In vitro measurements of radiation exposure with different modalities (computed tomography, cone beam computed tomography) for imaging the petrous bone with a pediatric anthropomorphic phantom.

BACKGROUND: Various imaging modalities, such as multi-detector computed tomography (CT) and cone beam CT are commonly used in infants for the diagnosis of hearing loss and surgical planning of implantation hearing aid devices, with differing results. OBJECTIVE: We compared three different imaging modalities available in our institution, including a high-class CT scanner, a mid-class CT scanner and an angiography system with a cone beam CT option, for image quality and radiation exposure in a phantom study. MATERIALS AND METHODS: While scanning an anthropomorphic phantom imitating a 1-year-old child with vendor-provided routine protocols, organ doses, surface doses and effective doses were determined for these three modalities with thermoluminescent dosimeters. The image quality was evaluated using the signal difference to noise ratio (SDNR) and the spatial resolution of a line-pair insert in the phantom head. The dose efficiency, defined as the ratio of SDNR and effective dose, was also compared. RESULTS: The organ and surface doses were lowest with the high-class CT protocol, but the image quality was the worst. Image quality was best with the cone beam CT protocol, which, however, had the highest radiation exposure in this study, whereas the mid-class CT was in between. CONCLUSION: Based on our results, high-end CT should be used for surgical planning because it has the lowest dose, while the image quality is still sufficient for this purpose. However, if highest image quality is needed and required, e.g., by ENT surgeons, the other modalities should be considered.

Modification of chest radiography exposure parameters using a neonatal chest phantom.

BACKGROUND: The acquisition of chest radiographs in neonates is of critical importance in diagnostics because of the risk of respiratory distress syndrome and pneumothorax in preterm infants. OBJECTIVE: To achieve a dose reduction while preserving a diagnostic image quality for chest radiographs of neonates. MATERIALS AND METHODS: All radiographs, generated on a fully digital X-ray unit by using a neonatal chest phantom, were evaluated under variation of the tube voltage (40-70 kV) and mAs levels (1-10.2 mAs) with and without an additional 0.1-mm copper (Cu) filtration. Noise, contrast and contrast-to-noise ratio for bronchus, heart, lungs and vessels were determined. Visual assessment of the image quality was carried out by three radiologists using a Likert scale. To evaluate a maximally possible dose reduction, the dose of the radiographs with still acceptable image quality at a minimal dose was compared to the dose of the radiographs with the standard settings used in clinical routine. RESULTS: The noise showed decreasing values with increasing dose, while the contrast values were increased. For the contrast-to-noise ratio, a digressive course of the values as a function of the tube voltage was found. The visual evaluation of image quality showed the best evaluation of the structures at the lowest possible dose in the settings (44 kV, 3.36 mAs) with copper filtration and in the settings (44 kV, 1.56 mAs) without copper filtration. A maximum dose reduction from 8.29 µSv to 2.21 µSv (about 73%) was obtained. CONCLUSION: A dose reduction while preserving diagnostic image quality in a digital X-ray system is generally possible by reducing the tube voltage and simultaneous adaptation of the mAs settings.

PAE planning: Radiation exposure and image quality of CT and CBCT.

PURPOSE: To determine accurate organ doses, effective doses, and image quality of computed tomography (CT) compared with cone beam CT (CBCT) for correct identification of prostatic arteries. METHOD: A dual-energy CT scanner and a flat-panel angiography system were used. Dose measurements (gallbladder (g), intestine (i), bladder (b), prostate (p), testes (t), active bone marrow of pelvis (bmp) and femura (bmf)) were performed using an anthropomorphic phantom with 65 thermoluminescent dosimeters in the pelvis and abdomen region. For the calculation of the contrast-to-noise ratio (CNR) of the pelvic arteries, a patient whose weight and height were almost identical to those of the phantom was selected for each examination type. RESULTS: The effective dose of CT was 2.7 mSv and that of CBCT was 21.8 mSv. Phantom organ doses were lower for CT than for CBCT in all organs except the testes (g: 1.2 mGy vs. 3.3 mGy, i: 5.8 mGy vs. 23.9 mGy, b: 6.9 mGy vs. 19.4 mGy, p: 6.4 mGy vs. 13.2 mGy, t: 4.7 mGy vs. 2.4 mGy, bmp: 5.1 mGy vs. 18.2 mGy, bmf: 3.3 mGy vs. 6.6 mGy). For human pelvic arteries, the CNR of CT was better than that of CBCT, with the exception of one prostate artery that showed stenosis on CT. Evaluation by experienced radiologists also confirmed the better detectability of prostate arteries on CT examination. CONCLUSIONS: In our study preprocedural CT had lower organ doses and better image quality comparedd with CBCT and should be considered for the correct identification of prostatic arteries.

Image Guided Intraoperative Radiation Therapy After Surgical Resection of Brain Metastases: A First In-Human Feasibility Report.

Purpose: A correct placement of the applicator during intraoperative radiation therapy for brain metastasis is of paramount importance, to deliver a precise and safe treatment. The applicator-to-surface contact assessment cannot be performed under direct observation because the applicator itself limits the visual range. No image guided verification is currently performed intracranially. We hypothesize that image guided intraoperative radiation therapy would assure a more precise delivery in the target area. We describe our workflow in a first in-human experience. Methods and Materials: Phantom-based measurements were performed to reach the best cone beam computed tomography imaging quality possible. Once defined, a clinical feasibility study was initiated. An in-room cone beam computed tomography device is used to acquire intraoperative images after placing the applicator. Repositioning the applicator is thereafter discussed with the surgeon, according to the imaging outcomes, if required. Results: An optimal image quality was achieved with 120-kV voltage, 20-mA current, and a tube current time product of 150 mAs. An additional 0.51 mSv patient exposure was calculated for the entire procedure. The wide dynamic range (-600 HU to +600 HU) of cone beam computed tomography and a 27 HU mean computed tomography values difference between brain tissue and spherical applicator allows distinguishing both structures. In this first in-human experience, the applicator was repositioned after evidencing air gaps, assuring full applicator-to-surface contact. Conclusions: This first in-human procedure confirmed the feasibility of kilovoltage image guided intraoperative radiation therapy in a neurosurgical setting. A prospective study has been initiated and will provide further dosimetric details.

Radiology meets archaeology: digital restoration and 3D printing using CT data. / Radiologie trifft Archäologie: Restaurierung und 3D-Druck anhand von CT-Daten.

AIM: Archaeological objects are often recovered in blocks since highly porous materials and unstable and highly decayed objects cannot always be uncovered undamaged or time and resources for classic uncovering are lacking. Therefore, clinical computed tomography (CT) combined with freely available software solutions should be tested as a simple and fast method for visualizing and analyzing archaeological finds as an alternative to time-consuming restoration. MATERIALS AND METHODS: As an example, a block with a shield boss was selected from a block excavation and examined by means of CT. Using the freely available software 3D-Slicer (https://www.slicer.org/), the shield boss and handle were segmented in the surrounding soil with different tools. They were then digitally reconstructed and then restored using Meshmixer (Autodesk Inc., San Francisco, CA). A 3D print was generated based on the reconstructed model of the shield boss. RESULTS: The individual steps of CT examination of the block recovery, segmentation, reconstruction, and 3D printing were successfully performed. Based on the restored fragments of the shield boss, it was possible to date the object and to determine the initial properties of the find non-destructively without classic restoration. CONCLUSION: Radiological imaging combined with digital reconstruction and 3D printing makes it possible to determine decisive characteristics of the archaeological find before it is uncovered and restored, which is a time-consuming process. This opens up new opportunities for cooperation between radiology and archaeology for the evaluation and analysis of archaeological finds. KEY POINTS: · "The transfer of medical technology, digital image processing and 3D printing to archaeology has been demonstrated.". · "The digital restoration and reconstruction of archaeological objects using CT images is possible.". · "Medical imaging could make a significant contribution to the investigation and reconstruction of archaeological objects.". CITATION FORMAT: · Frohwerk E, Dürr A, Fiebich M et al. Radiology meets archaeology: digital restoration and 3D printing using CT data. Fortschr Röntgenstr 2023; DOI: 10.1055/a-2206-5741.

Comparison of the radiation protection effect of different radiation protection aprons made of different materials.

OBJECTIVE: The objective of this study is to examine the performance of new generation protection aprons as alternative to conventional lead aprons regarding their radiation protection effectiveness. METHOD AND MATERIALS: Radiation protection aprons made of lead-containing and lead-free materials from a total of seven companies were compared. Furthermore, different lead equivalent values of 0.25, 0.35 and 0.5 mm were compared. For quantitative assessment, radiation attenuation was determined with increasing voltage in steps of 20 kV from 70 kV up to 130 kV. RESULTS: New generation aprons and conventional protection lead aprons showed a similar shielding performance at lower tube voltages below 90 kVp. When tube voltage was increased above 90 kVp, significant (p < 0.05) differences between the three apron types were observed, with conventional lead material as best shielding performer over lead composite and lead-free aprons. CONCLUSION: We observed a similar radiation protection performance between conventional lead aprons and new generation aprons at low intensity radiation workplaces, with lead aprons being dominant for all energies. Only new generation aprons of 0.5 mm thickness would adequately replace 0.25 and 0.35 mm conventional lead aprons. For healthy radiation protection, the possibility of using weight-reduced X-ray aprons is very limited.

CAN THE SIZE-SPECIFIC DOSE ESTIMATE BE DERIVED FROM THE BODY MASS INDEX? A FEASIBILITY STUDY.

Size-specific dose estimate ($\mathbf{SSDE}$) index appears to be more suitable than the commonly used volume computed tomography dose index ($\mathbf{C}{\mathbf{TDI}}_{\mathbf{vol}}$) to estimate the dose delivered to the patient during a computed tomography (CT) scan. We evaluated whether an ${\mathbf{SSDE}}_{\mathbf{BMI}}$ can be determined from the patient's body mass index ($\mathbf{BMI}$) with sufficient reliability in the case that a $\mathbf{SSDE}$ is not given by the CT scanner. For each of the three most used examination types, CT examinations of 50 female and 50 male patients were analyzed. The $\mathbf{SSDE}$ values automatically provided by the scanner were compared with ${\mathbf{SSDE}}_{\mathbf{BMI}}$ determined from $\mathbf{C}{\mathbf{TDI}}_{\mathbf{vol}}$ and $\mathbf{BMI}$. A good accordance of ${\mathbf{SSDE}}_{\mathbf{BMI}}$ and $\mathbf{SSDE}$ was found for the chest and abdominal regions. A low correlation was observed for the head region. The presented method is a simple and practically useful surrogate approach for the chest and abdominal regions but not for the head.

[Prenatal Radiation Exposure in Nuclear Medicine]. / Pränatale Strahlenexposition aus nuklearmedizinischer Indikation.

Radiation exposure from nuclear medicine procedures during pregnancy may cause uncertainty among patients and medical professionals. In 2019, the German Society of Medical Physics (DGMP) and the German Society of Radiology (DRG) published a fully revised version of the report "Prenatal Radiation Exposure Arising from Medical Indication, Dose Calculation, Conclusions for Physicians and Pregnant Women". This report offers a basis for dose calculation and determination of radiation exposure to the unborn. This review summarizes the most notable general adaptions made in the report's newest version and specifically points out the changes relevant to the field of nuclear medicine.The DGMP report provides physicians and medical physicists with means to estimate prenatal radiation exposure to the unborn conservatively, in a prompt and comprehensible approach. The rapidly evolving field of indications in nuclear medicine and radiology gave rise to the initiative of profoundly revising the previous version of the report from 2002. It now accounts for the extended range of devices, nuclear medicine hybrid imaging and radiotracers recently introduced. The most extensive change is a shift from the former 3-step-concept for the dose calculation to a 2-step-concept. In diagnostic nuclear medicine the first step comprises a conservative approximation of radiation exposure on the basis of current diagnostic reference levels (DRL). If exposure is assessed to be below 20 mSv, risk to the unborn child is sufficiently low, no further approaches are considered necessary. If calculated doses exceed 20 mSv, for diagnostic studies without existing DRL or in case of radionuclide therapies step 2 requires dose calculation based on administered activity and the stage of pregnancy.The DGMP report on prenatal radiation exposure offers valuable guidance for physicians and medical physicists in the field of nuclear medicine. The calculation concept provides an important basis to estimate radiation exposure to the unborn. Its extensive revision in 2019 accounts for recent scientific and technical developments and a reform of the stepwise approach to dose estimation.

Prenatal radiation exposure in diagnostic and interventional radiology. / Pränatale Strahlenexposition in der diagnostischen und interventionellen Radiologie.

BACKGROUND: The exposure of a pregnant woman to X-rays is an event that can cause uncertainty for all concerned. This review provides guidance on how to assess such a situation and how to determine the dose to the unborn child. In general, the use of X-rays in pregnant women in radiology should be avoided. If possible, alternatives should be used, or examinations postponed to a time after the pregnancy. This review gives a summary of the procedure for determining the radiation exposure of a pregnant woman. METHOD: Based on the previous report of 2002 and the literature on prenatal radiation exposure published thereafter, the DGMP/DRG report on the procedure for the assessment of prenatal radiation exposure was adapted to the current state of science and technology. RESULTS: Typically, only relatively low radiation exposures of less than 20 mSv occur for the unborn child in X-ray diagnostics in the vast majority of cases. At these dose level the additional risk of damage to the embryo or fetus caused by the radiation is low and therefore only a rough conservative estimate using tabulated values are made. Only in a few types of examination (CT and interventional radiology) higher doses values might occur in the uterus. Instead of dose estimates (step 1 in the two-step model) in these cases the calculation of dose (step 2) are required and further action by the physician may be necessary. CONCLUSIONS: During the assessment, it is useful to initially use simple conservative estimation procedures to quickly determine whether a case falls into this large group less than 20 mSv, where there is a very low risk to the unborn child. If this is the case, the pregnant woman should be informed immediately by the doctor who performed the examination/treatment. This avoids a psychological burden on the patient. The DGMP/DRG report suggests a relatively simple, clearly structured procedure with advantages for all parties involved (physician, medical physics experts, MTRA and patient). KEY POINTS: · The DGMP/DRG report on prenatal radiation exposure describes the procedure for calculating radiation exposures and the associated risks for the unborn child.. · Using the two-step model, only a simple assessment based on the first step is necessary for most prenatal radiation exposures.. · With the given tables it is possible to estimate individual risks for the unborn child taking into account the radiation exposure.. · Only in the rare case that the first estimate results in a uterine dose larger 20 mSv a more accurate calculation is necessary.. CITATION FORMAT: · Fiebich M, Block A, Borowski M et al. Prenatal radiation exposure in diagnostic and interventional radiology. Fortschr Röntgenstr 2021; 193: 778 - 786.

Feasibility of Monte Carlo simulations in quantitative tissue imaging.

PURPOSE: The feasibility of Monte Carlo simulations as a tool to facilitate quantitative image analysis is investigated by means of simulating light transport in skin phantoms. METHODS: A Monte Carlo tool is used to compare if simulated fluorescent signals show agreement with measured data. The lipophilic fluorescent probe Nile Red and dedicated skin phantoms are also used in simulations to investigate the influence of the optical properties of the skin on the signal. RESULTS: It is shown that the simulated and measured fluorescence signals show linear behavior up to a certain concentration of Nile Red. The simulations of the skin phantoms show the varying influence of single skin layers on the fluorescence signal. A calibration factor for quantitative analysis can be determined for the different skin layers. CONCLUSION: Characterizing the influence of different media on imaging signals is a primary task in developing quantitative analysis methods. Monte Carlo simulations are a useful tool to investigate imaging properties of biological specimen where quantifying signals is important. However, detailed models must be provided.

Watershed phenomena during extracorporeal life support and their clinical impact: a systematic in vitro investigation.

AIMS: Extracorporeal life support (ECLS) during acute cardiac failure restores haemodynamic stability and provides life-saving cardiopulmonary support. Unfortunately, all common cannulation strategies and remaining pulmonary blood flow increase left-ventricular afterload and may favour pulmonary congestion. The resulting disturbed pulmonary gas exchange and a residual left-ventricular action can contribute to an inhomogeneous distribution of oxygenated blood into end organs. These complex flow interactions between native and artificial circulation cannot be investigated at the bedside: only an in vitro simulation can reveal the underlying activities. Using an in vitro mock circulation loop, we systematically investigated the impact of heart failure, extracorporeal support, and cannulation routes on the formation of flow phenomena and flow distribution in the arterial tree. METHODS AND RESULTS: The mock circulation loop consisted of two flexible life-sized vascular models (aorta and vena cava) driven by two paracorporeal assist devices, resistance elements, and compliance reservoirs to mimic the circulatory system. Several large-bore antegrade and retrograde access ports allowed connection to an ECLS system for extracorporeal support. With four degrees of extracorporeal support-that for cardiac failure, early recovery, late recovery, and weaning-we investigated aortic blood flow velocity, blood flow, and mixing zones using colour-coded Doppler ultrasound in the aorta and its corresponding branches. Full retrograde extracorporeal support (3-4 L/min) perfused major portions of the aorta but did not reach the supra-aortic branches and ascending aorta, resulting in an area in the thoracic aorta demonstrating nearly stagnant blood flow velocities during cardiogenic shock and early recovery (0 ± 4 cm/s; -10 ± 15 cm/s, respectively) confined by two watersheds at the aortic isthmus and renal artery origin. Even increased ECLS flow was unable to shift the watershed towards the aortic arch. Antegrade support resulted in homogeneous flow distribution during all stages of cardiac failure but created a markedly negative flow vector in the ascending aorta during cardiogenic shock and early recovery with increased afterload. CONCLUSIONS: Our systematic fluid-mechanical analysis confirms the clinical assumption that despite restoring haemodynamic stability, extracorporeal support generates an inhomogeneous distribution of oxygenated blood with an inadequate supply to end organs and increased left-ventricular afterload with absent ventricular unloading. End-organ supply may be monitored by near-infrared spectroscopy, but an obviously non-controllable watershed emphasizes the need for additional measures: pre-pulmonary oxygenation with a veno-arterial-venous ECLS configuration can allow a transpulmonary passage of oxygenated blood, providing improved end-organ supply.

Breast phantoms for 2D digital mammography with realistic anatomical structures and attenuation characteristics based on clinical images using 3D printing.

The aim of this work was to develop a production process for breast phantoms for 2D digital mammography (DM) with realistic anatomical structures and attenuation characteristics based on clinical images using 3D printing. The presented production process is based on PolyJet 3D printing technology using a polypropylene like printing material. First, an attenuation calibration function for this material and the achievable lateral resolution of the printing process of about 200 µm was determined. Subsequently, to generate the digital 3D model of the breast phantom, the pixel intensities of the unprocessed clinical image that are related to the attenuation along the z-axis of the breast, were converted to corresponding phantom heights using the calibration function. To validate the process, an image of the 3D printed breast phantom was acquired on the full field digital mammography (FFDM) system used for calibration and compared with the clinical image in terms of anatomical structures and associated attenuation characteristics. The exposure parameters and image impression of the phantom were evaluated using five other FFDM systems of different manufacturers and types. Results demonstrated that the anatomical structures in the images and the attenuation characteristics of a female breast and the derived phantom agreed on the FFDM system used for calibration. The automatic exposure control segmentation, the automatically selected exposure parameters and the image postprocessing of the clinical and phantom image indicated a high level of conformity. As shown, the phantom is also suitable for other FFDM systems. In conclusion, an approach to produce anthropomorphic breast phantoms for DM offering realistic anatomical structures and attenuation characteristics based on clinical images was successfully developed. As shown, the phantom realistically simulated the original female breast. Therefore, it is expected that such phantoms are promising to support bridging the gap between physical-technical and diagnostic image quality assessment. In addition, they enable a variety of practical and scientific applications for which present technical phantoms are not suitable.

Development and Validation of a Life-Sized Mock Circulatory Loop of the Human Circulation for Fluid-Mechanical Studies.

Mock circulatory loops (MCLs) are usually developed for assessment of ventricular assist devices and consist of abstracted anatomical structures represented by connecting tubing pipes and controllable actuators which could mimic oscillating flow processes. However, with increasing use of short-term peripheral mechanical support (extracorporeal life support [ECLS]) and the upcoming evidence of even counteracting flow processes between the failing native circulation and ECLS, MCLs incorporating the peripheral vascular system and preserved anatomical structures are becoming more important for systematic assessment of these processes. For reproducible and standardized fluid-mechanical studies using magnetic resonance imaging, Doppler ultrasound, and computational fluid dynamics measurements, we developed a MCL of the human circulation. Silicon-based life-sized dummies of the human aorta and vena cava (vascular module) were driven by paracorporeal pneumatic assist devices. The vascular module is placed in a housing with all arterial branches merging into peripheral resistance and compliances modules, and blood-mimicking fluid returns to the heart module through the venous dummy. Compliance and resistance chambers provide for an adequate simulation of the capillary system. Extracorporeal life support cannulation can be performed in the femoral and subclavian arteries and in the femoral and jugular veins. After adjusting vessel diameters using variable Hoffmann clamps, physiologic flow rates were achieved in the supraaortic branches, the renal and mesenteric arteries, and the limb arteries with physiologic blood pressure and cardiac output (4 L/min). This MCL provides a virtually physiologic platform beyond conventional abstracted MCLs for simulation of flow interactions between the human circulation and external circulation generated by ECLS.

[Evaluation of intratherapeutic 177Lu-HA-DOTATATE treatment in neuroendocrine tumors: dosimetry with SPECT, whole-body imaging and gamma probe]. / Evaluation der intratherapeutischen Dosimetrie bei der 177Lu-HA-DOTATATE Therapie neuroendokriner Tumoren mittels SPECT, Ganzkörperszintigraphie und Gammasonde.

AIM: Peptide receptor radionuclide therapy (PRRT) with 177Lu-HA-DOTATATE has evolved as a new path in the treatment of somatostatin-receptor-expressing neuroendocrine tumors. The kidneys are proven as organs at risk and should be evaluated dosimetrically. Overlap with other organs will make dosimetry based on planar scintigraphy inaccurate. Aim of this study was to approximate the contribution of the kidneys to conjugated planar views without the use of a SPECT/CT. MATERIAL AND METHOD: An algorithm was developed to determine the kidney dose using an EXCEL (Microsoft) based program. Dosimetric data were drawn and merged from three modalities: an individually calibrated gamma probe, a whole-body scintigraphy (WBS) and SPECT-acquisitions. The method was evaluated for 85 kidneys. Kidney masses were obtained via CT volumetry. RESULTS: The developed algorithm combines data from the three modalities. The ratio of the events within a kidney-VOI and the events from the summed coronary SPECT views (kidney ROI) represents the contribution of the kidney to the whole-body kidney ROI. This fraction was calculated to 49 % (17 % - 78 %) and 45 % (18 % - 75 %) for the left and the right kidney, respectively. Quantification of activity was deduced from equalizing the WBS count with the concurrent gamma probe measurement. Monoexponential curves were fitted to the obtained kidney activities, with resulting doses of 0,13 to 0,77 Gy/GBq (average 0,36 and 0,39 Gy/GBq for the left and the right kidney). CONCLUSION: The presented method is suitable to perform kidney dosimetry by using a gamma probe and a gamma camera, without using SPECT/CT.

[Determination of the arterial input function in mouse-models using clinical MRI]. / Bestimmung der arteriellen Inputfunktion in einem Mausmodell an einem klinischen MRT-system.

Dynamic contrast enhanced Magnetic Resonance Imaging is a promising method for quantitative analysis of tumor perfusion and is increasingly used in study of cancer in small animal models. In those studies the determination of the arterial input function (AIF) of the target tissue can be the first step. Series of short-axis images of the heart were acquired during administration of a bolus of Gd-DTPA using saturation-recovery gradient echo pulse sequences. The AIF was determined from the changes of the signal intensity in the left ventricle. The native T1 relaxation times and AIF were determined for 11 mice. An average value of (1.16+/-0.09) s for the native T1 relaxation time was measured. However, the AIF showed significant inter animal variability, as previously observed by other authors. The inter-animal variability shows, that a direct measurement of the AIF is reasonable to avoid significant errors. The proposed method for determination of the AIF proved to be reliable.

Effectiveness of a new radiation protection system in the interventional radiology setting.

OBJECTIVES: The goal of this study was to examine a new weightless-like radiation protection garment regarding its radiation protection efficacy and to compare it to a conventional two-piece apron suit plus thyroid collar and standard ancillary shields. MATERIAL AND METHODS: All measurements were carried out using a clinical angiography system with a standardized fluoroscopy protocol for different C-arm angulations. An anthropomorphic torso phantom served as a scattering body. In addition, an ionization chamber was used to measure the radiation exposure on five different representative heights and at two different positions of an examiner during a typical fluoroscopic-guided intervention. RESULTS: The new weightless-like radiation protection garment and the conventional protection concept showed a mean dose reduction of 98.1% (p < 0.01) and 90.1% (p < 0.01) when compared to no shielding, respectively. By adding ancillary shields to both systems, an average reduction of 99.0% (p < 0.01) and 98.2% (p < 0.01) was found. In addition, the efficacy of both systems varied depending on the height, the C-arm angulation and position of the examiner. CONCLUSION: Combined with ancillary shields as an overall protection system, the recently introduced weightless-like radiation protection garment showed a significant better radiation protection efficacy when compared to conventional radiation protection measures.

Optimizing radiation exposure for CT localizer radiographs.

INTRODUCTION: The trend towards submillisievert CT scans leads to a higher dose fraction of localizer radiographs in CT examinations. The already existing technical capabilities make dose optimization of localizer radiographs worthwhile. Modern CT scanners apply automatic exposure control (AEC) based on attenuation data in such a localizer. Therefore not only this aspect but also the detectability of anatomical landmarks in the localizer for the desired CT scan range adjustment needs to be considered. MATERIALS AND METHODS: The effective dose of a head, chest, and abdomen-pelvis localizer radiograph with standard factory settings and user-optimized settings was determined using Monte Carlo simulations. CT examinations of an anthropomorphic phantom were performed using multiple sets of acquisition parameters for the localizer radiograph and the AEC for the subsequent helical CT scan. Anatomical landmarks were defined to assess the image quality of the localizer. CTDIvol and effective mAs per slice of the helical CT scan were recorded to examine the impact of localizer settings on a helical CT scan. RESULTS: The dose of the localizer radiograph could be decreased by more than 90% while the image quality remained sufficient when selecting the lowest available settings (80kVp, 20mA, pa tube position). The tube position during localizer acquisition had a greater impact on the AEC than the reduction of tube voltage and tube current. Except for the use of a pa tube position, all changes of acquisition parameters for the localizer resulted in a decreased total radiation exposure. CONCLUSION: A dose reduction of CT localizer radiograph is necessary and possible. In the examined CT system there was no negative impact on the modulated helical CT scan when the lowest tube voltage and tube current were used for the localizer.

Comparison of Diagnostic Accuracy of Radiation Dose-Equivalent Radiography, Multidetector Computed Tomography and Cone Beam Computed Tomography for Fractures of Adult Cadaveric Wrists.

PURPOSE: To compare the diagnostic accuracy of radiography, to radiography equivalent dose multidetector computed tomography (RED-MDCT) and to radiography equivalent dose cone beam computed tomography (RED-CBCT) for wrist fractures. METHODS: As study subjects we obtained 10 cadaveric human hands from body donors. Distal radius, distal ulna and carpal bones (n = 100) were artificially fractured in random order in a controlled experimental setting. We performed radiation dose equivalent radiography (settings as in standard clinical care), RED-MDCT in a 320 row MDCT with single shot mode and RED-CBCT in a device dedicated to musculoskeletal imaging. Three raters independently evaluated the resulting images for fractures and the level of confidence for each finding. Gold standard was evaluated by consensus reading of a high-dose MDCT. RESULTS: Pooled sensitivity was higher in RED-MDCT with 0.89 and RED-MDCT with 0.81 compared to radiography with 0.54 (P = < .004). No significant differences were detected concerning the modalities' specificities (with values between P = .98). Raters' confidence was higher in RED-MDCT and RED-CBCT compared to radiography (P < .001). CONCLUSION: The diagnostic accuracy of RED-MDCT and RED-CBCT for wrist fractures proved to be similar and in some parts even higher compared to radiography. Readers are more confident in their reporting with the cross sectional modalities. Dose equivalent cross sectional computed tomography of the wrist could replace plain radiography for fracture diagnosis in the long run.

Design and evaluation of a Monte Carlo based model of an orthovoltage treatment system.

The aim of this study was to develop a flexible framework of an orthovoltage treatment system capable of calculating and visualizing dose distributions in different phantoms and CT datasets. The framework provides a complete set of various filters, applicators and x-ray energies and therefore can be adapted to varying studies or be used for educational purposes. A dedicated user friendly graphical interface was developed allowing for easy setup of the simulation parameters and visualization of the results. For the Monte Carlo simulations the EGSnrc Monte Carlo code package was used. Building the geometry was accomplished with the help of the EGSnrc C++ class library. The deposited dose was calculated according to the KERMA approximation using the track-length estimator. The validation against measurements showed a good agreement within 4-5% deviation, down to depths of 20% of the depth dose maximum. Furthermore, to show its capabilities, the validated model was used to calculate the dose distribution on two CT datasets. Typical Monte Carlo calculation time for these simulations was about 10 minutes achieving an average statistical uncertainty of 2% on a standard PC. However, this calculation time depends strongly on the used CT dataset, tube potential, filter material/thickness and applicator size.