Ysio Max (R2)	Abdomen and pelvis in AP projection	72.9 kV; 34.99 mAs
		2	Siemens Luminos (R1)	Abdomen and pelvis in AP projection	72.9 kV; 62.44 mAs
		3	Siemens Aristos (R1)	Abdomen and pelvis in two positions	81 kV; 22 mAs
					81 kV; 76 mAs
Nephrolithiasis, appendicitis, abdominal pain	CT	1	GE Revolution Frontier (CT1)	NCCT abdomen and pelvis (lung bases—great trochanters)	120 kV; CTDI 17.0 mGy; DLP 846 mGycm
		1	Siemens Definition As (CT2)	NCCT abdomen and pelvis (lung bases—great trochanters	120 kV; CTDI 7.1 mGy; DLP 334 mGycm
		1	Philips Ingenuity (CT3)	NCCT abdomen and pelvis (lung bases—great trochanters	140 kV; CTDI 14.3 mGy; DLP 744 mGycm
		1	Siemens X.cite (CT4)	NCCT abdomen and pelvis (lung bases—great trochanters	120 kV; CTDI 10.2 mGy; DLP 513 mGycm
		2	Siemens X.cite (CT1)	NCCT abdomen and pelvis (lung bases—great trochanters	120 kV; CTDI 10.8 mGy; DLP 585 mGycm
		2	Siemens Definiton As (CT2)	NCCT abdomen and pelvis (lung bases—great trochanters	80 kV; CTDI 1.7 mGy; DLP 100 mGycm
		3	GE Revolution EVO (CT1)	NCCT abdomen and pelvis (lung bases—great trochanters	120 kV; CTDI 14.5 mGy; DLP 810 mGycm
		3	Siemens Definiton Edge (CT2)	NCCT abdomen and pelvis (lung bases—great trochanters	120 kV; CTDI 10.1 mGy; DLP 566 mGycm
Polytrauma	CT	1	GE Revolution Frontier (CT1)	NCCT head	120 kV; CTDI 62.9 mGy; DLP 1035 mGycm
				NCCT C spine	120 kV; CTDI 36.4; DLP 735 mGycm
				Art CECT thorax and abdomen	120 kV; CTDI 8.0 mGy; DLP 435 mGycm
				Venous CECT abdomen and pelvis	120 kV; CTDI 12.4 mGy; DLP 628 mGycm
		1	Philips Ingenuity (CT3)	NCCT head and neck	120 kV; CTDI 49.0 mGy; DLP 1064 mGycm
				Venous CECT thorax and abdomen and pelvis	120 kV; CTDI 12.0 mGy; DLP 878 mGycm
		1	Siemens X.cite (CT4)	NCCT head	120 kV; CTDI 73.0 mGy; DLP 1142 mGycm
				NCCT C spine	90 kV; CTDI 19.3 mGy; DLP 354 mGycm
				Venous CECT thorax and abdomen and pelvis	120 kV; CTDI 10.8 mGy; DLP 747 mGycm
		2	Siemens X.cite (CT1)	NCCT head	120 kV; CTDI 56.4 mGy; DLP 1335 mGycm
				NCCT C spine	120 kV; CTDI 16.8 mGy; DLP 359 mGycm
				NCCT thorax and abdomen and pelvis	120 kV; CTDI 9.5 mGy; DLP 669 mGycm
				Venous CECT thorax and abdomen and pelvis	100 kV; CTDI 7.8 mGy; DLP 535 mGycm
		2	Siemens Definiton As (CT2)	NCCT head	120 kV; CTDI 68.5 mGy; DLP 1450 mGycm
				NCCT C spine	120 kV; CTDI 11.5 mGy; DLP 224 mGycm
				NCCT thorax and abdomen and pelvis	120 kV; CTDI 8.4 mGy; DLP 571 mGycm
				Venous CECT thorax and abdomen and pelvis	100 kV; CTDI 8.4 mGy; DLP 575 mGycm
		3	GE Revolution EVO (CT1)	NCCT head and neck	120 kV; CTDI 55.0 mGy; DLP 980 mGycm
				NCCT thorax and abdomen and pelvis	100 kV; CTDI 10.5 mGy; DLP 880 mGycm
				Art CECT thorax and abdomen and pelvis	100 kV; CTDI 10.5 mGy; DLP 880 mGycm
				Venous CECT thorax and abdomen and pelvis	100 kV; CTDI 10.5 mGy; DLP 880 mGycm
		3	Siemens Definition Edge (CT2)	NCCT head and neck	120 kV; CTDI 77.0 mGy; DLP 1960 mGycm
				NCCT thorax and abdomen and pelvis	120 kV; CTDI 10.0 mGy; DLP 730 mGycm
				Art CECT thorax and abdomen and pelvis	120 kV; CTDI 10.0 mGy; DLP 560 mGycm
				Venous CECT thorax and abdomen and pelvis	120 kV; CTDI 10.0 mGy; DLP 560 mGycm

Table 4

Absorbed dose for each specific clinical scenario measured in the fetal head and body. CT—computed tomography, DSA—digital subtraction angiography.

Clinical Scenario	Imaging Modality	Unit	Fetal Dose—Head (mGy)	Fetal Dose—Body (mGy)
Non-specific abdominal pain	Radiography	Siemens Luminos dRF Max	1.6	1.9
Nephrostomy tube placementnephro/urolithiasis	Fluoroscopy	Siemens Uroskop Omnia Max	0.5	0.1
Nephrolithiasis, appendicitis, abdominal pain	CT	GE Revolution Frontier	23.7	19.6
Polytrauma	CT	GE Revolution Frontier	34.7	32.5
Pulmonary embolism	CT	GE Revolution Frontier	0.3	0.2
Ischemic stroke	CT	GE Revolution Frontier	0.05	0.03
	Fluoroscopy and DSA	Philips Azurion	0.0	0.02

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